XPS study on surface modification of NiTi alloy by acidic solution immersion and subsequent heating in air
XPS study on surface modification of NiTi alloy by acidic solution immersion and subsequent heating in air
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DOI：
10.1002/sia.7046
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发表时间：
2021-12
影响因子：
1.7
通讯作者：
Kota Sakamoto;Fumio Hayashi;N. Ohtsu
中科院分区：
文献类型：
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作者：
Kota Sakamoto;Fumio Hayashi;N. Ohtsu
采用X射线光电子能谱（XPS）分析了近等原子镍钛（NiTi）合金在HNO3和H2SO4水溶液中浸泡以及随后在723 K空气中加热后表面化学状态的变化。采用角度解析技术和数学反褶积技术的XPS分析表明，在环境气氛中形成的被动层以TiO2为主态，Ni(OH)2和NiO为次要态。在723 K的空气中加热时，合金上的Ni(OH)2仍留在该区域。因此，生成的层成为表面有Ni偏析区的Ti -氧化物层，这是Ni(OH)2脱水形成的NiO。然而，浸泡在HNO3或H2SO4水溶液中会使Ni(OH)2态溶解在NiTi合金的钝化层中；因此，加热后的氧化层中很少出现Ni偏析区。表面的Ni偏析区成为氧向内扩散的障碍；因此，这种分离区域的湮灭导致氧化层厚度的增加。
Changes in the surface chemical state of a nearly equiatomic nickel–titanium (NiTi) alloy caused by immersion in aqueous solutions of HNO3 and H2SO4 as well as subsequent heating in air at 723 K were analyzed using X‐ray photoelectron spectroscopy (XPS). An XPS analysis using angle‐resolved technique and a mathematical deconvolution technique revealed that a passive layer formed in an ambient atmosphere contained TiO2 as a major state and Ni(OH)2 and NiO as minor states. The Ni(OH)2 on the alloy remained in the region even when heated in air at 723 K. Therefore, the resulting layer became a Ti‐oxide layer with Ni segregated region at the surface, which was NiO formed via dehydration of Ni(OH)2. However, immersion in an aqueous solution of HNO3 or H2SO4 enables Ni(OH)2 state to dissolve in the passive layer of a NiTi alloy; thereby, the Ni segregated region rarely appeared in the oxide layer by heating. The Ni segregated region at the surface becomes an obstacle for the inward diffusion of oxygen; thus, the annihilation of such a segregated region results in an increase in the thickness of the oxide layer.