The unusually formation of porous silica nano-stalactite structure by high temperature heat treatment of SiO2 aerogel synthesized from rice hull

Abstract The SiO2 aerogel has attracted the attention of many researchers in recent years in terms of energy saving due to its properties such as very low density, high porosity, and superior insulation. The primary purpose of this study was to synthesize SiO2 aerogel. For this purpose, the sodium silicate obtained from rice hull ash was used as pre-initiator and dried at ambient pressure and SiO2 aerogel was synthesized. BET surface area of the obtained SiO2 aerogel was found as 241 m2/g. The difference of this study is the structures obtained after this stage. After obtaining SiO2 aerogel, it was subjected to heat treatment at a high temperature to increase the BET area of aerogel and after examining under SEM, it was noticed that some uncommon structures that have not seen before formed. After observing nano-stalactite type structures in the sample, the study was expanded on the causes of the formation of these structures. It was seen that this structure forming after heat treatment was a stalactite composed of SiO2 nanoparticles having a crystal structure. This study examined the formation mechanism and some properties of this structure which was not encountered in previous studies. Brunauer-Emmett-Teller (BET), Transmission electron microscopy (TEM), Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis were conducted in order to determine the physical and chemical properties of both synthesized SiO2 aerogel and nano-stalactite type structure.