Yoshihiro Ebata

Joining of silicon carbide ceramics with Si3N4Y2O3La2O3MgO mixture

Normally sintered silicon carbide was joined with a Si3N4-Y2O3-La2O3-MgO mixture having a composition, Si3N4:Y2O3+La2O3=35-65:65-35 (mol%), at 1600°-1800°C for 30-90min in argon (provided that Y2O3/La2O3 molar ratio is unity and MgO content equals to 20wt%). The highest room temperature joining strength, 397MPa, was obtained by joining at 1700°C for 60min with a composition, Si3N4:Y2O3+La2O3=55:45 (mol%). The strength measurement at high temperature (holdihg time: 10min) showed that the strength of the same specimen was more than 300MPa up to 1000°C, but decreased rapidly above 1000°C. The joining strength decreased with holding time above 900°C. The thickness of the joining layer was about 20μm. No diffusion into silicon carbide matrix of Y, La and Mg, ingredients in the joining agent, was observed, and the joining agent formed a glassy phase after joining. These results imply that joining of silicon carbide ceramics occurred only by the wetting of oxynitride of Si3N4-Y2O3-La2O3-MgO system (the bending strength: about 280MPa). The lowering of jointing strength at high temperature was attributed to the softening above Tg and to the brittleness due to crystallization of oxynitride glass.

Thermal resistance of direct adhered layer between magnesia ceramics and copper.

マグネシアセラミックスと銅板をろう材を使用せず直接に接着したものは,耐熱性および機械的強度がすぐれている.しかし,この接着層はかなりの熱抵抗がある.この熱抵抗の主原因を解明した.その結果,接着面に存在する亜酸化銅層が,熱抵抗の主な原因であり,その厚さは,接着温度および接着時間と,ほとんど無関係である.実効の接着面積は,気泡などにより,みかけより小さくなっており,これが,熱抵抗のばらつく主原因である.

Electric discharge welding of ceramics

An electric discharge method for welding ceramics has been developed. A joining material electrically conductive at high temperature is inserted between two pieces of ceramics to be joined, and the joint region is preheated by a pair of burners of spouting combustion gas. When the joint region is heated to high temperature, a high voltage is applied between a pair of electrodes combined with the burners. The ceramics are joined by electric discharge through gas flame and the joint region. Pressureless-sintered Si3N4 ceramics were joined using a mixture of kaolin and CaF2 as a joining material. Ceramics can be joined easily, in a short time, and economically by this method.