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Dihua Wang

Publications and source records attributed to Dihua Wang.

9 recordsLinked to original sources
PubMed2007

Three-phase interlines electrochemically driven into insulator compounds: a penetration model and its verification by electroreduction of solid AgCl.

A dynamic three-phase interline model has been developed for the reduction of a solid insulating metal compound to the metal in a suitable electrolyte, focusing on the electrochemically driven penetration of the process (or the three-phase interlines) into the insulator. Consideration is given to the effects of electrochemical, concentration and ohmic polarizations in the reduction-generated porous metal layer on top of the solid compound. Under potentiostatic conditions, reduction in the depth direction (penetration) becomes progressively slower as a result of the rising ohmic and concentration polarizations, whilst the electrochemical polarization exerts a declining effect. The quantitative equations established here also provide simple methods for the determination of some kinetic parameters of the reduction process, including rho (total resistivity) and D(R) (diffusion coefficient). The model has been experimentally verified by electrochemical reduction of solid AgCl with two novel metal|AgCl cylinder electrodes in aqueous solutions.

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PubMed2006

Electrochemically driven three-phase interlines into insulator compounds: electroreduction of solid SiO2 in molten CaCl2.

The electrochemical reduction of solid SiO2 (quartz) to Si is studied in molten CaCl2 at 1173 K. Experimental observations are compared and agree well with a novel penetration model in relation with electrochemistry at the dynamic conductor|insulator|electrolyte three-phase interlines. The findings show that the reduction of a cylindrical quartz pellet at certain potentials is mainly determined by the diffusion of the O(2-) ions and also the ohmic polarisation in the reduction-generated porous silicon layer. The reduction rate increases with the overpotential to a maximum after which the process is retarded, most likely due to precipitation of CaO in the reaction region (cathodic passivation). Data are reported on the reduction rate, current efficiency and energy consumption during the electroreduction of quartz under potentiostatic conditions. These theoretical and experimental findings form the basis for an in-depth discussion on the optimisation of the electroreduction method for the production of silicon.

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PubMed2006

A direct electrochemical route from ilmenite to hydrogen-storage ferrotitanium alloys.

An unrecognised but predictable need for a hydrogen-supported society is tens or even hundreds of million tonnes of hydrogen-storage materials, and thus challenges existing technologies in terms of resource and economical realities. Ilmenite is an abundant mineral, and ferrotitanium alloys are among the earliest known hydrogen-storage materials. At present, industrial production of ferrotitanium alloys goes through separate extraction of individual metals, followed by a multistep arc-melting process. In particular, the extraction of titanium from ilmenite is highly energy intensive and tedious, accounting for titanium's high market price and restricted uses. This article reports the electrochemical synthesis of various ferrotitanium alloy powders directly from solid ilmenite in molten calcium chloride. More importantly, it demonstrates, for the first time, that such produced alloy powders can be used without further treatment for hydrogen storage and perform comparably with or better than similar products by means of other methods, but cost just a fraction.

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PubMed2005

Electrochemistry at conductor/insulator/electrolyte three-phase interlines: A thin layer model.

A thin layer model is proposed to assist in the understanding of the electrochemical conversion of insulator to conductor at the conductor/insulator/electrolyte three-phase interline (3PI) when the influence of mass diffusion in the electrolyte phase is negligible. The model predicts, under potentiostatic conditions, a linear variation of the current or the length of the 3PI with time. When polarization is sufficiently large, the logarithm of the current/time ratio or the 3PI-length/time ratio, according to the model, increases linearly with the applied potential. These predictions were tested against and agreed very well with two practical systems: the electroreduction of solid AgCl to Ag in aqueous KCl and of solid SiO2 to Si in molten CaCl2. Kinetic parameters were derived from experimental data using the model. Particularly, the electron transfer coefficient, alpha, was found to be about 0.29 for the reduction of AgCl to Ag in the aqueous KCl solution at room temperature but about 10(-2) for the reduction of SiO2 to Si in molten CaCl2 at 850 degrees C.

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PubMed2005

Voltammetric studies of through-space and through-bond electrostatic interactions in alkyl linked ferrocene and benzoaza-15-crown-5 receptor molecules in acetonitrile.

Six new ferrocene alkyl-benzoaza-15-crown-5 molecules with different alkyl spacer lengths were synthesized and investigated by voltammetry in acetonitrile. Their mean potentials (E(o)') were more negative than that of ferrocene. The changes were greater for the bis-substituted ligands than for the monosubstituted ones. Increasing the alkyl spacer length shifted E(o)' negatively from -CH2- to -(CH2)2- but positively from -(CH2)2- to -(CH2)4-. This unusual variation is attributed to the combined electron donating and withdrawing influences and also the steric effect from the substituents on the ferrocene moiety. Analyses of the potentials of the molecules and their fully protonated forms suggested intramolecular electrostatic signaling through not only the space but also the alkyl chain which is usually considered to be an insulator for through-bond communication. Diffusion coefficients with insignificant differences between the receptors and their fully protonated forms were derived from cyclic voltammograms, suggesting insignificant further conformational variation upon protonation.

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