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Gold used to be regarded as catalytically inert until about 20 years ago when it was shown that supported gold clusters < 5 nm in diameter exhibited some unique catalytic properties. Based on this revelation, several studies have demonstrated the feasibility of reactions previously thought of as impossible on gold. The ability of gold to oxidize CO below ambient temperatures at rates higher than conventional CO oxidation catalysts (Pd and Pt) has been shown to hold potentials for technological applications. Extensive past and on-going research are geared towards elucidating the mechanistic details of this reaction. The nature of the active sites, the effect of the supports and the effect of moisture are still debated in literature. I therefore present some experimental results supported with density functional theory calculations to shed additional light on some of the issues concerning gold catalysis in general, and low temperature CO oxidation in particular. Previous studies of the effect of moisture on oxide-supported gold reported that although water promotes CO oxidation on this surface by as much as two orders of magnitude, it is only a spectator molecule on the surface. I present here evidence for strong water-oxygen interactions when water is co-adsorbed with atomic oxygen on Au(111). Impinging a CO beam on the surface co-adsorbed with oxygen and water produces water-enhanced CO oxidation. Based on these results, I propose that CO reacts with hydroxyls formed from water-oxygen interactions to form CO₂, similar to a previous observation on Pt(111). Exposing a Au(111) surface pre-covered with ¹⁶O to isotopically labeled carbon dioxide (C¹⁸O₂) showed that ¹⁶O¹⁸O (m/e = 34) was produced from carbonate formation and decomposition. Estimates of reaction probability and activation energy gave ~ 10⁻⁴ - 10⁻⁵ and -0.15 eV respectively. The effect of annealing on the reactivity of oxygen pre-covered Au(111) was investigated using water, carbon monoxide and carbon dioxide as probe molecules. Precovering Au(111) with atomic oxygen followed by annealing resulted in surfaces that were less reactive towards water, CO and CO₂. Annealing is believed to stabilize the reactive metastable oxygen thereby increasing the barrier to reaction similar to what is reported on other surfaces. / text

The accumulation of undesired matter at heat transfer surfaces (fouling) is a severe problem to industry. The growth of calcium sulphate dihydrate on heated metal surfaces has been examined and a mechanism for the effect of surface roughness on the amount of deposition has been proposed. A novel piece of equipment was designed and constructed in which the growth of crystals on heat transfer surfaces with different surface roughnesses could be observed under controlled solution conditions. The test section was a transparent rectangular channel into Rhich three 25 mm diameter test pieces could be inserted such that the polished faces were planar with the rear face of the channel. The back faces of these test pieces were heated by contact with hot Mater. Using Reynolds numbers of 300 to 13,500 and calcium sulphate 2+ solutions with bulk concentrations from 20 to 50 mH Ca , no gross effect due to surface roughness was seen. However a limited effect, which distinguished grit-blasted surfaces from polished surfaces, was 2+ found in experiments with a bulk concentration from 28 to 33 mH Ca . In all of the experiments it was observed that the presence of bubbles enhanced crystal growth. It was also found that the amount of deposition formed on any surface decreased with decreasing dissolved oxygen content of the bulk solution. It is suggested that a bulk concentration of approximately 33 mH 2+ Ca is a critical level of supersaturation, which corresponds with the so-called metastable limit of supersaturation. The surface roughness effect may be associated with two factors. Firstly, as the critical supersaturation is approached crystal growth is enhanced at certain sites. in particular the edges of bubbles. Secondly, very rough surfaces. such as grit-blasted surfaces. more readily support and initiate bubble formation and consequently the grit-blasted surface shows greater growth. Additional work with a different test rig. using a stagnant solution, indicated that suppression of bubble formation during an experiment, either by initially degassing the surface or by pressurising the system, decreased the amount of crystal growth. This work suggests that a surface roughness effect exists which is related to the presence of bubbles at the surface. Consequently the amount of deposition can be decreased either by controlling the formation of the bubbles (e.g. by completely degassing both the solution and the surface. and pressurising the system). or by polishing the surface. However. the surface roughness effect was most apparent between the very coarse, grit-blasted surfaces (R ~ 2.90 um) and the a medium finish 180 or 240 Grit surfaces (R ~ 0.23 um). a Little or no further improvement was obtained in polishing to a mirror finish. i. e. 0.25 or 0.1 um (R ~ 0.03 um). a further polishing beyond removing gross roughness would not appear to Therefore. for industrial purposes, yield sufficient benefit to justify the large cost involved. It is recommended that further work be undertaken to determine whether the deposition which occurs in the absence of bubbles is influenced by the surface roughness, and whether other chemical system and surfaces behave similar to the calcium sulphate - stainless steel system studied in this work. Moreover, additional work should be undertaken to examine the effect of surface physical properties on crystal and bubble nucleation and growth.

Digital heterodyne methods are employed in conjunction with periodic fringe projection to produce a fast automated surface relief measurement technique. A method of sampling the image with a solid state detector array which produces a moire fringe image free of the noise terms normally present with moire techniques is presented along with an extension to Whittaker-Shannon sampling theory to cover the moire aliasing phenomena. The limitations imposed on the surface slopes by the requirement that the properly moire sampled image spectra must be confined to a moire interval are given. Moire sampling allows an optical processing step (removal of the reference surface tilt), while classical nonaliased sampling produces the same information with respect to a tilted surface. General additive noise is analyzed as regards both integrating bucket and phase stepping algorithms and yields a signal to noise ratio dependent error with twice the frequency of the fringes for some algorithms. A phase averaging technique which eliminates these oscillatory errors as well as those caused by reference phase shift errors in all the algorithms is demonstrated. Both parallel and divergent geometries are discussed. The feasibility is experimentally demonstrated with results for the parallel case based on a system composed of commercially obtainable components.

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published_or_final_version / abstract / toc / Physics / Master / Master of Philosophy

published_or_final_version / Electrical Engineering / Master / Master of Philosophy

published_or_final_version / Physics / Master / Master of Philosophy