The chemical reactivity of a solid is influenced to a marked degree by the presence of imperfections or defects in the solid. Bond strengths are considerably weaker at points of imperfection than elsewhere in the solid, and hence the initiation of reaction is favoured at these sites due to the relative ease of bond rupture. Line defects, such as edge or screw dislocations, jogs, Smekul cracks etc, are of prime importance in such changes. The surface of a solid or in intergranular boundaries, where a state of strain exists, are also favourable places for the initiation of a reaction, Point defects e.g. vacancies or interstitialions or atoms also play important roles in chemical change, often in conjuction with line defects.

Philosophiae Doctor - PhD / Low thermal conductivity is a primary limitation in the development of energy-efficient heat transfer fluids that are required in numerous industrial sectors. Recently submicron and high aspect ratio particles (nanoparticles and nanotubes) were introduced into the heat transfer fluids to enhance the thermal conductivity of the resulting nanofluids. The aim of this project was to investigate the physico-chemical properties of nanofluids synthesized using submicron and high aspect ratio particles suspended in heat transfer fluids. / South Africa

Thesis (DTech( Mechanical Engineering)-- Cape Peninsula University of Technology, 2014 / Magnetohydrodynamic (MHD) boundary layer flow of an electrically conducting viscous incompressible fluid with a convective surface boundary condition is frequently encountered in many industrial and technological applications such as extrusion of plastics in the manufacture of Rayon and Nylon, the cooling of reactors, purification of crude oil, textile industry, polymer technology, metallurgy, geothermal engineering, liquid metals and plasma flows, boundary layer control in aerodynamics and crystal growth etc. Nanofluid is envisioned to describe a fluid in which nanometer-sized particles are suspended in conventional heat transfer base fluids to improve their thermal physical properties. Nanoparticles are made from various materials, such as metals (Cu, Ag, Au, Al, Fe), oxide ceramics (Al2O3, CuO, TiO2), nitride ceramics (AlN, SiN), carbide ceramics (SiC, tiC), semiconductors, carbon nanotubes and composite materials such as alloyed nanoparticles or nanoparticle core–polymer shell composites. It is well known that, conventional heat transfer fluids, such as oil, water, and ethylene glycol, in general, have poor heat transfer properties compared to those of most solids. Nanofluids have enhanced thermophysical properties such as thermal conductivity; thermal diffusivity, viscosity and convective heat transfer coefficients compared with those of base fluids like oil or water. Owing to their enhanced properties, nanofluids can be used in a plethora of technical and biomedical applications such as nanofluid coolant: electronics cooling, vehicle cooling, transformer cooling, computers cooling and electronic devices cooling; medical applications: magnetic drug targeting, cancer therapy and safer surgery by cooling; process industries; materials and chemicals: detergency, food and drink, oil and gas, paper and printing and textiles.

Thesis (MTech (Chemical Engineering))--Cape Peninsula University of Technology, 2012. / Emulsion explosives are classified as highly concentrated Water-in-Oil emulsions with an internal phase volume fraction of approximately 94%, i.e. far beyond the close packing limit of spherical droplets of 74%. These emulsions are thermodynamically unstable compounds and their instability is related to the crystallisation in the dispersed phase, which is a supersaturated solution of ammonium nitrate salt in water. This presents a problem, because the emulsion weakens or becomes unstable, which results in droplet crystallisation, so that the explosive generally loses at least some of its sensitivity to detonation. Considerable effort has been applied to the improvement of emulsion stability by explosive manufacturers, but important aspects such as the effect of salt and surfactant content/type in emulsions are not fully understood and described in the literature. The purpose of this study was to investigate these shortcomings and to focus on the effect of surfactant nature and concentration and electrolyte concentration/type on the interfacial properties and interactions in emulsion explosives. Interfacial properties (interfacial tension and interfacial elasticity), thermal behaviour (freezing temperatures) of emulsions and rheological aspects (viscoelastic and flow properties) were investigated in terms of surfactant-electrolyte interactions.

Vidros boratos contendo óxidos modificadores vêm sendo estudados por apresentarem um número atômico efetivo próximo ao do tecido humano, o que os tornam materiais interessantes para o desenvolvimento de dosímetros termoluminescentes. O objetivo deste trabalho foi estudar as propriedades térmicas e estruturais do sistema xCaB4O7-(100-x)CaB2O4, com x variando de 0 a 100 % em massa. As amostras sem dopantes foram previamente estudadas a fim de determinar uma composição que apresentasse a melhor resposta termoluminescente (TL) para a inclusão do íon Dy como dopante e Li como co-dopante, aumentando a eficiência TL da mesma. Pelo método de fusão e moldagem, foram obtidos amostras vítreas e vitrocerâmicas. A fase cristalina presente nas amostras vitrocerâmicas foi determinada por difratometria de raios X e identificada como fase única CaB2O4. A composição vitrocerâmica 20CaB4 (% em massa) apresentou a melhor resposta TL, sendo dopada com Dy e co-dopada com Li para o estudo das propriedades dosimétricas. Este estudo mostrou uma resposta linear num intervalo de 5 a 70 minutos de exposição à radiação ultravioleta e uma boa reprodutibilidade do sinal TL provando ser um material promissor para a utilização em dosimetria pessoal e clínica. / Borate glasses containing modified oxides have been studied on account of their effective atomic number close to that of the human tissue, what makes them interesting materials for the development of the thermoluminescent dosimeters. The purpose of this work was to study the thermal and structure properties of the xCaB4O7-(100-x)CaB2O4 system with x ranging from 0 to 100 wt%. The undoped samples were previously studied in order to determine a composition that would present a better thermoluminescent response for the incluision of the Dy íon as dopant and Li as co-dopant, thus increasing its TL efficiency. By the melting/molding method, the glass-ceramic samples was determined by the X-ray difractometry and identified as a unique CaB2O4 phase. The glass-ceramic 20 CaB2O4 (wt%) composition presented the best TL response being doped with Dy and co-doped with Li for the study of the dosimetric properties. This study has shown a linear response within an interval of 5 to 70 minutes of exposure to the UV radiation and good reproducibility of the TL signal, thus proving to be a promising material for using in the personal and clinical dosimetry.

Submitted in fulfillment of the requirements for the degree of Doctor of Technology: Chemistry, Durban University of Technology, Durban, South Africa, 2017. / The thermodynamic properties of mixtures involving ionic liquids (ILs) with organic acid (acetic acid or propanoic acid) or acetonitrile at different temperatures were determined. The ILs used were imidazolium-based: 1-ethyl-3-methylimidazolium ethyl sulphate [EMIM]+[EtSO4]-, 1-butyl- 3-methylimidazolium thiocyanate [BMIM]+[SCN]- and 1-butyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide ([BMIM]+[Tf2N]-. The ternary excess molar volume (V E ), isentropic compressibility (ks) and deviation in isentropic compressibility ( ks123 ) were determined for four ternary liquid mixtures of {[EMIM]+[EtSO4]- or [BMIM]+[SCN]− + acetic or propionic acid + acetonitrile} at different temperatures (293.15, 298.15, 303.15, 308.15 and 313.15) K and at a pressure of 0.1 MPa with aid of the experimental density (ρ), speed of sound (u) data. The calculated data were correlated by using the Cibulka equation with the help of Redlich–Kister parameters obtained from fitting the Redlich–Kister equation for the corresponding binary systems. Furthermore, the density and speed of sound were also measured for eight corresponding binary systems at the same experimental conditions. The binary excess molar volume, isentropic compressibility and deviation in isentropic compressibility were also calculated for measured systems and fitted to the Redlich–Kister equation to obtain the Redlich–Kister parameters as well as to check the accuracy of measured data which were used to correlated experimental data using Cibulka equation. These results were discussed, in terms of how the sign and magnitude of thermodynamic functions were influenced by the addition of a third component to liquid systems. Also, the possible molecular and pair-wise interactions between component molecules and the effect of temperature on the thermophysical and thermodynamic properties were predicted. In addition, the work focussed on application of ([BMIM]+[Tf2N]-) ionic liquid for the separations of (alkane/aromatic), (alkane/alk-1-ene), (cycloalkane/aromatic) and (water/alkan-1-ol) using gas- liquid chromatography (GLC) technique. The activity coefficients at infinite dilution, , for 31 organic solutes (alkanes, cycloalkanes, alkenes, alkynes, aromatics, alkanol and ketones) and water in ionic liquid were measured at temperatures of (323.15, 333.15, 343.15, 353.15 and 363.15) K. Stationary phase loadings of (42.83 and 68.66) % by mass were used to ensure repeatability of E , measurements. Partial molar excess enthalpies at infinite dilution, H1 , were also determined. The selectivities, S , and capacities, k , were determined for the above separations. The separating ij j ability of the investigated ionic liquid was compared with previously investigated ionic liquids and industrial solvents such as sulfolane, n-methyl-2-pyrrolidine (NMP) and n-formylmorpholine (NFM). The results obtained suggested that in general, the [BMIM]+[Tf2N]− had outperformed the conventional solvents such as sulfolane, NMP and NFM in terms of selectivity, while the [BMIM][Tf2N] had in general, performed better overall when the performance index was used for comparison. / D

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The thermal decomposition of silver permanganate, pre-irradiated in BEPO and in a ⁶°C₀ Ϫ 'hot spot' has been investigated in the temperature range 100 - 125°C. The results are similar to those for irradiated KMn0₄ and the mechanism proposed for the latter is again suggested. The activation energy for the migration of point defects over the induction period is 1.03 ev. The decompositions of unirradiated and irradiated crystals differ in that the latter undergo physical disintegration over the acceleratory period. X-ray studies immediately prior to disintegration show strain and fragmentation in the irradiated crystal. An explanation involving the annealing of point defects at dislocation is advanced to explain the changes produced in the p/t plots with increased dosage, and fixed decomposition temperature. Summary, p. 94.

The thermophysical properties of supercritical CO₂ and H₂O-CO₂ mixtures are reviewed and their computation and prediction improved through theory and experiment. A resolution is attempted among inconsistencies between and within data sets, including P-V-T measurements, phase equilibrium experiments and equations of state. Pure carbon dioxide: Equations of state for CO₂ (Kerrick & Jacobs, 1981; Bottinga & Richet, 1981; Holloway, 1977) are based solely on P-V-T data up to 8 kbar and lead to deviations from phase equilibrium data at pressures greater than 10-20 kbar. Mathematical programming analysis has been applied to the fitting of parameters for an equation of state using simultaneously constraints from phase equilibrium and P-V-T data. Phase equilibrium data up to 42 kbar are used to define a feasible region for the adjustable parameters in free energy space. Each half-bracket places an inequality constraint on the fugacity of CO₂ provided the thermophysical properties of the solid phases are known. Except for magnesite thermophysical data from the mineral data base of Berman (1988) were used. A least squares objective function served to optimize parameters to P-V-T data. The enthalpy of formation of magnesite was revised on the basis of recent low pressure phase equilibrium experiments by Philipp (1988) to —1112.505 kj/mole. Piston-cylinder experiments were performed to constrain the equilibrium magnesite ⇌ periclase + CO₂ at high pressure. The equilibrium boundary is located at 12.1(±1) kbar, 1173-1183 °C (±10), and at 21.5(±1) kbar, 1375-1435 °C (±10). A van der Waals type equation of state with five adjustable parameters has been developed for CO₂. The function is smooth and continous above the critical region, behaves well in the high and low pressure limits, and the calculation of ʃ VdP for free energy does not require numerical integration. Computed free energies are consistent with all phase equilibrium data at high pressure, and computed volumes agree reasonably with P-V-T measurements. The proposed equation is: [ Equation omitted ] with B₁ = 28.0647, B₂ = 1.7287.10⁻⁴, B3 = 83653, A₁ = 1.0948.10⁹, A₂ = 3.3 7 47.10⁹, and R = 83.147, in units of Kelvin, bar and cm³/mole. The equation is recommended up to 50 kbar and above 400 K with reasonable extrapolation capabilities. A FORTRAN source code to evaluate the volume and fugacity is provided. Thermophysical properties for the calcium carbonate polymorphs calcite-I, IV, V, and aragonite were derived that are consistent with phase equilibrium experiments. Data required for further improvement include high pressure phase equilibria involving CO₂, constraints on the thermal expansion of magnesite, and P-V-T data to resolve inconsistencies among existing measurements. Water-carbon dioxide mixtures: The two widely used equations of state for H₂O-CO₂ mixtures are those proposed by Kerrick & Jacobs (1981) and by Holloway (1977)-Flowers (1979). Evaluation of existing equations and data is difficult due to inconsistencies among experimental studies. P-V-T-X data by Franck ＆ Todheide (1959) are inconsistent with data by Greenwood (1973) and Gehrig (1980), and cannot be reconciled with measured phase equilibria in H₂O-CO₂ fluid mixtures. Data by Greenwood and Gehrig are in loose agreement but extend only to 600 bar and do not constrain activities at higher pressures. A procedure is developed for using experimental phase equilibrium constraints to put limits on the fugacities of components of the fluid mixture. Inconsistencies among phase equilibrium studies are discussed. It is concluded that the data base available is not yet adequate to derive a reliable equation of state for H₂O-CO₂ mixtures. Future work must include P-V-T-X measurements to 8 kbar and phase equilibrium studies to resolve inconsistencies. These can constrain deviations from ideal mixing in the fluid phase, and constrain specific volumes at high pressures where P-V-T-X data connot be obtained. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate