Thomas M. Harris

Oxygen incorporation during the electrodeposition of Ni, Fe, and Ni-Fe alloys

This study sought to quantify the oxygen content of electrodeposited Ni, Fe, and Ni-Fe alloys and to identify mechanisms by which the oxygen is incorporated in the deposits. In the absence of boric acid in the bath, the oxygen content of electrodeposited Ni increases with increasing applied current density. This behavior corresponds to a significant increase in the pH of the solution adjacent to the cathode, which results in the precipitation of Ni(OH) 2 on the cathode and occlusion of this material in the growing deposit. The incorporation of oxygen during Ni-Fe electrodeposition is similar, except that an increase in the Fe 2+ concentration in the bath reduces the oxygen content. This behavior results from buffering provided by Fe 3+ that accompanies the Fe 2+ in this system. When boric acid is present in the bath, oxygen incorporation is low in all three electrodeposition systems. This observation is consistent with buffering of the cathode pH resulting from boric acids ability to complex with Ni 2+ , which generates H + as a by-product. The oxygen that is incorporated may be attributed to hydroxide ion that fails to leave the surface following its participation in the electroreduction process. In Ni-Fe electrodeposition, oxygen incorporation by Fe(OH) 3 particle codeposition is shown to play an insignificant role.

Effect of Ethylenediamine on the Electrodeposition of Ni‐Fe Alloys

Ethylenediamine (EDA) greatly affects the phenomenon of anomalous codeposition observed in the nickel‐iron electrodeposition system. EDA increases the Ni/Fe ratio of the deposit when the bath is chloride based and the pH is at least 5. Ion microprobe analysis indicates that EDA is incorporated in the deposit. It is hypothesized that EDA adsorbs on the deposit surface and serves as a bridge for deposition in preference to that for , which forms less stable complexes with EDA. Chloride ion in the bath is necessary for the adsorption of EDA and thus the relative increase in the nickel deposition rate.

Effect of gel modulus on the porosity of low-density silica

Abstract The extent of shrinkage that occurs during the early stages of ambient pressure drying (APD) of silica gel is greatly affected by the stiffness of the silica network. This parameter was manipulated through modification of the second step of the two-step acid–base process. The modulus of the gel, which was measured with a new technique based on the compression of rod-shaped specimens, decreased to roughly the same extent by increasing the gel volume (through the addition of extra ethanol or water) or by decreasing the amount of base added. However, following APD and calcination, these modifications resulted in quite different pore volume distributions. In general, the pore volume corresponding to large and intermediate mesopores decreased with increasing gel volume; however, a uniform pore volume distribution (possibly due to localized rupture of the silica network during drying) was observed only with the addition of ethanol. Decreasing the amount of ammonium hydroxide produced the greatest loss of large and intermediate mesopores; this observation amplifies the importance of the highly branched silica clusters, created through the addition of base, to the stiffness of the gel.