Journal of Iranian Ceramic Society
Journal of Iranian Ceramic Society
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Saveh Branch, Islamic Azad University , ab_najafi@iust.ac.ir
Abstract: (181 Views)
In this research, the effect of adding nickel and manganese ions in the low- zinc phosphating process on the surface of 41Cr4 steel was investigated. At first, the basic phosphating solution was prepared based on previous experiences, including phosphoric acid, nitric acid, accelerators and modifiers to create an optimal coating structure. The concentration of compounds and operational parameters of temperature, time and solution pH were fixed during the process. The amounts of zinc-nickel-manganese cations by zinc oxide 0-1-1.5-2-2.5 g/lit; Nickel nitrate 1-2-3-4- 6 g/lit and manganese carbonate 0.8-1.6-3.2-4- 4.8 g/lit were added to the bath. Examining the changes in weight and apparent density of the surface unit of the coating showed that the optimal amount of bath composition includes 1.5 zinc oxide, 4 nickel nitrate and 3.8 g/lit manganese carbonate. By increasing the concentration of nickel and manganese ions in the bath, the weight of the coating decreases. The scanning electron microscope images showed that the structure of the optimized Zn-Ni-Mn triple cation coating is often cubic and lamellar. EDX studies also showed that with the increase in the concentration of nickel and manganese in the bath, the weight percentage of these elements in the phosphate coating increases. The X-ray diffraction pattern showed that the phases containing phosphate compounds were successfully formed to cover the substrate. The results of the roughness, salt spray and paint adhesion tests show that tri-cationic phosphate coating with fine crystals, high uniformity, low porosity and in the presence of nickel and manganese elements improves paint adhesion and prevents re-hydration of the coating. Therefore, paint separation does not occur in the scratched area, and the paint coating is free of blisters and rust.
Keywords: phosphate coating, three cations, zinc, nickel, manganese, corrosion resistance, paint adhesion
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