Thesis (Ph. D.)--University of Wisconsin--Madison, 1982. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 53-54).

Thesis (Ph. D.)--University of Wisconsin, 1967. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (M.S.)--University of Wisconsin--Madison, 1968. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis--Wisconsin. / Includes bibliographical references (leaves 106-109).

Submitted by Marcele Costal de Castro (costalcastro@gmail.com) on 2017-12-14T13:31:22Z No. of bitstreams: 1 ROBERTO GOMES DE OLIVEIRA D.pdf: 3867483 bytes, checksum: 78ad2fbf8f7d233065438b4f60942947 (MD5) / Made available in DSpace on 2017-12-14T13:31:22Z (GMT). No. of bitstreams: 1 ROBERTO GOMES DE OLIVEIRA D.pdf: 3867483 bytes, checksum: 78ad2fbf8f7d233065438b4f60942947 (MD5) Previous issue date: 1969-05 / The analysis of pulsed neutron experiments in multiplying and in nonmultiplying domains is considered. The analysis is based on the one-dimensional diffusion theory modelo In one-group models, a scalar version of problems similar to those of Sturm Liouville systems is generated; while in multigroup models, a vector version is required. An algorithm is suggested which allows the complete solution of the general scalar problem in all separable geometries of interest, for homogeneous boundary conditions. The results are the time igenvalues and the spatial eigen functions. The algorithm is suitable for direct computer implementation. Examples of application are given. The multigroup problem can be solved by adequate extensions of the one-group algorithm. Since the associated operators are nonselfadjoint, the eigenvalues form in general a spectrum that has a discrete plus a continuous part. All of the discrete spectrum can be obtained using the suggested method. An example with two groups of neutrons in a three-region domain is given. Extensions to inhomogeneous equations and boundary conditions are considered. Application of the methods to other problems rather than the pulsed neutron problem are studied. The method is shown to be useful in the solution of nonlinear boundary-value problems. Pulsed neutron experiments can be analyzed as problems similar to Sturm-Liouville systems. The scalar problems are completely solved here. The vector problems are partially solved. Some progress in the mathematical theory of nonselfadjoint operators is required for the complete solution of the vector problem.

The effective diffusion coefficient of the binary gas pair, hydrogen and nitrogen, has been measured for diffusion through several types of porous solids. Electrical conductivities through the pore spaces of the same solids were also measured with a view towards testing the analogy between ordinary diffusion and electrical conductivity. The results obtained show some discrepancies (up to 25%) from exact equivalence, especially in porous solids with a mean hydraulic diameter of less than 1 micron. The diffusion apparatus was also used to determine the temperature dependence of the ordinary diffusion coefficient in the range 20 - 300°C. The results obtained show close agreement with the Hirschfelder, Bird and Spotz theoretical equation for non-polar gas pairs. The data were also compared with other values reported for this system and good agreement was found. It is therefore concluded that the flow apparatus used is satisfactory for the investigation of the temperature dependence of the binary diffusion coefficient. Calibration of the apparatus at one temperature will yield satisfactory absolute values for binary diffusion coefficients at other temperatures. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

Diffusion has been studied in a range of systems having intermediate phases in the diffusion zone. It has been found that in some systems (Ag-Sb, Ag-Se, Ni-Sb, Cu-Se and Cu-Sb) the diffusion rates are very sensitive to compressive stress, with a load of 100 psi making a significant difference to the width of the diffusion zone. In other systems (Cu-Zn, Cu-Sn and Al-Zr) stresses up to the maximum of 1500 psi had no effect on the diffusion rate. The growth rates of all phases in the pressure sensitive systems were found to be parabolic with time indicating diffusion control. In Cu-Se and Cu-Sb there was a nucleation time at the beginning of diffusion. However, growth of the phases in these systems was also found to be parabolic once this effect was accounted for. The effect of compressive stress was, generally, to increase the growth rate of one of the intermetallic phases. In Ag-Sb,- Ag-Se and Cu-Sb, there was a limiting stress above which growth rates of the intermediate phases were constant. Such a limiting stress was not observed in Ni-Sb and Cu-Se and the growth rates of the Ni_Sb_ and Cu^Se phases in these systems increased apparently linearly with applied stress. In experiments in which diffusion took place at low stress following an initial high stress anneal, it was generally found that the growth rate characteristic of the new stress was attained after long times of diffusion. In Cu-Se and Cu-Sb however, it was found that the stress-sensitive phases disappeared on ageing, although a finite growth was observed in the normal growth experiments. From the existing knowledge of diffusion theories, this particular phenomenon could not be explained. However, it is thought that this may possibly be due to a significant decrease in specific volume on formation of these phases. Non-appearance of certain stable phases predicted from the phase diagram has been attributed to their small diffusion coefficients. Hydrostatic tests were carried out to see if there was any difference in growth rates between uniaxial compressive stress and triaxial hydrostatic pressure. It was found in general that the growth rate under hydrostatic pressure was very similar to that for a compressive test of zero psi, indicating that applying a hydrostatic pressure does not have any effect on the growth rate and that only compressive loading is of any significance. All the stress-sensitive systems investigated showed a very large Kirkendall effect. The tungsten markers interfered with diffusion and the width of the diffusion zone adjacent to the markers was less than elsewhere. This gave rise to ledges of the pure metals with the tungsten wires being at the top of the ledges. The development of ledges was much greater in pressure sensitive systems than in other systems and could be attributed to slow lateral diffusion due to the lack of compressive stress in this direction. The experimental results can be explained on the basis of porosity which forms at a single interface in these systems owing to the large Kirkendall effect. This decreases the effective cross-sectional area of diffusion and so reduces the width of the diffusion zone. The effect of compressive stress is to decrease the amount of porosity and hence increase the effective interface area and the atomic flux into the diffusion zone. The limiting stress observed in Ag-Sb, Ag-Se and Cu-Sb was thus attributed to the complete absence of porosity in the diffusion zone. In Ni-Sb and Cu-Se it is believed that the pressure sensitive phases have very high growth rates and the maximum stress of 1500 psi was insufficient to obtain a good interface. All the other results can be explained satisfactorily by the mechanism suggested. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

The object of this thesis is to establish the diffusion coefficient of Na ion in PbCl2-NaCl mixtures and to compare its relationship to the other species.

No description available.

No description available.