In relation to the joining of silicon nitride ceramics to metal, the reaction products between Si₃N₄ and Co have been investigated under Ar or N₂ atmosphere at temperatures from 1423 to 1673K. Using Si₃N₄-Co powder mixtures, the reaction rate was determined thermogravimetrically and the reaction products were examined by X-ray diffraction. Above 1423K, the reaction proceeded under both atmospheres. The Co-Si solid solution was formed at low temperatures. At higher temperatures and on prolonged heating, the reaction products changed in the following order: Co-Si solid solution, Co₂Si, CoSi and CoSi₂. Under Ar atmosphere, the formation of cobalt silicides was enhanced, because of low partial pressures of N₂.