Effects of electrolysis conditions on the formation of electrodeposited invar Fe-Ni alloys with low thermal expansion

Synopsis: To elucidate the effects of electrolysis conditions on the formation of electrodeposited invar Fe-Ni alloys with low thermal expansion, Fe-Ni electrodeposition was performed at 10-5000 A·m ^-2 and 5×10 ⁵ C·m ^-2 in agitated solution containing NiSO ₄ , NiCl ₂ , H ₃ BO ₃ , FeSO ₄ , C ₇ H ₄ NNaO ₃ S and C ₃ H ₄ O ₄ at 40-60°C. Ni content in deposits significantly decreased in the low current density region with increasing current density, reached a minimum, and then increased due to reaching at diffusion limiting current density for Fe deposition as the current density increased further. With increasing the concentration of FeSO ₄ in solution, Ni content in deposits decreased at lower current density region, reached a constant at lower current density, and then began to increase at higher current density. As a result, the current density range where Ni content in deposits was minimum and constant became wider with higher concentration of FeSO ₄ . With decreasing pH in solution, since the partial polarization curve for H ₂ evolution and total polarization curve sifted to higher current density region, Ni content in deposits-current density curve shifted to higher current density region. With stirring the solution, Ni content in deposits reached a minimum as the current density increased, and then began to increase at higher current density than without stirring due to increase in diffusion limiting current density for Fe deposition. The change of the composition in deposits by electrolysis condition can be explained by the changes of the total polarization curve for Fe-Ni alloy deposition and the partial polarization curves for Fe and Ni depositions and H ₂ evolution.