电解抛光态690TT合金在顺序溶氢/溶氧的高温高压水中表面氧化膜结构分析
张志明, 男, 1983年生, 副研究员, 博士
修回日期: 2014-07-01
网络出版日期: 2015-01-25
基金资助
*国家重点基础研究发现计划项目2011CB610502, 国家科技重大专项项目2011ZX06004-009和国家自然科学基金项目51025104资助
ANALYSIS OF SURFACE OXIDE FILM FORMED ON ELETROPOLISHED ALLOY 690TT IN HIGH TEMPERATURE AND HIGH PRESSURE WATER WITH SEQUENTIALLY DISSOLVED HYDROGEN AND OXYGEN
Revised date: 2014-07-01
Online published: 2015-01-25
Supported by
Supported by National Basic Research Program of China (No.2011CB610502), National Science and Technology Major Project (No.2011ZX06004-009) and National Natural Science Foundation of China (No.51025104)
将电解抛光态690TT合金样品在325 ℃, 15.6 MPa,含1500 mg/L B, 2.3 mg/L Li, 2.5 mg/L H2的高温高压水中连续浸泡720 h后, 取出一半样品用于腐蚀产物的分析, 其余样品继续在含2.0 mg/L O2的该高温高压水中连续浸泡720 h. 采用SEM, GIXRD和TEM分析了在上述2种条件下样品表面生长的氧化膜的微观结构. 结果表明, 电解抛光态690TT合金在单一溶氢的高温高压水中表面生长的氧化膜具有双层结构: 外层是分散的富含Ni和Fe大颗粒氧化物和富含Ni的疏松的针状氧化物; 内层是近连续的富含Cr的氧化物; 内外层氧化物均具有尖晶石结构. 在溶氢/溶氧的溶液中连续浸泡后, 样品表面生长的氧化膜也具有双层结构: 外层的形貌、化学组成和物相结构与在单一溶氢条件下生长的氧化膜相似, 仅针状氧化物的长度明显增加; 而氧化膜内层变成了纳米尺寸的NiO. 后期溶解氧扩大了电位-pH图中含Ni的氧化物稳定存在的相区, 促进了外层富含Ni的针状氧化物的快速生长; 更加重要的是, 溶解氧提高了含Fe和Cr氧化物的腐蚀电位, 促进了在溶氢条件下生长的内层富Cr氧化物的溶解, 破坏了氧化膜的保护性结构, 提高了电解抛光态690TT合金的腐蚀速度. 在一回路溶氢/溶氧连续浸泡过程中, 电解抛光处理并不能降低690TT合金的腐蚀速度.
张志明 , 王俭秋 , 韩恩厚 , 柯伟 . 电解抛光态690TT合金在顺序溶氢/溶氧的高温高压水中表面氧化膜结构分析[J]. 金属学报, 2015 , 51(1) : 85 -92 . DOI: 10.11900/0412.1961.2014.00351
The electropolished (EP) alloy 690TT samples were first oxidized in the simulated B and Li containing primary water with 2.5 mg/L H2 at 325 ℃ and 15.6 MPa for 720 h, and then half of the samples were continuously immersed in this solution with 2.0 mg/L O2 for another 720 h. The microstructures and chemical composition of the oxide films formed under the above two conditions were analyzed. The results show that the dual layered oxide film formed under the single hydrogen water chemistry is mainly composed of spinel oxides. The outer layer is composed of big oxide particles rich in Ni and Fe and the underlying loose needle-like oxides rich in Ni. The inner layer is continuous Cr-rich oxides. The oxide film formed on EP alloy 690TT under the hydrogen/oxygen water chemistry also shows a dual layered structure. The surface morphology and chemical composition of the outer layer are similar to the oxide film formed under the hydrogen water chemistry. However, the inner layer is changed to the nano-sized NiO. The stable phase region in the potential-pH diagram for the Ni oxides is enlarged by the later dissolved oxygen. As a result, the oxygen promotes the fast growth of the outer needle-like oxides rich in Ni. Further, the oxygen promotes the dissolution of the inner Cr-rich oxides formed under the hydrogen water chemistry and increases the corrosion rate of the EP alloy 690TT. Electropolishing treatment can not reduce the corrosion rate of alloy 690TT in the simulated primary water with sequentially dissolved hydrogen and oxygen.
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