2010 Volume 50 Issue 4 Pages 556-560
The corrosion resistance Ni–P–Fe alloy coating was obtained on rebar surface by an electroless process using glycolic acid as a complexing agent. During dipping of the iron scale free rebar in electroless solution, Fe first dissolves and the surface is activated. Subsequently, Ni, P and Fe are co-deposited by an autocatalytic process. The coating was characterised using SEM, EDS and XRD techniques. The weight percentage of Ni, P and Fe in the coating showed a relationship with the coating time. The Tafel and salt spray tests were conducted to find out corrosion resistance performance of coated samples. Electrochemical behavior of the coated rebar in simulated concrete environment is influenced by the pH of the concrete pore solution and the P content in the coating. Corrosion potential and the corrosion rate of the coatings increased with the increase in P content in the coating and pH of the pore solution whereas the resistance against chloride attack increased with increase in P content in the coating. Coated rebars showed reduction in bond strength in the range of 8 to 14% compared to the bare rebars. The maximum (~14%) drop in bond strength was observed for longer coating time. This can be attributed to the smoother coating surface. The coating obtained under longer coating time showed higher amount of P which contributed to maximum surface smoothness. However, this bond strength was much above the necessary strength requirement according to Indian standard specification.
