Three‐Phase Interlines Electrochemically Driven into Insulator Compounds: A Penetration Model and Its Verification by Electroreduction of Solid AgCl

Abstract

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.

Electroreduction of Iron(III) Oxide Pellets to Iron in Alkaline Media: A Typical Shrinking-Core Reaction Process

“…Then, the currents converge to about 30 mA with further increasing electroreduction time to 2.5 hours (second period). The increase of current in the first period (from 0 to~1 hours) may be mainly attributed to the three-phase interlines (3PIs) [44,45] expand along the surface of the Fe 2 O 3 pellet. The decrease of current in the second period (from~1 to 2.5 hours) may be caused by the relatively low electronic conductivity of the reduction-generated iron layer and the relatively slow mass transfer from the interior of pellet precursor to the bulk aqueous NaOH solution.…”

“…The decrease of current in the second period (from~1 to 2.5 hours) may be caused by the relatively low electronic conductivity of the reduction-generated iron layer and the relatively slow mass transfer from the interior of pellet precursor to the bulk aqueous NaOH solution. [44,45] The second current increase during the intermediate stage (~1.5 to 2.5 hours) for 1273 K (1000°C) case in Figure 5 may be caused by various factors, such as the catalytic effects of the reaction intermediates. Moreover, the reductiongenerated iron particles can grow and interconnect together gradually to increase the electronic conductivity of the iron layer, which may also contribute to create the second current increase during the intermediate process.…”

“…Actually, this observation can be generally explained by the 3PIs reaction mechanism. [9,44,45] However, the catalytic effects of the reaction intermediates and the improvement in the accessibility of NaOH aqueous electrolyte to the reaction area may also be partially responsible for the sudden increase of current. Moreover, the current-time curves ( Figures 5 and 8(a)) show different initial current values, which are mainly attributed to the different volumes (surface areas/ reaction areas) of the Fe 2 O 3 pellets sintered at different temperatures (as shown in Figure 2) and the different concentrations/viscosities of aqueous NaOH solution.…”

Production of Ni-35Ti-15Hf Alloy via the FFC Cambridge Process

“…10. The three-phase interline model [21,22] can be applied to explain the current changes. It can be seen from Fig.…”

Near-Net-Shape Production of Hollow Titanium Alloy Components via Electrochemical Reduction of Metal Oxide Precursors in Molten Salts

“…The answer is yes if diffusion is disregarded in the pores of the cathode according to the recently proposed three-phase interline (3PI) models. [21,29,30] However, oxide ion diffusion through the pores in the formed metal layer would eventually become the control step in determining the overall speed of the reduction process when the metal layer becomes thicker with electrolysis. This effect of diffusion will lead to a declining current density.…”