Now showing 1 - 10 of 34
  • Publication
    Experimental and economic study of aluminium-gallium alloys as a fuel/catalyst for hydrogen propulsion
    An investigation was carried out into the feasibility of using Al-Ga alloys as a renewable agent to produce hydrogen from water, following positive claims from a research group in the USA. The hypothesis was that pellets of Al-Ga would oxidise in water, resulting in hydrogen evolution which could be directly used in a fuel cell to power a vehicle. This paper reports on new experiments on the reaction of a range of compositions of binary Al-Ga pellets in contact with water. It was found that the reaction does not go to completion, resulting in only a fraction of theoretical hydrogen evolution, and that – contrary to research findings of others – gallium is not a passive catalyst and is also partially oxidised in water. A new proposal on the reaction mechanism is presented. Even if theoretical H2 output was achieved, we show that the aluminium cycle is uneconomic and impractical, and that total CO2 emissions per km travelled are significantly higher than those from an equivalent petrol engine. Guidelines for improved alloy design and optimum microstructure for renewable hydrogen production from water are suggested.
  • Publication
    Validation of a Front-Tracking Model of the Columnar to Equiaxed Transition using Solidification Results from the Maxus 7 Microgravity Platform
    (The Japan Society of Microgravity Application, 2008-03) ; ; ; ;
    To study the columnar-to-equiaxed transition (CET) in alloy castings, three aluminum-silicon samples were solidified onboard the MAXUS 7 sounding rocket. Temperature measurements were made during the flight and the samples were retrieved and analyzed for their solidified macrostructure. Two of the samples produced a CET while the third sample produced a mixed structure with grains nucleating on the crucible walls. A novel front tracking model of solidification and a model of the MACE test apparatus are presented. Validation of the solidification code is carried out. Cooling curves from the experiments are predicted. A simulation of the solidified macrostructure is also given for each experiment. The CET positions are predicted in agreement with the experimental results.
  • Publication
    Twin roll casting of bulk amorphous alloys: modelling and experimental validation
    There is a growing commercial need for semi-finished flat bulk metallic glass product (BMG), in sheet or strip form, for further shaping into components or containers by forming when in the supercooled liquid state. It has been shown tha ttwin roll casting is a viable method to continuously produce flat amorphouse allow strip of a few mm in thickness. However the process has to be carefully designed and controlled to ensure successful production of a fully amorphous product. To assist with the design of experiments, a steady state model of twin roll casting of BMGs has been developed and used to simulate the continuous casting a Mg65Cu25Y10 alloy. The alloy's thermophysical properties were measured to ensure reliable modelling. Twin roll casting experiments were carried out to assess the validity of the model simulations. The model predicted that it would be possible to roll cast the alloy to a thicness of 1.5 mm at speeds of up to 7cm/s using Cu-Be rolls of 190 mm diameter. This was found to be in good agreement with the outcome of the twin roll casting trials which successfully produced fully amorphous strip at these parameter settings.
  • Publication
    Meso-scale thermal and solidification modelling for metallic additive manufacturing processes
    The emergence of additive manufacturing (AM) in recent decades signifies a paradigm shift in how we think about manufacturing. Throughout history, breakthroughs in manufacturing were focused on mass production, with a “one size fits all” mentality. Whilst for large batch size applications this has invariably decreased unit manufacturing costs, increased throughput and decreased prices for customers, it also imposes significant limitations for small batch production. Conventional manufacturing requires many highly specialised steps and equipment, requiring significant resources to establish and setting the barrier to entry unfeasibly high for fledgeling SMEs to enter the manufacturing space. Coupled with this, it inevitably forces manufacturers to be unresponsive to their customers’ needs, as changes to a product or manufacturing process are costly, and require significant machine downtime. Additive manufacturing on the other hand offers virtually limitless freedom to the manufacturer to make changes to a product, even for a one-off bespoke application, without significant machine downtime or costly modification to the manufacturing process. Perhaps even more importantly, since parts are generated additively many of the restrictions that traditional machining imposes on part design no longer apply, allowing for near-net- shape, highly optimised structures to be realised. However, these advantages do not come without a cost. Widespread adoption of AM is still hampered by less than ideal mechanical performance.
  • Publication
    Characterization of Micro Injection Molding Process for the Replication of Micro/Nano Features Using Bulk Metallic Glass Insert
    Microsytems are motivating the development of complex, net-shape products weighing a few milligrams or having micro/nano features. Such small components or micro/nano features are subject to extreme shear rates and thermal gradients in the micro injection molding process due to their large surface to volume ratio. Detailed process monitoring and characterization are desirable to create a viable manufacturing process with acceptable part quality for MEMS and Microsystems. This work covers the replication of micro/nano scale features using Bulk Metallic Glass (BMG), implementation of a suite of PT (pressure and temperature) sensors on a commercial reciprocating micro injection molding machine, and detailed analysis of the relationship between process-rheology-replication. The results indicate that injection velocity dominates the average viscosity of polymer melts; holding pressure can adjust the input pressure history for micro/nano features and mold temperature can enhance feature filling by elevating the po-mold interface temperature. Tailored strategies to set machine parameters for different molds and plastics can be developed to meet the quality requirement for both small components and micro/nano features.
  • Publication
    Comparison of crystalline and amorphous versions of a magnesium-based alloy: corrosion and cell response
    (AO Research Institute Davos, 2015-08-28) ; ;
    Mg-Ca-Zn alloys have been identified as potential materials for bioresorbable orthopaedic implants –e.g. for bone fixation. It is important, however, to tailor the resorption rate of the alloy to the healing rate of the bone and the rate at which the metal ion release can be tolerated by the human body. Recent work has shown that bulk metallic glass (or amorphous) alloys corrode more slowly than their conventional crystalline counterparts1, and the rate may be more suited to orthopaedic applications. It has also indicated a slower evolution of hydrogen gas during resorption2. This paper presents an experimental study on the casting of a Mg75-Zn22-Ca5 into bulk amorphous form, and testing of the resultant material in vitrofor corrosion and cytotoxicity.
  • Publication
    XRMON-SOL microgravity experiment module on Maser-13
    The XRMON-SOL microgravity experiment observed spatially isothermal equiaxed solidification of an Al–Cu alloy in microgravity on board the MASER 13 sounding rocket, launched in December 2015. It is the first time that isothermal equiaxed solidification of a metallic alloy has been observed in situ in space, providing unique benchmark experimental data. The experiment used a newly developed isothermal solidification furnace in the re-used module of the MASER 12 experiment XRMON-GF. A grain-refined Al–20 wt%Cu sample was fully melted and solidified during 360 s of microgravity and the solidification sequence was recorded using time-resolved X- radiography. Equiaxed nucleation, dendritic growth, solutal impingement, and eutectic transformation were thus observed in a gravity-free environment. This paper describes the technology development of the experiment module.
  • Publication
    Review of the Maxus 8 Sounding Rocket Experiment to Investigate Solidification in a Ti-Al-Nb Alloy
    (European Space Agency, 2009) ; ; ;
    A review of the MAXUS 8 sounding rocket microgravity experiment to investigate solidification structures in a Ti-Al-Nb intermetallic alloy is presented. The experiment was part of the Intermetallic Materials Processing in Relation to Earth and Space Solidification (IMPRESS) EU FP6 project. Key objectives were to investigate columnar and equiaxed solidification, and to achieve Columnar-to-Equiaxed Transition (CET) in the alloy. A microgravity experiment was designed to achieve this using a controlled power-down method. Two alloys were tested: one inoculated with a grain refiner and the other without grain refinement. Unrefined samples displayed axial and radial columnar growth. Boride inoculated samples displayed an equiaxed structure. No clear CET was achieved. The design, details, and results of the experiment are presented.
  • Publication
    In Situ X-ray Studies of metal alloy solidification in microgravity conditions – The XRMON project
    The performance of structural metallic materials is associated with the solidification microstructures, which are strongly dependent on gravity effects. Experimentation in a microgravity environment is a unique way to suppress these effects and to provide benchmark data for testing current theories of grain and microstructure formation. This contribution presents a summary of results obtained for directional solidification of Al-Cu alloys within the framework of the XRMON project. It is focussing on (i) the first ever microgravity experiment on solidification with in situ monitoring of metal alloys performed on board a sounding rocket and (ii) solidification experiments performed on board parabolic flights, where the effects of varying gravity level have been studied.
  • Publication
    Manufacturing microstructured tool inserts for the production of polymeric microfluidic devices
    Tooling is critical in defining multi-scale patterns for mass production of polymeric microfluidic devices using the microinjection molding process. In the present work, fabrication of various microstructured tool inserts using stainless steel, nickel and bulk metallic glasses (BMGs) is discussed based on die-sinking EDM (electrical discharge machining), electroforming, focused ion beam milling and thermoplastic forming processes. Tool performance is evaluated in terms of surface roughness, hardness and tool life. Compared to stainless steel, nickel and BMGs are capable of integrating length scales from 100 to 10−8 m and are good candidates for producing polymeric microfluidics. Selection of tool materials and manufacturing technologies should consider the end-user requirements of actual applications.
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