Review on micropore grade inorganic porous medium based form stable composite phase change materials: Preparation, performance improvement and effects on the properties of cement mortar

Building energy consumption is an important part of energy consumption. Popularizing latent heat storage technology in building is beneficial to reducing building energy consumption. Phase change materials (PCMs) are important carriers of latent heat energy storage technology. The application of PCMs in building materials is helpful in increasing the latent heat storage capacity of the building. The leakage of PCMs can be prevented and the thermal conductivity of PCMs can be improved by incorporation of PCMs into inorganic porous media. Among various types of inorganic porous materials, the materials containing mainly micropores (0.1 lm–100 lm) such as expanded perlite (EP), expanded vermiculite (EV), diatomite and expanded graphite (EG) have characteristics of high porosity, moderate pore diameter, low price and wide sources. The four kinds of inorganic porous medium based composite PCMs are suitable for largescale usage in cement mortar. In this paper, the preparation, thermal properties, and performance improvement of the four composite PCMs are reviewed. The effects of them on the properties of cement mortar are also summarized.

Construction and Building Materials 194 (2019) 287–310 Contents lists available at ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat Review Review on micropore grade inorganic porous medium based form stable composite phase change materials: Preparation, performance improvement and effects on the properties of cement mortar Min Li ⇑, Junbing Shi Jiangsu Key Laboratory for Construction Materials, Southeast University, Nanjing 211189, China h i g h l i g h t s  The micropore grade inorganic porous medium are appropriate for the adsorption of PCMs  The performances of the inorganic porous medium based form-stable CPCMs were reviewed  The effects of the CPCMs on cement mortar were summarized a r t i c l e i n f o Article history: Received May 2018 Received in revised form 22 October 2018 Accepted 29 October 2018 Keywords: Phase change materials Micropore Inorganic porous media Thermal energy storage Cement mortar a b s t r a c t Building energy consumption is an important part of energy consumption Popularizing latent heat storage technology in building is beneficial to reducing building energy consumption Phase change materials (PCMs) are important carriers of latent heat energy storage technology The application of PCMs in building materials is helpful in increasing the latent heat storage capacity of the building The leakage of PCMs can be prevented and the thermal conductivity of PCMs can be improved by incorporation of PCMs into inorganic porous media Among various types of inorganic porous materials, the materials containing mainly micropores (0.1 lm–100 lm) such as expanded perlite (EP), expanded vermiculite (EV), diatomite and expanded graphite (EG) have characteristics of high porosity, moderate pore diameter, low price and wide sources The four kinds of inorganic porous medium based composite PCMs are suitable for largescale usage in cement mortar In this paper, the preparation, thermal properties, and performance improvement of the four composite PCMs are reviewed The effects of them on the properties of cement mortar are also summarized Ó 2018 Elsevier Ltd All rights reserved Contents Introduction The preparation method and characterization of micropore grade inorganic porous medium based FSCPCMs Expanded vermiculite based FSCPCM 3.1 Thermal properties of EV based FSCPCM 3.2 Performance improvement of the EV based FSCPCM 3.2.1 Improvement of the adsorption performance and heat storage performance 3.2.2 Improvement of the thermal conductivity Expanded perlite based FSCPCM 4.1 Thermal properties of EP based FSCPCM 4.2 Performance improvement of the EP based FSCPCM 4.2.1 Improvement of the adsorption performance and heat storage performance 4.2.2 Improvement of the thermal conductivity Diatomite based FSCPCM ⇑ Corresponding author E-mail address: limin.li@163.com (M Li) https://doi.org/10.1016/j.conbuildmat.2018.10.222 0950-0618/Ó 2018 Elsevier Ltd All rights reserved 288 288 290 290 293 294 294 295 296 298 298 298 299 288 M Li, J Shi / Construction and Building Materials 194 (2019) 287–310 5.1 5.2 Thermal properties of the diatomite based FSCPCM Performance improvement of the diatomite based FSCPCM 5.2.1 Improvement of the adsorption performance and heat storage performance 5.2.2 Improvement of the thermal conductivity Expanded graphite based FSCPCM 6.1 Thermal properties of the EG based FSCPCM 6.2 Thermal conductivity of the EG based FSCPCM The effect of the micropore grade inorganic porous medium based FSCPCMs on cement mortar 7.1 Effect of the micropore grade inorganic porous medium based FSCPCMs on the heat storage performance of cement 7.2 The influence of the micropore grade inorganic porous medium based FSCPCM on the strength of cement mortar Conclusions and outlook Conflict of interest Acknowledgements References Introduction With the development of economy, the demand for energy is increasing in all walks of life However, due to the decrease of traditional fossil energy reserves and inefficient usage of existing energy sources, the contradiction between supply and demand of energy is becoming tense Improving energy utilization and developing new energy have become an important way to ease this contradiction At present, the thermal energy storage (TES) is regarded as an important method to increase energy efficiency [1] It includes sensible heat storage and latent heat storage The sensible heat storage can be implemented easily through heating or cooling the medium However, its utilization is limited by the low heat storage capacity and large volume requirement [2] The latent heat storage can be realized through the phase change process (solid–solid, solid–liquid and gas–liquid) of the materials during which large amount of heat can be utilized without a significant change of temperature [3] Because of the advantages of latent heat storage, the related materials and technologies have become research hotspots in the field of energy saving [4,5] PCM is a kind of important latent heat storage material The PCMs can be divided into solid–solid PCMs, solid–liquid PCMs, gas–solid PCMs and liquid–gas PCMs according to the type of phase change Besides, PCMs can be divided into inorganic PCMs, organic PCMs and composite PCMs according to the chemical composition For solid–gas PCMs and liquid–gas PCMs, due to the generation of gaseous substances during the phase change process, the volume change of them is larger than that of the other kinds of PCMs As a result, even though the heat storage density of these PCMs is higher than the other PCMs, the application of them was limited Solid-solid PCMs and solid–liquid PCMs were proved to have good application potential in building energy conservation, solar energy utilization, heat recovery, temperature control and other fields [6–9] Although PCMs have high thermal storage capacity, there are still some problems in practical applications The leakage during the solid–liquid phase change process and low thermal conductivity of the PCMS are considered to be the two outstanding issues [10,11] At present, incorporation techniques and macro/microencapsulating method are effective methods to prevent leakage The incorporation technique is to prepare composite PCMs by combining pure PCM with layered materials or porous materials Microencapsulation is a process of encapsulating pure PCM with polymer or organic shell [12,13] Adding high thermal conductivity materials such as expanded graphite and nanometal can improve the thermal conductivity of PCMs [14] Inorganic porous medium, which has large surface area and abundant pore structure, is an ideal supporting material to prepare form stable composite phase change materials (FSCPCMs) [15,16] In the inorganic porous medium based FSCPCM, the leakage issue 300 302 302 302 302 303 304 304 306 307 308 308 308 308 can be effectively solved due to the micro capillary force and the interfacial adsorption effect of inorganic porous medium Moreover, the heat conduction of the PCMs can be improved because of the high thermal conductivity of the inorganic materials [17] The pore sizes of some inorganic porous materials [18–23] such as zeolite, molecular sieve and porous silica are nanoscale (0– 100 nm) Such nanopores will hinder the phase transformation of PCMs during adsorbing the PCMs As a result, the adsorption capacity and heat storage capacity of the composite PCMs are decreased [24] However, the pore sizes of expanded perlite, expanded vermiculite, diatomite and expanded graphite are mainly microscale (0.1 lm–100 lm) These micron scale pores have little interference on the phase transition behavior of PCMs [25] Besides, the four porous materials have the advantages of wide sources and low cost [26,27] Some reviewers have presented classifications, applications and performance, however few reviewers focused on the micron pore grade inorganic porous medium based FSCPCMs The preparation, characterization, thermal properties, and performance improvement of the EP based FSCPCM, EV based FSCPCM, diatomite based FSCPCM and EG based FSCPCM are reviewed in this paper The effects of the four FSCMs on cement mortar are summarized The preparation method and characterization of micropore grade inorganic porous medium based FSCPCMs The preparation method of micropore grade inorganic porous medium based FSCPCMs included direct impregnation method and vacuum adsorption method [28,29] The schematic diagram of preparing FSCPCMs by direct impregnation method was shown in Fig [28] It included two kinds of mixing process One was Fig Schematic diagram of direct impregnation method [28] M Li, J Shi / Construction and Building Materials 194 (2019) 287–310 289 Fig Schematic diagram of vacuum adsorption method [29] heating the PCMs to a molten state and then mixing them with the supporting materials, the other was mixing the PCMs and supporting materials at solid state and then heating to a molten state The first mixing process was usually used to prepare composite materials with low phase change temperature and the second mixing process was suitable for composites with high phase change temperature The vacuum adsorption method was more complex than the direct immersion method The schematic diagram of preparing PCMs by vacuum adsorption method was shown in Fig [29] For vacuum adsorption, except the capillary force and the surface tension of the porous materials, the pressure difference of the environment was also helpful to the adsorption of the liquid PCMs The characterization methods of micropore grade inorganic porous medium based FSCPCMs mainly included differential thermal analysis (DSC), thermogravimetric analyzer (TG), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), thermal conductivity analysis and thermal cycling test Among them, DSC was used to analyze the heat storage capacity of composite PCMs The melting temperature, freezing temperature and the latent heat of the composite PCMs could be calculated through the DSC curve The DSC curves of paraffin/expanded vermiculite based FSCPCM were shown in Fig [30] The FTIR was mainly used to determine whether there were chemical reactions between PCMs and the inorganic porous medium The FTIR testing curves of capric acid/ expanded perlite based FSCPCM were revealed in Fig [31] The distribution of PCMs in supporting materials could be observed by SEM [32] The XRD was used to analyze the crystallinity of the PCMs [33] The thermal stability of composite PCMs was often analyzed by TG and thermal cycling The TG curves of Stearic acid/ Expanded vermiculite based FSCPCM were shown in Fig [34] Fig FTIR testing curves of capric acid/expandead perlite based FSCPCM [31] Fig TG curve of Stearic acid/expanded vermiculite based FSCPCM [34] Fig The DSC curve of paraffin/expanded vermiculite based FSCPCM [30] The leakage of PCMs could be estimated by observing the oil stains on filter papers after FSCPCMs were put on filter papers and heated to the melting point, as shown in Fig [35] The thermal conductivity of FSCPCMs was characterized by thermal conductivity analysis The methods of thermal conductivity analy- 290 M Li, J Shi / Construction and Building Materials 194 (2019) 287–310 skeleton and the magnesium hydroxide layer or the hydrogen oxygen aluminum layer Moreover, there is a large amount of bound water and free water existing among the unit layers of vermiculite The structure of vermiculite is shown in Fig [37] The vermiculite can expand more than ten times in the vertical direction during calcination due to the loss of internal moisture The structure varied to be layer structure of 2:1 The bulk density of the vermiculite decreases and the porosity increases after expansion The EV mainly consists of two dimensional lamellar pores between 0.1 lm and 10 lm Figs and 10 present the appearance of vermiculite and expanded vermiculite, respectively [38] Fig 11 shows the pore distribution of EV [39] EV has many advantages such as wide source, high fire resistance, non-toxic, sound absorption and low cost [40] Especially, EV has good adsorption properties because of the well-developed pore structures Fig 12 showed the adsorption of mercury ions by EV [41] 3.1 Thermal properties of EV based FSCPCM Fig Observation on leakage of the FSCPCM [35] Fig Pores distribution of expanded graphite [25] sis in literatures were different Apart from the directly testing, some researchers investigate the thermal conductivity by heating and cooling rate The pore structure of the inorganic porous materials was characterized by mercury intrusion method and low temperature nitrogen adsorption method The mercury intrusion test was more accurate for micropore grade inorganic porous medium The pore distribution of EG tested by mercury intrusion method was shown in Fig [25] The EV has been selected as the supporting material to prepare the EV based FSCPCM by many researchers because of its good porous structure The direct impregnation and vacuum adsorption method were common preparation method The prepared FSCPCMs showed good thermal reliability and chemical stability Chung et al [39] fabricated n-octadecane/EV FSCPCM via vacuum incorporation method and investigated the thermal properties and chemical stability of it The highest mass percentage of n-octadecane in the FSCPCM was 80.65% Under this condition, the melting temperature and latent heats of the FSCPCM were 26.1 °C and 142 J/g The solidification temperature and latent heats were 24.9 °C and 126.5 J/g Moreover, the TG analysis and FIIR analysis showed that the FSCPCM has good thermal stability and chemical stability The lauric acid/EV FSCPCM was prepared by Wen et al [42] The content of the lauric acid (LA) in the composite FSCPCM without leakage reached 70 wt% The melting temperature of the composite phase change material was 41.88 °C and the melting latent heat was 126.8 J/g Thermal cycling test showed that the FSCPCM still had good thermal reliability and chemical stability after 200 times of melting/freezing cycling The SEM morphology in Fig 13 showed that the EV empty interlayer spaces were largely occupied by the impregnated LA The results from FIIR analysis showed that there was no chemical interaction between the EV and the lauric acid The phase change temperatures can be adjusted to a proper temperature by blending different PCMs when the phase change temperature of pure PCMs are too high for building applications The Capric–myristic acid/EV FSCPCM was prepared by Karaipekli [43] via vacuum incorporation The capric acid (CA)–myristic acid Expanded vermiculite based FSCPCM The expanded vermiculite is obtained by calcination of mineral vermiculite at high temperature [36] The mineral vermiculite belongs to the trioctahedron structure Most of them are formed by hydrothermal alteration or weathering of biotite, mica and chlorite Vermiculite crystal consists of three structural unit layers The silicon oxygen skeleton exists between the structural unit layers The tetrahedron is formed by the combination of silicon oxygen Fig Schematic diagram of vermiculite structure [37] M Li, J Shi / Construction and Building Materials 194 (2019) 287–310 291 Fig The appearance of vermiculite [38] Fig 10 The appearance of expanded vermiculite [38] (MA) eutectic mixture was selected as PCMs The phase change temperature of the eutectic mixture was adjusted to 25 °C by controlling the mass ratio between capric acid and myristic acid at 3:7 The eutectic acid was absorbed into the pore structures of the EV The maximum content of eutectic acid was 20% under the condition of no leakage The melting and solidification temperature of this FSCPCM were 19.8 °C and 17.1 °C and the latent heat was 27 J/g The FSCPCM still had good thermal reliability and chemical stability after 3000 thermal cycles Wen et al [44] used capric acid (CA) – lauric acid (LA)eutectics mixture as PCM to prepare EV based FSCPCM The highest mass percentage of this eutectics mixture was 57.48% Only physical combination existed between the eutectics and the EV The phase change temperature and latent heat of this FSCPCM are 21–23 °C and 81.34 J/g In addition, the TG analysis and the 200 times melting/freezing cycling test showed that this FSCPCM has good thermal stability In the study of Karaipekli et al [45], a series of FSCPCMs were prepared by incorporation of eutectic mixtures of fatty acids (capric–lauric, 292 M Li, J Shi / Construction and Building Materials 194 (2019) 287–310 Fig 11 The pore distribution of the expanded vermiculite [39] Fig 12 Adsorption of mercury ions [41] capric–palmitic and capric–stearic acids) and EV by vacuum impregnation method In order to meet the requirements of indoor temperature controlling, the mass ratios of capric–lauric acids, capric–palmitic acids and capric–stearic acids were adjusted to 64:36, 76.5:23.5 and 83:17, respectively The maximum content of these eutectic mixtures in the FSCPCMs were 40 wt% The melting temperatures and latent heats of these FSCPCMs are in the range of 19.09–25.64 °C and 61.03–72.05 J/g, respectively Moreover, the results of the 5000 times heating and cooling cycle tests showed that these FSCPCMs had good thermal reliability and chemical stability The capric(CA)–palmitic(PA)–stearic acid(SA)/ EV FSCPCM was prepared by Zhang et al [29] via vacuum impregnation method When the mass ratio of CA:PA:SA was 79.3:14.7:6, the melting and freezing temperature was 19.3 °C and 17.1 °C, respectively The research showed that the CA–PA–SA was sufficiently absorbed in the porous network of EV There was no chemical interaction between the expanded vermiculite and the CA–PA–SA The 70 wt% CA–PA–SA/EV sample melted at 19.3 °C with a latent heat of 117.6 J/g and solidified at 17.1 °C with a latent heat of 118.3 J/g Moreover, the FSPCMs exhibited adequate stability even after being subjected to 200 melting–freezing cycles These literatures showed that the eutectic mixture was combined with EV physically, which was similar to the pure PCM The eutectic mixture/EV FSCPCM also showed good thermal reliability and chemical stability Compared with organic PCMs, inorganic PCMs have larger thermal capacity, higher thermal conductivity, higher operating temperatures and the better compatibility with the micropore grade inorganic porous media The phase change temperature of the inorganic PCMs is higher than that of the organic PCMs The sodium nitrate/EVFSCPCM was prepared by the incorporation of sodium nitrate into EV with directing impregnation method [28] The results showed that sodium nitrate and expanded vermiculite in the composites only undergo physical combination, not a chemical reaction The adsorptive capacity of the EV to sodium nitrate was about 88% The phase change temperature of the FSCPCM was 300.9 °C and the latent heat was 157.2 J/g In addition, after 200 h of heat treatment, the supercooling degree of the FSCPCM were between 0.1 °C and 3.9 °C and the thermal enthalpy change rate was lower than 5.0% The thermal properties of the EV based FSCPCMs were summarized and listed in Table 293 M Li, J Shi / Construction and Building Materials 194 (2019) 287–310 Fig 13 SEM images of (a), (b) EV; (c) composite PCM (70 wt% LA/EV); (d) SEM image and EDS spectra of composite PCM(70 wt% LA/EV); Appearance photo of 70 wt% LA/EV (e) at room temperature (f) after heating at 80 ◦C for 30 [42] Table1 Thermal properties of EV based FSCPCMs EV based FSCPCMs Adsorption capacity (%) Melting temperature (°C) Latent heat of melting (J/g) Freezing temperature (°C) Latent heat of freezing (J/g) Thermal cycling (times) Decrease percentage of the latent heat References n-octadecane/EV LA/EV CA –LA/EV CA – PA/EV CA–SA/EV CA–PA–SA/EV sodium nitrate/EV 80.65 70 57.48 40 40 70 87.9 26.1 41.88 23.61 22.61 25.64 19.3 300.9 142 126.8 81.34 61.03 72.05 117.6 157.2 24.9 39.89 20.93 21.53 23.47 17.1 299.6 126.5 125.6 79.30 60.35 68.52 118.3 156.8 – 200 200 5000 5000 200 – – – 6.3% 2.8% 0.1% 3.4% – [39] [42] [44] [45] [45] [29] [28] 3.2 Performance improvement of the EV based FSCPCM Until now, many kinds of EV based FSCPCM has been developed Although they exhibited good thermal stability and chemical stability, the disadvantages such as limited adsorption capacity and low thermal conductivity hindered their application in thermal energy storage To solve these problems, some researchers have devoted to improve the adsorption capacity, heat storage density and thermal conductivity 294 M Li, J Shi / Construction and Building Materials 194 (2019) 287–310 3.2.1 Improvement of the adsorption performance and heat storage performance The latent heats of EV based FSCPCMs are mainly decided by PCMs in the EV based FSCPCM because the expanded vermiculite has no phase change ability With the increase of the content of PCMs, the adsorption capacity of the EV based FSCPCMs increased As a result, the thermal storage density is increased Wei et al [46] conducted an experimental study of the performance improvement of the EV based FSCPCMs The EV was modified by means of acid treating method followed by loading Al2O3 particles as shown in Fig 14 Then, the Al2O3-loaded EV (aEV/AO) was used as supporting matrix to absorb the lauric(LA)-myristic(MA)-stea ric(SA) acid eutectic mixture (LA-MA-SA acid) Compared to the EV, the adsorption capacity of aEV/AO to LA-MA-SA acid was increased by 32.3 wt% Due to the modification, the melting and freezing latent heats of the FSCPM were increased by 51 J/g and 50.6 J/g, respectively According to their study, the Si-OH groups on the surface of EV were exposed after EV was partially delaminated and corroded by acid treatment, which was the reason for the improvement of the adsorption capacity Similar to the study of Wei et al., Li et al [47] treated titanium dioxide-loaded EV with nitric acid firstly Then the modified EV was used as stearic acid (SA) supporting matrix to prepare a SA/modified EV FSCPCM via vacuum impregnation method The results showed that the melting latent heat of the SA/modified expanded vermiculite FSCPCM were increased by 69.2 J/g compared to the unmodified FSCPCM Wei et al [48] used methyl ammonium bromide and nitric acid to modify the EV and obtained in-situ carbonation expanded vermiculite (EVC) The modification method was shown in Fig 15 The EVC was used as a carrier to adsorb capric acid(CA)–myristic acid(MA)–stearic acid(SA) ternary eutectic acid to prepare FSCPCM It was found that the melting latent heat of the CA-MA-SA/ modified expanded vermiculite FSCPCM was 86.4 J/g, which was 39.1% higher than the unmodified EV based FSCPCM The reason for this improvement is the same with the explanation in Ref [46] 3.2.2 Improvement of the thermal conductivity Low thermal conductivity is a major drawback of the EV based FSCPCM because it will lead to low heat transfer rate and heat storage efficiency Researchers have done a great deal of work to enhance the thermal conductivity The thermal conductivity of the EV based FSCPCM was increased by modifying the EV and adding high thermal conductivity components Guan et al [30] modified the EV with sucrose solution to form carbide film between the layers of the EV The EV was altered to the EV/carbon (EVC) through this method Then the paraffin/EMVC FSCPCM was prepared by vacuum impregnation method The schematic diagram Fig 14 Schematic diagram of the preparation process of aEV/AO [46] Fig 15 Schematic diagram of the preparation process of EVC [48] 295 M Li, J Shi / Construction and Building Materials 194 (2019) 287–310 of the preparation process of the FSCPCM was shown in Fig 16 The results showed that the maximum content of paraffin in paraffin/ EMVC FSCPCM was 53.2 wt% The thermal conductivity of the paraffin/EMVC FSCPCM was increased by 193% The authors believed that the improvement was attributed to implanting high thermal conductivity carbon network in vermiculite layers Similarly, Zhang et al [34] modified the EV by in situ carbonation with starch solution The result indicated that the maximum content of stearic acid in the stearic/modified EV FSCPCM could reach 63.12 wt% The thermal conductivity of FSCPCM prepared with the modified EV was increased by 52.9% compared to unmodified EV based FSCPCM In addition to the above modification methods, it was often adopted to add thermal conductivity enhancement components during the preparation process of the FSCPCM to improve the thermal conductivity Deng et al [49] developed a thermal conductivity enhanced FSCPCM with polyethylene glycol(PEG) as the phase change material and the EV as the supporting material The nano-silicon carbide was used as the thermal conductivity reinforcement material The results revealed that the thermal conductivity of this FSCPCM was 0.53 W/mÁK when the addition of nano-silicon carbide was 3.29 wt% The thermal conductivity was increased by 96.2% compared to the FSCPCM without nanosilicon carbide The authors contributed the enhancements to the rapid heat transfer of nano-silicon and their effective dispersion in the pore structures of EV The same research group also studied the effects of nano-silver wire on the thermal conductivity of the PEG/EV FSCPCM [50] The diameter of the nano-silver was 50– 100 nm and the length was 5–20 lm It was founded that the nano-silver wire could be well dispersed in the pore of expanded vermiculite After being added with 19.3 wt% of nano-silver wire, the thermal conductivity of the PEG/EV FSCPCM was 0.68 W/mÁK, which was increased by 172% Deng et al [51] used the Alumina to enhance the thermal conductivity of the Na2HPO4Á12H2O/EV FSCPCM The thermal conductivity of the Na2HPO4Á12H2O/EV FSCPCM was increased by 45.6%” after adding 5.3 wt% alumina Besides, the EG was commonly used as thermal conductivity enhancement components in EV based FSCPCMs The thermal conductivities of the EV based FSCPCM were provided in Table Expanded perlite based FSCPCM Perlite is the acidic vitreous lava with a structure of pearl cracks About 95% of the perlite ore is glassy phase, in which the amorphous quartz accounts for 65–75% and alkali metal oxides accounts for about 8–9%.The internal moisture in the perlite is about 2–6% A porous EP with a low bulk density can be formed after perlite is heated rapidly at the temperature of 700–1200 °C [27,52].The pores in the EP range from lm to 100 lm The microscopic appearance of perlite before and after expansion was shown in Fig 17 [53] The structure and distribution of the pores inside the EP were shown in Figs 18 and 19, respectively [39,54] The EP displayed good adsorption property due to the developed pores Fig 16 Schematic diagram of the preparation process of EVC composite materials [30] Table The thermal conductivities of the EV based FSCPCM EV based FSCPCMs Thermal conductivity W/(mÁK) Adding amount (wt%) Increase ratio of the thermal conductivity References Lauric acid/EV Lauric acid/EV/EG 0.28 0.5 10 78.5% [42] Capric-myristic Acid/EV Capric-myristic Acid/EV/EG 0.12 0.22 83.3% [43] Capric Acid – Lauric Acid/EV Capric Acid – Lauric Acid/EV/EG 0.135 0.253 87.4% [44] Capric Acid – Palmitic Acid – Stearic Acid/EV Capric Acid – Palmitic Acid – Stearic Acid/EV/Copper 0.242 0.362 49.6% [29] Polyethylene glycol/EV Polyethylene glycol/EV/nano-silicon nitride 0.27 0.53 3.29 96.2% [49] Polyethylene glycol/EV Polyethylene glycol/EV/nano-silver wire 0.25 0.68 19.3% 172% [50] 296 M Li, J Shi / Construction and Building Materials 194 (2019) 287–310 Fig 17 The micro-morphology of perlite before (a) and after expansion (b)[53] and moderate pore size The adsorption effect of EP on p-nitrophenol was shown in Fig 20 [55] 4.1 Thermal properties of EP based FSCPCM Fig 18 Internal pore structure of expanded perlite [54] A series of form-stable EP based FSCPCMs have been prepared Organic materials with low phase change temperature are often used as the phase change substance in the EP based FSCPCM The preparation methods of EP based FSCPCM mainly included vacuum adsorption and melt impregnation According to the research of Takahiro et al [56], the latent heat of the FSCPCM prepared by vacuuming was larger than the FSCPCM prepared without vacuuming, as shown in Fig 21 In the preparation process of EP based FSCPCM, the liquid PCM was impregnated through capillary forces in EP However, the air pressure within the pores prevented the Fig 19 Internal pore distribution of expanded perlite [39] M Li, J Shi / Construction and Building Materials 194 (2019) 287–310 Fig 20 Effect of pH on the adsorption of Co and Pb onto EP [55] Fig 21 The Comparison between vacuum impregnation treatment and impregnation treatment for each porous material [56] impregnation It was difficult to evacuate the air within the pores without vacuuming As a result, the adsorption effect of the direct impregnation was worse than the vacuum adsorption method Lu et al [57] prepared a EP based FSCPCM in which paraffin was used as PCM The maximum content of paraffin can reach 60% without leakage occurring The phase change temperature is 27.56 °C and the latent heat of transformation is 80.9 J/g The results showed that paraffin and EP were physically combined, which was the same as the EV based FSCPCM Paraffin was distributed in the pores of the EP after impregnation The FSCPCM still maintain stable after 2000 times of heating and cooling cycles The thermal stability of the FSCPCM was shown in Fig 22 Lauric acid/ EP FSCPCM was prepared by Sari et al [58] via vacuum adsorption method The melting and solidification temperatures of the composite were 44.13 °C and 40.97 °C, respectively The latent heat of fusion and latent heat of solidification were 93.36 J/g and 94.87 J/g, respectively It was found that no chemical reaction occurred between lauric acid and EP In addition, the latent heat value of melting reduced by 1.2% and the latent heat of freezing reduced by 4.1% after 1000 times of thermal cycles The decreases in the latent heat capacity of the composite PCM were in a reasonable level for TES applications in buildings The same authors [28] also prepared capric acid/EP FSCPCM The maximum adsorption capacity of capric acid was up to 55% The melting point was 31.8 °C and the latent heat of FSCPCM was 98.1 J/g The latent heat of melting decreased by 2.6% and the latent heat of freezing changed by 0.6% after 5000 times of thermal cycles Liu et al [59] 297 Fig 22 DSC curves of paraffin/expanded perlite composites before and after hot and cold cycles [57] prepared a lauric acid/EP FSCPCM by the method of melting impregnation The maximum adsorption amount of lauric acid in the EP can reach 70 wt% The phase change temperature and latent heat were 43.2 °C and 105.58 J/g, respectively In order to meet the demand of phase change temperature of the PCMs, binary or multiple eutectic acids has been developed by adjusting the content ratio of them The preparing and thermal properties of the EP based FSCPCMs with binary or multiple eutectic acids as PCM were investigated by some researchers They drew some similar conclusions with the EP based FSCPCMs with pure PCM Zhang et al [60] prepared a capric acid-palmitic acid/EP FSCPCM via vacuum adsorption The maximum adsorption capacity of the EP to the eutectic acid was 65 wt% The FSCPCM has a melting temperature of 24.1 °C and a latent heat of 88.39 J/g Jiao et al [61] used binary eutectic acid of capric acid and stearic acid as the phase change material to prepare the EP based FSCPCM by vacuum adsorption method The content of the eutectic acid was 43.4% The eutectic acid and the expanded perlite were simply physically bonded The melting temperature of the FSCPCM was 33 °C and the latent heat of phase transformation was 131.3 J/g The melting temperature and the latent heat of the specimen were 33.5 °C and 131.1 J/g after 1000 thermal cycles Zhang et al [62] prepared lauric-palmitic-stearic acid/EP FSPCM using vacuum impregnation method The maximum adsorption amount of the EP to the eutectic acid was 55 wt% The melting temperature of the FSCPCM was 31.8 °C, and the latent heat of melting was 81.5 J/g The solidification temperature of the FSCPCM was 30.3 °C and the latent heat of solidification was 81.3 J/g Moreover, the melting and freezing latent heats of the FSCPCM dropped slightly by 4.29% and 5.54%, respectively after 1000 times of thermal cycles The FITR curves of the FSCPCM were shown in Fig 23 The infrared spectrum without significant new peaks indicated that there were no chemical reactions between the lauricpalmitic-stearic acid and EP The TG curves were shown in Fig 24 It can be seen that the 5% weight loss temperature of the LA–PA–SA and LA–PA–SA/EP form-stable PCM were higher than 180 °C, which means that the LA–PA–SA/EP form-stable PCM had a good thermal stability in the working temperature range which was always designed as below 80 °C Considering the application of the EP based FSPCM under high temperature, some researchers have attempted to prepare FSCPCM by adsorbing inorganic PCMs into the pores of EP Li et al [63] used sodium nitrate as the PCM to prepare sodium nitrate/EP FSCPCM The phase change temperature of the FSCPCM was 300 °C and the latent heat of the FSCPCM increased with the content of 298 M Li, J Shi / Construction and Building Materials 194 (2019) 287310 PPCM pD2 ỵ 4pcDcosh > Pair pD2 where P, D, c, and h represent the pressure, pore diameter, surface tension of the PCM, and contact angle, respectively Liquid PCM was impregnated through capillary forces in a porous material, but the air pressure within the pores prevented the impregnation In contrast, the air within the pores was evacuated before the impregnation treatment during the vacuum adsorption process [56] The prepared EP based FSCPCM have good thermal stability and chemical stability The thermal properties of the EP based FSCPCMs were summarized and listed in Table 4.2 Performance improvement of the EP based FSCPCM Although the EP based FSCPM has excellent thermal properties, some problems still should be solved to meet the requirement of application On the on hand, the thermal conductivity of the EP based FSCPM is low due to the low thermal conductivity of EP (0.07 W/(mÁK)) On the other hand, the leakage of the PCM would be increased when the EP based FSCPM was used in cement Until now, the researchers have taken some measures to solve the two problems Fig 23 FT-IR spectra of LA–PA–SA, EP and LA–PA–SA/EP [62] 4.2.1 Improvement of the adsorption performance and heat storage performance Undesired adverse effects of the form-stable PCMs with the cementitious composites have been reported when the PCM melting temperature was lower than the ambient temperature That was PCM leakage occurring during the mixing process with cementitious materials when water was added Some measured had been taken to avoid the leakage Ramakrishnan et al [64] covered the surface of EP with a hydrophobic coating and then prepared FSCPCM by vacuum adsorption using the hydrophobic EP as a support material The maximum adsorption capacity of paraffin in the hydrophobic EP was 50% The paraffin adsorption ratio of the hydrophobic EP was increased about 43% compared to the uncoated EP The latent heat of melting of the FSCPCM was increased from 35.5 J/g to 60.9 J/g The leakage of the FSCPCM before and after modification was shown in Fig 25 The reason for the improvement was that the hydrophobic coated EP can prevent the contact between water molecules and porous EP due to the hydrophobicity of EP Fig 24 TG curves of the LA–PA–SA and LA–PA–SA/EP [62] sodium nitrate The results indicated that there was only a physical combination between sodium nitrate and EP The EP can absorb 90 wt% of sodium nitrate without leakage occurring In the EP based FSCPCMs, there was no chemical reactions between EP and PCMs including pure organic PCMs, binary or multiple eutectic acid and inorganic PCMs The vacuum adsorption was beneficial for the adsorption of PCMs in EP Under the impregnation treatment, the actual relationship was expressed by the following equation: 4.2.2 Improvement of the thermal conductivity In the field of latent thermal energy storage, the heat transfer technology that has to be employed to achieve high enough heat charging/retrieval rates was the major cost Therefore, it was a key point in both energy and economic aspects to enhance the heat transfer performance of the EP based FSCPCM In order to increase the thermal conductivity of EP based FSCPCM, researchers have done a great deal of work Zhang et al [65] adopted in-situ car- Table Thermal properties of EP based FCPCMs EP based FSCPCMs Adsorption capacity(%) Melting temperature (°C) Latent heat of melting (J/g) Freezing temperature (°C) Latent heat of freezing (J/g) Thermal cycling (times) N-octadecane/EP Paraffin/EP Lauric acid/EP Capric acid/EP Capric – palmitic acid/EP Capric – stearic acid/EP Lauric – palmitic – stearic acid/EP Sodium nitrate/EP 59.63 60 60 55 65 43.4 55 87.9 26.2 27.56 44.13 31.8 24.1 33 31.8 300.9 132.2 80.9 93.36 98.1 88.39 131.3 81.5 157.2 25.3 26.38 40.97 31.6 31 31 30.3 299,6 174.3 79.3 94.87 97.9 85.6 127.5 81.3 156.8 – 2000 1000 5000 – 1000 1000 – Decrease percentage of the latent heat 3% 1.2% 2.6% 0.1% 4.29% References [39] [57] [58] [31] [60] [61] [62] [63] 299 M Li, J Shi / Construction and Building Materials 194 (2019) 287–310 Fig 25 Leakage of paraffin/expanded perlite composite before (a) and after modification (b) [64] bonization method to modify EP They conducted in-situ carbonation of the EP with sucrose solution to form a layer of carbonized film on the surface of the EP and obtained an expanded perlite composite with carbon layer (EPC) Then, they prepared a polyethylene glycol/EPC FSCPCM by vacuum impregnation The schematic for the preparation of the EPC composite was shown in Fig 26 The results showed that the thermal conductivity of the modified FSCPCM was 0.479 W/(mÁK), which was 2.9 times of the unmodified FSCPCM The high thermal conductivity of the carbonized film on surface of the EP was the reason for the improvement of the thermal conductivity of the composite PCM Besides, some researchers reported methods of adding thermal conductivity enhancement components into the EP based FSCPCM The most commonly used thermal conductivity enhancement Fig 26 Schematic for the preparation of EPC composite [65] component was expanded graphite (EG) Zhang et al [62] conducted an experimental investigation on the EP based FSCPCM with EG It was found that the addition of wt% EG would cause an increase of 95% for the thermal conductivity of the ternary fatty acid/EP FSCPCM In addition to EG, graphene carbon nanotubes were also used to enhance the thermal conductivity Ramakrishnan et al [66] tested experimentally the heat enhancement of the EP based FSCPCM by nano-graphene The results indicated that a significant enhancement of the thermal conductivity was achieved The thermal conductivity was increased by 49% when the nanographene particles were added about wt% A similar study was also conducted by Sun et al [67] They added graphite to the paraffin/EP FSCPCM to increase the thermal conductivity by 192% with the addition of 5% of graphite Karaipekli et al [68] chose the carbon nanotubes(CNTs) as the thermal conductive reinforcement component It was found that the thermal conductivity of the paraffin/EP FSCPCM was increased by 113.3% with the addition of wt% CNTs The improvement was attributed to the high thermal conductivity (2000–6000 W/(mÁK)) of CNTs, which provided a large heat transfer area for the paraffin/EP FSCPCM Furthermore, this phenomenon may be resulted from the reduction of void space within the composite PCM and extension of contact surface area between CNTs and the composite particles The thermal conductivity improvement of the EP based FSCPCMs were shown in Table Diatomite based FSCPCM Diatomite is formed by ancient diatoms after long geological processes The mineral composition of diatomite is amorphous opal The main chemical composition of diatomite is amorphous silicon dioxide There are a small amount of Al2O3, Fe2O3, CaO, MgO, TiO2, Na2O and so on besides silicon dioxide A lot of silicon hydroxyl and hydrogen bonds exist in the surface and the micropores of diatomite, which is an important reason for having the adsorption properties of diatomite Because of the different shapes of diatom before diagenesis, the micro-morphology of diatomite is various including round sieve shape, banded shape and cylindrical shape The structure diagram and the microscopic morphology of diatomite are shown in Figs 27 and 28 respectively [69,70] The density of Chinese-made diatomite is usually in the range of 0.4– 0.9 g/cm3 and the pore radius is from 0.1 to lm The pore volume is in the range of 0.45–0.98 cm3/g and the specific surface is in the range of 33–65 m2/g Roasting, pickling and other modifications are helpful to increase the specific surface area and volume of the pores The pore size distribution of diatomaceous is shown in Fig 29 [71] Diatomite has excellent adsorption capacity due to its abundant pore structures The influence of initial Cr (VI) concentration on the removal effect of Cr(VI) are shown in Fig 30 [72] Table The thermal conductivity improvement of the EP based FSCPCM EP based FSCPCMs Thermal ConductivityW/(mÁ K) Adding amount(wt%) Increase ratio of thermal conductivity References Laurie/EP Laurie/EP/EG 0.07 0.13 10 85.7% [58] Capric Acid/EP Capric Acid/EP/EG 0.087 0.143 10 64.3% [31] Capric Acid-Laurie/EP Capric Acid – Lauric Acid/EP/EG 0.135 0.253 87.4% [44] Capric Acid – Palmitic Acid – Stearic Acid/EP Capric Acid – Palmitic Acid – Stearic Acid/EP/EG 0.44 0.86 95.4% [62] Paraffin/EP Paraffin/EP/Nano Graphene 0.35 0.52 48.6% [66] Paraffin/EP Paraffin/EP/Carbon Nanotubes 0.15 0.32 113.3% [68] 300 M Li, J Shi / Construction and Building Materials 194 (2019) 287–310 Fig 27 The structure diagram of diatomite [69] Fig 28 SEM images of the diatomite [70] Fig 30 Influence of initial Cr (VI) concentration on the removal effect of Cr (VI) (experimental conditions: catalyst amount = g/L, UV light intensity = 500 W, pH = 2.1) [72] Fig 29 The pore distribution of diatomite [71] 5.1 Thermal properties of the diatomite based FSCPCM PCMs used for preparing diatomite based FSCPCM are abundant, including paraffin, fatty acid, eutectic acids, polyethylene glycol, sulfates, nitrates and so on Phase change temperature of the FSCPCM covers from low temperature to high temperature The prepared diatomite based FSCPCMs showed good thermal reliability and chemical stability Su et al [73] prepared a series of diatomite based FSCPCMs by vacuum absorption and investigated the structure of them They used n-hexadecane, n-octadecane and paraffin as PCM respectively The results showed that the maximum content of the three PCMs in the FSCPCM was 47%, 47% and 42%, respectively The PCM and the diatomite were physically combined The microstructures of the three FSCPCMs were shown in Fig 31 Fu et al [74] used diatomite to absorb capric acid by direct melt impregnation method to prepare a diatomite based FSCPCM The maximum adsorption capacity to capric acid was 40% The melting and solidification temperatures were 40.9 °C and 38.7 °C, respectively The latent heat of melting and latent heat of freezing were 57.4 J/g and 57.2 J/g The FSCPCM did not decompose when the surrounding temperature was lower than 157 °C, which suggested the prepared diatomite based FSCPCMs had good thermal stability Karaman et al [75] prepared polyethylene glycol 1000 (PEG 1000)/diatomite based FSCPCM by vacuum adsorption The maximum content of PEG 1000 could reach 50% The melting temperature of the prepared FSCPCM was 27.7 °C and the latent heat of melting was 87.09 J/g The result indicated that there was no chemical reaction between PEG 1000 and diatomite Similar to PEG1000/diatomite based FSCPCPM Qian et al [76] prepared polyethylene glycol 2000/diatomite based FSCPCPM In addition to pure PCM, Li et al [77] prepared capric–lauric acid/diatomite based FSCPCM by melting impregnation under ordinary pressure The maximum of the eutectic acid in the FSCPCM was 47% The melting temperature of the FSCPCM was 16.74 °C and the latent heat was 66.81 J/g Tang et al [78] carried out an experimental study of preparing a carpic-palmic acid/diatomite based FSCPCM The maximum content of the eutectic acid in the FSCPCM was 63.5% The melting and solidification temperature of the FSCPCM were 26.7 °C and 21.85 °C respectively The latent heat of melting was 98.3 J/g and the latent heat of freezing was 90.03 J/g Qian et al [76] prepared two kinds of FSCPCMs by melting impregnation with inorganic materials as phase change substance One was lithium nitrate/diatomite based FSCPCM and the other was sodium sulfate/diatomite based FSCPCM The results showed 301 M Li, J Shi / Construction and Building Materials 194 (2019) 287–310 Fig 31 The microstructure of diatomite and diatomite based FSCPCM [72] that the highest content of lithium nitrate and sodium sulfate in the FSCPCMs were 60% and 65%, respectively The melting temperature and the latent heat of the lithium nitrate/diatomite based FSCPCM were 250.7 °C and 215.6 J/g For sodium sulfate/diatomite based FSCPCM, the melting temperature was 887.61 °C and the latent heat of melting was 101.59 J/g Compared with the pure PCM, the supercooling extents of the prepared FSCPCMs were reduced by 23.7% and 19.9%, respectively The results suggested that the supercooling extent of PCMs can be favorably reduced by impregnation with diatomite supporter After 200 thermal cycling, the melting latent heat value of these two kinds of FSCPCMs changed by 9.3% and 1.7%, which were acceptable in application The potassium nitrate/diatomite based FSCPCM was prepared by Deng et al [79] via melt impregnation The melting temperature of the FSCPCM was 330.23 °C and the latent heat of melting was 60.52 J/g The solidification temperature and the latent heats were 332.9 °C and 47.3 J/g The melting point for of the FSCPCM varied from 330.23 °C to 330.11 °C and the latent heats varied from 60.52 J/g to 54.64 J/g after 50 times of thermal cycles Xu et al [80] prepared sodium nitrate/diatomite based FSCPCM The maximum content of sodium nitrate in FSCPCM was 70% The melting temperature of the FSCPCM was 307.8 °C and the melting latent heat was 115.79 J/g The above researches showed that there was no chemical interaction between the inorganic PCMs and diatomite The FSCPMCs all showed good thermal reliability and good form stable due to the capillary force and the surface tension force of the diatomite The thermal properties of the diatomite based FSCPCMs were shown in Table Table The thermal properties of the diatomite based FSCPCM Diatomite based FSCPCMs Adsorption capacity(%) Melting temperature (°C) Latent heat of melting (J/g) Freezing temperature (°C) Latent heat of freezing (J/g) Thermal cycling (Times) Decrease ratio of the latent heat References N-octadecane/Diatomite Paraffin/Diatomite Hexadecane/Diatomite lauric Acid/Diatomite Polyethylene Glycol 1000/Diatomite Polyethylene Glycol 2000/Diatomite Capric Acid – Lauric Acid/Diatomite Capric Acid – palmic Acid/Diatomite Lithium Nitrate/Diatomite Sodium Sulfate/Diatomite Potassium Nitrate/Diatomite 47 42 47 40 50 58 47 63.5 60 60 65 31.29 57.09 23.68 40.9 27.7 57.92 16.74 26.7 250.7 887.61 330.23 116.8 61.96 120.1 57.4 87.09 105.7 66.81 98.3 215.6 101.59 60.52 23.65 50.23 13.17 38.7 32.2 46.03 – 21.85 243.58 887.61 332.9 112.9 59.74 118.0 57.2 87.05 95.46 – 90.03 190.3 102.34 47.3 – – – – 1000 200 – – 200 200 50 – – – – 1.1% 2.2% – – 9.3% 1.7% 9.7% [73] [73] [73] [74] [75] [76] [77] [78] [76] [76] [79] 302 M Li, J Shi / Construction and Building Materials 194 (2019) 287–310 5.2 Performance improvement of the diatomite based FSCPCM Although the thermal stability and chemical stability of the diatomite based FSCPCM are good, the adsorption performance, storage capacity and thermal conductivity are unsatisfactory So far, researchers have made some efforts to improve these properties 5.2.1 Improvement of the adsorption performance and heat storage performance Like the EV based FSCPCM and the EP based FSCPCM, the latent heats of the diatomite based FSCPCM were also mainly decided by the content of PCMs in the FSCPCM The heat storage performance of the diatomite based FSCPCM are enhanced with the increase of the adsorption capacity of the diatomite Modifying diatomite by grinding, calcinations and surface treatment is helpful to improve its adsorption capacity Sun et al [81] investigated the effects of calcination conditions including calcination temperature and calcination time on specific surface area of diatomite The results were shown in Fig 32 It demonstrated that the specific surface area of the diatomite increased initially with increasing the calcination temperature and the specific surface became stable when the calcination temperature reached 450 °C For diatomite, higher specific surface leaded to better adsorption capacity, so the optimum calcinations temperature was 450 °C Li et al [82] studied the adsorption capacity of diatomite with different particle sizes The results showed that the adsorption capacity of diatomite to paraf- fin was increased from 35% to 50% with the decreasing of particle size The latent heat of the FSCPCM was increased accordingly from 45.96 J/g to 63.98 J/g Qian et al [83] treated diatomite with sodium hydroxide and then prepared polyethylene glycol/diatomite FSCPCM using the modified diatomite as the supporting material The results indicated that the maximum content of polyethylene glycol in FSCPCM was increased from 48% to 70% The melting and freezing latent heats of the FSCPCM were increased by 40.8 J/g and 35.2 J/g, respectively The author reported that soluble silicates SiO2À formed after the treatment with sodium hydroxide, which resulted in the creation of larger pores, flaws, cracks and a larger surface area Therefore, the adsorption capacity of the diatomite was increased 5.2.2 Improvement of the thermal conductivity When the diatomite based FSCPCMs were used in the thermal energy storage systems, the high thermal conductivity was an important parameter, which could assure the high heater transfer efficiency For diatomite based FSCPCMs, the mainly method to improve the thermal conductivity was adding high thermal conductivity components such as Ag nanoparticles, carbon nanotubes and expanded graphite Xu et al [84] developed a thermal conductivity enhanced diatomite based FSCPCM with multi-walled carbon nanotubes The thermal conductivity of the modified FSCPCM was 1.8 W/mÁK with the addition of 0.26 wt% multi-walled carbon nanotubes The promotion percentage of the thermal conductivity was 42.5% compared to the FSCPCM without multi-walled carbon nanotubes Qian et al [85] chose the Ag nanoparticles as the thermal conductivity components They found that the thermal conductivity of the FSCPCM was increased by 127% after the addition of 7.2 wt% of Ag nanoparticles The authors contributed the improvement of the thermal conductivity to the Ag nanoparticles The same group also studied the improvement effect of the singlewalled carbon nanotubes [86] The result indicated that the thermal conductivity of the FSCPCM was increased by 180% when the addition of the single-walled carbon nanotubes was 2% The thermal conductivities of the diatomite based FSCPCMs were shown in Table 6 Expanded graphite based FSCPCM Fig 32 Variation of specific surface area of diatomite with different calcination temperature and time [81] Expanded graphite (EG) is a kind of carbonaceous raw materials obtained from natural flake graphite, which is treated by chemical or electrochemical intercalation and then been heated instantaneously to produce high-temperature expansion Graphite is consisted of multiple ‘‘microcells” There are many tiny pores within the micro-cells to form abundant pore structures of EG The figure schematic structural and magnification image of EG were shown in Figs 33 and 34, respectively [87,88] After the expansion, mainly Table The thermal conductivities of the diatomite based FSCPCM Diatomite based FSCPCMs Thermal Conductivity W/(mÁK) Adding amount (wt%) Increase ratio of the thermal conductivity References Polyethylene Glycol 1000/Diatomite Polyethylene Glycol 1000/Diatomite/EG 0.32 0.67 10 109.3% [75] Capric Acid – Palmitic Acid/Diatomite Capric Acid – Palmitic Acid/Diatomite/EG 0.19 0.292 53.7% [78] Paraffin/Diatomite Paraffin/Diatomite/Multi-walled Carbon Nanotubes 1.3 1.8 0.26 42.5% [84] Polyethylene Glycol 2000/Diatomite Polyethylene glycol 2000/Diatomite/Ag nanoparticles 0.35 0.82 7.2 127% [85] Polyethylene glycol 2000/diatomite Polyethylene glycol 2000/Diatomite/Single-walled Carbon Nanotubes 0.35 0.87 180% [86] M Li, J Shi / Construction and Building Materials 194 (2019) 287–310 Fig 33 The structure diagram of expanded graphite [87] 10 lm–100 lm two-dimensional layered pores are formed in the EG, as shown in Fig 35 [89] EG not only retained many advantages of natural graphite, but also possesses the features that natural graphite does not possess such as porous structure, high reactivity, large specific surface area, high compressibility and high elastic modulus Due to these characteristics, EG has excellent adsorption capacity Fig 36 showed the adsorption capacity of the EG to oil [90] Fig 35 The pore size distribution of expanded graphite [89] 6.1 Thermal properties of the EG based FSCPCM The preparation process of expanded graphite is simple and the cost of EG is low So, expanded graphite is often used as inorganic porous media to adsorb PCMs The excellent adsorption capacity of EG comes from the interconnected open pores and good compatibility with many surfaces The research results suggested that the adsorption capacity of EG to PCMs was much better than that of EP, EV and diatomite The adsorption capacity of EG varied from 80 wt% to 93 wt%, whereas the adsorption capacity of the EP and EV was about 60 wt% The adsorption capacity of the diatomite was much lower, which was about 50 wt% Accordingly, the heat storage capacity of the EG based FSCPCM was much better than that of the EP, EV and diatomite based FSCPCM The adsorption capacity and the latent heat of EP, EV, diatomite and EG based FSCPCM with paraffin as the phase change substance were compared in Table Zhang et al [91] used EG with thermal treatment to prepare EG/paraffin FSCPCM The mass content of paraffin in the FSCPCM Fig 36 The adsorption result of expanded graphite to oil [90] Fig 34 Low (a) and high (b) magnification image of expanded graphite [88] 303 304 M Li, J Shi / Construction and Building Materials 194 (2019) 287–310 Table The adsorption capacity and the latent heat of FSCPCMs with paraffin as the phase change substance Samples Adsorption capacity (%) Melting temperature (°C) Latent heat of melting (J/g) Freezing temperature (°C) Latent heat of freezing (J/g) References Paraffin/EG Paraffin/EG Paraffin/EV Paraffin/EP Paraffin/diatomite 85.56 92 67 60 42 48.79 52.2 48.0 27.56 57.09 161.45 170.3 135.5 80.9 61.96 – – 52.5 26.38 50.23 – – 137.6 79.3 59.74 [91] [92] [93] [56] [72] was 85.56% The melting temperature and latent heats of this FSCPCM were 48.79 °C and 161.45 J/g, respectively Due to the paraffin was held by the strong capillary force and the strong surface tension force of the EG, no leakage was occurred while paraffin was performing the phase change from solid to liquid in spite of the high content of paraffin The capric acid(CA)/EG FSCPCM, lauric acid(LA)/EG FSCPCM and myristic acid(MA)/EG FSCPCM were prepared by Sari et al [94] The maximum content of these fatty acids in the FSCPCMs were 80 wt% The melting latent heats of CA/EG FSCPCM, LA/EG FSCPCM and MA/EG FSCPCM were 132.64 J/g, 138.43 J/g and 145.64 J/g respectively The freezing latent heats of these FSCPCMs were 134.21 J/g, 139.16 J/g and 146.22 J/g respectively The leakage did not occur when the FSCPCMs melted, the reason for which was the same with the Ref [91] EG could be obtained after microwave treatment of graphite Compared with the high temperature heating process, microwave irradiation could be performed at room temperature in a very short time with less energy-consuming Zhang et al [92] prepared a paraffin/EG FSCPCM The graphite powder was dried in a vacuum oven at 70 °C for 20 h, followed by irradiating using a domestic microwave oven with an overall power of 800 W to yield the EG The maximum content of paraffin in this FSCPCM was 92 wt% and the latent heat of the FSCPCM was 173.1 J/g The octadecane/ EG FSCPCM was prepared by Li et al [95] and Kim et al [96] The EG they used was obtained after microwave treatment It was founded that there was no chemical reactions between the PCMs and the EG The tetradecyl alcohol(TD)/EG FSCPCM was developed by Zeng et al [97] In the preparation process, a certain amount of ethanol was added to improve the uniformity of the FSCPCM The results revealed that the maximum content of TD could reach up to 93 wt% in the FSCPCM The melting temperature and latent heats were 35.35 °C and 202.6 J/g, respectively It was observed from the SEM images that the pores of the EG were not fully occupied by TD The form-stability of the TD/EG composite form-stable PCMs under certain pressure comes from these partially occupied pores The SEM images of natural flake graphite, EG and TD/EG-2 was shown in Fig 37 No liquid D-Mannitol was observed on the surface of the FSCPCM during the solid–liquid phase change process when the mass content of the D-Mannitol was 85% The author believed the reason was that D-Mannitol was hold by the tension force and capillary force of the porous EG [98] The adsorption of the binary or multiple eutectic fatty acids in EG was studied by some researches The results showed that the preparation process and the properties of the prepared composite PCMs were similar with those using pure PCM as the phase change substance The succinic- adipic/EG FSCPCM was prepared by Liu et al [99] The mass content of eutectic acid was 90 wt% There were no chemical reactions between them The melting temperature and latent heats of the FSCPCM was 135 °C and 206 J/g respectively After 100 times of thermal cycles, the latent heat of the FSCPCM only decreased by 1.3% For the palmitic- stearic acid eutectic mixture/EG FSCPCM obtained by Yuan et al [100], the mass ratio of eutectic acid and expanded graphite was13:1 The melting temperature and melting latent heats of the FSCPCM was 53.89 °C and166.27 J/g, respectively After 720 times of thermal cycles, the latent heats of the FSCPCM changed slightly to 161.4 J/g, which showed the FSCPCM has good thermal reliability Except the above FSCPCMs, Capric-Palmitic-Stearic acid/EG FSCPCM [101], Luaric-Myristic-Palmitic acid/EG FSCPCM [102], Myristic-Palmitic-Stearic acid/EG FSCPCM [103] and CapricMyristic-Palmitic acid/EG FSCPCM [104] were also been prepared The results showed that the eutectic acid and EG were all combined by physical bonding The thermal cycling tests and TG analysis showed that these PCMs all have good thermal stability and chemical stability Inorganic PCMs such as sodiumnitrate, potassium nitrate, and their eutectic mixture [105] were also used in the EG based FSCPCMs The thermal properties of the EG based FSCPCMs were shown in Table 6.2 Thermal conductivity of the EG based FSCPCM The thermal conductivity of the EG based FSCPCM was much higher than the EP, EV and diatomite based FSCPCM because EG was used as not only the supporting material but also the heat conduction reinforced material Xia et al [110] researched the influence of the content of EG on the thermal conductivity of paraffin/ EG FSCPCM The results indicated that the thermal conductivity of the FSCPCM increased with the content of EG When the content of the EG was 10 wt%, the thermal conductivity of the FSCPCM was 3.83 W/mÁK, which was more than 10-fold higher than that of pure paraffin (0.305 W/mÁK) Mills et al [111] prepared EG based FSCPCM through capillary forces between liquid RT-24 paraffin and the EG The thermal conductivity of the FSCPCM (16.6 W/mÁK) was roughly 8200% higher than the thermal conductivity of the RT-24 paraffin (0.2 W/mÁK) The study of Xu et al [98] showed that the D-mannitol/EG FSCPCM loading 15 wt% EG has a thermal conductivity of 7.31 W/mÁK, which was increased by approximately 12 times compared with the thermal conductivity of pure D-Mannitol (0.60 W/mÁK) The thermal conductivity of FSCPCM of the palmitate-stearic acid/EG FCPCM [100] was 2.51 W/mÁK, which was 865% of the eutectic fatty acid Li et al [106] mixed EG and the lithium nitrate-potassium nitrate to prepare FSCPCM When the content of EG was 10 wt%, the thermal conductivity of the FSCPCM was up to 8.5–9.5 W/mÁK, which was more than times of the pure PCM The improvement of the thermal conductivity came from the high thermal conductivity of EG and the spatial network structure of EG, which caused an increase of the contact areas with the PCM The effect of the micropore grade inorganic porous medium based FSCPCMs on cement mortar Cement mortar as the common building materials was used in walls, floors, ceilings and other parts The current studies showed that adding micropore grade inorganic porous medium based FSCPCM into cement mortar would make the cement mortar possessing the ability of thermal storage and temperature-control The building energy could be saved consequently However, it would cause the decrease of the strength of the cement mortar 305 M Li, J Shi / Construction and Building Materials 194 (2019) 287–310 Fig 37 SEM images of natural flake graphite (a and b), EG (c and d) and TD/EG-2 (e and f) [97] Table Thermal properties of EG based FSCPCMs EG based FSCPCMs Adsorption capacity (%) Melting temperature (°C) Paraffin/EG Capric acid/EG Lauric acid/EG Myristic acid/EG Tetradecyl alcohol/EG D-Mannitol/EG 92 80 80 80 93 85 52 27 41 21 51 35 35 151 82 Succinic – Adipic acid/EG Palmitic – Stearic acid/EG Capric – Palmitic – Stearic acid/EG 90 92 90 136 53 89 21 33 Lithium nitrate-potassium nitrate/EG sodium sulfate decahydrate-sodium phosphate dibasic dodecahydrate/EG Calcium chloride hexahydrate/EG Lithium nitrate- potassium chlorid/EG 90 87 126.1 32.05 90 90 309.92 165.5 Latent heat of melting (J/g) Freezing temperature (°C) Latent heat of Freezing (J/g) Thermal cycling (times) Decrease ratio of the latent heat References Single organic PCMs 170 132 64 28 52 138 43 40 30 145 64 50 70 202 34 93 267 – 134 139 146 201 – – – – – – – – – – – – – [92] [94] [94] [94] [97] [98] Organic eutectic acid 207 134 166 27 54 37 131 19 01 203 166 13 127 100 720 500 1% 0.7% 5.6% [99] [100] [101] 152.4 140.8 100 100 0.8% 5.69% [106] [107] – – – – – – [108] [109] Inorganic PCMs 149.1 114.1 172.3 17.11 160.9 178.1 – – 21 16 22 306 M Li, J Shi / Construction and Building Materials 194 (2019) 287–310 7.1 Effect of the micropore grade inorganic porous medium based FSCPCMs on the heat storage performance of cement The effects of paraffin/expanded perlite FSCPCM on thermal properties of cement were studied by Li et al [112] They reported details of a testing device used to investigate the heat storage efficiency of a cement board with EP based FSCPCM The thermal behavior testing scheme was shown in Fig 38 The thermal behaviors of cement with and without EP based FSCPCM were shown in Fig 39 The results indicated that the maximum temperature difference between top and bottom surfaces of the panels (point A and B) for the cement board without EP based FSCPCM was °C and the maximum temperature difference for the cement board cement with EP based FSCPCM was 1.5 °C A higher temperature difference means greater thermal inertia This means the thermal inertia of the cement with EP based FSCPCM was improved compared to the cement without EP based FSCPCM The same authors also studied the effects of the paraffin/diatomite FSCPCM on the thermal property of the cement [81] The proportion of raw materials, the size of the cement board and the testing device were same with Ref [112] The thermal inertia of cement panels was shown in Fig 40 For R0, the temperature difference increases at certain rate before point After point 1, the difference stays nearly constant at °C For D30, the temperature difference develops similarly with R0 before point However, after point 1, the temperature differences of D30 increases sharply compared with R0 The results showed that the thermal inertia of cement panel was improved after addition of paraffin/diatomite FSCPCM in cement panel Ramakrishnan [113] developed a setup to measure the heat storage capacity of the cement with EP based FSCPCM, which was shown in Fig 41 The indoor temperature variation during two consecutive days was shown in Fig 42 The results illustrated Fig 38 thermal behavior testing scheme [112] Fig 40 Thermal inertia of cement panels: Ordinary cement (R0), Cement with paraffin/diatomite FSCPCM (D30) [81] that the peak temperature in the PCM enhanced test cell was 2.67 °C lower than that in the cement test cell over two consecutive days This meant the heat storage capacity of the cement with this EP based FSCPCM was improved In order to avoid leakage in the cement, He et al [114] coated the EP based FSCPCM with sealing materials They first prepared fatty acid/expanded perlite FSCPCM, and then coated the FSCPCM with paraffin Finally, the coated FSCPCM was added in cement to prepare heat storage mortar The results showed that the delay time of air temperature was for the normal mortar, whereas the delay time of the heat storage mortar was 24 This suggested that the heat storage performance of the mortar was increased with the addition of this EP based FSCPCM Similarly, Sun et al [115] developed a method of coating the paraffin/expanded perlite FSCPCM with epoxy resin They added the coated paraffin/expanded perlite FSCPCM in the cement mortar It was founded that the absorb/release heat time of cement mortar with paraffin/EP FSCPCM was approximately double compared to the ordinary cement mortar Xu et al [116] studied the influence of this FSCPCM on the heat storage performance of mortar The results revealed that the thermal energy storage capacity of the mortar with paraffin/diatomite FSCPCM was increased by 5.438 J/g compared to the mortar without FSCPCM The same authors also prepared lightweight mortar with heat storage capacity by replacing river sand with paraffin/EV FSCPCM [117] The results indicated that the elapsed time of the mortar with paraffin/EV FSCPCM was increased by 174.6% compared to the mortar without paraffin/EV FSCPCM The air temperature inside the holder box was reduced 4.3% Zhang et al [118] prepared a FSCPCM with high thermal conductivity and analyzed the influence of the FSCPCM on cement Fig 39 Thermal behaviors of R0 and E30 under low temperature change rate: Ordinary cement (R0), Cement with EP based FSCPCM (E30) [112] M Li, J Shi / Construction and Building Materials 194 (2019) 287–310 307 Fig 41 Prototype experiment set up (a) schematic diagram of test cell [units: mm] (b) physical set up [113] Fig 42 Indoor temperature variation during summer design days [113] Fig 43 SEM image of broken piece of cement/EPOP paste [115] mortar It was founded that, with the addition of this FSCPCM, the effective thermal value of cement mortar was decreased Moreover, the onset time of temperature peak was delayed and the cooling amplitude was increased, which means the mortar with this FSCPCM showed proper temperature controlling effects mortar was decreased by 66.7% compared to the ordinary mortar The similar results were obtained by Li et al [112] In the study of Xu et al [116], 30 wt% cement was replaced by paraffin/diatomite FSCPCM The results indicated that, compared with the mortar before replacement, the maximum 28 day compressive strength and flexural strength of the new mortar were decreased by 48.7% and 47.5%, respectively The compressive strength of cement with FSCPCM (TESC) and cement without FSCPCM (NC) at and 28 days was shown in Fig 44 They also prepared the 7.2 The influence of the micropore grade inorganic porous medium based FSCPCM on the strength of cement mortar It should be paid attention to that adding the EP based FSCPCM, EV based FSCPCM, diatomite based FSCPCM and EG based FSCPCM PCM into the cement mortar would reduce the compressive strength of the cement mortar In order to make FSCPCM acceptable for application in building, the content of the FSCPCM should be controlled appropriately to balance the demands between the heat storage performance and the strength and make Sun et al [115] used epoxy resin to coat the paraffin/EP FSCPCM firstly, and then studied the effect of the coated FSCPCM on the compressive strength of the cement mortar It was found that the compressive strength and flexural strength of mortar decreased with the increasing of the FSCPCM When 30% of cement was replaced by the FSCPCM, the compressive strength of the mortar decreased from 23.88 MPa to 9.27 MPa In the authors’ opinion, this was because the strength of paraffin/EP FSCPCM was obviously lower than that of sand and cement With more ‘‘soft” paraffin/EP based FSCPCM being added into cement mortar, the mechanical properties of the cement mortar became lower The broken FSCPCMs were visible on the failure surfaces, as shown in Fig 43 Ramakrishnan [113] replaced 80% of volume quartz sand with paraffin/ hydrophobic EP FSCPCM to prepare the heat storage mortar It was found that the 28 day compressive strength of the prepared Fig 44 Compressive strength of NC and various TESCs at and 28 days [116] 308 M Li, J Shi / Construction and Building Materials 194 (2019) 287–310 lightweight mortar with heat storage capacity by replacing the river sand with the paraffin/expanded vermiculite FSCPCM completely [117] The 28 day compressive strength of the lightweight mortar was 18.1 MPa, which was reduced by 56.5% compared to the mortar with river sand The lower stiffness of the fabricated FSCPCM compared to the river sand was the major reason for the mechanical strength reductions Zhang et al [119] carried out an investigation of the compressive strength of cement mortar containing the octadecane/EG FSCPCM The compressive strength of the mortar decreased from 23.7 MPa to 10.5 MPa when the content of the FSCPCM reached 2.5% The influence of the micropore grade inorganic porous medium based FSCPCM on the microstructure and hydration products of cement mortar should be further studied in order to get the mechanism of the strength decrease The influence of the micropore grade inorganic porous medium based FSCPCM on the durability of cement mortar, which was unclear presently, should be studied for the application in the field of the building Conflict of interest None Conclusions and outlook This paper reviewed the structure, morphology, pore size distribution and application characteristics of four micropore grade inorganic porous materials: expanded vermiculite, expanded perlite, expanded graphite and diatomite The preparation of FSCPCMs with these four kinds of materials as the supporting material was reported The thermal properties, performance improvement of the EP based FSCPCM, EV based FSCPCM, diatomite based FSCPCM and EG based FSCPCM was summarized The effect of the four FSCPCM on the cement mortar was also analyzed The conclusions were drawn as follow: Expanded vermiculite, expanded perlite, diatomite and expanded graphite with mainly micropore grade pores have abundant pore structures and appropriate pore size distribution for the adsorption of PCMs EG presented outstanding adsorption property among the four micropore grade inorganic porous materials, the adsorption capacity of which to PCM was up to 93% The more the adsorption capacity to PCM, the higher heat storage capacity the FSCPCMs had The EP based FSCPCM, EV based FSCPCM, diatomite based FSCPCM and EG based FSCPCM have the advantage of simple preparation process, wide source of raw materials and good thermal properties Especially, the EG based FSCPCM showed prominent thermal property For EP based FSCPCM, EV based FSCPCM, diatomite based FSCPCM and EG based FSCPCM, PCMs were stabilized in the pore structure of the supporting materials by the capillary force and surface tension The supporting material and the PCM were all combined physically The adsorption property, heat storage property and thermal conductivity of the EP based FSCPCM, EV based FSCPCM and diatomite based FSCPCM was enhanced by adding the thermal enhancement components and modifying EP, EV and diatomite The EG based FSCPCM itself showed outstanding properties because EG was used as not only the supporting material but also the thermal enhancement component The content of the FSCPCM in cement mortar should be controlled because the addition of the four FSCPCM into cement mortar would reduce the strength of the cement mortar although it endowed the cement mortar with the thermal storage property Based on the research status of the micropore grade inorganic porous medium based FSCPCM, the following aspects that should be researched further in the future was put forward The effect of the pore structure of the micropore grade inorganic porous medium on the heat transfer and phase change behavior of phase change materials needs to be further explored New methods to improve the thermal storage capacity and the thermal conductivity should be developed Acknowledgements The work was supported by the National Natural Science Foundation of China (51178102) and the key project of National Natural Science Foundation of China (51738003), which are financed by the National Natural Science Fund Committee References [1] L Nkhonjera, T Bello-Ochende, G John, C.K King’Ondu, A review of thermal energy storage designs, heat storage materials and cooking performance of solar cookers with heat storage, Renew Sustain Energy Rev 75 (2010) 157– 167 [2] M.M Farid, A.M Khudhair, S.A.K Razack, S Al-Hallaj, A review on phase change energy storage: materials and applications, Energy Convers Manage 45 (2004) 1597–1615 [3] Y Xu, Q Ren, Z.J Zheng, Evaluation and optimization of melting performance for a latent heat thermal energy storage unit partially filled with porous media, Appl Energy 193 (2017) 84–95 [4] P Arce, M Medrano, A Gil, E Oró, L.F Cabeza, Overview of thermal energy storage (TES) potential energy savings and climate change mitigation in Spain and Europe, Appl Energy 88 (2011) 2764–2774 [5] Y Wang, D Liang, F Liu, A polyethylene glycol/hydroxyapatite composite phase change material for thermal energy storage, Appl Therm Eng 113 (2017) 1475–1482 [6] H Zhang, J Baeyens, G Cáceres, J Degrève, Y Lv, Thermal energy storage: recent developments and practical aspects, Prog Energy Combust Sci 53 (2016) 1–40 [7] A Sharma, V.V Tyagi, C.R Chen, D Buddhi, Review on thermal energy storage with phase change materials and applications, Renew Sustain Energy Rev 13 (2009) 318–345 [8] S Jegadheeswaran, S.D Pohekar, Performance enhancement in latent heat thermal storage system: a review, Renew Sustain Energy Rev 13 (2009) 2225–2244 [9] D.P Bentz, R Turpin, Potential applications of phase change materials in concrete technology, Cem Concr Comp 29 (2007) 527–532 [10] P Zhang, X Xiao, Z.W Ma, A review of the composite phase change materials: fabrication, characterization, mathematical modeling and application to performance enhancement, Appl Energy 165 (2016) 472–510 [11] N.P Sharifi, A Sakulich, Application of phase change materials to improve the thermal performance of cementitious material, Eenerg Buildings 103 (2015) 83–95 [12] M Li, Z Wu, A review of intercalation composite phase change material: preparation, structure and properties, Renew Sustain Energy Rev 16 (2012) 2094–2101 [13] A Jamekhorshid, S.M Sadrameli, M Farid, A review of microencapsulation methods of phase change materials (PCMs) as a thermal energy storage (TES) medium, Renew Sustain Energy Rev 31 (2014) 531–542 [14] Y Lin, Y Jia, G Alva, G Fang, Review on thermal conductivity enhancement, thermal properties and applications of phase change materials in thermal energy storage, Renew Sustain Energy Rev 82 (2017) 2730–2742 [15] P Lv, C Liu, Z Rao, Review on clay mineral-based form-stable phase change materials: preparation, characterization and applications, Renew Sustain Energy Rev 68 (2017) 707–726 [16] N.P Sharifi, H Jafferji, S.E Reynolds, Application of lightweight aggregate and rice husk ash to incorporate phase change materials into cementitious materials, J Sustain Cem Mater (2016) 349–369 [17] C Amaral, R Vicente, P Marques, A Barros-Timmons, Phase change materials and carbon nanostructures for thermal energy storage: a literature review, Renew Sustain Energy Rev 79 (2017) 1212–1228 [18] H.N Tran, P.V Viet, H.P Chao, Surfactant modified zeolite as amphiphilic and dual-electronic adsorbent for removal of cationic and oxyanionic metal ions and organic compounds, Ecotoxicol Environ Saf 147 (2017) 55–63 [19] T Kadoono, M Ogura, Heat storage properties of organic phase-change materials confined in the nanospace of mesoporous sba-15 and cmk-3, PCCP 16 (2014) 5495–5498 M Li, J Shi / Construction and Building Materials 194 (2019) 287–310 [20] Y Wang, T.D Xia, H Zheng, H.X Feng, Stearic acid/silica fume composite as form-stable phase change material for thermal energy storage, Energy Build 43 (2011) 2365–2370 [21] X Fang, Z Zhang, A novel montmorillonite-based composite phase change material and its applications in thermal storage building materials, Energy Build 38 (2006) 377–380 [22] M Li, Z Wu, H Kao, Study on preparation, structure and thermal energy storage property of capric–palmitic acid/attapulgite composite phase change materials, Appl Energy 88 (2011) 3125–3132 [23] A Sari, Fabrication and thermal characterization of kaolin-based composite phase change materials for latent heat storage in buildings, Energy Build 96 (2015) 193–200 [24] J Wang, M Yang, Y Lu, Z Jin, L Tan, H Gao, Surface functionalization engineering driven crystallization behavior of polyethylene glycol confined in mesoporous silica for shape-stabilized phase change materials, NANO Energy 19 (2016) 78–87 [25] C Wang, L Feng, W Li, J Zheng, W Tian, X Li, Shape-stabilized phase change materials based on polyethylene glycol/porous carbon composite: the influence of the pore structure of the carbon materials, Sol Energy Mater Sol Cells 105 (2012) 21–26 [26] C Minkervillemin, P Bowen, J Lemtre, T.A Ring, Preparation and properties of potassium-vermiculite films, J Mate Res 13 (1998) 228–236 [27] D Shastri, H.S Kim, A new consolidation process for expanded perlite particles, Constr Build Mater 60 (2014) 1–7 [28] R Li, J Zhu, W Zhou, X Cheng, Y Li, Thermal properties of sodium nitrateexpanded vermiculite form-stable composite phase change materials, Mater Des 104 (2016) 190–196 [29] W Zhang, X Zhang, Z Huang, Z Yin, R Wen, Y Huang, Preparation and characterization of capric-palmitic-stearic acid ternary eutectic mixture/expanded vermiculite composites as form-stabilized thermal energy storage materials, J Mater Sci Technol 34 (2017) 379–386 [30] W.M Gua, J.H Li, T.T Qian, X Wang, Y Deng, Preparation of paraffin/expanded vermiculite with enhanced thermal conductivity by implanting network carbon in vermiculite layers, Chem Eng J 277 (2015) 56–63 [31] A Sari, A Karaipekli, Preparation, thermal properties and thermal reliability of capric acid/expanded perlite composite for thermal energy storage, Mater Chem Phys 109 (2008) 459–464 [32] H Wang, Z Xie, Xin, Enhancing thermal conductivity of palmitic acid based phase change materials with carbon nanotubes as fillers, Sol Energy 84 (2010) 339–344 [33] Y Zhang, L Wang, B Tang, R Lu, S Zhang, Form-stable phase change materials with high phase change enthalpy from the composite of paraffin and cross-linking phase change structure, Appl Energy 184 (2016) 241–246 [34] X Zhang, Z Yin, D Meng, Z Huang, R Wen, Y Huang, Shape-stabilized composite phase change materials with high thermal conductivity based on stearic acid and modified expanded vermiculite, Renew Energy 112 (2017) 113–123 [35] Z Lu, J Zhang, G Sun, B Xu, Z Li, C Cong, Effects of the form-stable expanded perlite/paraffin composite on cement manufactured by extrusion technique, Energy 82 (2015) 43–53 [36] D.G Schulze, J.B Dixon, D.G Schulze, An introduction to soil mineralogy, Mineralogy (2002) 1–35 [37] W Yang, Y Zheng, A Zaoui, Swelling and diffusion behaviour of navermiculite at different hydrated states, Solid State Ionics 282 (2015) 13– 17 [38] A.M Rashad, Vermiculite as a construction material – a short guide for civil engineer, Constr Build Mater 125 (2016) 53–62 [39] O Chung, S.G Jeong, S Kim, Preparation of energy efficient paraffinic PCMs/expanded vermiculite and perlite composites for energy saving in buildings, Sol EnergyMater Sol Cells 137 (2015) 107–112 [40] W.A Schacko, C Effting, M.V Folgueras, S Güths, G.A Mendes, Mechanical and thermal properties of lightweight concretes with vermiculite and EPS using air-entraining agent, Constr Build Mater 57 (2014) 190–197 [41] F.N Do, J.C Masini, Influence of humic acid on adsorption of Hg(ii) by vermiculite, J Environ Manage 143 (2014) 1–7 [42] R Wen, Z Huang, Y Huang, X Zhang, X Min, M Fang, Synthesis and characterization of lauric acid/expanded vermiculite as form-stabilized thermal energy storage materials, Energy Build 116 (2016) 677–683 [43] A Karaipekli, A Sari, Capric–myristic acid/vermiculite composite as formstable phase change material for thermal energy storage, Sol Energy 83 (2009) 323–332 [44] R Wen, X Zhang, Y Huang, Z Yin, Z Huang, M Fang, Preparation and properties of fatty acid eutectics/expanded perlite and expanded vermiculite shape-stabilized materials for thermal energy storage in buildings, Energy Build 139 (2017) 197–204 [45] A Karaipekli, A Sari, Preparation, thermal properties and thermal reliability of eutectic mixtures of fatty acids/expanded vermiculite as novel form-stable composites for energy storage, J Ind Eng Chem 16 (2010) 767–773 [46] H Wei, X Li, Preparation and characterization of a lauric-myristic-stearic acid/ Al2 O3-loaded expanded vermiculite composite phase change material with enhanced thermal conductivity, Sol EnergyMater Sol Cells 166 (2017) 1–8 [47] X Li, H Wei, X Lin, Preparation of stearic acid/modified expanded vermiculite composite phase change material with simultaneously enhanced thermal conductivity and latent heat, Sol Energy Mater Sol Cells 155 (2016) 9–13 309 [48] H Wei, X Xie, X Li, X Lin, Preparation and characterization of capricmyristic-stearic acid eutectic mixture/modified expanded vermiculite composite as a form-stable phase change material, Appl Energy 178 (2016) 616–623 [49] Y Deng, J Li, H Nian, Polyethylene glycol-enwrapped silicon carbide nanowires network/expanded vermiculite composite phase change materials: Form stabilization, thermal energy storage behavior and thermal conductivity enhancement, Sol Energy Mater Sol Cells 174 (2018) 283–291 [50] Y Deng, J Li, T Qian, W Guan, Y Li, X Yin, Thermal conductivity enhancement of polyethylene glycol/expanded vermiculite shape-stabilized composite phase change materials with silver nanowire for thermal energy storage, Chem Eng J 295 (2016) 427–435 [51] Y Deng, J Li, H Nian, H Jiang, Supercooling suppression and thermal conductivity enhancement of na2hpo4Á12h2o/expanded vermiculite formstable composite phase change materials with alumina for heat storage, ACS Sustain Chem Eng (2018) 6792–6801 [52] L Meesuk, S Seammai, The use of perlite to remove dark colour from repeatedly used palm oil, J Environ Sci Health A Toxic Hazard Subst Environ Eng 41 (2006) 1189–1200 [53] A Kanm, M Karadasß, M Dog˘an, O Demirbasß, Adsorption of CTAB onto perlite samples from aqueous solutions, J Colloid Interf Sci 291 (2005) 309–318 [54] H Allameh-Haery, E Kisi, J Pineda, L.P Suwal, T Fiedle, Elastic properties of green expanded perlite particle compacts, Powder Technol 310 (2017) 329– 342 [55] H Ghassabzadeh, M Torab-Mostaedi, A Mohaddespour, M.G Maragheh, S.J Ahmadi, P Zaheri, Characterizations of Co (ii) and Pb (ii) removal process from aqueous solutions using expanded perlite, Desalination 261 (2010) 73– 79 [56] T Nomura, N Okinaka, T Akiyama, Impregnation of porous material with phase change material for thermal energy storage, Mater Chem Phys 115 (2009) 846–850 [57] Z Lu, B Xu, J Zhang, Y Zhu, G Sun, Z Li, Preparation and characterization of expanded perlite/paraffin composite as form-stable phase change material, Sol Energy 108 (2014) 460–466 [58] A Sari, A Karaipekli, C Alkan, Preparation, characterization and thermal properties of lauric acid/expanded perlite as novel form-stable composite phase change material, Chem Eng J 155 (2009) 899–904 [59] J Liu, Y Yu, X He, Research on the preparation and properties of lauric acid/expanded perlite phase change materials, Energy Build 110 (2016) 108– 111 [60] J Zhang, X Guan, X Song, H Hou, Z Yang, J Zhu, Preparation and properties of gypsum based energy storage materials with capric acid–palmitic acid/expanded perlite composite PCM, Energy Build 92 (2015) 155–160 [61] C Jiao, B Ji, D Fang, Preparation and properties of lauric acid – stearic acid/expanded perlite composite as phase change materials for thermal energy storage, Mater Lett 67 (2012) 352–354 [62] N Zhang, Y Yuan, T Li, X Cao, Lauric–palmitic–stearic acid/expanded perlite composite as form-stable phase change material: preparation and thermal properties, Energy Build 82 (2014) 505–511 [63] R Li, J Zhu, W Zhou, X Cheng, Y Li, Thermal compatibility of sodium nitrate/expanded perlite composite phase change materials, Appl Therm Eng 103 (2016) 452–458 [64] S Ramakrishnan, J Sanjayan, W Wang, M Alam, J.A Wilson, Novel paraffin/expanded perlite composite phase change material for prevention of PCM leakage in cementitious composites, Appl Energy 157 (2015) 85–94 [65] X Zhang, R Wen, C Tang, B Wu, Z Huang, Thermal conductivity enhancement of polyethylene glycol/expanded perlite with carbon layer for heat storage application, Energy Build 130 (2016) 113–121 [66] S Ramakrishnan, X Wang, J Sanjayan, J Wilson, Heat transfer performance enhancement of paraffin/expanded perlite phase change composites with craphene nano-platelets, Energy Procedia 105 (2017) 4866–4871 [67] D Sun, L Wang, C Li, Preparation and thermal properties of paraffin/expanded perlite composite as form-stable phase change material, Mater Lett 108 (2013) 247–249 [68] A Karaipekli, A Biỗer, A Sar, V.V Tyagi, Thermal characteristics of expanded perlite/paraffin composite phase change material with enhanced thermal conductivity using carbon nanotubes, Energy Convers Manag 134 (2017) 373–381 [69] Q Zhou, H Yang, C Yan, W Luo, X Li, J Zhao, Synthesis of carboxylic acid functionalized diatomite with a micro-villous surface via UV-induced graft polymerization and its adsorption properties for Lanthanum(iii) ions, Colloids Surfaces A Physicochemical Eng Aspects 501 (2016) 9–16 [70] Y He, B Jiang, Y Jiang, J Chen, Y.X Zhang, Evaluation of MnO2-templated iron oxide-coated diatomites for their catalytic performance in heterogeneous photo fenton-like system, J Hazardous Mater 344 (2017) 230–240 [71] W Yuan, P Yuan, D Liu, L Deng, J Zhou, W Yu, A hierarchically porous diatomite/silicalite-1 composite for benzene adsorption/desorption fabricated via a facile pre-modification in situ, synthesis route, Chem Eng J 294 (2016) 333–342 [72] Q Sun, H Li, S Zheng, Z Sun, Characterizations of nano-TiO2/diatomite composites and their photocatalytic reduction of aqueous Cr (vi), Appl Surface Sci 311 (2014) 369–376 [73] S.G Jeong, J Jeon, J.H Lee, S Kim, Optimal preparation of PCM/diatomite composites for enhancing thermal properties, Int J Heat Mass Tran 62 (2013) 711–717 310 M Li, J Shi / Construction and Building Materials 194 (2019) 287–310 [74] X Fu, Z Liu, Y Xiao, J Wang, J Lei, Preparation and properties of lauric acid/diatomite composites as novel form-stable phase change materials for thermal energy storage, Energy Build 104 (2015) 244–249 [75] S Karaman, A Karaipekli, A Sari, A Bier, Polyethylene glycol (PEG)/diatomite composite as a novel form-stable phase change material for thermal energy storage, Sol Energy Mater Sol Cells 95 (2011) 1647–1653 [76] T Qian, J Li, X Min, Y Den, W Guan, L Ning, Diatomite: a promising natural candidate as carrier material for low, middle and high temperature phase change material, Energy Convers Manage 98 (2015) 4–45 [77] M Li, Z Wu, H Kao, Study on preparation and thermal properties of binary fatty acid/diatomite shape-stabilized phase change materials, Sol Energy Mater Sol Cells 95 (2011) 2412–2416 [78] F Tang, D Su, Y Tang, G Fang, Synthesis and thermal properties of fatty acid eutectics and diatomite composites as shape-stabilized phase change materials with enhanced thermal conductivity, Sol Energy Mater Sol Cells 141 (2015) 218–224 [79] Y Deng, J Li, et al., Preparation and characterization of kno3/diatomite shapestabilized composite phase change material for high temperature thermal energy storage, J Mater Sci Technol (2016) 198–203 [80] G Xu, G Leng, Sodium nitrate – Diatomite composite materials for thermal energy storage, Energy Build 146 (2017) 494–502 [81] Z Sun, Y Zhang, S Zheng, Y Park, R.L Frost, Preparation and thermal energy storage properties of paraffin/calcined diatomite composites as form-stable phase change materials, Therm Acta 558 (2013) 16–21 [82] X Li, J.G Sanjayan, J.L Wilson, Fabrication and stability of form-stable diatomite/paraffin phase change material composites, Energy Build 76 (2014) 284–294 [83] T Qian, J Li, Y Deng, Pore structure modified diatomite-supported peg composites for thermal energy storage, Sci Rep (2016) 32392 [84] B Xu, Z Li, Paraffin/diatomite/multi-wall carbon nanotubes composite phase change material tailor-made for thermal energy storage cement-based composites, Energy 72 (2014) 371–380 [85] J Li, T Qian, et al., Enhanced thermal conductivity of peg/diatomite shapestabilized phase change materials with Ag nanoparticles for thermal energy storage, J Mater Chem A (2015) 8526–8536 [86] T Qian, J Li, W Feng, H Nian, Enhanced thermal conductivity of form-stable phase change composite with single-walled carbon nanotubes for thermal energy storage, Sci Rep (2017) 44710 [87] L Yi, L Liu, et al., Expanded graphite@sno @ polyaniline composite with enhanced performance as anode materials for lithium ion batteries, Electrochim Acta 240 (2017) 63–71 [88] Q Wang, Y Li, S Jin, S Sang, Catalyst-free hybridization of silicon carbide whiskers and expanded graphite by vapor deposition method, Ceram Int 41 (2015) 14359–14366 [89] H.N Wang, Y.P Zheng, F.Y Kang, Quantitative analysis of the pore structure of expanded graphite, J Inorganic Mater 18 (2003) 606–612 [90] C Xu, C Jiao, R Yao, A Lin, W Jiao, Adsorption and regeneration of expanded graphite modified by ctab-kbr/h3po4 for marine oil pollution, Environ Pollut 233 (2017) 194–200 [91] Z Zhang, X Fang, Study on paraffin/expanded graphite composite phase change thermal energy storage material, Acta Energiae Solaris Sin 47 (2006) 303–310 [92] Z.G Zhang, N Zhang, J Peng, X.M Fang, X.N Gao, Y.T Fang, Preparation and thermal energy storage properties of paraffin/expanded graphite composite phase change material, Appl Energy 91 (2012) 426–431 [93] C Li, H Yang, Expanded vermiculite/paraffin composite as a solar thermal energy storage material, J Am Ceram Soc 96 (2013) 2793–2798 [94] A Sari, A Karaipekli, K Kaygusuz, Fatty acid/expanded graphite composites as phase change material for latent heat thermal energy storage, Energy Sources 30 (2008) 464–474 [95] H Li, X Liu, G.Y Fang, Synthesis and characteristics of form-stable noctadecane/expanded graphite composite phase change materials, Appl Phys A 100 (2010) 1143–1148 [96] D Kim, J Jung, Y Kim, M Lee, J Seo, S.B Khan, Structure and thermal properties of octadecane/expanded graphite composites as shape-stabilized phase change materials, Int J Heat Mass Transf 95 (2016) 735–741 [97] J.L Zeng, J Gan, et al., Tetradecanol/expanded graphite composite form-stable phase change material for thermal energy storage, Sol Energy Mater Sol Cells 127 (2014) 122–128 [98] T Xu, Q Chen, G Huang, Z Zhang, X Gao, S Lu, Preparation and thermal energy storage properties of d-mannitol/expanded graphite composite phase change material, Sol Energy Mater Sol Cells 155 (2016) 141–146 [99] S Liu, L Han, et al., A novel medium-temperature form-stable phase change material based on dicarboxylic acid eutectic mixture/expanded graphite composites, Sol Energy 143 (2017) 22–30 [100] Y Yuan, Y Yuan, N Zhang, L.I Tianyu, X Cao, Preparation and properties of lauric-palmitic-stearic acid eutectic mixture/expanded graphite composite phase change material for energy storage, Ciesc J (2014) [101] H Zhang, X Gao, C Chen, T Xu, Y Fang, Z Zhang, A capric–palmitic–stearic acid ternary eutectic mixture/expanded graphite composite phase change material for thermal energy storage, Compos A Appl Sci Manuf 87 (2016) 138–145 [102] N Zhang, Y Yuan, X Wang, X Cao, X Yang, S Hu, Preparation and characterization of lauric–myristic–palmitic acid ternary eutectic mixtures/expanded graphite composite phase change material for thermal energy storage, Chem Eng J 231 (2013) 214–219 [103] X Yang, Y Yuan, N Zhang, X Cao, C Liu, Preparation and properties of myristic–palmitic–stearic acid/expanded graphite composites as phase change materials for energy storage, Sol Energy 99 (2014) 259–266 [104] Y Yuan, Y Yuan, N Zhang, Y Du, X Cao, Preparation and thermal characterization of capric–myristic–palmitic acid/expanded graphite composite as phase change material for energy storage, Mater Lett 125 (2014) 154–157 [105] X Xiao, P Zhang, M Li, Thermal characterization of nitrates and nitrates/expanded graphite mixture phase change materials for solar energy storage, Energy Convers Manage 73 (2013) 86–94 [106] Y Li, P Li, Q.Z Zhu, Q.F Li, Preparation and thermal characterization of nitrates/expanded graphite composite phase-change material for thermal energy storage, Int J Thermophys 37 (2016) 104 [107] Y Wu, T Wang, Hydrated salts/expanded graphite composite with high thermal conductivity as a shape-stabilized phase change material for thermal energy storage, Energy Convers Manage 101 (2015) 164–171 [108] Z.J Duan, H.Z Zhang, L.X Sun, Z Cao, F Xu, Y.J Zou, et al., Cacl 6h o/expanded graphite composite as form-stable phase change materials for thermal energy storage, J Therm Anal Calorim 115 (2014) 111–117 [109] Z Huang, X Gao, T Xu, Y Fang, Z Zhang, Thermal property measurement and heat storage analysis of lino 3/kcl – expanded graphite composite phase change material, Appl Energy 115 (2014) 265–271 [110] L Xia, P Zhang, R.Z Wang, Preparation and thermal characterization of expanded graphite/paraffin composite phase change material, Carbon 48 (2010) 2538–2548 [111] A Mills, M Farid, J.R Selman, S Al-Hallaj, Thermal conductivity enhancement of phase change materials using a graphite matrix, Appl Therm Eng 26 (2006) 1652–1661 [112] X Li, H Chen, L Liu, Z Lu, J.G Sanjayan, W.H Duan, Development of granular expanded perlite/paraffin phase change material composites and prevention of leakage, Sol Energy 137 (2016) 179–188 [113] S Ramakrishnan, X Wang, J Sanjayan, J Wilson, Thermal performance assessment of phase change material integrated cementitious composites in buildings: experimental and numerical approach, Appl Energy (2017) [114] Y He, X Zhang, Y Zhang, Preparation technology of phase change perlite and performance research of phase change and temperature control mortar, Energy Build 85 (2014) 506–514 [115] D Sun, L Wang, Utilization of paraffin/expanded perlite materials to improve mechanical and thermal properties of cement mortar, Construct Build Mater 101 (2015) 791–796 [116] B Xu, Z Li, Paraffin/diatomite composite phase change material incorporated cement-based composite for thermal energy storage, Appl Energy 105 (2013) 229–237 [117] B Xu, H Ma, Z Lu, Z Li, Paraffin/expanded vermiculite composite phase change material as aggregate for developing lightweight thermal energy storage cement-based composites, Appl Energy 160 (2015) 358–367 [118] Y He, X Zhang, Y Zhang, Q Song, X Liao, Utilization of lauric acid-myristic acid/expanded graphite phase change materials to improve thermal properties of cement mortar, Energy Build 133 (2016) 547–558 [119] Z Zhan, G Shi, S Wang, X Fang, X Liu, Thermal energy storage cement mortar containing n-octadecane/expanded graphite composite phase change material, Renew Energy 50 (2013) 670–675  ... FSCPCMs on the heat storage performance of cement 7.2 The influence of the micropore grade inorganic porous medium based FSCPCM on the strength of cement mortar Conclusions... FSCMs on cement mortar are summarized The preparation method and characterization of micropore grade inorganic porous medium based FSCPCMs The preparation method of micropore grade inorganic porous. .. the thermal enhancement component The content of the FSCPCM in cement mortar should be controlled because the addition of the four FSCPCM into cement mortar would reduce the strength of the cement