An enclosable vessel for containing a silicon nitride article during sintering in a furnace to protect the silicon nitride article from thermal decomposition and contamination reactions with furnace materials comprises a closeable walled container formed of a reaction bonded silicon nitride material having an opening to allow interior placement of the silicon nitride article within the walled container. This box is used to replace silicon nitride powder which has heretofore been used to cover silicon nitride articles during sintering.
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