Processing of vacuum heat-treated MgO-densified silicon nitride crucible for molten cast iron handling

Silicon nitride with 3% MgO powder mix is uniaxially and cold isostatically pressed to form a green Si3N4 crucible. Liquid phase sintering was applied to the green Si3N4 crucible at 1600 °C for 30 min under the nitrogen atmosphere. Intergranular Mg–Si–O–N glass remained between the silicon nitride grains which reacted with the molten metal during melting. This grain boundary glass was removed by vacuum heat treatment at 1575 °C for 5 h. The vacuum heat treated crucible was used to melt cast iron to examine reactions between the molten metal and Si3N4 ceramic crucible. EDX spectra across the Si3N4–cast iron interface and XRD for silicon nitride sample after cast-iron melting side surface analysis were carried out. Optical microscopy and SEM image analysis were made to examine the interaction between Si3N4 crucible and cast iron melt. Surprisingly, no reaction was observed between the vacuum heat treated crucible and melted cast iron.