黄铜晶间腐蚀机理的实验及模拟研究

目的为了探究黄铜在含氨介质中的晶间腐蚀加速试验方法,明确黄铜中Zn含量对晶间腐蚀敏感性的影响规律和机理。方法采用电化学方法加速实现了黄铜表面的晶间腐蚀过程,利用XRD和金相显微镜分析腐蚀产物及表面形貌,对比分析H70和H80黄铜的晶间腐蚀规律。使用Materials Studio中的DMol3模块模拟NH4+和NH3在H70和H80黄铜晶界表面的吸附和反应过程,对比腐蚀粒子在黄铜表面的吸附规律和反应能垒,揭示黄铜晶间腐蚀敏感性的机理。结果试验结果表明,在NH4Cl溶液中,以100倍自腐蚀电流密度恒电流处理的黄铜,在4 h内能够发生明显的晶间腐蚀。黄铜晶间腐蚀的产物主要为铜氨络合物和锌氨络合物,H70黄铜的晶间腐蚀敏感性大于H80黄铜。模拟研究表明,NH4Cl溶液中的NH4+会优先在黄铜表面的晶界处发生物理吸附,随后NH4+跨越1.15 e V(H70)和1.17 e V(H80)反应能垒分解为NH3和H+,其中NH3优先吸附于晶界中偏析的Zn原子顶位形成络合物,其次与晶界的Cu形成络合物,H70晶界中的Zn含量更高,因此H70的晶间腐蚀敏感性更强。结论通过电化学恒电流处理法将黄铜的晶间腐蚀发生时间从7 d减少到4 h,并通过量子化学计算和腐蚀产物分析确定了黄铜在NH4Cl溶液中发生晶间腐蚀的机理。

Experimental and Simulation Study on Intergranular Corrosion Mechanism of Brass

The work aims to explore intergranular corrosion accelerated testing method of brass in ammoniated medium, and clarify law and mechanism of influence of Zn content on brass intergranular corrosion susceptibility. During the experiment, intergranular corrosion process of brass surface was accelerated in electrochemical method, then corrosion products and surface morphology were analyzed by XRD and metallographic microscope, and intergranular corrosion rules of brass H70 and H80 were comparatively analyzed. During the simulation, adsorption and reaction process NH4 +/NH3 on the surface of H70/H80 grain boundaries were simulated by using DMol3 module in Materials Studio. Adsorption law and reaction energy barrier of corrosion particles on brass surface were compared to reveal the mechanism of intergranular corrosion susceptibility of brass. Experimental study showed that, in the NH4Cl solution, obvious intergranular corrosion could happen in 4 hours to the brass treated at 100 times self-corrosion current density. Main products of intergranular corrosion were Cu(NH3)4]Cl2 and Cu(NH3)4]Cl2, and intergranular corrosion susceptibility of brass H70 was higher than that of H80. Simulation study showed that physical adsorption of NH4 + in the NH4Cl solution would preferentially occur on the grain boundary, then NH4 + was decomposed into NH3 and H+ beyond reactive barrier of 1.15 eV (H70) and 1.17 eV (H80), respectively. NH3 was preferentially adsorbed on Zn atom being segregated on the grain boundary to form a complex, then it formed a complex with Cu on grain boundary. The Zn content on H70 grain boundary was higher than that on H80 grain boundary, thus brass H70 had higher intergranular corrosion susceptibility. This work cuts intergranular corrosion time of brass in NH4Cl solution solution from 7 days to 4 hours in electrochemical galvanostatic method. Besides, intergranular corrosion mechanisms of brass are clarified based upon quantum chemistry calculation and corrosion products analysis.