Radiation synthesis of porous calcium silicate aerogel derived from polyacrylamide hydrogel as thermal insulator

In this article, the first aerogels synthesis through cross-linked polyacrylamide (PAAm) hydrogel was reported through the use of gamma irradiation technique. Hydrogel obtained from gamma irradiation of acrylamide monomer dissolved in a solution of sodium silicate as a silicon precursor. Various irradiation doses (10 up to 60 kGy) and various acrylamide (AAm) contents (6.25, 9.37, 12.5, and 30%) were utilized in the polymerization process. The polyacrylamide (PAAm) hydrogel loaded with sodium silicate inside is soaked in a solution of CaCl2 and then heated at a temperature of 250 °C for 2 h to provide Ca-silicate aerogels with density around 0.16–0.095 gm/cm3 and porosity of 84–94.8%. Almost all samples of the obtained (Ca-Si) aerogels have porosity >80% and low thermal conductivity (thermal conductivity value around 0.114 and 0.096 W/m.K) at ambient condition. This work discusses the effects of preparation conditions like the gamma-irradiation doses and the total solids content (wt%) of PAAm on the formation of Ca-silicate aerogels. It was found that PAAm plays a crucial role in the thermal conductivity and porosity (%) of the obtained Ca-Si aerogel samples. The increasing of PAAm content (wt%) from 6.25 to 30% increased the pores (v%) from 84 to 90.5% and reduced the thermal conductivity from 0.114 to 0.096 W/(m.K). This is because the presence of PAAm at higher concentrations increases the free volume and reduces interfacial interactions to give a high-porous structure of the Ca-Si aerogel.