AN XPS INVESTIGATION INTO THE PASSIVITY OF AN AMORPHOUS NI-20P ALLOY
AN XPS INVESTIGATION INTO THE PASSIVITY OF AN AMORPHOUS NI-20P ALLOY
复制标题
DOI：
10.1149/1.2095880
复制
发表时间：
1988-05-01
影响因子：
3.9
通讯作者：
YU, YC
中科院分区：
文献类型：
--
作者：
DIEGLE, RB;SORENSEN, NR;YU, YC
在H_2SO_4和HCI电解液中的阳极极化实验表明，非晶态Ni-20P合金在-0.3~0.2V(SCE)之间钝化，在0.2V(SCE)以上透明溶解。在0.2N HCI中，晶态Ni很容易出现凹坑，Ni-20P的抗点蚀和钝化效果与在0.2N H_2SO_4中一样有效。对极化后的Ni-20P表面的X射线光电子能谱分析表明，元素P在合金表面富集物，存在次亚磷酸盐阴离子，没有被氧化的镍物种。因此，Ni-20P合金不会因为形成三维氧化膜而钝化，例如在镍上形成的NiO膜。提出了一种化学钝化过程，该过程由次亚磷酸盐阴离子的形成和表面保留控制，次亚磷酸盐阴离子在合金和电解液之间起到阻挡作用。相比之下，晶态镍的钝化行为得到了广泛的研究。根据MacDougall和他的同事(1-4)的说法，镍在酸性Na2SO4溶液中通过形成厚度约1纳米的NiO层来钝化。由于目前NiO的生成效率只有20%左右，他们认为标准的高场氧化生长机制在镍的恒流氧化过程中是不起作用的。这一结果可以用缺陷氧化膜的存在来解释，在缺陷氧化膜中，恒电流极化期间的电位变化与膜的完好状态的增加有关。根据氧化膜缺陷模型解释了不同外加阳极电位下的电流-时间关系，其中氧化膜的完整性随时间呈对数增长(5)。Kawashima等人(6)发现，添加或不添加钼或钨的非晶态Ni-P合金在硫酸中不会被阳极极化钝化。相反，这些合金会形成厚厚的多孔表面膜，并在酸性氯化物溶液中遭受点蚀。对Ni-18P在IM HCI中极化后的X射线光电子能谱(XPS)分析表明，相对于Ni(7)，磷主要集中在表面膜中。薄膜中P~2p电子的结合能表明了磷酸盐物种的存在。此外，磷酸镍中的Ni2+离子与膜中总Ni2+的比例表明，在0.1V(SCE)及更高的电位下形成的表面膜的主要成分是磷酸镍。这种膜是灰黑色的，因此，相对于在镍上形成的钝化膜来说，它是厚的。
Anodic polarization experiments in H2SO4 and HCI electrolytes show that amorphous Ni-20P alloy passivates at potentials between-0.3 and about 0.2 V (SCE) and dissolves transpassively above 0.2 V (SCE). In 0.2 N HCI, in which crystalline Ni pits readily, Ni-20P resists pitting and passivates as effectively as in 0.2 N H2SO4. Analysis by x-ray photoelectron spectroscopy of Ni-20P surfaces after polarization indicates an enrichment of elemental P on the alloy surface, the presence of hypophosphite anions and the absence of oxidized nickel species. Thus, the Ni-20P alloy does not passivate by development of a three-dimensional oxide film, such as the NiO film that forms on nickel. A chemical passivation process is proposed that is controlled by the formation and surface retention of hypophosphite anion, which acts as a barrier between the alloy and the electrolyte.This paper describes an electrochemical investigation into the passivity of an amorphous Ni-base alloy, about which little is known. By contrast, the passivation behavior of crystalline nickel has been studied extensively. According to MacDougall and co-workers (1-4), nickel passivates in acidic Na2SO4 solution through the formation of a NiO layer about 1 nm in thickness. Because the current efficiency for NiO formation is only about 20%, they propose that the standard high field oxide growth mechanism is not operative during galvanostatic oxidation of nickel. The results are explained by the presence of a defective oxide film where the change of potential during galvanostatic polarization is associated with an increase in the state of film perfection. Current-time relationships at various applied anodic potentials were also interpreted in terms of a defect model of the oxide film where film perfection increases logarithmically with time (5). Kawashima et al.(6) found that amorphous Ni-P alloys with or without addition of molybdenum or tungsten are not passivated by anodic polarization in sulfuric acid. Instead, the alloys form thick porous surface films and suffer pitting corrosion in acidic chloride solutions. Analysis by x-ray photoelectron spectroscopy (XPS) of Ni-18P after polarization in IM HCI showed phosphorus concentrated in the surface films, relative to nickel (7). The binding energy of the P 2p electrons from the film suggested the presence of phosphate species. In addition, the ratio of Ni 2. ions in nickel phosphate, Ni3 (PO4) 2, to the total Ni 2~ ions in the film indicated that the main constituent of the surface film formed at 0.1 V (SCE) and higher potentials is nickel phosphate. This film was grayish black in color and, hence, thick relative to the passive film formed on nickel.