Laser sintering (LS), an additive manufacturing (AM) technology, allows for the production of 3-dimensional parts by fusing together successive layers of polymer powder without the need for tooling. Its potential and applicability, however, is still constrained due to the limited repertoire of materials available and the lack of detail in understanding both the important process-material interactions and consequently the requirements for the development of new materials. Past research has mainly focused on polyamide 12 (PA12) as the standard material, hence most of the empirically grown or theoretical, often idealized, process models are based on this polymer. As a result, it was shown that there are strong interactions between the material and the process leading to an undesired deviation of part properties. Thermoplastic elastomers (TPEs) for LS have gained more and more popularity for the production of, for example flexible parts in the recent past but they are a group of polymers that is neither well studied nor understood regarding their use in LS. Therefore, this PhD investigation has focused on TPEs in order to reveal their process specifics throughout the processing chain in LS. As the properties of parts manufactured by LS are, amongst others, influenced by the packing and flow efficiencies of the powders, the bulk (static) and flow (dynamic) characteristics of the observed TPEs were examined on the powder scale as well as their effects on the process and parts. The resulting part properties were evaluated in terms of their tensile properties, surface roughness and density. In contrast to previous studies which have rarely taken into account the characteristics of the un-sintered particles, this work provided a novel approach quantifying and describing the interconnection between the powder characteristics as well as its performance and the part properties, thus providing valuable input on future material design. As mentioned before, for typical semi-crystalline thermoplastics such as PA12, different idealized process models describing the Pre-Process specifics exist, but they might not necessarily be applicable for thermoplastic elastomers with significantly different thermal characteristics. Consequently, the important interactions during processing of TPEs have been studied by high speed and high resolution thermography helping to indicate the most important material properties in combination with calorimetric analysis. The resulting understanding of crystallization and melting behaviour helped to derive a design of experiments revealing the possible range for the process management in terms of temperature control as well as energy input and the resulting part properties. Moreover, it is known that polymers used in LS change their intrinsic properties due to processing conditions that are close to the crystalline melting temperature. As a result, within this PhD investigation the ageing behaviour of TPEs was studied. Both the powder and the sintered parts were examined for chemical and physical ageing effects. The results showed that the materials observed could be used without refreshing throughout the applied ageing cycles, however, changes in the processing behaviour as well as in the parts’ mechanical properties were evident. These changes were due to the differing ageing states of the LS-powder showing an increase in the particle size affecting the bulk materials packing density. In the literature, modifications in the rheological properties due to thermal loads during LS are already known on basis of PA12. It was shown that they tend to experience an increase in molecular weight with increasing processing cycles. In this work it was found that TPEs exhibit the exact opposite trend in a slight decrease of molecular weight likely to reduce the mechanical strength of tensile specimens. By using novel process adapted methods in order to reveal vital interactions of TPE powders for LS, this thesis makes a significant contribution to an AM database. In addition, the comprehensive observation and applications of these methods over the whole processing chain helped expanding the understanding of important requirements for the development of new polymers for LS and builds a substantial basis for future work and quality assurance.

A study was made of the rate of absorption of sulphur in grams per minute from sulphur dioxide - nitrogen gas mixtures by molten iron and iron containing four per cent carbon, The maximum rate of nitrogen flow and partial. pressure of sulphur dioxide was 350 ml/minute and 0·06 atmospheres respectively. The melts were contained in alundum and magnesia crucibles at 14000 - l550 [deg] C, the gas being blown on to the surface of the metal and occasionally bubbled through the metal for mixing purposes by means of an alumina tube. Samples or metal were taken periodically and analysed for carbon and sulphur by combustion methods.

A study on the chlorination of Basic Oxygen Steelmaking (BOS) by-product dusts followed by water leaching was conducted. The samples used for the studies sourced from the earth works and beneficiation of BOS byproduct from the stockpile. Comprehensive reports resulted from the excavation, beneficiation, physical and chemical analysis are reported. Zinc and iron removal studies from BOS by-product were investigated by means of chlorination roasting. Chlorination roasting of the BOS material by means of pyrometallurgical extraction was undertaking, assessing parameters such as roasting temperature, roasting time and chemical stoichiometry. A preliminary study was carried out using a solid chlorination agent, Ammonium Chloride (NH4Cl) in a muffle furnace for a 3 stage roasting conducted for 15 minutes to 180 minutes at 450C to 750C. Selected studies were carried out with 1-stage roasting. Further experimental studies then took place for chlorination using gaseous Cl2/N2 mixture gas in the tube furnace with 5 times chemical stoichiometry for a roasting time from 5 minutes to 90 minutes, with various temperatures from 150C to 750C. A 1 times and 2 times stoichiometry were added in selected procedure to foresee the effects of starvation agent. Additional surface area affects were also added to the chlorination with Cl2/N2 gas using bigger sample boat. Water leaching for 1 hour and 24 hours were conducted on the sample roasted with Cl2/N2 to investigate the leachability of Zn to assist further removal. The chemical and mineralogical composition of the BOS stockpile varied widely. The pH value were highly alkaline ranging from 10.2 – 13.5, while the moisture content showed a very wide range from 6 – 43%. The particle size analysis of the earth works excavation on the study site established five stockpile particle size fraction, ranging from as fine as <0.8mm to >38.22 mm. The composition of zinc ranging from 2.78% - 5.96%, while the iron content ranging from 41.36 to 62.18% respectively. This amount of iron has the potential for recovery and reused within a steel making process. It is possible to recover 97% of Zn and 30% Fe by roasting at 750C for a period of 135 minutes with NH4Cl salt. Roasting with 3 stages of NH4Cl addition proved to be more appropriate to increase the percentage of zinc removal. 97% Zn are removed Cl2/N2 gas for a period of 30 minutes roasting. The water leaching was conducted More than 90% Zn are recovered using bigger surface area sample boat with only 2.5 times stoichiometry. The extraction of Zn was greatly enhanced by the water leaching following the chlorination roasting using Cl2/N2 gas. 95% of Zn was leached while only 7% Fe was extracted after chlorination at 650C for 20 minutes roasting. It is possible to leach up to 98% Zinc after the chlorination roasting at 450C at 20 mins. The research has demonstrated that chlorination extraction has potential application in the steel sector for removal of Zn from steelmaking BOS dusts. In conducting the chlorination roasting, operational parameters such as temperature, roasting, chlorine agent stoichiometry, and surface area are important in determining the best operational condition. Hybrid process of chlorination roasting with leaching could highly assist in the further removal of Zn from BOS dust.

The growth in the use and wear of Ti-based alloy components in mining and offshore explorations has led to a search for techniques to re-engineer such components for reuse. The most desirable method of restoring/protecting the component surfaces is by hard-facing to enhance longevity in service. Laser cladding is one of the viable techniques to achieve a thick coating on such components which involves the addition of reinforcing particulates to improve surface properties such as hardness, wear and erosion resistance amongst others. A fundamental study and understanding of the resultant microstructure-property of the laser clad, hard-facing composite becomes necessary. In this study, laser cladding of Ti-6Al-4V wire with Spherotene particulate reinforcement and laser cladding of modified pre-blend of Ti-6Al-4V and TiB_2 powder were undertaken. The resulting physical and microstructural characteristics, hardness, and performance characteristics of laser clad composites were investigated. Samples from the as-deposited laser clad composites were characterised using optical microscopy, scanning electron microscopy (with chemical microanalysis) and X-ray diffraction. Performance characteristics were examined via erosion testing of the laser clad Ti-6Al-4V/Spherotene using plain and abrasive water jetting, and tensile testing of the laser clad Ti-6Al-4V/TiB_2 composite. The results showed that a crack and pore free clad containing as high as 76 wt.% Spherotene in the Ti matrix was achieved at an energy density of 150 J.mm^-2, 275 mm/min traverse speed, 700 mm/min wire feed rate and 30 g/min powder feed rate. The microstructure of the laser clad Ti-6Al-4V/Spherotene is characterised by nano-sized precipitates of reaction products (W and TiC) uniformly distributed in a beta-Ti solid solution matrix. Matrix hardness is enhanced by the presence of the reaction products in the Ti ranging between 410-620 kgf.mm^-2. Moreover, the modication made to the 90 wt.% Ti-6Al-4V/10 wt.% TiB2 feedstock by attaching the TiB2 to Ti-6Al-4V allowed uniform distribution of reinforcing element in the deposited composite. The composite microstructure on solidication is characterised by TiB eutectic needle-like features uniformly distributed in a Ti-rich primary phase. The hardness of the composite ranged between 440-480 gf.mm^-2. Tensile tests showed that the mean elastic modulus of Ti-6Al-4V/TiB_2 composite is 145 GPa, which is a 27% improvement when compared to that of Ti-6Al-4V. Erosion test indicated that the Ti-6Al-4V/Spherotene composite offered as high as 13 and 8 times resistance of that of Ti-6Al-4V when subjected to PWJ and AWJ impacts respectively.

This thesis covers in detail a study of the excavation of rock salt by roadheader, the factors affecting performance and finally a specification with operational results of a new production machine to suit the South African Coal Mining Industry. Dosco Overseas Engineering Ltd. the author's employer, is introduced. Reference is made to how, over the years, performance prediction has radically changed from a mere approximation to a position where an accurate value with a performance guarantee is a necessity. Reference is made to the Universities of Newcastle-upon-Tyne, Nottingham and Leeds who have been the main suppliers of rock testing facilities. The University of Newcastle-upon-Tyne has had further responsibilities for a specific test programme, funded by Dosco, to establish a Performance Prediction Methodology. A general introduction to the trial site at Domtar Salt, located in Canada, is given, along with the current mining methods and the particular aspects requiring consideration if machine mining were to be adopted. A detailed study over a twelve month period covering three main topics; fines production, performance rates, and cutter pick suitability is described. Results are discussed at length and valuable conclusions are drawn. Extrapolation of the results to predict the performance of a larger machine suitable to Domtar's high production requirements is shown. The ability to relate this study to other applications and, in particular, the aspect of pick penetration and its effect on machine design is discussed. A prediction curve suitable for South African coal is shown, along with the necessary calculations to enable a high production rate and the corresponding effect on machine design. Specification features, such as boom force, cutter head design and cutter motor power, are considered at length. The implications for the machine manufacturer for even larger, more powerful machines is shown. An early correlation· of findings is established by comparison to field results from a smaller single boom, Dosco roadheader. The study concludes that current or new machine design can be favourably influenced to reflect varying market requirements and that accurate prediction of machine performance is possible. A later, overall study of the TB2500 shows achieved production rates and comments in particular, on machine mining rate and available mining time. Recommendations having particular reference to the equipment suppliers involvement in the sales procedure are given.

Early produced water treatment technologies were developed before carbon dioxide emissions and hazardous waste discharge were recognised as operational priority. These technologies are deficient in the removal of dissolved hydrocarbons and dissolved heavy metal ions which have been identified as major contributors to the high environmental impact factor of produced water. The simultaneous removal of heavy metals and polycyclic aromatic hydrocarbon (PAH) from produced water via photoelectrochemical process was identified in this work as a produced water treatment alternative with the potential to virtually eliminate the cost for chemical reagents and high energy input. Several grades of simulated produced water were synthesised and used to understand different parameters necessary for developing a successful photoelectrochemical treatment. The process demonstrated in this work followed a simple two–electrode photoelectrochemical cell where heavy metals were recovered on a platinum electrode with simultaneous degradation of PAH (phenanthrene) on a photoanode, with the aid of sunlight (simulated) and an applied cell voltage of 1.0 V. Multiwall CNT-TiO2 synthesised via a modified sol-gel method served as the photoanode after it was immobilised at a loading of 2.5 mg/cm2 on a titanium plate. The results obtained from the photoelectrochemical treatment showed a recovery of 1.6 g/cm2 of lead, 0.2 g/cm2 of copper and 0.1 g/cm2 of nickel from produced water on a 0.1 cm diameter platinum electrode after 24 hours of irradiation with simulated sunlight at 1.0 V cell voltage and a simultaneous degradation of up to 16 % phenanthrene on the photoanode, which gives a potential of scaling up the process to a commercial throughput.

There is growing interest in Al-TM (transition metal)-RE (rare earth) amorphous alloys because of the combination of their good mechanical properties and corrosion resistance. However, the high critical cooling rate required to form the amorphous structure leads to difficulties in generating bulk amorphous material. Therefore, there has been greater interest in producing amorphous Al-TM-RE alloys as surface layers. In this study, wedge mould casting, laser surface melting (LSM) and large area electron beam (LAEB) surface melting were used to fabricate Al Co-Ce alloys in both crystalline and amorphous form. An eutectic Al 33Cu (wt.%) alloy was also used to quantify the solidification conditions based on the well-known relationship. The microstructures formed by different processes were investigated by scanning electron microscopy, energy dispersive X-ray spectroscopy, image analysis and X ray and glancing angle X-ray diffraction. In particular, LAEB surface melting was found to be able to provide a sufficiently high solidification velocity for the generation of an amorphous layer on the remelted surface of bulk crystalline Al Co-Ce alloys. Experimental results show that the LAEB treatment can remelt, homogenise the multiphase crystalline starting material and generate a predominantly amorphous layer, although it also caused cracking of the treated layer. However, the cracking was largely reduced in the laser refined starting microstructure. Laser microstructural refinement also improved the homogenisation and amorphisation generated by the subsequent LAEB treatment. The temperature field of multi-pulse LAEB irradiated Al-Co-Ce and Al-Cu alloys was numerically simulated through a finite difference method. The simulation results were generally consistent with the experimental results. The corrosion behaviour of Al-Co-Ce alloys with different microstructures was studied through potentiodynamic polarisation tests. Al-Co-Ce amorphous layer exhibited an enhanced corrosion resistance compared to the crystalline counterpart, although cracking in the amorphous layer greatly influenced the effectiveness of the amorphous layer protecting the substrate.

The research is directed towards modelling the chiller set, the heat rejection and the load subsystems of a complete mine refrigeration system and simulating the performance in order that the design can be optimised and the most cost effective control system determined. The refrigeration load profile for a mechanised mine is complex and primarily a function of surface climatic variations, the strongly cyclic sources of heat resulting from the operation of diesel powered mining equipment and the associated differences in thermal environmental acceptance criteria. Modelling of the central element of the system, the compressor, is based on empirical relationships which use the actual cooling duty and input power rather than general compressor curves using theoretical flow and head coefficients. This has a more general application and is not restricted to a single compressor type. The steady state modelling of five refrigeration systems has included two types of compressor, four types of evaporator, three types of condenser, two types of cooling tower and five types of mine cooling appliances. The research has extended modelling of refrigeration systems by incorporating fully the heat rejection and load subsystems and has demonstrated that relatively complex mine refrigeration systems can be modelled and the simulation results related to actual measurements with an acceptable accuracy. This has been further improved by testing the system elements and adjusting the theoretical performance analysis where necessary. These adjustments concern either the more difficult to assess factors such as evaporating and condensing heat transfer coefficients or factors influenced by unusual operating conditions. The research has shown that, despite the complexity of the load profile and the refrigeration system, modelling and simulation can be used effectively to optimise both the design and the control system.

The current trends towards increased coal production from seams at greater depth has led to increased demands being placed on the methane drainage and mine ventilation systems. This study has been directed towards the development of computer models to simulate and analyse the gas flows in methane drainage ranges and the airflow and pressure distribution in mine ventilation networks. The first part of this thesis describes the conventional techniques of methane drainage currently employed and the mathematical approach used to model gas flow in the methane drainage range. It also discusses how, when combined with measured underground data, predicted results can be used to assess the performance of the range. Subsequent analysis techniques will suggest measures that can be undertaken to optimise this performance and assess the effect of selective network reconfiguration. The second part of the thesis includes a discussion of the increasing application of booster fans in U.K. underground coal mines and a critical analysis of the mathematical methods used to model airflow and pressure distribution in mine ventilation networks. One particular method was adopted in a simulation model used to analyse networks with booster fans and specified face airflows. Both simulation models developed have been used to analyse representative underground methane drainage ranges and mine ventilation networks. The thesis concludes that the accuracy of the methane drainage models can only be guaranteed when developed in conjunction with suitable measured data. The mine ventilation model requires user guidance through the solution and analysis procedure. Results are presented in a simple graphical manner and this approach, rather than the 'black box' non interactive approach, is to be favoured in the analysis of mine ventilation networks.

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