ニッケルめっき膜の引張応力に及ぼす溶液内アルミニウムイオンの影響

抄録

A study of the effects of aluminum ions added as Al₂(SO₄)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 Al₂(SO₄)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 Al₂(SO₄)₃, causing numerous cracks on the surface of nickel deposits at a concentration of 5.0mM Al₂(SO₄)₃. The dependence of aluminum oxide and aluminum hydroxide content on Al₂(SO₄)₃ concentration showed that these two compounds enhanced internal tensile stress in nickel deposits.