热镀锌层在饱和Ca(OH)_2溶液中的腐蚀行为

Corrosion Behavior of Hot Dip Galvanized Coating in Saturated Ca(OH)_2 Solution

热浸镀锌是保护混凝土钢筋的有效措施之一。用饱和Ca(OH)2溶液模拟混凝土孔隙液,研究热镀锌层在该模拟液中的腐蚀行为。采用电化学测试、SEM、EDS和XRD手段分别分析了试样在不同浸泡阶段的电化学参数、表面微观形貌以及腐蚀产物的化学成分和相组成,结果表明:在浸泡腐蚀过程中,锌晶粒的晶界处优先出现腐蚀小孔,然后在小孔附近开始生成锌酸钙晶体Ca[Zn(OH)3]2.2H2O,随着锌酸钙晶体不断生长,逐渐覆盖锌层表面,形成耐蚀性逐渐增强的保护层。当锌基底被锌酸钙晶体完全覆盖后,腐蚀电流密度Jcorr降至临界钝化值附近,锌层处于钝化状态。

Hot-dip galvanizing is one of the efficient measures to protect rebar in concrete. The hot dip galvanized samples were immersed into the saturated Ca（OH）2 solution, which was adopted as pore concrete simulating solutions, with different immersion time, and tested by the electrochemical measurement. The micro-structure on the surface of the samples were observed by scanning electron microscopy（SEM）, the chemical composition and phases of the corrosion products were analyzed by energy dispersive spectrometry （EDS） and X-ray diffraction （XRD）. The results show that, during the immersion process, some tiny holes are occurred along the zinc grain boundary with the corrosion reaction between zinc and the solution at the initial time, then the calcium hydroxyzineate Ca[Zn（OH）3]2 · 2H2O （CaHZn） crystal are formed near the tiny holes and grown steadily, while the anti-corrosion of the products film is increasing accordingly. When the calcium hydroxyzincate crystal film covers the surface of the samples, the zinc coating is passivated and the corrosion current density is almost similar to passivation threshold.