Studies have been made of the effects of thermo-mechanical treatment variables on the recrystallization of austenite, the transformation of austenite and precipitation strengthening in C-Hn steel containing niobium, niobium plus vanadium, vanadium and vanadium plus nitrogen. The amounts of niobium and vanadium were varied across the stoichiometric ratio of H:C and H:N in order to investigate the effect of stoichiometric ratio on the precipitation strengthening.

No description available.

Most of the early studies using peroxycarbamates concerned their synthesis, decomposition and use as initiators in vinyl or diene polymerisation. The only attempt to use one as a crosslinking agent was reported in 1960 for a plastic. The author's research work is an attempt to prepare new bisperoxycarbamates and to evaluate them as crosslinking agents in natural rubber (DPNR) and polyisoprene rubber (Cariflex IR 305).

The strength and failure behaviour of nylon 6 reinforced with short E-glass fibres has been studied. The fibres were treated with different sizing compounds in order to modify the interface between the glass and polymer. The principal objective of the work was to assess, by means of mechanical testing and microscopy, the role of the interfacial bond in controlling the properties of these materials. It has been shown that the mechanical behaviour of glass reinforced nylon 6 is controlled mainly by the fibre concentration, length, and orientation and that stiffness enhancement can be adequately predicted by a modified rule of mixtures expression. The behaviour is also strongly influenced by the type of sizing compound employed on the fibres. The results clearly demonstrate the beneficial effects of silane coupling agents. In the 'dry' condition some composites exhibited a 30% strength reduction on omission of the silane, but in others this caused little variation. In the wet state however, silane treatments produced far superior properties in all cases. In addition, the size apparently exerts considerable control over the properties, indirectly, by effecting the fibre dispersion and breakage during compounding and moulding. The failure mechanism as assessed by optical and scanning electron microscopy and by acoustic emission analysis, was shown to be of a dual nature. Failure was initiated by fibre-matrix debonding in the core region of the mouldings, the debonded areas interlinked and became visible on a macroscopic scale as strain bands across the samples. The strain banding phenomenon in turn initiated a catastrophic brittle failure sequence, the resulting fracture surfaces exhibiting the characteristics of both weak and strongly bonded systems.

The use of polymers in bituminous materials has been gaining popularity over the last decade. Despite their superiority in enhancing the performance of bituminous mixtures, problems have been experienced due to limitations on the applicability of currently available assessment techniques. This thesis is concerned with the mechanical behaviour of polymer modified bitumens and the performance of polymer modified bituminous mixtures. The first part of the thesis presents different pavement distresses and the importance of using polymer modified binders to improve the performance of bituminous mixtures. The second part deals with identification of properties of polymer modified binders and their mixtures by using dynamic mechanical analysis. The third part attempts to develop a novel technique for assessing resistance to permanent deformation of HRA mixtures using a dissipated energy method. Some polymer modified binders are susceptible to storage instability. However, this work has demonstrated that certain empirical tests are unsuitable for assessing the temperature susceptibility and storage stability of polymer modified binders. Viscoelastic behaviour of bituminous materials is better presented by dynamic mechanical analysis. The dynamic mechanical analysis provides a basis for explaining the unsuitability of some empirical tests on polymer modified binders. Determination of dissipated energy during creep testing enables more comprehensive and accurate assessment of the resistance to permanent deformation of Hot Rolled Asphalt (HRA) mixtures. This study reveals that assessment of the resistance to permanent deformation based upon permanent strain rate in the linear region is in good agreement with the dissipated energy method. The end of the linear region, N1, can be accurately determined by the dissipated energy method and provides a confidence that analysis will always be conducted in the linear region. As expected, polymer modified mixtures are superior to the unmodified ones in their resistance to permanent deformation which confirm by the wheeltracking test, but was not evident from the Marshall tests.

Many conventional biomaterials fail to meet the demands required of them with respect to their surface and bulk properties. This problem can be addressed by developing novel biomaterials that have the desired bulk properties and increased biocompatibility. Alternatively the surfaces of biomaterials which have the desired bulk properties can be modified to increase their biocompatibility without compromising these bulk properties. Phosphorylcholine (PC) based coatings mimic the surface of biological membranes and so offer a novel method for modifying bulk materials, or can be incorporated into novel bulk biomaterials. One of the key issues of biocompatibility is the continual stimulation of the inflammatory response by biomaterials characterised in part by complement activation, macrophage adhesion and granulocyte activation.

No description available.

No description available.

In the electrostatic powder coating industry an increase in deposition efficiency and a controlled decrease in film thickness are constantly strived for. If adjustments to the size distribution of powders are made in order to improve the process in any way it is important that the excellent physical properties of the coating are not sacrificed. The aim of this study is to gain an understanding of the effects of particle size on the packing and final film properties of electrostatically sprayed coatings so that-recommendations can be made to increase the effectiveness of the process. Experimental studies involved the production of stoved sample coatings of various thicknesses obtained by spraying narrow size ranges of a commercial powder using a reproducible coating method. A testing programme was developed to assess the effect of particle size on the physical properties of the films produced. A three way comparison of physical property, size of sprayed powder and coating thickness has been compiled and results are discussed. It was observed that particle size had no significant physical effect on film properties. A method for determining a spreading factor, representative of the flow characteristics of a given powder, was developed. Observations from these stoving experiments suggested that the excellent flow properties of the powder used in earlier experiments accounted for the small variations in those results. However photomicrographs of typical coatings showed that large particles were dominant in the upper layers of packings. A loss of fines was identified from size analysis of various powders on coated plates compared to the original feed materials. Computer plots simulating the packing of particles on a substrate showed similar trends. Integration of the trajectory equation for individual particles, represented by means of a force balance, was carried out with consideration of all interparticulate electrostatic forces of the packed layer together with field and aerodynamic forces. Simulations of packings of monosized and size distributed powders sprayed at various transport air velocities show that, as a packing increases in thickness, various sizes behave differently. The results from these theoretical experiments give indications for the explanation of previous results.

No description available.