Abstract
The tin-nickel deposit is composed of about 65% of tin and 35% of nickel. It has high resistance to corrosion and tarnish, but is considerably brittle and easily cracked on bending. Such an imperfection of the tin-nickel alloy was not improved by the amendment of the composition of the plating bath.
Then, the tin-cobalt alloy deposit was pursued, instead of the tin-nickel alloy. A deposited layer composed of 75-80% of tin and 25-20% of cobalt was steadily obtained from the bath containing 50g/l of stannous fluoride, 20g/l of sodium bifluoride, and 500g/l of cobalt chloride.
The plating conditions were as follows.
Temperature of bath: 65-80°C Current density: 0.5-4amp./dm2 pH: 2.0
The effects of operating conditions and the bath composition on the deposit composition and cathodic current efficiency were investigated. For example, the current efficiency was above 90% for pH=2.0 at 70°C and under the current density of 2.0amp./dm2. On addition of a brightner, the thickness of the deposit allowable was 100μ at maximum, and the electrolyte was stable for prolonged use. The deposit was similar to chrome plating in appearance. Moreover, it had high resistance to corrosion and tarnish, and was not so brittle as the tin-nickel alloy plating.
