Sol-gel synthesis of SiC@Y3Al5O12 composite nanopowder and preparation of porous SiC-ceramics derived from it

Highlights: • Y,Al-containing precursors [M(O₂C₅H₇)_3-x(O₅H₁₁ⁱ)_x] were synthesized. • A highly dispersed SiC@Y₃Al₅O₁₂ composite powder was obtained by the sol-gel method. • Samples of porous SiC ceramics were produced by SPS of SiC and SiC@Y₃Al₅O₁₂ powders. • The role of 2 vol% Y₃Al₅O₁₂ additive was shown on the property of SiC-ceramics. -- Abstract: 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° (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°. 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.