Watts solution

The Watts Solution, is a relatively cheap, simple solution which is easy to control and keep pure. The nigkel sulphate acts as the main source of nickel ions, though nickel chloride is an additional source. Higher deposition rates can be, used when the ratio of nickel chloride to nickel sulphate is raised and some proprietary bright nickel solutions are available in a high-speed version which contains an increased concentration of nickel chloride. 

At normal current densities, about 96-98% of the cathodic current in a Watts solution is consumed in depositing nickel the remainder gives rise to discharge of hydrogen ions. The boric acid in the solution buffers the loss of acidity arising in this way, and improves the appearance and quality of the deposit. Although phosphides, acetates, citrates and tartrates have been used, boric acid is the usual buffer for nickel solutions. 

Hard nickel deposits When the plating variables are adjusted to give deposits with a hardness much above 200 Hy with a Watts solution, internal stress is usually too high and ductility too low for the deposits to be fully satisfactory. Higher hardness coupled with reasonable ductility can be achieved by addition of ammonium salts and operation at higher solution pH. A solution used for this purpose and some deposit properties are as follows ... 

Deposits from all-chloride solution Nickel deposits from a solution of nickel chloride and boric acid are harder, stronger and have a finer grain size than deposits from Watts solution. Lower tank voltage is required for a given current density and the deposit is more uniformly distributed over a cathode of complex shape than in Watts solution, but the deposits are dark coloured and have such high, tensile, internal stress that spontaneous cracking may occur in thick deposits. There is therefore little industrial use of all-chloride solutions. 

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