No description available.

No description available.

No description available.

This investigation involved the experimental study of molten salt solutions containing magnesium chloride, sodium chloride and calcium chloride--an electrolyte of importance in magnesium production. Emf measurements were made on an electrochemical formation cell with pure chlorine gas and magnesium-bismuth alloy electrodes. Good agreement was obtained with the existing data on the thermodynamic properties of pure MgCl(,2) and MgCl(,2) - NaCl binary melts. Nearly ideal (Raoultian) solution behaviour was observed in the binary MgCl(,2) - CaCl(,2) melts. Although the thermodynamic data in this system was different than the reported vapour pressure data it was found to be in accord with the reported phase diagram measurements. The properties of MgCl(,2) in the ternary melts were measured for the first time. / A multiple discrete complex anion (MDCA) model was proposed to correlate all thermodynamic findings in MgCl(,2) - NaCl - CaCl(,2) molten salt solutions. Successful interrelations were obtained when both MgCl(,4)('=) and CaCl(,4)('=) were assumed to coexist in a state of equilibrium with the elementary ions Cl('-), Na('+), Mg('2+) and Ca('2+).

A fundamental study was undertaken in order to establish the mechanisms of the leaching of pre-reduced nickel laterites in ammonia-ammonium carbonate solution. Although the process has undergone various improvements since it was first introduced, the total recoveries are still relatively low, averaging at 80% for nickel and 45-50% for cobalt. The lack of sound fundamental information regarding the mechanisms and the kinetics of the dissolution of nickel and cobalt from iron-alloy grains produced by the reduction roasting of lateritic ores is seen as the main obstacle to establishing the reasons for the lack of adequate recovery and to defining alternative processing strategies which would lead to improved extraction and better process optimisation. Based on fimdamental electrochemical studies and bench scale leaching tests, as well as on-site measurements at an industrial plant where this process is applied, the work presented in the thesis introduces significant new evidence and sheds more light on the understanding of the mechanism of the dissolution process and on the reasons for the low extractions of nickel and cobalt. It has been established that the oxidative dissolution of the iron-alloy grains formed during the reduction roasting takes place primarily via a reaction involving reduction of dissolved cobalt (111) to cobalt (11), and also that the reduction of water is not a significant component of the reactions involved in the dissolution process. Open-circuit potential measurements with various metals and iron-alloys selected to model the reduced material in various solutions which simulated the leaching conditions were also conducted and revealed that passivation takes place during the leaching process. This brings to light a possible new reason for the low recoveries of nickel and cobalt which has not been previously considered. In addition, a kinetic study was conducted, in which the dissolution rates for the various metals, iron-alloys and solutions were measured as a function of time, and the results of which shed more light on the development of the process of passivation. The passivation itself is attributed to formation of iron-oxide on the surface of the dissolving iron-alloy grains, which restricts the transfer of electrons to the reduced metal and brings the oxidative leaching reaction to an end. It has been shown that the passivation can occur in two ways. On the one hand, particularly high concentration of dispersed and dissolved oxygen in the leaching reactors causes passivation by overcoming the limiting current density for the oxidation of iron to divalent iron ions and taking the potential to the region where the direct oxidation to trivalent ions becomes favourable resulting in the formation of an iron-oxide film on the surface. On the other hand, in normally aerated solutions, the passivation of the dissolving ironalloy grains occurs due to the formation of a cobalt and nickel sulphide layer, as a byproduct of the reduction of thiosulphate on the metal surface, which in turn gradually shrinks the area available for the oxidation of iron, again leading to a situation where the oxidising agents present in the solution under standard aerated conditions become sufficient to shift the mixed potential to the region where the iron-oxide forming reaction becomes favourable. The presence of thiosulphate has a decisive role in the second type of passivation. What is more, besides preventing further dissolution of the nickel and cobalt locked in the iron-alloy matrix, the loss of nickel and cobalt by precipitation in the presence of thiosulphate can further reduce the recovery of these metals. For this reason, a method was developed for the oxidation and removal of thiosulphate fkom the actual plant liquor.

Thesis (Ph. D.)--University of Michigan, 1920.

Thesis (Ph. D.)--University of Michigan, 1920.

Different mechanisms are proposed in the literature to describe the formation and behaviour of inclusions during electroslag remelting: - dissolution in the liquid metal of the inclusions already present in the electrode and then renucleation in the freezing ingot. - total or partial dissolution in the slag. - exchange reactions between inclusions in the metal and the slag. - entrapment in the freezing ingot of pieces of slag skin or droplets of slag. The mechanism of dissolution of alumina inclusions in a 70/30 CaF₂/Al₂0₃ slag has been studied in detail. For this a new equilibrium diagram for the system CaF₂/Al₂0₃ has been proposed and the diffusion coefficient of alumina in the slag has been determined by the rotating disk system. In a 70/30 CaF₂/Al₂0₃ slag at 1518°C the diffusion coefficient was estimated as D = 8.5 10⁻⁹ m² sec⁻¹. Calculations of the extent of the dissolution of alumina particles in the slag predicted that big particles (800 μ) might dissolve only partially in the slag. Particles of this size were introduced artificially in electrodes, but after electroslag remelting a much larger number of relatively small (15 μ max) alumina, iron aluminates and iron oxide inclusions were found in the ingot. The same types of inclusions could also be observed in ingots obtained after remelting a Ferro Vac-E electrode. The presence of these inclusions cannot be explained by one the mechanisms proposed precedently (dissolution in the liquid metal and then renucleation or partial dissolution in the slag), but only by an electrolytic oxidation and electrolytic aluminum dissolution on the electrodes and then nucleation of deoxidation products in the freezing ingot. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

It has been suggested by others that hot working is an extension of high temperature creep because of the similar observed dependencies of stress, strain rate, temperature and the similar activation energies of the two types of deformation. This suggestion has been evaluated for commercial purity aluminum by obtaining stress, strain rate and temperature data in the strain rate range 10⁻⁴ to 10¹/second. Published hot compression, hot torsion, and high temperature creep work of others is used to provide supplementary data. A combination of the published work of others with the present experimental work provides data in the strain rate range 10⁻⁷ to 10⁺²/second. From the present analysis, contradictions arise against the theory that hot working is an extension of high temperature creep. First, the method of evaluation of the material constant α in the hyperbolic stress-strain rate relation, [formula omitted], must change in going from creep to hot working. Secondly, the activation energy varies. Those that have suggested that hot working is an extension of high temperature creep found that α and the activation energy were independent of strain rate. Their work is compared to the present analysis and many discrepancies were found. The work in the literature left a data gap in the strain rate range 10⁻³ to 10⁰/second. Hot tensile tests and hot rolling tests were used to provide data in this gap. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

No description available.