Effect of processing on the structural characteristics of sintered silicon oxycarbide materials

• Different nanodomain redistributions are obtained when sintering agents were changed.
• The phase separation is enhanced when uniaxial pressing is used.
• Crystallization mechanism follows different pathways depending on sintering conditions.

Large monoliths of silicon oxycarbide (SiOC) glasses have been prepared from sol–gel derived hybrids. SiOC powders were shaped by using different binders, pressing techniques and with varying dwelling times at the sintering temperature. The influence of the sintering conditions has been studied. The resulting sintered materials are comprised by a strong glassy matrix where amorphous silica, glassy carbon and amorphous and crystalline SiC coexist. The carbon phase presents three-dimensional ordering formed by nanodomains of glassy carbon of 1.5–2.0 nm. Silicon carbide presents nanodomains of 2.2–2.4 nm independently of the processing conditions. The data obtained from characterization suggest that the use of either the uniaxial die pressing technique or PARALOID leads to a bond redistribution and phase separation before the carbothermal reduction, a fact that has been attributed to the presence of defects in the green bodies.