Browsing by Author "Holmes, R"
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- ItemCorrosion performance of Ni-16%wt.Mo-X%wt.SiC alloys in FLiNaK molten salt(Elsevier, 2018-10-01) Yang, C; Muránsky, O; Zhu, HL; Karatchevtseva, I; Holmes, R; Avdeev, M; Jia, YY; Huang, HF; Zhou, XTThe corrosion performance of Ni-16%wt.Mo-X%wt.SiC (X = 0.5, 1.5, 2.0, 2.5 and 3.0) alloys prepared via mechanical alloying followed by consolidation using spark plasma sintering (SPS) from pure Ni, Mo and SiC powders is investigated. Corrosion testing at 650 °C/200 h in FLiNaK molten salt showed that increasing the volume fraction of SiC in the initial Ni-Mo-SiC powder mixture leads to formation of large amount of Mo2C precipitates, which readily dissolve into FLiNaK molten salt. Hence, only the corrosion resistance of NiMo-SiC alloys with a low SiC content (<2 wt.%) is comparable to that of Hastelloy-N® alloy. © 2018 Elsevier Ltd. All rights reserved.
- ItemGd2Zr2O7 and Nd2Zr2O7 pyrochlore prepared by aqueous chemical synthesis(Elsevier, 2013-12-01) Kong, L; Karatchevtseva, I; Gregg, DJ; Blackford, MG; Holmes, R; Triani, GPyrochlore structured Gd2Zr2O7 and Nd2Zr2O7 are produced via complex precipitation processing. A suite of characterization techniques, including FTIR, Raman, X-ray and electron diffraction, TEM, SEM as well as nitrogen sorption are employed to investigate the structural and grain size evolution of the synthesized and calcined powder. Results show that Gd2Zr2O7 with the pyrochlore structure are produced after calcination at 1400 °C for 12 h while Nd2Zr2O7 has already formed the pyrochlore structure at 1200 °C. This method allows the formation of dense materials at relatively low temperature, with bulk densities over 92% of the theoretical values achieved after sintering at 1400 °C for 50 h. This unique aqueous synthetic method provides a simple pathway to produce pyrochlore lanthanide zirconate without using either organic solvent and/or mechanical milling procedures, making the synthesis protocol an attractive potential scale-up production of highly refractory ceramics. © 2013, Elsevier Ltd.
- ItemHigh-temperature corrosion of helium ion-irradiated Ni-based alloy in fluoride molten salt(Elsevier, 2015-02-01) Zhu, HL; Holmes, R; Hanley, TL; Davis, J; Short, KT; Edwards, LA comparison of the effect of helium-ion-radiation damage on a Ni–Mo–Cr–Fe alloy exposed to high-temperature (750 °C) corrosion in eutectic LiF–NaF–KF molten salt has been made. Microstructural examination showed that both the corroded-only and irradiated and corroded samples exhibit the characteristics of intergranular corrosion. However, helium ion irradiation introduces defects such as helium bubbles and cavities into the microstructure, greatly increasing intragranular corrosion of the irradiated sample. The thickness of the remaining corrosion zone for the irradiated sample was much greater than that for the unirradiated sample. © 2014 Elsevier Ltd.
- ItemHot isostatically pressed (HIPed) fluorite glass‐ceramic wasteforms for fluoride molten salt wastes(John Wiley & Sons, Inc., 2020-06-07) Gregg, DJ; Vance, ER; Dayal, P; Farzana, R; Aly, Z; Holmes, R; Triani, GMolten pyroprocessing salts can be used to dissolve used nuclear fuel from a reactor allowing recovery of the actinides. Previously, ANSTO have demonstrated hot isostatically pressed (HIPed) sodalite glass‐ceramic wasteforms for eutectic (Li,K)Cl salts containing fission products, but this system cannot be used for the analogous molten alkali fluoride salts (eg, FLiNaK), which have utility in the application of the next generation of nuclear reactors. In this work, a novel glass‐ceramic composite wasteform has been prepared by HIPing, as a candidate for the immobilization of fission product‐bearing FLiNaK salts. The wasteform has been tailored to immobilize the high fluoride content of the waste within fluorite, whereas the waste alkali elements are incorporated in a durable sodium aluminoborosilicate glass, with total waste loadings of ~17‐21 wt% achieved. It was also demonstrated that the speciation of Mo‐ and Sb‐simulated fission products was altered by adding Ti metal due to a controlled redox environment. The resulting candidate wasteform has been studied by X‐ray diffraction and scanning electron microscopy, including the HIP canister‐wasteform interaction zone, and its performance assessed via leaching studies using the PCT and ASTM C1220 leaching protocols. Dr Vance very much enjoyed the challenge of wasteform design for problematic nuclear wastes, for which fission product‐bearing FLiNaK salts are a clear example. His ability to hone in on a wasteform solution with viable waste loadings that meet performance requirements was testament to his nearly 40 years experience in nuclear waste immobilization. The samples discussed in this work represent the last wasteform materials that he prepared. © 1999-2020 John Wiley & Sons, Inc.
- ItemMolten FLiNaK salt infiltration into degassed nuclear graphite under inert gas pressure(Elsevier B.V., 2015-04-01) He, ZT; Gao, L; Qi, W; Zhang, BL; Wang, X; Song, JL; He, XJ; Zhang, C; Tang, H; Holmes, R; Xia, HH; Zhou, XTInfiltration of molten FLiNaK salt into degassed nuclear graphite samples under inert gas pressure was studied. The weight gain of different grades (2020, 2114, IG-110, NBG-8, G1 and G2) of nuclear graphite during infiltration with different pressures was measured. Molten salt infiltration was compared with mercury intrusion porosimetry where it was found that mercury infiltration was a useful predictor of the threshold pressure and infiltration volume per gram graphite for molten salt infiltration. The distribution and morphology of salt in the graphite were observed by scanning electron microscopy, with very little difference between the molten salt content at the center and edge of samples for samples infiltrated at pressure higher than the threshold pressure. Increased molten salt infiltration with increased pressure resulted from the occupation of smaller pores and full occupation of the larger irregular pores. The similarity of weight gain between molten salt infiltration equilibrated at 20 and 100 h showed 20 h was adequate to obtain equilibrium. © 2014 Elsevier Ltd.
- ItemNew synthesis route for lead zirconate titanate powder(Elsevier, 2016-05-01) Kong, L; Karatchevtseva, I; Holmes, R; Davis, J; Zhang, YJ; Triani, GPhase pure lead zirconate titanate (PZT) powder was produced via a new aqueous coprecipitation method. A suite of characterization techniques, including FTIR, Raman, X-ray diffraction, SEM as well as nitrogen sorption were employed to investigate the structural evolution of the synthesized and calcined powder. The dried precipitate formed in aqueous phase yielded approximately 80 wt% final product after calcination. The PZT perovskite structure was obtained after calcination at 550 °C for 3 h. Milling of the calcined powder reduced the mean particle size from approximately 10 µm to 2 µm. With increasing calcination temperature from 550 °C to 700 °C, both surface area and pore volume decreased while pore size increased from 3.4 nm to 9.8 nm. The bulk density of pelletized samples increased from 4.83 to 7.57 g/cm3 with increasing sintering temperature from 800 °C to 1200 °C. Powder processing using this aqueous route is simple and reproducible leading to a method that is readily scalable for industrial applications. © 2016 Elsevier Ltd.
- ItemA novel chemical route to prepare La2Zr2O7 pyrochlore(John Wiley and Sons, 2012-11-09) Kong, L; Karatchevtseva, I; Gregg, DJ; Blackford, MG; Holmes, R; Triani, GLanthanum zirconate has been prepared via a new chemical synthesis method by combining sol–gel processing and complex precipitation. The synthesis was carried out in aqueous solution under ambient conditions. The synthesized powder possessed the pyrochlore superstructure upon calcination above 1200°C. A suite of characterization techniques, including FTIR, Raman, X-ray and electron diffraction, TEM, SEM, and nitrogen sorption were employed to investigate the microstructural evolution and bulk properties. Dense ceramics (>90% relative density) were obtained after sintering at 1400°C, without need for additional processing (i.e., hot or cold isostatic pressing) or any milling steps. A mechanism has been proposed that elucidates molecular assembly of this chemical synthesis method. © 2012, The American Ceramic Society.
- ItemOne-step approach for synthesis of nanosized Cu-doped zeolite A crystals using the Cu–EDTA-complex(Elsevier, 2014-11-14) Yordanov, I; Karatchevtseva, I; Chevreau, H; Avdeev, M; Holmes, R; Thorogood, GJ; Hanley, TLCopper-doped nanosized zeolite A crystals were synthesized by an in situ templating approach using [Cu(EDTA)]2−-complex. The structural properties of the copper containing zeolite crystals were characterized by a suite of different techniques including SEM–EDX, ESR, mid-IR and Far-IR, Raman, in situ XRD and non-ambient neutron powder diffraction. The SEM investigations on the morphology show spheroidal zeolite A crystals with average size ∼200 nm. The asymmetric ESR spectrum shows that the Cu2+ ion is in a tetragonal-distorted octahedral crystal field. FT-IR and Raman spectroscopies provide information on coordination environment of the copper ion. The band due to stretching vibration of C–N bond, where N is coordinated to the copper ion (C–N–Cu), was observed at 1109 cm−1 in the mid-infrared region. The Raman band due to the Cu–O bond is present at 630 cm−1 indicating the coordination of the Cu2+-cation to COO−-group of the EDTA-ion. The XRD data shows an enlarged d-spacing between the adjacent zeolite lattice planes due to the presence of the [Cu(EDTA)]2−-complex in comparison to template-free LTA zeolite structure. LeBail fitting approach on temperature-dependent in situ X-ray and neutron diffraction profiles have demonstrated the expansion of the zeolite cell during the thermal treatment followed by subsequent contraction with the decomposition of the organic template. © 2014, Elsevier
- ItemProfiling hot isostatically pressed canister–wasteform interaction for Pu-bearing zirconolite-rich wasteforms(John Wiley & Sons, Inc, 2022-04-02) Dayal, P; Farzana, R; Zhang, YJ; Lumpkin, GR; Holmes, R; Triani, G; Gregg, DJZirconolite-rich full ceramic wasteforms designed to immobilize Pu-bearing wastes were produced via hot isostatic pressing (HIP) using stainless steel (SS) and nickel (Ni) HIP canisters. A detailed profiling of the elemental compositions of the major and minor phases over the canister–wasteform interaction zone was performed using scanning electron microscopy combined with energy-dispersive X-ray spectroscopy (SEM-EDS) characterization. Bulk sample analyses from regions near the center of the HIP canister were also conducted for both samples using X-ray diffraction and SEM-EDS. The sample with the Ni HIP canister showed almost no interaction zone with only minor diffusion of Ni from the inner wall of the canister into the near-surface region of the wasteform. The sample with the SS HIP canister showed ∼100–120 μm of interaction zone dominated by high-temperature Cr diffusion from canister materials to the wasteform with the Cr predominantly incorporated into the durable zirconolite phase. We also examined, for the first time, changes to the HIP canister wall thickness caused by HIPing and demonstrated that no canister wall thinning occurred. Instead, in the areas examined, the canister wall thickness was observed to increase (up to ∼20%) due to the compression occurring during the HIP cycle. Further, only sparse formation of (Cr, Mn)-rich oxide particles were noted within the HIP canister inner wall area immediately adjacent to the ceramic material, with no evidence for reverse diffusion of ceramic materials. Though the HIP canister–wasteform interaction extends to ∼120 μm when using an SS HIP canister for the system investigated, this translates to <<1 vol.% for an industrial scale HIPed wasteform. Importantly, the HIP canister–wasteform interactions did not produce any obviously less durable phases in the wasteform or had any detrimental impact on the HIP canister properties. © 2022 Commonwealth of Australia. Journal of the American Ceramic Society published by Wiley Periodicals LLC on behalf of American Ceramic Society.
- ItemPyrochlore glass-ceramics for the immobilization of molybdenum-99 production wastes: demonstrating scalability and flexibility to waste stream variance(Elsevier, 2021-11) Farzana, R; Zhang, YJ; Dayal, P; Aly, Z; Holmes, R; Triani, G; Vance, ER; Gregg, DJPyrochlore glass ceramics have been fabricated via in-situ crystallization under reducing conditions by both sintering and hot isostatic pressing (HIPing) as candidate wasteforms for the acidic waste biproduct of Mo-99 radiopharmaceutical production. The tailored wasteform demonstrates flexibility in the wasteform design to receive the required waste variability, it also suitably passes high-level waste performance requirement, and successfully scales to 1 kg scale with 45 wt.% waste loading. U-rich pyrochlore as the major phase was confirmed by X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy, with residual glass and minor secondary phases. The presence of both U4+ and U5+ valences in the wasteforms was revealed by diffuse reflectance spectroscopy. Addition of glass content had little influence on the pyrochlore composition but facilitated minor perovskite formation. The up-scaled dense, HIPed sample showed elemental releases of < 2 g/L for all elements in durability experiments. © 2021 Elsevier Ltd
- ItemPyrolysis behaviour of titanium dioxide-poly(vinyl pyrrolidone) composite materials(Elsevier, 2009-10) Holmes, R; Campbell, JA; Burford, RP; Karatchevtseva, IInorganic–organic hybrid materials are studied due to the unique properties they exhibit. As these materials become more widely applied, particularly as precursor materials for forming inorganic materials, it is essential that the pyrolysis behaviour is understood. Transparent yellow hybrid materials consisting of titanium dioxide and poly(vinyl pyrrolidone) were prepared using sol–gel processing techniques. The hybrids maintained their transparency up to the highest achieved inorganic loading of 57 wt.%. These materials were characterised using thermogravimetric analysis in which the organic component was pyrolysed. The resultant chars were then investigated using optical microscopy, x-ray diffraction, scanning electron microscopy, and atomic force microscopy. The inorganic loading had an effect on char formation, with higher loadings leading to the formation of pyrolysis intermediates which were less apparent in samples of lower inorganic content. The pyrolysis intermediates were found to be carbon-rich. © 2009, Elsevier Ltd.
- ItemSynroc technology: perspectives and current status (review)(John Wiley & Sons, Inc., 2020-06-22) Gregg, DJ; Farzana, R; Dayal, P; Holmes, R; Triani, GDr Eric (Lou) Vance spent 32 years at the Australian Nuclear Science and Technology Organisation (ANSTO), where he was dedicated to the development of Synroc technology, a waste treatment solution for intractable nuclear wastes. The original form of Synroc, a multiphase ceramic wasteform based on stable and leach resistant titanate minerals, was invented by Australian scientists in the late 1970s. This formulation was directed toward the immobilization of PUREX wastes from the reprocessing of nuclear fuels. Synroc at ANSTO under the scientific leadership of Dr Vance since evolved beyond these original titanate ceramics into a waste treatment technology platform. This platform can be applied to produce glass, glass‐ceramic and ceramic wasteforms and offers distinct advantages in terms of waste loading and suppressing volatile losses. The platform therefore provides an opportunity to treat those waste streams that are problematic for glass matrices alone or existing vitrification process technologies. Such wastes include, for example, actinide‐bearing wastes, those that contain large proportions of refractory elements, those with significant fission product or corrosive volatile emissions and those wastes resulting from radiopharmaceutical production. The implementation of the latter will see the industrialization of Synroc technology via a first‐of‐a‐kind Synroc Waste Treatment Facility that is currently under construction at ANSTO. This paper will review Synroc technology, particularly noting the substantial and essential contributions from the late Dr Vance. The review will also provide some perspective on the development of the technology for nuclear waste immobilization and describe the significant recent advancements at ANSTO. © 1999-2020 John Wiley & Sons, Inc.
- ItemSynroc waste treatment facility for fission-based molybdenum-99 production(Australian Nuclear Science and Technology Organisation, 2019-09-27) Gregg, DJ; Holmes, R; Triani, GANSTO is currently building a Synroc Waste Treatment facility, a first of a kind plant for the treatment of intermediate-level liquid waste derived from molybdenum-99 production. This industrial scale facility shall deploy ANSTO’s Synroc technologies; a wasteform tailored for immobilizing fission products and an automated process designed for remote operation that will include waste and additive mixing, powder production, canister filling and sealing, and hot isostatic pressing (HIP). The HIP represents the last processing step to consolidate the wasteform into a final durable solid compact with the required performance characteristics. Molybdenum-99 production at ANSTO results in three predominant waste streams, one of which is a highly caustic intermediate-level liquid waste solution of fission products and is the target waste for the Synroc facility. The engineered wasteform for this caustic waste stream was designed with the key requirements of high waste loading and high aqueous durability whilst incorporating sufficient chemical flexibility to manage the specified variations in the waste chemistry. The tailored wasteform has the required performance properties suitable for final disposal in a geological repository and achieves substantial waste volume reductions compared to a cementation option. The technology maturation plan for delivering the Synroc Waste Treatment Facility for the production of the tailored wasteform is aimed at identifying project and technical risks and mitigating these risks through specific work packages. As part of this strategy, a highly automated inactive engineering demonstrator has been constructed by ANSTO Synroc engineers. The role of this facility is to mitigate a number of the technology risks associated with a first of a kind project by addressing process integration, process operation, process recovery, maintenance, and operator training. Further, the plant is being used to develop the quality assurance framework to ensure that the waste package produced meets the waste acceptance criteria for final disposition. This presentation shall discuss the wasteform design for the wastes produced from molybdenum-99 production. It will also outline the various stages of development in realising the final plant design as well as timelines to progress through cold- and hot-commissioning. Once realized, the facility will represent a significant step change in the treatment of intermediate-level waste from molybdenum-99 nuclear medicine production and a major advance in the development pathway for ANSTO’s Synroc Technologies.