The Anti-corrosion Modification Of Sulfosalicylic Acid On The Corrosion Of Fluoferrate Conversion Coating On Iron And Steel

To prevent corrosion of iron and steel, two kinds of surface treatment technology，chromate conversion treatment process on galvanized steel and phosphatingconversion on iron and steel， are most widely used. However, the wastewater ofphosphating process contains large amounts of phosphates, resulting in seriouseutrophication problems. Chromate conversion on galvanized steel due to the use ofcarcinogenic hexavalent chromium has been banned to used.“Heavy metal pollutioncomprehensive prevention and control12th five year plan”, the first12th five year plan,was put forward in2011, giving strict control requirements over the five heavy metalsof industrial production including hexavalent Cr. Therefore, phosphorus-free andchromium-free conversion coating technology research become the hot spot ofcorrosion protection research on iron and steel.Based on the previous research of fluroferrite conversion coating on iron and steelby our group, the effect of the complexing agent (EDTA, sodium citrate, sulfosalicylicacid, sodium pyrophosphate, sodium polyphosphate, sodium tartaric) on the corrosionresistance of potassium fluroferrite conversion coating on iron and steel was studied byusing the method of comparative tests and single-factor test. EDTA, sodium citrate,sulfosalicylic acid and sodium tartaric was further researched. The results showed thatfluroferrite conversion coating modified by sulfosalicylic acid had the best corrosionresistance. Treated under the condition of sulfosalicylic acid was7.5g/L,45℃and90min, iron and steel’salt spray’time increased from the12h before modification to54hafter modification and its anti-corrosion performance was greatly improved. Scanning electron microscopy (SEM), EDS, infrared spectroscopy (IR) andelectrochemical test results showed that: the crystal particles of the conversion coatingwas smaller, more compact and more uniform. The modified conversion coatingcontained12.12%C、9.80%O、17.28%Fe、23.53%K、2.22%Ti、33.87%F、1.18%S and absorption peaks relating with organic function group of sulfosalicylic acid. Itindicated that the modified conversion coating contained organic ingredients inaddition to potassium fluoferrite conversion coating. The polarization curves showedthat corrosion potential was about10mV more positive than fluoferrate conversioncoating and16mV more positive than bare iron. The corrosion resistance of iron andsteel was further enhanced.