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Glassceramics are polycrystalline materialscomposed of at least one crystalline phase and avitreous matrix phase, which is produced by thecontrolled crystallization. Wideranging propertiesof glassceramics can be modified in a predictableway by controlling the chemical compositions andheat treatment scheduleE163. AlzO3SiOzZrOz system is seldom reported due to the high meltingtemperature. ZrOz, TiOz and PzO5 are commonnucleating agents. In glassceramics, ZrO2 is an effective nucleating agent due to the characteristicsof high electrovalency and electric field intensity,which facilitate the accumulation of glass fabric,but the solubility of ZrOz in silicate glass system islow ( ~ 5 % , mass fraction). Chen et al¢781 reported that ZrO2 in glassceramics improved the mechanical properties, especially fracture toughnessKlc and wear resistance. But Liu et alE93 pointedout that ZrO2 used as nucleating agent individuallydid not induce bulk crystallization in KzOMgOSiO2 system. PiersonE1°3found that the solubility ofTiO2 was so high (2%20°~) that lots of hypomicrons were precipitated during reheating or cooling, and the hypomierons facilitated the mainphase to be precipitated from glass matrix. Doherty et alEu3 pointed out that TiO2 was beneficial tophase separation and the subsequent formation of
Journal of Non-Crystalline Solids 368 (2013) 98–104 Contents lists available at SciVerse ScienceDirect Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/ locate/ jnoncrysol Effects of nano silica on synthesis and properties of glass ceramics in SiO2–Al2O3–CaO–CaF2 glass system: A comparison Debasis Pradip Mukherjee, Sudip Kumar Das ⁎ Department of Chemical Engineering, University of Calcutta, 92, A P C Road, Kolkata, 700 009, India a r t i c l e i n f o Article history: Received December 2012 Received in revised form March 2013 Available online April 2013 Keywords: Glass ceramics; Nano-SiO2; Crystallization; DTA; SEM a b s t r a c t Glass ceramics of composition 34SiO2–29Al2O3–25CaO–12CaF2 (wt.%) was made by conventional melting and quenching process using either normal or nano-SiO2 respectively The glasses were characterized by differential thermal analysis (TG/DTA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) The crystallization, microstructure, mechanical and chemical properties were compared for the two systems With nano-SiO2 addition, the crystallization peak temperature (Tp) decreases, activation energy (E) and Avrami parameter (n) have very little change, and the mechanism of crystallization of the glass ceramics changed from surface crystallization to two-dimensional crystallization The crystallite size of nano-SiO2 containing glass is lower than the normal SiO2 containing glass Introduction of nano-SiO2 particles in glass ceramics gives higher Vickers hardness, shrinkage, lower water absorption, and higher acid resistance than the normal silica containing glass ceramics, thus making it more useful for industrial building, internal and external wall facing and tiles applications © 2013 Elsevier B.V All rights reserved Introduction Experimental procedure There is considerable interest in the glass ceramic materials for their clinical and household applications [1] Glass ceramics can be prepared either by heat treatment of preformed glass or by sintering techniques [2,3] However, the properties depend on the composition of phases and the microstructure developed during the manufacturing process [4] The basic materials are SiO2–Al2O3–CaO and the nucleating agent, which serve the proper nucleation and crystallization It is observed that the use of CaF2 as a nucleating agent in this system gives better crystallization and microstructure [4].The physical properties like strength, permeability, chemical resistance and Vickers hardness are depending on its structure The nano-SiO2 has drawn much attention as its application in industries like the production of pharmaceuticals, pigments and catalyst etc, [5] Researchers show that the addition of nano-SiO2 in concrete improved its mechanical properties [6–14] The nano-SiO2 has a uniform size and shape The use nano-SiO2 may provide more homogeneous distribution within the glass ceramic and hence enhance properties like hardness, chemical resistance, shrinkage and water absorption etc This paper deals with the preparation of SiO2–Al2O3–CaO–CaF2 glass ceramics using normal silica (BS) and nano-SiO2 (BNS) and compared their characteristic, physical, chemical and mechanical properties The glass batches with weight percent composition (Table 1) were prepared using high-purity chemicals of Calcium carbonate, CaCO3 (99.9%, Merck Specialties Private Limited, India), alumina, Al2O3 (99.3%, Merck Specialties Private Limited, India), silica, SiO2 (particle size 40–150 mesh, 99.8%, Merck Specialties Private Limited, India), calcium fluoride CaF2 (99.0%, Merck Specialties Private Limited, India) and nano-SiO2 (particle size 0.014 μ, 99.9%, Sigma-Aldrich, St Louis, MO, USA) by the conventional melt-quench technique The samples have been designated as BS and BNS respectively About 100 g of glass batch was mixed thoroughly by attrition mill and then melted in an alumina crucible in an electrically heated furnace at 1450 °C and kept at this temperature for h in air with intermittent stirring The glass melt was poured into a preheated iron mold to make glass block, followed by annealing at 600 °C for h to removed the internal stresses of the prepared glass followed by natural cooling to room temperature The as-prepared annealed block was shaped into desired dimensions (50 mm × mm × mm) by cutting machine (Buehler, Lake Bluff, IL) These cut samples were subjected in heat treatment at a rate °C/min at temperature range from 850 °C to 1150 °C and soaked for h ⁎ Corresponding author Tel.: +91 9830638908 E-mail address: drsudipkdas@vsnl.net (S.K Das) 0022-3093/$ – see front matter © 2013 Elsevier B.V All rights reserved http://dx.doi.org/10.1016/j.jnoncrysol.2013.03.012 2.1 Measurement and characterization techniques The thermal behavior of the glasses was evaluated by differential thermal analyzer (Pyris Diamond TG/DTA, PerkinElmer, Singapore) in nitrogen atmosphere (150 ml/min) at constant heating rate 10 °C/min D.P Mukherjee, S.K Das / Journal of Non-Crystalline Solids 368 (2013) 98–104 99 30 4.30 Table Chemical composition of the investigated glass (wt.%) a CaO Al2O3 SiO2 Nano-SiO2 CaF2 BS BNS 25 25 29 29 34 – – 34 12 12 25 4.25 20 H v ¼ 1:8544  P d2 ð1Þ where Hv is the Vickers hardness number (VHN) in kg/mm 2, P is the normal load in kg, and d is the average diagonal length of the indentation in mm Results and discussion The DTA curves for two different specimens BS and BNS at a heating rate of 10 °C/min are shown Fig (a)–(b) respectively One exothermic peak was observed in both the specimens The exothermic peak corresponds to wollastonite, anorthite and gehlenite Nano-SiO2 affected the glass transition temperature (Tg) and the crystallization peak temperature (Tp) as shown in Fig 1(b) It can be seen that the crystallization peak temperature occurred at nearly 951 °C for BS and 895 °C for BNS The kinetics of crystal growth can be described from the Johnson– Mehl–Avrami (JMA) equation [18–21], n 4.15 o 951.03 C 10 4.10 4.05 500 600 700 800 900 -5 1000 Temperature(oC) 13.90 b 20 15 13.85 Weight (%) 10 13.80 o 895.14 C 13.75 -5 -10 13.70 500 600 700 800 900 -15 1000 Temperature(oC) Fig (a)–(b) DTA curves of the two glass batches at a heating rate at 10 °C/min the reaction rate constant which is related to the absolute temperature T, as given by Arrhenius type equation, E k ¼ ν exp − RT ð2Þ where, v is the frequency factor, R gas constant and E activation energy of crystal growth From Eqs (1) and (2), non–isothermal crystallization kinetics of glass can be described by the expression [17–20], 3.1 Differential thermal analysis (DTA) − lnð1−xÞ ¼ ðkt Þ 15 Heat flow endo down (mW) with α-Al2O3 powder as reference material to evaluate the glass crystallization peak temperature (Tp) 20 mg of glass samples were taken in platinum crucible and heated at the rate of 5, 10, 15 and 20 °C/min in TG/DTA to study the kinetics of crystallization and also to calculate the activation energy using Kissinger equation and Avrami parameter using Augis–Bennett equation Precipitated crystalline phases present in the heat treated glass ceramics were identify by using X-ray diffractometers (PANalytical PW3040/60, The Netherlands) with Ni filtered Cu Kα X-rays and a scanning speed of 1°/min The XRD pattern was recorded within Bragg angle from 5° to 80° 2θ range The FTIR spectra of the heat treated glasses were recorded using a Fourier transform infrared spectrometer (Alpha FTIR, Bruker, Germany), on potassium bromide (KBr) pellets prepared by mixing of mg samples to 20 mg KBr The microstructures of the samples were carried out by scanning electron microscope (FEI-QUANTA-200, the Netherland) after polishing and then chemically etched using 10% HF solution for 15–20 s The densities of ceramized glasses were measured via the Archimedes' method The chemical resistance was estimated by immersing the rectangular specimens (50 mm × mm × mm) into 150 ml of 0.1 N NaOH and 0.1 N HCl solutions and reheated at 95 °C for h The linear shrinkage was calculated from the dimension of bulk and sintered samples Water absorption was evaluated by the ISO-standard 10545-3, 1995, (i.e., weight gain of the samples after immersion into boiling water for h) [15] The hardness was measured by taking micro-indentation on the polished surface of the samples Using 160 microhardness testers (Carl Zeiss Jena, Germany) equipped with a conical Vickers indenter at an indent load of 40 g Ten indents were taken for each sample with identical loading condition and average of this was used to calculate the hardness using the standard equation for the Vickers geometry as [16,17], Weight (%) 4.20 Heat flow endo down (mW) Batches ð1Þ where x is the volume fraction of crystallized phase at time t, n is the Avrami exponent related to the mechanism of crystallization, and k is ln Tp E E ¼ þ ln RT p Rν β ð3Þ where, Tp is the crystallization peak maximum temperature of the DTA curve, β heating rate of DTA, R gas constant and E activation energy of crystal growth The plots of ln(Tp2/β) versus 1/Tp for two glass samples are shown in Fig 2, they are linear in nature These values of the E and ν are calculated from the intercept and slope of these straight lines and reported in Table From the value of activation energy E, the Avrami parameter (n) is calculated by using the Augis–Bennett equation [22], n¼ 2:5 RT p  ΔT E ð4Þ D.P Mukherjee, S.K Das / Journal of Non-Crystalline Solids 368 (2013) 98–104 13.0 Table JCPDS files used to identify the crystalline phase formed at different temperatures ln( T p / 12.0 11.5 11.0 10.5 10.0 10.2 10.4 10.6 10.8 11.0 11.2 11.4 (1/Tp) x104 Fig Variation of ln(Tp2/β) vs 1/Tp for BS and BNS glass batches where, ΔT is the full width of the exothermic peak at half maximum intensity The Avrami exponent (n) depends upon the actual nucleation and crystal growth mechanism According to the JMA theory, Avrami exponent (n) is also related to crystallization pattern, n ≅ means that the surface crystallization dominants the overall crystallization, n ≅ means two dimensional crystallization, n ≅ means that three dimensional crystallization for bulk materials [23–25] Table shows the Avrami exponents that were 2.69 and 2.85 respectively, which are close to 3, and this means that bulk nucleation and two dimensional growths occur for the glass-ceramics 3.2 X-ray diffraction analysis (XRD) The JCPDS reference files are used to identify the crystal phases formed in the glass ceramics batches are shown in Table In BS, at 850 °C, peaks of anorthite (CaAl2Si2O8) and wollastonite (CaSiO3) appeared as major phases The intensity and amount of this phases increases with increasing sintering temperature as shown in Fig 3(a) At 950 °C, several peaks of anorthite at 23.7° (d = 3.7389 Å), 27.2° (3.2737 Å), 28.0° (3.1949 Å), 31.1° (2.8775 Å), 39.1° (2.2992 Å), 43.0° (2.1076 Å) due to diffractions from the triclinic form (cell constants a = 8.186 Å, b = 12.876 Å, c = 14.182 Å; JCPDS Card No 70-0287) wollastonite at 29.3° (3.0363 Å), 29.9° (2.9901 Å), 43.9° (2.0720 Å), 48.9° (1.8661 Å) due to diffractions from the triclinic form (a = 7.94 Å, b = 7.32 Å, c = 7.07 Å; JCPDS Card No 76-0186) and a new phase, gehlenite (Ca2Al2SiO7) at 10.2° (8.6844 Å), 17.7° (4.9930 Å), 59.5° (1.5650 Å), and 67.9° (1.3790 Å) due to diffractions from the tetragonal form (a = 7.6858 Å, c = 5.0683 Å; JCPDS Card No 35-0755) appeared At 1050 °C, peaks of anorthite at 24.1° (3.6369 Å), 27.3° (3.2672 Å), Table DTA for the two glass specimen at different heating rates Batch no Heating rate (β) (°C/min) Crystallization peak temperature (Tp) (K) Activation energy (kJ mol−1) Avrami exponent (n) ‹n› BS 10 15 20 10 15 20 931.05 951.03 963.06 971.01 883.12 895.14 904.11 911.09 293.17 2.50 2.57 2.63 2.67 2.66 2.73 2.78 2.83 2.69 BNS 305.21 Crystal phase JCPDS reference no Anorthite (CaAl2Si2O8) — A Gehlenite (Ca2Al2SiO7) — G Wollastonite (CaSiO3) — W 00-70-0287 00-35-0755 00-76-0186 27.9°(3.1920 Å), 31.0° (2.8782 Å), 39.5° (2.3013 Å), 42.9° (2.1061 Å) wollastonite at 29.4° (3.0381 Å), 29.8°(2.9893 Å), 43.6° (2.0730 Å), 47.8° (1.8645 Å) and gehlenite at 10.8° (8.7139 Å), 18.0° (5.0035 Å), 21.4°(4.1431 Å), 57.9° (1.5926 Å), 60.1° (1.5202 Å), 68.3° (1.3767 Å) appeared along with the anorthite and wollastonite At 1150 °C, there are no such changes in the peak intensity but the sharpness of the peaks has been increased In BNS, at 850 °C, peaks of anorthite (CaAl2Si2O8) and wollastonite (CaSiO3) appeared at 38.3° (2.3607 Å) and 44.5° (2.1445 Å) as a major phase as shown in Fig 3(b) At 950 °C, peaks of gehlenite (Ca2Al2SiO7) appeared at 10.2° (8.6844 Å), 24.6° (3.6315 Å), 61.0° (1.5189 Å) and 68.1° (1.3770 Å) along with anorthite and wollastonite At 1050 °C, one fresh peak of wollastonite at 22.0° (3.9369 Å) appeared along with anorthite, wollastonite and gehlenite but a peak of gehlenite at 10.2° disappeared From 1050 °C to 1150 °C, there are changes in the intensity of the peaks of wollastonite at 16.2° (5.4668 Å), 29.1° (3.0733 Å), 37.1° (2.4122 Å), 52.2° (1.7579 Å) and anorthite at 17.4° (5.0921 Å), 19.9° (4.4129 Å), 24.0° (3.7206 Å), 36.9° (2.4385 Å), 44.3° (2.0445 Å) W a G Intensity (a.u.) BNS BS 12.5 G G W A A A A A-Anorthite G-Gehlenite W-Wollastonit e A W A W GG G o 1150 C o 1050 C o 950 C o 850 C 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 (o) W b WA A A-Anorthite G-Gehlenite W-Wollastonite A W W AW G A W A WAWW G G o 1150 C Intensity (a.u.) 100 o 1050 C o 950 C o 850 C 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 2.85 (o) Fig (a)–(b) X-ray diffraction patterns of the glass batches after heat treated at different temperature soaked for h (a) BS and (b) BNS D.P Mukherjee, S.K Das / Journal of Non-Crystalline Solids 368 (2013) 98–104 Kλ B cosθ ð5Þ where K = 0.94 (the Scherrer constant), λ = wavelength of the X-ray radiation (Cu Kα = 0.154 nm), B = full width at half maximum (FWHM) and θ = Bragg angle of the XRD peak Fig presents the calculated mean crystallite sizes with acceptable errors, as a function of temperature of the BS and BNS samples after heat treated for h It is clear from the Fig that at 850 °C, minor quantities of small crystal with sizes of approximately 23 nm and 17 nm for BS and BNS respectively have been observed After heat treated at temperature 950 °C, a number of much larger crystals with the average size of 31 nm of sample BS and 21 nm of sample BNS are observed After heat treated at temperature 1050 °C and 1150 °C, the crystallite size increased with increase in the heat treated temperature with sizes in range 42 to 63 nm for sample BS and 27 to 49 nm of sample BNS within the limits of errors In the whole temperature range studied, a steady increase of the crystallite size with the heat treated temperature is observed and it is observed that using nano-SiO2 into the glass system (BNS) the mean crystallite sizes is comparatively small other than the normal Silica 3.3 Fourier transform infrared spectroscopy (FTIR) Mean crystallite size (nm) BNS BS 60 50 40 30 20 10 800 900 1000 1100 1400 1200 1000 800 600 400 Wavenumbers (cm-1) o b 850 C o 950 C o 1050 C o 1150 C 1400 1200 1000 800 600 400 Wavenumbers (cm-1) Fig (a)–(b) FTIR spectra of glass batches after heat treatment at different temperature soaked for h (a) BS and (b) BNS Fourier transform infrared spectroscopy (FT-IR) was carried out in order to obtain more structural information on both the specimen BS and BNS The silica-based glass structure is generally viewed as a matrix composed of SiO4 tetrahedral connected at the corners to form a 70 o 850 C o 950 C o 1050 C o 1150 C Transmittance (%) d¼ a Transmittance (%) appeared along with gehlenite At 1150 °C, there are no changes in intensity, as sintering temperature increased the sharpness of the peaks has been increased The formations of anorthite and wollastonite are major phases in BS and BNS respectively, but both the phases appeared simultaneously along with gehlenite In general the gehlenite phase appears at a higher crystallization peak temperature containing glass ceramics In BS the crystalline peak temperature is higher than that of BNS Similar results are also observed by another researcher [26] In BNS, with the increased in sintering temperature, the formation of high peak intensity wollastonite phase increased along with anorthite and gehlenite More wollastonite crystal phases in BNS indicated higher mechanical strength [27] In order to determine the mean crystallite sizes of the wollastonite (CaSiO3) phases calculated by Scherrer equation [28], 101 1200 Temperature(oC) Fig Mean crystallite sizes calculated by Scherrer equation from XRD-line broadening as a function of the temperature of the samples BS and BNS, heat treated at 850–1150 °C soaked for h continuous tri-dimensional network with all bridging oxygen (BOs) Fig 5(a)–(b) illustrates the FTIR spectra of the specimen BS and BNS sintered at various temperatures At 850 °C–950 °C, the peak was observed at 3424 cm –1 which may be due to the O–H stretching of the surface water and the peak at 1638 cm –1 may be due to the deformation mode of H\O\H bond or due to the bending of the surface O-H group [29] The small absorption peaks at about 1550 and 1610 cm –1 are related to CO group and molecular water, respectively The CO absorption peak might be due to chemisorptions of atmospheric CO2 on the surface The peaks at 1144 cm–1 and 1024 cm–1 are assigned to the asymmetric stretching vibrations of the silicate tetrahedral network The peak at 1090 cm–1 is attributed to the symmetric stretching vibration of the Si\O\Si bonds, the band at 800 cm–1 is associated symmetric stretching vibration of Si\O\Si and one at around 464 cm–1 is assigned as rocking vibration Si\O\Si bonds [30–32] The peak observed near 940 cm–1 is assigned to the stretching vibration of the Si\O bond in the Si(OAl/Ca)2 group containing non bridging oxygen The Si(OAl/Ca)2 group is a silicon-oxygen tetrahedral that has two corners shared with aluminum-oxygen or calcium-oxygen polyhedral [33,34] The peaks at 1030 cm–1 to 1080 cm –1 is identified to the vibration of the Si(OAl/Ca) group The presence of wollastonite in the (BS and BNS) specimens is indicated by the spectra of 1060 cm–1, 900 cm–1, 560 cm–1 The peaks at 650 cm–1,648 cm–1 are attributed to the spectrum of both the specimens with the presence of CaF2 102 D.P Mukherjee, S.K Das / Journal of Non-Crystalline Solids 368 (2013) 98–104 Fig (a)–(d) SEM micrograph of BS glass after heat treatment at different heat treatment temperature (a) 850 °C, (b) 950 °C, (c) 1050 °C and (d) 1150 °C soaked for h Fig (a)–(d) SEM micrograph of BNS glass after heat treatment at different heat treatment temperature (a) 850 °C, (b) 950 °C, (c) 1050 °C and (d) 1150 °C soaked for h D.P Mukherjee, S.K Das / Journal of Non-Crystalline Solids 368 (2013) 98–104 103 3.02 16 Water Absorption (%) 2.98 2.96 2.94 BNS BS 14 12 BNS BS 2.92 Shrinkage (%) Density (gm/cm3) 3.00 10 2.90 800 900 1000 1100 800 1200 1000 Temperature Temperature(oC) Fig Variation of density with different ceramization temperature of the glass batches BS and BNS soaked for h 900 1100 1200 (oC) Fig Properties of the two glass batches and dependence on the composition and the heat treatment temperature: water absorption and shrinkage 3.5 Physical measurements components of wollastonite [35] At 1050 °C and 1150 °C in BNS specimen, new vibration bands appeared at 975 cm –1, 915 cm–1, and 819 cm–1 Band of 975 cm –1 and 915 cm–1 corresponds to the Si\O\Ca bonds containing non-bridging oxygen and at 819 cm–1 corresponds to the stretching mode of the O\Si\O bonds [29–31] 3.4 Scanning electron microscopy (SEM) Figs 6(a)–(d) and 7(a)–(d) show the micrograph of specimen BS and BNS after heat treated at 850 °C to1150°C temperatures for h The sample BS formed large size of needle like crystals at 1050 °C (Fig 6(c)) and also showed the surface cracks Similar observations were reported by other researchers [26,27] Fig (d) showed that, at 1150 °C specimen BS are crystallized, and that many acicular grains with long axis were observed This acicular characteristic, a typical microstructural morphology in wollastonite is clear in specimen BS The microstructure of BNS specimens at low temperature (850 °C) heat treatment showed very small inter-stars phase or small white spheres like crystal structures distributed around the surface of the glass sample, the crystallization is observed to start at surface Sample BNS heated at 850 °C–1150 °C for h exhibited a large number of slightly bigger inter-stars phase crystals (Fig 7(b), (c), (d)) compared to that of at 850 °C (Fig 7(a)) As the higher temperature the conditions for nucleation and formation of new crystalline phase, i.e gehlenite is favorable and microstructure with good crystallinity appear Fig 7(d) showed the gehlenite crystal As the temperature increased from 850 °C to 1150 °C, the crystal size increased along with the aspect ratio, similar observations also observed by Scherrer calculation in connection with XRD analysis Fig showed the densities of as prepared glass ceramuics, BS and BNS, heat treated at 850–1150 °C for h were about 3.01 and 2.92 g/cm respectively (Table 4) For sample BS, density increased with increasing in heat treatment temperature But sample BNS, density achieves the maximum value (2.99 g/cm3) at 1050 °C, beyond this the density decreased with increasing the heat treatment temperature The decrease in density may be attributed to the formation of gehlenite crystalline phase and propagation of a large number of slightly bigger inter-stars phase crystals interlocked with each other accompanied by crystal growth This has been proofed by the SEM observations Fig and Table depict the shrinkage (%) and water absorption (%) of the samples sintered in the temperature range of 850 °C–1150 °C, respectively It can be noted that the increase in sintering temperature from 850 °C–1150 °C reduced the linear shrinkage of the both samples, which is probably due to volatility of these glass ceramics In BS the crystallization peak temperature (Tp) is more than compared to BNS, hence the sinterability depends on the Tp, i.e., with increase in Tp the glassy phase would have enough time for viscous flow and it leads to complete densification [36] 3.6 Chemical measurements Fig 10 shows the chemical resistance, i.e., percentage of weight loss in NaOH and HCl test of glass specimen BS and BNS after sintered at different temperature It is clear from the figure that BNS is more acid resistant than BS whereas BS is more alkali resistant than BNS Being more acid resistant of BNS is due to presence of more wollastonite phases Table Physical and mechanical measurement values of glass samples heat treated at different temperature Batch no BS BNS Temperature Density Water absorption Shrinkage Microhardness (Hv) (°C) (g/cm3) (%) (%) (GPa) 850 950 1050 1150 850 950 1050 1150 2.92 2.95 2.97 3.01 2.93 2.97 2.99 2.98 6.25 4.12 1.51 0.53 5.091 1.925 0.26 0.04 ± ± ± ± ± ± ± ± 0.002 0.002 0.003 0.002 0.003 0.003 0.003 0.003 ± ± ± ± ± ± ± ± 0.31 0.20 0.07 0.02 0.25 0.19 0.01 0.01 10.012 12.098 12.568 12.992 15.235 15.623 15.931 15.986 ± ± ± ± ± ± ± ± 0.13 0.12 0.19 0.21 0.15 0.16 0.16 0.16 5.57 5.41 5.29 5.45 5.94 5.81 5.78 5.87 ± ± ± ± ± ± ± ± 0.03 0.03 0.02 0.02 0.03 0.03 0.04 0.03 104 D.P Mukherjee, S.K Das / Journal of Non-Crystalline Solids 368 (2013) 98–104 1.2 Conclusions BNS BS 1.4 1.0 1.2 0.6 1.1 0.4 0.2 800 HCL NaOH 1.3 0.8 900 1000 1100 1.0 1200 Temperature (oC) Fig 10 Chemical resistance of the two glass batches and dependence on the composition and the heat treatment temperature: NaOH and HCl Microhardness, Hv, (GPa) Acknowledgments The authors would like to thank the UPE scheme of University Grants Commission and the Center for Research in Nanoscience and Nanotechnology (CRNN), University of Calcutta for the financial support One of the authors, Debasis Pradip Mukherjee thanks the Center for Research in Nanoscience and Nanotechnology (CRNN), University of Calcutta, Kolkata, India, for providing the fellowship 6.0 5.8 BNS BS 5.6 References [1] [2] [3] [4] [5] 5.4 5.2 5.0 800 Glass ceramic systems of 34SiO2–29Al2O3–25CaO–12CaF2 have been prepared by used normal SiO2 and nano-SiO2 The glass crystallization peak temperature (Tp) is lowered in nano silica containing glass system XRD analysis conclusively proved that introduction of nano silica in the glass ceramic system wollastonite and anorthite crystal phases are more than the glass ceramic containing normal silica The mean crystallite sizes of wollastonite (CaSiO3) were in the range from 17 to 49 nm for nano-SiO2 and for normal SiO2 range from 23 to 63 nm Increasing the heat treated temperature from 850 to 1150 °C resulted in an increase of crystallite size for both the cases The nano-SiO2 containing glass ceramics gives superior physical and mechanical properties, and also showed the improvement of microstructure properties, hence is suitable for industrial building, internal and external wall facing and tiles applications 900 1000 1100 1200 Temperature (oC) Fig 11 Variation of Vickers hardness (Hv) with different heat treatment temperature for BS and BNS samples [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] 3.7 Mechanical measurements Fig 11 shows the hardness of the heat-treated glass ceramic specimens BS and BNS are measured by acquiring micro-indentation at an indent load of 40 g and the average diagonal length of the hardness impression is calculated It is clear from Table that Vickers hardness values decrease with heat treatment temperature and reaches minimum at 1050 °C and then increases with temperature at 1150 °C But it is lower than the 850 °C values for both the cases At lower temperature formation of anorthite and wollastonite phases is due to the higher Vickers hardness values At 1150 °C the Vickers hardness increases might be due to the ghelenite crystal phase The maximum hardness of 5.9 GPa and 505 GPa is observed in for BNS and BS samples at 850 °C heat treatment temperature 3.8 Uses Nano-SiO2 containing glass gives superior physical, chemical and mechanical 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