A3钢及304不锈钢孔蚀保护电位的确定

STUDY ON THE PROTECTION POTENTIAL AGAINST PITTING CORROSION OF A3 STEEL AND 304 SS

采用模拟闭塞电池法和模拟闭塞区溶液法 ,测定了 0Cr18Ni9奥氏体不锈钢 (30 4SS)在 0 .5mol·L- 1NaCl(pH =7)以及A3钢在 0 .0 1mol·L- 1NaCl(pH =12 )两种体系 ,孔蚀的不同阶段孔内外间电流的换向电位ET.结果表明 ,ET 值随闭塞区溶液组成的变化而变化 ,但存在一个范围 .将30 4不锈钢的ET 值与用孔蚀滞后环法在不同扫描速度 ,不同回扫电流时所测得的孔蚀保护电位EP 值作比较 ,发现EP 值范围处于ET 值范围之内 .ET

Two methods simulated occluded cell and simulated occluded solution have been developed to determine the protection potential against pitting of A3 steel and 0Cr18Ni9 stainless steel.They are based on the theory that the pitting protection potential( E P) is actually the transition potential of the direction of current between the occluded cell and the external surface( E T).The E T of 304 SS in 0.5 mol·L -1 NaCl solution is in the range of 220 mV to 440 mV(SCE), the E T of A3 steel in 0.01 mol·L -1 NaCl solution(pH=12) is in the range of 390～ 670 mV, the lowest of which can be considered as cathode protection potential( E P).The E P of 304 SS determined with “cyclic” potentiodynamic polarization method is included in the E T with above methods.As for electrochemical protection against pitting, if the potential of the external surface is controlled below the E P,the active passive transition will occur inside the occluded cell, so the pitting will be stifled.