Aerogel Composite from fly ash is an environmentally friendly material and applcation as an thermal insulating material. The synthesis of aerogel composite from fly ash using cross linked technique and freeze-drying method. The general condition of the material to be investigated factors such as fly ash concentration and adhesive, assimilation time, reaction temperature, drying condition.
Hóa học – Sinh học – Mơi trường AEROGEL COMPOSITE FROM FLY ASH AND APPLICATION AS THERMAL INSULATION MATERIAL Pham Quoc Nghiep*, Le Anh Kien Abstract: Aerogel Composite from fly ash is an environmentally friendly material and applcation as an thermal insulating material The synthesis of aerogel composite from fly ash using cross linked technique and freeze-drying method The general condition of the material to be investigated factors such as fly ash concentration and adhesive, assimilation time, reaction temperature, drying condition Physical properties such as porosity, density, thermal conductivity and mechanical property were determined from the completely dried samples As a result, this study has synthesized materials with porosity up to 90 %, density less than 0.5 g/cm3, thermal conductivity less than 0.1 W/(m.K) Therefore, composite aerogel from fly ash is a lightweight, highly insulating material Keywords: Aerogel Composite; Fly Ash; Thermal Insulating Material; Lightweight Material; Freeze-drying INTRODUCTION An aerogel is a highly porous solid that holds gas inside the porosity of its solid network They are renowned for their low densities (0.003 to 0.5 g/cm3) and high porosities (70-99.8%) [1-5] Kistler et al [6] invented the first aerogel in 1931, which was a relatively transparent silica aerogel In the same year, they also prepared a variety of different aerogels such as introducing other mediums such as alumina, nickel tartarate, stannic oxide, tungstic oxide, gelatine, agar, nitrocellulose, cellulose, and egg albumin [6] Their aerogel inventions concerned both the organic and inorganic aspects of the solid substance In later years, Kistler [7] also initialized the fabrication of aerogels at industrial scale In addition, aerogels such as carbon aerogels, silica aerogels, and cellulose aerogels have served as absorbents for oils and other organic pollutants [8] One of the famous applications of aerogels is thermal insulation, as aerogels with thermal conductivity of 0.0089–0.05 W/m.K are among the best known thermal insulation materials [9-11] Cohen et al [11] reported a silica aerogel, fabricated by using separated catalysts for hydrolysis, condensation, and gelation steps, with a thermal conductivity of 0.0089 W/m.K under ambient conditions In contrast, air has a thermal conductivity of around 0.025 W/m.K, which also implies that the low thermal conductivity of the silica aerogel is not the result of the high porosity [12-13] The low thermal conductivity of silica aerogels can be explained by the Knudsen effect, where the pore size of a material is smaller than the mean free path of air This results in the material’s thermal conductivity being dramatically reduced [14] MATERIAL AND METHODS 2.1 Materials and methods The coal fly ash powder was collected from Duyen Hai factory in Vietnam with a specific chemical composition as shown below in table Polyvinyl alcohol (PVA, MW 89,000~98,000g/mol) All the reagents used without further purification Deionised (DI) water was used for fabrication of samples as well The reaction solution was prepared by dissolving Polyvinyl Alcohol (PVA) powder into warm deionised (DI) water of 100ml using a magnetic stirrer, at temperature below 80 °C Following which, CFA was added into the solution with a desired ratio and stirred for hours at 80 °C to facilitate the cross-linking reaction Then, the mixture is frozen in the refrigerator overnight before thawing and forming a gel at 60 °C for 30 minutes The mixture was then homogenised by stirring it at room temperature for hours and then 408 P Q Nghiep, L A Kien, “Aerogel composite from fly ash … thermal insulation material.” Nghiên cứu khoa học công nghệ frozen to form a uniform distribution Lastly, the frozen sample was then placed in the freeze dyer for 48 hours to remove all the solvent in order to produce a CFA aerogel The base case ratio is set at 2.5/2 wt% as with consistent testing, a ratio of 2.5/2 wt% is able to produce the most stable aerogel in terms of quality Following which, ratios of PVA or CFA were altered in creation of subsequent aerogel samples for comparison and determination of the best CFA/PVA ratio Table Chemical composition of a fly ash, Duyen Hai factory, Vietnam Chemical Composition Content (wt%) SiO2 55.8 Al2O3 25.8 Fe2O3 7.4 MgO 1.3 CaO 1.1 SO3 0.1 K2 O 4.3 Na2O 0.4 TiO3 0.8 C