为了进一步探讨无铬型耐指纹电镀锌板发生黑变的原因及机理,采用SEM,EDX,XRD,色差仪以及原子吸收光谱等技术对耐指纹电镀锌钢板黑变试样表面形貌、腐蚀产物的组成进行分析.结果表明:由于耐指纹有机膜固化温度低(工艺要求:10～150℃,实际95℃)、水质质量差(含大量Cl~-)、清洗次数少,使耐指纹镀锌板的明度值(L)由79.15下降到63.25,表面明显"黑化";黑变膜是由ZnO,Zn(OH)_2,ZnCl_2·4Zn(OH)_2等组成,原因主要是有机膜下形成的氧浓差电池诱发的锌的阳极活性溶解,镀锌层表面低pH值和残存的Cl~-对锌层腐蚀有促进作用.据此揭示了耐指纹板发生黑变的原因,并提出了消除黑色的相应对策.
The processes for industrial production of Cr-free anti-fingerprint galvanized steel sheet were analyzed,while the morphology and composition of the anti-fingerprint galvanized steel sheet after black tarnishing were investigated using a scanning electron microscope,an energy dispersive X-ray analyzer,an X-ray diffractometer,a chromatism meter,and an atomic absorbance spectrometer.This aims at revealing the causes leading to black tarnishing of the galvanized steel sheet and exploring the mechanism of black tarnishing as well.The countermeasures to get rid of the black tarnishing of the galvanized steel sheet were suggested.Results show that the main factors leading to black tarnishing of the Cr-free anti-fingerprint galvanized steel sheet include low curing temperature of the organic coating(required:100～150℃,in practice 95℃),poor water quality,and insufficient cleaning.These factors,by acting synergistically,led to decrease of the lightness L of the galvanized steel sheet from 79.15 to 63.25 and hence obvious surface "blacking".The black film was mainly composed of ZnO,Zn(OH)_2,and ZnCl_2·4Zn(OH)_2,which was originated from the anodic dissolution of zinc induced by oxygen concentration cell.Besides,the low pH value on the zinc surface and remnant Cl-also accelerated the corrosion of the zinc layer.
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