Vacuum Heat Treatment of MgO-densified Pressureless Sintered Silicon Nitride Ceramics

摘要

Silicon nitride samples were pressureless sintered with up to 5 w/o MgO to give densities in the range 98-99% of theoretical. After pressureless sintering, selected samples were placed in a vacuum heat treatment furnace surrounded by a carbon bed in a carbon crucible at a pressure of less than 4×10~(-4) mbar, and vacuum heat treated at different temperatures and times to remove grain-boundary glass. The results showed that this was substantially achieved at 1575℃ for 3h and that increasing the time to 5 hours gave still further improvement. SEM images, EDX analysis and oxidation tests provided additional evidence for the removal of Mg from the samples.