AGING REACTIONS IN A HIGH CARAT GOLD ALLOY FOR DENTAL PORCELAIN BONDING

The phase transformation during continuous heating of a high carat gol d alloy used for porcelain bonding was investigated by electrical resi stivity measurements, hardness tests, X-ray diffraction and scanning a nd transmission electron microscopy. Four reaction stages (I, II, III and IV) were found. Stage I corresponded to the formation of a short-r ange order. A discontinuous precipitation took place in stage II, whic h contributed to remarkable hardening. Stages III and IV were reaction s to the stable phases at each temperature region, and resulted in sof tening. The activation energies for stages I, II and III are 27.1, 33. 8 and 58.2 kcal/mol, respectively.