Now showing 1 - 10 of 11
  • Publication
    EIRSAT-1 - The Educational Irish Research Satellite
    The Educational Irish Research Satellite, "EIRSAT-1", is a collaborative space project that aims to build, launch and operate the first ever Irish satellite. The EIRSAT-1 spacecraft is a 2U CubeSat incorporating three novel experiment payloads: GMOD, a gamma-ray detector; EMOD, a thermal management coating demonstration; and WBC, an attitude control algorithm. The spacecraft is currently under construction at University College Dublin and will be delivered to ESA in late 2019.
  • Publication
    Accurate measurement of nanofluid thermal conductivity by use of a polysaccharide stabilising agent
    Measuring the thermal conductivity of low viscosity fluids such as aqueous nanofluids is challenging due to the formation of convection currents. In the current work, a modification of the transient hot-wire thermal conductivity measurement technique was investigated to address this problem. The polysaccharide agar was used as a gelling agent to prevent the formation of convection currents, thereby enabling measurement of thermal conductivity. The experimental method was validated by comparison of experimentally measured thermal conductivity values with published reference values over a range of temperatures for two reference fluids stabilised by agar: water and an ethylene glycol/water solution. The precision of thermal conductivity measurements was found to be significantly improved by use of this gelling agent. These findings indicate that agar, or a similar gelling agent, can be used to enable accurate measurement of the thermal conductivity of aqueous fluids. This measurement technique was utilised to accurately measure the thermal conductivity enhancements of copper and alumina aqueous nanofluids with low nanoparticle concentrations, over a range of temperatures. The thermal conductivities of these nanofluids were found to be within ± 2 % of those predicted by the Maxwell model.
      550Scopus© Citations 8
  • Publication
    Ultrafine grain formation and coating mechanism arising from a blast coating process: a transmission electron microscopy analysis
    This article examines the substrate/coating interface of a coating deposited onto mild steel and stainless steel substrates using an ambient temperature blast coating technique known as CoBlast. The process uses a coincident stream of an abrasive blast medium and coating medium particles to modify the substrate surface. The hypothesis for the high bond strength is that the abrasive medium roughens the surface while simultaneously disrupting the passivating oxide layer of the substrate, thereby exposing the reactive metal that then reacts with the coating medium. The aim of this study is to provide greater insight into the coating/substrate bonding mechanism by analysing the interface between a hydroxyapatite coating on both mild and stainless steel substrates. The coating adhesion was measured via a tensile test, and bond strengths of approximately 45 MPa were measured. The substrate/coating interface was examined using transmission electron microscopy and selected area diffraction. The analysis of the substrate/ coating interface revealed the presence of ultrafine grains in both the coating and substrate at interface associated with deformation at the interface caused by particle impaction during deposition. The chemical reactivity resulting from the creation of these ultrafine grains is proposed to explain the high adhesive strength of CoBlast coatings.
      508Scopus© Citations 5
  • Publication
    Regression analysis of temperature-dependent mechanical and thermal properties of dielectric technical ceramics
    Regression analysis is performed on a dataset of temperature-dependent material properties of several ceramic materials. The materials considered are alumina, aluminium nitride, beryllia, fused quartz, sialon and silicon nitride. The properties considered are density, Young's, bulk and shear moduli, Poisson's ratio, tensile, flexural and compressive strength, thermal conductivity, specific heat capacity, and thermal expansion coefficient. The dataset, previously reported by de Faoite et al. (J Mater Sci 47(10):4211, 2012), was compiled to facilitate the materials selection and design of a ceramic component for the Variable Specific-Impulse Magnetoplasma Rocket (VASIMR®). Temperature-dependent material property data are required for accurate thermo-structural modelling of such ceramic components which operate over a wide temperature range. The goal of this paper is to calculate a set of regression coefficients to reduce this dataset to a tractable format for use in the materials selection and design of such components. Regression analysis could not be performed for all material properties for all of these materials, due to a lack of data in the literature, and these gaps in the available data are highlighted.
      915Scopus© Citations 17
  • Publication
    Development of glass-ceramic scintillators for gamma-ray astronomy
    Scintillators synthesised as glass-ceramics have several potential benefits compared to the currently-used halide scintillators, including non-hygroscopicity, mechanical ruggedness, ease of producing customisable shapes, and the potential for low-cost synthesis. The use of these scintillators is considered for a gamma-ray telescope operating in the 0.2 MeV¿50 MeV photon range. Inorganic scintillator compounds suitable for incorporation into glass-ceramics are assessed. In addition, several families of glass suitable for use as hosts for scintillating compounds are also reviewed.
      369Scopus© Citations 20
  • Publication
    A review of the processing, composition and temperature-dependent mechanical and thermal properties of dielectric technical ceramics
    The current review uses the material requirements of a new space propulsion device, the Variable Specific Impulse Magnetoplasma Rocket (VASIMR®) as a basis for presenting the temperature dependent properties of a range of dielectric ceramics, but data presented could be used in the engineering design of any ceramic component with complementary material requirements. A material is required for the gas containment tube (GCT) of VASIMR® to allow it to operate at higher power levels. The GCT's operating conditions place severe constraints on the choice of material. A dielectric is required with a high thermal conductivity, low dielectric loss factor, and high thermal shock resistance. There is a lack of a representative set of temperature-dependent material property data for materials considered for this application and these are required for accurate thermo-structural modelling. This modelling would facilitate the selection of an optimum material for this component. The goal of this paper is to determine the best material property data values for use in the materials selection and design of such components. A review of both experimentally and theoretically-determined temperature-dependent & room temperature properties of several materials has been undertaken. Data extracted are presented by property. Properties reviewed are density, Young's, bulk and shear moduli, Poisson's ratio, tensile, flexural and compressive strength, thermal conductivity, specific heat capacity, thermal expansion coefficient and the factors affecting maximum service temperature. Materials reviewed are alumina, aluminium nitride, beryllia, fused quartz, sialon and silicon nitride.
      1638Scopus© Citations 113
  • Publication
    Preparation of Morselised Bone for Impaction Grafting using a Blender Method
    Impaction bone grafting is a method of restoring bone stock to patients suffering significant bone loss due to revision total hip surgery. The procedure requires morselised bone (MB) to be impacted into the site of bone loss in order to stabilise the prosthesis with the aim of the long term resorption and reintegration of the impacted bone graft. Currently, the method for producing MB requires the use of expensive surgical bone mills or manually-intensive rongeurs that can produce a limited variety of particle sizes and may have a low throughput. This study examines the potential to produce suitable MB using a domestic blender. The method produces a wide range of particle sizes without the need for an adjustment of the system. It was found through packing modelling that this particle distribution resulted in reduced initial graft porosity and thus a theoretical potential to increase the graft stiffness and ability of the graft to stabilise a prosthesis in comparison to a manually prepared roughly cut morselised bone samples. Mechanical testing confirmed the increased mechanical performance of the graft through both impaction testing and subsidence testing. The blended MB was found to exhibit greater graft stiffness under the same impaction conditions. The graft was also found to have subsided less in comparison to the rough cut, less well graded MB. Scanning electron imaging also confirmed the retention of the trabecular structure necessary for revascularisation and host bone ingrowth. In conclusion, the blender method offers a rapid and cheap way of obtaining morselised bone with favourable particle size distribution, particle morphology and mechanical properties with preservation of the bone trabecular structure. 
      385Scopus© Citations 1
  • Publication
    Inverse estimate of heat flux on a plasma discharge tube to steady-state conditions using thermocouple data and a radiation boundary condition
    The heat flux incident upon the inner surface of a plasma discharge tube during a helicon plasma discharge was estimated using an inverse method. Temperature readings were taken from the outer surface of the tube using thermocouples, and the temperature data were interpolated over the tube surface. A numerical inverse procedure based on the Alifanov iterative regularisation method was used to reconstruct the heat flux on the tube inner surface as a function of space and time. In contrast to previously-used inverse models for this application, the current model implements a thermal radiation boundary condition to realistically model the energy exchange in the device. Additionally in these experiments, steady-state operation was reached, and the accurate modelling of the steady-state condition was facilitated by the thermal radiation boundary condition. The variation of heat flux with helicon discharge power, propellant flowrate, and electromagnet current was studied, and it was found that the waste heat flux increased with applied RF power and propellant flowrate, and decreased with current supplied to the electromagnets, over the range of parameter variation tested.
      422Scopus© Citations 13
  • Publication
    Nanostructured apatite-mullite glass-ceramics for enhanced primary human osteoblast cell response
    This work investigates the difference in viability of primary human foetal osteoblast cells on a glass-ceramic surface with nanoscale topography relative to viability on a smooth glass-ceramic surface containing a bioactive phase. Apatite-mullite glass-ceramics containing bioactive fluorapatite (Ca10(PO4)6F2) and bioinert mullite (Si2Al6O13) were synthesised and subsequent heat-treatment was optimised to form nano-sized fluorapatite crystals. Etching was used to selectively remove the bioactive phase, producing a surface with disordered nanoscale topography. Cells were seeded onto a smooth polished glass-ceramic substrate with the bioactive phase intact, an etched nanostructured glass-ceramic with the bioactive phase removed, and a borosilicate glass control. Cell viability after 24 h and 48 h was significantly greater on the nanostructured surface compared to the smooth bioactive surface, while cell viability at both time points was significantly greater on both nanostructured and smooth bioactive surfaces compared to the control.
      270Scopus© Citations 5
  • Publication
    Thermo-structural modelling of a plasma discharge tube for electric propulsion
    Potential thermal management strategies for the plasma generation section of a VASIMR® high-power electric propulsion space thruster are assessed. The plasma is generated in a discharge tube using helicon waves. The plasma generation process causes a significant thermal load on the plasma discharge tube and on neighbouring components, caused by cross-field particle diffusion and UV radiation. Four potential cooling system design strategies are assessed to deal with this thermal load. Four polycrystalline ceramics are evaluated for use as the plasma discharge tube material: alumina, aluminium nitride, beryllia, and silicon nitride. A finite element analysis (FEA) method was used to model the steady-state temperature and stress fields resulting from the plasma heat flux. Of the four materials assessed, aluminium nitride would result in the lowest plasma discharge tube temperatures and stresses. It was found that a design consisting of a monolithic ceramic plasma containment tube fabricated from aluminium nitride would be capable of operating up to a power level of at least 250 kW.
      484Scopus© Citations 3