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A new type of liquid state electrode assembly based on a natural rubber membrane and using a graphite rod as internal reference electrode, has been developed for use with organic salts which are soluble in organic solvent. Electrodes have been developed for determination of zinc(II)j perchlorate and tetrafluoroborate ions, using basic dye salts containing those arAons. In general, natural rubber sheeting is treated with a water immiscible organic solvent containing the salt; swollen sheeting is used as the membrane. These electrodes respond in a Nernstian manner, giving a potential-concentration slopes of 29.5,57.5 and 58.5 mV for zinc(II), perchlorate and tetrafluoroborate electrodes respectively. The slope is stable for a reasonable length of time, e.g. potential-concentration slope is decreased by 0.5 W after about three to five weeks, depending on the type of electrode. In the preparation of these electrodes, the choice of solvent and the kind of natural rubber has been carefully selected, as these factors influence the operation of the membrane. Effects of solution pH and the temperature variations on response of the electrodes, have also been studied. Further work also has been done on studying the Gmelin reaction (reaction of nitroprusside and sulphide ions) with a sulphide ionselective electrode. This reaction involves a study of the reaction between nitroprusside and sulphide ions, where nitrosyl group is modified to pentacyanothionitroferrate(II) imparting a purple colour to the solution. For determination of sulphide and nitroprusside by potentiometric titration optimum conditions have been developed. Also a colorimetric procedure for sulphide determination is recommended.

Experimental measurements have been made on the growth of dendritic y phase precipitates from aß phase matrix in the alloy systems copper/zinc and silver/zinc. These data are then applied. to the current most general theoretical model of dendrite growth (Trivedi Theory), but without making the normal assumption that the dendrite growth velocity corresponds to the maximum velocity predicted by the theory. It is found that there is doubt as to the validity of the application of such a criterion in the alloy systems, copper/zinc and silver/zinc. The fundamental interfacial instability theory of Mullins and Sekerka has been modified and applied to these two alloy systems to calculate the values of the critical radii of instability. These values are in agreement with the observed values of length and tip radii of the dendritic precipitates. A correlation has been found between the experimental measured tip radius (p exp and the critical radius for relative instability (RC) such that fexp is of the order RC of 1. This suggests that some form of stability criterion determines the tip radius of the crowing dendrite and the dendrite travels with the velocity associated with this particular tip radius. This velocity need not correspond to the predicted maximum velocity of the theory. As a result of the work presented in this thesis, the above analyses were applied to data reported in the literature for the growth of succinonitrile dendrites. Similar conclusions were reached.. The paper is included as an Appendix

Bismuth ferrite (BiFeO3) is an inorganic chemical compound with a distorted rhombohedral (R3c) perovskite structure. It is a base for promising PbO-free piezoelectric and ferroelectric materials and also exhibits multiferroic properties at room temperature. However, the major drawback of the material is its high leakage current particularly under high electric field. It is postulated that the high leakage currents arise from the presence of oxygen vacancies, VO formed by the reduction of Fe3+ to Fe2+ during sintering. Recently, RE doping has been shown by Karimi et al. (2009) to induce a transition from a ferroelectric (FE) to antiferroelectric (AFE) structure similar in character to that observed in Pb(Zr,Ti)O3 (PZT). The main goal of this work therefore, was to fabricate compositions in the solid solution Bi1-xNdxFeO3 but additionally utilise Ti4+ doping on the B-site to control conductivity with the intention of achieving greater understanding of the intrinsic ferroelectric and dielectric properties. Initially, Bi0.85Nd0.15FeyTi1-yO3 0 ≤ y ≤ 0.1 compositions were fabricated. For y = 0, a mixture of FE (R3c) and AFE (Pbam) phases were present in XRD spectra. For 0.01 ≤ y ≤ 0.03, all XRD peaks could be indexed according to the PbZrO3 (PZ)-like AFE phase. For higher values of y, the absence of unique PZ-like reflections and broad rather than split peaks in XRD spectra suggested that long range antipolar order was destroyed. The substitution of 1% Ti for Fe resulted in a large decrease in the room temperature bulk conductivity from ~ 1 mS cm-1 to < 1 μS cm-1 and a large increase in activation energy (Ea) for conduction from 0.29 eV to > 1.0 eV. Increasing the Ti concentration further had little effect on either conductivity or Ea. As a result of the decrease in conductivity, large fields (5kV/cm) could be applied to ceramic samples which resulted in linear dielectric behaviour typical for an AFE structure below the field required to switch to the FE state. Subsequently, phase transitions as a function of Nd concentration were investigated in 3% Ti doped Bi1-xNdxFeO3 ceramics. Paraelectric (PE) to FE transitions were observed for compositions with x ≤ 0.125 which manifested themselves as peaks in permittivity. In contrast, PE to AFE transitions for 0.15 ≤ x ≤ 0.20 gave rise to a step-like change in the permittivity, with x = 0.25 exhibiting no sharp anomalies and remaining PE until room temperature. The large volume changes at the PE to FE/AFE transitions reported by Levin and co-workers [Phys. Rev. B, 81, 020103 (2011)] were also observed by dilatometry. It is proposed that the large volume change coupled with their 1st order character constrains the transitions in Nd-doped BiFeO3 to occur uniformly throughout the material in an avalanche-like manner. Hence, anomalies in DSC, permittivity and thermal expansion were observed over commensurately narrow temperature intervals. Despite the large volume change and eye-catching anomalies in DSC, the latent heats for the transitions in Ti-doped Bi1-xNdxFeO3 are similar to Pb(Zr,Ti)O3 (1-3 kJ/mol) with each an order of magnitude greater than BaTiO3 (~0.2 kJ/mol). Thin films of Bi0.825Nd0.175Fe0.97Ti0.03O3, which in bulk ceramic has the PZ-like structure, were deposited by Pulsed Laser Deposition on Pt/Si substrates in collaboration with the group of Professor Trolier-Mckinstry at Pennsylvania State University, PA, USA. Thin films deposited at 625 oC and 650 oC were predominantly PZ-like but contained regions composed of the R3c phase. Polarisation vs. field measurements revealed large coercive fields (~400 kV/cm) and high remanent polarisation (100 C/cm2) which are speculated to at least in part arise from AFE-FE switching in the system.

Detection and sizing of corrosion in pipelines and pressure vessels over large, partially accessible areas is of growing interest in the petrochemical and nuclear industries. Traditionally, conventional ultrasonic thickness gauging and eddy current techniques have been used to precisely measure the thickness in structures. These techniques only allow the measurement of the local thickness under the probe. Consequently obtaining the remnant thickness of a specimen over a large area requires the probe to be scanned, which is a long and tedious process. Moreover, with these techniques, the scanning may become impossible when the area of inspection is inaccessible. There is therefore a need for a rapid, accurate, long range inspection technique to measure the remaining thickness in corrosion patches. Low frequency guided waves are now routinely used to screen large area of pipes and other structures for cracks and corrosion. Their detection and location capability is very good, but the standard screening technique only gives a rough estimate of the remaining wall thickness. Guided waves have multiple properties which can be used for thickness mapping over large partially accessible areas e.g. dispersion and cutoff frequency thickness product of the high order modes. The present work aims to demonstrate the potential of guided waves for thickness mapping over large partially accessible areas. It starts with a general introduction on ultrasonic guided waves and a literature review of the different techniques for the evaluation of thickness with guided waves. The severity of the errors introduced in time-of-flight tomography for thickness reconstruction by breaking the assumption of the ray theory are investigated. As these errors are significant, the possibility of using the cutoff property of the high order modes is investigated in a frequency range where the ray theory is valid. It is found that the attenuation due to the scattering of the waves in corrosion is too large for this technique to work. Finally the use of low frequency guided wave for diffraction tomography is examined. Finite element simulations of a 64 element circular array on a plate show that when the scattering mechanism of the object to be reconstructed satisfies the Born approximation the reconstruction of the thickness is accurate. However the practical implementation is more challenging when the incident field is not known. Experimental results demonstrate that ultimately the scattering from the array of transducer is a major source of error in the tomographic reconstruction, but when there is no scattering from the array of transducers the reconstructions are very similar to the finite element simulations.

This thesis reports on results of a novel process to recover metals selectively by electrodeposition by pumping aqueous acidic chloride solutions produced by leaching of shredded waste electrical and electronic equipment (WEEE) through the potentiostatically controlled cathode of an electrochemical reactor. The WEEE solutions contained low concentrations of precious metals, including Ag, Au, Pd and high concentrations of Cu. Electrodeposition from low concentrations of such dissolved metals requires electrodes with high mass transport rate coefficients and specific surface areas to increase cross-sectional current densities and optimise capital and operating costs. Hence, to recover gold from solutions with concentrations < 10 mol m-3 in the WEEE leachate, a three-dimensional cathode was used consisting of a circulating particulate bed of 0.5-1.0 mm diameter graphite particles, on which (AuIIICl4 - + AuICl2 -) ions were reduced. The temporal decay of the solution absorbance of AuCl4 - ions at 312 nm was recorded on-line by a quartz flow cell connected to a UV-visible spectrophotometer using fibre optics, enabling its time dependent concentration to be determined in real time. Total dissolved gold concentrations were determined by Inductively-coupled Plasma Optical Emission Spectroscopy (ICP-OES). The results from the reactor experiments were modelled in terms of a mass transport controlled reaction in a plug flow electrochemical reactor operated in batch recycle with a continuous stirred tank reservoir. As copper is the dominant element in WEEE, and hence in the leach solution, its electrodeposition was investigated using an electrochemical reactor with a Ti/Ta2O5-IrO2 anode, cation-permeable membrane and a Ti mesh cathode in a fluidised bed of 590-840 μm glass beads to enhance mass transfer rates and to improve copper deposit morphologies. As for other metals, the effects were determined of cathode potential and solution flow rate on electrodeposition rates, charge yields, specific electrical energy consumptions, and deposit morphologies, imaged subsequently by scanning electron microscopy, and purities determined by X-ray fluorescence (XRF) and X-ray diffraction spectroscopy (XRD). While depleting CuII concentrations from 500 to 35 mol m-3, copper purities of > 99.79 %, as required for commercial purity Cu, were achieved with charge yields of 0.90 and specific electrical energy consumptions of 2000 kW h tonne-1. In addition, the circulating particulate bed cathode depleted solutions rapidly from 15 mol m-3 CuII ca. 100 ppm. Experiments with a rotating vitreous carbon cathode confirmed predictions from a kinetic model for a small electrode potential window within which to achieve selective electrodeposition of tin from synthetic SnIV-PbII aqueous chloride solutions, from which Pb could be electrodeposited subsequently. AlIII, FeII, ZnII and NiII remained in solution after the recovery of Au, Cu, Sn and Pb from the WEEE leachate. Unlike Al, it is possible to electrodeposit Fe from aqueous solution, and it was decided to add NaOH (+ air) to increase the pH to ca. 3.25 to precipitate ‘Fe(OH)3’, which was recovered by filtration. This option also enabled subsequent electro-co-deposition of Ni and Zn with high charge yields, as the higher pH decreased the driving force for H2 evolution. A one- dimensional mathematical model was developed in MAPLETM to predict the kinetics of Ni-Zn electro-co-deposition, which was validated experimentally. The model also considered the potential and concentration profiles in the cathode | electrolyte boundary layer for conditions in which migration and convective diffusion all contribute to overall transport rates, to predict the behaviour and optimize the process parameters of the electrochemical reactors.

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