Due to high hydrogen capacity, good reversibility and low cost, magnesium hydride is one of the most promising hydrogen storage materials. However, the high desorption temperature and slow hydriding kinetics hinder the application of magnesium hydrides. To improve the hydrogen storage characteristics of magnesium hydrides, many effective treatments have been developed and applied, such as ball milling, melt spinning, alloying with other metals, adding catalysts and using thin film technique. In this work, melt spinning and alloying with Ni were the main sample modification methods used to improve hydrogen storage properties for magnesium hydrides. At the beginning of this project, it was found that it was difficult to repeat the methodology of sample preparation in the literature. Therefore, sample synthesis method was developed after numerous preliminary trials and a series of Mg-Ni alloys were melt-spun successfully. The structural characterization and analysis of hydrogen storage property were performed on the melt-spun Mg-Ni samples in a range of compositions. It was found that a nanocrystalline / amorphous structure was produced by melt spinning, and a metastable intermediate phase, Mg\(_6\)Ni, was discovered in the melt-spun materials. The melt-spun Mg-Ni ribbons exhibited fast kinetics of both absorption and desorption at 300 °C, with a high capacity. Moreover, they exhibited low temperature and even room temperature hydrogen sorption, with slow kinetics.\(\gamma\)-MgH\(_2\) phase, which forms usually under high pressure, has been found in the samples, which probably caused the ambient hydrogen absorption.

This work investigated the effect of transition metal additions on the double oxide film defects in Al alloys. A bubble trapping experiment was initially conducted, which deliberately trapped an air bubble inside the aluminium melt for a period of time in three different Al alloys (Commercial purity aluminium, 2L99(Al-7Si-0.35Mg) and Al-5Mg alloy), as an analogy of the consumption of the entrapped atmosphere in double oxide film defects in castings. Several elements, namely, Mo, Ti, Zr, Hf, Sc were selected and added into the aluminium melt. The result suggested that the three different alloys behaved differently with regard to the consumption of the entrapped bubble and the different oxide/nitride layers formed. Only the addition of Sc and Mo altered the structure of the oxide surface and promoted the consumption of the air in the trapped bubble in the 2L99 aluminium alloy melt. Sand casting was subsequently conducted for 2L99 alloy with different element additions. Mo and W were found to improve the Weibull moduli of the UTS. Statistical analysis confirmed that such improvement was significant. For the castings with Mo addition, a nitride was found in some double oxide film defects, on the fracture surface of the tensile testbars. This was unusual, as bi-film defects in aluminium castings usually have a short solidification time and do not have enough time to consume the majority of their entrapped oxygen. The formation of the nitride on the surface of bi-film defects in +Mo castings, suggested that the majority of the oxygen was depleted and a reaction was going on between nitrogen and liquid aluminium. The formation of the permeable nitride surface layer on the bifilm defect might promote the consumption of the entrapped gas. This should lead to reductions in the bi-film size and an improvement in mechanical properties. For +W casting, W containing intermetallic compound might be nucleated on the sides of the bifilm and drag the bi-film to the bottom of the casting, resulting in a clean melt and improving mechanical properties. The effect of Si modifier addition on the bi-film defect (Na, Sr and Ba) in 2L99 sand castings was also investigated, which suggested the addition of modifiers resulted in a reduction in the mechanical properties of the 2L99 castings while the bi-film defect content in the casting was high but significantly improved the Weibull moduli of the UTS of 2L99 castings while the bi-film defect content was reduced. The results suggested that the modifier addition tended to aggravate the effect of bi-film defects on mechanical properties by increasing the defect size. Ti and Mn additions into 2L99 alloy were found to not significantly affect the mechanical properties of the casting. A porous oxide structure was found on only one of the fracture surfaces (out of ten) of Ti containing testbar examined, which hardly affect the mechanical properties of the casting. For the +Mn casting, the composition and structure of the oxide was not affected by the addition. The reduction of the mean value of the UTS for both element additions could be due to bi-film defects being introduced during master alloy preparation, master alloy addition and during degassing before casting.

Synthetic hydroxyapatite (HA) has been widely used for biomedical applications, in particular as a bone substitute and coating for implants, due to its similarity to the inorganic component of human bone. The aim of this study was to incorporate three divalent cations (silver, zinc and magnesium) into the hydroxyapatite structure via a wet chemical precipitation method to enhance its antibacterial properties, to avoid the need for the use of antibiotics. Material characterisation techniques such as XRD and Raman Spectroscopy confirmed that these ions were substituted within the crystal structure of HA, though did not follow the expected reaction stoichiometry and substitution ratios. HA material properties, such as crystal size, crystallinity and solubility were shown to change after ion substitution. Metal-substituted HA showed varying strengths of antibacterial properties against two bacterial strains of \(E\).\(coli\) and \(S\).\(epidermidis\), which was attributed to different type of ions and substitution ratios and also different release profiles from the solid phase to the culture medium. The results from cell biological studies confirmed that the rate of osteoblast cell proliferation and cell differentiation were improved after cells being incubated with disks of substituted HA.

Grain size refinement can be achieved by recrystallisation during hot deformation, with multiple deformation steps during rolling or forging being used to generate fine grain sizes. Whilst the mode (or average) grain size after recrystallisation can be determined from standard equations the full grain size distribution is required for predicting a range of mechanical properties. In this work an approach has been proposed to allow prediction of the full grain size distribution by varying the value of the D’ parameter value in the Dutta - Sellars equation developed to predict the recrystallised mode/average grain sizes. It has been found that D’ is a function of strain at high strain values (above 0.3) and the relative position of the grain size in the grain size range (D*). Results for recrystallised grain size distributions for a range of steel grades (including model Fe - Ni steels, commercial Nb-microalloyed plate and high alloy (9Cr) forging steel) with different initial grain sizes and following deformation to different deformation strains, show that the predictions give good agreement with the experimental data except for samples with larger mode grain sizes deformed to a strain of 0.15.

A series of isothermal and cyclic oxidation tests were carried out on two thermal barrier coating systems consisting of a CMSX-4 nickel-based superalloy substrate, NiCoCrAlY overlay bond coat applied by two different techniques and a yttria stabilised zirconia topcoat applied by electron beam physical vapour deposition (EBPVD). The bond coats were applied by either high velocity oxy-fuel spraying (HVOF) or EBPVD. Isothermal oxidation tests were carried out at 950°C, 1050°C and 1150°C for both coating system for up to 3000 hours. Cyclic oxidation testing was conducted at 1150°C in one hour cycles to coating failure on both coatings. A detailed examination on the oxide thickness was conducted on all specimens, along with characterisation of the bond coat and TGO. This was coupled with examination of specimen cross-sections for cracking and signs of coating degradation. Isothermal oxidation showed sub parabolic oxide growth consistent with the literature. Detailed analysis of oxide thickness showed a normal distribution but with increasing standard deviation with increasing oxidation time. Both bond coats were dual phase, β + γ. The EBPVD applied bond coat only, was found to contain yttrium rich precipitates in the bond coat and TGO. Both coatings showed no increase in surface roughness after either isothermal or thermal cycle testing. Short sub-critical cracks were observed at the TGO/topcoat interface in the HVOF applied bond coat only associated with the flanks of asperities. Coating failure in both coatings occurred at the TGO/bond coat interface on cooling and was likely driven by the thermal expansion mismatch between the TGO, topcoat and substrate. The initial mechanism of crack formation was not determined conclusively but could be a wedge cracking type mechanism.

The work presented within this thesis describes an investigation into the selective flocculation behaviour of coal/shale slurries using commercially available polyacrylamide polymers. It is considered that selective flocculation may eventually offer a method of recovering the valuable combustibles which are presently discarded. To date, although numerous, mainly laboratory scale, investigations using organic polymers have been conducted on a variety of mineral combinations, little work has been undertaken on coal/shale slurries. Selective flocculation depends essentially on differences in the adsorption of a flocculant on different minerals, which in turn depends on the comparative mineral surface chemistry. The effective dispersion of one component is also essential i.e. it must form a relatively stable suspension, either inherently or after modification with a suitable reagent. The effect of these two factors on both single specie flocculation and selective flocculation is discussed in some detail. Testwork was conducted throughout using pure coal and shale samples in order to minimise any natural variation in surface properties which may occur. In order to define possible conditions under which a separation may be feasible, the flocculating ability of various types of polyacrylamides on separate coal and shale slurries was initially established. However, the predictions were not entirely successful with the results indicating that, in a 50/50 w/w mixed slurry, under approximately neutral conditions, coal was the preferentially flocculated component. This was apparent for polymers of various molecular weights and ionic characters. Variations in the surface chemistry of the coal and shale may be influenced by several factors such as pH, dispersant concentration and promoter effects. Solids concentration is another important physical aspect. Each of these were studied and discussed. Zeta potentials of the individual coal and shale samples at various pH levels were also determined and related to the selectivity and efficiency of separation under similar conditions. It was apparent that although coal was preferentially flocculated, the major problem was that of entrainment. This inevitably arises during the formation of the coal floes, trapping some unwanted, and essentially dispersed, shale. In addition polyacrylamide may possess a weak affinity for the shale surface. These two mechanisms lead to products with a minimum ash content of between 31 - 36%. It was also found that the floes formed were so weak that they ruptured even on gentle agitation - hence trapped material could not be released. The effect of pre-conditioning the coal surface prior to flocculant addition was also assessed and achieved some degree of success, but again products of below 30% ash were not possible. It was therefore concluded that while coal may be selectively flocculated from a coal/shale slurry, using commercial polyacrylamide polymers, without an additional cleaning stage(s) the system is not economically viable.

No description available.

Problems of Rock Mechanics related to mines are usually concerned with stress distributions and the properties of the rock mass surrounding mine excavations. Neither aspect at present can be reduced to absolute values. Stress distribution in mines is being studied mathematically, photoelastically through various types of models, and also by measurements in situ. [...]

No description available.

An investigation has been made into the behaviour of short fatigue cracks in the β-processed titanium alloy, Ti6Ss. The effect on the material of a number of different variables was studied, particularly microstructure, as well as stress level, specimen design and specimen size. Initiation of cracks was found to occur at similar microstructural features in smooth specimens, regardless of a-platelet morphology. Cracks initiated from slip bands across small bundles of α-platelets, despite the presence of longer, more intense slip bands across α-colonies. α-platelet morphology was found to have a significant effect on short crack propagation rates when crack length was of the order of, or less than, the α-colony size - the more aligned the α-platelets, the greater the short crack propagation rates at equivalent ΔKs. Increasing the prior β-grain size (and hence the a-colony size) led to higher short crack propagation rates at equivalent ΔKs. Specimen design appeared to have an effect on short crack growth rates a uniaxial tension specimen design gave slightly higher growth rates than a four point bend specimen design. Variation in specimen size had no effect on short crack growth rates for the same microstructural condition, but a larger specimen size was found to reduce the scatter in specimen lives observed in smaller specimens. Short crack growth rates were apparently insensitive to stress level when compared at the same nominal ΔK values. Crack shape was found to vary considerably at crack depths below approximately 0.75mm. At crack depths greater than this value, cracks took an approximately semi-circular form. In keeping with many recent studies of short crack behaviour, short cracks were found to grow faster than long cracks at the same nominal ΔKs and at ΔKs below the long crack threshold value, ΔKth· A case study was carried out to determine the behaviour of short cracks in a cheese forged from an ingot slice of IMI685. Crack growth behaviour was found to be the same as that of Ti65s, but initiation behaviour was affected by the presence of pores in the IMI68S, leading to a significant reduction in fatigue life.