3.4. Deposition process of phosphating layer
The steel specimens were polycrystalline, and there were
numerous micro-electric cells on the surface of the specimens
when immersed in the phosphating solution. The anode of the
micro-electric cells, iron, was dissolved as ferrous ions, and then
was oxidized to ferric ions in the phosphating solution. Hydrogen
ions near the cathode were reduced to hydrogen after capturing
electrons. The pH value at the liquid–solid interface increased, and
phosphate ions were released (Kouisni et al., 2004).