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

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°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.