| Iron and steel is widely used but corrodes easily. In order to improve the corrosion resistance, at present, the most common methods are phosphating and chromate chemical conversion treatment after galvanization. But there is a certain degree of inadequacy and subsequent problems for the two methods: the process of chromate conversion on galvanized steel uses carcinogenic hexavalent chromium; the wastewater of phosphating process contains large amounts of phosphates, resulting in serious eutrophication problems. Both cause a serious impact on the environment and human health. Cr(VI) was limited to use by the European Union RoHS Directive in 2006 and China "Heavy metal pollution prevention12 th five-year plan" in 2011. "Environmental protection 12 th five-year plan" also ruled to control the total phosphorus discharge in some areas. Therefore, the research and application on the new technology of conversion coating on iron and steel is great significance.On the basis of our potassium fluoferrite conversion coating prepared with high and low concentration of KF on the surface of iron and steel, in order to improve their anti-corrosion performance, the effect of phytic acid on the corrosion resistance of K2FeF6 conversion coatings was researched by single factor experiment, respectively.The modification research of phytic acid on the effect of the corrosion resistance of K2FeF6 conversion coating prepared with high KF concentration showed: a conversion coating with 36 h salt spray time was obtained under the condition of phytic acid 2.5mL/L(w=50%), KF 125g/L, HNO377mL/L, promoter 0.5~1.0g/L,(NH4)2S2O8 7.5g/L, 45℃,pH 1~2 and 80 min. The results from SEM and EDS analysis showed that the conversion coating modified by phytic acid was denser,consisted of O, F, K, Fe and C, P, The formation of potassium fluoferrite conversion coating and phytic acid iron improved the anti-corrosion performance of iron and steel greatly.The sealing research of phytic acid on the effect of the corrosion resistance of K2FeF6 conversion coating prepared with low KF concentration showed: a conversion coating with 90 h salt spray time was obtained under the condition of phytic acid 30mL/L(w=50%), pH 4~5, 40°C and 5min. The results from SEM and EDS,infrared spectroscopy(IR) and electrochemical analysis showed that the conversion coating sealed by phytic acid was more homogeneous and denser, contained a cellulous network structure. The sealed conversion coating contained C, O, F, P, K, Fe and organic function group of phytic acid. The formation of potassium fluoferrite conversion coating and phytic acid iron made the salt spray time of the conversion coating increase from 16 h before sealing to 90 h after sealing, the corrosion potential increase 0.1V, the corrosion current density decrease about 12%, the anti-corrosion performance of iron and steel was greatly enhanced. |
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