Effect of Zr on the Microstructure and High-Temperature Phase Separation Evolution of SiOC Aerogels

SiZrOC aerogels were synthesized through the pyrolysis of the zirconium source-doped SiOC system using zirconyl chloride octahydrate (ZrOCl28H(2)O) at temperatures ranging from 900 to 1300 degrees C. This study investigates the microstructure evolution and phase separation of SiOC and SiZrOC aerogels during the pyrolysis process. Upon pyrolysis, both aerogels exhibited a Si-O-C structure with a high thermal stability. The introduction of zirconium elements significantly enhanced the pore volume (3.20 cm(3)/g) and porosity (96.0%) and reduced the thermal conductivity (0.023 Wm(-1)K-1) of the organic-inorganic precursor aerogel. Moreover, the three-dimensional pore structure was retained even under high-temperature pyrolysis conditions. SiZrOC-1100 displayed a high specific surface area of 273.52 m(2)/g, a high pore volume of 1.70 cm(3)/g, and a low thermal conductivity of 0.033 Wm(-1)K-1. At high temperatures, the SiZrOC phase transformation produces tetragonal ZrO2, which inhibits the graphitization process of free carbon and the growth of SiC grains. Furthermore, the phase separation process of the SiOxCy matrix structure generated oxygen-rich SiOxC4-x units, while carbon-rich SiOxC4-x units were negligible below a pyrolysis temperature of 1200 degrees C. Between 900 and 1200 degrees C, SiZrOC is composed of amorphous SiOC, amorphous ZrO2, microcrystalline t-ZrO2, and free carbon phase. These findings provide valuable insights into the preparation of high-performance SiOC aerogels.

Automated summary

SiZrOC aerogels were successfully synthesized through the pyrolysis of the zirconium source-doped SiOC system. The introduction of zirconium elements significantly enhanced the pore volume and porosity, while reducing the thermal conductivity of the aerogels. The phase transformation at high temperatures inhibited the graphitization process of free carbon and the growth of SiC grains.