weight of ag and 5 percent of cu at 1100 u00b0 c under vacuum and when air was introduced the sintered surface was impregnated with silver alloy after treatment the sintered alumina pieces were lifted out of the molten pool and the depth of impregnation of the silver alloy into the sintered surface was measured to be about 1 6 mm again the sintered alumina pieces were dipped for 5 minutes in said molten pool and in this state the pool of silver alloy was placed in a metal mold then under a pressure of 1000 kg cm 2 the sintered alumina was impregnated with silver alloy and solidified the same treatment as in example 1 was then followed and the resulting sintered alumina exhibited a metal impregnation rate of 98 3 percent and a breaking strength of 3210 kg cm 2 sintered silicon nitride pieces having a porosity of 27 1 percent 10 mm u00d7 10 mm u00d7 100 mm was submerged in a molten pool of aluminum alloy jis ac8a consisting of 11 percent by weight of si 1 5 percent cu 1 5 percent ni 1 0 percent mg 0 4 percent fe 0 15 percent ti the rest being ag and held under a partial vacuum of 10.