EFFECTS OF ALUMINUM ION ON INTERNAL TENSILE STRESS IN NICKEL DEPOSITS ELECTROPLATED FROM WATTS BATH

摘要

A study of the effects of aluminum ions added as Al_2(SO_4)_3 on average internal tensile stress in nickel deposits electroplated form 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 a 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.