镁合金牺牲阳极对贮水式家用电热水器的阴极保护

CATHODIC PROTECTION OF DOMESTIC ELECTRIC WATER HEATERS BY MAGNESIUM ALLOY SACRIFICIAL ANODES

在水温50℃,以贮水箱容积50L的电热水器为研究对象.取内胆、镁合金阳极、加热器3者的面积比为140:2:1.采用恒电流极化法,考察了维持热水器内胆达到阴极保护电位-83OmV(Ag/AgCI)所需的阴极保护电流密度和阴极保护效果.加阴极保护的内胆试片在试验期7d(天)内不出现锈蚀,而不加阴极保护的内胆不到1d就出现了明显的锈蚀.内胆所需的阴极保护电流密度约为1.8mA/m^2,若使内胆与加热器短接,阴极保护电流密度则需约15mA/m^2,较前者增大了7.3倍;此时内胆有可能成为偶合系统中的阳极,腐蚀加快,穿孔的危险性增大.因此,这种情况要设法避免.

Electric water heaters with 50L tank's capacity was simulated and tested, the protective current density and effect of magnesium sacrificial anode's electrochemical protection was investigated. The tank with ca-thodic protection could be kept rustless in 7 testing days, whereas it would become rusted in 1 day. To keep the protective potential-830mV (Vs Ag/AgCl) of tank's inside surface, the protective current density would be about 1. 8mA/m2. When the tank was short circuited with heating elements, a much greater current density of about 15mA/m2 was needed. In this condition, the tank sometimes would become an anode versus to the copper heating elements, and the corrosion rate of tank was even more rapid than that of not protectedone, So, the short-circuit between heating elements and tank should be avoided.