Browsing by Author "Chavara, DT"

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    Colloidal processing of zirconium diboride ultra-high temperature ceramics
    (John Wiley and Sons, 2013-05-21) Tallon, C; Chavara, DT; Gillen, AL; Riley, D; Edwards, L; Moricca, SA; Franks, GV
    Colloidal processing of the Ultra-High Temperature Ceramic (UHTC) zirconium diboride (ZrB2) to develop near−net-shaping techniques has been investigated. The use of the colloidal processing technique produces higher particle packing that ultimately enables achieving greater densification at lower temperatures and pressures, even pressureless sintering. ZrB2 suspension formulations have been optimized in terms of rheological behavior. Suspensions were shaped into green bodies (63% relative density) using slip casting. The densification was carried out at 1900°C, 2000°C, and 2100°C, using both hot pressing at 40 MPa and pressureless sintering. The colloidally processed materials were compared with materials prepared by a conventional dry processing route (cold pressed at 50 MPa) and subjected to the same densification procedures. Sintered densities for samples produced by the colloidal route are higher than produced by the dry route (up to 99.5% relative density by hot pressing), even when pressureless sintering is performed (more than 90% relative density). The promising results are considered as a starting point for the fabrication of complex-shaped components that can be densified at lower sintering temperatures without pressure. © 2013, The American Ceramic Society.
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    Hot isostatic pressing of ceramics, glass and glass-ceramics for immobilisation of intermediate-and high-level nuclear waste
    (Australian Institute of Physics, 2018-01-31) Vance, ER; Gregg, DJ; Chavara, DT
    Different classes of nuclear wastes are briefly described, together with an idea of the required qualities of the processed waste for geological disposal. The main Synroc project at ANSTO these days is immobilisation of the upcoming ~5000L/yr intermediate-level waste from the production of the 99Mo radiopharmaceutical and this has been demonstrated inactively by hot isostatic pressing (HIP) a glass at full scale, together with showing its resilience to compositional variations of 10% for all main components, minor impurities and HIP temperature and pressure. Other work deals with HIP immobilisation of zirconolite-based glass-ceramics for surplus PuO2 immobilisation, glass-ceramics and ceramics for U-rich legacy ANSTO 99Mo intermediate-level and low-level waste, immobilisation of pyroprocessing fluoride-salt waste, spent power plant fuel, refractory glasses and CuI.
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    Neutron diffraction measurements of residual stress and mechanical testing of pressure sintered metal-ceramic composite systems
    (Materials Research Forum LLC., 2016-12-22) Toppler, K; Luzin, V; Saleh, M; Ruys, AJ; Kabir, K; Chavara, DT
    Abstract. Functionally graded materials (FGMs) are composite materials which vary in phase composition, microstructure and properties over one or more dimensions. They are a good potential choice for nuclear reactor components as they can be engineered to effectively resist corrosion and radiation damage. In the case of a metal-ceramic FGM, they can mate the strength and ductility of a metal with the hardness and toughness of a ceramic. A series of composite samples of variable metal-ceramic ratios was manufactured by hot uniaxial pressing in cylinders. Bulk uniform samples of a certain composition were manufactured as a more efficient way of studying FGMs without the extreme gradient required in practical applications. Thermally and mechanically generated stresses, inherent in composites, frequently create conditions for micro-cracking development, depending on the material’s micro-structural characteristics and the thermo-mechanical processing route. Bulk stress measurements in the prepared samples were carried out on the Kowari diffractometer on the OPAL reactor at ANSTO. Both phases – metal matrix and ceramic inclusions – were measured in both axial and lateral directions for full characterisation of the composite stress state. When compared against analytical evaluation, experimental results, for some samples, demonstrated significant stress relaxation with micro-cracking being the main suspect. Copyright © 2016 by the author(s)