<正> 一、前言 确定应力腐蚀临界破裂电位对于研究应力腐蚀的机理及进行电化学保护具有重要意义。目前主要有几种测定方法,如控制电位应力腐蚀破裂试验法、动电位扫描法、模拟闭塞电池法、电化学计算法及电流衰减法等,以控制电位的应力腐蚀试验法最为准确可靠。本实验采用控制电位固定载荷法,对浸泡在铜氨稀溶液中的黄铜试件进行恒电位拉伸,从而确定其破裂临界电位。
Constant load and potentiostatic techniques were used to study the susceptibility of SCC for H62 brass in 0.1N NH_4OH+0.1g Cu~(2+)/L solution at 30℃. It was found that a critical potential existed in this system, being about —620mV(SCE), below which the SCC would not occur. Above the critical potential, the cracks propagating along the β′ phase which dissolved prior to α phase were observed with SEM and metalloscope, and the most sensitive potential for cracking was about —200mV (SCE). Also, the simulated occluded corrosion cell designed previously by the authors was modified and used to investigate the chemical changes within S. C. cracks of this system. As anodic currents passed the cell, the pH value of occluded cell (0C) solution dropped down from about 11 to 6. 2 or less, the Zn contents of the 0C solutions increased rapidly with time, and the Cu/Zn ratio on the surface of occluded specimens increased. These facts indicate that acidification within cracks existed and dezincification occurred at the crack tips for this system.
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