Surfactants from the 'Triton' range, manufactured by Rohm and Haas, Germany, were used to study the adsorptive behaviour of non-ionic surfactants (of the alkyl polyoxyethylene type) from aqueous solution onto mineral oxide surfaces. The oligomeric distributions of the surfactants were characterised using the HPLC technique. Two gradients were used: a normal phase gradient was used to study the surfactants from non-aqueous solution; an unusual gradient, which could not be definitively categorised as either normal or reversed phase and which was developed at Brunel, was used to analyse surfactants directly from aqueous solution. Quartz was used as a model mineral oxide surface. The quartz surface was characterised using a range of techniques: scanning electron microscopy (SEM), X-ray photoelectron spectroscopy, X-ray fluorescence -analysis, Fourier transform-infra red spectroscopy and BET analysis. It was found that washing the quartz with concentrated HCI removed any calcium ions present on the surface and also removed 02- ions. Calcining the sample removed carbonaceous materials from the surface and also caused a decrease in the surface area. The quartz was shown to be non-porous by SEM and BET analysis. The adsorption experiments for this study were carried out using a simple tumbling method for which known ratios of surfactant in aqueous solution and quartz silica were mixed together for a known length of time. The amounts of surfactant present were measured using ultra-violet analysis and the HPLC techniques mentioned above. It was found that the smallest oligomers were adsorbed the most. An addition of salt to the system caused an overall increase in adsorption of the bulk surfactant, and increase in temperature caused an initial decrease in adsorbed amounts before the plateau of the isotherm and a final increase in bulk adsorption at the plateau of the isotherm. The oligomeric adsorption generally appeared to mirror the behaviour of the bulk surfactant. Atomic force microscopy (AFM), dynamic light and neutron scattering studies were used to analyse the character of the adsorbed surfactant layer. It was shown that the layer reached a finite thickness that corresponded to a bilayer of adsorbed surfactant. According to AFM data, this value of thickness was not consistent over the whole of the quartz surface.

This thesis evaluate the state of art ROHM SCT3080KR silicon carbide mosfet in a synchronous buck converter. The converter was using the ROHM P02SCT3040KR-EVK-001 evaluation board for driving the mosfets in a half bridge configuration. Evaluation of efficiency, waveforms, temperature and a theoretical comparison between a silicon mosfet (STW12N120K5) is done. For the efficiency test the converter operate at 200 V input voltage and 100 V output voltage at output currents of 7 A to 12 A, this operation was tested at switching frequencies of 50 kHz, 80 kHz and 100 kHz. The result of the efficiency test showed an efficiency of 98-97 % for 50 kHz, 97.7-96.4 % for 80 kHz and 97-96.2 % for the 100 kHz test. The temperature test shows a small difference in comparison of the best case scenario and the worst case scenario, temperature ranges from 25.5 to 33.5 °C for the high side mosfet while the low side mosfet temperature ranges from 29.8 to 35 °C. The waveform test was conducted at 50 kHz and 100 kHz for output currents of 4 A and 12 A (at 200 V input and 100 V output). The result of the waveform test shows a rise and fall time of the voltages in range of 10-12 ns while the current rise and fall time was 16 ns for the 4 A test and 20 ns for the 12 A test. Overall SiC mosfet show a clear advantage over silicon mosfet in terms of efficiency and high power capabilities.