[Influence of metal elements in Pd alloys on the bonding to porcelain]

The influence of metal elements in three Pd alloys on the bonding to porcelain was examined. The high-temperature oxidation behavior of metal elements in alloys, structure and morphology of oxidation zones on the alloy surface and the appearance of bonding between alloy and fused porcelain at the interface were studied by ESCA and EPMA. From ESCA analysis, metal oxides such as PdO, SnO2, In2O3, CuO or Cu2O, Sb2O3 or Sb2O5 were formed on the surface of the alloy after degassing (preheating) and heating following casting. The amount of metal elements concentrated on the alloy surface was measured by their characteristic X-rays using area analysis of EPMA under the technical conditions of A) Acc. voltage 10 kV, Abs. current 40 nA, and B) Acc. voltage 20 kV, Abs. current 10 nA. Consequently, the amount of additive metal elements concentrated on the alloy surface which was detected in condition A) was larger than that detected in condition B). However, the amount of main element (Pd) concentrated on the alloy surface which was detected in condition A) was smaller than that detected in condition B). From the EPMA observation of the interface between alloy and fused porcelain, cross-section of alloys showed that the additive metal elements were oxidized in the alloy matrix, forming an internal oxide layer or particles. The structure and morphology of oxidation zones showed a significant difference between degassed and not-degassed alloys. Cross-sections inclined approximately 5 degrees 43' to the fusing boundary were also analyzed to enlarge the oxidation zones. This analytical technique effectively revealed the structure and morphology of oxidation zones. In conclusion, not only additive metal elements but also the main element at the surface of alloys play important roles on the bonding to porcelain. Degassing of the alloy was considered to an essential procedure to obtain the adequate bonding to porcelain.