Development of Novel Process for the Deposition of Nanostructured Ternary Alloys and Composites for Replacement of Cadmium Coatings

摘要

The objective of this investigation was to develop novel processes for depositing ternary Zn-Ni-X (X=Cu or P) alloys for replacement of Cd coatings in sacrificial protection of steel substrates. Introducing small amounts of Cu in the Zn-Ni plating bath results in alloys with reduced amount of Zn in the final deposit. This alloy shows improved corrosion performance that is 4 times higher than that of Cd coatings. Also, the use of autocatalytic method was investigated to deposit amorphous Ni-Zn-P alloys. The electroless Ni-Zn-P alloy shows improved corrosion performance that is 5 times higher than that of Cd coatings and reduces the hydrogen ingress into steel to 94%. A novel electrolytic process was developed to deposit Ni-Zn alloys with high Ni content. Deposition parameters like pH and temperature were optimized based on composition and the surface morphology of the coating. The Zn content in the coating was optimized based on the corrosion resistance of the final deposit. Finally. corrosion studies shows that Ni-Zn coatings obtained using these methods show a 5 times increase in barrier resistance as compared to Cd coatings. Also a mathematical model was developed to study the electroless Ni- Zn-P deposition.