Steel Phosphate And Hydroxylamine Catalytic Mechanism In Phosphating

This article focuses on Zn and Zn-Ca series phosphating technology. Two new phosphatesolutions are developed. The function of every component in the developed phosphatingsolution and the influence of technical parameters on the phosphating coating are discussed.In normal temperature zinc series phosphating, measure φ-t(potential-time) curve ofphosphate process parameters such as temperature, dosage of free acidity, hydroxylaminesulfate affecting the performance speed and phosphating film. Microstructure, chemicalcomposition and phase of phosphating film have been characterized through SEM, EDS,XRD and other test means. Here are also using the quantum chemistry density functionalmethods for quantum chemical ab initio calculation, illustrates hydroxylamine(NH2OH)catalytic mechanism in Zn series acidic phosphating solution. The experimental results showthat the optimum phosphating process as following, temperature range for25to30℃, the bestfree acidity4.1, hydroxylamine sulfate concentration6.5g/L (working fluid). Phosphatingfilm is made up of monoclinic Zn3(PO4)2·4H2O and orthogonal Zn3(PO4)2·4H2O acicularcrystal membrane.Add Ca2+in zinc series phophating solution forming Zn-Ca series phosphating systemand adopt hydroxylamine nitrate as promote agent. By measuring the φ-t curve film-formingprocess in different conditions, the optimum film forming condition was chosen.Microstructure, chemical composition and phase of phosphating film have been characterizedthrough SEM, EDS, XRD and other test means. Here are also using the quantum chemistrydensity functional methods for quantum chemical ab initio calculation, illustrateshydroxylamine(NH2OH) catalytic mechanism in Zn-Ca series acidic phosphating solution.The results showed that the optimum film forming condition as following, phodphatingtemperature70℃, Ca2+content is52.89g/L, hydroxylamine3.2g/L, the dosage of citric acidis6.0g/L, free acidity8.0point. The phosphating film formed under the condition is ahomogeneous dense rock crystal film made by Zn2Ca(PO4)2·2H2O.It was shown that two phosphating bath is stable, less sludge and higher film formationrate. The phosphating coating formed in bath has a good anticorrosion property.Experimental results show that they all overcome such problems as yellow-out, surfacedusting and poor corrosion resistance of conventional phosphatization.