Methods For Evaluating Anti-corrosion Performance Of Zinc-rich Coating

A new method for rapid detection of corrosion resistance of zinc-rich paint wasdesigned and studied in this thesis, it is named galvanostatic dissolution method(GD).Four groups of coated specimens were prepared. The first group contains coating withdifferent Q values (Q=PVC/CPVC and PVC means pigment volume concentration,CPVC means critical pigment volume concentration), the second group contains coatingsprepared from spherical shaped zinc pigments and lamellar shaped zinc pigments, thethird group contains coatings whose partial spherical shaped zinc pigments were replacedby high titanium ash, talcum powder, and aluminum powder respectively and the lastgroup contains coatings whose5%,10%,15%,20%,25%spherical zinc powder inweight were replaced by graphite and acetylene black respectively. Conventionalmethods including Open circuit potential test method (OCP), electrochemical impedancespectroscopy (EIS), salt spray test method were employed to compare with galvanostaticdissolution method.Experimental results showed that dissolution time from GD and galvanic time fromOCP is consistent for both coatings prepared from spherical shaped zinc pigments andlamellar shaped zinc pigments, while test period is much shorter for GD method thanOCP method. It was also revealed that dissolution time from GD is also consistent withthe scores gained in salt spray test roughly for coatings with spherical shaped zincpigments.It was also found in OCP test that the weights of coatings with Q=1.0and preparedfrom spherical shaped zinc pigments only and lamellar shaped zinc pigments onlyfluctuated seriously in galvanic protection period and slightly in barrier protection period.Q value was found to effect the anti-corrosion performances of zinc-rich coatingsgreatly. Performances in salt spray test, performances in salt solution immersion test andgalvanic protection life got worse with Q value decreasing. The coating Q=1.0was foundto be permeated easily and its excellent anti-corrosion performances come from its longgalvanic protection life. The coating Q=0.8and Q=0.62were found difficult to bepermeated but their barrier protection time were short.The anti-corrosion performances of coatings Q=1.0and prepared from sphericalshaped zinc pigments only are much the same with that of coatings Q=1.0and prepared from lamellar shaped zinc pigments, while the former was somewhat better in salt spraytest and the latter was somewhat better in salt solution immersion test. The coatingsQ=1.0and prepared from lamellar shaped zinc pigments were difficult to be permeatedand their barrier protection time were long.Both the performances in salt spray test and that in SD test got worse for coatingsprepared from spherical shaped zinc pigments when partial zinc pigments were replacedwith high titanium ash, talcum powder, aluminum powder, graphite and acetylene black...