Quantitative Evaluation of Chemical Stability of Dental Alloys

本研究的目的是定量评价牙科合金的化学稳定性。腐蚀电阻率用参数Q表示，该参数对应于试样表面发生的电化学反应总量。用测试前后的色差DELTAE评价耐污性。主要结果总结如下：(1)单相组织合金的腐蚀行为主要由合金的高贵程度决定。(2)多相结构合金的阳极动电位极化曲线较为复杂。在两个不同的电位下出现腐蚀速率自发增加的特征电位（Ec）。但这些复杂的曲线可以通过叠加每个单相的两条简单曲线来解释。两个不同的电导率对应于每一相的电导率，电位处的电流密度可以用每一相电导率的算术平均值来表示。(3)合金的DELTAE。其中部分金被钯取代，最高可达10%左右，随钯含量的增加而降低。但进一步更换会增加AE。DELTAE的增加是由于用钯取代金而降低了化学稳定性。少量钯的加入降低了DELTAE，可以用钯在硫化物层下方富集的机制来解释。这种富集可能抑制S^<- >离子的扩散。导致硫化物层生长速率降低。(4)低高贵合金的失光泽敏感性对其显微组织非常敏感。相分离使DELTAE达到均匀单相的2倍左右。但少量钯的加入提高了双相合金的失光泽敏感性。这可能与钯在富铜相中富集有关。

The purpose of this study was to evaluate the chemical stability of dental alloys quantitatively.Corrosion resistivity was expressed by the parameter Q which correspond to the total amount of electrochemical reaction occurred on the specimen surface. Tarnish resistance was evaluated by color difference DELTAE between those of prior and after testing.Principal results were summarized as follows;(1) Corrosion behavior of alloys with single phase structure were principally determined by the nobility of the alloy.(2) Anodic potentiodynamic polarization curves of the alloys with multiphase structure were rather complicated. Characteristic potential (Ec) at which corrosion rate increased spontaneously appeared at two different potentials. But these complicated curves can be explained by superposing two simple curves of each single phase. Two different Ec correspond to those of each phase, and current density at a potential can be expressed by the arithmetical mean of those of each phase.(3) DELTAE of alloys. in which a part of gold was replaced with palladium up to about 10at%, decreased with palladium content. But further replacement increased AE. This increase in DELTAE was attributed to the decrease in chemical stability by the replacement of gold with palladium. Decrease in DELTAE by the addition of small amount of palladium may be explained by the mechanism of palladium enrichment just below the sulfide layer. This enrichment may suppress the diffusion of S^<--> ion. resulting in the decrease in the growth rate of sulfide layer.(4) Tarnish susceptibility of low-nobility alloy was very sensitive to its microstructure. Phase separation increased DELTAE to about two times of homogenized single phase state. But a small amount of palladium addition improved this tarnish sensitivity of dual phase alloy. This may be attributed to the enrichment of palladium in the copper-rich phase.