The Research Of Several Typical Zinc-Rich Coating Eletrochenical Characteristics

The electrochemical characteristics of three kinds of typical zinc-rich coatings, namely organic coating with spherical zinc powder(OR-S), organic coating with lamellar zinc powder(OR-L) and inorganic coating with spherical zinc powder(IN-S), were researched in this thesis by means of open circuit potential method, constant-current coulometric method, polarization curves method, electrochemical impedance spectroscopy method and electrochemical noise method.The experimental results showed that the IN-S coatings protected steel from rust for 705 h in saline while the OR-S did for only 400 h. Their length of shielding protection time for steel is approximately the same, differences in corrosion resistance resulted from differences in cathodic protection performances. The length of cathodic protection time for IN-S is 532 h, about OR-S’ 3.4 times. IN-S coating actively dissolved under 1m A/cm2 for 10.8h, consumed electric quantity 2.58 C, exhibited excellent high current protection performances, while OR-S coating possessed no high current protection. Their protection differences diminished under 0.05 m A/cm2 as IN-S consumed 1.944 C while OR-S consumed 0.478 C. The self-corrosion current of IN-S in initial immersion in saline was 2 orders of magnitude higher than that of OR-S. The impedance of IN-S was always lower than that of OR-S during immersion. Their changing rules of noise resistance with time is different.The experimental results also showed that the OR-L coatings protected steel from rust for 619 h in saline, that was longer than OR-S. The shielding protection time of OR-L is a little longer than that of OR-S, but the cathodic protection time is much longer than that of OR-S. The cathodic protection time of OR-L is 283 h, about OR-S’ 1.7 times. Both OR-L and OR-S possessed no high current protection, performance of low current protection under 0.05 m A/cm2 for OR-L was better than that for OR-S as OR-L consumed 1.491 C while OR-S consumed 0.478 C. The self-corrosion current of OR-L in initial immersion in saline was about 1 order of magnitude higher than that of OR-S. Their changing rules of noise resistance with time is the same, that is, the noise resistance kept decreasing until shielding protection stage.The ranking of the three coatings in order of cathodic protection time from long to short, in order of actively dissolution time under 0.05 m A/cm2 from long to short, in order of self-corrosion current in initial immersion from high to low, all agreed with their ranking in order of corrosion resistance in saline from strong to weak, namely, IN-S, OR-L and OR-S. A positive correlation relationship can be seen between cathodic protection time and actively dissolution time under 0.05 m A/cm2.