Table 2: Design factors and their levels.

Design factorsUnitLevels
123

Concentration of source of nickel (nickel sulphate solution) (A)g/L2025a30
Concentration of reducing agent (sodium hypophosphite solution) (B)g/L1417a20
Concentration of source of tungsten (sodium tungstate) (C)g/L1520a25
Annealing temperature (D) °C400500600

a I nitial coating condition.