Thermal evolution of ladder-like silsesquioxanes during formation of black glasses

Abstract

Pyrolysis of ladder-like silsesquioxanes in oxygen-free atmosphere leads to the formation of silicon oxycarbides (black glasses). Black glasses are materials of amorphous silica structure where some amount of O2− ions were replaced by C4− ions. This exchange leads to local increase in bonds density and therefore improvement in mechanical, thermal, and chemical properties. Thanks to this modification, silicon oxycarbide glasses can be used in a variety of applications like: protective coatings and interconnectors in solid oxide fuel cells. Xerogels were prepared by sol–gel method, and ladder-like silsesquioxanes were used as precursors. Samples were burned at 200–1000 °C in inert atmosphere. Structural studies in the middle infrared range (MIR) and SEM with EDX confirmed the presence of SiOC bonds in obtained materials. MIR analysis of solid samples together with TG/dTG measurements allowed defining the process for the formation of black glasses.