High-temperature XRD Analysis Research Articles

Manufacturing of High Purity Cr2AlC MAX Phase Material and Its Characterization

AbstractPresent study discusses about a technique for producing high-purity Cr2AlC MAX phase materials and gaining insight into their thermal behavior for high-temperature applications. The research conducted involved synthesizing a pure layered ternary carbide Cr2AlC MAX phase material by mixing powders of Chromium, Aluminum, and Carbon and then subjecting them to two-step pressureless sintering process in argon atmosphere. First step involves the annealing of ball-milled mixture at 750 °C for 2 h followed by the second step in which the annealed mixture is subjected to heat-treatment at 1350 °C for 2 h. Analysis using XRD and Raman techniques revealed that the synthesized product consists of Cr2AlC phase, without any impurities. SEM studies confirmed that the Cr2AlC had a layered topography, while EPMA analysis indicated that the atomic percentage of Cr, Al, and C was consistent with the XRD phase analysis. XPS investigations confirmed the presence of Cr-C bonds representing Mn+1Xn of the MAX phase material. TG-DSC results showed an approximately 2% increase in weight. The Cr2AlC phase exhibited an endothermic pattern below 725 °C, an exothermic pattern above it, and did not decompose up to 1400 °C in vacuum environment. High-temperature XRD analysis at various temperatures also confirmed no formation of Al2O3 or CrO impurity compounds.

Azo-linked room temperature columnar liquid crystals with bisphenol A core: Structure property relationship and photophysical properties

A series of bent-shaped liquid crystals containing an azo group and a bisphenol A core were synthesized, and characterized using various techniques. The presence of mesogenic properties in these azo-based dimers was confirmed through POM, DSC, and high-temperature XRD analysis. The structure-property relationship is further studied to confirmed the effect of the variable alkyl side chain on the terminal position, which also affects the liquid crystalline properties of the compounds in terms of mesophase temperature range and thermal stability. All the compounds exhibited enantiotropy columnar hexagonal phase with wide temperature range and thermal stability. Their photophysical properties were investigated using UV–visible spectroscopy and spectrofluorometry. It was observed that all four columnar mesogens underwent cis and trans azo isomerization upon exposure to photoisomerization.

Crystal structure, microhardness and thermal expansion of ternary TaIr2B2 boride

The ternary TaIr2B2 boride was prepared by the reaction between iridium and TaB2 powders. It was shown that a choice in favor of any crystal structure of TaIr2B2 boride using only X-ray powder diffraction analysis and single-crystal XRD is rather difficult to make. The DFT calculations were carried out to predict the energetically preferred crystal structure of TaIr2B2. The 11B solid-state NMR spectrum of TaIr2B2 was recorded for the first time. A combination of diffraction and spectroscopic methods, as well as theoretical calculations, allowed us to make clear choice in favor of the triclinic space group P-1 for the crystal structure of TaIr2B2. The Vickers microhardness value for TaIr2B2 was found to be 17.9 ± 2.3 GPa, and the ternary TaIr2B2 boride can be considered a hard material. Therefore, the family of hard ternary boride phases got a new member. The coefficients of thermal expansion of TaIr2B2 measured by in situ high-temperature XRD analysis are independent of temperature along the a and b axes, but the CTE along the c axis deviates noticeably at elevated temperatures. The findings for the new ternary TaIr2B2 boride are of interest for the rational design of complex structural materials containing Ta–Ir–B-based components and prediction of their high-temperature behavior. Further research into this ternary boride as well as other iridium-containing ternary borides will provide a tool to solve the problems faced by high-temperature materials science.

Thermochemical Expansion and Protonic and Electronic Hole Conductivity of Grain Interior and Grain Boundaries in 10 Mole% Y-Substituted SrZrO3.

Proton conducting acceptor-doped SrZrO3 has a history as long as that of BaZrO3 , but has attracted less interest. Inspired by its higher transport number of ionic conduction in wet oxygen revealed by our recent work, we here explore further aspects of doped SrZrO3 as electrolyte in proton ceramic electrochemical cells. In-situ high temperature XRD (HT-XRD) analysis of SrZr0.9 Y0.1 O3-δ (SZY10) indicated an anisotropic chemical expansion of hydration, stronger along the b than the a direction, and negative in the c direction. A systematic electromotive force (EMF) and impedance spectroscopy study as a function of and allowed determination of partial conductivities of electron holes and ions (mainly protons) in bulk (grain interior) and grain boundaries. Enthalpies and preexponentials were determined and interpreted for bulk and grain boundary partial conductivities based on defect chemistry and a brick layer model. The hole conductivity in bulk is modest and ensures high ionic transport numbers in oxidizing atmospheres, while grain boundaries exhibit lower ionic transport numbers from a relatively higher hole conductivity attributed primarily to tunnelling past the deepest part of the space charge region. Y-doped SrZrO3 (SZY) materials exhibit lower proton conductivities but excel over Y-doped BaZrO3 (BZY) in terms of thermal expansion compatibility with electrode materials and higher ionic transport numbers in oxidizing atmospheres and may hence be candidates for functional layers between BZY-based electrolytes and positrodes in proton ceramic electrochemical cells.

Flower-like Sc2Mo3O12 nanosheet clusters: Synthesis, thermal expansion and photocatalytic properties

In this work, Sc2Mo3O12 has been synthesized via one-pot hydrothermal reaction. The effects of process conditions on the crystal structure, morphology, photocatalytic activity and negative thermal expansion (NTE) behaviors of flower-like Sc2Mo3O12 were systematically investigated. Results indicate that orthorhombic flower-like Sc2Mo3O12 assembled by nano-size flaky crystal grains can be synthesized by one-pot hydrothermal reaction at a temperature as low as 120 °C for 2 h. The hydrothermal reaction temperature and time have no obvious effects on the crystal structure and morphology. However, the photocatalytic property of synthesized Sc2Mo3O12 is sensitive to the above parameters. The sample synthesized at 200 °C for 2 h shows the best photocatalytic degradation of methyl orange, and the degradation rate is 73.32% in 2 h 1The coefficient of thermal expansion (CTE) of Sc2Mo3O12 is −1.99 × 10−6 °C−1 in 50–500 °C tested using TMA. The high-temperature XRD analysis reveals that Sc2Mo3O12 exhibits anisotropic NTE and the intrinsic CTE is measured to be −2.09 × 10−6 °C−1 in 25–800 °C.

Investigating negative thermal expansion property of decahedral Sc2Mo3O12 prepared via hydrothermal method

Orthorhombic Sc2Mo3O12 with decahedral structure have been prepared via hydrothermal method. The phase evolution, morphology and negative thermal expansion (NTE) behavior of the decahedral Sc2Mo3O12 were investigated using XRD, SEM, TMA and high-temperature XRD. XRD and SEM analyses indicate that orthorhombic Sc2Mo3O12 particles with decahedral structure were obtained after annealing at 800 °C. The decahedral Sc2Mo3O12 particles are uniform and regular with a size of about 20 μm × 20 μm × 5 μm. Decahedral Sc2Mo3O12 shows stable NTE. TMA analysis shows the coefficient of thermal expansion (CTE) of decahedral Sc2Mo3O12 is −4.12 × 10−6 K−1 in 25–700 °C. High-temperature XRD analysis reveals that it displays anisotropic NTE at the same temperature range. The axial CTEs of decahedral Sc2Mo3O12 are αa = −4.37 × 10−6 K−1, αb = 3.61 × 10−6 K−1 and αc = −2.96 × 10−6 K−1, respectively. The linear CTE is −1.22 × 10−6 K−1.

Setting Behavior and Phase Evolution on Heat Treatment of Metakaolin-Based Geopolymers Containing Calcium Hydroxide.

The setting behavior of geopolymers is affected by the type of source materials, alkali activators, mix formulations, and curing conditions. Calcium hydroxide is known to be an effective additive to shorten the setting period of geopolymers. However, there is still room for improvement in the understanding of the effect of calcium hydroxide on the setting and phase evolution of geopolymers. In this study, the setting behavior and phase evolution of geopolymer containing calcium hydroxide were investigated by XRD analysis. The setting time of the geopolymer was inconsistently shortened as the amount of calcium hydroxide increased. A low calcium hydroxide dose of up to 2% of the total mix weight could contribute to the enhancement of compressive strength of geopolymers besides a fast-setting effect. The C-S-H gel is rapidly precipitated at the early stage of reaction in geopolymers containing high calcium hydroxide with some of the calcium hydroxide remaining intact. The ex-situ high-temperature XRD analysis and Rietveld refinement results revealed that geopolymer and C-S-H gel transformed into Si-rich nepheline and wollastonite, respectively. The wollastonite was also observed in heat-treated geopolymers with a low calcium hydroxide dose. It is believed that C-S-H gel can be precipitated along with geopolymers regardless of how much calcium hydroxide is added.

High Temperature Performance of Spark Plasma Sintered W0.5(TaTiVCr)0.5 Alloy

The phase stability, compressive strength, and tribology of tungsten alloy containing low activation elements, W0.5(TaTiVCr)0.5, at elevated temperature up to 1400 °C were investigated. The spark plasma sintered W0.5(TaTiVCr)0.5 alloy showed body centered cubic (BCC) structure, which was stable up to 1400 °C using in-situ high temperature XRD analysis and did not show formation of secondary phases. The W0.5(TaTiVCr)0.5 alloy showed exceptionally high compressive yield strength of 1136 ± 40 MPa, 830 ± 60 MPa and 425 ± 15 MPa at 1000 °C, 1200 °C and 1400 °C, respectively. The high temperature tribology at 400 °C showed an average coefficient of friction (COF) and low wear rate of 0.55 and 1.37 × 10−5 mm3/Nm, respectively. The superior compressive strength and wear resistance properties were attributed to the solid solution strengthening of the alloy. The low activation composition, high phase stability, superior high temperature strength, and good wear resistance at 400 °C of W0.5(TaTiVCr)0.5 suggest its potential utilization in extreme applications such as plasma facing materials, rocket nozzles and industrial tooling.

Experimental study of thermodynamic properties and phase equilibria in Na2CO3–K2CO3 system

Sodium and potassium carbonates and their mixtures are important for different applications, e.g. for latent thermal energy storage, die-casting processes and molten carbonate fuel cells. In this work the phase diagram and thermodynamic properties of Na2CO3–K2CO3 system were studied by differential thermal analysis, differential scanning calorimetry and high temperature X-ray diffraction. Three carbonate mixtures (56, 25 and 75 mol% of Na2CO3) have solid-solid transition in a wide temperature range between 648 K and 823 K. The high temperature XRD analysis has shown that this transition is a continuous process of changing of the unit cell volume without structural changing of the hexagonal lattice. This phenomenon has also been observed on the measured heat capacity curves. The obtained experimental results were compared with calculations performed using the previous thermodynamic datasets. The comparison of these results shows that further thermochemical assessment of this system needs to be performed to achieve better agreement with the available experimental data.

Crystallization kinetics of binary Yb2O3–Al2O3 glass

The ytterbium aluminum garnet composition YbAG (62.5 mol.% Al2O3, 37.5 mol.% Yb2O3) was prepared in the form of glass microspheres by flame synthesis. Precursor powder for flame synthesis with high homogeneity was prepared by modified sol–gel Pechini method. XRD pattern of prepared glass microspheres indicated predominantly amorphous nature of the sample. Detailed study of morphology of the microspheres by scanning electron microscopy revealed the presence of a small fraction of partially or fully crystallized microspheres. The high-temperature X-ray powder diffraction analysis (HT XRD) was carried out in the temperature interval 750–1450 °C: The temperature dependence of phase composition was determined. Crystallization of Yb3Al5O12—ytterbium aluminum garnet phase—was observed in the temperature range 900–1200 °C. The DSC analysis with heating rates 2, 4, 6, 8, 10 °C min−1 in temperature interval 25–1200 °C was performed in N2 atmosphere to study thermal behavior and crystallization kinetics of prepared glass microspheres. The two exothermic effects at 918 and 939 °C were observed, which were attributed to Yb3Al5O12 crystallization. The crystallization kinetics of prepared sample was examined with the use of JMAK model, and the kinetic triplet—frequency factor A = (1.8 ± 2.2) 10+28 min−1 (for the first peak), A = (1.2 ± 1.6) 10+55 min−1 (for the second peak), apparent activation energy Eapp = (6.4 ± 0.1) 10+02 kJ mol−1 (for the first peak), Eapp = (1.3 ± 0.1) 10+03 kJ mol−1 (for the second peak) and the Avrami coefficient m = 3 (for the first peak) and m = 2 (for the second peak)—was determined using RSS, Radj2 , AIC and WAIC criteria.

Influence of hydrothermal treatment parameters on the phase composition of zeolites

Analcime was prepared by hydrothermal transformation of metakaolin-based geopolymer activated by means of sodium water glass. Gradual transformation of geopolymer through primary and unstable zeolitic phases up to final analcime was studied as a function of hydrothermal treatment duration (6–48 h) and access of water vapour under the selected conditions (165 °C, 0.5 MPa). Composition, microstructure, and thermal stability of the prepared samples were assessed using simultaneous thermogravimetry and differential scanning calorimetry, X-ray diffraction and high-temperature XRD analyses, and scanning electron microscopy. In the case of shorter autoclaving and access of water vapour, the mix of different zeolitic phases was formed: analcime, zeolite P2 gmelinite-Na, and chabazite-Na. From the time of 24 h and autoclaving in the closed moulds, pure cubic analcime was detected. Uniform microstructure of these samples comprised of trapezoid particles with the diameter between 50 and 60 µm. Prolongation of autoclaving time did not lead to the significant change of particle size and their composition. Dehydration of detected zeolites took place through the formation of defect or unknown zeolitic structures before the structural collapse happened.

Influence of strain rate and strain at temperature on TRIP effect in a metastable austenitic stainless steel

Metastable TRIP (TRansformation-Induced Plasticity) steel strips with a microstructure comprising ferrite, retained austenite and martensite were subjected to tensile tests at different strain rates of 10−5s−1, 10−4s−1, 10−3s−1 and temperatures 27 °C, 50 °C and 100 °C. The TRIP steel specimens exhibited very high tensile strengths (up to ~1700 MPa) in tests carried out at room temperature, which is attributed to the TRIP effect. Thermal stability of the phases present in the TRIP steel in the as-received condition was assessed by in-situ high temperature XRD and DSC (Differential Scanning Calorimetry) analysis to determine the retained austenite decomposition temperature. Microstructural analysis by XRD, optical microscopy and electron microscopy was used before and after the tensile tests to identify the features present at micro- and nano-scales, which are responsible for the observed mechanical properties. Macrographs taken from the surface of the specimens after the tensile tests showed the presence of Lüders bands and their occurrence was concurrent with the TRIP effect. The effect of strain rate and temperature on the TRIP effect and the associated mechanical response are discussed in detail.

Investigation of YAP/YAG powder sintering behavior using advanced thermal techniques

The fabrication process of transparent YAG (Y3Al5O12) ceramics with an emphasis on examination of the sintering process and microstructural analysis is reported herein. Nanometric powder with an equivalent spherical diameter dBET = 60 nm consists mainly of hexagonal YAP phase (YAlO3). According to sintering analysis carried out using a dilatometer and high-temperature XRD analysis, the phase composition and phase transformation taking place at elevated temperatures accompany the sintering process and the fastest sintering rate was observed at temperatures of YAG formation. Based on the dilatometric and XRD analyses vs temperature, three temperatures were selected for pressureless sintering. Presintered samples were subjected to sintering under isostatic pressure using a hot isostatic pressing, after which transparent YAG was obtained. The best results were obtained for samples presintered at a relatively low temperature of 1600 °C, and for thus obtained sample, the in-line transmittance was 64% at λ = 808 nm.

The high-temperature volatilization of sylvite and solid reaction process between sylvite and minerals

The effects of volatilization of sylvite were investigated when the mineral was added in it and the reaction mechanism of solid phase between potassium and minerals such as CaCO3, SiO2, Al2O3, Fe2O3 were conducted at the same time by means of high temperature calcination, thermal analysis and XRD analysis. Results show that four kinds of mineral components can restrain the volatilization of potassium in different extents, KCl and K2SO4 are relatively stable at high temperatures, which can only react with Al2O3 to produce KAl5O8; K2CO3 is the most active, and it can not only react with CaCO3 to produce K2Ca(CO3)2 in low temperature but also decompose to K2O that co-melt with SiO2, which can also react with Al2O3 or Fe2O3 to form stable and high melting point KAlO2 and KFeO2 respectively.

Thermal Treatment of Aerosol Deposited NiMn₂O₄ NTC Thermistors for Improved Aging Stability.

This paper examines the influence of a short-term thermal treatment of aerosol deposited negative temperature coefficient (NTC) thermistor films on the NTCR characteristics and their long-term stability with different electrode materials. An aerosol deposition of a spinel-based NiMn2O4 powder on alumina substrates with screen-printed AgPd and Au interdigital electrode structures was performed. The manufactured components of the typical size of 1206 were tempered in a moderate temperature range of 200 °C to 800 °C and aged for 1000 h at 125 °C in air. Based on R-T measurements in a high-precision silicone oil thermostat bath and high temperature XRD analyses, the influence of the thermal treatment was analyzed and discussed. A 60-min tempering at 400 °C proved to be optimal, as both the NTCR parameters and their ageing stability could be significantly improved. The findings are explained.

Research on the formation of M1-type alite doped with MgO and SO3—A route to improve the quality of cement clinker with a high content of MgO

This paper discusses the effect of SO3 dopants on the M1 polymorph formation and mechanical properties of alite containing a high content of MgO. The structure of the M1 alite is identified by XRD, high-temperature XRD and TEM analysis. A characteristic XRD pattern of M1 alite doped with MgO and SO3 is determined, and TEM results show that M1 alite has an incommensurate modulated structure feature with 2.4 times the subcell dimension along [2¯10]H∗ and could be expressed as ha∗ + kb∗ + lc∗ + m/[2.4(−2a∗ + b∗)], where m = ±1. The First-Principles method is used to simulate the structure of M1 alite, and the calculated Delta Cohesive Energy is approximately 11–12 eV between the M1 and M3 alite. Quantitative analysis is performed by the Rietveld method. The SO3/MgO (mass ratio from SO3 to MgO) and M1% in alite M1-C3S%M1-C3S%+M3-C3S%×100% are shown to have a strong linear relationship, which can be defined as M1-C3S%M1-C3S%+M3-C3S%×100% = 24.73 + 108.11 * SO3/MgO (%). Mechanical properties results show that appropriate SO3 dopant can improve the compressive strength of alite containing high MgO while over dosed SO3 will lead to a contrary effect because of the decomposition of alite. The relationship between M1% in the alite and the compressive strengths at different ages is also given. The optimal M1% in alite is approximately 68% and the best SO3/MgO ratio is approximately 0.43 because the compressive strength could be maximized at each age.

In Situ X-ray Diffraction Study of the Thermal Decomposition of Selenogallates Cs2[Ga2(Se2)2- xSe2+ x] ( x = 0, 1, 2).

The selenogallates CsGaSe3 and Cs2Ga2Se5 release gaseous selenium upon heating. An in situ high-temperature X-ray powder diffraction analysis revealed a two-step degradation process from CsGaSe3 to Cs2Ga2Se5 and finally to CsGaSe2. During each step, one Se22- unit of the anionic chains in Cs2[Ga2(Se2)2- xSe2+ x] ( x = 0, 1, 2) decomposes, and one equivalent of selenium is released. This thermal decomposition can be reverted by simple addition of elemental selenium and subsequent annealing of the samples below the decomposition temperature. The influence of the diselenide units in the anionic selenogallate chains on the optical properties and electronic structures was further studied by UV/vis diffuse reflectance spectroscopy and relativistic density functional theory calculations, revealing increasing optical band gaps with decreasing Se22- content.

Crystallization kinetics of binary La2O3-Al2O3 glass

The ALaE glass with eutectic composition (76.2 mol% Al2O3, 23.8 mol% La2O3) and the ALaP glass with LaAlO3 (lanthanum-aluminium perovskite) composition (50 mol% Al2O3, 50 mol% La2O3) were prepared by combination of sol-gel Pechini method and flame synthesis in the form of glass microspheres (diameter ≈ 10 μm). The prepared glasses were characterized by OM, SEM, XRD and DSC. The prepared samples contained only completely re-melted spherical particles. However, more detailed study by SEM revealed small fraction of crystalline microspheres. Traces of crystalline LaAlO3 were detected in X-ray powder diffraction patterns of both glasses. DSC analysis in the temperature range 35–1200 °C with heating rates 2, 4, 6, 8 and 10 °C/min was performed in nitrogen atmosphere to study the thermal behaviour and crystallization kinetics of prepared glasses. In the DSC curve of the eutectic ALaE glass recorded at 10 °C/min two exothermic effects were observed at 920 and 936°. Only one exothermic effect at 868 °C was present in the DSC curve of the ALaP sample with perovskite composition. The high-temperature X-ray powder diffraction analysis was carried out in the temperature interval 25–1200 °C. For both compositions formation of LaAlO3 as the main crystalline phase was observed in the whole measured temperature range. In order to study the crystallization kinetics, the DSC curves were transformed into dependence of fractional extent of crystallization, α on temperature. The JMAK model was found suitable for description of crystallization kinetics of both studied systems. The kinetic parameters (A, Eapp and m) were calculated for this model and crystallization mechanisms have been proposed.

The phase diagram of the Ga–S system in the concentration range of 48.0–60.7 mol% S

Our goal is to study the phase T–x diagram of the Ga–S system in the concentration range of 48.0–60.7 mol% S at temperatures up to 1423 K. For this we chose differential thermal analysis (DTA) at low heating rates (< 1 K min−1) as the main research method. In addition to this, we used a new author’s method of chromatic-thermal analysis (CrTA), enabling the experiments to be conducted in a static mode. The obtained DTA data were compared with the results of both CrTA and high-temperature XRD analysis. It was established that, in contrast to the low-temperature part of the diagram, where only Ga2S3 and GaS phases are present, the high-temperature part (1151–1383 K) of this diagram is complicated. It is argued that in a narrow composition range (for the sulfur content from 59.0 to 60.7 mol%) there exist three phases of different compositions; they are denoted as σ, Ga2S3′ and Ga2S3. σ-phase with a sulfur content of about 59.0 mol% S exists in a very narrow temperature range (1151–1195 K) and decomposes at a temperature of about 1195 K according to the peritectic reaction.

Production and characteristics of substituted lanthanum niobate LaNb1–x W x O4 + δ

Solid solutions LaNb1–x W x O4 + δ (x = 0.02–0.10, Δx = 0.02) were investigated, which crystallize in the monoclinic system (space group I2/c) at room temperature and undergo a phase transition into the tetragonal modification with increasing temperature. The stability of various modifications was analyzed by high-temperature X-ray powder diffraction analysis. The electrical conductivity of sintered samples was studied by impedance spectroscopy. Insertion of tungsten into the niobium sublattice leads to an increase in the conductivity of the solid solutions.