393 results found
Ojovan M, Lee W, Burakov B, 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.
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., Temperature dependence of electrical conductivity of a green porcelain mixture, Journal of the European Ceramic Society, 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.
Al Nasiri N, Patra N, Ni N, et al., 2016, Oxidation behaviour of SiC/SiC ceramic matrix composite in air, Journal of the European Ceramic Society, Vol: 36, Pages: 3293-3302, ISSN: 1873-619X
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.
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
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.
Horlait D, Grasso S, Al Nasiri N, et al., 2016, Synthesis and Oxidation Testing of MAX Phase Composites in the Cr-Ti-Al-C Quaternary System, JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Vol: 99, Pages: 682-690, ISSN: 0002-7820
Chroneos A, Horlait D, Lee WE, et al., 2016, Synthesis and DFT investigation of new bismuth- containing MAX phases, Scientific Reports, Vol: 6, ISSN: 2045-2322
The Mn + 1AXn phases (M = early transition metal; A = group A element and X = C and N) are materials exhibiting many important metallic and ceramic properties. In the present study powder processing experiments and density functional theory calculations are employed in parallel to examine formation of Zr2(Al1−xBix)C (0 ≤ x ≤ 1). Here we show that Zr2(Al1−xBix)C, and particularly with x ≈ 0.58, can be formed from powders even though the end members Zr2BiC and Zr2AlC seemingly cannot. This represents a significant extension of the MAX phase family, as this is the first report of a bismuth-based MAX phase.
Pettina M, Harrison RW, Vandeperre LJ, et al., 2015, 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: 1873-619X
Jayaseelan DD, Zapata-Solvas E, Chater RJ, et al., 2015, Structural and compositional analyses of oxidised layers of ZrB2-based UHTCs, JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, Vol: 35, Pages: 4059-4071, ISSN: 0955-2219
Zapata-Solvas E, Jayaseelan DD, Brown PM, et al., 2015, Effect of oxidation on room temperature strength of ZrB2- and HfB2-based ultra high temperature ceramics, ADVANCES IN APPLIED CERAMICS, Vol: 114, Pages: 407-417, ISSN: 1743-6753
Al Nasiri N, Patra N, Horlait D, et al., 2015, 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.
Patra N, Al Nasiri N, Jayaseelan DD, et al., 2015, Low-temperature solution synthesis of nanosized hafnium carbide using pectin, Ceramics International, Vol: 42, Pages: 1959-1963, ISSN: 0272-8842
Nano-sized hafnium carbide was synthesized from organic–inorganic hybrid polymer based on polycondensation and carbothermal reduction reaction from pectin and hafnium tetrachloride followed by thermal treatment. Orthorhombic and monoclinic hafnia formed on pyrolysis which above 1300 °C transformed to hafnium carbide. Conversion of amorphous to crystalline hafnia was initiated at ~800 °C while the endothermic carbothermal reduction reaction started at ~1275 °C. Total yield of hafnium carbide was ~62%. The resulting carbide powders were equiaxed with narrow size distribution of crystallite size ~50 nm. SEM and EDX mapping confirm the uniform distribution of Hf and C. The high ceramic yield, uniform size particles, and simplicity of the process make it a promising route for polymer infiltration pyrolysis of carbon fiber/ultra high temperature composites.
Jayaseelan DD, Xin Y, Vandeperre L, et al., 2015, Development of multi-layered thermal protection system (TPS) for aerospace applications, COMPOSITES PART B-ENGINEERING, Vol: 79, Pages: 392-405, ISSN: 1359-8368
Patra N, Jayaseelan DD, Lee WE, 2015, Synthesis of ZrB2/SiC composite powders by single-step solution process from organic-inorganic hybrid precursor, Advances in Applied Ceramics, Vol: 115, Pages: 36-42, ISSN: 1743-6761
A precursor of a zirconium diboride/silicon carbide (ZrB2/SiC) composite was synthesised via an organic–inorganic hybrid derived from gum karaya, tetraethyl orthosilicate, boric acid and zirconyl chloride starting materials. Fourier transform infrared spectroscopy of the as-synthesised dried hybrid revealed the formation of Si–O, Zr–O–C and B–O–B. X-ray diffraction revealed that the powder consists of only ZrB2 and β-SiC. Scanning electron microscopy and TEM of the composite powders showed that SiC and ZrB2 occurred in intimately mixed aggregates of spheroidal submicron sized particles for low (3M) boric acid concentration, while at high (5M) boric acid concentration, the two phases are larger with the ZrB2 adopting a blocky, angular morphology (∼10–30 μm long by 5 μm wide and thick), while the SiC remains spheroidal with ∼1 μm diameter particles in 10–20 μm diameter aggregates. Thermogravimetry–differential thermal analysis with the help of X-ray diffraction analysis revealed that the formation temperature was low at 1275°C for ZrB2 and 1350°C for the SiC with 40 wt-% yield.
Liao C-Z, Shih K, Lee WE, 2015, Crystal Structures of Al-Nd Codoped Zircon lite Derived from Glass Matrix and Powder Sintering, INORGANIC CHEMISTRY, Vol: 54, Pages: 7353-7361, ISSN: 0020-1669
Jayaseelan DD, Zapata-Solvas E, Carney CM, et al., 2015, Microstructural evolution of HfB2 based ceramics during oxidation at 1600-2000 degrees C, ADVANCES IN APPLIED CERAMICS, Vol: 114, Pages: 277-295, ISSN: 1743-6753
Harrison R, Rapaud O, Pradeilles N, et al., 2015, On the fabrication of ZrCxNy from ZrO2 via two-step carbothermic reduction-nitridation, JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, Vol: 35, Pages: 1413-1421, ISSN: 0955-2219
Harrison R, 2015, Mechanism and Kinetics of Oxidation of ZrN Ceramics, Journal of the American Ceramic Society, ISSN: 1551-2916
Oxidation of ZrN ceramics from 973–1373 K under static conditions reveals parabolic rate behavior, indicative of a diffusion-controlled process. In-situ high temperature powder XRD found the oxidation mechanism begins with destabilization of ZrN through formation of a ZrN1−x phase with oxide peaks initially detected at around 773 K. The zirconium oxide layer was found to be monoclinic by in-situ XRD with no evidence of tetragonal or cubic polymorphs present to 1023 K. Bulk ceramic samples oxidized at 1173 and 1273 K underwent slower oxidation than those oxidized at 973 and 1073 K. This change in oxidation rate and hence mechanism was due to formation of a denser c-ZrO2 polymorph stabilized by nitrogen defects. This N-doped dense ZrO2 layer acts as a diffusion barrier to oxygen diffusion. However, at an oxidation temperature of 1373 K this layer is no longer protective due to increased diffusion through it resulting in grain boundary oxidation.
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