A study of the effects of aluminum ions added as Al
2(SO
4)
3 on average internal tensile stress in nickel deposits electroplated from a Watts bath of pH3.0 enabled us to detect variations in elastic deformation in deposits
in situ using a resistance wire strain gauge on the reverse side of a copper electrode.
Aluminum ions close to the electrode surface changed to aluminum hydroxide due to increased solution pH during nickel electroplating with hydrogen evolution. This is included in deposits as aluminum oxide and aluminum hydroxide.
With increasing Al
2(SO
4)
3 concentration, total aluminum oxide and aluminum hydroxide in deposits increased and average internal tensile stress in deposits rose. Internal tensile stress rose markedly at ca. 2.5mM Al
2(SO
4)
3, causing numerous cracks on the surface of nickel deposits at a concentration of 5.0mM Al
2(SO
4)
3. The dependence of aluminum oxide and aluminum hydroxide content on Al
2(SO
4)
3 concentration showed that these two compounds enhanced internal tensile stress in nickel deposits.
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