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Thesis (Ph. D.)--Lehigh University, 2001. / Includes vita. Includes bibliographical references (leaves 220-228).

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Understanding the behaviour of actinide species is of importance when removing and processing all nuclear waste. Examples include the safe clean-up of contaminated waste ponds and aspects of the TALSPEAK (Trivalent Actinide-Lanthanide Separation by Phosphorus Reagent Extraction from Aqueous Komplexes) process. The chemistry of the ponds and the TALSPEAK process has been studied by probing the aqueous solution behaviour of Ln(III), Am(III), Cm(III) and Th(IV) ions in the presence of organic (EDTA4- (ethylenediamine tetraacetate), DTPA5- (diethylenetriamine pentaacetate) and lactate) and inorganic (CO32- (carbonate) and OH- (hydroxide)) ligands by a variety of techniques including Nuclear Magnetic Resonance (NMR), Ultra Violet-Visible (UV-Vis) and luminescence spectroscopies, as well as potentiometry. Various ternary complexes have been shown to exist, including [M(EDTA)(CO3)]3-(aq), (where M = LnIII, AmIII or CmIII) and [Th(EDTA)(CO3)2]4-(aq), which form approximately over the pH range 8 to 11, and also [M(EDTA)(lactate)]2-(aq) (where M = Ln(III) or Am(III)) and [Th(EDTA)(lactate)]-(aq), which predominantly occur over the pH range 4 to 6. The nature of lactate interaction with [M(DTPA)]2-(aq) complexes (where M = Ln(III) or Am(III)) is unclear, as it may be possible that lactate can coordinate directly to the metal ion or to the acetate groups of DTPA5- (via a H-bonding interaction). The knowledge gained in this research has given a deeper insight into the nature of lanthanide and actinide coordination chemistry in mixed-ligand environments. For example, the increasing solubility of actinide metal ions in the contaminated waste ponds is probably due to the ability of organic ligands present in the ponds to solubilise metal ions at high pH, and also under TALSPEAK conditions of pH 3.5, there is likely to be minimal interaction of lactate with the [Ln(DTPA)]2-(aq) complexes. The determination of metal ion speciation using a combination of NMR, UV-Vis and luminescence spectroscopies, coupled with potentiometry, could be applied to new characterisation challenges faced in the future of the nuclear industry.

An integral quadratic form is said to be strictly regular if it primitively represents all integers that are primitively represented by its genus. The goal of this dissertation is to extend the systematic investigation of the positive definite ternary primitive integral quadratic forms and lattices that are candidates for strict regularity. An integer that is primitively represented by a genus, but not by some specific form in that genus, is called a primitive exception for that form. So, the strictly regular forms are those forms for which there are no primitive exceptions. Our computations of primitive exceptions for each of the 119 positive definite regular ternary forms which lie in multiple-class genera, and of the companion forms in their genera, show that there are 45 inequivalent such forms that are candidates for strict regularity. We provide a proof of the strict regularity of one of these candidates, bringing the total number of forms for which such proofs are known to 15, and prove partial results on the integers primitively represented by the other form in its genus. The theory of primitive spinor exceptional integers is used to analyze the primitive exceptions for the forms in two other genera known to contain a regular ternary form. In these cases, results are obtained relating the primitive representation of certain integers c by a given form in one of these genera to the primitive representation of the integers 4c and 9c by the forms in the genus.

Abstract The main focus of this work was on exploratory preparation of thermoelectric materials and analyses of their physical properties. A thermoelectric material is capable of converting heat to electricity or vice versa. Usually, narrow band gap semiconductors are good candidates for thermoelectric applications, because such materials have large Seebeck coefficient, reasonably high electrical conductivity and low thermal conductivity. In this work, two different systems were studied, ternary layered tellurides and quaternary derivatives of Tl9BiTe6. I tried to prepare Pb1−xBi2+xTe4 with x = 0.30, 0.10, −0.10 and = 0.30 and Pb1−xBi4+xTe7 with x = 0.15, 0.00, −0.15 and −0.35, and two pure compounds, Pb0.8Bi2.2Te4 and Pb0.9Bi2.1Te4 were obtained. Powder X-ray diffraction was used to confirm the purity of the compounds, and physical properties were measured on cold-pressed samples with densities around 80% of the theoretical value. The figure of merit of the ternary tellurides is comparable to the published values of PbBi2Te4 (0.5 at 600 K). I also investigated the quaternary series Tl8.67PbxBi1.33−xTe6 with x between 0.50 and 1.00. The purity was confirmed by powder X-ray diffraction data, and physical properties were measured on Spark Plasma Sintered (SPS) samples. Low thermal conductivity was observed as well as competitive power factors. The highest ZT value was 0.57 for the compound Tl8.67Pb0.60Bi0.73Te6 at 575 K.

Solid-liquid equilibrium in isomorphous amino acid systems has been investigated as a model for systems that form solid solutions. Solid- and liquid-phase compositions in L-valine + L-leucine, L-valine + L-isoleucine, and L-isoleucine + L-valine in water were measured over the entire range of solid composition, and it was shown (from mass balance and phase rule considerations) that these systems form solid solutions. The solid- phases resulting from isothermal and cooling crystallization experiments were also investigated using powder x-ray diffractometry which showed that homogeneous solid solutions could only be obtained in cooling crystallization experiments, whereas isothermal experiments generally produced inhomogeneous solids. This suggests that data reported in the literature from isothermal experiments may not represent true equilibrium values. Solid-phase activity coefficients were estimated using binary and ternary equilibrium data and the UNIFAC-Kuramochi model for liquid-phase nonidealities. The solid phases in the three systems investigated exhibited significant nonidealities that were correlated using the Margules model. The model parameters exhibited a linear relationship with the ratio of binary solubilities of the two solutes. Such simple relationship may be advantageous when solid-liquid equilibrium of thermally unstable solutes or components with unknown physical properties are crystallized.

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