Evaluation of high temperature resistance of white Si–O–C(–H) ceramics in an inert atmosphere

• Major degradation of white Si–O–C(–H) ceramics in Ar occurs beyond 1400 °C.
• Degradation process is accompanied by mass loss and particle fusing.
• Si–O–C(–H) ceramics decarbonized at 900 °C becomes black up to 1400 °C.
• Si–O–C(–H) ceramics decarbonized at 1100 °C becomes light gray up to 1400 °C.
• Fluorescence images are useful to detect degradation of Si–O–C(–H).

Two kinds of white Si–O–C(–H) ceramic powders, named S900 and S1100, were prepared from cross-linked polysiloxane particles with an average diameter of 6 μm. S900 was the product obtained in a hydrogen gas flow at 900 °C with a holding time of 1 h, whereas S1100 was the product obtained at 1100 °C with a holding time of 3 h. Heat stability of these ceramic powders in graphite boats were examined within the temperature range of 1200–1600 °C in an Ar gas flow. The powder substantially began to degrade beyond 1400 °C, which was accompanied by mass loss, fusing of particles and partial cristobalite precipitation. The color of S900, however, became black after the heat treatment at 1400 °C before the substantial mass loss, whereas the color of S1100 showed small change to light gray after the heat treatment at 1400 °C. The apparent color change of the samples during the heat treatment possibly corresponded to defect incorporation in the Si–O–C(–H) network, whereas the change in chemical composition was minor. At high temperature region, SiO and CO were evolved as a result of SiC–SiO2 reaction, although SiC and SiO2 were defined as virtual phases in the Si–O–C(–H) amorphous.