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A method for the production of porous SiC-ceramics from finely dispersed starting system SiO2–C by means of single-stage carbothermal process involving spark plasma sintering at moderate temperatures (≤1800 °C) is proposed. Synthesis of finely-dispersed SiO2–C system was performed by sol–gel as follows: tetraethoxysilane was hydrolyzed in the presence of polymeric source of carbon (phenolformaldehyde resin) with the subsequent drying and thermal treatment under inert atmosphere at 850 °C. The density of the obtained ceramic samples was found to vary within the range 1.43–1.84 g·cm−3 depending on the experimental conditions (the estimated porosity amounted to 42–55%). Ultimate compression strength was measured to be 94–279 MPa. Thermal behavior of materials in air flow up to 1400 °C, as well as microstructure and volumetric pore distribution (X-ray computerized microtomography), were studied.

A sol-gel method with aluminium and yttrium alkoxoacetylacetonates as precursors was used to modify highly dispersed silicon carbide powder, with the formation of SiC@Y3Al5O12 with a low content of Y3Al5O12 ∼2 vol%. Two series of porous silicon carbide-based ceramics were produced by spark plasma sintering (SPS) of SiC and SiC@Y3Al5O12 powders at temperatures of 1,400–1,700°С (exposure time 5 min) and sintering pressures of 47 and 58 MPa. The relative density was 38–51 and 26–49% for materials obtained without and with modification, respectively. It was shown that the greatest influence of the sintering additive on the compaction process was observed at elevated SPS temperatures of 1,600–1,700°С. This was related to easier sliding of SiC particles during high-temperature sintering, due to the formation of a liquid Al2O3-Y2O3-SiO2 film on their surface under given temperature conditions. A significant (by 2.5 times) increase in compressive strength for modified samples, compared to ceramics obtained based on an individual, highly dispersed SiC powder, was observed at the maximum SPS temperature (1,700 °C); the microhardness value rose sharply (by 5.9 times) at an SPS temperature of 1,600 °C. The effect of sintering pressure increase at an SPS temperature of 1,500 °C was not so significant, and this was mainly observed for samples obtained by liquid-phase sintering of SiC@Y3Al5O12.