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The promising role of structural ceramics in many useful devices and structures has in turn led to realization of the importance of developing ceramic joining techniques, which is perhaps one of the most important areas in the ceramic field for research and development. The increasing demand for joining ceramics arises from: a) fabrication of ceramic components of complicated shape or large size in one piece can be very expensive and in some cases impractical, and b) in many cases, because of the limitation of ceramics resulting from poor impact properties and lack of tensile ductility they have to be attached to metals, which must withstand stresses or temperature gradients too great for ceramics. This paper covers methods and problems of joining of ceramics with emphasis on brazing technique. This also includes examples of joining silicon nitride ceramic to itself and to molybdenum.

Improved of chemical corrosion resistance of silicon nitride (Si₃N₄) ceramics is strongly desired. However, there is not enough information on chemical corrosion at present. In this paper, corrosion resistance of two kinds of Si₃N₄ based ceramics with different additives developed for bearing material was investigated. One of the specimens is composed of Si₃N₄-Y₂O₃-Al₂O₃-AlN-TiO₂, the other of Si₃N₄-SiC-MgAl₂O₄-SiO₂-TiO₂. A corrosion test was conducted under conditions of 240h-soaking at 30°C and 100h-soaking at 80°C in acid and base solutions. The weights of both specimens after soaking were confirmed to decrease with decreasing concentration of sulfuric acid. The bending strength also decreased in proportional to the weight change. Contrary to the results in acid solutions, the weights of the specimens decreased with increasing concentration of sodium hydroxide solutions. The weight changes at 80°C were much larger than those at 30°C. The extent of corrosion was found to depend on the composition of the ceramics. Specimens with additives of Y₂O₃, Al₂O₃, AlN, and TiO₂ tended to corrode more easily than those with SiC, MgAlO₄, SiO₂ and TiO₂. A correlation between the weight loss and the bending strength was established.