Reactions of copper and copper oxides with nitride ceramics (AlN, SIALON Si3N4) and their oxide additives (Al2O3, Y2O3, SiO2, MgO)

In order to evaluate the feasibility of applying ceramics (AIN, SIALON, Si2N4) to casting equipment for copper-based alloys, the reactivity of copper oxides with nitride ceramics and their oxide additives (Al2O3, Y2O3, SiO2, MgO) was examined. Ten weight percent Cu, Cu2 O and CuO were mixed with powders of nitrides and oxides, and kept at temperature between 700° and 1300°C in air and at 1200°C in a nitrogen atmosphere having oxygen partial pressure (PO(2)) of approximately 3 × 10-1 and approximately 3 × 10-2 Pa for one hour. In air, CuO accelerated the oxidation of the nitride ceramics, and the three kinds of nitride samples oxidized above 1200°C. Silicon nitride ceramics did not oxidize below 1000°C, and may be used to brass casting. Al2O3 and Y2O2 reacted with the copper oxides. SiO2 did not react, but melted above 1050°C. MgO seemed to form a solid solution with CuO. On the other hand, CuO in the mixture was reduced to Cu, and all the seven kinds of ceramics were stable above 1200°C under nitrogen atmosphere with PO(2) below 1 Pa. Therefore, the seven kinds of ceramics may be used for casting of copper-based alloys at PO(2) below 1 Pa.