Rapid synthesis of scaly SiO₂ coating on flake carbonyl iron powders by plasma electrolysis

The scaly SiO₂ coating was rapidly synthesized on the flake carbonyl iron powders by plasma electrolysis to solve the poor corrosion resistance. The effect of the processing numbers on the microstructure and corrosion resistance was systematically investigated. A fully covered and dense thin film was formed, excepted for the processing number of two and three times, where several typically smooth uncoated flake particles were observed. The corrosion test during immersion in NaCl solution for 60 days evidenced the greatly improved corrosion resistance with the one-time powders showed the best. The initial oxidation temperatures of the coated powders were increased by 50–85 °C with the one-time best, again revealing the effective protection of the film. The formation mechanism was also discussed mainly based on the electrochemical process and the plasma effects. We believe the plasma electrolysis will find a wide range of applications in the surface modification of metal powders.