High-temperature Thermal Expansion Research Articles

High-temperature structure, elasticity, and thermal expansion of ε-ZrH1.8

Zirconium hydride is a promising candidate material for nuclear microreactor applications as a solid-state moderator component, owing to its favorable neutronics properties and good thermal stability over other metal hydrides. In the present work, the crystal structure, thermal expansion, and elastic properties of the hydrogen-rich ε phase hydride were measured at elevated temperatures in the range 300–900 K. Samples were prepared by direct hydriding Zircaloy-4 metal – a nuclear-grade zirconium alloy. Room-temperature lattice parameters agree well with those reported from literature for unalloyed zirconium hydride and fall within an observed quadratic H-content dependence. The coefficients of thermal expansion, determined from lattice expansion and dilatometry, agree well within our work but were about 30 % lower than those reported by others for unalloyed hydrides. Density functional theory-based molecular dynamics simulations were used to compare with thermal expansion and elasticity measurements. Results showed lattice parameter temperature dependence and slope of thermal expansion align with those from measurements. Based on diffraction scans at select temperatures, ε phase remained stable in air up to at least 770 K. Likewise, dilatometry showed smooth thermal expansion up to the thermal decomposition temperature around 950 K. The precise decomposition temperature was not determined via diffraction due to sparse scanning. The complete elastic property measurements were gathered for ε-phase Ziracloy-4 hydride for the first time. Young's modulus was lower compared to the metal and δ hydride phases. High-temperature elasticity measurements were limited to <350 K due to acoustic dissipation effects.

Investigation of the effects of rare earth element doping on the thermophysical properties of Gd2Zr2O7 by first principles

Gd2Zr2O7 is one of the most promising new generation of ceramic materials for high temperature thermal barrier coatings. However, it still has great potential of improving thermal and mechanical properties and contributing tobetter thermal cycling performance of the coating. Doping rare earth elements in Gd2Zr2O7 is an effective method to enhance its thermal and mechanical properties. In this paper, the first principles is used to calculate the thermophysical properties of doped Gd2Zr2O7 with 16 rare earth elements, including modulus of elasticity, Debye temperature, minimum high-temperature thermal conductivity, high temperature thermal expansion coefficient, and fracture toughness, by which all doped Gd2Zr2O7 ceramics were ranked using the entropy method. The results show that doping with Pr, Sm, Yb, and Nd showed superior comprehensive performance. Specially, (Gd0.875Pr0.125)2Zr2O7 has the lowest Young's modulus of 244 MPa, Pugh ratio of 0.53, Debye temperature of 523.4 K, thermal conductivity of 1.27 W/(m·K), and the largest coefficient of thermal expansion of 9.19 × 10−6 K−1, and (Gd0.875Ho0.125)2Zr2O7 has the highest fracture toughness of 2.21 MPa·m1/2.

Molecular dynamics simulation of Sc2O3-Gd2O3-Y2O3 dopant effect on the crystal structure and thermophysical properties of zirconia-based ceramic materials

This paper aims to provide an insight into the effects of different doping ratios on the crystal structure, thermal conductivity, ion diffusion, and high-temperature thermal expansion coefficient of Sc2O3-Gd2O3-Y2O3 co-doped ZrO2 (ScGdYSZ) materials. They were investigated by a non-equilibrium molecular dynamics method. The results show that with Gd2O3-Sc2O3-Y2O3 co-doping, the thermal expansion of the resulting materials is all relatively close to that of 8YSZ materials and linear with temperature. At 1473 K, 1 mol%Sc2O3–3 mol%Gd2O3–4 mol%Y2O3 stabilized ZrO2 (1Sc3Gd4YSZ) coating material has the smallest thermal conductivity, with a thermal conductivity of 5.66 W·(m·K)−1. The mean square displacement (MSD) of O2− was linear with the time when the sum of the doping ratio of Sc2O3 and Gd2O3 was 4 mol%, and the MSD of O2− in the material increased with the doping ratio of Sc2O3. increases, the MSD of O2− in the material increases, and the migration diffusion rate is accelerated.

Design and application testing of imaging probe for strain measurement

To address the challenge of obtaining key device strain parameters within narrow spaces, this paper presents the design of a small-sized optical imaging probe with an independent optical system based on the basic principle of digital image correlation (DIC). To validate the strain measurement accuracy of the probe, a high-temperature heating system was built under in a laboratory setting, and experimental tests involving room temperature strain measurement and high temperature thermal expansion coefficient measurement were conducted. The findings demonstrate the potential of the developed probe for strain measurement in critical components situated in restricted spaces.

FEM Simulation of AlSi10Mg Artifact for Additive Manufacturing Process Calibration with Industrial-Computed Tomography Validation.

Dimensional accuracy of selective laser melting (SLM) parts is one of manufacturers' major concerns. The additive manufacturing (AM) process is characterized by high-temperature gradients, consolidation, and thermal expansion, which induce residual stress on the part. These stresses are released by separating the part from the baseplate, leading to plastic deformation. Thermo-mechanical finite elements (FE) simulation can be adopted to determine the effect of process parameters on final geometrical accuracy and minimize non-compliant parts. In this research, a geometry for process parameter calibration is presented. The part has been manufactured and then analyzed with industrial computed tomography (iCT). An FE process simulation has been performed considering material removal during base plate separation, and the computed distortions have been compared with the results of the iCT, revealing good accordance between the final product and its digital twin.

Synthesis, crystal structure, photoluminescence of Ba3Y2(BO3)4:Er3+ and thermal expansion of Ba3Y2(BO3)4

The Ba3Y2–xErx(BO3)4 (х = 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3) phosphors were obtained by crystallization from a melt. The Ba3Y2(BO3)4 crystal structure was refined from single crystal X-ray diffraction data to R = 0.037. Its anisotropic atomic displacement parameters for all atoms were refined for the first time. The borate crystallizes in the orthorhombic crystal system, space group Pnma with unit cell parameters a = 7.673(1), b = 16.44(1), c = 8.977(2) Å, V = 1132.3(3) Å3, Z = 4. These phosphors are isotypical to those of the A3M2(BO3)4 (A = Ca, Sr, Ba, M = Ln, Y, Bi) family. The crystal structure contains the isolated BO3 triangles, two general and a special one independent crystallographic sites for large cations, which are disordered over sites. Thermal behavior of Ba3Y2(BO3)4 was investigated by high-temperature X-ray powder diffraction and thermal expansion coefficients are calculated in a wide temperature range. An inflections of temperature dependencies of the unit cell parameters is observed in a range 600–740 °C. Luminescence spectra, excitation and kinetic curves of the Ba3Y2(BO3)4:Er3+ series are reported. A maximum luminescence intensity is observed for the x = 0.1 sample. According to vibrational spectroscopy data no structural changes upon activation of the Ba3Y2(BO3)4 matrix with the Er ions are observed.

Numerical study on mechanical erosion behaviour of the burning-free Al2O3–C bottom nozzle during casting

The burning-free bottom nozzle is a novel component for accurately controlling the molten steel flow during the casting steel process. The effect of the thermal mechanical behaviour of burning-free Al2O3–C bottom nozzle materials under extreme temperatures during casting on the thermally induced failure was investigated. First, the high-temperature dynamic Young's modulus and thermal expansion of the bottom nozzle materials were tested in the temperature range of 300–1473 K. A composite material constitutive model, a thermal conductive model and the concrete damage plasticity model (CDP) were adopted to examine the mechanical erosion behaviour of the Al2O3–C bottom nozzle in the casting process based on Finite Element Method (FEM). Results shown that the area near the core of the bottom nozzle was at a high temperature and under tensile stress conditions, whereas the edge area restricted by the external steel shell was mainly under compressive stress conditions. Then, the cracking tendency was evaluated, and an optimised bottom nozzle with a composite structure was proposed. The burning-free Al2O3–C bottom nozzle with a composite structure has an advantage in reducing the risks of cracking and extending the service life compared with the nozzle made of homogeneous materials. This work can make a significant contribution to the design of high performance bottom nozzles.

Density-functional-theory predictions of mechanical behaviour and thermal properties as well as experimental hardness of the Ga-bilayer Mo2Ga2C

Mo2Ga2C is a new MAX phase with a stacking Ga-bilayer as well as possible unusual properties. To understand this unique MAX phase structure and promote possible future applications, the structure, chemical bonding, and mechanical and thermodynamic properties of Mo2Ga2C were investigated by first-principles. Using the “bond stiffness” model, the strongest covalent bonding (1162 GPa) was formed between Mo and C atoms in Mo2Ga2C, while the weakest Ga-Ga (389 GPa) bonding was formed between two Ga-atomic layers, different from other typical MAX phases. The ratio of the bond stiffness of the weakest bond to the strongest bond (0.33) was lower than 1/2, indicating the high damage tolerance and fracture toughness of Mo2Ga2C, which was confirmed by indentation without any cracks. The high-temperature heat capacity and thermal expansion of Mo2Ga2C were calculated in the framework of quasi-harmonic approximation from 0 to 1300 K. Because of the metal-like electronic structure, the electronic excitation contribution became more significant with increasing temperature above 300 K.

Theoretical study of electronic properties and chemical stability of cubic phase zirconia nanowires

Zirconia bulk is one of the most studied materials around the world due to different properties such as a high melting temperature, biocompatibility and high thermal expansion, among many others. However, there is little experimental research about Zirconia nanowires and until now there are few theoretical papers on the subject. In this work, Density Functional Theory (DFT) calculations on bare ZrO2 nanowires with diameter variation were performed. In order to get the more accurate parameters for calculation on nanowires, we employed the Murnaghan equation of state in a perfect cubic crystal of ZrO2 (c-ZrO2) and we compared the results obtained with some experimental data as well as the lattice parameter and the bulk modulus. The nanowires were grown along the [1 1 1] direction with five different diameters. All calculations were carried out by DFT implemented in SIESTA code. According to our results, the functional PBE of the Generalized Gradient Approximation (GGA-PBE) is the more accurate functional for describing the E xc on ZrO2. The calculation of formation and surface energies shows that these nanowires are chemically stable. Furthermore, nanowires larger than 8.78 Å present a direct band gap. These results indicate the possibility of applying ZrO2 nanowires in the optoelectronic field.

A novel high-entropy cathode with the A2BO4-type structure for solid oxide fuel cells

For the first time, A2BO4 type high-entropy oxide is applied to SOFC cathode. In this paper, a (La0.2Pr0.2Nd0.2Sm0.2Gd0.2)2CuO4 high-entropy oxide (HE-LCO) is synthesized. The phase structure, DC conductivity, high-temperature thermal expansion and electrochemical performance of HE-LCO are studied in detail. HE-LCO crystallizes in tetragonal symmetry with space group I4/mmm. The thermal expansion coefficient of HE-LCO is 12.19 × 10−6 K−1 in the range of 100–800 °C, which is compatible with GDC electrolyte. The area-specific resistance (ASR) of HE-LCO cathode is 0.52 Ω cm2, and the peak power density of the anode support fuel cell attains 528 mW cm−2 at 700 °C. In addition, the dissociation of molecular oxygen on HE-LCO cathode is recognized to be the rate-limiting step of the ORR kinetics.

Analysis of the chemical composition and phase structure of ‘Ru-type ware’ bodies under the influence of firing temperature

AbstractThe Qingliang Temple kiln located in Baofeng County, Henan Province, China, is the discovery site of Ru Kuan porcelain, which is one of the five famous porcelain types of the Song dynasty in China. The ‘Ru-type ware’ and unglazed firing bodies were unearthed from the Qingliang Temple kiln in 2014, and the excavation site was very close to the central firing area of Ru Kuan porcelain. In this paper, the chemical composition, firing temperature and phase structure of the Ru-type ware and unglazed firing bodies from the Qingliang Temple kiln were analysed systematically using energy-dispersive X-ray fluorescence spectrometry, high-temperature thermal expansion and X-ray diffraction. The raw-material sources of the Ru-type ware bodies with various glaze colours are consistent but differ significantly from those of the unglazed firing bodies. The firing temperatures of the Ru-type ware and unglazed firing bodies are 1150–1200°C and 950°C, respectively, which are considered underfired. Mullite, α-quartz, β-cristobalite and α-Fe2O3 are the main constituents of the Ru-type ware bodies, whereas α-quartz and anatase were identified in the unglazed firing bodies. The Ru-type ware is related to the Ru Kuan ware in terms of firing techniques and official use.

High-temperature thermal expansion behaviour of C/SiC studied using an in-situ optical visualisation method and numerical simulations in a quartz lamp array heating environment

The thermal expansion behaviour and thermal insulation performance of high-temperature structural ceramics have attracted considerable attention in the aerospace field. To further understand the high-temperature deformation behaviour and mechanism of C/SiC, an in-situ optical visualisation system was used to observe the variation in the gap width between C/SiC specimens in a quartz lamp array heating test. By using sub-pixel edge detection for the images recorded by the CCD camera and calculating the variation in gap width, it was found that the gap width first decreased and then increased during the heating process. Numerical simulations showed that the variation was caused by heat conduction and expansion of the base under the C/SiC specimens. The variation in the gap width under different working conditions was studied, and the thermal insulation performance of the specimens with and without thermal barrier coatings was compared. This work provides a new route with theoretical support for the study of the thermal expansion behaviour of high-temperature structural ceramics.

Phase Diagram and Thermal Expansion of orthopyroxene-, clinopyroxene- and ilmenite-structured MgGeO3

Abstract The MgGeO3 system is a low-pressure analog for the Earth-forming (Mg,Fe)SiO3 system and exhibits recoverable orthopyroxene, clinopyroxene, and ilmenite structures below 6 GPa. The pressure-temperature conditions of the clinopyroxene to ilmenite phase transition are reasonably consistent between studies, having a positive Clapeyron slope and occurring between 4 and 7 GPa in the temperature range 900–1600 K. There are, though, significant discrepancies in the Clapeyron slope of the orthopyroxene to clinopyroxene phase transition in existing works that also disagree on the stable phase at ambient conditions. The most significant factor in these differences is the method used; high-pressure experiments and thermophysical property measurements yield apparently contradicting results. Here, we perform both high pressure and temperature experiments as well as thermal expansion measurements to reconcile the measurements. High-pressure and -temperature experiments yield a Clapeyron slope of −1.0−0.7+1.0 MPa/K for the MgGeO3 orthopyroxene-clinopyroxene phase transition, consistent with previous high-pressure and -temperature experiments. The MgGeO3 orthopyroxene-clinopyroxeneilmenite triple point is determined to be at 0.98 GPa and 752 K, with the ilmenite phase stable at ambient conditions. The high-temperature (&amp;gt;600 K) thermal expansion of the clinopyroxene phase is greater than that of the other phases. Debye-Grüneisen relationships fitted to the volume-temperature data give Debye temperatures for the orthopyroxene, clinopyroxene, and ilmenite phases of 602(7), 693(10), and 758(13) K and V0 of 897.299(16), 433.192(10), and 289.156(6) Å3, respectively. The Clapeyron slopes calculated directly from the Debye-Grüneisen relationships are consistent with previous thermophysical property measurements. The presence of significant anharmonicity and/or formation of defects in the clinopyroxene phase at high-temperatures, which is not apparent in the other phases, accounts for the previous contradictions between studies. The inferred increased heat capacity of the clinopyroxene corresponds to an increase in entropy and an expanded phase field at high temperatures.

Synthesis and Study of (Sr,La)2FeCo0.5Mo0.5O6 − δ Oxides with Double Perovskite Structure

Complex oxides Sr2 − xLaxFeCo0.5Mo0.5O6 − δ, (x = 0.2, 0.4; δ ≈ 0.03–0.15) have been first synthesized by the sol-gel method. Their crystal structures have been refined by the Rietveld method; the refinement showed that the complex oxides have the structure of cubic double perovskite (a ≈ 2aper, space group Fm3m) with partial ordering of Fe(Co) and Mo in the B positions. Based on the 57Fe Mossbauer measurements, the average formal oxidation state of iron has been found to decrease from +3.20 (x = 0.0) to +3.04 (x = 0.4). Our study of the behavior of perovskites in a reducing Ar/H2 atmosphere (8%) revealed a decrease in the reduction resistance with decreasing La content (x = 0.4 → 0). The combination of the properties studied, namely chemical stability with respect to the reaction with Ce1 − xGdxO2 − x/2 and Zr1 − xYxO2 − x/2, high-temperature thermal expansion, and electrical conductivity in air and Ar/H2, shows that Sr1.6La0.4Fe-Co0.5Mo0.5O6 − δ (δ ≈ 0.03) perovskite is more attractive as an electrode material for medium-temperature symmetric solid oxide fuel cells than Sr2FeCo0.5Mo0.5O6 − δ.

High temperature mechanical properties of zirconia metastable t'-Phase degraded yttria stabilized zirconia

Abstract Air plasma sprayed (APS) 8 wt%-yttria stabilized zirconia (8YSZ) with metastable tetragonal prime phase (t′) has been widely applied as thermal barrier coatings (TBCs) for gas turbine blades because of its outstanding mechanical properties at high temperatures. In the present research, a carefully designed process was used to prepare 8YSZ samples with different phase composition (t′, t and c) simulating the phase degradation of the material during operation conditions. High temperature (1000–1200 °C) bending strength, elastic modulus, and thermal expansion coefficient were measured, which exhibit strong dependence on the phase degradation during heat treatment. Effect of the phase composition on high temperature thermo-mechanical properties and the enhancement of the bending strength have been discussed, providing a new perspective for further improvements.

Phase transformations in oxides above 2000°C: experimental technique development

ABSTRACTThe oxidation of boride and carbide-based ultra-high-temperature ceramics is the primary limiting factor for their use as aerodynamic surfaces. Understanding the behaviour of the oxides that can result from oxidation of metal borides and carbides at very high temperatures is essential to optimise and tailor the performance of these materials; yet experimental thermodynamic and structural data for refractory oxides above 2000°C are mostly absent. The following techniques that can be applied to fill this gap are discussed: (i) commercial ultra-high-temperature differential thermal analysis for investigation of phase transformations and melting in inert environments to 2500°C, (ii) a combination of laser heating with a splittable nozzle aerodynamic levitator for splat quenching and drop calorimetry from temperatures limited only by sample evaporation, (iii) synchrotron X-ray and neutron diffraction on laser-heated aerodynamically levitated oxide samples for in situ observation of phase transformations in variable atmospheres, refinement of high-temperature structures and thermal expansion. Recent experimental findings include anomalous thermal expansion of the defect fluorite phase of YSZ, thermodynamics of pyrochlore–fluorite transformation from high-temperature structure refinements, and measurement of thermal expansion to the melting temperatures and fusion enthalpies of Zr, Hf, La, Yb and Lu oxides. These methods provide temperatures, enthalpies and volume change for phase transformations above 2000°C, which are required for thermodynamic assessments and calculation of phase diagrams of multicomponent systems.

Formation process and properties of aluminium–chromium slag

In order to realize the application of aluminium–chromium slag for economical recycling, its formation process and properties, including the chemical composition and phase composition, physical properties, and microstructure, were studied. The main chemical components of aluminium–chromium slag are Al2O3 and Cr2O3； Cr, CaO, and MgO, among others, are also present as impurities. The main phase is a solid solution of aluminium and chromium oxides; this possesses high refractoriness, good mechanical properties at high temperature, and relative stability in chemical composition. CaO is the main volatile component; variations in the CaO levels affect the thermal conductivity and high-temperature linear thermal expansion, and thus, the mechanical properties of the slag.

Correction: High-temperature X-ray diffraction and thermal expansion of nanocrystalline and coarse-crystalline acanthite α-Ag2S and argentite β-Ag2S.

Correction for 'High-temperature X-ray diffraction and thermal expansion of nanocrystalline and coarse-crystalline acanthite α-Ag2S and argentite β-Ag2S' by S. I. Sadovnikov et al., Phys. Chem. Chem. Phys., 2016, 18, 4617-4626.

Highly transparent polyhydroxyimide/TiO2 and ZrO2 hybrid films with high glass transition temperature (Tg) and low coefficient of thermal expansion (CTE) for optoelectronic application

Highly transparent polyhydroxyimide/TiO2 and ZrO2 hybrids films with high glass transition temperature and low thermal expansion coefficient for optoelectronic application.

Selective preparation of oligomeric naphthylene ether and its applications to epoxy resin for silicon carbide power semiconductor device materials

ABSTRACTIn this study, a novel method for selective synthesis of naphthylene ether trimers by self‐condensation of 2,7‐dihydroxynaphthalene in the presence of catalytic amount of potassium hydroxide was reported. An epoxy resin from the trimers was prepared and properties of the cured epoxy resin were examined. The cured resin showed not only good physical thermal stability, such as high glass transition temperature and low thermal expansion coefficient, but also good chemical thermal stability like high thermal decomposition temperature. Additionally, low moisture absorption of the cured resin was confirmed. From these results, the newly prepared epoxy resin with naphthylene ether skeletons was considered to be suitable for advanced applications such as silicon carbide power semiconductor device. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43339.