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Dithiocarbamate-mediated nickel(II) uptake was studied in five cell lines: 1) cultured human B-lymphoblasts, 2) rabbit alveolar macrophages, 3) human peripheral lymphocytes, 4) human erythrocytes and 5) human polymorphonuclear leukocytes. Two different incubation protocols were employed: concurrent incubation of nickel(II) with the ligand, and sequential incubation of ligand followed by nickel(II) incubation. The effects of various experimental parameters such as ligand concentration, cell number and available nickel(II) concentration on nickel (II) uptake were examined for most of the above cell types. During concurrent incubations, the effect of ligand concentration on nickel (II) was maximum at 10⁻⁶ M sodium diethyldithiocarbamate (DDC) or ammonium pyrrolidinedithiocarbamate (APDC) for all cell types (except polymorphonuclear leukocytes). Enhanced uptake was evident at higher concentrations (≥ 10⁻³ M DDC or APDC) for sequential incubations. By contrast, ammonium dithiocarbamate (AD) had no enhancing effect on nickel(II) uptake in either protocol (tested only for human peripheral lymphocytes and human erythrocytes). Distribution studies indicated that enhanced cytosolic uptake of nickel(II) occurred for 10⁻⁷ - 10⁻⁵ M DDC. The observed effects on nickel (II) uptake of ligand concentration, Ni² concenration and cell number were interpreted on the basis of an 'Equilibrium Model' with several possible pathways. The nickel(II) uptake data were consistent with the possibility that ligand uptake precedes metal-ion uptake. The latter process may well involve the protonated form of the dithiocarbamate as an ionophore. As a means of enhancing cell-associated nickel(II), peripheral lymphocytes from nickel-sensitized and non-sensitized individuals were pretreated with APDC in veronal buffer. The transforming ability of these cells were then studied by use of a lymphocyte transformation (proliferation) test. This approach was not successful in enhancing the response to nickel (II) because of the inherent toxicities of the veronal buffer and APDC. / Thesis / Master of Science (MS)

A new technique for measuring doublet separation is described, and some recent mass spectroscopic measurements of the Ni60 mass are reported. The new value is compared with some previously reported values, and its effect on some existing discrepancies between mass spectroscopic and transmutation data is discussed. / Thesis / Master of Science (MS)

A computer model for diffusion-controlled internal precipitation was used to simulate the corrosion behavior of Ni-based superalloys in carburizing atmospheres. The model is based on Crank-Nicholson finite difference solution of the diffusion equation. The code also includes the ternary cross diffusion effect due to substitutional alloying elements that are preferentially oxidized. The model can treat two sets of boundary conditions corresponding to the presence or absence of a protective oxide scale. It accounts for internal precipitation of corrosion products whenever thermodynamic solubility limits are exceeded. Up to four different carbides can be treated simultaneously. The solubility product is computed for each reaction and the amount of carbon that reacts is removed from the diffusion process. Under non-protective conditions, the predictions of model were compared to carburization profiles obtained experimentally in H₂-CH₄ environment tests. Results are presented for the formation of Cr, Mo, Ti, W, and Nb carbides in Ni-based superalloys. The predicted corrosion profiles are in qualitative agreement with experimental data. / Master of Science

[Truncated abstract] The study of NiTi shape memory alloys, although comprehensive and diverse, still encounters numerous uncertainties and misunderstandings that often jeopardise the effective use of these alloys in various applications. One such key area is the understanding of the micromechanics and thermodynamics of the deformation mechanisms, such that their deformation behaviour can be accurately predicted and modelled. Furthermore, most research involves polycrystalline NiTi of varying compositions and processing history, both of which complicate and damage the internal structure of the matrix even before deformation. This work aims to study the micromechanisms of deformation of near-equiatomic NiTi alloys, both in polycrystalline and single crystal forms, with particular attention given to the commonly observed phenomena of Luders-like deformation behaviour and deformation induced martensite stabilisation. This work was carried out in three sections. Firstly, the tensile deformation of polycrystalline NiTi samples via martensite reorientation and stress-induced martensitic transformations was carried out. The samples were deformed to various stages of deformation and then thermally cycled to study the thermomechanical response to deformation as a means to explore the various mechanisms of deformation. Next, the deformation and post-deformation transformation behaviour of NiTi single crystals were studied to verify the effect of grain boundaries and other hypotheses raised regarding the deformation mechanisms. The single crystal samples were deformed along three low-index axial orientations. Finally, microscopic analysis was carried out on as-annealed and the deformed polycrystal and single crystal samples by means of transmission electron microscopy. The microstructural analyses accompanied the thermodynamic study and provided evidences to support various hypotheses