化學成份對牙科用Ni-Cr -Mo合金耐蝕性質之影響

Compositional Influence on the Corrosion Resistance of Ni-Cr-Mo Dental Alloys

本研究的目的是探討化學成份對牙科用Ni-Cr-Mo鑄造合金耐蝕性質的影響。利用循環動電位測試（cyclic potentiodynamic test）和定電位測試（potentiostatic test）評估不同Ni-Cr-Mo合金在除氧人工唾液（pH 5/37℃）中的耐蝕性質。循環動電位測試後，利用光學顯微鏡觀察試片表面腐蝕型態。定電位測試後，利用X光光電子能譜及歐傑電子能譜分析試片表面鈍化膜的化學成份及結構。耐蝕性質測試結果顯示：Ni-Cr-Mo合金的耐蝕性質與表面生成的鈍化膜（包括Ni(OH)2、NiO、Cr2O3及MoO3）有關。含較高Cr（約21%）及Mo（約8%）含量的Ni-Cr-Mo合金，因表面鈍化膜含有高Cr（最大值約31-35%）及高Mo（最大值約12%），故其極化曲線中有較寬廣的鈍化範圍，並對孔蝕免疫。添加少量的鈦（<4%）對Ni-Cr-Mo合金的耐蝕性質並無影響。當抗孔蝕當量（pitting resistance equivalent）達到49時，Ni-Cr-Mo合金便有良好抗孔蝕能力。

The objective of this investigation was to study the compositional influence on the corrosion behavior of Ni-Cr-Mo dental casting alloys in acidic artificial saliva. Cyclic potentiodynamic and potentiostatic tests were used to evaluate the corrosion behavior of different Ni-Cr-Mo dental casting alloys in deaerated artificial saliva with pH 5 at 37℃. Optical microscope observations were carried out after the cyclic potentiodynamic tests. Surface chemical analyses were characterized by X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) after potentiostatic tests. The results of corrosion tests showed that the corrosion resistance of Ni-Cr-Mo casting alloys was associated with the formation of passive film, containing Ni(OH)2, NiO, Cr2O3 and MoO3, on the surface. The Ni-Cr-Mo alloy with higher Cr (≈21 %) and Mo (≈8 %) contents had much larger passive region in the polarization curve and was immune to pitting corrosion, which was due to the presence of high Cr (maximum≈31-35 %) and Mo (maximum 12 %) contents in the surface passive film. The presence of Ti lower than 4 % in the Ni-Cr-Mo casting alloy had no effect on the corrosion resistance. A pitting resistance equivalent (PRE) of about 49 could provide the Ni-Cr-Mo alloy with a good pitting corrosion resistance.