Identification of the cause of embrittlement in annealed low current density nickel electrodeposits

An attempt has been made to identify the nature and cause of grain boundary gas bubbles which are formed during the annealing of low current density (21.5 A/m²) Watts nickel electrodeposits. Chemical analysis has shown that low c.d. nickel contains greater quantities of oxygen and hydrogen than do higher c.d. deposits, and that carbon is present in all deposits. Changes in the slopes of Tafel slopes measured at low c.d. possibly indicate a cathodic oxygen reduction reaction which may explain the analysis result. Mass spectrometry experiments indicate that carbon monoxide gas is evolved at temperatures above 600°C from 21.5 A/m² nickel. It is suggested that the higher concentrations of carbon and oxygen in low c.d. material favour the formation of high densities of gas filled pores and thus produce the observed embrittlement.