Preparation of nickel nanoparticle composites for corrosion resistant coatings

Nickel – nanoalumina (50 to 100 nm size) composites have been electrodeposited using parallel plates from a Watt’s bath containing various particle loadings. Experiments have been conducted to examine the effect of surfactant addition, ionic strength, electrolyte additive addition, current type (Pulse versus Direct current), current density, duty cycle, frequency, agitation type (mechanical and ultrasonic) and mechanical agitation speed on particle incorporation. It was found that the best conditions for depositing coatings with non-agglomerated nano-alumina particles were pulse plating at a current density of 10 A.dm-2, with a duty cycle of 50 % and frequency of 1000 Hz from a HISA15S1 bath with 15 g.dm-3 Al2O3 loading and 1g.dm-3saccharin loading. These conditions produce a Nickel-nanoalumina composite containing 10 vol.% Al2O3 with a grain size in the order of 250 nm. The hardness of this coating is 6.3 GPa, Young’s modulus 221 GPa and wear resistance is improved by 60 %. The rest potential (Erest) in a 3.5wt % NaCl aqueous solution is -0.16 V compared with -0.26 V for a coating without nanoalumina particles. The nanocomposite coating had a life, before the first signs of corrosion, of 8 weeks when submerged in acidic 3.5 wt % NaCl solution.