Development and Corrosion Rate and Corrosion Mechanism of Dental Ag-Pd-Cu-Au alloys.

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1. Corrosion rate (I_<corr>) is obtained using the following equation; I_<corr> = K/Rp (K:constant value). Six kinds of Ag-Pd alloys, four kinds of Ag-Pd-Cu alloys, one Ag-Cu alloy, and four kinds of commercial dental Ag-based casting alloys were used for the specimen and 0.1% H Cl ringer solution at pH=2, was used at the test solution in the study. In summary, I_<corr>, which changed in proportion to I/Rp, ranged from 2.3 x 10^<-8> at minimum and 4.4 x 10^<-5>(A/cm^2) at maximum, whereas the K values were localized between 13.5 and 25.9mV. The average K value was 20mV. Therefore, the Icorr of dental Ag-based alloys was estimated simply from the Rp substituting 20mV for K of the above equation. These findings revealed that the Coulostatic method is useful for rapid determination of the corrosion rate of dental alloys. 2. The corrosion behavior of a commercial Ag-Pd-Cu-Ag alloy in 0.9% NaCl solution was investigated by an electrochemical technique, surface analysis of X-ray photoelectron spectroscopy and reflection electron diffraction. No corrosion of the alloy examined was observed at negative potentials of -100mV or loss. In the potential region from OmV to +300mV, the alloy may be oxidized to form surface films of AgCl, AgO, Cu_2O, CuO, Cu(OH)Cl, CuO and CuCl_2 on the basis of the equilibrium potential for this system. Pd in the alloy was oxidized to form PdO_2 at +400mV and at +500mV. AgCl and Cu(OH)_2 were found on the sample surface anodized at +400mV and +500mV. The amount of AgCl was greater than that of Cu(OH)_2.