Polymer Technology of Porous SiC Ceramics Using Milled SiO2 Fibers

Resumo

The paper describes a developed polymer composition and a process for manufacturing highporous chemically pure silicon carbide ceramics from this composition, using milled industrial wastes of quartz fiber non-woven fabrics as the source of silicon dioxide, which is important as a rational utilization of these wastes. The necessity of pre-milling of the SiO₂ fibers was experimentally substantiated. Without this stage, the duration of treatment at 1400°C under dynamic vacuum considerably (≥12 h) increased, because of the non-uniform distribution of the components in the polymer composite. In the case of stoichiometric ratio of SiO₂ and carbon formed upon pyrolysis of the polymeric phenol binder, the obtained SiC ceramic contained a large amount of unreacted carbon. This indicaties that side reactions take place to give volatile silicon monoxide, which is distilled off from the reactor. The effects of the milling time of SiO₂ fibers and the carbothermal reduction temperature on the elemental and phase composition, density, and porosity of the obtained samples and the ultimate compressive strength were studied. Analysis of the experimental results served for optimization of the composition of the initial polymer composites. As a result, highly porous (83%) and relatively strong (ultimate compressive strength of 8.2MPa) SiC-ceramic samples free from unreacted carbon and silicon dioxide and other stubborn impurities were fabricated at 1400°C (dynamic vacuum, heat treatment for 4 h).