Ernest W. Dewing

Bio: Ernest W. Dewing is an academic researcher from Alcan. The author has contributed to research in topics: Cryolite & Aluminium. The author has an hindex of 14, co-authored 40 publications receiving 532 citations.

Joining of metal surfaces

Abstract: In methods of joining metal surfaces involving heating to a temperature above about 560°C, the use of a flux comprising a mixture of potassium fluoaluminates. Particularly for brazing aluminum, a flux consisting essentially of potassium fluoaluminate complexes (e.g. KAlF 4 and K 3 AlF 6 ) may be employed, having a composition corresponding to an AlF 3 /KF ratio, in parts by weight, between about 65:35 and about 45:55. The flux is essentially free of unreacted potassium fluoride and may be in divided solid form.

Solubility of some transition metal oxides in cryolite-alumina melts: Part I. Solubility of FeO, FeAl2O4, NiO, and NiAl2O4

Abstract: The solubilities of FeO, FeAl2O4, NiO, and NiAl2O4 were measured in cryolite-alumina melts at 1020 °C. FeO was found to be the stable solid phase at alumina concentrations below 5.0 wt pct, while FeAl2O4 was stable above that. The corresponding figure for the nickel system was 3.0 wt pct Al2O3. These values correspond to Gibbs energies of formation of the aluminates (from the constituent oxides) of −17.6 and −29 kJ/mol, respectively. In alumina-saturated melts in the range 980 to 1050 °C, the solubilities of both aluminates increased with increasing temperature, the apparent enthalpies of solution being 65 kJ/mol for FeAl2O4, and 249 kJ/mol for NiAl2O4. Investigation of the solubilities of the aluminates as a function of the NaF/AlF3 ratio in alumina-saturated melts at 1020 °C showed maxima at a molar ratio of around 5. The results are discussed in terms of the species apparently existing in the solution, and are consistent with the solute species being fluorides, not oxyfluorides. The activity coefficients of FeF2 (liquid) and NiF2 (solid) in dilute solution in cryolite are found to be 0.22 and 1.2, respectively.

Electrolytic reduction cells

Abstract: In an electrolytic reduction cell for the production of a molten metal by electrolysis of a molten electrolyte, the product metal collects on a cathodic carbon floor having embedded steel current collector bars for leading out the cathodic current. In order to reduce the wave motion of the metal due to interaction of horizontal currents in the product metal with the magnetic fields due to currents in conductors associated with the cell, electrically non-conductive barrier members are arranged on the floor of the cell transversely of horizontal currents in the product metal. Such barrier members have at least a surface layer of material resistant to product metal and extend upwardly from the cell floor to a height approximating to the normal maximum operating level of product metal.

Process for the production of aluminium

Abstract: A B S T R A C T In a process for the production of aluminium a molten alumina slag, containing combined carbon is circulated through one or more alternately arranged relatively low temperature zones where carbon is added to increase the combined carbon content of the slag by reaction with the alumina slag and high temperature zones where aluminium metal is released by reaction of aluminium carbide and alumina in the slag with consequent depletion of the combined carbon content. Alumina is supplied to the slag at one or more locations. The energy to drive the reactions is preferably supplied by resistance heating of the slag particularly in transit from a low temperature zone to a high temperature zone although usually additional energy is supplied to the slag in the return from a high temperature zone to the next low temperature zone. In most instances the aluminium-liberating reaction is carried out in an upwardly inclined passage and the gas evolved is employed to achieve the circulatory movement of the slag. It is a preferred feature to scrub the gas with carbon without admixed alumina to avoid formation of sticky aluminium oxycarbide in the carbon, which is subsequently added as process charge.

Loss of current efficiency in aluminum electrolysis cells

Abstract: Consideration of the mechanism of loss of current efficiency (CE) leads to a form of equation which is simple, likely to give reasonable extrapolation beyond the range where experimental data are available, and convenient for responding to practical questions. With coefficients generated from plant experiments (performed by others), the equation is log (pct loss of efficiency) = 0.0095 (superheat) -−0.019 (pct A1F2) − 0.060 (pct LiF) + const where superheat is the difference (in °C) between cell temperature and the pseudo-binary eutectic temperature with A12O3, and pct A1F3 is excess A1F3. The coefficient for CaF2 is zero. The constant is characteristic of the cell design. The question of reconciling the values of the coefficients with literature data on the solubility of Al in cryolite melts and current theories of loss of efficiency is discussed.

The effect of hydrothermal conditions on the mesoporous structure of TiO2 nanotubes

Abstract: A systematic analysis of the influence of preparation conditions in the alkali hydrothermal synthesis on the morphology of TiO2 nanotubes is performed using HRTEM and low temperature nitrogen adsorption. The possible mechanisms of nanotube formation are reviewed and a mechanism based on the key stage of wrapping of intermediate multilayered titanate nanosheets is suggested. The driving force for wrapping is considered to be the mechanical stress arising during crystallisation/dissolution. The average diameter of the nanotubes was found to depend on the temperature and on the ratio of weight of TiO2 to the volume of sodium hydroxide solution. An increase in the temperature from 120 to 150 °C results in an increase in the average nanotube diameter. Subsequent increases in the temperature result in the formation of non-hollow TiO2 nanofibers with an average diameter of 75 nm, a wide distribution in diameter and a length in excess of 10 µm. The increase of the TiO2 : NaOH molar ratio results in an increase in the average diameter of nanotubes and a decrease of surface area. The average inner diameter of TiO2 nanotubes varied between 2 and 10 nm. The pore-size distribution was evaluated from TEM, and low-temperature nitrogen adsorption data using the BJH method. It was shown that nitrogen adsorption is a suitable method for characterisation of the pore morphology of nanotubes.

Processing and properties of monolithic TiB2 based materials

Abstract: Titanium diboride (TiB2) based materials have received wide attention because of their high hardness and elastic modulus, good abrasion resistance, and superior thermal and electrical conductivity. Potential applications include high temperature structural materials, cutting tools, armour, electrodes in metal smelting and wear parts. Despite its useful properties, the application of monolithic TiB2 is limited by poor sinterability, exaggerated grain growth at high temperature and poor oxidation resistance above 1000°C. Pure TiB2 can be densified only at high temperatures (∼2000°C), with an applied pressure generally being necessary during sintering. However, these high sintering temperatures cause abnormal grain growth and microcracks, which are detrimental to the mechanical properties. Various sinter additives are commonly added to obtain dense TiB2 with optimised mechanical properties at lower sintering temperature. The present review surveys the current state of knowledge on development of bulk...

Method to increase the oil production from an oil reservoir

Abstract: A method to increase the production of oil from an oil reservoir is described. The method includes injecting a magnetic or magnetostrictive material through an oil well into the oil reservoir, vibrating the material with the aid of an alternating electric field and removing oil from the oil well.

System and process for solid-state deposition and consolidation of high velocity powder particles using thermal plastic deformation

Abstract: The invention relates to an apparatus and process for solid-state deposition and consolidation of powder particles entrained in a subsonic or sonic gas jet onto the surface of an object. Under high velocity impact and thermal plastic deformation, the powder particles adhesively bond to the substrate and cohesively bond together to form consolidated materials with metallurgical bonds. The powder particles and optionally the surface of the object are heated to a temperature that reduces yield strength and permits plastic deformation at low flow stress levels during high velocity impact, but which is not so high as to melt the powder particles.

A long-life rechargeable Al ion battery based on molten salts

Abstract: Affordable and scalable energy storage systems are necessary to mitigate the output fluctuation of an electrical power grid integrating intermittent renewable energy sources. Conventional battery technologies are unable to meet the demanding low-cost and long-life span requirements of a grid-scale application, although some of them demonstrated impressive high energy density and capacity. More recently, the prototype of an Al-ion battery has been developed using cheap electrode materials (Al and graphite) in an organic room-temperature ionic liquid electrolyte. Here we implement a different Al-ion battery in an inorganic molten salt electrolyte, which contains only an extremely low-cost and nonflammable sodium chloroaluminate melt working at 120 °C. Due to the superior ionic conductivity of the melt electrolyte and the enhanced Al-ion interaction/deintercalation dynamics at an elevated temperature of 120 °C, the battery delivered a discharge capacity of 190 mA h g−1 at a current density of 100 mA g−1 and showed an excellent cyclic performance even at an extremely high current density of 4000 mA g−1: 60 mA h g−1 capacity after 5000 cycles and 43 mA h g−1 capacity after 9000 cycles, with a coulombic efficiency constantly higher than 99%. The low-cost and safe characteristics, as well as the outstanding long-term cycling capability at high current densities allow the scale-up of this brand-new battery for large-scale energy storage applications.