Porous silicon nitride body coated with a mix of silicon - plus flux and then coating is nitrided

摘要

The body is made by pressing Si-powder and heating in N2 at 1600 degrees C or higher. A paint which contains 5% wt. plasticiser (polyvinylalcohol), 80-95% Si and 5-15% flux (e.g. iron oxide, iron, silicon dioxide, calcium fluoride, alkaline earth oxides) is brushed on. The coating is dried and the body is heated at 1350-1450 degrees C in vacuum or inert atmosphere (argon) and then in N2 atmosphere. - The process makes SiN bodies whose surface is so impervious that the body is impermeable to gas. In addition the surface is hard gives good protection, is stable at temperatures up to 1000 degrees C and is unchanged by water at room temp.