High-temperature Thermal Expansion Research Articles

Ln2NiO4+δ (Ln = La, Pr) As Suitable Cathodes for Metal Supported Cells

In the last decade, thanks to their mixed ionic and electronic conductivity (i.e. MIEC properties), the lanthanide nickelates, Ln2NiO4+ δ (Ln = La, Pr, Nd) have attracted much attention as cathode for solid oxide fuel cells. Simultaneously, Metal Supported Cells (MSCs) for IT-SOFC application (typically 600 – 700 °C) have been developed in respect of several advantages including reduced cost and better thermal cycling resistivity. Nevertheless, the use of porous metal implies to sinter the constitutive elements of the cells under low pO2 (e.g. under N2, pO2 » 10-4 atm). In that respect, the chemical stability, thermal and chemical expansion when exposed to temperatures as high as 1400 °C, under pO2 as low as 10-4 atm of Ln2NiO4+ δ phases were studied through TGA (Thermal Gravimetry Analysis), XRD analyses, high temperature X-ray diffraction and Thermal Expansion Coefficient measurements. Electrochemical Impedance Spectroscopy measurements on Ln2NiO4+ δ//GDC//YSZ symmetrical half-cells sintered either in air or under argon at various temperatures have been performed in the range 500 °C to 800 °C, in air, at idc = 0 A. Pr2NiO4+δ, either sintered in air or under nitrogen at 1150 °C and then re-oxidized, shows the lowest polarization resistance values (Rp = 0.12 Ω.cm2 at 600 °C) while La2NiO4+δexhibits smaller polarization resistances when sintered under nitrogen, compared to air. Finally, the suitability of lanthanide nickelates in MSCs will be demonstrated and the relationship between cathode performances and structural and microstructural features will be discussed in details. Besides,modelling of the impedance data will be emphasized.

High-temperature thermal expansion of ScAlMgO4 for substrate application of GaN and ZnO epitaxial growth

High-temperature powder X-ray diffraction measurements for ScAlMgO4 ( in space group) grown by Czochralski method were carried out from 303 to 1473 K. The obtained temperature-dependent unit cell parameters were expressed as for the a-axis and for the c-axis, where T is temperature in kelvin. The axial thermal expansion coefficients for the a-axis estimated from the unit cell parameters were comparable to those of GaN and ZnO. A c-plane ScAlMgO4 substrate can be easily obtained with using cleavage plane along c-plane, which is parallel to a-axis. Thus, ScAlMgO4 is one of the promising substrates for c-plane epitaxial growth of GaN and ZnO. High temperature X-ray single crystal structural analysis of ScAlMgO4 demonstrated the mechanism of the nonlinear variation of the obtained cell parameters as a function of temperature.

Crystal structure and high-temperature properties of the Ruddlesden–Popper phases Sr3−xYx(Fe1.25Ni0.75)O7−δ (0≤x≤0.75)

Ruddlesden–Popper n=2 member phases Sr3−xYxFe1.25Ni0.75O7−δ, 0≤x≤0.75, have been investigated by X-ray and neutron powder diffraction, thermogravimetry and Mössbauer spectroscopy. Both samples as-prepared at 1300°C under N2(g) flow and samples subsequently air-annealed at 900°C were studied. The as-prepared x=0.75 phase is highly oxygen deficient with δ=1, the O1 atom site being vacant, and the Fe3+/Ni2+ ions having a square pyramidal coordination. For as-prepared phases with lower x values, the Mössbauer spectral data are in good agreement with the presence of both 5- and 4-coordinated Fe3+ ions, implying in addition a partial occupancy of the O3 atom sites that form the basal plane of the square pyramid. The air-annealed x=0.75 sample has a δ value of 0.61(1) and the structure has Fe/Ni ions in both square pyramids and octahedra. Mössbauer spectroscopy shows the phase to contain only Fe3+, implying that all Ni is present as Ni3+. Air-annealed phases with lower x values are found to contain both Fe3+ and Fe4+. For both the as-prepared and the air-annealed samples, the Y3+ cations are found to be mainly located in the perovskite block. The high-temperature thermal expansion of as-prepared and air-annealed x=0.75 phases were investigated by high-temperature X-ray diffraction and dilatometry and the linear thermal expansion coefficient determined to be 14.4ppmK−1. Electrical conductivity measurements showed that the air-annealed samples have higher conductivity than the as-prepared ones.

Characterization and thermal expansion of Sr2Fe1-xInxMoO6 (x=0.0, 0.1 and 0.4 wt. %) double perovskites

Double perovskite oxides of Sr2Fe1-xInxMoO6 (x = 0.0, 0.1 and 0.4 wt. %.) were prepared by sol-gel growth followed by annealing under reducing atmosphere conditions of 10% H2/Ar flow. These samples were characterized by X-ray diffraction, Scanning Electron Microscopy and Electron Spin Resonance studies. High temperature thermal expansion studies were carried out using Netzsch 402PC dilatometer in the temperature range from 40 to 400°C. The coefficient of thermal expansion (α) was calculated at different temperature for all the samples. The value of α was found to increase with increase of temperature while average value of coefficient of thermal expansion found to decrease with indium composition in SFIMO materials.

Effects of Electromagnetic Stirring on the Microstructure and High-Temperature Mechanical Properties of a Hyper-eutectic Al-Si-Cu-Ni Alloy

A liquid treatment method by electromagnetic stirring was applied to a hyper-eutectic Al-15wt pctSi-4wt pctCu-3wt pctNi alloy for the piston manufacturing with diecasting process in order to improve high-temperature mechanical properties of the piston heads. The mechanical properties, such as hardness, high-temperature tensile stress, thermal expansion, and high-temperature relative wear resistance, were estimated using the specimens taken from the liquid-treated diecast products, and the results were compared with those of a conventional metal-mold-cast piston.

High temperature thermal expansion of BaAl2Si2O8, CaAl2Si2O8, and Ca2Al2SiO7 studied by high-temperature X-ray diffraction (HT-XRD)

Sealing of components for high temperature applications with coefficients of linear thermal expansion (CTE) > 10·10−6 K−1 can be achieved by glasses from which crystalline phases with high CTE are precipitated. Many sealing glasses also contain further components as e.g. aluminium and hence, not only the desired phase is crystallized, but also additional phases. For this purpose, high temperature XRD was performed in order to determine the CTE of BaAl2Si2O8, CaAl2Si2O8, and Ca2Al2SiO7. In the case of BaAl2Si2O8 and Ca2AlSi2O7 the CTEs were 7.8·10−6/K and 7.9·10−6/K, respectively. In the case of CaAl2Si2O8 the CTE is 4.4·10−6/K. Especially the formation of the latter phase should be avoided for a sealing material of high temperature fuel cells. Sintered specimens of the respective compounds were also characterized by dilatometry.

Strip Width Model in Hot Strip Rolling

This paper has researched strip width model in hot strip rolling. Analyzed physical phenomena influencing strip width, established calculation model in production including width spread during flat rolling, width change induced by bending, width changed by high temperature creep and thermal expansion and contraction during rolling. Practical applications in domestic 1500 hot strip mill show that the width model achieved good effect and enhanced the calculation precision.

A high-resolution powder neutron diffraction study of the crystal structure of neighborite (NaMgF3) between 9 and 440 K

The temperature dependence of the unit-cell dimensions and the crystal structures of the fluorperovskite neighborite, NaMgF 3 (analyzed in the Pbnm setting of the space group), have been determined at 88 temperatures between 9 and 440 K from high-resolution, time-of-flight, powder neutron diffraction data. Lattice parameters exhibit saturation at low temperatures, before developing linear thermal expansion coefficients at temperatures above ~ 350 K. The temperature dependence of each axis has been analyzed, and fitted, using a two-term expression related to an Einstein internal energy function. The unit-cell parameters a and c behave in a conventional manner, however, an unexpected, and previously unobserved, region of negative linear thermal expansion has been found for the b axis in the temperature interval 20 ≤ T ≤ 90 K. Estimated, high-temperature axial thermal expansion coefficients derived from the lattice parameter fitting are in good agreement with those experimentally determined from an earlier synchrotron study, and indicate that high-temperature saturation has been achieved in neighborite by 440 K. The unit-cell volume varies smoothly and monotonically over the whole temperature interval, and the two-term Debye model of Barron has been successfully used to fit these data with characteristic temperatures of 369(2) and 1055(14) K. For the temperature interval 313.15-443.15 K, the thermodynamic Grüneisen constant has been determined using the Debye parameterization of the unit-cell volume, coupled with literature values of the isobaric molar heat capacity. The evolution of the crystal structure as a function of temperature is presented, and explained, in terms of the temperature dependence of the amplitudes of the seven symmetry-adapted basis-vectors of the aristotype phase that are consistent with the orthorhombic space group. The calculated temperature variations of the bond lengths are in excellent agreement with those experimentally determined. The primary order parameters for centrosymmetric, zone-boundary phase transitions in perovskite-structured compounds, i.e., the amplitudes of the basis vectors that transform as the irreducible representations R + 4 (anti-phase tilt) and M + 3 (in-phase tilt), have been fitted to a Landau free energy expansion that incorporates low-temperature saturation. Within the temperature range studied, the temperature dependence of the displacement corresponding to the anti-phase tilt is consistent with tricritical behavior. Experimental evidence is presented for a quadratic coupling of the in-phase tilt to the anti-phase tilt for temperatures greater than ~ 135 K, suggesting critical behavior at the orthorhombic-cubic transition is purely related to an instability at the R point of the pseudocubic Brillouin zone.

Thermal Expansion Analysis Based on Forming Limit Diagram for Improving the Formability of Automotive Hot-forming Advanced High Strength Steel Parts

Based on the high-temperature thermal expansion analysis, the formability at different temperature of hot-forming 22 Mn B5 is studied and also verified by Dynaform simulation. Comparing the thermal expansion characteristics at forming temperature 800 ℃ and 700 ℃, the results suggest that:Forming at 800 ℃, the sample results in a tensile rupture since the principal strain in plane strain direction is too large, while the secondary strain in tensile-compressive zone is negative; forming at 700 ℃, the formability is significantly improved since the strain of all parts remain in a safety area and sample has a uniform deformation in biaxial stretching region and tensile-compressive zone. In addition, this work puts forward that the optimized forming temperature of hot-forming advanced high strength steel(AHSS) sample is not in the range of 800 ℃ to 850 ℃ reported in present literatures. This conclusion provides directions for deep exploration of optimized forming temperature and improvement of formability. A rapid cooling method is designed to provide a cooling rate over 27 ℃/s, with which the sample is cooled to 700 ℃-the target temperature for quenching. The experiment shows that by this method, there is a significant improvement on the formability, and the microstructure is denser

Assessment of thermal expansion coefficient for pure metals

Abstract In this paper, thermal expansion coefficients of 42 pure metallic elements were evaluated on the basis of empirical and theoretical methods and the adjusted Debye–Gruneisen model. In Debye–Gruneisen model, Debye temperature was regarded as an undetermined constant. Parameters in the model were determined via the nonlinear least square fit method through MATLAB program. Besides, for pure metallic elements with phase transition, segment fitting can be realized and the computational results fit experimental data well; meanwhile, reliable forecast for high-temperature or low-temperature thermal expansion can be provided, and a set of average Debye temperatures based on thermal expansion coefficients have been obtained.

Investigation of thermal expansion and specific heat of cesium loaded iron phosphate glasses

High temperature thermal expansion and specific heat measurements were carried out on iron phosphate glass (IPG) and a series of cesium substituted iron phosphate glasses. Thermal expansion of the bare IPG and the effect of cesium loading on expansion behavior were determined by push rod dilatometry in the temperature range of 300–700K in air. Specific heat was also measured in the same temperature range by differential scanning calorimetry (DSC) under flowing argon atmosphere. Enthalpy increment was computed using the specific heat data. The enthalpy increments were also measured using isoperibol drop calorimetry in air in the same temperature range. Specific heat was evaluated from the experimental enthalpy increment data. The experimentally measured enthalpy increment data were compared with those evaluated from DSC data for iron phosphate and cesium loaded iron phosphate glasses.

SOFC 연결재용 Al이 도핑된 (La0.8Ca0.2)(Cr0.9Co0.1)O3(LCCC)계 세라믹스의 합성 및 치밀화 특성

In the (LCCC), which has been using as interconnector materials in SOFC, Al ions were substituted for Co because ionic radius of Al is similar to that of Co. Because of the almost identical ionic radius of Al and Co, the substitution was not thought to be affect the tolerance factor of LCCC, and the densification behavior, high temperature electrical conductivity and thermal expansion coefficient were examined as a function of Al concentration. In the cases of the x

Structure and high-temperature properties of the (Sr,Ca,Y)(Co, Mn)O3−y perovskites — perspective cathode materials for IT-SOFC

Oxygen deficient perovskites Sr0.75Y0.25Co1−xMnxO3−y, x=0.5 and 0.75, were prepared by using the citrate route at 1373–1573K for 48h. The cubic Pm-3m perovskite structure for x=0.5 was confirmed by electron diffraction study and refined using neutron powder diffraction (NPD) data. For x=0.75, the superstructure corresponding to a=2×aper, b=2×aper, c=2×aper (a0b−b− tilt system, space group Imma) was revealed by electron diffraction. The solid solution Sr0.75−xCaxY0.25Co0.25Mn0.75O3−y, 0.1≤x≤0.6 and compound Ca0.75Y0.25Mn0.85Co0.15O2.92 were prepared in air at 1573K for 48h. The crystal structure of Ca0.75Y0.25Mn0.85Co0.15O2.92 was refined using NPD data (S.G. Pnma, a=5.36595(4), b=7.5091(6), c=5.2992(4)Å, Rp=0.057, Rwp=0.056, χ2=4.26). High-temperature thermal expansion properties of the prepared compounds were studied in air using both dilatometry and high-temperature X-ray powder diffraction data (HTXRPD). They expanding non-linearly at 298–1073K due to the loss of oxygen at high temperatures. Calculated average thermal expansion coefficients (TECs) for Sr0.75Y0.25Co1−xMnxO3−y, x=0.5, 0.75 and Ca0.75Y0.25Mn0.85Co0.15O2.92(1) are 15.5, 15.1, and 13.8ppmK−1, respectively. Anisotropy of the thermal expansion along different unit cell axes was observed for Sr0.15Ca0.6Y0.25Co0.25Mn0.75O3−y and Ca0.75Y0.25Mn0.85Co0.15O2.92. Conductivity of Sr0.75Y0.25Co1−xMnxO3−y, x=0.5 and 0.75 increases with the temperature reaching 110S/cm for x=0.5 and 44S/cm for x=0.75 at 1173K. Samples of Sr0.75−xCaxY0.25Co0.25Mn0.75O3−y, 0.1≤y≤0.6 were found to be n-type conductors at room temperature with the similar temperature dependence of the conductivity and demonstrated the increase of the σ value from ∼1 to ∼50S/cm as the temperature increases from 300 to 1173K. Their conductivity is described in terms of the small polaron charge transport with the activation energy (Ep) increasing from 340 to 430meV with an increase of the calcium content from x=0 to x=0.6.

Estimation of the heat capacity of some uranium-rare earth mixed oxides from thermal expansion and vice versa

Estimation of the high temperature heat capacity (C p) data from experimental high temperature thermal expansion (α v) data and vice versa from the known values of the ratio (αv/C p) at low temperatures were carried out by assuming linear relationship of the ratio α v /C p with temperature (at T > θ D). The assumption was examined using the known α v and C p values of single phase fluorite systems such as UO2, ThO2 and PuO2. It was also examined using the known α v and C p of the mixed oxides (U1−y Lay) O2±x (y = 0.2, 0.4, 0.6 and 0.8). The estimated values of α v and C p are in good agreement with the experimental values within ±3%. Using the assumption the high temperature heat capacity data of (U1−y Ce y ) O2 (y = 0.2, 0.8) and (U1−y Gd y ) O2±x (y = 0.2, 0.5) were computed from the experimental high temperature α v data.

Tracking of high-temperature thermal expansion and transport properties vs. oxidation state of cobalt between +2 and +3 in the La2Co1+z(Ti1−xMgx)1−zO6-system

The high-temperature thermal expansion and electronic transport properties of the B-site substituted LaCoO3 with both variable oxidation state of cobalt between +2 and +3 (La2Co(Ti1−xMgx)O6, 0 ≤ x ≤ 0.5) and variable Co3+-content relative to the other B-cations (La2Co1+z(Ti0.5Mg0.5)1−zO6, 0.2 ≤ z ≤ 0.6) have been investigated. Based on the temperature dependence of the thermal expansion, electronic transport properties and Seebeck coefficient, three different groups of compositions according to their symmetries can be allocated. It was found that the thermal expansion coefficients (TECs) of the studied compounds are mainly dependent on the proportion of Co2+/Co3+. For La2Co(Ti1−xMgx)O6, the TEC increases from ∼9 (x = 0) to ∼19 ppm K−1 (x = 0.5) with an increase of the oxidation state of cobalt from +2 to +3, respectively. The TECs of La2Co1+z(Ti0.5Mg0.5)1−zO6, z = 0.2–0.6 with Co3+-only, remain constant at ∼21 ppm K−1 independent of the cobalt content. Thermoelectric measurements of the system indicate that all samples in the system, except La2Co1.6(Ti0.5Mg0.5)0.4O6, are p-type conductors over the whole temperature range, 300 < T < 1175 K. The conductivities were found to increase with an increase of both Co3+ and total cobalt content and are described with a small polaron hopping model. Due to an insignificant number of oxygen vacancies of La2Co1+z(Ti1−xMgx)1−zO6 samples prepared in air at elevated temperatures, the investigated system is proposed as an excellent model system for the investigation of the influence of the Co oxidation state and stoichiometry on different properties in perovskite cobalt oxides.

Free energy of defect formation: Thermodynamics of anion Frenkel pairs in indium oxide

The temperature-dependent free energies, entropies, and enthalpies for the formation of anion Frenkel pairs in In2O3 are reported, as calculated within the Mott-Littleton embedded-cluster approach, by exploiting the relationship between isobaric and isochoric thermodynamic processes. Our model for In2O3 proves particularly successful in the reproduction and prediction of the thermoelastic properties, including heat capacity, compressibility, and thermal expansion in the high-temperature regime. We employ this model to predict the thermal behavior of oxygen vacancy and oxygen interstitial defects. Aggregation of the point defects is energetically favorable and dampens the temperature dependence of defect formation, with a decreased free volume of defect formation. The results highlight the contribution of point defects to the high-temperature thermal expansion of indium sesquioxide, as well as the appreciable temperature dependence of the thermodynamic potentials, including enthalpy and free energy, associated with defect formation in general. A transferable procedure for calculating such thermodynamic parameters is presented.

Raman spectra and X-ray diffraction of tuite at various temperatures

High-temperature Raman spectra and thermal expansion of tuite, γ-Ca3(PO4)2, have been investigated. The effect of temperature on the Raman spectra of synthetic tuite was studied in the range from 80 to 973 K at atmospheric pressure. The Raman frequencies of all observed bands for tuite continuously decrease with increasing temperature. The quantitative analysis of temperature dependence of Raman bands indicates that the changes in Raman frequencies for stretching modes (ν3 and ν1) are faster than those for bending modes (ν4 and ν2) of PO4 in the present temperature range, which may be attributed to the structural evolution of PO4 tetrahedron in tuite at high temperature. The thermal expansion of tuite was examined by means of in situ X-ray diffraction measurements in the temperature range from 298 to 923 K. Unit cell parameters and volume were analyzed, and the thermal expansion coefficients were obtained as 3.67 (3), 1.18 (1), and 1.32 (3) × 10−5 K−1 for V, a, and c, respectively. Thermal expansion of tuite shows an axial anisotropy with a larger expansion coefficient along the c-axis. The isothermal and isobaric mode Gruneisen parameters and intrinsic anharmonicity of tuite have been calculated by using present high-temperature Raman spectra and thermal expansion coefficient combined with previous results of the isothermal bulk modulus and high-pressure Raman spectra.

Effect of Cr 7C 3 on the mechanical, thermal, and electrical properties of Cr 2AlC

In this work, phase pure Cr 2AlC and impure Cr 2AlC with Cr 7C 3 have been fabricated to investigate the mechanical, thermal, and electrical properties. The thermal expansion coefficient is determined as 1.25 × 10 −5 K −1 in the temperature range of 25–1200 °C. The thermal conductivity of the Cr 2AlC is 15.73 W/m K when it is measured at 200 °C. With increasing temperature from 25 °C to 900 °C, the electrical conductivity of Cr 2AlC decreases from 1.8 × 10 6 Ω −1 m −1 to 5.6 × 10 5 Ω −1 m −1. For the impure phase of Cr 7C 3, it has a strengthening and embrittlement effect on the bulk Cr 2AlC. And the Cr 2AlC with Cr 7C 3 would result in a lower high-temperature thermal expansion coefficient, thermal conductivity, specific heat capacity and electrical conductivity.

High Temperature Thermal Expansion and Elastic Modulus of Steels Used in Mill Rolls

The high temperature thermal expansion coefficient (TEC) and elastic modulus of five steels used in mill rolls production were investigated by dilatometer and impulse excitation techniques (IET). The measurements were provided at heating from room temperature till temperatures of about 1000 °C and subsequent cooling. The obtained data were attributed to the properties of predominating phases (austenite, martensite, pearlite, and bainite). The TEC and elastic modulus of corresponding phases were similar for all investigated steels despite the difference in their chemical composition. The steels with a chromium content of 2.95 wt.% and more show enhanced ability to quench hardening. This is an important prerequisite for production of high quality mill rolls.

High temperature structure and thermal expansion of Co 3 Al 2 Si 3 O 12 garnet

Periodico di Mineralogia (2011), 80, 1 (Special Issue), 135-144 - DOI: 10.2451/2011PM0011 Special Issue in memory of Sergio Lucchesi High temperature structure and thermal expansion of Co 3 Al 2 Si 3 O 12 garnet Mario Tribaudino 1,* and Haruo Ohashi 2 1 Dipartimento di Scienze della Terra, Universita di Parma, Italy 2 Hashi Institute for Silicate Science, Nishinakanobu 1-9-25, Shinagawa, Tokyo 142-0054, Japan *Corresponding author: mario.tribaudino@unipr.it Abstract Synchrotron radiation powder diffraction patterns were taken on synthetic Co 3 Al 2 Si 3 O 12 garnet at BM8-GILDA (ESRF), at T = 298, 423, 573, 723 and 873 K. The cell parameters and atomic positions were refined by Rietveld analysis; the volume thermal expansi on coefficient is α V = 28.5(9) x10 -6 K -1 . The results on synthetic Co 3 Al 2 Si 3 O 12 garnet were compared with the high temperature structure data of X 3 Al 2 Si 3 O 12 garnets with X = Mg, Ca, Mn and Fe taken from literature. The thermal expansion of the unit cell is very similar in X 3 Al 2 Si 3 O 12 garnets, whereas the thermal expansion of the longest bonds in the distorted cubic cage surrounding the X cation decreases with increasing cation size. Contrarily to the compression behaviour, the thermal expansion in X 3 Al 2 Si 3 O 12 garnets does not change significantly as a function of composition. Key words : garnet; thermal expansion; Cobalt; synchrotron radiation; powder diffraction; crystal structure.