Study on application of phosphogypsum oxalic acid pretreatment liquid in oriented silicon steel coatings
Pretreatment is necessary for high value utilization of phosphogypsum,and the filtrate produced by water washing pre-treatment has not yet been well utilized.After component analysis,it was found that the filtrate contained components such as phosphates and aluminum,which were effective components for improving the corrosion resistance of coatings.The present study involved the preparation of phosphogypsum pretreatment filtrate and its incorporation into an inorganic chro-mium-free anti-corrosion coating for oriented silicon steel.A comparative analysis was conducted to evaluate the impact of pretreatment filtrate generated using water and oxalic acid solution at different temperatures on the corrosion resistance properties of the coating,and the substances present in the filtrate and their improvement mechanism on the anti-corrosion performance of the coatings were studied.Under the pretreatment of oxalic acid solution,pretreatment temperature of 20℃,and the addition of 5%pretreatment solution,the neutral salt spray experiment of oriented silicon steel sheet coating was de-creased from 11%corrosion area after 36 hours to less than 1%corrosion area,and the corrosion current density was de-creased to 0.317 1 μA/cm2,overall impedance modulus of coating was increased by 17%.The orthophosphate generated by the reaction between oxalic acid and phosphorus impurities accounted for more than 95%of the total phosphorus in the fil-trate.The filtrate promoted deep cross-linking of the AlPO4 network to form the main network structure of the coating,high-lights the role of MgO,and generated Mg3(PO4)2 network branches at high temperatures,forming microcrystalline Mg2P2O7 and AlF3 to fill the network pores,jointly improving the corrosion resistance of the coating.
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