Abstract
The suitability of MgO as a densification aid for α-SiC has been investigated. Samples of SiC containing additions of MgO, both alone and in combination with A1 2O 3 and Y 2O 3, have been hot pressed at temperatures between 1500 and 1900°C and pressureless sintered at temperatures up to 2000°C. The MgO reacts with surface SiO 2 from the SiC grains to form a liquid phase which promotes densification by particle rearrangement and solution-reprecipitation processes. With combined additions of MgO, Al 2O 3 and Y 2O 3, a eutectic in the system MgO –Al 2O 3 –Y 2O 3 allows extensive liquid formation at ∼1700°C independent of the SiO 2 content of the SiC powder, enabling efficient densification by hot-pressing. Volatilisation due to reactions between the MgO and the SiC or with the furnace environment, however, oppose densification by pressureless sintering, and must be compensated for by the use of Mg-containing powder beds.
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