Tetsuji Hirato

The leaching of chalcopyrite with ferric sulfate

The leaching kinetics of natural chalcopyrite crystals with ferric sulfate was studied. The morphology of the leached chalcopyrite and the electrochemical properties of chalcopyrite electrodes also were investigated. The leaching of chalcopyrite showed parabolic-like kinetics initially and then showed linear kinetics. In the initial stage, a dense sulfur layer formed on the chalcopyrite surface. The growth of the layer caused it to peel from the surface, leaving a rough surface. In the linear stage, no thick sulfur layer was observed. In this investigation, chalcopyrite leaching in the linear stage was principally studied. The apparent activation energy for chalcopyrite leaching was found to range from 76.8 to 87.7 kJ mol−1, and this suggests that the leaching of chalcopyrite is chemically controlled. The leaching rate of chalcopyrite increases with an increase in Fe(SO4)1.5 concentration up to 0.1 mol dm−3, but a further increase of the Fe(SO4)1.5 concentration has little effect on the leaching rate. The dependency of the mixed potential upon Fe(SO4)1.5 concentration was found to be 79 mV decade−1 from 0.01 mol dm−3 to 1 mol dm−3 Fe(SO4)1.5. Both the leaching rate and the mixed potential decreased with an increased FeSO4 concentration. The anodic current of Fe(II) oxidation on the chalcopyrite surface in a sulfate medium was larger than that in a chloride medium.

Improvement of the stripping characteristics of Fe(III) utilizing a mixture of di (2-ethylhexyl) phosphoric acid and tri-n-butyl phosphate

Abstract It has long been known that the stripping of Fe(III) extracted with D2EHPA is difficult since a high concentration of HCl is required. To overcome this difficulty, the usage of a mixture of D2EHPA-TBP-kerosene in the stripping of Fe(III) was investigated. It was found that this mixture is effective in the stripping of Fe(III), and that less concentrated acid solution is required as a stripping agent. Batch-type extraction or stripping experiments were conducted to simulate multi-stage counter-current extraction or stripping. It was found that use of the mixture in a three-stage operation can easily yield above 98% extraction or stripping. To examine the role of TBP in the improvement of Fe(III) stripping from the mixed solvent, the extraction of HCl with TBP and the spectrum of Fe(III) loaded organic phases were investigated. The experimental results indicated that Fe(III) exchange reaction between Fe(III)-loaded D2EHPA and HCl-loaded TBP proceeds in the mixed solvent. A possible mechanism for Fe(III) stripping from the mixed solvent, involving the reaction between the Fe(III)-D2EHPA complex and TBP in the organic phase, has been proposed.

Aluminium composite coatings containing micrometre and nanometre-sized particles electroplated from a non-aqueous electrolyte

The electrolytic codeposition of micro- and nano-sized particles with aluminum from a nonaqueous electrolyte is investigated. SiC, SiO2, Al2O3, TiB2 and hexagonal BN particles were codeposited with aluminium from an AlCl3/dimethylsulfone (DMSO2) electrolyte. The effect of particle concentration and current density on the codeposition rate of SiO2 with aluminium was investigated. The codeposition of the various particles with Al from AlCl3:DMSO2 solutions is very high. The amount of codeposited particles is Langmuir dependent on the particle concentration in the electrolyte. In contrast, the effect of the current density on the amount of codeposited SiO2 is small.

Microtexture and electromigration-induced drift in electroplated damascene Cu

In this work, the electromigration (EM) performance of electroplated damascene Cu is investigated by drift experiments on Blech-type test structures in both polycrystalline and bamboo microstructures. For the first, microtexture data were obtained from electron backscatter diffraction as well. While both bonding areas and 10 μm wide lines were found to have a predominantly random grain orientation, the drift studies indicated the importance of strongly segregating impurities in controlling Cu grain-boundary EM. For the bamboo lines, the impact of different barrier layers has been investigated, comparing Ta, TaN, and TiN. Drift was shown to proceed in all cases at the metallic Cu barrier interface, but faster for the Ta as compared to the TaN and TiN barriers. Cu drift data were finally compared to available literature results and to our previous drift studies on Al(Cu).

Electrodeposition of CdTe Films from Ammoniacal Alkaline Aqueous Solution at Low Cathodic Overpotentials

Cathodic electrodeposition of CdTe films was studied using aqueous ammonia-alkaline electrolytic baths (pH 10.7; temperature 343 K) in which Cd(II) and Te(IV) species were dissolved to form Cd(NH{sub 3}){sub 4}{sup 2+} and TeO{sub 3}{sup 2{minus}} ions, respectively. From the solution, 60 mM Cd(II)-10 mM Te(IV)-4.0 M NH{sub 3}-1.0 M NH{sub 4}{sup +} (M = mol dm{sup {minus}3}), a flat and smooth polycrystalline CdTe film (thickness, ca. 1 {micro}m) with nearly stoichiometric composition was deposited at a constant cathode potential, ranging from {minus}0.70 to {minus}0.30 V vs. SHE, whereas dendrite CdTe accompanying elemental cadmium was obtained at {minus}0.80 V. The deposition behavior was fully explained by an underpotential deposition mechanism taking the calculated redox potentials of Te{sup 0}/Te{sup IV}O{sub 3}{sup 2{minus}} and Cd{sup 0}/Cd{sup II}(NH{sub 3}){sub 4}{sup 2+} pairs into consideration. During electrodeposition of nearly stoichiometric crystalline CdTe, the current density was decreasing monotonously.

Concentration of uranyl sulfate solution by an emulsion-type liquid membrane process

Abstract The applicability of the emulsion-type liquid membrane process using tri-n-octylamine (TNOA) as an extractant to concentrate uranium from sulfuric acid solutions was investigated. It was found that this liquid membrane process yields much higher extraction percentages than the conventional solvent extraction process using the same amount of TNOA. The liquid membrane process is particularly suitable for dilute solutions such as leach and wash solutions of uranium ores. Effects of various factors on the stability of emulsions and the extraction rate and percent extraction of U(VI) were examined. Among various agents tested, Na 2 CO 3 was found to be preferable to strip sulfato-complexes of U(VI) in the internal phase. Batch-type extractions of U(VI) by the emulsion-type liquid membrane method were performed to simulate a two-stage counter current extraction, and the experimental results suggest that the U(VI) concentration in the final raffinate can be lowered to below 1 g m −3 when the feed solution containing 1 kg m −3 U(VI) is treated by a two-stage extraction.

Potential‐pH Diagram of the Cd ‐ Te ‐ NH 3 ‐ H 2 O System and Electrodeposition Behavior of CdTe from Ammoniacal Alkaline Baths

A potential‐pH diagram of the system was constructed based on diagrams of the and systems and discussed in connection with the redox behavior of an ammonia‐alkaline CdTe electrolytic bath with pH 10.7. CdTe has a wide domain of stability throughout the acidic and alkaline regions, and the redox behavior was well explained with the diagram. The diagram indicated that the cathodic electrodeposition of CdTe occurs across a domain of stability of tellurium metal, i.e., at lower potentials than the deposition potential of bulk Te and higher than that of bulk Cd, with respect to the bath with pH < ca. 11.5, while in the higher pH region, CdTe is expected to deposit directly from Te(IV) and Cd(II) ions. The deposition mechanism is considered as follows: (i) deposition of tellurium layer followed by (ii) an immediate underpotential deposition of Cd on it, which prevents the bulk deposition of tellurium. It can be considered that the stoichiometric CdTe is more easily electrodeposited from alkaline baths, since the domain for tellurium metal is narrower in the alkaline region compared to the conventionally employed acidic region with pH 0–2. Therefore, the bulk deposition of elemental tellurium is less apt to occur from an alkaline bath.

Electrical Properties of CdTe Layers Electrodeposited from Ammoniacal Basic Electrolytes

CdTe is a promising material for solar cell application because its bandgap of 1.44 eV at room temperature is suitable for energy conversion from sunlight to electricity. In addition to dry processes such as screen printing and close-spaced sublimation, electrodeposition 1-3 has been investigated for the preparation of polycrystalline CdTe layers, and thin layered n-CdS/p-CdTe heterojunction solar cells have already been manufactured industrially. Although aqueous sulfate electrolytes with pH 1-2 have historically been studied for CdTe electrodeposition, we have proposed that ammoniacal basic aqueous electrolytes are also suitable, because basic solutions have a relatively high solubility of Te ~IV! species. 4-9 From the ammoniacal basic electrolytes, we successfully obtained smooth and flat polycrystalline CdTe deposits with a nearly stoichiometric composition at potentials positive to that of bulk-Cd deposition. 6 Furthermore, it turned out that the deposition rate was considerably increased by photoirradiation of the cathode surface during the electrodeposition. 10 The mechanism of the CdTe deposition is considered to be ~i! cathodic electrodeposition of surface tellurium atoms (TeO32 1 6H 1 1 4e ! Te(ads) 1 3H2O), followed by ~ii! an adsorption of Cd~II! ions on the tellurium, and ~iii! underpotential deposition of the Cd~II! ions to form CdTe @Cd(II) 1 Te(ads) 1 2e ! CdTe#. 9 It is known that electrodeposited CdTe from acidic sulfate electrolytes without intentional doping are n-type and that a heattreatment in air is necessary to obtain p-type. If as-deposited p-type CdTe can be obtained by electrodeposition from aqueous electrolytes without the heat-treatment process, it will lead to a less energyconsuming fabrication of p-n junction solar cells. Therefore, it is important to investigate the electrical properties, including conduction type, of electrodeposited CdTe. Generally, undoped CdTe with a nearly stoichiometric composition is known to have a high resistivity, or a low carrier density. We previously tried conventional MottSchottky plots using CdTe layers electrodeposited from an ammoniacal basic electrolyte to determine the majority carrier type and carrier density of the CdTe. However, reliable data could not be derived from the results, since the CdTe/electrolyte interface capacitance was almost constant and independent of the electrode potential. This is attributable to a high internal resistivity of the CdTe layer. In the present study, we tried to determine the majority carrier type of the electrodeposited CdTe layer by means of photoelectrochemical investigation using an aqueous solution containing sulfite ion as a hole scavenger and, then, resistivity and Hall effect measurements were carried out. The Hall effect measurement is a standard, reliable, and more direct method for obtaining fundamental electrical properties such as carrier type, carrier density, and mobility. Nevertheless, limited numbers of Hall effect measurements on electrodeposited materials have so far been carried out. As for the electrodeposited undoped CdTe, for example, the Hall effect for the deposits from an organic bath 11,12 has only been reported and there have been no papers regarding that from aqueous media. A possible reason for there being few reports is that the sample preparation for Hall effect measurements is difficult because the conducting substrate must be removed from the electrodeposited layer, while the CdTe layer is maintained intact. In the present work, we employed a method in which the CdTe layer was mechanically transferred from the conducting substrate onto a nonconductive epoxy resin without the formation of cracks. Experimental

Determination of Mo(VI) Species and Composition in Ni-Mo Alloy Plating Baths by Raman Spectra Factor Analysis

The equilibrium constants of the formation of isopolymolybdates H x Mo 7 O 24 (6 x) (x = 0-2), heteropolymolybdate NiMo 6 O 24 H 6 4- , and Mo(VI)-citrate complexes H r (MoO 4 ) 2 Cit (7-r)- and H r MoO 4 Cit (5-r)- (Cit 3- = C 6 H 5 O 7 3- ) were determined from factor analysis of Raman spectra and visible absorption spectra to calculate the chemical species present in acidic Ni-Mo alloy plating baths. On the addition of citrate to a Ni(II)-Mo(VI) bath, (i) the polymolybdates were decomposed by the formation of H r (MoO 4 ) 2 Cit (7-r)- complex, and then (ii) H r MoO 4 Cit (5-r)- and NiCit - complexes formed. This complex formation was necessary for the alloy deposition, but an excess addition of citrate, which results in the formation of NiCit 2 4 complex, lowered the current efficiency. The deposition behavior of Ni-Mo alloy from Ni(II)-Mo(VI)-citrate baths was compared with that of pure Ni from Ni(II)-citrate baths, in which concentrations of Ni(II)-species are identical to those in the corresponding Ni(II)-Mo(VI)-citrate baths, The alloy deposition behavior is strongly governed by the ease of Ni deposition, indicating that the electrodeposited nickel induces the deposition of molybdenum.

Electrolytic Codeposition of Silica Particles with Aluminum from AlCl3-Dimethylsulfone Electrolytes

The electrolytic codeposition of silica particles with aluminum was investigated from an AlCl 3 -dimethylsulfone electrolyte containing monodisperse silica particles with a diam of 0.2 μm. The electrodeposition was done at 110°C and at current densities between 6 and 13 A/dm 2 . Dense aluminum coatings with a thickness of 20 μm were obtained at a plating rate of 77 μm/h. The coatings contained a homogeneous dispersion of individual silica particles. The amount of codeposited silica particles was found to depend on the concentration of silica particles suspended in the electrolyte and the current density.