No description available.

Literature concerning composite materials, including their physical and chemical properties, and their corrosion and anodizing behaviour, has been reviewed. Stemming from this it is evident that their detailed corrosion behaviour, with resultant protective methods, requires further elucidation. A composite material consisting of AI-alloy 8090 (AI, 2.4 Ll, 1.2 Cu, 0.7 Mg, 0.09 Si, 0.09 Fe, 0.12 wt % Zr) with 20 wt % silicon carbide particulates, fabricated by powder metallurgy, has been characterised in terms of structure and physical appearance, using optical and electron microscopy. The composite contains irregularly-shaped silicon carbide particles, up to 12 um in size, which are distributed non-uniformly within the matrix. Sharp and distinct interfaces between particles and the matrix, containing no readily visible reaction zone, have been revealed. The elemental chemistry of the composite has been investigated using EDX analysis associated with transmission electron microscopy, X-ray diffraction, Auger electron spectroscopy and secondary ion mass spectrometry. A reaction zone at the particle/matrix interface is not readily evident. However, alloying elements such as copper, magnesium, silicon and iron are revealed at the interfaces which indicates diffusion of these elements towards interfaces. This presumably implies the formation of a reaction zone or fine precipitates, however, such zones are not observed directly. Lithium is segregated and non-uniformly distributed in the matrix. Electropolishing and etching of the surface of the composite in acidic and alkaline solutions are unable to provide a smooth, particle-free surface; therefore, particle/matrix interfaces cannot be eliminated to improve corrosion resistance and a particle-free surface is not available for subsequent anodizing. Corrosion behaviour of the composite has been examined using immersion and salt spray tests, and with electrochemical techniques, in sodium chloride and sodium sulphate solutions; sodium chloride is an aggressive solution for the composite, whereas sodium sulphate is comparat ively mild. Corrosion of the composite in sodium chloride solution initiates by the dissolution of aluminium mainly adjacent to particle/matrix interface and is enhanced by crevice corrosion effects. The crevices are provided by the interfaces between the differently natured materials. Silicon carbide particles are chemically inert in the previously mentioned environments but enhance corrosion by providing crevices at the interfaces with the matrix. No galvanic corrosion is evident between silicon carbide and aluminium. The anodizing behaviour of the composite has been investigated in phosphoric and sulphuric acids. Anodizing of the composite in phosphoric acid is impractical since only the matrix is anodized and particles are lost during anodizing; due to the high chemical and relatively low field assisted dissolution rates in the acid. formation of a continuous and relatively thick anodic film is not possible. The compositeo however. is more readily anodized in sulphuric acid; the matrix 15 anodized and particles are occluded within the anodic film. The porous anodic film formed in sulphuric acid can afford corrosion resistance to the composite material during subsequent exposure to chloride-containing environments

The treatability of six Malaysian timbers namely Red Balau (Shorea guiso), Kapur (Dryobafanops aromatica), Kasai (Pometia pinnata), Kulim (Scorodocarpus borneensis), Kempas (Koompassia malaccensis) and Keruing (Dipterocarpus grandiflorus) using the applied pressure processes (oscillating pressure, conventional Bethell and a modified Bethell process) was investigated. Treatments were carried out with a commercial water-borne copper-chromearsenic (CCA) preservative, known as Celcure-AP. The conventional Bethell process was the most effective method of wood treatment followed by the modified Bethell and the oscillating pressure process. While sufficient preservative retention and absorption was achieved in Kempas and Keruing to meet the Malaysian Standard MS 386 : 1986 specifications for exterior timber used in ground contact, the other four timbers - Red Balau, Kapur, Kasai and Kulim did not fulfil this requirement, even when treated at the most extreme treatment conditions. Using the three pressure processes, seasoning period and treatment time were found to have significant effects on preservative retention and penetration in all timber species. Investigations into the effect of three pretreatment procedures - steaming, incising and ponding to improve the treatability of the six timber species were carried out. Incising was the most effective pretreatment procedure in enhancing the treatability of these timbers. However, at the highest incising density employed (4,500 incisions/m2), it was still not possible to treat Red Balau, Kapur, Kasai and Kulim timber to achieve satisfactory target preservative retention and penetration. The less effective incising procedure was due mainly to the low incising density used. The possibility of improving the treatability of these four timber species further using higher incising densities and other methods of inCising pretreatment is discussed. Steaming, incising and ponding pretreatments had a pronounced effect on the strength properties of timbers based on reduction of their modulus of elasticity (M.D. E.), modulus of rupture (M.O.A.), compressive strength and hardness. The highest strength losses were observed in timbers that had been ponded for 6 months. Significant strength losses were also observed in incised and steamed timbers, but the magnitudes were lower than the 6 month ponding regime. This was attributed to low incising density and the short steaming period. The performance of Celcure-AP in the six timber species was evaluated in laboratory and field tests. In addition, a copper-azole formulation (Tanalith-3485) was also evaluated on Kempas timber. Laboratory tests involved exposure of treated wood blocks to five decay fungi - Pycnoporus sanguineus, Trametes versicolor, Coniophora puteana, Gloeophyllum trabeum and Oligoporus placenta. The less durable timbers - Kempas and Keruing needed a higher loading of Celcure-AP in order to give equal performance compared to the more durable timbers - Red Balau, Kapur, Kasai and Kulim. Based on copper retention in treated samples, a higher loading of Tanalith-3485 was required in Kempas to achieve comparable results to Celcure-AP treated samples. However, the concentration levels of Tanalith-3485 used in the present study were sufficient to afford protection to Kempas stakes exposed for 36 months in the field test. A longer exposure period is however, recommended for a full evaluation of timber/preservative combinations against wood deteriorating organisms under Malaysian conditions. In the field test, soft rot fungi were the main causal organisms in the attack of timbers in test site A (fungal test bed), while in test site B stake failure was due mainly to termite attack.

The ingress of carbon dioxide and chloride ions into reinforced concrete can cause corrosion of the steel reinforcement. Cracks and poor quality cover can accelerate this process. Coating the surface of the concrete can increase the life of the structure. A coating must have the ability to bridge cracks that form in the substrate concrete and to accommodate any subsequent movement of that crack without failure. If the coating itself is damaged by substrate cracking then the coating becomes less effective as it no longer provides a barrier to the deleterious agents. There are currently few methods to assess the performance of a coating on a reinforced concrete surface subject to crack formation and subsequent movement. In this thesis a test specimen, machine and methodology are developed to evaluate the crack bridging and crack accommodation performance of these coatings. The specimen is 40mm x 40mm x 160mm mortar prism, coated on one face and axially reinforced with an 8mm steel bar. A crack in the specimen is opened by the application of a tensile load to the ends of the reinforcing bar by a pneumatically powered testing machine. Initial investigations confirmed that the testing machine was reliable and gave reproducible results. A testing program was then carried out to investigate the effects of temperature, coating thickness, artificial weathering and crack width on the crack bridging and crack accommodation behaviour of the coatings. It was found that increasing the thickness of a coating allowed wider cracks to be bridged. Crack accommodating behaviour was found to fall into three regions dependent upon the test temperature. At the lowest temperatures both crack bridging and crack accommodation did not occur. As the temperature was increased crack bridging and crack accommodation occurred but the crack accommodation behaviour was highly variable. As the temperature was increased further a region is encountered where reliable crack bridging and crack accommodation occurred and the variability in crack accommodation behaviour was reduced. Artificial weathering was found to have a detrimental effect on both crack bridging and accommodation performance

The natural degradation of processed black and white cellulose acetate based 35mm motion picture film material has been investigated using 1H and 13C NMR spectroscopy. According to current standards only this material is considered to be an archival recording medium. It has been recognised that understanding the relationship between structure and physical properties would provide knowledge to help inhibit motion picture film degradation. A correlation between observed changes in molecular structure and physical property changes namely, % moisture regain, acidity and viscosity has been obtained. Results of these studies indicate that the primary mode of degradation is hydrolysis of ester groups leading to deacetylation of the C6 acetyl group in the polymer chain. On further deactylation, the C3 acetyl group is lost in preference to the C2 acetyl group. Therefore, it can be concluded that a decrease in viscosity retention and an increase in acidity concurs with deacetylation of the polymer chain. On this basis mechanisms of deacetylation would predominate since oxidative chain-scission would take place through the C2 acetyl group which is less accessible. NMR spectroscopy also reveals that the plasticisers, namely triphenyl phosphate and diethyl phthalate incorporated into cellulose acetate base, influence its stability. Under archival conditions the triphenyl phosphate plasticiser appears not to undergo degradation but becomes increasingly incompatible with the cellulose acetate base. Diethyl phthalate however was seen to degrade as the cellulose acetate base itself degrades. A more detailed understanding of the macromolecular structure of cellulose acetate based motion picture film has been obtained with the use of Molecular Modelling and Graphics studies using QUANTA software. This supports the NMR study indicating that the C6 and C3 acetyl groups are clearly more exposed in the polymer matrix and therefore, are more likely to be lost as hydrolysis of the polymer chain occurs. Modelling studies also supported reduced stability of the polymer in the presence of plasticisers. When plasticisers were docked within the polymer matrix distortions of the polymers chains were observed as chains were pushed apart and dihedral angles altered. The role of the emulsion in film degradation was also examined by electrophoresis. This separation of proteins has shown that under archival conditions, naturally aged gelatin emulsion layers show a decrease in molecular weight. This has been attributed to the acid catalysed deacetylation of the cellulose acetate base lowering the pH of the film and inducing hydrolysis of gelatin. Only when considerable amounts of acid have been evolved are changes to the emulsion observed. Finally, the effects of storage containers were characterised using viscosity and acidity measurements. Accelerated ageing studies at 50%RH 70°C to emulate archival storage conditions revealed that in the early stages of degradation polyethylene and polypropylene cans were more detrimental to film stability than the more traditional metal can. The plastic cans were shown to promote oxidative degradation of the film and polypropylene was shown to lead to higher levels of peroxide in films than polyethylene

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

No description available.

No description available.

No description available.