Electrochemical Machining (ECM) is a non-conventional, non-contact technique, popular in the aerospace and automotive industries, used to machine ultra hard metal alloys. This work details a novel system, using ultrasound to dynamically measure the interelectrode gap. For greater accuracy, thermocouples have also been incorporated into the system to allow for the often significant temperature variation due to resistive heating. This gives time-resolved data for the discussion valency and overpotential during ECM. The time averaged dissolution valencies found using this technique are the same, to within experimental error, as those found in previous literature demonstrating the accuracy of this approach. These parameters determine the ECM process and are used in computer modelling; generally these have been assumed to be time invariant however, significant variation is found in this work. This variation has also been used to give insight into high current dissolution processes. Iron machined in sodium chloride (NaCl) electrolyte was initially studied to eliminate any possible effects of alloy composition which might be seen when machining more complex materials. More pertinent to industrial ECM, the machining parameters of the hard metal alloys Inconel 718 (In718) and Titanium 6/4 (Ti6/4) in both NaCl and NaNO₃ were also investigated. The current-voltage characteristics were found to have some similarities to those of iron and stainless steels. Similar results were also found for In718 and Ti6/4 using an ECM cell of a longer electrolyte flow path length.

Barium is also known for having two hexagonally close packed phases at lower and higher pressures than the hotel structure. Although the two hexagonally close packed phases have different properties we show that barium would transform continuously between these phases but for the intercession of the hotel phase. The differences between the two are predominantly caused by the progressive transfer of electrons from s-type orbitals to d-type orbitals. At ambient pressures the group-V elements have a rhombohedral structure which is a distortion of a simple-cubic arrangement. As the pressure is increased, the distortion decreases and the rhombohedral structure transforms continuously back to simple cubic. Experimentally, however, a first-order discontinuous transformation is seen in arsenic. In bismuth and antimony, transitions to completely different structures occur before the rhombohedral to simple cubic transition can occur. A Landau-type model is developed to describe the rhombohedral distortion. This model predicts a gradual transfer to simple cubic, not only with increasing pressure but also with increasing temperature. Although this prediction is confirmed with some molecular dynamics calculations there is unfortunately no experimental data. As well as <i>ab initio </i>calculations we also present a many-body interaction potential which is based on that of Finnis and Sinclair but which describes separately s- and d-type electrons. With this potential it is possible to get a transfer of electrons from s-type orbitals to d-type orbitals as the pressure is increased. It is able to produce an iso-structural transition with a volume collapse. By considering spin bands, the model can also be modified to model magnetic systems.

This thesis extends earlier work at the University of Edinburgh aimed at opening up new flowsheets for the hydrometallurgical recovery of base metals using tetradentate ligands which are capable of transporting metal salts {both a metal cation and its attendant anion(s)}. Prototypes were based on salicylaldimine derivatives of diamines, “salen” ligands in which coordination of a metal dication releases the two phenolic protons which are captured by pendant secondary amine groups generating a preorganised dicationic binding site for the anion(s). The thesis initially deals with the design, synthesis and evaluation of ligands to improve the strength, selectivity and speed of binding of nickel(II) sulfate by incorporating two additional donors in the salen unit to generate N₂X₂O₂^2- binding sites for the nickel yielding pseudo octahedral complexes. The ligands N,N or O,O or S,S <i>o</i>-aminophenyl-substituted 1,2-diaminoethane, 1,2-dioxaethane, 1,3-dioxapropane or 1,2-diethioethane were also used in a screening study with some other divalent metal salts (calcium, cobalt, copper, magnesium, manganese and zinc) commonly found in the feed solutions in commercial processes. Chapter two deals with the nickel(II) coordination chemistry of a series of sexadentate (N₂X₂O₂^2-) ligands. Nickel-ligand-anion complexes have been synthesised for sulfate, nitrate and chloride salts and neutral nickel-ligand complexes have been made. Crystal structures of complexes all contain the same isomer which has a planar<i> mer</i> arrangement of the salicylaldimato XNO^- units. A “nickel only” complex for an X₂N₂O₂^2- ligand with pendent piperidine groups shows that these could provide a cavity to encapsulate a single sulfate anion. All the ligands were found to be very weak extractants and showed slow complexation kinetics and phase transfer of nickel sulfate. The synthesis and characterisation of a series of tridentate ligands related to the sexadentate ligands, with NXO^- binding sites, are reported in chapter three. In theory these could form complexes with a ligand: nickel ratio of 2:1, with a more nearly “ideal” octahedral donor set. Solid state structures of the ligands show them to be pre-organised with an approximately 90° X˙˙˙N˙˙˙O angle. Nickel complexes have been synthesised for sulfate, chloride and acetate salts. Analysis indicates that complexes with ligand: nickel: dianion ratios of 2:1:1 were formed. The tridentate ligands were found to be very weak extractants for nickel sulfate. Chapter four describes the screening of the potentially sexadentate N₂X₂O₂^2-, tridentate NXO^- and the tetradentate “salen” ligands N₂O₂^2- in which the complexation and phase transfer of calcium(II), cobalt(II), copper(II), magnesium(II), manganese(II), nickel(II) and zinc(II) sulfates and chlorides were studied.

The thesis considers the development of new reagents which could transport transition metal <i>salts</i> in extractive hydrometallurgy and addresses the ligand design features which are needed to control the strength and selectivity of binding of both a particular metal cation and its attendant anions(s). Extractive metallurgy of base metals is surveyed in chapter 1 and suggests that more efficient recovery processes are needed. One new approach, which could lead to much better materials balances in many cases, is to use hydrometallurgical techniques which involve co-extraction and transport of metal cations and their attendant anion(s). The problems in obtaining the selective extraction of anions makes the development of such a process very challenging, especially for hydrophilic anions such as sulphate which would be present in many pregnant solutions generated in processing sulfides ores. The rapidly emerging field of anion coordination chemistry and approaches to the development of selective ligands are discussed. Chapter 2 focuses on the pH dependence of sulfate-loading from an aqueous solution into chloroform solutions of a selection of zwitterionic ditopic ligands containing two 3-dialkylaminomethylsalicylaldimine units. These “salen-type2 ligands have quadridentate N₂O₂^2- binding sites for divalent metal cations and the <i>cis</i>-coordination of the phenolate aligns the pendant protonated 3-dialkylaminomethyl groups to bind to a sulfate dianion. Studies of the pH dependence of sulfate-loading confirm that sulfate binding is enhanced significantly by the incorporation of a divalent cation such as Cu²⁺ in the salen N₂O₂^2- site. Metal dication loading is very dependent on the nature of the bridging group between the two imines in the “salen” unit; Cu²⁺ loading follows the order <i>ortho</i>-phenylene > 1,2-ethane > 2,2’-biphenyl. The ethane-bridged ligand, 4,4’-di-<i>tert</i>-butyl-6,6’-bis(dihexylaminomethyl)-2,2’-(ethylenedinitrilodimethylidyne) diphenol, was found to have a nearly ideal loading profile for CuSo₄. Stability to hydrolysis and oxidation is a key requirement for commercial metal solvent extractants. The stability of the imine bond in the “salen-type” extractants investigated in chapter 2 was tested in a two phase chloroform: water systems under conditions likely to be used for loading or stripping of metal <i>salts.</i> Stability is dependent on the nature of the bridging unit between the two imines varying in this order 2,2’-biphenyl > <i>ortho</i>-phenylene > 1,2-ethane. Two new ligands, 4,4’-di-<i>tert</i>-butyl-6,6’-bis(dihexylaminomethyl)-2,2’-(ethylenedinitrilo-1,1’-phenyldimethylidyne) diphenol and <i>N,N’-</i>dimethyl-<i>N,N’</i>-bis(2-hydroxy-3-[(E)-phenyliminomethyl]-5-<i>tert</i>-butylbenzyl)hexane-1,6-diamine, which exhibit improved stabilities at low pH are also discussed.

Ferrous oxide activity has been determined in titania rich slags. Molten synthetic slag mixtures of the ternary systems FeO-TiO₂- SiO₂ and FeO-TiO₂-CaO and of the system FeO-TiO₂-SiO₂ containing MnO and CaO at constant levels of each have been investigated. The slags were contained in iron crucibles and were equilibrated for four hours at 1475°C or 1470°C with gas mixtures containing CO₂, H₂, and argon of varying oxygen potentials. The equilibration technique made use of the equilibrium reaction: - Fe (solid) + ¹/₂ O₂ (gas) = FeO (slag). Each gas mixture used had an oxygen potential corresponding to a certain ferrous oxide activity in the slag and after equilibration the final chemical analysis of the slags gave the compositions having this particular ferrous oxide activity. In the course of determining the activity in the ternary systems, the binary systems FeO-SiO₂ and FeO-CaO were investigated at 1475°C and 1470°C respectively. The ferrous oxide activities determined had a satisfactory agreement with other investigators of these systems. Silica activity was calculated by Gibbs-Duhem equation and calcium oxide activity was calculated by both Gibbs-Duhem equation and regular solution model. In the ternary system FeO-TiO₂-SiO₂ at 1475°C, FeO isoactivity curves are bowed towards FeO corner and this was related to the miscibility gap in the binary system TiO₂-SiO₂ which show that the two liquid oxides are incompatible and must have a positive deviation from ideality. Ferrous oxide activity in this system was compared to MnO activity in the system MnO-TiO₂-SiO₂ and the comparison showed that MnO have lower activity than FeO. Silica activity was calculated by Gibbs-Duhem equation. FeO iso-activity curves in the system FeO-TiO₂-CaO at 1470°C are bowed away from FeO corner. The formation of a series of interoxide compounds in the phase diagram of CaO-TiO₂ explain the increase in FeO activity with the addition of CaO to FeO-TiO₂ binary or vice versa. TiO₂ and CaO activities were calculated by Gibbs-Duhem equation and regular solution model. Basic oxide additions to the ternary FeO-TiO₂-SiO₂ increased FeO activity. Increasing MnO additions from about 8 mole % to about 24 mole % Increased FeO activity but had no effect on the direction of bowing of the curves. Increasing CaO additions reversed the direction of bowing of the iso-activity curves. For all TiO₂ : SiO₂ ratios the addition of 16.1 mole % CaO Increased FeO activity more than the same addition of MnO.

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The patent literature describing the development of the foil electroforming technology has been reviewed. A review of the literature covering the development of iron plating electrolytes has also been completed. A detailed study of the effects of solution parameters on the conductivity of iron chloride solution and the effect of addition of a number of 'conductivity salts' has been carried out. The operation of a pilot plant for the continuous production of iron foil has. been investigated and the parameters of foil production characterised. Preliminary cathodic polarization studies were made at low current densities on the iron chloride electrolyte showing the effects of temperature on the system. A number of possible materials for use as insoluble anodes have been investigated using anodic polarization to determine· their behaviour in the aggressive hot iron chloride electrolyte environment. The possibility of reducing depassivation of the cathode by the addition of a less aggressive anion was studied but no significant improvement achieved. For a more detailed and controlled study of the hot iron chloride electrolyte, a closed, divided-cell incorporating a rotating-cylinder electrode was designed and constructed to operate near to the boiling polnt.of the electrolyte. The cell enabled a more rigorous-study of the electrolyte to be made as the solution parameters could be better controlled. The concentration of the ferric ion in the solution could be reduced and held constant while other factors could be measured. This system has been used to demonstrate the electrochemical reduction of ferric ion in addition to demonstrating that chemical reduction of the electrolyte was feasible and to study the effect of ferric ion concentration on cathode current efficiency. Control of ferric ion concentration by use of the divided cell has also enabled study of some of the deposition characteristics, the effects of stirring on the deposit and an investigation into the use of surface-active agents in further optimising the electrolyte performance.

No description available.