The effect of synthesis parameters on density and thermal conductivity of MMT based aerogel. Application of experimental design model

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Aerogels are a class of materials largely composed of air with very low bulk densities. Due to their extremely porous nature, aerogels are very promising materials for thermal and acoustic insulation applications. While their majority described in the literature are silica-based, there are a limited number of references to clay-based aerogels. The abundance of clay and its limited toxicity make them particularly attractive. Clay aerogels formation involves mixing of clay with water, freezing of the suspension and freeze-drying of the frozen gel. This work concerns the use of montmorillonite as a raw material for the synthesis of aeroclays with low density. Clay aerogels were synthesized by mixing montmorillonite clay and water and their density was measured. Various agents were used for the reinforcement of the brittle structure of clay aerogel. A multifactorial experimental design model is applied in order to study the combined effect of synthesis parameters on the density of aeroclays. The thermal conductivity of the optimized sample was determined by means of the Heat Flow method, on a Netzsch HFM 436 lamda Heat Flow Meter. As it is concluded, aeroclays, derived from a solution of montmorillonite clay and water alone were brittle so the addition of reinforcement agent is crucial. Depending on the synthesis conditions, a density range from 0.05 to 0.4 g/cm3 and thermal conductivity in the range of 0.04 W/mK was achieved. The factors with the highest impact on the density of the final product were the content of MMT and reinforcement agent in the precursor solution. The optimized synthesis in terms of density and thermal conductivity was proved to be inflammable.