High-temperature X-ray Diffraction Analysis Research Articles

Crystallization kinetics of glass microspheres with yttrium aluminium garnet (YAG) composition

A combination of sol–gel Pechini method and flame synthesis was used to prepare yttrium aluminate glass microspheres with the garnet composition (YAG, 62.5 mol% aluminium oxide, 37.5 mol% yttrium oxide). Prepared glass microbeads were studied by optical microscopy, SEM, X-ray diffraction (XRD), differential scanning calorimetry (DSC) and high-temperature (HT) XRD analysis. Formation of YAG as the only crystalline phase was observed during HT XRD experiment in the temperature interval (750–1200 °C), with the onset of YAG phase crystallization in the temperature interval 860–870 °C and most prominent increase in the YAG phase content between 905 and 910 °C. The experimental data obtained by DSC analysis and the Johnson–Mehl–Avrami–Kolmogorov model were used for determination of crystallization behaviour of the studied system. The frequency factor A = 5.2 × 1048 ± 9.6 × 1048 min−1, apparent activation energy E app = 1100 ± 10 kJ mol−1 and the Avrami coefficient m = 4 were determined. The linear temperature dependence of nucleation rate, reaction-controlled crystal growth interface and a 3-D crystal growth were confirmed in the studied system.

Synthesis and structural characterization of ultrafine terbium oxide powders

Glycine-nitrate self-propagating high-temperature synthesis was used to synthesize terbium oxide nanopowders whose phase transformations were investigated by methods of high-temperature differential scanning calorimetry, dilatometry, and X-ray diffraction analysis. The as-prepared powders consisting of Tb7O12 and Tb11O20 phases were converted to Tb2O3 after calcination at 600–800°C in reducing atmosphere. The sintering behavior of Tb2O3 was studied under microwave heating up to 1780°C. The microstructure of the powders and ceramics was investigated by scanning electron microscopy. Near full-density material was obtained at about 1620°C. Further temperature increases causes a deterioration of the ceramics microstructure due to monoclinic Tb2O3 phase formation.

In Operando Electrochemical High-Temperature X-Ray Diffraction Study of Ni-Ce0.9 Gd0.1O2-δ Redox Properties

A new in operando measurement cell has been developed for simultaneous monitoring of electrochemical (EC) properties and crystallographic structure using high temperature (HT) X-ray diffraction analysis (XRD) of solid oxide fuel cell (SOFC) anodes at working conditions. The influence of oxide ion flux on crystallographic structure of Gd0.1Ce0.9O2- d (GDC) in Ni-GDC cermet anode as well as impact of Ni ⇌ NiO redox cycles on the performance of anode has been studied. Influence of temperature, pO2 in gas stream and oxide ion flux through the membrane on the GDC lattice parameters was observed. Decrease of electrode polarization, i.e. increase of oxide ion flux lead to decrease of unit cell volume of the GDC lattice. The observed diminishing of GDC lattice parameter caused by oxide ion flux at -0.9 V was approximately same as the change caused by 50 degree of temperature decrease.

Comparison of Kinetics, Oxide Crystal Growth and Diffusivities of Nano- and Micrometer-Sized Copper Particles on Oxidation in Air

The oxidation of nanometer-sized and micrometer-sized copper particles with diameters of 60nm and 20 μm is investigated in air in the temperature range from 323 to 1273 K, using high-temperature X-ray diffraction and thermal analysis with multiple heating rates. The oxidation of both particle types occurs in two steps to Cu2O and to CuO in a similar way, the nanometer-sized particles at substantially lower temperatures and the two steps separated. The kinetics are investigated for both steps using a least squares fit procedure, comparing three different mechanisms: consecutive reaction steps of 1st order, step one with 1st order followed by a step modeled with Shrinking Core (SC) model and two steps connected with two SC models. The diffusivities with lowest standard deviations are: Log10(Z1d)=−5.234 cm2 s−1, E1=88.5 kJ/mol, and Log10(Z2d)=−3.873 cm2s−1, E2=122.7 kJ/mol from the X-ray study for the 20 μm particles. For the 60nm particles Log10(Z1)=8.08 s−1 (1st order reaction), E1=89.15 kJ/mol and Log10(Z2d)=−5.09 cm2s−1 (diffusion), E2=107.4 kJ/mol are found. These values are within the range of those obtained from copper plates. The crystallite size of the oxide particles begins at about 3–10nm to be evaluated. It increases on temperature rise to be described by a nucleation mechanism, the kinetics being evaluated.

Investigating phase formations in cast AlFeCoNiCu high entropy alloys by combination of computational modeling and experiments

Selection and thermal stability of phases are important in design of high entropy alloys (HEA). In this study, phase formations in cast AlFeCoNiCu HEA were investigated. Ab-initio molecular dynamics (AIMD) simulations were used to determine crystal structures of phases at different temperatures in equiatomic composition of AlFeCoNiCu. The AIMD results showed a possible coexistence of a face-centered cubic (fcc) phase and a body-centered cubic (bcc) phase at the room temperature and indicated stabilization of a single fcc phase above 1070K at the equiatomic composition of AlFeCoNiCu. The phase diagrams of AlFeCoNiCu system were calculated using a modified thermodynamic approach based on CALPHAD and Muggianu's methods. The calculated phase diagrams showed formation of the same two phases at the room temperature, and a phase transformation at about 1010K to form a single fcc phase. The characterization experiments utilizing scanning electron microscopy (SEM), X-ray diffraction (XRD), and electron backscatter diffraction (EBSD) confirmed the crystal structures and composition of phases determined by AIMD simulations and phase diagram calculations. High temperature XRD (HTXRD) analysis showed a significant increase in weight fraction of the fcc phase at high temperatures confirming the predicted phase transformation.

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.

Determination of the initial ash sintering temperature by cold compression strength tests with regard to mineral transitions

Ash deposition, fouling, and slagging are commonly undesirable occurrences in coal utility boilers and gasifiers. Ash deposit formation is usually initiated by sintering of the particles. The sintering characteristics of the ash have to be evaluated to understand the process of deposit formation. Cold compression strength (CCS) tests on heat treated ash pellets produced under defined conditions can be applied for the determination of the initial sintering temperature (IST). Scanning electron microscopy (SEM) in combination with energy dispersive X-ray spectroscopy (EDX), high temperature X-ray diffraction analysis (HT-XRD), and thermogravimetric differential scanning calorimetry (TG-DSC) are analytical methods to characterize the mineral transitions responsible for sintering.CCS tests were done on ashes of three different coals to determine their IST. For this purpose ash pellets were pretreated at different temperatures. The influence of oxidizing, inert, and reducing conditions at ambient pressure was investigated. The IST were compared with the characteristic temperatures from ash fusibility tests (AFT). HT-XRD, TG-DSC, and SEM/EDX were applied for a more detailed characterization of sintering.The IST determined by CCS tests are considerably lower than the respective initial deformation temperature (IDT) obtained by AFT. Thus, the AFT is not suitable to detect IST. Major mineral transitions were found which are responsible for initial sintering in the case of the investigated ashes. The formation of silicates or the crystallization of iron-aluminum-oxides were found to induce sintering at oxidizing and inert conditions. Sintering at reducing conditions was initiated by carbonation of calcium compounds, silicate formation, or melting of iron sulfide. These phases can be understood as the relevant phases for initial strengthening of fouling deposits in coal utility boilers and gasifiers in the case of the investigated ashes.

Reducibilities of Wüstite and Calcio-wüstite in Terms of High Temperature X-ray Diffraction Analysis

Reducibilities of Wüstite and Calcio-wüstite in Terms of High Temperature X-ray Diffraction Analysis

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.

New data on “kerolite–pimelite” series and the colouring agent of Szklary chrysoprase, Poland

Green clay and chrysoprase samples from the Ni-laterite deposit in Szklary, Poland, were studied by X-ray diffraction (XRD), electron microprobe analysis (EMPA), Raman, infrared and UV–VIS–NIR absorption spectroscopies. The clay samples proved to be Ni-rich “kerolite” and “pimelite”, and as these minerals are currently discredited, their nature was studied in more detail by high-temperature X-ray diffraction and thermal analysis coupled with mass spectrometry. These methods showed that “kerolite” and “pimelite” contain interlayer water, i.e. they differ from the non-hydrated talc–willemseite mineral series. Subsequently, the XRD and EMPA analyses of Szklary chrysoprase indicated that chrysoprase’s colouring agent is “pimelite”, which was further corroborated by Raman and UV–VIS–NIR spectroscopies. In addition, the Szklary chrysoprase, which has been quarried since the Middle Ages and used in jewellery and wall decorations (e.g. in the Prague Cathedral), was described from the gemmological point of view.

Ultra high-pressure spark plasma sintered ZrC-Mo and ZrC-TiC composites

Ultra-high-pressure spark plasma sintering was applied to ZrC-20wt%Mo and ZrC-20wt%TiC composites with a pressure up to 7.8GPa and temperatures of 1550°C and 1950°C. Mechanical performance of the composites was benchmarked against a plain ZrC produced by the same method. Both composites outperformed the pure ZrC with superior hardness and indentation fracture toughness of 2239HV1 and 5.4MPam1/2, and 1896HV1 and 5.9MPam1/2, respectively, for ZrC-Mo and ZrC-TiC composites. It was shown that ultra-high compaction pressure affected the ZrC-20 wt%TiC miscibility gap by lowering the temperature threshold from the usually applied 1800°C down to 1550°C resulting in formation of the solid state solution of (Zr,Ti)C. In contrast, the high pressure does not inhibit the carburisation of Mo with ZrC to form MoC, even when experiments were performed in a graphite free environment. The equiaxed morphology of ZrC grains along with a right-shift in XRD peaks for ZrC indicates dissolution of Mo in ZrC resulting in formation of the solid solution of (Zr,Mo)C. High-temperature X-ray diffraction analysis under oxidation conditions was performed on the samples showing degradation of ZrC-20wt%Mo due to the oxidation of Mo at high-temperature leading to MoO3 vaporisation. Conversely, the oxidation of ZrC-20wt%TiC composites was characterised by formation of ZrO2 and TiO2 remaining stable up to 1500°C.

Transmission electron microscopy of topochemical conversion interface between La2Ti2O7 reactive template and perovskite product Li0.16La0.62TiO3 electrolyte

The topochemical conversion interface between a layered perovskite La2Ti2O7 and an ordered regular perovskite Li0.16La0.62TiO3, (LLTO) electrolyte was investigated using high-resolution transmission electron microscopy and scanning-transmission electron microscopy (STEM) for platelike La2Ti2O7 particles semi-reacted (at 1273K) with the complementary reactants Li4Ti5O12 and TiO2. High-temperature X-ray diffraction analysis confirmed that regular perovskite-type product was formed in situ at 1173K and above without the formation of any intermediate phases. The crystallographic relationship between the product and the template at the interface was determined by selected area electron diffraction to be orthorhombic LLTO [001](110) || monoclinic La2Ti2O7 [001](100). STEM revealed that the alternating La-rich and La-poor planes in the LLTO phase were aligned perpendicular to the interface, which was parallel to the interlayers, i.e., the (200) planes of the La2Ti2O7 template. At the interface, a unit-cell-thick La2Ti2O7 or a block of four-layered TiO6 octahedra between two interlayers is a basic unit converted into a regular perovskite-type product by shifting the block with La along the c-axis. This microscopic observation of the interface suggests the possibility of designing domain structures with improved ionic conductivity.

Effect of Ba concentration on phase stability and mechanical and thermal properties of La2Mo2O9

Ba-substituted La2Mo2O9 ((La1−xBax)2Mo2O9−δ, x=0–0.12) was prepared and the thermal and mechanical properties were evaluated. The thermal expansion coefficients (TECs) were determined from high-temperature X-ray diffraction (XRD) analysis. Phase transition in La2Mo2O9 was suppressed via substitution of Ba for La, as demonstrated by differential scanning calorimetry (DSC) analysis. The mechanical properties, such as the bulk modulus, shear modulus, Young’s modulus, compressibility, and Debye temperature were evaluated from the measured sound velocities. The thermal conductivity was evaluated from the thermal diffusivity, heat capacity, and density in the temperature range from room temperature to 1073K. The thermal conductivity decreased with increasing Ba content. Theoretical calculations based on the Klemens–Callaway model were performed to analyze the thermal conductivity, and the results suggest that the reduction of the thermal conductivity was mainly attributed to oxygen defects in the anion sublattice of La2Mo2O9.

Phase diagram of the Co–Al–W system. structure and phase transformations near the Co3(Al, W) intermetallic composition range

Low-temperature portion of the polythermal section for the Co–Al–W system in the vicinity of the Co3(Al, W) intermetallic composition has been studied experimentally using electron microscopy and hightemperature X-ray diffraction analysis. Low-temperature structural phase transformations and temperature ranges of the existence of phases have been determined. The morphology of Co3(Al, W) intermetallic particles was studied as a function of the tungsten content in alloys.

Solid-state synthesis of undoped and Sr-doped K0.5Na0.5NbO3

The solid-state synthesis of undoped K0.5Na0.5NbO3 (KNN) and KNN doped with 1, 2 and 6 mol% Sr, from potassium, sodium and strontium carbonates with niobium pentoxide, was studied using thermal analysis and in situ high-temperature X-ray diffraction (HT-XRD). The thermogravimetry and the differential thermal analyses with evolved-gas analyses showed that the carbonates, which were previously reacted with the moisture in the air to form hydrogen carbonates, partly decomposed when heated to 200 °C. In the temperature interval where the reaction was observed, i.e., between 200 and 750 °C, all the samples exhibited the main mass loss in two steps. The first step starts at around 400 °C and finishes at 540 °C, and the second step has an onset at 540 °C and finishes with the end of the reaction between 630 and 675 °C, depending on the particle size distribution of the Nb2O5 precursor. According to the HT-XRD analysis, the perovskite phase is formed at 450 °C for all the samples, regardless of the Sr content. The formation of a polyniobate phase with a tetragonal tungsten bronze structure was detected by HT-XRD in the KNN with the largest amount of Sr dopant, i.e., 6 mol% of Sr, at 600 °C.

Synthesis, Cu incorporation, and deposition behavior of apatite-type La x Ca10−x (PO4)6−x (SiO4) x Cu y O z

Cu-containing, apatite-type phosphate–silicate solid solutions, La x Ca10−x (PO4)6−x (SiO4) x Cu y O z (x = 3, 5, and 6), were synthesized by an impregnating method into the channels of apatite-type lattice by heat treatment after Cu loading. The unit cell volume of the apatite increased with increasing amount of Cu, y = 0–0.6 for x = 3 and 6, indicating successful incorporation of Cu into the channels of the apatite lattice. The result of Rietveld analysis of a La5Ca5(PO4)(SiO4)5Cu y O z (x = 5) sample indicated that the distribution of La3+ and Ca2+ cations in both 4f and 6 h sites were maintained during Cu incorporation. X-ray photoelectron spectroscopy and thermogravimetric analyses revealed that oxidation and reduction of Cu species occurred during heating up to 1100 °C and cooling in air, respectively. In addition, high-temperature X-ray diffraction analysis of the La3Ca7(PO4)3(SiO4)3Cu0.6O z (x = 3) sample in the temperature range from 500 to 1100 °C revealed that reversible incorporation/deposition of Cu occurred, accompanied by Cu oxidation/reduction.

Method for the Accelerated Testing of the Durability of a Construction Binder using the Arrhenius Approach

Abstract The single most reliable indicator of a material’s durability is its performance in long-term tests, which cannot always be carried out due to a limited time budget. The second option is to perform some kind of accelerated durability tests. The aim of the work described in this article was to develop a method for the accelerated durability testing of binders. It was decided that the Arrhenius equation approach and the theory of chemical reaction kinetics would be applied in this case. The degradation process has been simplified to a single quantifiable parameter, which became compressive strength. A model hydraulic binder based on fluidised bed combustion ash (FBC ash) was chosen as the test subject for the development of the method. The model binder and its hydration products were tested by high-temperature X-ray diffraction analysis. The main hydration product of this binder was ettringite. Due to the thermodynamic instability of this mineral, it was possible to verify the proposed method via long term testing. In order to accelerate the chemical reactions in the binder, four combinations of two temperatures (65 and 85°C) and two different relative humidities (14 and 100%) were used. The upper temperature limit was chosen because of the results of the high-temperature x-ray testing of the ettringite’s decomposition. The calculation formulae for the accelerated durability tests were derived on the basis of data regarding the decrease in compressive strength under the conditions imposed by the four above-mentioned combinations. The mineralogical composition of the binder after degradation was also described. The final degradation product was gypsum under dry conditions and monosulphate under wet conditions. The validity of the method and formula was subsequently verified by means of long-term testing. A very good correspondence between the calculated and real values was achieved. The deviation of these values did not exceed 5 %. The designed and verified method does not also consider the influence of other effects, for instance, chemical corrosion or corrosion caused by frost-thaw cycles. However, this method could be a supplementary tool applicable to the study of degradation processes and the estimation of a binder´s durability as well.

Crystallization kinetics of Al86Ni8Ho6 amorphous alloy

We investigate the processes of crystallization and determined the structure and thermal properties of Al86Ni8Ho6 amorphous alloy in a wide temperature range. A three-stage nature of the crystallization process upon heating to a temperature of 700 K is found. According to data of high-temperature X-ray diffraction analysis, the crystallization of an Al86Ni8Ho6 amorphous ribbon is rather complex: aluminum crystallites grow in the amorphous phase to a temperature of 470 K, a Ho3Ni5Al19 phase is formed above 563 K, and a HoAl3 phase appears above 598 K. The phases of Ho3Ni5Al19 and HoAl3 are retained up to a temperature of 723 K. A three-stage kinetic model of the crystallization process with the reaction sequence is proposed based on calculations by multivariate nonlinear regression. The values of the total activation energy for each crystallization stage reach 239, 378, and 247 kJ/mol.

Phase transitions in mayenite

This paper was devoted to explanation of the phase transitions nature in Ca12Al14O33±δ which were studied by a combination of methods: simultaneous thermal analysis, high-temperature X-ray diffraction analysis, Raman spectroscopy. One of the phase transitions is assumed to be connected with peroxide ions appearance/disappearance in mayenite at 922 K. The peroxide ions appearance reduces the system’s energy. Peroxide ions are responsible for the interaction of mayenite with water giving hydroxyl ions. Another phase transition at 1268 K is caused by changing in stability of electronic defects in mayenite. This paper enlightens correlations between the electronic defects state, the peroxide ions existence and chemical properties of Ca12Al14O33±δ.

Thermal structural stability of a multi-component olivine electrode for lithium ion batteries

In this paper, the structural evolution of Li(Mn1/3Fe1/3Co1/3)PO4, which is a promising multi-component olivine cathode materials, is investigated using combined in situ high-temperature X-ray diffraction and flux neutron diffraction analyses at various states of charge.