Thomas C. Franklin

Some mechanisms of action of additives in electrodeposition processes

Abstract A review is given of mechanisms by which additives have been postulated to affect the rate of deposition of metals. These mechanisms include (1) blocking the surface, (2) changes in Helmholtz potential, (3) complex formation including induced adsorption and ion bridging, (4) ion pairing, (5) changes in interfacial tension and filming of the electrode, (6) hydrogen evolution effects, (7) hydrogen absorption, (8) anomalous codeposition and (9) the effect on intermediates.

The electrolytic oxidation of simple aldehydes and alcohols at platinum electrodes

Abstract The electrolytic oxidation of methyl, ethyl, and isopropyl alcohol, formaldehyde and formic acid in the potential region between 0.3 V (S.C.E) and oxygen evolution has been studied using cyclic voltammetry, chronopotentiometry, potential-decay and controlled potential techniques. The reaction is first order with respect to the organic compound and first order with respect to the area of the electrode. It is concluded that the electrode is first oxidized to PtOH and then to Pt(OH) 2 . These compounds in turn chemically oxidize the organic compounds.

Electrochemical oxidation of thiourea in a micelle system

Abstract Electrochemical oxidation of thiourea, which is not possible on platinum electrodes in strongly basic solutions, was found to be possible when a cationic surfactant. Hyamine 2389, was added to the aqueous solution to form micelles. The Hyamine solubilized the product of the oxidation and prevented the electrode from becoming passive. A study of the effect of pH on the voltammetric oxidation waves showed waves for the oxidation of the protonated species, the neutral thiourea, the thiourea anion and an adsorbed film of the first oxidation product. It was shown that the voltammetric oxidation waves obtained in the micelle system could be treated mathematically using the same equations used in the treatment of homogeneous solutions. It was found that it was a one-electron, irreversible, diffusion-controlled process producing formamidine sulfide. However, the pH in the surfactant film on the anode was apparently not the pH of the solution.

The effect of anionic poisons on the catalytic oxidation of formaldehyde on platinum

Abstract The coulometric method of measuring the relative catalytic activity of platinum black by determining its ability to adsorb hydrogen has been studied in the presence of several anions. The catalytic reaction studied was the catalytic oxidation of formaldehyde. It was found that the technique was suitable in the presence of several different anions but that it did not furnish a reliable measure of the catalytic activity in acid solutions in the presence of chloride ions. It was felt that the cause of this difficulty could be the adsorption of hydrogen on top of the adsorbed chloride ions.

The anodic dehydrodimerization of dimethyl malonate

Abstract As a part of a study of the anodic dehydrodimerization of diethyl malonate on platinum in emulsions and micelles some experiments were run to obtain an insight on the mechanism of the reaction. It was determined that although some catalytic dehydrodimerization was obtained with pure diethyl malonate at elevated temperatures the yield from this type of reaction at room temperature was negligible. In pure acetonitrile, confirmation was obtained for the previously postulated mechanism which involved reaction at the anode of electrogenerated halogen with diethyl malonate anions which had been generated at the cathode. In aqueous emulsion and micelle systems it was found that yields of the dimer were obtained in the presence of bromide ions and a quaternary ammonium salt but were not obtained using other supporting anions including chloride. The best yields were obtained in emulsions composed of tetrabutylammonium bromide and water. It was concluded that the dimerization proceeded by a reaction between electrochemically generated bromine molecules and the diethyl malonate anion. No large amounts of bromine were found adjacent to the electrode if potassium bromide was the supporting electrolyte but bromine stayed in the neighborhood of the electrode if tetrabutylammonium ions were present.

A study of solutions of titanium of low oxidation states

Abstract A study of a series of aqueous and non-aqueous solutions of titanium of low valence has shown that titanium exists in these solutions in the form of titanium (III). Polar titanium (II) chloride does not dissolve in the non-polar solvents studied. Solvents with active hydrogens react with the titanium (II) and in acetonitrile and dimethylformamide titanium (II) chloride undergoes disproportionation. TiCl 2 (solid) → TiCl 3 (solution) + Ti (solid)

Voltammetric studies using a hyamine 2389—polystyrene-filmed electrode

Abstract A study was made of the effect of the surfactant Hyamine 2389 (predominantly methyldodecylbenzyltrimethylammonium chloride) on the electro-oxidation of organic compounds when the Hyamine was immobilized on the electrode in a polymeric film. From cyclic voltammetric measurements it was found that the Hyamine molecules in the film adjacent to the electrode could be reorganized by sweeping the potential in the cathodic direction past a desorption peak. The oxygen evolution potential on platinum in aqueous NaOH increased from 0.7 V with no additive present and 1.7 V with Hyamine present in solution to 2.0 V in the presence of the immobilized hydrophobic film. The polystyrene-Hyamine-filmed electrode was more convenient to use than Hyamine in solution in that the residual current was very low and the electrode was so stable that it could be moved to other solutions and be used in acid systems. Both soluble and insoluble substances could be oxidized on the electrode. Insoluble substances apparently adhere to the tacky polymer electrode. The oxidation of compounds such as p-bromophenol forms insoluble passive films which can be removed by introducing solubilizing Hyamine micelles into the system. Although the oxidation potentials indicate that a number of compounds in the base are oxidized by a mediated mechanism involving chemical oxidation of the compounds by electrochemically oxidized Hyamine, a number of compounds in basic solutions and the inorganic compounds in acidic solutions were indicated to be oxidized by an electron transfer mechanism.

Poisoning of platinized platinum electrodes by hydrogen in dimethylsulphoxide

Abstract A study of hydrogen sorption on platinized platinum in dimethylsulphoxide solutions has shown that there is a heterogeneous reaction between hydrogen and dimethylsulphoxide to form a tightly bound film of reduction products, probably dimethylsulphide.

The Effect of Several Benzyl Alcohols and Electron Bridging Anions on the Current Efficiency for Deposition of Cadmium

Because of the ability of millimolar concentrations of substituted benzyl alcohols to block hydrogen evolution and to form complexes with the cadmium ions, their addition to cadmium sulfate and chloride plating baths increased the current efficiency for depositing cadmium. In sulfate baths there was generally a linear correlation between the concentration of the cadmium-alcohol complex and the current efficiency. In the cadmium-chloride system, in which the alcohol could not displace chloride and form a complex, the current efficiency was primarily related to the blocking of hydrogen evolution. Addition of electron bridging anions also catalyzes the deposition of cadmium, and this mechanism or catalysis does not change upon addition of the alcohol. The catalysis decreases in a very regular fashion as the size of the bridging anion increases, indicating that the electron bridging occurred through holes in the alcohol film. Addition of millimolar nonbridging strong complexing agents inhibits metal deposition and decreases current efficiency. Addition of millimolar surfactants increases the current efficiency by blocking hydrogen evolution.

The effect of quaternary ammonium salts on the anodic oxidation of ethanol

Abstract A study was made of the effect of additives on the rate of deactivation of platinized platinum in the anodic oxidation of ethanol in order to determine whether additives that form a hydrophobic layer on platinum would protect against normal poisoning processes. The data were interpreted in terms of a mechanism in which the oxidation of the alcohol proceeded at different rates on the bare and inhibited surface in a reaction that was zero order with respect to alcohol and first order with respect to the areas of each type of surface, while the inhibition reaction was second order with respect to the fraction of the surface that was bare. Without additives this mechanism agreed with data at 0.9 V (measured with respect to a saturated calomel electrode) but at 0.5 V the contribution from the inhibited route was negligible and the rate became approximately independent of the area on the more heavily platinized surfaces. Tetrabutylammonium perchlorate did not influence any of the rate constants, indicating that it was not adsorbed on the platinum. Solutions containing chlorides caused marked decreases in the rates of oxidation on the bare surface, but at 0.9 V caused only small decreases in the rate of oxidation on the inhibited surface, indicating that chlorides are only weakly adsorbed on the inhibited surface. The addition of a large quaternary ion together with the chlorides increased the effect of the chloride, confirming the fact that these salts acted by ion pairing with the adsorbed chloride. None of the additives had a significant effect on the rate of poisoning of the electrode at 0.5 V. At 0.9 V neither sodium chloride nor tetrabutylammonium perchlorate affected the rate of inhibition, but the addition of tetrabutylammonium perchlorate to the sodium chloride or the use of the commercial surfactant Hyamine 3500 (a large quaternary ammonium chloride) caused significant decreases in the rate of the inhibition reaction.