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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Precipitation and fracture in a ferritic stainless steel

Scott, Adam James Lidstone January 2000 (has links)
Includes bibliographical references. / A dual stabilised ferritic stainless steel with titanium and niobium additions had been experiencing failures during production. Following hot rolling and cooling while coiled and prior to annealing, the steel had been prone to shattering across its width during uncoiling. This project was initiated by the manufacturers, Columbus Stainless, so that the present understanding of this stainless steel could be expanded, with the ultimate aim of avoiding production losses. This stainless steel is designed for high temperature use in automotive exhaust systems. This requires a good blend of hot strength, creep and corrosion resistance. The composition (notably the niobium addition) and manufacturing processes (where the precipitation and grain size are major concerns) are intended to provide these properties. This thesis puts the steel into the broader context of the ferritic stainless steels and discusses its high temperature use and its dual stabilisation.
2

The role of complexing agents in the flotation of pentlandite-pyroxene mixtures

Shackleton, Natalie Jean January 2003 (has links)
Bibliography: leaves 137-146. / This study examines the role complexing agents play in pentlandite-pyroxene flotation and focuses on the surface chemistry and interaction between valuable and gangue minerals as well as the interaction of complexing agents and reagents (xanthate, copper sulphate) in the system at pH 9. Microflotation, zeta potential measurements, ToF-SIMS analyses (time of flight secondary ion mass spectrometry) and X-ray photoelectron spectroscopy (XPS) were used as tools in determining the extent of surface alteration.
3

The influence of substitutional elements on the transformability of 3CR12 steel

Jungbacke, Nils Gene January 1996 (has links)
Includes bibliographical references. / An investigation has been carried out on a dual-phase 12 % chromium steel, designated 3CR12, with the aim of developing its composition to improve its properties. By the addition of appropriate alloying elements, it was hoped to produce a fully austenitic structure in the rolling temperature range, and at the same time to enhance the kinetics of the decomposition of austenite so that a fully ferritic structure could be obtained after air cooling. The absence of delta ferrite during hot rolling would eliminate the highly anisotropic structure currently found in 3CR12, whilst accelerating the transformation to alpha ferrite might eliminate the need for an annealing treatment. Volume fraction analysis (VF A) of specimens quenched from a soaking temperature of 1000°C showed that Co, Ni and Cu stabilise austenite, whilst Si and Al have the opposite effect. These results were confirmed by finding the equilibrium transformation temperatures of the decomposition of austenite to ferrite using dilatometry, and by investigating the partition of alloying elements between delta ferrite and austenite at I 000°C using the electron microprobe. The effects of the alloying elements on the kinetics of the transformation were investigated by VF A of specimens transformed from 1000°C, and by the use of dilatometry. Dilatometry was used to find the slowest cooling rate at which the alloy was fully untransformed. It was found that Si and Al enhance the kinetics of transformation, whilst Co, Ni and Cu hinder them. The effect of each element is discussed with respect to three factors: the delta ferrite content prior to the transformation, the temperature range of transformation, and the thermodynamic effects of the element.
4

An investigation of a pattern recognition system to analyse and classify dried fruit

Henry, Karen Jane January 1996 (has links)
Includes bibliographical references. / Both the declining cost and increasing capabilities of specialised computer hardware for image processing have enabled computer vision systems to become a viable alternative to human visual inspection in industrial applications. In this thesis a vision system that will analyse and classify dried fruit is investigated. In human visual inspection of dried fruit, the colour of the fruit is often the main determinant of its grade; in specific cases the presence of blemishes and geometrical fault are also incorporated in order to determine the fruit grade. A colour model that would successfully represent the colour variations within dried fruit grades, was investigated. The selected colour feature space formed the basis of a classification system which automatically allocated a sample unit of dried fruit to one specific grade. Various classification methods were investigated, and that which suited the system data and parameters was selected and evaluated using test sets of three types of dried fruit. In order to successfully grade dried fruit, a number of additional problems had to be catered for: the red/brown coloured central core area of dried peaches had to be removed from the colour analysis, and Black blemishes upon dried pears had to be isolated and sized in order to supplement the colour classifier in the final classification of the pear. The core area of a dried peach was isolated using the Morphological Top-Hat transform, and Black blemishes upon pears were isolated using colour histogram thresholding techniques. The test results indicated that although colour classification was the major determinant in the grading of dried fruit, other characteristics of the fruit had to be incorporated to achieve successful final classification results; these characteristics may be different for different types of dried fruit, but in the case of dried apricots, dried peaches and dried pears, they include the: peach core area removal, fruit geometry validation, and dried pear blemish isolation and sizing.
5

Aromatization over platinum/zeolite L catalysts : the effect of oxygenates

Nash, Robin John January 1997 (has links)
Bibliography: leaves 269-280. / In 1980, Bernard reported that platinum dispersed on zeolite LTL (Pt/KU had exceptionally high selectivity for the aromatization of n-hexane to benzene. The selectivity was ca. 95 at 99 conversion of n-hexane. This Pt/KL catalyst has been extensively studied to determine the reasons for the exceptional stability and benzene yields relative to platinum supported on silica (Pt/Si0₂ ) and alumina (Pt/Al₂0₃). The Pt/KL catalyst was found to be monofunctional with all the activity occurring on platinum metal clusters inside the pores of zeolite L. The catalyst exhibits excellent stability and the Aromax Process developed by Chevron Ltd., using I a barium doped Pt/KL catalyst, PtBa/KL, has been reported to operate continually for the equivalent of one year during accelerated deactivation testing at 450°C and a hydrogen partial pressure of 6 bar. However, sulphur-containing I compounds such as thiophene, result in rapid and irreversible deactivation of the catalyist due to sintering of platinum clusters. Thus the level of sulphur-containing I compounds, especially thiophene, must be kept below 50 ppb of the feed to avoid deactivation by sintering. SASOL Ltd. may be in a unique position to use Pt/KL as a catalyst for the aromatization of hexanes and heptanes to benzene and toluene respectively, as their products which are produced by the Fischer-Tropsch process are sulphur free. However, a substantial amount of oxygenates are formed in the Fischdr-Tropsch process and as yet no study has been undertaken to determine the effect of these compounds on the activity and selectivity of the catalyst.
6

Rural energy development in developing countries : South and East Sub-Saharan Africa

Lithole, Thifhelimbilu Christopher January 1997 (has links)
Includes bibliographical references. / There are some common characteristics of rural communities throughout the world. They tend to lack a good economic infrastructure, essential social amenities, tourist potential, good road infrastructure, literacy, and most importantly, scarcity of sufficient energy supply to meet basic needs, and deteriorating environments due to increasing pressure on available traditional energy resources. Furthermore, rural areas in the developing countries of South and East Sub-Saharan Africa are characterised by high population ratios, low levels of income, concentration of poverty, significant socio-economic disparities relative to urban area, and a high rate rural-urban migration. The availability of adequate and convenient energy is essential in addressing these priorities of rural development. The development of energy resources for rural areas is, therefore, closely linked to the economic, social and environmental concerns of mainstream rural development. Unlike growth-driven energy development for industrialisation and urbanisation, rural energy development must consider social and environmental development. More importantly, it must be people-oriented. The result of the study has indicated that the pace of energy transition from traditional to commercial energy in the rural areas of countries in the region has lagged behind that in urban areas, a similar situation to that existing between developing countries and developed countries. Significant rural-urban inequalities in commercial energy supply and consumption exist. Rural communities still continue to rely heavily on traditional energy, mainly biomass resources.
7

The synthesis of aluminium hydroxide and oxyhydroxide

Louw, Linda-Ann January 1993 (has links)
Includes bibliographical references. / Beta alumina is a ceramic with the ability to conduct certain ions. It is conventionally formed through the high temperature solid state reaction of α-alumina with soda and lithia, which results in a mixture of β- and β"-alumina phases. To maximise the amount of β"-alumina formed, a second heat treatment step is required. Beta alumina may also be synthesised directly from the various aluminium hydroxide ( Al(OH)₃ ) and aluminium oxyhydroxide (AIOOH) polymorphs. The particular oxygen sublattice of the starting material is critical in determining which phases of beta alumina are formed. Boehmite and bayerite are known to yield pure β"-alumina. In this investigation, the differences in structure and the identification of the polymorphs is discussed. A review of the methods of synthesis and concomitant mechanisms of reaction proposed in the literature are presented. Of these, the synthesis of boehmite and bayerite are investigated experimentally. Attempts to synthesise boehmite at ambient conditions resulted in the formation of pseudoboehmite, and confirmed that boehmite can only be formed by the introduction of a hydrothermal step. However, it was possible to form bayerite at ambient conditions by sμnple chemical reaction. Control of the reaction pH and the removal of inhibiting ions were found to facilitate the formation of well crystallised bayerite. Although the factors governing the successful synthesis of bayerite need further investigation, the possibility of a direct synthesis route for β"-alumina has been demonstrated. Finally, the synthesis of β"-alumina by the solid state reaction of the hydroxide and oxyhydroxide polymorphs was successfully completed.
8

A comparative evaluation of manufacturing technologies and their effect on morphology and mechanical properties of poly-(propylene-ethylene) copolymers

Sello, Maitse P January 2002 (has links)
Includes bibliographical references. / This project is a technological benchmark exercise for Sasol Polymers where different poly (propylene-ethylene) copolymer grades from five foremost licensed manufacturing PP technologies are evaluated. These copolymer grades were manufactured using the following processes: Novolen PP technology (Sasol grades), Innovene PP technology (BP grades), Spheripol PP technology (Basell grades), Univation PP technology (DOW grades) and Borstar PP technology (Borealis grades). Form this investigation, thirty different grades where evaluated to determine their structural morphology in relation to their physical and mechanical properties. For the ease of analysis, the grades are grouped into three ethylene content ranges; low ethylene contents (below 8%), medium ethylene contents (between 8 -10%) and high ethylene contents (above 10%). Within each of these ethylene content ranges, there is a melt flow index (MFI) range, which increases from low to high. The differences in the MFI added further complications, especially when trying to determine optimum mechanical properties of the copolymer grades. The impact test results show that the toughness is at a maximum at low MFI, and then drops drastically as the MFI increases. Since an addition of ethylene improves the toughness of the copolymer, it was observed that by considering MFI's below 35 g/10 min, the toughness could be enhanced by increasing ethylene content. Grades with MFI's below 35 g/10 min show a drastic increase in impact strength at ethylene content around 8.5%. SEM results show that particle size and spacing are independent of ethylene contents for the grades examined. However, for the BP and DOW grades, the ratio between interparticle distance and particle size decrease steadily with increasing ethylene content. The Basell and BP grades showed a narrow rubber particle size distribution followed by Sasol grades. The DOW grades showed a broad particle size distribution. TEM results show that the internal morphology of the rubber particles differ from grade to grade, with the Sasol and BP grades showing several numbers PE inclusions within the rubber particles, whilst Basell grades having only few PE inclusions. It was observed that those grades with several PE inclusions have a better impact performance compared with those with fewer inclusions.
9

Investigation of the characteristics of kenaf fibre reinforced polypropylene composites

Kim, Soeyeh January 2008 (has links)
Includes abstract. / Includes bibliographical references (leaves 135-140). / This research work focus on the characterisation of the mechanical and thermal properties of kenaf fibre reinforced polypropylene composites. The composites were fabricated by extrusion followed by injection and compression moulding. The effects of fibre content, coupling agent content (MAPP), different types of moulding processes and addition of filler materials (kenaf core) were observed through mechanical, thermal and microscopic testing.
10

The effect of temperature on the Fischer-Tropsch selectivity and further mechanistic insights

Fletcher, Jack Vincent January 2009 (has links)
Includes bibliographical references (p. 133-145). / Concern’s that the world’s energy supply will not be able to keep pace with rising energy demands, have surfaced periodically for much of the petrochemical industry’s nearly 150 year history, but each time the industry has responded with technological advances and innovations to satisfy the global energy needs. Future advances will most likely include the enhanced recovery of conventional oil, the production of extra-heavy oil / tar sands and the utilization of alternative energy production technologies (technologies other than crude oil refining). The Fischer-Tropsch Synthesis (FTS) discovered in 1923 by Fischer and Tropsch, is one of these alternative fuel production technologies and can briefly be defined as the means used to convert synthesis gas containing hydrogen and carbon monoxide over a group VIII metal catalyst to hydrocarbon products and water. Given the vast product spectrum possible for the FTS (paraffins, olefins, alcohols, carbonyls, acids and aromatics), a great deal of controversy still exists as to the chemical identity of the monomeric building block and the propagation of the hydrocarbon chain on the catalyst surface [van Dijk., 2001]. Several mechanisms have been published with the four most popular (alkyl, alkenyl, enol and CO-insertion), recently reviewed by Claeys and van Steen (2004). It must however, be appreciated that given the complexity of the FT reaction it is generally accepted that more than one mechanism may operate on the catalyst surface at any one time. Furthermore, process parameters such as temperature, total pressure, partial pressure, hydrogen to carbon monoxide ratio, space velocity and residence time all have an influence on the FT product selectivity. Because of this it becomes exceptionally complicated to determine the effects of just one parameter while taking the effects of the additional parameters into account.

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