Effects of Hydroxylamine Sulfate and Sodium Nitrite on Microstructure and Friction Behavior of Zinc Phosphating Coating on High Carbon Steel

Hydroxylamine sulfate (HAS) and sodium nitrite are used as the accelerators for zinc phosphate coating on high carbon steel. Phase evolution of phosphate coating was investigated by X-ray diffraction. It is found that the phosphating coatings are mainly composed of hopeite Zn3Fe(PO4)(2)center dot 4H(2)O and phosphophyllite Zn2Fe(PO4)(2)center dot 4H(2)O. The microstructural changes of the phosphate coating, as a function of phosphating time, were evaluated by scanning electron microscopy. Four-ball friction experiments reveal that hydroxylamine sulfate instead of sodium nitrite can effectively reduce the friction coefficient of lubricated phosphating coating. Therefore, it may be expected that HAS will be widely used as a fast and EGO-friendly accelerator in phosphate industry.