Gold Anode Research Articles

Photoconduction in poly(3-alkylthiophene) II. Charge transport

Hole motion in poly(dodecylthiophene) has been investigated by means of time of flight (TOF) studies and space charge limited conduction involving hole injection from a gold anode. The decrease of the hole mobility with temperature above 290 K parallels the increase of disorder manifest in the absorption spectra. At lower temperatures TOF signals become dispersive. The results are interpreted in terms of hopping motion within an energetically random array of hopping sites formed by ordered chain segments. The polaron contribution towards the activation energy for charge carrier motion is found negligible relative to the disorder contribution.

精銅工場における貴金属製錬（住友金属鉱山（株））

Niihama Copper Refinery of Sumitomo Metal Mining Co., Ltd. has been producing mainly electrolytic copper and precious metals since 1919.The production of gold has been quadrupled during the latest decade because of increasing copper concentrate smelting at Toyo smelter and starting treatment of high gold ores. The ores come from Sumitomo's Hishikari Gold Mines and contain about 80 grams gold per ton.Copper anode slimes produced from Niihama Refinery and Toyo Refinery are decopperized with sulphuric acid, deselenized by roasting and smelted by use of an electric furnace to concentrate precious elements. Lead refinery slimes produced at Harima ISP Refining Works are also charged to the furnace.The bunions from the electric furnace are treated and refined in a cupel after antimony and lead removal. The resulted crude silver is casted into silver anodes.In order to cope with increasing slime production, a new method, chloridizing furnace for lead removal has been adopted and a new cupel has been introduced.The treatment process for silver anode slimes has been improved to obtain up-grade quality of gold anodes. The productivity of gold electrolytic processes are advanced by use of the anodes.

Borohydride Oxidation at a Gold Electrode

The multistage process of borohydride oxidation in an reaction to borate at a Au electrode has been studied by means of fast‐scan cyclic voltammetry (CV) and scanning electrochemical microscopy (SECM). The total irreversibility of this process observed previously is shown to be a result of the presence of very unstable intermediates. CV measurements showed that at least two stages of the process are quasi‐reversible, and the presence of a coupled homogeneous chemical reaction was proved by SECM. The rate constant for this reaction as well as the electrochemical kinetic parameters for the first stage of oxidation are evaluated using digital simulation. The adsorption of the electroactive species associated with the first two‐electron stage of the oxidation becomes apparent at scan rates higher than 200 V/s. A very small fractional surface coverage (estimated to be less than 0.001) is shown to produce CV waves characteristic of adsorption‐ rather than diffusion‐controlled processes. The second chemical stage of this process is much faster than the first. The oxidation of borohydride at a gold anode is shown to have a different mechanism than that proposed earlier for a platinum electrode.

Oxidation of some reducing agents used in electroless plating baths at gold anodes in aqueous media

The oxidation of four reductants, two of direct interest in electroless plating baths, at gold electrodes in base was investigated using cyclic voltammetry and the results were interpreted in terms of the incipient hydrous oxide model of electrocatalysis. Dimethylamine borane and tert-butylamine borane reacted in a similar manner; the results were interpreted in terms of the oxidation of the hydroxytri-hydroborate anion; potential/pH studies indicate that the important mediator at the interface for this reaction is a cationic, Au(I), species. Pyridine borane reacted in a significantly different manner; the mediating species in this case appeared to be an Au(III) hydrous oxide; further work is required to explain the behaviour of this system. The oxidation of hypophosphite on gold in base was quite sluggish, as was the oxidation of hypophosphorous aicd at low potentials in solutions of low pH; it was assumed here that in this system there is a complication due to phosphorous atoms adsorbing at, and thus deactivating, the gold surface.

Anodic synthesis and characterization of millimeter crystals of Ba 0.6K 0.4BiO 3

Anodic electrosynthesis of Ba 0.6K 0.4BiO 3 leads to millimeter-sized crystals of this cubic superconductor with transition temperatures of 30.5 K. Clusters of these lustrous blue-black crystals are grown on gold anodes in graphite crucibles which conveniently serve as the cathode. Details of the electrochemical procedure utilizing a hydroxide melt are given, along with the characterization of the superconductive transition by microwave absorption and magnetic measurements, and confirmation of the composition and structure with X-ray diffraction. The availability of crystals with cubic facets of up to 10 mm 2 has facilitated characterization and application of this material.

Problems associated with the miniaturization of a voltammetric oxygen sensor: Chemical crosstalk among electrodes

The possible chemical crosstalk between electrodes in microfabricated voltammetric oxygen sensors has been studied with an interdigitated electrode assembly. Experimental results show that significant amounts of hydrogen peroxide can be produced at the Au or Pt cathode and transferred to the surface of nearby counter and reference electrodes. Such chemical crosstalk may not only distort the sensing signal, but also affects the stability of the gold anode and the Ag/AgCl reference electrode.

Development of a miniature clark-type oxygen electrode using semiconductor techniques and its improvement for practical applications

A disposable minature Clark-type oxygen electrode has been fabricated using semiconductor techniques. The oxygen electrode consists of: (a) anisotropically etched U- or V-grooves on a (100) silicon substrate as the electrolyte container; (b) a calcium alginate gell containing a 0.1 M KCl electrolyte; and (c) a directly formed gas-permeable membrane. A two-electrode configuration is used with a gold cathode and a gold anode. A novel fabrication process has been developed to allow miniaturization and mass production. Several important factors which influence the oxygen electrode characteristics have been examined. A 90% response time of 10 s is attained. A linear relationship is observed for a wide range of oxygen concentrations at 27°C. 34% of the oxygen electrodes work normally after sterlization in an autoclave. The oxygen electrode can be operated continuously for more than 40 h.

The importance of superficial (adatom) surface oxidation in the electrocatalytic behaviour of noble metals in aqueous media

The conventional, activated chemisorption, model of electrocatalysis is unable to explain fully the surprisingly high level of activity of gold anodes in base for certain organic electrooxidation reactions or even the ability of platinum to catalyse certain oxygen insertion reactions, e.g. methanol or formaldehyde oxidation in acid, at low potentials (in the hydrogen or double layer region) where the surface is considered usually to be oxygen-free. It was demonstrated that such behaviour can be rationalized by postulating the involvement of a quite low coverage of hydrous oxide species, generated at low potential at adatom sites, which act as mediators or catalysts in many electrooxidation reactions. The converse situation was also shown to arise, i.e. the reduction of certain species, e.g. HNO3 or NO 3 − , which requires the involvment of adatoms, was shown to be inhibited as long as the latter existed in the oxidized, hydrous oxide, form. An appreciation of hydrous oxide electrochemistry was shown to be very useful in interpreting electrocatalytic effects at noble metal electrodes in aqueous media.

The role of oxygen ion diffusion in the electrode reactions of β″ alumina

A model has been proposed to explain the current-time curves obtained by applying fixed voltages to polycrystalline β alumina at elevated temperatures using gold contacts. It is proposed in the model that the oxygen electrode reaction can occur at the gold “blocking” contacts. The observed current-time curves can be explained in terms of the diffusion and migration of oxygen ions to the gold anode and sodium ion transport within the bulk of the β alumina. The model provides a new method for determining the oxygen ion diffusion coefficient within the polycrystalline β alumina.

Electrosynthesis of cobalt (III) ions in concentrated H3PO4 medium

The electrosynthesis of cobalt(III) ions from cobalt(II) ions has been studied in 29, 57 and 85 wt % H3PO4 solutions. It has been shown that the conversion of Co(II) to Co(III) is limited by the chemical reaction between Co(III) ions and water. A kinetic study demonstrated that this reaction becomes more rapid as the Co(III) ion concentration increases. In order to find the best conditions for the electrolysis, the effect of some experimental parameters on the current yield and the chemical efficiency has been examined. A comparison between gold and platinum anodes has also been made. The following conditions were found to be the best: anode material, gold; initial Co(II) ion concentration, 5×10−3 M; solvent, 85 wt % H3PO4 solution; current density, 1 mA cm−2; temperature, 20–30° C. Under these conditions the maximum value of current yield, and chemical efficiency are 66% and 48% respectively.

Intense Ion Beam Flux of Adsorbed Gases and Metallic Anode Materials in the “Point Pinch Diode” Measured with Thomson-Parabola Ion Spectrometer

An intense flux of ion beams was observed in a “Point Pinch Diode” which consists of concentric elliptic or spherical electrodes and a slender magnetically insulated transmission line. The ion beam had an energy of about 380 keV, which was equivalent to the supplied diode voltage. The peak current density of the ion beam ranged from 5 to 7.5 kA/cm2 in spite of a small input energy (less than about 1 kJ). Measurements with a Thomson-parabola ion spectrometer show that the major components were hydrogen, carbon, and oxygen, the origins of which were oil and water adsorbed on the surface of the metallic anodes. A significant flux of the metallic ion beams was also detected in the cases of aluminium, copper and gold anodes.

Field-induced silver injection into lithium disilicate glass

The objective of this work was to study field-induced silver injection into Li2O · 2SiO2 glass by the techniques of secondary ion mass spectrometry and thermally stimulated polarization/depolarization current (TSPC/TSDC), with an emphasis on the comparison experiments between gold and silver electrodes. For both anode materials, accumulation of lithium was found near the cathode. The blocking nature of the gold anode was demonstrated by the closeness of the observed and estimated width of the alkali-depleted region near the anode. For silver-anode samples, field-induced silver injection as well as lithium conduction occured and increased the TSPC slope from that of the gold-anode samples.

Anodic gold corrosion in plastic encapsulated devices : E. Brambilla, P. Brambilla, C. Canali, F. Fantini and M. Vanzi. Microelectron. Reliab.23 (3) (577 (1983)

Anodic gold corrosion in plastic encapsulated devices : E. Brambilla, P. Brambilla, C. Canali, F. Fantini and M. Vanzi. Microelectron. Reliab.23 (3) (577 (1983)

Anodic gold corrosion in plastic encapsulated devices

Experimental results of gold metallization failures in semiconductor devices due to the corrosion of gold in the absence of a complexing medium or contaminants are reported. In particular we show the corrosion of anodically biased lines which was observed on unpassivated plastic encapsulated high-frequency transistors and on passivated linear integrated circuits operating at 85°C, 85% relative humidity (R.H.), for a few thousand hours. The anodic corrosion gives rise to the formation of a voluminous and conductive product, Au(OH) 3, and leads to the short-circuiting of adjacent stripes.

Oxidation of halogenated benzaldehydes at aurized gold anodes

The oxidation of seven chloro- and bromobenzaldehydes was studied in 1.0 M aqueous NaOH with 10% tert-butanol cosolvent. Gold rotating disk electro

Thick oxide growth on gold in base

The formation of thick oxide films (ca. 100 monolayer equivalents at 2.3 V) on a gold anode was observed under steady-state polarization conditions in base. As reported by other authors for acid, the layer produced was of duplex character with a compact, largely anhydrous inner film at the metal surface, and a much thicker, porous, highly hydrated outer film at the oxide-solution interface. These deposits were readily distinguished, and quantified coulometrically, due to differences in reduction potential under cathodic sweep conditions. The onset of thick film growth occurred in a potential region where linear Tafel behaviour is observed for oxygen gas evolution on gold, and changes in oxygen coordination of cations in the outer region of the compact layer under these conditions is assumed to enhance the conversion of material in the outer region of the latter to the more hydrated form. As compared with acid, oxide growth was much slower (and reached a limiting value) in base, the outer film was reduced less readily and inhibition of oxygen gas evolution in the thick film region (at ca. 2.35 V) was observed. The results were accounted for by assuming increasing hydroxide ion coordination by cations in the hydrous layer with increasing pH — the more highly coordinated species being thermodynamically more stable but kinetically less capable of rearranging to form a crystalline product. The relationship between the hydrous film on gold and those produced on a wide range of other transition metals is briefly outlined.

Thick oxide growth on gold in base

The formation of thick oxide films (ca. 100 monolayer equivalents at 2.3 V) on a gold anode was observed under steady-state polarization conditions in base. As reported by other authors for acid, the layer produced was of duplex character with a compact, largely anhydrous inner film at the metal surface, and a much thicker, porous, highly hydrated outer film at the oxide-solution interface. These deposits were readily distinguished, and quantified coulometrically, due to differences in reduction potential under cathodic sweep conditions. The onset of thick film growth occurred in a potential region where linear Tafel behaviour is observed for oxygen gas evolution on gold, and changes in oxygen coordination of cations in the outer region of the compact layer under these conditions is assumed to enhance the conversion of material in the outer region of the latter to the more hydrated form. As compared with acid, oxide growth was much slower (and reached a limiting value) in base, the outer film was reduced less readily and inhibition of oxygen gas evolution in the thick film region (at ca. 2.35 V) was observed. The results were accounted for by assuming increasing hydroxide ion coordination by cations in the hydrous layer with increasing pH — the more highly coordinated species being thermodynamically more stable but kinetically less capable of rearranging to form a crystalline product. The relationship between the hydrous film on gold and those produced on a wide range of other transition metals is briefly outlined.

Activation Energies of Anodic Gold Reactions in Aqueous Alkaline Cyanide

The kinetics of the anodic reactions of gold in aqueous alkaline cyanide in the potential range −0.81 to +0.64V were studied by means of potentiostatic and potentiodynamic measurements for the temperature range 0°–50°C. The effects of mass transfer were also investigated. As in earlier works, three distinct regions of anodic activity (i.e., regions of anodic reactions) were found in potentiostatic measurements. The kinetic behavior of the gold reaction in each of these regions was found to behave in the manner predicted by the single reaction mechanismThe dissolution reaction in the most cathodic of the three regions (−0.56 to −0.26V) was characterized by a high apparent activation energy and a lack of dependence on mass transfer. The second step in the reaction mechanism was identified as the rate‐determining step. The gold dissolution reaction in the intermediate potential region −0.26 to +0.39V was found to have a relatively high apparent activation energy (47–55 kJ/mol) and a small dependence on the mass transfer. The second step in the reaction mechanism was identified as the rate‐determining step. In the most anodic of the three regions (−0.39 to +0.64V), the gold dissolution reaction was found to be under diffusion control with an apparent activation energy of 16–18 kJ/mol. The third step in the reaction mechanism was identified as the rate‐determining step. A fourth region (−0.81 to −0.56V) observed in potentiodynamic measurements was found to have an apparent activation energy of with little dependence on mass transfer. The reaction was identified as an adsorption reaction.

Electrogeneration of coulometric reagents: Applications to drug control

The coulometric electrogeneration of titanium(III) is applied to the quantitative reduction of quinone and naphthoquinone compounds of biological interest. Current efficiencies of 100% are obtained at a platinum cathode with titanium tetrachloride as supporting electrolyte in strong acidic media. Benzoquinones, which can be partially or totally destroyed in such media, are determined by using a mixture of TiCl4 and EDTANa4. The choice of experimental parameters is discussed in detail. For oxidimetric determinations, silver(II), which is well known as a very strong oxidizing agent (E0+1.90 Vvs. NHE), is produced with 100% current efficiency on a gold anode at low temperature (−10° C). The best conditions for the electrogeneration of vanadium(V) from vanadyl sulphate in dilute sulphuric acid have also been investigated. The use of amperometric or potentiometric end-point detection is discussed. Organic compounds such as hydroquinone and hydrazide derivatives can be titrated with a good accuracy.

Analysis of impedance on platinum and gold anodes in glacial acetic acid

The analysis of impedance with an adsorbed intermediate for the Kolbe reaction was studied on platinum and gold in glacial acetic acid saturated with potassium acetate. The analysis by the complex impedance plane and complex capacitance plane plot showed that the rate-determining step of the Kolbe reaction is the process of the electrochemical desorption of radical-ion for both anodes, and that the value of double layer capacity C dl is 7–10 μF/cm 2 at more noble potentials than 2.00 V where the Kolbe dimer products are obtained. It was found that the capacity peak at around 1.50 V for platinum and capacity hump for gold appear in the parallel capacity—potential curves in acetic acid containing small amounts of water, respectively. These phenomena are considered to be caused by the competitive adsorption reaction of CH 3COO − and water.