Development of Corrosion resistant Ag-Pd-Cu-Au alloys for patient with metal hypersensitivity

研究了18种不同成分的Ag-Pd-Cu-Au合金在0.9% NaCl和0.1% Na_2S溶液中的腐蚀行为，制备了高耐蚀性和生物相容性（无过敏）的牙科铸造合金。研究了微量Ga对Ag-Pd-Cu-Au合金浇注性能、机械强度和耐腐蚀性的影响。采用电化学技术和原子吸收分光光度法对其耐腐蚀性能进行了评价。采用x射线光电子能谱（IPS）对合金表面进行了分析。Ag-Pd-Cu-Au合金在0.9% NaCl和0。1% Na2S溶液随着Pd含量的增加而增加。结果表明，Pd质量为45%的Pd- 25ag - 18cu - 12au合金在0.1% Na_2S溶液中钝化，形成富Pd的硫化膜，不像普通的Ag-Pd-Cu-Au合金那样因Ag_2S的结晶腐蚀产物而失去光泽。在0.9% NaCl溶液中，Pd-25Ag-18Cu-12Au合金的金属离子释放量约为Ag-Pd-Cu-Au合金的10%。少量Ga（小于5质量%）的加入降低了Pd-25Ag-18Cu-12Au合金的液点，提高了合金的浇注性能，但不降低合金的耐腐蚀和抗失光泽性。少量的Ga也提高了合金的维氏硬度值。上述结果表明，Pd-25Ag-18Cu-12Au合金具有良好的抗腐蚀、抗霉变能力和良好的生物相容性，适合作为铸造修复材料。

The corrosion behaviors of eighteen Ag-Pd-Cu-Au alloys with different compositions were examined in 0.9 % NaCl and 0.1 % Na_2S solutions to develop a high corrosion resistant and biocompatible (allergy free) dental casting alloy. The effects of small amount of Ga on the castability, mechanical strength, and corrosion resistance of the Ag-Pd-Cu-Au alloy were also examined. The corrosion resistance was evaluated by electrochemical techniques and the analysis of released metal ions by atomic absorption spectrophotometry. The surface of the alloy was analyzed by X-ray photoelectron spectroscopy (IPS). The corrosion resistance of the Ag-Pd-Cu-Au alloy both in 0.9 % NaCl and 0. 1% Na2S solutions increased with an increase in Pd content. It was found that the Pd-25Ag-18Cu-12Au alloy with 45 mass% Pd was passive in 0.1 % Na_2S solution with the formation of Pd-rich sulfide film and did not tarnish unlike commercial Ag-Pd-Cu-Au alloys which tarnished with the formation of crystalline corrosion product of Ag_2S. The amount of released metal ions from the Pd-25Ag-18Cu-12Au alloy in 0.9 % NaCl solution was approximately 10 % of that from the commercial Ag-Pd-Cu-Au alloys. The addition of small amount of Ga (less than 5 mass%) lowed the liquids point of the Pd-25Ag-18Cu-12Au alloy and improved its castability without decreasing the resistance to corrosion and tarnish. The small amount of Ga also increased the value of Vickers hardness number. These results suggested that high level of resistance to corrosion and tarnish and excellent biocompatibility of the Pd-25Ag-18Cu-12Au alloy make this alloy suitable as a material for dental casting restoration.