Publications
493 results found
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 [001] 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.
Pletser D, Chinnam RK, Kamoshida M, et al., 2016, Immobilisation process for contaminated zeolitic ion exchangers from Fukushima, MRS Advances, Vol: 1, Pages: 4089-4094, ISSN: 2059-8521
The clean-up of the Fukushima Daiichi site, after the March 2011 earthquake and tsunami, continues to generate large amounts of spent adsorbents. These adsorbents need to be disposed of permanently in a low temperature immobilisation process to avoid volatilising radioactive Cs and Sr species. To this end an immobilisation process with a maximum temperature of 600 °C was developed by sintering model waste with glass frit to form a dense Glass Composite Material (GCM) wasteform. A zeolitic model wasteform, chabazite, was sintered with a lead borosilicate glass composition at a maximum temperature of 600 °C. The sintering process was optimised with various thermal treatment steps to ensure that volatile species, aqueous or otherwise, were released before full sintering to yield a dense final wasteform. With this process dense wasteforms of up to 40 wt. % chabazite have been achieved.
Ojovan M, Lee W, Burakov B, 2016, Destruction of Micro-crystal Containing Wasteforms by Charge-induced Crystal Shape Change on Self-irradiation., MRS Advances
Gasparrini C, Podor R, Horlait D, et al., 2016, Zirconium carbide oxidation: Maltese Cross formation and interface characterization, Oxidation of Metals, Vol: 88, Pages: 509-519, ISSN: 1573-4889
Oxidation of dense hot pressed ZrC specimens from 1073 –1473 K was investigated using an in-situtechnique:HT-ESEM. Cuboid specimens were monitored on the surface and on edges and corners during oxidation in order to understand the influence of crack formation and propagation on the Maltese cross shapedevelopmentof the oxide. The oxidation mechanism comprisedthree steps: (1) delamination of sample edges,(2) crack formation at corners and (3) crackpropagation towards the inner core and formation of microcracks parallel to the interfacethat increase the accessible surface areafollowed by a drastic volume expansion.The microcrackpattern is found to berepetitive as if a cyclicdebonding of the interfaceoccurred. Characterization of the interface by TEM and HRTEMrevealed the interface between ZrC and ZrO2 tocomprise a 2μm thick amorphouscarbonmatrix with ZrO2nanocrystals embedded in it.
Cedillos-Barraza O, Manara D, Boboridis K, et al., 2016, Investigating the highest melting temperature materials: A laser meltingstudy of the TaC-HfC system, Scientific Reports, Vol: 6, ISSN: 2045-2322
TaC, HfC and their solid solutions are promising candidate materials for thermal protection structures in hypersonic vehicles because of their very high melting temperatures (> 4000 K) among other properties. The melting temperatures of slightly hypostoichiometric TaC, HfC and three solid solution compositions (Ta1-xHfxC, with x=0.8, 0.5 and 0.2) have long been identified as the highest known. In the current research, they were reassessed, for the first time in the last fifty years, using a laser heating technique. They were found to melt in the range of 4041-4232 K, with HfC having the highest and TaC the lowest. Spectral radiance of the hot samples was measured in situ, showing that the optical emissivity of these compounds plays a fundamental role in their heat balance. Independently, the results show that the melting point for HfC0.98, (4232 ± 84) K, is the highest recorded for any compound studied until now.
Al Nasiri N, Patra N, Ni N, et al., 2016, Oxidation behaviour of SiC/SiC ceramic matrix composites in air, Journal of the European Ceramic Society, Vol: 36, Pages: 3293-3302, ISSN: 0955-2219
Oxidation of silicon melt infiltrated SiC/SiC ceramic matrix composites (CMC) was studied in air at 1200–1400 °C for 1, 5, 24 and 48 h. Weight gain and oxide layer thickness measurements revealed the oxidation follows parabolic reaction kinetics with increase in temperature and time. XRD showed the extent of oxide layer (SiO2) formation was greatest after 48 h at 1400 °C: an observation confirmed by X-ray photoelectron spectroscopy (XPS), energy dispersive spectroscopy (EDS) and transmission electron microscopy (TEM) analyses. Oxide layer thickness varied from 1 μm after 48 h at 1200 °C to 8 μm after 48 h at 1400 °C. Oxidation of SiC/SiC composites is both temperature and time dependent with an activation energy of 619 kJ mol−1. BN coatings around SiC fibres showed good resistance to oxidation even after 48 h at 1400 °C.
Burr PA, Horlait D, Lee WE, 2016, Experimental and DFT investigation of (Cr,Ti)<inf>3</inf>AlC<inf>2</inf> MAX phases stability, Materials Research Letters, Vol: 5, Pages: 144-157, ISSN: 2166-3831
Using a synergistic combination of experimental and computational methods, we shed light on the unusual solubility of (Cr,Ti)3AlC2 MAX phase, showing that it may accommodate Cr only at very low concentrations (<2 at%) or at the exact Cr/(Cr + Ti) ratio of 2/3, even when the ratio of reactants is far from this stoichiometry (1/2 ≤ Cr/(Cr + Ti) ≤ 5/6). In both phases, Cr exclusively occupies the 4f sites, bridging carbide layers with the Al layer. Despite this, the peculiar stability of (Cr2/3Ti1/3)3AlC2 is attributed to the formation of strong, spin-polarized Cr–C bonds, which result in volume reduction and a marked increase in c/a ratio. IMPACT STATEMENT Solubility of Cr and Ti in (Cr,Ti)3AlC2 was investigated using experimental and DFT techniques. It was also determined that (Cr2/3Ti1/3)3AlC2 owe its remarkable stability to the formation strong Cr–C bonds.
Kota S, Zapata-Solvas E, Ly A, et al., 2016, Corrigendum: Synthesis and Characterization of an Alumina Forming Nanolaminated Boride: MoAlB., Scientific Reports, Vol: 6, ISSN: 2045-2322
Skinner SJ, Lerdprom W, Li C, et al., 2016, Temperature dependence of electrical conductivity of a green porcelain mixture, Journal of the European Ceramic Society, ISSN: 0955-2219
Pettina M, Harrison RW, Vandeperre LJ, et al., 2016, Diffusion-based and creep continuum damage modelling of crack formation during high temperature oxidation of ZrN ceramics, Journal of the European Ceramic Society, Vol: 36, Pages: 2341-2349, ISSN: 0955-2219
ZrN’s good thermal and mechanical properties make it suitable for many commercial applications including in nuclear fuels. An understanding of its oxidation behaviour is essential to prevent catastrophic failures and ensure it is employed safely in nuclear power plants. Based on available experimental results on oxidation of ZrN in the temperature range 1173–1373 K, a continuum damage mechanics-based combined creep and time-dependent material oxidation model is proposed. The model allows for the development of a surface oxide layer combined with damage due to creep under an applied load. A representative grain structure has been modelled according to ZrN microstructural characteristics in order to allow intergranular cracking and individual oxidation damage rates for grains and grain boundaries. The proposed damage model is implemented as a user subroutine and runs in a coupled temperature-displacement analysis using the commercial finite element software Abaqus. Available data on ZrN are used to validate the capability of the model to predict oxidation damage in ceramics at high temperatures.
Lerdprom W, Chinnam RK, Jayaseelan DD, et al., 2016, Porcelain production by direct sintering, JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, Vol: 36, Pages: 4319-4325, ISSN: 0955-2219
Bai Y, Duff A, Jayaseelan DD, et al., 2016, DFT Predictions of Crystal Structure, Electronic Structure, Compressibility, and Elastic Properties of Hf-Al-C Carbides, Journal of the American Ceramic Society, ISSN: 0002-7820
To understand the potential for use of the Hf-Al-C ternary compounds, (HfC)nAl3C2 (Hf2Al3C4 and Hf3Al3C5) and (HfC)nAl4C3 (Hf2Al4C5 and Hf3Al4C6) were investigated using density functional theory, including crystal structure, electronic structure, compressibility, and elastic properties. The theoretical density of (HfC)nAl3C2 (4.10-4.16 g/cm3) is higher than that of (HfC)nAl4C3 (3.92-3.98 g/cm3), due to the smaller number of lighter Al-C layers. With increasing numbers of Hf-C layers, the Hf-C and Al-C bond lengths remain almost unchanged. In none of the compounds is there a gap around the Fermi energy (Ef), which implies they are metal-like conductors. With increasing pressure, there is greater shrinkage along the c axis than the a axis. The bond stiffness increases with increasing pressure. In general, (HfC)nAl3C2 has higher elastic stiffness than (HfC)nAl4C3, with the moduli increasing with the number of Hf-C layers. The Hf-Al-C compounds as well as the brittle Zr-Al-C compounds all have low shear moduli/bulk moduli ratio (G/B) from 0.71 to 0.78, suggesting that the G/B ratio is not always a suitable measure of ductility.
Kota S, Zapata-Solvas E, Ly A, et al., 2016, Synthesis and Characterization of an Alumina Forming Nanolaminated Boride: MoAlB, Scientific Reports, Vol: 6, ISSN: 2045-2322
The ‘MAlB’ phases are nanolaminated, ternary transition metal borides that consist of a transition metal boride sublattice interleaved by monolayers or bilayers of pure aluminum. However, their synthesis and properties remain largely unexplored. Herein, we synthesized dense, predominantly single-phase samples of one such compound, MoAlB, using a reactive hot pressing method. High-resolution scanning transmission electron microscopy confirmed the presence of two Al layers in between a Mo-B sublattice. Unique among the transition metal borides, MoAlB forms a dense, mostly amorphous, alumina scale when heated in air. Like other alumina formers, the oxidation kinetics follow a cubic time-dependence. At room temperature, its resistivity is low (0.36–0.49 μΩm) and – like a metal – drops linearly with decreasing temperatures. It is also a good thermal conductor (35 Wm−1K−1 at 26 °C). In the 25–1300 °C temperature range, its thermal expansion coefficient is 9.5 × 10−6 K−1. Preliminary results suggest the compound is stable to at least 1400 °C in inert atmospheres. Moderately low Vickers hardness values of 10.6 ± 0.3 GPa, compared to other transition metal borides, and ultimate compressive strengths up to 1940 ± 103 MPa were measured at room temperature. These results are encouraging and warrant further study of this compound for potential use at high temperatures.
Harrison RW, Lee WE, 2016, Processing and properties of ZrC, ZrN and ZrCN ceramics: a review, Advances in Applied Ceramics, Vol: 115, Pages: 294-307, ISSN: 1743-6761
ZrC and ZrN ceramics are of interest in the application of materials in extreme high temperature environments, particularly for nuclear applications in generation IV reactors. These materials demonstrate desirable characteristics such as high thermal and electrical conductivities along with high hardness and melting temperatures. Data reported in the literature often suffer from scatter due to differences in processing techniques and difficulty determining stoichiometry, which will significantly affect thermophysical properties. This article reviews the current available data for the properties of ZrC, ZrN and mixed carbonitrides phases and identifies causes of scatter in the literature and areas requiring further research.
Patra N, Al Nasiri N, Jayaseelan DD, et al., 2016, Synthesis, characterization and use of synthesized fine zirconium diboride as an additive for densification of commercial zirconium diboride powder, Ceramics International, Vol: 42, Pages: 9565-9570, ISSN: 1873-3956
Zirconium diboride (ZrB2) was synthesized by a solution-based technique using zirconyl chloride (ZrOCl2·8H2O, ZOO), boric acid (H3BO3, BA) and gum karaya (GK) as the sources of zirconium, boron and carbon, respectively. The initial formation temperature of ZrB2 was 1200 °C and complete conversion was achieved by 1400 °C. Preceramic precursors and as-synthesized ZrB2 powders were characterized by XRD, TG-DTA, SEM, TEM, EDX and compared with commercial ZrB2 powder made by carbothermic reduction. FT-IR of as-synthesized dried preceramic precursor revealed the formation of Zr–O–C and Zr–O–B whereas SEM showed agglomerated spherical particles with mean diameter of <1 µm. Commercial ZrB2 and as-synthesized fine ZrB2 powder were spark plasma sintered (SPS) at 1900 °C for 10 min. Addition of 10 wt% of synthesized fine powder improved the fired density from 87% to 93% of theoretical. A significant cost benefit arises for the utilization of cheap synthesized fine powder as an additive for the densification of the more expensive commercial powder.
Alex J, Vandeperre L, Lee WE, et al., 2016, Effect of Sodium on Microstructures and Thermoelastic Properties of Calcium Aluminate Cement-Bonded Refractories, JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Vol: 99, Pages: 1079-1085, ISSN: 0002-7820
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Cedillos-Barraza O, Grasso S, Al Nasiri N, et al., 2016, Sintering behaviour, solid solution formation and characterisation of TaC, HfC and TaC-HfC fabricated by spark plasma sintering, Journal of the European Ceramic Society, Vol: 36, Pages: 1539-1548, ISSN: 1873-619X
Solid solution formation and sintering behaviour of TaC–HfC ceramics made from commercial TaC and HfC powders prepared using spark plasma sintering (SPS) at temperatures up to 2450 °C was investigated. Phase analysis and lattice parameter measurements using X-ray Diffraction (XRD) showed mutual diffusion of Hf and Ta with increasing sintering temperature. High Resolution Transmission Electron Microscopy (HRTEM) confirmed that solid solution formation and densification were achieved by a solid-state mechanism. Solid solutions were achieved for 4TaC–1HfC, 1TaC–1HfC and 1TaC–4HfC powders after sintering at temperatures of at least 2350 °C. Fracture toughness (KIC) values were in the range of 2.7–3.4 MPa m1/2 for all ceramics measured using Vickers indentation. Thermal conductivity of TaC was 55.8 W/m K at 1400 °C. Coefficients of thermal expansion (CTE) varied from 7.08–7.66 × 10−6/K (in the range of 25–2000 °C), with TaC at the lower end.
Chroneos A, Horlait D, Lee WE, et al., 2016, Attempts to synthesise quaternary MAX phases (Zr,M)2AlC and Zr2(Al,A)C as a way to approach Zr2AlC, Materials Research Letters, Vol: 4, Pages: 137-144, ISSN: 2053-1591
Despite having never been synthesized, the MAX phase Zr2AlC attracts a lot of interest owing to its foreseen properties. A possible way to circumvent this obstacle is to stabilize Zr2AlC by partially substituting one of its constituting elements. Here we report on attempts to synthesise quaternary MAX phases (Zr,M)2AlC and Zr2(Al,A)C where M = Cr, Ti or Mo and A = S, As, Sn, Sb and Pb. We were notably able to produce Zr2(Al0.2Sn0.8)C, Zr2(Al0.35Pb0.65)C, and Zr2(Al0.3Sb0.7)C, with the latter representing the first antimony-based MAX phase ever reported.
Humphry-Baker S, Lee WE, 2016, Tungsten carbide is more oxidation resistant than tungsten when processed to full density, Scripta Materialia, Vol: 116, Pages: 67-70, ISSN: 1872-8456
Previous studies report that WC oxidises in air more readily than W.However, systematic thermogravimetric studies reveal considerably sloweroxidation kinetics in WC samples, which outperform previous measurements by1-2 orders of magnitude. By combining X-ray diffraction and electronmicroscopy, the enhanced stability in WC is explained by a dense interlayer ofsub-stoichiometric WO3, approximately 10 microns in thickness, which formsadjacent to the substrate/oxide interface. The faster oxidation kinetics fromprevious studies are explained by the comparatively low densities of samplesused.
Al Nasiri N, Patra N, Horlait D, et al., 2016, Thermal properties of rare-earth monosilicates for EBC on Si-based ceramic composites, Journal of the American Ceramic Society, Vol: 99, Pages: 589-596, ISSN: 0002-7820
Rare-earth (RE) monosilicates are promising candidates as environmental barrier coating (EBC) materials for ceramic matrix composites for aerospace applications. Five rare-earth monosilicate materials have been investigated: Y2SiO5, Gd2SiO5, Er2SiO5, Yb2SiO5, and Lu2SiO5 produced from RE oxides and silica starting materials pressed and sintered at 1580°C under flowing air. Relative densities above 94% were obtained for all samples and ceramics were made containing 85–100 wt% of the RE monosilicate according to X-ray diffraction (XRD) with RE disilicates as the second phase in the Gd, Yb, and Lu silicate systems. Microstructures were characterized using scanning electron microscopy and XRD, and thermal properties measured including specific heat, thermal expansion, and thermal diffusivity. For the first time, specific heat capacity values are reported for the monosilicates [0.45–0.69 J·(g·K)−1]. Thermal expansion coefficients (TECs) of the dense samples ranged between 5.9 and 10.3 × 10−6 K−1 measured for 473 to 1473 K. All EBCs have low thermal conductivities [1.8 W·(m·K)−1 or less] making them excellent EBC insulators.
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