环氧酚醛/镀锡薄钢板体系在功能饮料中的腐蚀行为

Corrosion Behavior of Novolac Epoxy Coated Tinplate System in Energy Drink

利用电化学阻抗谱(EIS)和电化学噪声技术,并结合扫描电镜、能量散射X射线谱等表面分析技术,研究了环氧酚醛/镀锡薄钢板体系在功能饮料中的腐蚀过程并探讨了腐蚀机制.实验结果表明,浸泡前3,d EIS图呈现单容抗弧特征,涂层防护性能良好;浸泡28,d后EIS图呈现双容抗弧特征,电解质溶液已经渗透通过有机涂层;220,d后EIS图呈现3个时间常数的特征,镀锡层与基体金属发生了腐蚀;364,d后EIS图又呈现单容抗弧特征,涂层基本失去防护性能.随浸泡时间的增加,电流噪声的幅值逐渐增加,表明腐蚀程度越来越严重.环氧酚醛/镀锡薄钢板体系在功能饮料中的腐蚀过程,大致分为3个阶段:①涂层的润湿过程;②腐蚀性离子的传输并引发腐蚀;③腐蚀加剧.其腐蚀机制首先是涂层发生破损形成微孔,接着是涂层下的镀锡层在功能饮料的有机酸中发生腐蚀;镀锡层遭到腐蚀破坏后,由于基体金属碳钢具有更高的电化学活性,腐蚀过程转化为碳钢基体的溶解.

The corrosion process of novolac epoxy coated tinplate system in energy drink was investigated by using electrochemical impedance spectroscopy （EIS） and electrochemical noise （EN） techniques, and the corrosion mecha- nism was discussed based on the surface characterization by scanning electron microscopy （SEM） and energy disper- sive X-ray spectroscopy （EDS）. The results show that in the first 3 days there was only one time-constant in EIS plot, indicating that the organic coating had good protective performance. After 28 days＇ corrosion, EIS plots showed 2 time-constants, indicating that the electrolyte had permeated through the organic coating. There were 3 time-constants in the EIS plots after 220 days＇ corrosion, indicating that corrosion had occurred on the tinplate. One time-constant was seen in EIS plots after 364 days＇ corrosion, indicating that the organic coating had basically lost its protective performance. The amplitude of current noise increased as time got prolonged, which indicated that the corrosion of the substrate metal was more and more serious. The entire deterioration process of novolac epoxy coated tinplate system in energy drink could be divided into three main stages. Stage I was the wetting of organic coating, stage Ⅱ was the corrosion initiation beneath the coating, and stage Ⅲ was the corrosion extension. The corrosion mechanism was firstly the damage of organic coating and the formation of micropores during the corrosion process, and then the dissolution of tinplate under the organic coating. After the tinplate was corroded, the carbon steel substrate started to dis- solve and became the dominated corrosion process due to its higher electrochemical activity.