Effect Of Surfactants On The Corrosion Resistance Of Fluroferrite Conversion Coating On Iron And Steel

Iron and steel plays an important role in the national economy, but its corrosion is aproblem plaguing people. Corrosion can not only result in economic losses, but alsocause casualties. It has been a long concerned problem that how to prevent iron andsteel from corrosion. There are two widely used methods of preventing iron and steelfrom corrosion: One is phosphating process, the other is chromate treatment ongalvanized steel. Although both are effective protective measures, they also bring a hugeenvironmental problem. The wastewater from phosphating process contains largeamounts of phosphates, which cause eutrophication and be ultimately harm to humans.Similarly, the wastewater from chromate treatment on galvanized steel containscarcinogenic chromates, which also are harm to the environment and human beings. EUbanned the use of hexavalent chromium and other harmful substances on metal surfacetreatment in the RoHS Directive. China Integrated Control of Heavy Metal Pollution--Twelfth Five Plan lists five key control objects, hexavalent is one of them. With thegrowing importance of environmental protection, new free-phosphates andfree-chromates corrosion protection technology on iron and steel has become a viableway.Based on the research of fluoferrite conversion coating on iron and steel by ourresearch group?this paper studied the effect of surfactants on the corrosion resistance offluoferrite conversion coating on Iron and Steel. The results show that:1. Anionic surfactants, sodium dodecyl sulfate prevent conversion coatingformation?but sodium dodecyl benzene sulfonate slightly does not affect conversioncoating formation. Cationic surfactants (CTAB, DTAB and cetylpyridinium bromide) can improve the corrosion resistance of conversion coating. Amphoteric compound,glycine, can improve the corrosion resistance of conversion coating. Nonionicsurfactant, polyoxyethylene alkylphenol ether, reduces the corrosion resistance ofconversion coating.2. The further study on DTAB and glycine shows that the neutral salt spray time oftheir conversion coating prepared under optimal conditions could be up to13h and16h,respectively.3. The study on the combination of DTAB and glycine shows the neutral salt spraytime of fluoferrite conversion coating on iron and steel, which is prepared from125g/LKF?77ml/L HNO3?7.5g/L?NH4?2S2O8?1.0g/L titanium salt accelerator,0.8g/L DTABand10g/L glycine under the condition of28?and90min, could be up to36h.Thereason is that DTAB and glycine makes the thickness of fluoferrite conversion coatingincrease from30?m to70?m, which results in corrosion potential more positively andcorrosion current density smaller, the corrosion resistance of conversion coatingincreases significantly.