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

• Published in: Journal of sol-gel science and technology 2021-06, Vol.98 (3), p.593-604
• Main Authors: Othman, Amr M., Ghobashy, Mohamed Mohamady, Abd El‐Sattar, Nour E. A.
• Format: Article
• Language: English
• Subjects: Acrylamide; Aerogels; Calcium chloride; Calcium silicates; Ceramics; Chemistry and Materials Science; Composites; environment and building applications; Gamma irradiation; Glass; Heat conductivity; Heat transfer; Hydrogels; Inorganic Chemistry; Materials Science; Nanotechnology; Natural Materials; Optical and Electronic Materials; Original Paper: Sol-gel and hybrid materials for energy; Polyacrylamide; Porosity; Radiation; Silicon; Sodium silicates; Synthesis; Thermal conductivity
• ISSN: 0928-0707; 1573-4846
• DOI: 10.1007/s10971-021-05534-w

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 CaCl 2 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/cm 3 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. Preparation procedure of the calcium silicate aerogels using gamma irradiation technique. In particular, the cross-linked polyacrylamide has higher modulus as reinforced silica aerogels of low density. The reinforced Ca-silicate aerogels can be an outstanding thermal insulating material used for different industrial and space exploration, with their very porous texture. Highlights Performed the radiation synthesis of macro porous calcium silicate aerogels based different ratio of polyacrylamide hydrogel. Investigated the effects of preparation conditions on the properties of Ca-silicate aerogels. All obtained (Ca-Si) aerogels samples have porosity greater than 80%. All obtained (Ca-Si) aerogels samples have thermal conductivity around 0.114 and 0.096 W/m.K).