394 results found
Middleburgh SC, Ipatova I, Evitts LJ, et al., 2020, Evidence of excess oxygen accommodation in yttria partially-stabilized zirconia, Scripta Materialia, Vol: 175, Pages: 7-10, ISSN: 1359-6462
© 2019 Yttria partially stabilized zirconia (ZrO2)x(Y2O3)½-x has been investigated to understand accommodation of excess oxygen into its structure. ZrO2 powder with 8 wt% Y2O3 additions was treated in 30 vol% H2O2 solution to promote oxidation of the material. A new Raman peak was observed after treatment at 840 cm−1, consistent with previous reports of solid state peroxide ions (O22−). This was corroborated using atomic scale simulation based on density functional theory; these also highlighted the near-zero solution enthalpy for excess oxygen in the monoclinic structure via the formation of a peroxide ion defect.
Hsieh YH, Rushton MJD, Fossati PCM, et al., 2020, Thermal footprint of a geological disposal facility containing EURO-GANEX wasteforms, Progress in Nuclear Energy, Vol: 118, ISSN: 0149-1970
© 2019 Elsevier Ltd Synroc-Z is a new wasteform being developed to be specifically suited to waste from the advanced EURO-GANEX reprocessing route. This type of waste contains nuclides that release significant amounts of heat during their decay. Here, predictions for radiogenic heat generation from EURO-GANEX wasteforms based on Synroc-Z ceramic and R7T7 glass materials are presented. During reprocessing, any actinides present in the waste-stream are removed to leave only fission products. Simulation results are given demonstrating that, although initially classified as high level waste, the effects of decay mean the wasteforms effectively become intermediate level after 140 years of storage. Furthermore, many of the issues arising from alpha decay will be avoided. During the first 600 years, it is shown that the main source of self heating comes from the decay of Cs-137 and Sr-90. Our calculations show how the significant radiogenic heating by these wasteforms must be considered when defining package sizes and waste loadings. These effects are discussed for both ceramic and glass wasteforms and demonstrate that Synroc-Z provides more flexibility allowing larger packages even at higher waste loadings than R7T7.
Al Nasiri N, Patra N, Pezoldt M, et al., 2019, Investigation of a single-layer EBC deposited on SiC/SiC CMCs: Processing and corrosion behaviour in high-temperature steam, Journal of the European Ceramic Society, ISSN: 0955-2219
© 2019 The Authors Two rare earth monosilicates (Yb 2 SiO 5 , and Lu 2 SiO 5 ) were deposited using a low-cost coating application method to produce a single-layer coating. RE- oxides slurries were dip coated on oxidised CMC samples and subsequently heat treated at high temperature to ensure reaction between SiO 2 and RE-oxides to form the RE-monosilicate. A single, continuous, homogeneous thick coating of 25 μm was obtained. X-ray diffraction (XRD) confirmed formation of, RE-monosilicates in Yb and Lu silicate systems. Coated samples were exposed to 90% H 2 O static steam environment at 1350 °C for 25, 50, 100, and 150 h. Scanning Electron Microscopy (SEM) indicated that both coatings adhered strongly to the substrate. Coating thickness reduced from 22 μm to 11 μm for Yb-coating and 13 to 4 μm for Lu-coating with increasing corrosion time from 25 to 150 h, however there was no significant attack of the CMC for all steam exposure times.
Rushton MJD, Ipatova I, Evitts LJ, et al., 2019, Stoichiometry deviation in amorphous zirconium dioxide, RSC ADVANCES, Vol: 9, Pages: 16320-16327, ISSN: 2046-2069
Zhang H, Jayaseelan DD, Bogomol I, et al., 2019, A novel microstructural design to improve the oxidation resistance of ZrB2-SiC ultra-high temperature ceramics (UHTCs), JOURNAL OF ALLOYS AND COMPOUNDS, Vol: 785, Pages: 958-964, ISSN: 0925-8388
Oxidation of UC was studied from 873 to 1173 K in air and in 10 Pa oxygen using a High Temperature Environmental SEM (HT-ESEM). Conversion to U 3 O 8 improved when using 873 K as the oxide product was a fine powder. At higher temperatures (973 K to 1173 K) oxidation slowed due to a densification process with formation of coarse fragments. The oxide fragmentation at 973 K and 1073 K and oxide pulverisation at 873 K were observed in situ in a HT-ESEM. Cracking induced fragmentation and pulverisation was linked to stresses generated from the volumetric transformation from UC to U 3 O 8 .
Giorgi E, Grasso S, Zapata-Solvas E, et al., 2018, Reactive carbothermal reduction of ZrC and ZrOC using Spark Plasma Sintering, ADVANCES IN APPLIED CERAMICS, Vol: 117, Pages: S34-S47, ISSN: 1743-6753
Pletser D, Ohashi T, Yoshii Y, et al., 2018, Temperature dependent volatilisation behaviour of Cs from two commercial adsorbents used at Fukushima measured using novel experimental apparatus, PROGRESS IN NUCLEAR ENERGY, Vol: 109, Pages: 214-222, ISSN: 0149-1970
Hsieh Y-H, Humphry-Baker SA, Horlait D, et al., 2018, Durability of hot uniaxially pressed Synroc derivative wasteform for EURO-GANEX wastes, JOURNAL OF NUCLEAR MATERIALS, Vol: 509, Pages: 43-53, ISSN: 0022-3115
A new candidate fusion engineering material, WC-FeCr, has been irradiated with He ions at 25 and 500 °C. Ions were injected at 6 keV to a dose of ~15 dpa and 50 at. % He, simulating direct helium injection from the plasma. The microstructural evolution was continuously characterised in situ using transmission electron microscopy. In the FeCr phase, a coarse array of 3–6 nm bubbles formed. In the WC, bubbles were less prominent and smaller (~2 nm). Spherical-cap bubbles formed at hetero-phase interfaces of tertiary precipitates, indicating that enhanced processing routes to minimise precipitation could further improve irradiation tolerance.
Patra N, Lee WE, 2018, Facile Precursor Synthesis of HfC-SiC Ultra-High-Temperature Ceramic Composite Powder for Potential Hypersonic Applications, ACS APPLIED NANO MATERIALS, Vol: 1, Pages: 4502-4508, ISSN: 2574-0970
Fossati PCM, Rushton MJD, Lee WE, 2018, Atomic-scale description of interfaces in rutile / sodium silicate glass-crystal composites, Physical Chemistry Chemical Physics, Vol: 20, Pages: 17624-17636, ISSN: 1463-9076
In this work interfaces between (Na2O)x(SiO2)1−x glasses (for x=0.0, 0.1 and 0.2) and TiO2 crystals are simulated using molecular dynamics and empirical potentials. Interfaces are presented for the distinct terminat- ing surfaces of TiO2 with Miller indices ≤ 2, the properties of which have been investigated using atomistic models. Simulations showed that par- tially ordered layers had been induced in the glass close to the interfaces, with successive oxygen-rich and cation-rich planes being noted. The first silicate layer in contact with the crystal tended to be highly-structured, with Si ions occupying well-defined positions that depend on the orien- tation of the crystal at the interface, and showing 2-dimensional ordering depending on glass composition. Finally, interface energies were calcu- lated. These indicated that the interface formation may stabilise a crystal surface in comparison to maintaining a free surface. Results are pre- sented suggesting that the structural flexibility of the glass network allows it to conform to the crystal, thereby providing charge compensation and avoiding large relaxation of the crystal structure close to the interfaces. Such interfacial properties could be crucial to improving phenomenologi- cal models of glass-crystal composite properties.
Gasparrini C, Chater RJ, Horlait D, et al., 2018, Zirconium carbide oxidation: kinetics and oxygen diffusion through the intermediate layer, Journal of the American Ceramic Society, Vol: 101, Pages: 2638-2652, ISSN: 0002-7820
Oxidation of hot‐pressed ZrC was investigated in air in the 1073‐1373 K range. The kinetics were linear at 1073 K, whereas at higher temperature samples initially followed linear kinetics before undergoing rapid oxidation leading to a Maltese cross shape of the oxide. The linear kinetics at 1073 K was governed by inward oxygen diffusion through an intermediate layer of constant thickness between ZrC and ZrO2 which was comprised of amorphous carbon and ZrO2 nanocrystals. Diffusion of oxygen through the intermediate layer was measured to be 9 × 10−10 cm2 s−1 using 18O as a tracer in a double oxidation experiment in 16O/18O. Oxidation at 1073 and 1173 K produced samples made of m‐ZrO2 and either t‐ or c‐ZrO2 with an adherent intermediate layer made of amorphous carbon and ZrO2, whereas oxidation at 1273 and 1373 K produced samples with a voluminous oxide made of m‐ZrO2 showing a gap between ZrC and the oxide. A substoichiometric zirconia layer was found at the gap at 1273 K and no carbon uptake was detected in this layer when compared with the top oxide layer. The loss of the intermediate layer and the slowdown of the linear rate constant (g m−2 s−1) at 1273 K compared to 1173 K was correlated with the preferential oxidation of carbon at the intermediate layer which would leave as CO and/or CO2 leaving a gap between ZrC and substoichiometric zirconia.
Patra N, Al Nasiri N, Jayaseelan DD, et al., 2018, Thermal properties of C-f/HfC and C-f/HfC-SiC composites prepared by precursor infiltration and pyrolysis, JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, Vol: 38, Pages: 2297-2303, ISSN: 0955-2219
Chinnam RK, Fossati PCM, Lee WE, Degradation of partially immersed glass: A new perspective, Journal of Nuclear Materials, Vol: 503, Pages: 56-65, ISSN: 0022-3115
The International Simple Glass (ISG) is a six-component borosilicate glass which was developed as a reference for international collaborative studies on high level nuclear waste encapsulation. Its corrosion behaviour is typically examined when it is immersed in a leaching solution, or when it is exposed to water vapour. In this study, an alternative situation is considered in which the glass is only partially immersed for 7 weeks at a temperature of 90ºC. In this case, half of the glass sample is directly in the solution itself, and the other half is in contact with a water film formed by condensation of water vapour that evaporated from the solution. This results in a different degradation behaviour compared to standard tests in which the material is fully immersed. In particular, whilst in standard tests the system reaches a steady state with a very low alteration rate thanks to the formation of a protective gel layer, in partially-immersed tests this steady state could not be reached because of the continuous alteration from the condensate water film. The constant input of ions from the emerged part of the sample caused a supersaturation of the solution, which resulted in early precipitation of secondary crystalline phases.This setup mimics storage conditions once small amounts of water have entered a glass waste form containing canister. It offers a more realistic outlook of corrosion mechanisms happening in such situations than standard fully-immersed corrosion tests.
Ojovan MI, Burakov BE, Lee WE, 2018, Radiation-induced microcrystal shape change as a mechanism of wasteform degradation, Journal of Nuclear Materials, Vol: 501, Pages: 162-171, ISSN: 0022-3115
Experiments with actinide-containing insulating wasteforms such as devitrified glasses containing 244 Cm, Ti-pyrochlore, single-phase La-monazite, Pu-monazite ceramics, Eu-monazite and zircon single crystals containing 238 Pu indicate that mechanical self-irradiation-induced destruction may not reveal itself for many years (even decades). The mechanisms causing these slowly-occurring changes remain unknown therefore in addition to known mechanisms of wasteform degradation such as matrix swelling and loss of solid solution we have modelled the damaging effects of electrical fields induced by the decay of radionuclides in clusters embedded in a non-conducting matrix. Three effects were important: (i) electric breakdown; (ii) cluster shape change due to dipole interaction, and (iii) cluster shape change due to polarisation interaction. We reveal a critical size of radioactive clusters in non-conducting matrices so that the matrix material can be damaged if clusters are larger than this critical size. The most important parameters that control the matrix integrity are the radioactive cluster (inhomogeneity) size, specific radioactivity, and effective matrix electrical conductivity. We conclude that the wasteform should be as homogeneous as possible and even electrically conductive to avoid potential damage caused by electrical charges induced by radioactive decay.
Lerdprom W, Bhowmik A, Grasso S, et al., 2018, Impact of spark plasma sintering (SPS) on mullite formation in porcelains, JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Vol: 101, Pages: 525-535, ISSN: 0002-7820
Kota S, Zapata-Solvas E, Chen Y, et al., 2017, Isothermal and Cyclic Oxidation of MoAlB in Air from 1100 degrees C to 1400 degrees C, JOURNAL OF THE ELECTROCHEMICAL SOCIETY, Vol: 164, Pages: C930-C938, ISSN: 0013-4651
Lerdprom W, Zapata-Solvas E, Jayaseelan DD, et al., 2017, Impact of microwave processing on porcelain microstructure, CERAMICS INTERNATIONAL, Vol: 43, Pages: 13765-13771, ISSN: 0272-8842
Zapata-Solvas E, Gomez-Garcia D, Dominguez-Rodriguez A, et al., 2017, High temperature creep of 20 vol.% SiC-HfB2 UHTCs up to 2000 °C, Journal of the European Ceramic Society, Vol: 38, Pages: 47-56, ISSN: 0955-2219
High temperature compressive creep of SiC-HfB2 UHTCs up to 2000 °C has been studied. Microstructural analysis after deformation reveals formation of new phases in the Hf-B-Si and Hf-B-Si-C systems, which are responsible for the poor creep resistance. RE oxide additions have a negative effect reducing the creep resistance of SiC-HfB2 UHTCs. A simplistic analysis for the required creep resistance is described, indicating that only SiC-HfB2 UHTCs could withstand re-entry conditions for 5 min in a single use. However, RE oxide addition to SiC-HfB2 UHTCs does not provide the required creep resistance for them to be candidate materials for hypersonic applications.
Gasparrini C, Podor R, Horlait D, et al., 2017, Oxidation of UC: An in situ high temperature environmental scanning electron microscopy study, JOURNAL OF NUCLEAR MATERIALS, Vol: 494, Pages: 127-137, ISSN: 0022-3115
In situ HT-ESEM oxidation of sintered UC fragments revealed the morphological changes occurring during the transformation between UC to UO2 and UO2 to U3O8 at 723–848 K and in an atmosphere of 10–100 Pa O2. Two main oxidation pathways were revealed. Oxidation at 723 K in atmospheres ≤25 Pa O2 showed the transformation from UC to UO2+x, as confirmed by post mortem HRTEM analysis. This oxidation pathway was comprised of three steps: (i) an induction period, where only surface UC particles oxidised, (ii) a sample area expansion accompanied by crack formation and propagation, (iii) a stabilisation of the total crack length inferring that crack propagation had stopped. Samples oxidised under 50 Pa O2 at 723 K and at 773–848 K for 10–100 Pa O2 showed an “explosive” oxidation pathway: (i) sample area expansion occurred as soon as oxygen was inserted into the chamber and crack propagation and crack length followed an exponential law; (ii) cracks propagated as a network and the oxide layer fragmented, (iii) an “explosion” occurred causing a popcorn-like transformation, typical for oxidation from UO2 to U3O8. HRTEM characterisation revealed U3O8 preferentially grow in the  direction. The explosive growth, triggered by ignition of UC, proceeded as a self-propagating high-temperature synthesis reaction, with a propagation speed of 150–500 ± 50 μm/s.
Bai Y, Qi X, Duff A, et al., 2017, Density functional theory insights into ternary layered boride MoAlB, ACTA MATERIALIA, Vol: 132, Pages: 69-81, ISSN: 1359-6454
Faber KT, Asefa T, Backhaus-Ricoult M, et al., 2017, The role of ceramic and glass science research in meeting societal challenges: Report from an NSF-sponsored workshop., Journal of the American Ceramic Society, Vol: 100, Pages: 1777-1803, ISSN: 0002-7820
Under the sponsorship of the U.S. National Science Foundation, a workshop on emerging research opportunities in ceramic and glass science was held in September 2016. Reported here are proceedings of the workshop. The report details eight challenges identified through workshop discussions: Ceramic processing: Programmable design and assembly; The defect genome: Understanding, characterizing, and predicting defects across time and length scales; Functionalizing defects for unprecedented properties; Ceramic flatlands: Defining structure‐property relations in free‐standing, supported, and confined two‐dimensional ceramics; Ceramics in the extreme: Discovery and design strategies; Ceramics in the extreme: Behavior of multimaterial systems; Understanding and exploiting glasses and melts under extreme conditions; and Rational design of functional glasses guided by predictive modeling. It is anticipated that these challenges, once met, will promote basic understanding and ultimately enable advancements within multiple sectors, including energy, environment, manufacturing, security, and health care.
Zapata-Solvas E, Hadi MA, Horlait D, et al., 2017, Synthesis and physical properties of (Zr1-x,Tix)3AlC2 MAX phases, Journal of the American Ceramic Society, Vol: 100, Pages: 3393-3401, ISSN: 1551-2916
MAX phase solid solutions physical and mechanical properties may be tuned via changes in composition, giving them a range of possible technical applications. In the present study, we extend the MAX phase family by synthesizing (Zr1−xTix)3AlC2 quaternary MAX phases and investigating their mechanical properties using density functional theory (DFT). The experimentally determined lattice parameters are in good agreement with the lattice parameters derived by DFT and deviate <0.5% from Vegard's law. Ti3AlC2 has a higher Vickers hardness as compared to Zr3AlC2, in agreement with the available experimental data.
Lerdprom W, Grasso S, Jayaseelan DD, et al., 2017, Densification behaviour and physico-mechanical properties of porcelains prepared using spark plasma sintering, ADVANCES IN APPLIED CERAMICS, Vol: 116, Pages: 307-315, ISSN: 1743-6753
Humphry-Baker S, Lee WE, Peng K, 2017, Oxidation resistant tungsten carbide hardmetals, International Journal of Refractory Metals and Hard Materials, Vol: 66, Pages: 135-143, ISSN: 0958-0611
We present a new method for retarding the oxidation rate of hardmetals. By diffusion impregnating a WC-FeCr hardmetal with silicon, we manufacture two-layered silicide coatings consisting of an FeSix outer crust and WSi2 beneath. The structure results from a preferential reaction between silicon and the metallic binder. The FeSix outer layer is crucial to providing oxidation resistance as when exposed to oxygen it passivates, forming a protective SiO2 surface film – while simultaneously preventing exposure of the underlying WSi2, which is known to oxidise in an active manner. Our analysis shows the coating method is applicable to various hardmetals structures.
Al Nasiri N, Patra N, Jayaseelan D, et al., 2017, Water vapour corrosion of rare earth monosilicates for environmental barrier coatings application, Ceramics International, Vol: 43, Pages: 7393-7400, ISSN: 1873-3956
Water vapour corrosion resistance of five rare earth monosilicates Y2SiO5, Gd2SiO5, Er2SiO5, Yb2SiO5, and Lu2SiO5 was investigated during testing at 1350 °C for up to 166 h in static air with 90% water vapour. Four of the RE-silicates showed little weight gain (0.859 mg cm−2) after 166 h of exposure. Prior to testing the microstructure consists of equiaxed grains of 4- 7±0.4 µm. XRD analysis showed that after 50 h exposure to water vapour corrosion Y, Er, Yb and Lu-silicates had both mono and disilicates present on their surfaces as a result of the reaction between monosilicate and water vapour to form disilicate, while Gd-silicate has converted completely to G4.67Si3O13 making it less stable for environmental barrier coating application. The microstructures of corroded Y, Er, Yb and Lu-silicates contain ridges and cracks, while that of Gd-silicate contains rounded grains suggesting melting along with striped contract grains.
Zapata-Solvas E, Christopoulos SRG, Ni N, et al., 2017, Experimental synthesis and density functional theory investigation of radiation tolerance of Zr₃(Al₁–ₓ,Siₓ)C₂ MAX phases, Journal of the American Ceramic Society, Vol: 100, Pages: 1377-1387, ISSN: 1551-2916
Synthesis, characterisation and density functional theory calculations have been combined to examine the formation of the Zr3(Al1–xSix)C2 quaternary MAX phases and the intrinsic defect processes in Zr3AlC2 and Zr3SiC2. The MAX phase family is extended by demonstrating that Zr3(Al1–xSix)C2, and particularly compositions with x ≈ 0.1, can be formed leading here to a yield of 59 wt.%. It has been found that Zr3AlC2 – and by extension Zr3(Al1–xSix)C2 – formation rates benefit from the presence of traces of Si in the reactant mix, presumably through the in situ formation of ZrySiz phase(s) acting as a nucleation substrate for the MAX phase. To investigate the radiation tolerance of Zr3(Al1–xSix)C2 we have also considered the intrinsic defect properties of the end members. Aelement Frenkel reaction for both Zr3AlC2 (1.71 eV) and Zr3SiC2 (1.41 eV) phases are the lowest energy defect reactions. For comparison we consider the defect processes in Ti3AlC2 and Ti3SiC2 phases. It is concluded that Zr3AlC2 and Ti3AlC2 MAX phases are more radiation tolerant than Zr3SiC2 and Ti3SiC2 respectively. Their applicability as cladding materials for nuclear fuel is discussed.
Juthapakdeeprasert J, Lerdprom W, Jayaseelan DD, et al., 2017, Cerium-Added alumina and cerium-Added zircon as high emissivity coatings for cement rotary kilns, Pages: 404-411
Chinnam RK, Hutchison C, Pletser D, et al., 2016, Degradation of International Simple Glass Cracks and Surface, MRS Advances, Vol: 1, Pages: 4215-4220, ISSN: 2059-8521
Water degradation of glass waste forms has been studied extensively under a variety of conditions including of bulk glass immersed completely in static or dynamic water. In practice, the vitrified nuclear waste cracks as soon as poured into a container because of differences in thermal expansion coefficients. In addition, in repository the canisters may be only partially immersed in water. Later, water condenses on the surface of glass which corrodes releasing ions. In this work experiments have been performed to understand these effects on the degradation of International Simple Glass (ISG). Simulated cracks were found to develop pitting corrosion in the crack openings when tested by immersing ISG in water. Under load, these pits concentrated stress and grew as large planar cracks inside the glass. The condensation of water on glass surfaces leads to formation of pits and growth of calcium silicate crystals.
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