Facile preparation of hopeite coating on stainless steel by chemical conversion method

Chemical conversion process has attracted more attention in recent years due to its significant potential use in biomedical areas such as surface modification of metal implants. In this study, uniform and fine coatings were fabricated on stainless steel 304 (304 SS) substrates using phosphate chemical conversion (PCC) treatment. The Fe2 + ions were introduced to initiate the coating formation. The experimental results showed that the coatings were composed of hopeite (Zn3(PO4)2 ∙ 4H2O) with minor phosphophyllite (Zn2Fe(PO4)2 ∙ 4H2O), with a crystal size of 2–4 μm. The substrates were fully covered with the coatings after PCC treatment at 70 °C for 30 and 45 min with the coating mass of 4.08 and 6.48 g/m2, respectively. Adhesive test indicated that the PCC coating was strongly attached on the substrate. The electrochemical analysis revealed that the as-prepared coatings imparted better corrosion resistance to the substrate.