No description available.

No description available.

This thesis concerns work on the structure solution and prediction of novel inorganic compounds, with specific focus on compounds that show potential use in commercial applications. The ability to predict structures at the atomic and molecular scale is a challenge at the forefront of inorganic and materials chemistry. Complex functional transition metal oxides can generally be described in terms of modules containing elements in particular chemical environments. This observation has led to the development of the Extended Module Materials Assembly (EMMA) approach for the generation of plausible candidate structures. The EMMA method is extended in this project to examine hexagonal perovskites and is first applied to Ba(Co,Nb)1-dO3, examining known structures to facilitate the discovery of new structures within the structural series. In the second instance, the EMMA method is applied to Ba3Nb2O8, which has an unconfirmed structure experimentally. It is in this case that the advantages and disadvantages of the EMMA method become increasingly apparent, with structures identified in the initial screening using classical lattice dynamics becoming less stable when re-ranked with density functional theory. Moving away from the EMMA method, a mixed system of LiMgPO4 and Li2MgSiO4 is investigated based on Monte Carlo site-swapping in an ideal oxide lattice. As with the EMMA approach, this method has several advantages and disadvantages, with successes seen for some compositions but not in others. The results in this thesis demonstrate the difficulty in rising to the challenge of crystal structure prediction and the exciting avenues that can be explored to help find answers. It is hoped that the work in this thesis can be built on in the future, through optimisation of the above methodologies and experimental synthesis of predicted compounds.

The dehydration reactions of the calcium sulphate hydrates have been studied at temperatures in the range 68-217 °C and under partial pressures of water vapour in the range 10-5 - 360mm of Hg. The reactions were found to be dependant on the partial pressure of water vapour surrounding the samples and the activation increased as the water pressure increased. The dehydration products have been shown to vary depending on the reaction conditions.

No description available.

No description available.

No description available.

This thesis is divided into three sections, an Introduction, the Experimental Section and finally the Discussion where the findings from the experiments have been analysed and discussed. The Introduction deals with the mechanisms of ester hydrolysis and the factors which affect its rate. This is then followed by a section dealing with surface active agents, where the basic concepts of micelle physical chemistry, including the structure of micelles, the CMC, the shape, size, and solubilisation are considered together with the factors affecting these parameters. The theories dealing with micelle formation and the effect of micelles on reaction kinetics with special emphasis on reactions involving cationic surfactants, particularly cetyl-trimethylammonium bromide (CTAB), are then reviewed. The experimental work describes the methods by which CMCs under various sets of conditions were determined. This is then followed by details of the kinetic investigations into the effect of CTAB on the base catalysed hydrolysis of p-nitrophenyl acetate. Kinetic studies were carried out in the absence of buffer at pHs between 8.0 and 9.2 using a pH-stat technique as well as in the presence of buffer at pH 9.2 and the results are compared. Below the CMC at pH 9.2 retardation in the rate was noticed which was associated with pre-micellar aggregation; this was not the case at lower pHs. CTAB above its CMC increased the rate of hydrolysis of the ester in all the cases up to a maximum in the region of 8.5 - 9.6 x 10 -3M surfactant and then the effect decreased. Changes in micellar structure in this critical region were evidenced by light scattering and viscosity studies but no change in counter-ion binding as measured by bromide activity was observed. The rate of hydrolysis in the presence of CTAB was found to be independent of the ester concentration giving support to the idea of constant partitioning. Potassium bromide was found to be a much more potent inhibitor of CTAB catalysis than the buffer of various strengths studied. The final section deals with the discussion of the experimental results obtained. The main conclusion drawn is that the mathematical model proposed by Winterborn et at (141) and Shetewi (67) is not suitable for this system where the surfactant accelerated the reactions. The qualitative model proposed by Cordes et at (10,11) based on competitive inhibition and counter-ion concentration also does not explain the maximum in the critical concentration region of CTAB satisfactorily. The change in the micellar structure in the region around 10-2M CTAB is however suggested as the precise reason for the change in surfactant effect at this concentration.

The anomalous dispersion associated with about 20 absorption lines relating three of the four (n+1) s and the ten (n+1) p levels in the first spectra of neon, argon and krypton has been quantitatively examined by means of the "hook method" in which a low pressure, low current discharge has been used in conjunction with a stigmatised Eagle spectrograph and a Mach-Zehnder interferometer. Details of the design, construction and adjustment of the latter are given. Argon has been most thoroughly considered but relative oscillator strengths and transition probabilities for lines with a common lower level are presented for each of the three gases. Values of these quantities relative to that of one line have been obtained by combining the anomalous dispersion data with the population relations derived from relative intensity measurements. Absolute values have been estimated by fixing an absolute f-value for this reference line from f-sum rule considerations'. Agreement has been obtained with previous results where they exist. The rather different configuration of the energy states of krypton as compared with neon and argon has been reflected in the appearance of • anomalous dispersion in a much smaller proportion of the equivalent s - p lines. Transition probabilities are given for eight krypton lines. The relative populations of the s states have been considered both on the grounds of the relative intensity measurements and from the f-sum data. A mean specific excitation temperature relating the s and ground levels has been evaluated in each case, and, together with reversal temperature studies in the case of argon, has shown the general absence of thermodynamic equilibrium in the plasma.

The first part of the thesis is a review of the literature related to the analytical chemistry of bismuth. The second part of the thesis is en account of the practical work carried cut by the candidate and is divided into three sections. Section one describes the critical investigation and modification of the gravimetric phosphate method era an investigation of volumetric E.P.T.A. methods far the determination of bismuth. Section two describes the work carried out on methods of separation. The general methods of separation investigated were the volatilisation, of bromides from perchloric acid solutions and the precipitation of bismuth as oxybromide, metal and sulphide. Several methods of separation are described for specific elements, e.g. the precipitation of tellurium by means of a mixture of hydrasine and sulphur dioxide. Section three describes methods for the analysis of alloys and ores. Some results obtained by these methods are reported. The behaviour of some elements present in complex materials has been followed by a semi-quantitative spectrographic method. The separations and the preparation of the samples were carried out by the candidate, but the actual spectrographic analysis was performed by Mr P.E. Croft under the candidate's supervision. The final part of this section is a critical discussion of the methods developed. In Appendix I are mentioned some methods that were cursorily examined but were abandoned for the reasons that are given.In Appendix II are given the calibrations of the weights and the volumetric glassware used. The weight-history of two porous-based Berlin porcelain crucibles aver a period of two yearn in also recorded. The final pages contain the bibliography.