水、氯离子在丙烯酸聚氨酯涂层中的扩散传输行为

DIFFUSION BEHAVIOR OF WATER AND CHLORIDE ION THROUGH ACRYLIC POLYURETHANE COATING

采用渗水率测试技术、渗氯离子浓度测试方法及交流阻抗测试技术研究了水、氯离子在丙烯酸聚氨酯涂层中的扩散传输行为.结果表明:在渗透初期,水在涂层中的传输符合Fick扩散定律,之后涂层渗水量达到饱和,随涂膜厚度的增加,涂层渗水量达到饱和的时间相对延长,饱和渗水量随膜厚的增加而降低;Cl-在涂层中的扩散在起始阶段呈一定值,达到某一临界点后(漆膜结构发生变化),透过涂层的Cl-的量突然呈线性增加,由直线斜率可求得氯离子在涂层中的扩散系数,随涂膜厚度的增加,溶液中Cl-浓度保持平衡的时间相对延长,涂层的平衡透氯离子浓度降低,Cl-在涂层中的扩散系数也随膜厚的增加而降低;采用EIS技术,据涂层、膜下金属阻抗及电容的变化及体系第二个时间常数出现的时间,可研究电解质溶液在涂层中的扩散渗透及膜下金属的腐蚀情况.

Diffusion behavior of water and chloride ion through acrylic polyurethane coating was studied using water vapor, chloride ion transmission rate technique of organic coatings and electrochemical impedance spectroscopy （EIS） technique in this paper. The results obtained indicated that diffusion behavior of water was suited for Fick diffusion law in early stage, later water percolating capacity was constant, constant water percolating capacity was reduced with the increasing of film thickness. Chloride ion percolating capacity was constant in early stage, later increased linearly, diffusion coefficient of chloride ion through coatings could be obtained by slope coefficient; with the increasing of film thickness, time of chloride ion concentration keeping balance was prolonged and equilibrium concentration of chloride ion was reduced, diffusion coefficient of chloride ion through coatings was also reduced. According to the change of resistance and capacity of coatings and metal, and time of the second time constant appeared, diffusing behavior of electrolyte through coatings and corrosion of metals under the coating could be evaluated by EIS.