A major factor limiting the use and longevity of rare earth based magnetic materials is their susceptibility to aqueous corrosion and associated detrimental effects upon the magnetic properties of the material. This process was investigated through a combination of exposure to simulated environmental conditions and hydrogen absorption/desorption studies (HADS) in conjunction with magnetic characterisation. This study utilises NdFeB MQP-B melt-spun ribbon manufactured by Magnequench, in the form of MQI bonded magnets and also in its unbonded state as MQ powder. Specifically, it was concerned with how effective a variety of bonding media (epoxy resin,PTFE, zinc) and surface coatings (PTFE, Qsil, zinc LPPS, Dex-Cool) were at limiting the impact of aqueous corrosion in MQI bonded magnets. To characterise the effect of hydrogen absorption upon the magnetic properties of the MQP-B, hydrogen uptake was induced followed by a series of outgassing heat treatments with subsequent magnetic characterisation accompanied by HADS techniques performed after each outgas. This allowed comparisons to be made between the effects of aqueous corrosion process and hydrogen absorption upon the magnetic properties of the alloy. This study has clearly demonstrated the link between the abundance of environmental moisture and rate of Hci losses in MQI bonded magnets. In addition to this the key mechanism responsible for the degradation of magnetic properties has been identified. These losses have been attributed to the absorption of hydrogen generated by the dissociation of water in the presence of NdFeB during the aqueous corrosion process. It has been shown that the use of a bonding media that is impermeable to water can limit the effects of aqueous corrosion by limiting water access to the Magnequench particles (MQP) and also the positive effects of the use of suitable surface coatings has been shown to be effective for the same reason.

Titanium aluminide alloys are prone to extensive shrinkage porosity, particularly interdendritic layer porosity. This research aims to develop a better understanding of shrinkage porosity in Ti-46Al-8Nb alloy and how to minimize it. Practical measurements in conjunction with computer simulations were carried out in order to study the effects of cooling rate and temperature gradient on shrinkage porosity in Ti-46Al-8Nb investment castings, through investigating the influence of casting geometry, specifically mould taper on cylindrical bars, and preheating mould temperature on the macrostructure and the formation of shrinkage porosity. The interface heat-transfer coefficient of the ceramic shell/surroundings was determined using measured cooling curves obtained in 200 mbar of Argon and in vacuum. Furthermore, the alloy/mould interfacial heat transfer coefficient was estimated and was verified by comparing measured and predicted cooling curves of Ti-46Al-8Nb. The Niyama criterion function was validated to predict shrinkage-related porosity in Ti-46Al-8Nb castings, through either thermal or tilt-filling ProCastTM simulation models. Positions in a casting with Niyama values above 4 (°C. min)0.5cm-1; (3 (K. s)0.5mm-1); could be considered completely sound. The critical value of the Niyama function was 2 (°C. min)0.5cm-1; (1.5 (K. s)0.5mm-1); below which the position tested was susceptible to macroshrinkage porosity.

The response of powder of the Nickel-based superalloy CM247LC to a range of Hot Isostatic Pressing (HIPping) conditions and post-HIP heat treatments has been investigated as a preliminary step in the assessment of net shape HIPping as a possible process-route for component production. A HIPping pressure of 150MPa was used at temperatures of 1100°C, 1200°C, 1260°C and 1320°C. 1260°C as-HIPped specimens had the best tensile and HCF fatigue properties at both room temperature and 750 °C; the influence of post-HIP solution treatment conditions and of subsequent ageing on the properties of samples which had been HIPped at 1260 °C was thus investigated. A solution treatment at 1100 °C for 1h followed by forced air cooling and ageing at 870 °C for 16h resulted in the optimum tensile, high cycle fatigue at both room temperature and 750 °C. The optimized microstructure consists of a ‘necklace’ structure of coarse γ′ particles along the grain boundaries; cuboidal γ′ distributed inside grains with hyper-fine γ′ precipitated in γ channels; and fine carbides homogeneously disperse in the matrix. The properties of samples with this microstructure were comparable with those of cast, directionally solidified CM247LC. Solution treatment at 1260 °C gives better creep resistance at 760 °C/ 350MPa. It was also concluded that with gas-atomised powder, solution treatment must be carried out below the HIP temperature to minimise porosity. Analytical scanning electron microscopy showed that Hf-rich inclusions, some of which had alumina cores, initiated failure in almost all tensile samples and in all fatigue samples. It was shown that this type of inclusion can be avoided by removal of Hf from the alloy; but the removal of Hf – which is added to the alloy to improve castings – degrade the creep properties over the temperature range of 700 °C to 950 °C and the stress range of 150 MPa to 550 MPa. Further work is required to assess the influence on the tensile and fatigue properties.

The present investigation has been focused on the design, deposition and characterisation of novel low-friction, wear-resistant multilayer nanocomposite CrAlTiCN coatings. Systematic materials characterisation and property evaluation were conducted on the as-deposited and oxidation-tested CrAlTiCN coatings, and the results are presented and discussed. It is possible to generate novel CrAlTiCN coatings with the carbon content up to 24.34 at% by closed-field unbalanced magnetron sputtering of graphite target. The microstructure of the CrAlTiCN coatings mainly depends on their carbon content. When the carbon content is low, carbon atoms are mainly dissolved in the fcc metastable phase (Cr, Al, Ti) (C, N); when the carbon content is high, the major carbon atoms will form amorphous carbon with a C-C bond state and in a sp\(^2\) dominated graphitic environment. Both the hardness and brittleness of CrAlTiCN coatings reduce with increasing the carbon content. When tested at room temperature under unidirectional sliding conditions, the friction coefficient and wear of the CrAlTiCN coatings decrease with the carbon content, and the thermal stability of CrAlTiCN coatings is similar to the CrAlTiN coating but better than graphite-like carbon coatings. The good performance of the new CrAlTiCN coatings can be attributed to the optimised design of the coating system: the Cr/Al for oxidation resistance, the amorphous C for lowfriction and the multi-layered nano-composite microstructure for high toughness.

There is an urgent desire to move from lead-based piezoelectric materials to lead-free alternatives. One of the most promising lead-free materials has been reported to be zBao.7oCao.3oTi0J-(1-z) BaZro.2oTio.soOJ (abbreviated as zBCT-(1-z)BZT) system, which has comparable piezoelectric performance to lead-based materials. However, there is a lack of systematic research to investigate the effects of fabrication on the structural and functional properties of this zBCT -(1-z)BZT system. In this work, the end member Bai-xCaxTiOJ (x=0-0.30) and BaZryTii-y03 (ji=0-0.30) systems have been investigated. The phase transition diagrams of the two systems have been successfully established by measuring temperature dependent Raman spectroscopy and functional properties. The optimized fabrication procedure for forming single phased Bao.7oCao.3oTi0J and BaZro.2oTio.soOJ ceramics by solidstate methods, has been applied as a novel way to form zBCT-(1-z)BZT (O:Sz:~:J) ceramics by sintering the pre-calcined Bao.7oCao.3oTi0J and BaZro.2oTio.soOJ powders. A new phase diagram of the zBCT-(1-z)BZT (0$z:S1) has been constructed by combing structural and functional property measurements. It indicates a vertical orthorhombic phase region separating rhombohedral and tetragonal phases below the Curie temperature. The highest piezoelectric properties have been observed for z=0.5 ceramics at room temperature, due to the increased potential polarization directions in the vicinity of the orthorhombic to tetragonal phase boundary.

The current work proposes a novel approach to the production of sorbent materials, which integrates recycling of calcium silicate-based industrial residues and sequestration of carbon dioxide in the process of accelerated carbonation. The concept was tested on model substrates of suitable mineralogy, namely Portland cement and dicalcium silicate, which were carbonated, and examined by nitrogen adsorption, XRD, NMR, SEM, TG-DTA analytical techniques. The carbonated materials were evaluated in batch sorption studies with the solutions of cadmium, lead, nickel, cobalt, zinc, strontium and cesium. The findings of the structural examination indicated the transformation of nesosilicate-type calcium silicates during carbonation into polymerized Ca-silicate frameworks, aragonite (in carbonated cement only) and calcite. The NMR investigation, for the first time, described in detail the nature of polymerized silicates (predominantly Q3 and Q4 silicon environment) in carbonated cement and dicalcium silicate. The carbon dioxide uptake measured by thermogravimetric analysis was equivalent to 480 kg/t and 370 kg/t of CO2 reacted with dicalcium silicate and Portland cement, respectively. Batch sorption experiments demonstrated better metal removal efficiencies by carbonated cement, particularly for cadmium and cesium. It was concluded that the metal removal mechanisms ranged from adsorption (e.g. ion-exchange, complexation, isomorphic substitution) to surface and bulk precipitation. The main solubility-limiting phases identified for cadmium, lead, strontium and zinc were otavite CdCO3 (only detected in carbonated cement), (hydro-)cerussite, strontianite, and hydrozincite. Cobalt, nickel, cesium were selectively sorbed within the Si-rich phase of both carbonated cement and dicalcium silicate. The leach study demonstrated an adequate containment of sorbed/precipitated metals within carbonated cement (= 2.5% leached) and carbonated dicalcium silicate (= 12% leached) in water. Metal mobility, however, increased during the exposure to acidic conditions, with = 5% of cadmium, lead, cobalt, nickel and 15- 75% of zinc, cesium, strontium being mobilized into leachates.

This thesis describes a programme of work which has been undertaken with the objective of obtaining data relating to the performance of on-line mass flow rate meters as applied to pulverised coal injection systems. Such injection systems are utilised widely in power generation, cement and steel manufacture. A technology review was carried out, incorporating an extensive literature survey. This review precipitated the conclusion that a number of techniques have been proposed, which may be applicable to the measurement under investigation. However, very little experimental verification of sensing systems based on these techniques had been undertaken. A test facility, suitable for such verification was therefore developed and an extensive programme of tests were carried out, of a sensing system based on an electrostatic technique. The development of a mathematical model of the sensor operation has also been undertaken, in an attempt to explain some of the more unusual aspects of the experimental results. The overall conclusion is that some aspects of the measurement can be achieved without major difficulties, whilst problems have yet to be resolved in respect of other aspects of the measurement system. The principle of the measurement system is such that the independent measurement of average particle velocity and suspension density are required in order to measure mass flow rate. The measurement of average particle velocity was shown to be achievable by either of two techniques, whilst the measurement of suspension density proved more problematic. Recommendations for further work, aimed at addressing these remaining aspects are detailed.

In this thesis aluminium alloys containing small additions of both tin (~ 0.1 wt %) and gallium (~ 0.05 wt %) dissolve anodically at high rates in brine media; at room temperature, current densities > 0.2 A cm-2 can be obtained at potentials close to the open circuit potential, ~ -1.5 V vs SCE. Alloys without both tin and gallium do not dissolve at such a negative potential. The tin exists in the alloys as a second phase, typically as ~ 1 μm inclusions throughout the aluminium structure. Anodic dissolution leads to rounded pits around the tin inclusions. The pits are different in structure from the crystallographic pits observed with Al and other alloys. Clearly, the AlMgSnGa alloys dissolve by a different mechanism. Although the distribution of the gallium in the alloy could not be established, it is essential to the formation of these pits and maintaining dissolution. In addition to the composition, mechanical working and heat treatment influence both the stability of the alloys to open circuit corrosion and the overpotential for high rate dissolution, factors critical to battery performance. The correlation between performance and alloy microstructure has been investigated. Imaging with a high speed camera with a resolution of 10 – 20 μm was used to observe the dissolution of AlMgSnGa alloys. Using microelectrodes with only a few Sn inclusions in their surface, allows confirmation that hydrogen evolution occurs only from the Sn inclusions and also showed that the evolution of H2 is not continuous. Therate of H2 evolution correlates with shifts in potential between - 1.5 V and much less negative potentials. The performance of a laboratory Al-air battery with 2 M NaCl electrolyte was limited by both the performance of the O2 cathode and the extent of dissolution of the alloy. Using a cell with a low electrolyte volume/surface area ratio, dissolution of the anode stopped after the passage of 1000 C cm-2 due to a high impedance, thick film of crystals clinging to the surface. Removal of this film allowed the dissolution to recommence. The charge limitation depends on cell design but a high charge density would be difficult to achieve with a low volume battery.

This thesis aims to describe the ultra-rapid synthesis of a number of important transition metal carbides as well as investigating their reaction mechanisms. 4 binary systems are discussed; Nb-C, Mo-C, Ta-C and W-C, and work carried out on the ternary system, Nb-Ta-C, is also evaluated. Carbide production was investigated from both the oxide and elemental precursors. Ultra-rapid synthesis has been achieved through the development of a reproducible experimental technique and the investigation into a plethora of reaction variables as well as microwave applicators and powers. This resulted in, specifically within the single mode cavity, the completion of the majority of reactions within 20 s. Further development was then built upon the direct relationship observed between phase fraction results (obtained from Powder X-ray Diffraction (PXD) data), in-situ temperature and ex-situ dielectric property measurements; allowing reaction profiles of the various carbides to be mapped, as well as a crucial understanding of the effects of microwave energy on materials at various temperatures. Powder Neutron Diffraction (PND) was also used to evaluate product purity and the C occupancy of the final products, revealing non-stoichiometry which relates directly to the Tc onset observed for the superconducting transition metal carbides. This, in turn, allowed the trends observed for the ternary carbides to be explained, a linear trend does not exist between Tc and C occupancy. In an effort to develop on the understanding of solid state microwave heating, in-situ reaction monitoring techniques were investigated. Through the use of thermal imaging and high speed photography, the W-C system was observed during the crucial initial stages of the reaction process. The information obtained both corroborated previously collected data and allowed a possible reaction mechanism to be alluded to. The observation of localised heating, prior to the beginning of carbide formation, suggests possible high temperatures far exceeding those observed by optical pyrometry. This could well explain the rapid reaction times as well as suggest an interaction mechanism between carbon, an efficient microwave absorber, and tungsten, a low dielectric loss metal.

This dissertation presents the findings of a project where, following investigation and assessment, a million tonnes of sand and gravel at a contaminated former US Air Force Base was excavated for use as aggregate. The process required on-site screening for petroleum hydrocarbons of over 7,000 soil samples and provided an opportunity to assess the efficiency of the investigation, assess the application of geophysics of hydrocarbon contaminated sites, and look at the role of aggregate extraction in the contaminated land industry.