Jan B. Talbot

Anomalous Electrodeposition of Nickel‐Iron

Experiments to study anomalous codeposition of iron and nickel were conducted from and solutions with pH adjusted to 3 with , using a rotating disk electrode. The effect of adding to the plating bath was also investigated. Anomalous codeposition occurred for all electrode rotational speeds and applied potentials considered. Boric acid was found neither to affect alloy deposition current efficiency, nor to eliminate anomalous codeposition for the experimental conditions investigated. Cyclic voltammetry indicates that a borate complex formed at −1.0 Vvs. SCE when boric acid was added to the plating bath. A model used to evaluate the surface pH from the experimental results shows that a sudden rise in pH is not necessary for anomalous codeposition to occur and that boric acid does not act as a buffer during codeposition of .

Electrodeposition of Thin Films of Nickel‐Iron II . Modeling

A mathematical model is developed to simulate the electrodeposition of the nickel‐iron alloy from simple sulfate solutions. Equilibrium calculations indicate the importance of the metal monohydroxide species in the codeposition mechanism. A one‐dimensional diffusion model of the codeposition is developed and agrees well with experimental results for different bath compositions and operating conditions. The sensitivity of the model is evaluated and a mechanism for the anomalous codeposition of nickel‐iron is proposed.

Electrodeposition of Iron‐Group Metals and Binary Alloys from Sulfate Baths. II. Modeling

A mechanism of iron‐group elemental metal and binary alloy electrodeposition is proposed. The one‐dimensional diffusion model of Grande and Talbot is used to determine near‐surface concentrations of the ionic species deemed important for electrodeposition; the current model expands upon the surface kinetics by including the effects of competitive adsorption, site blockage by hydrogen atoms, and a variance in the number of adsorption sites. Fitting of the model kinetic parameters to the elemental electrodeposition data was found to simulate the partial current densities extremely well. The proposed model was found to be extensible to the iron‐group binary alloys. Use of the elemental electrodeposition parameters in alloy codeposition was found to effectively characterize the experimental results, e.g., partial current densities, weight fractions, and the effect of electrode rotational rate.

Electrodeposition of Thin Films of Nickel‐Iron I . Experimental

The effects of the removal of dissolved oxygen and the addition of ferric ion in the presence and absence of 0.4M B(OH) 3 on the anomalous codeposition of iron and nickel from 0.5M NiSO 4 and 0.1M FeSO 4 solutions at pH 3 on a rotating disk electrode at a speed of 100 rpm were studied. The effect of sparging the solution containing boric acid with argon, which reduced the dissolved oxygen concentration to 1.2 ppm, was an increase in the iron content of the deposit by at least 10 weight percent for the range of current densities applied. With the addition of boric acid to a sparged bath, the rate of nickel deposition decreased and the rate of iron deposition increased

Electrodeposition of Binary Iron‐Group Alloys

Thin films of NiCo and CoFe have been galvanostatically electroplated onto a platinum rotating disk electrode from simple sulfate baths containing 0.5M of the more noble metal sulfate and 0.1M of the less noble metal sulfate. The experimental results are compared to those of previous studies of NiFe codeposition in order to study the anomalous codeposition behavior of the binary iron-group alloys. Comparison of the electrodeposition results indicates that codeposition of these binary alloys is not totally analogous. It was found that codeposition of NiCo and NiFe show more mass-transfer effects than does CoFe deposition within the range of current densities studied. A model of anomalous codeposition put forth previously for NiFe was applied to the electrodeposition of NiCo and CoFe to determine the extensibility of the model, which assumes metal mono hydroxides, MOH{sup +}, are the important charge-transfer species. This model was unable to characterize fully either NiCo or CoFe electrodeposition. However, with minor changes to the hydrolysis constants used in the model, the model predictions were found to agree with the data for CoFe codeposition and greatly, improve the fit for the NiCo results.

Electrodeposition of Iron‐Group Metals and Binary Alloys from Sulfate Baths I. Experimental Study

Thin films of the iron-group elemental metals (Ni, Co, and Fe, group VIIIB) and binary alloys (NiCo, CoFe, and NiFe) were galvanostatically electroplated onto a platinum rotating disk electrode from simple sulfate baths. In all cases, the increasing electrode rotational rate was found to decrease the partial current densities at a given cathodic potential. Experimental results indicate that for electrodeposition: two distinct rate-determining steps exist, partial current densities for metal deposition are not linearly related to bulk metallic concentration, and the partial current densities for hydrogen evolution are found to reach a plateau for each metal sulfate bath and rotational rate studied. For the conditions studied, comparison of the partial current densities for elemental and alloy deposition shows that the more noble metal deposition is unchanged or inhibited in alloy codeposition, while that for the less noble metal is promoted.

Investigation of Electrocodeposition Using a Rotating Cylinder Electrode

A rotating cylinder electrode was used to study the electrocodeposition of composite films containing alumina particles in a copper matrix. Deposition conditions ranging from kinetically controlled through mass-transfer limitation were investigated. The effects of hydrodynamics, particle loading in suspension, particle characteristics (size and crystallographic phase), as well as electrode orientation, were studied. Particle incorporation was analyzed using a precise, reproducible electrogravimetric technique.

A Study of the Adhesion of Electrophoretically Deposited Phosphors

In the manufacturing of screens for advanced displays, layers of small (1 to 10 μm diam) luminescent particles may be deposited by electrophoretic deposition (EPD). A set of processing variables that enhance the adhesion strength of EPD phosphor deposits has been determined. Postdeposition baking at 425°C for 1 h, addition of water or glycerin and use of Y(NO 3 ) 3 instead of Mg(NO 3 ) 2 in the deposition bath, and control of the particle size distribution can each enhance the adhesion strength of EPD phosphor deposits. When screens were excited by electron bombardment, the chromaticity was unchanged and the brightness was only slightly reduced by these processing conditions.

An Analysis of the Binder Formation in Electrophoretic Deposition

During the electrophoretic deposition of phosphor particles at a cathode, a material forms via electrochemical precipitation, which is necessary for adherence o the coating. The chemistry of binder formation was investigated, particularly the effect of water in the bath of isopropanol containing 10 -3 M Mg(NO 3 ) 2 . The type of binder material formed is dependent upon the amount of water in the deposition bath. For very low amounts of water, the binder material is an alkoxide, Mg(C 3 H 7 0) 2 . For high amounts of water in the bath (>5 vol %), the binder is predominantly a hydroxide, Mg(OH) 2 . At intermediate water concentrations, the binder is a mixture of the two compounds.

Synthesis of Superconductive Thin Films of YBa2Cu3 O 7 − x by a Nonaqueous Electrodeposition Process

High-temperature superconductor films of YBa 2 Cu 3 O 7-x were fabricated by electrochemical synthesis of precursors from a solution of nitrate salts of the metallic constituents in isopropanol. The precursor films were composed of hydroxides which when heat-treated in oxygen formed a YBa 2 Cu 3 O 7-x superconductor. The superconducting transition temperatures were 79 K for a film from a single simultaneous deposition of the metallic components and 88 K for a film from several successive depositions