High-temperature X-ray Diffraction Results Research Articles

Evaluation of the effect of oxygen incorporation on the thermo–chemical–mechanical properties of the proton-conducting oxide BaZr0.8Yb0.2O3-δ

This study aims to evaluate the effects of multiple defect species produced by water and oxygen incorporation on the lattice parameters of BaZr0.8Yb0.2O3-δ (BZYb20) and model its chemical expansion considering these effects. In this study, the lattice constant of BZYb20 was investigated under oxygen partial pressure (pO2 = 1–10−3 bar), water vapor partial pressure (pH2O = 0.0023 bar and dry) and over a wide range of temperatures (473–1173 K) using two approaches: model calculations and high-temperature X-ray diffraction (HT-XRD). HT-XRD measurements revealed that the lattice expansion of BZYb20 changed within 700–900 K in a humidified atmosphere. In a nonhumidified atmosphere, this temperature range shifts lower. High-temperature gravimetric measurements of oxygen incorporation showed that the change in oxygen vacancy concentration was sufficiently small, and the effect of oxygen incorporation on the lattice constant was negligible. High-temperature gravimetric measurements of water incorporation yielded thermodynamic parameters for the hydration reaction. Based on these results, the HT-XRD results were reproduced by fitting a lattice constant model that neglects the effects of oxygen. Therefore, the effect of oxygen incorporation on chemical expansion can be ignored, and the chemical expansion can be estimated using the model developed in this study.

Evaluation of mineral matter transformations in low-temperature ashes of South African coal feedstock samples and their density separated cuts using high-temperature X-ray diffraction

ABSTRACTCoal mineral matter is the leading cause of inevitable ash problems (fouling and slagging) during the combustion of coal. Low-temperature ash (LTA) samples of feed coals and the density separated fractions were subjected to high-temperature X-ray diffraction (HT-XRD) to identify the mineral reactions occurred at elevated temperatures under oxidizing conditions. Excluded minerals were mainly contained in the sink fractions, while included minerals were mainly present in the float fractions. QEMSCAN results indicate that the mineral associations in carbominerites and included minerals in Feeds A, B and C and sinks B and C are responsible for the melt formation during HT-XRD experiments. HT-XRD results indicate the presence of mullite, anorthite, and amorphous aluminosilicate materials formed in the thermally treated LTA samples. The formation of these slagging crystalline and glassy phases could be attributed to either crystallization during the cooling of the molten solution, or via solid-state reactions at elevated temperatures. A comprehensive knowledge of the included and excluded minerals can be used to prepare a blended feedstock for combustion processes. The operational ash-related problems in the combustion and gasification processes could be minimized by implementing this comprehensive knowledge of the transformation of coal minerals at elevated temperatures.

Stable lattice thermal expansion of ZIRLO™: High-temperature X-ray diffraction results

Crystallographic properties of Zr and ZIRLO™ in the temperature range of 30–1430 °C were investigated using in situ high-temperature X-ray diffraction (HT-XRD). Hexagonal Zr diffraction peaks observed at 30 °C started to vanish above 1110 °C for Zr and 1230 °C for ZIRLO™ owing to oxidation, resulting in a composition with monoclinic ZrO2, tetragonal ZrO2, and rhombohedral Zr3O. Furthermore, based on Pawley refinement of in situ HT-XRD spectra, we demonstrated that the lattice thermal expansion in ZIRLO™ occurred in a stable manner compared to that in Zr, which contribute to the enhancement of its mechanical properties via thermal treatment.

The electrochemical crystallization of the copper (II) oxide on multi-walled carbon nanotubes

Copper (II) oxide (CuO) crystal structures have been grown on multi-walled carbon nanotubes (MWCNT). For this purpose, functional –COOH and –OH groups were introduced on the surface of MWCNTs by ultra-wave mixing in the H2SO4 and HNO3 bath. The functionalized MWCNTs (fMWCNTs) were washed with distilled water and dried in plasma cleaner. Subsequently, the fMWCNTs were ultra-wave mixed with distilled water. CuO crystal structures were formed on the surface of the fMWCNTs during electrochemical dissolving of copper atoms from a copper electrode. The CuO crystal structures coated the fMWCNTs. These structures formed CuO nanotubes on the fMWCNTs at the specified conditions (colloid concentration, temperature, electric current density). The following annealing process at 500°C produced hollow CuO nanotubes preserving the precursor form. We used high-temperature X-ray diffraction (HTXRD), and Raman spectroscopy (RS) to study the chemical structures. Thermal gravimetric analysis (TGA) confirmed results of HTXRD and RS. Scanning electron microscopy (SEM) showed the tubular geometry of the CuO nanostructures. It was shown that powder of the structures features high specific surface area up to 300 m2/g at least. The possible applications of the structures in nanotechnology and of the powder as a catalyst are discussed.

Microstructure and Thermomechanical Properties of Atmospheric Plasma-Sprayed Yb2O3 Coating

In this study, a Yb2O3 coating was fabricated by the atmospheric plasma spray technique. The phase composition, microstructure, and thermal stability of the coating were examined. The thermal conductivity and thermal expansion behavior were also investigated. Some of the mechanical properties (elastic modulus, hardness, fracture toughness, and flexural strength) were characterized. The results reveal that the Yb2O3 coating is predominantly composed of the cubic Yb2O3 phase, and it has a dense lamellar microstructure containing defects. No mass change and exothermic phenomena are observed in the thermogravimetry and differential thermal analysis curves. The high-temperature x-ray diffraction results indicate that no phase transformation occurs from room temperature to 1500 °C, revealing the good phase stability of the Yb2O3 coating. The coefficient of thermal expansion of the Yb2O3 coating is (7.50-8.67) × 10−6 K−1 in the range of 200-1400 °C. The thermal conductivity is about 1.5 W m−1 K−1 at 1200 °C. The Yb2O3 coating has excellent mechanical properties and good damage tolerant. The unique combination of these properties implies that the Yb2O3 coating might be a promising candidate for T/EBCs applications.

Phase transitions in mixed-layer Aurivillius phases

The Aurivillius phases Bi7Ti4NbO21, CaBi8Ti7O27, and SrBi8Ti7O27 were synthesized by solid-phase reactions. The results of high-temperature X-ray diffraction and thermal analyses of certain Aurivillius phases are presented. Principal regularities of thermal expansion of the synthesized compounds are established. A correlation between the Curie temperature and the structure of the compounds was found.

Fundamental Investigation of High Temperature Reduction and Melting Behavior of Manganese Ore

Several studies have examined the reduction behavior of manganese ore at high temperature with the aim of reducing the manganese cost in the steelmaking process. However, the transformation behavior of manganese compounds at high temperatures had not yet been clarified. Therefore, in this paper, the effects of temperature and oxygen partial pressure, as well as chemical composition, on the transformation and melting behavior of manganese ore were investigated by using high temperature X-ray diffraction (XRD) and thermogravimetry-differential thermal analysis (TG-DTA) in order to obtain fundamental information on the pre-reduction process of manganese ore. The main manganese compound in the raw manganese ore used in this study was characterized as CaMn6SiO12 by XRD at room temperature, while the main Mn compounds in the sintered manganese ore were Mn3O4 and MnO. Under a vacuum condition, raw manganese ore and sintered manganese ore were reduced to MnO above 1473 K. However, under atmospheric conditions (pressure: 760 Torr), manganese ore was reduced to Mn3O4 rather than MnO at temperatures above 1073 K. The results of high temperature XRD agreed with thermodynamic calculations. The melting temperature of the raw manganese ore evaluated by TG-DTA was lower than that of the sintered manganese ore due to the difference in the manganese oxide in each ore rather than the difference in the content of gangue components such as Al2O3, CaO, MgO and Fe2O3. The higher melting temperature of the sintered manganese ore is interpreted in terms of a higher content of MnO due to heat treatment.

Elemental Clustering and Structure of Liquid LBE

Liquid Pb–Bi eutectic (LBE) alloy is of great interest as coolant and neutron spallation source for the accelerator driven systems (ADS). Scanning Photoemission Microscopy (SPEM) at the ELETTRA synchrotron radiation facility of Trieste was carried out on samples quenched from melt at different temperatures. SPEM analyses show that the two components (Pb and Bi) are not homogeneously distributed in the range of temperature from melting up to 518 °C, in particular they form clusters enriched in Pb and Bi. The cluster size decreases as temperature increases hence diffusion occurs between clusters and matrix leading to the progressive disgregation of clusters that is almost completed at 518 °C. Such micro-chemical evolution is accompanied by a structural change of the liquid evidenced by the results of High-temperature X-ray Diffraction (HT-XRD). In particular, radial distribution function (RDF) curves show a progressive change of the ratio between the shell radii of 1st and 2nd nearest neighbours.

In-situ analysis of chemical expansion and stability of SOFC cathodes

ABSTRACTIn this work high-temperature X-ray diffraction has been used to investigate thermal and chemical expansion as well as overall phase stability for various cathode materials: Ba0.5Sr0.5Co0.8Fe0.2O3 (BSCF), La0.3Sr0.7CoO3 (LSC37), La0.6Sr0.4CoO3 (LSC64) and La0.6Sr0.4Fe0.8Co0.2O3 (LSCF), as a function of temperature in reducing conditions. When perovskites materials are under a low oxygen partial-pressure condition, the lattice parameter and overall dimension increase. Their chemical expansion has comparable values. From the viewpoint of the stability of these phases, the high-temperature X-ray diffraction results indicate no phase decomposition can be one of the reasons for material failure at the current experimental oxygen partial pressure. LSF is most stable, while LSC and LSCF form oxygen vacancy-ordered phases and then decompose when heated to 1000°C under atmospheres with pO2 as low as 10-5 atm.

Phase transformation, thermal expansion and electrical conductivity of lanthanum chromite

This paper addresses discrepancies pertaining to structural, thermal and electrical properties of lanthanum chromite. Experimental evidence is provided to support the hypothesis for poor densification in air as well as reduction in electrical conductivity in reducing atmosphere. Sintering condition for the synthesis of LaCrO3 was optimized to 1450°C and 10h. Thermo-analytical (differential scanning calorimetry – DSC) and high temperature X-ray diffraction (HT-XRD) studies show that orthorhombic lanthanum chromite transforms into rhombohedral structure at ∼260°C and cubic structure above 1000°C. Co-existence of the structural phases and the variation in each polymorph with temperature in both air and 3%H2–Ar atmosphere is reported. Presence and absence of Cr-rich phase at inter-particle neck are observed in oxidizing and reducing atmospheres respectively. The linear thermal expansion co-efficient was calculated to be 10.8±0.2×10−6°C−1 in the temperature range of RT–1400°C. Electrical conductivity of lanthanum chromite was found to be 0.11S/cm in air. A decrease in electrical conductivity (0.02S/cm at 800°C) of LaCrO3, as observed in reducing atmosphere (3%H2–Ar), corresponds to lattice volume change as indicated by peak shift in HT-XRD results.

In situ structure characterization of Pb(Yb1/2Nb1/2)O3-PbTiO3 crystals under high pressure-temperature

The stability field of the piezoelectric/ferroelectric phase of solid solution 0.47Pb(Yb1/2Nb1/2)O3-0.53PbTiO3 (PYN-PT) has been studied using in situ x-ray diffraction (XRD) and Raman spectroscopy techniques under high pressure and high temperature conditions to observe the evolution of features. PYN-PT remains in the piezoelectric tetragonal phase up to approximately 6.5 GPa at room temperature then transforms to a paraelectric cubic phase, which exhibits local disorder. The cubic phase is stable up to 50 GPa. Based on the high pressure and high temperature XRD results, we present a pressure-temperature phase diagram of PYN-PT which constraints the stability region of the ferroelectric phase.

Investigation of structural phase transition behavior of SrZrO3 by thermal analyses and high-temperature X-ray diffraction

Structural phase transitions in SrZrO3, which is the mother phase of proton-conducting oxide, have been investigated with a combination of differential scanning calorimetry (DSC), high-temperature X-ray diffraction and dilatometry. In the DSC curve, reversible thermal anomalies due to phase transition were observed at 769°C, 846°C and 1102°C. The phase transitions have been concluded to be of second-order, first-order and second-order at 769°C, 846°C and 1102°C, respectively. From the baseline shift, the variation of heat capacity at the second-order phase transition, ΔCp, was evaluated to be 8J/molK and 5J/molK at 769°C and 1102°C, respectively. The variation of enthalpy, ΔH, of the first-order phase transition at 846°C has been estimated to be 58J/mol. High-temperature X-ray diffraction measurements have revealed that the crystal structure of SrZrO3 varies from orthorhombic distorted perovskite with the space group Pbnm to orthorhombic Ibmm, tetragonal I4/mcm, to ideal cubic perovskite, Pm3¯m with increasing temperature. The transition temperatures were in agreement with those obtained by DSC. The structural phase transitions have also been detected at the above temperatures by dilatometry as anomalies of thermal expansion coefficients. The general form of the linear thermal expansion and the linear thermal expansion coefficients obtained by dilatometry showed fair correspondence with the volume expansion estimated from the results of high-temperature X-ray diffraction.

In situ high temperature XRD studies of ZnO nanopowder prepared via cost effective ultrasonic mist chemical vapour deposition

Ultrasonic mist chemical vapour deposition (UM-CVD) system has been developed to prepare ZnO nanopowder. This is a promising method for large area deposition at low temperature inspite of being simple, inexpensive and safe. The particle size, lattice parameters and crystal structure of ZnO nanopowder are characterized by in situ high temperature X-ray diffraction (XRD). Surface morphology of powder was studied using transmission electron microscopy (TEM) and field emission electron microscope (FESEM). The optical properties are observed using UV-visible spectrophotometer. The influence of high temperature vacuum annealing on XRD pattern is systematically studied. Results of high temperature XRD showed prominent 100, 002 and 101 reflections among which 101 is of highest intensity. With increase in temperature, a systematic shift in peak positions towards lower 2θ values has been observed, which may be due to change in lattice parameters. Temperature dependence of lattice constants under vacuum shows linear increase in their values. Diffraction patterns obtained from TEM are also in agreement with the XRD data. The synthesized powder exhibited the estimated direct bandgap (E g) of 3.43 eV. The optical bandgap calculated from Tauc’s relation and the bandgap calculated from the particle size inferred from XRD were in agreement with each other.

Synthesis and structural characterization of nanostructured copper

In this paper, we report on the preparation and characterization of nanocrystalline powder of copper by dc-magnetron sputtering. Liquid nitrogen cooled cold finger arrangement has been used to prepare nanocrystalline powder. The particle size, crystal structure, and morphology of the samples were characterized by in situ high temperature X-ray diffraction (XRD) and transmission electron microscope (TEM). Results of high temperature XRD showed that highly oriented (111) phase becomes randomly oriented at higher temperature with a systematic shift in peak positions toward lower 2θ values due to changes in lattice parameters. Temperature dependence of lattice constants under vacuum shows linear increase in their values. Diffraction patterns obtained from TEM are also in accordance with the XRD data.

Structural stability of Co nanowire arrays embedded in the PAAM

The hcp-Co nanowire arrays with the diameter of 25 nm were successfully prepared using a direct-current electrodeposition in the holes of PAAM templates. The crystalline structures and morphologies of Co nanowires were investigated by field-emission scanning electron microscopy and transmission electron microscopy with selected-area electron diffraction. The results of high-temperature X-ray diffraction indicate the structural change from hcp to fcc for Co nanowires embedded in the PAAM has been inhibited. It is suggested that the inhibition of structural transformation be caused by the size finite effects of the PAAM.

Microstructural development of ZnO varistor during reactive liquid phase sintering

The microstructural evolution, grain growth and densification for the varistor systems ZnO-Bi2O3 (ZB), ZnO-Bi2O3-Sb2O3 (ZBS), ZnO-Bi2O3-Sb2O3-MnO-Cr2O3-CoO (ZBSCCM) were studied using constant heating rate sintering, scanning electron microscopy (SEM) andin situ phase formation measurement by high temperature X-ray diffraction (HT-XRD). The results showed that the densifying process is controlled by the formation and decomposition of the Zn2Bi3Sb3O14 pyrochlore (PY) phase for the ZBS and ZBSCCM systems. The addition of transition metals (ZBSCCM system) alters the formation and decomposition reaction temperatures of the pyrochlore phase and the morphology of the Zn7Sb2O12 spinel phase. Thus, the spinel grains act as inclusions and decrease the ZnO grain growth rate. Spinel grain growth kinetics in the ZBSCCM system showed ann value of 2.6, and SEM and HT-XRD results indicate two grain growth mechanisms based on coalescence and Ostwald ripening.

High-temperature X-ray diffraction study of the peritectic reactions of Bi-2212 with and without Ag additions

High-temperature X-ray diffraction (HTXRD) was used to determine the peritectic melting sequence of Bi 2Sr 2CaCu 2O 8 (Bi-2212) and Bi-2212 + 20 wt.% Ag thick films on MgO substrates. The residual carbon concentration of all samples was reduced to 1600 ppm by careful thermal treatment before the HTXRD analyses. Analysis of samples quenched in oil using XRD and EMPA supports the HTXRD results. Lattice-parameter analyses were used to determine the compositions of solid solutions present in the reaction sequence. In the case of pure Bi-2212, two phases form immediately on melting at 870°C, namely (Ca x , Sr 1− x )CuO 2 (1:1) and an unidentified phase. The unidentified phase decomposes by 900°C, while the 1:1 phase is present up to 920°C. (Ca 1.4Sr 0.6)CuO 3 (2:1) forms by 880°C, immediately after the 1:1 phase, and decomposes by 930°C, while (Ca 0.96Sr 0.04)O appears at 900°C, and coexists with the liquid up to at least 1350°C. Only slight changes in the solid-solution compositions were found with 20 wt.% Ag added to the system, with the phases and stability regions remaining the same.