E. J. Podlaha

Induced Codeposition III. Molybdenum Alloys with Nickel, Cobalt, and Iron

A comparison was made between the codeposition behavior of NiMo, CoMo, and FeMo alloys on rotating cylinder electrodes when the molybdate concentration in the electrolyte was much lower than that of the iron-group species. More molybdate was codeposited with Co than with either Fe or Ni from an ammonia-citrate electrolyte at pH 7.4. During the NiMo codeposition, the molybdate species is mass transport controlled. Substitution of the nickel by cobalt in the plating bath does not influence the molybdenum deposition rate. However, a higher concentration of molybdate is found in the deposits because the rate of cobalt deposition is lower than that of nickel. On the other hand, substitution of the nickel by iron results in a dramatic lowering of the molybdenum deposition rate. These observations were described by a mathematical model which assumes that iron-group species can adsorb on the electrode surface, competing with the molybdenum intermediate for free surface sites. Thus the diminished partial current density of the molybdenum in iron containing electrolytes can be explained by a blocking mechanism due to the adsorbed iron intermediate.

Induced Codeposition II. A Mathematical Model Describing the Electrodeposition of Ni‐Mo Alloys

A steady-state mathematical model was developed to predict the behavior of the induced codeposition of Ni-Mo alloys in the kinetic and mass-transport controlled regions on rotating cylinder electrodes. The kinetic regions were characterized by a simple Tafel expression. A Nernst boundary layer representation described the mass transfer of ions through a diffusion layer. The governing features of the induced codeposition mechanism included soluble nickel acting as a catalyst to the molybdenum deposition and the generation of an absorbed intermediate species on the electrode surface. The resulting alloy composition was simulated for two electrolytes over a wide range of current densities and electrode rotation rates. The model predictions agreed with the observed trends in the experimental data.

Anomalous Codeposition of Iron Group Metals: I. Experimental Results

The codeposition behavior of three alloy systems, FeNi, FeCo, and CoNi, was studied in acid sulfate electrolytes using rotating cylinder electrodes to control mass transport conditions. The partial current densities of the codepositing metals and of the side reaction were determined from an analysis of the deposit and were compared with those measured for the pure metals deposited under identical conditions. Results confirmed that Ni is inhibited by the presence of and ions. Fe deposition rate is enhanced by the presence of and ions. The ion of the less noble metal has a stronger influence on the deposition behavior of the partner ion. Co is inhibited by codeposition of ions and enhanced by ions. The present data demonstrate that anomalous codeposition of iron group metals involves both inhibiting and accelerating effects.

Synthesis of poly(methyl methacrylate) stabilized colloidal zero-valence metallic nanoparticles

Poly(methyl methacrylate) (PMMA) stabilized colloidal metallic iron nanoparticles without additional surfactant or stabilizer were fabricated by a wet chemical reduction method. The synthesized colloidal iron nanoparticles were found to be stable in tetrahydrofuran (THF) solution and the dried PMMA–Fe nanocomposites were ferromagnetic even at room temperature as illustrated by magnetometer measurement. The particle size increased with the decrease of the initial PMMA concentration and the magnetic properties also depended on the initial PMMA concentration.

Anomalous codeposition of iron group metals. II. Mathematical model

A mathematical model for anomalous codeposition of iron group metals is presented which describes effects of inhibition and enhancement observed experimentally during codeposition of FeNi, NiCo, and FeCo alloys. The model assumes three parallel reaction paths each one proceeding in two consecutive steps and it takes into account the effect of mass transport. The model assum es that deposition involves an adsorbed reaction intermediate containing both metal ions in partly reduced form. This reaction int ermediate is responsible for both the inhibition of the more noble species and the enhancement of the less noble species. Differe nces in the deposition behavior of the three alloy systems considered are due to differences in the surface coverage of the mixed re action intermediate. The theoretical predictions of the model are compared with experimental data obtained under well-defined mas s transport and current distribution conditions. The model can simulate in a satisfactory way the observed effects of inhibition and enhancement due to codeposition and it predicts correctly the influence of mass transport. It is less successful in the simulat ion of the influence of the concentration of reacting species. Possible reasons for this behavior are discussed and research direction s for improving the model are outlined.

Composite Electrodeposition of Ultrafine γ-Alumina Particles in Nickel Matrices; Part I: Citrate and chloride electrolytes

Electrodeposition of nanocomposite γ-alumina–nickel was examined using citrate and chloride electrolytes with rotating cylinder electrodes. Ultrafine alumina was detected in the nickel matrices and was found to depend on the applied current density. The particle incorporation rate dependence on the applied d.c. current density varied for the different electrolytes. In the chloride baths, higher particle concentrations were found in the deposits plated at low current densities compared to higher values. However, the opposite trend was noted for the citrate electrolyte where an increase in particle deposit content was observed with an increase in applied current density. Additionally, the nickel anodic behaviour was examined in order to devise a pulse-reverse (PR) plating method. PR deposition lead to an enhancement in the γ-alumina deposit concentration compared to DC plating in chloride electrolytes.

Pulse‐Reverse Plating of Nanocomposite Thin Films

A steady-state, pulse-reverse plating method has been developed which permits the enhancement of the particle concentration in electrodeposited metal matrix composite coatings. The procedure is demonstrated for the codeposition of nanosized, γ-alumina particles in a copper matrix.

Modeling of cylindrical alkaline cells; V: High discharge rates

A one-dimensional mathematical model of a AA size Zn-MnO{sub 2} alkaline cell is presented to describe nonisothermal, high constant current discharge conditions. The model accounts for the variation of the overpotential, current density, porosity, volume, average velocity, hydroxyl ion concentration, and zincate ion concentration throughout a complete cell, including the anode, cathode, and separator regions. This model is the first to examine the importance of the zincate ion concentration. Three variations of the model are presented: (1) the zincate ion is restricted to the anode region, (2) the zincate ion is unconfined in the cell, but can precipitate as ZnO in the anode, and (3) the zincate is unconfined in the cell but can precipitate in both the anode and separator. Experimental data are best represented by model (3). Pore plugging, particularly in the separator, has been found to be an important factor limiting cell performance. Additionally, the sensitivity of several parameters on the cell performance is evaluated.

Rotating cylinder Hull cell study of anomalous codeposition of binary iron-group alloys

The anomalous codeposition of the iron group metals was investigated using the rotating cylinder Hull (RCH) cell. Single metals and binary alloys of iron, nickel and cobalt were deposited in the RCH cell and the partial current densities were determined as a function of length by position sensitive X-ray fluorescence analysis. The measured overall polarization behaviour was used as a boundary condition for the numerical calculation of the potential distribution along the cylinder using the Laplace equation. By combining the results the partial current density potential curves were established. Experiments performed at different rotation rates confirmed the inhibiting effect of the less noble metal on the deposition of the more noble metal. The inhibiting effect of iron on nickel disappeared when iron reached the limiting current. Strong evidence was found that in binary alloy deposition of iron, cobalt and nickel the reaction rate of the less noble metal is promoted by the presence of the more noble component.

Displacement Synthesis of Cu Shells Surrounding Co Nanoparticles

Copper shells were fabricated by a displacement method around Co nanoparticles (3.2 ′ 0.6 nm) at room temperature in a copper-citrate aqueous electrolyte. The nanoparticles were synthesized by a wet chemical approach using the surfactant sulfobetaine, dodecyldimethyl (3-sulfopropyl) ammonium hydroxide (98%) in tetrahydrofuran. X-ray absorption near-edge structure analysis confirmed that cobalt oxide was not present in the nanoparticles upon exposure to air, consistent with a shell formation. Additionally, the presence of the shell resulted in an increase of the blocking temperature of the core-shell nanoparticles, stabilizing the ferromagnetic behavior up to 235 K.