Abstract
A measuring method of polarization resistane (Rp), Coulostatic method has been recently applied to rapidly determine the corrosion rate of alloys in the metallurgical area. Corrosion rate(Icorr) is obtained using the following equation; Icorr=K/Rp (K: constant value). The value of the method in evaluating Icorr of dental alloys which have a high corrosion resistance was determined. 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 a 0.1% HCl Ringer solution at pH=2, was used as the test solution in the study. Polarization resistance of the specimens was measured every 24 hours by the Coulostatic method for 20, 40, 60 days. Icorr of the alloys was calculated from mass loss and amounts of elements eluted into the solution by Faraday's law. K values were obtained using the equation. In summary, Icorr which changed in proportion to 1/Rp, ranged from 2.3×10-8 at minimum and 4.4×10-5 (A/cm2) at maximum, whereas the K values were localized between 13.5 and 25.9 mV. The average K value was 20 mV. Therefore, the Icorr of dental Ag-based alloys was estimated simply from the Rp substituting 20 mV 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.
