Congruent Melting Research Articles

Cetylpyridinium picrate: Spectroscopy, conductivity and DFT investigation of the structure of a new ionic liquid

A new cetylpyridinium picrate ionic liquid has been synthesized and characterized by differential thermal analysis, XRD, FT-IR, and NMR (1H and 13C) spectroscopy. Differential thermal analysis indicates the congruent melting of cetylpyridinium picrate and a temperature range of liquid state is 47–267 °C. A solid form of the sample characterized with a polymorphic transformation at 37 °C, which was confirmed via the XRD analysis.The interionic charge-transfer interactions, namely the charge transfer from the picrate anion to the cetylpyridinium cation, were detected by comparison of NMR spectra of DMSO solutions of the ionic liquid and cetylpyridinium chloride. The H–NMR chemical shifts’ differences of about 0.2 ppm and 0.1 ppm were observed in the case of the o-protons and the α-methylene group protons, respectively. Additionally, the charge-transfering between the attracted ions was confirmed by DFT calculations.Based on the solid state NMR technique, the higher ions mobility was suggested for the solid sample of the ionic liquid in comparison to the solid cetylpyridinium chloride monohydrate. Moreover, the association constants KA at 22, 30, 40, and 50 °C, obtained from the electrical conductivity measurements, clearly testifies much lower dissociation in the case of picrate. The KA values of cetylpyridinium picrate and chloride in DMSO medium at 22 °C equal 748.7 L/mol and 525.0 L/mol, respectively.The performed DFT computations of the reduced density gradient function in four proposed structures of the new ionic liquid cation-anion pair identifies the presence of weak non-covalent CH•••ON interactions between cetyl chain hydrogen atoms and nitro groups of picrate was explored through DFT calculations and analysis of the RDG function.

Congruent phase behavior of a binary compound crystal of colloidal spheres and dimpled cubes

Monte Carlo simulations were performed to study the phase behavior of equimolar mixtures of spheres and cubes having selective inter-species affinity. Such a selectivity was designed to promote the formation of the substitutionally ordered NaCl compound, the "C* phase," and to be driven not only by energetic bonds but also by entropic bonds generated by dimples on the cube facets. Nestling of the spheres in the cube indentations can promote negative nonadditive mixing and increase the C* phase packing entropy. The focus is on congruent phase behavior wherein the C* phase directly melts into, and can be conveniently accessed from, the disordered state. A specialized thermodynamic integration scheme was used to trace the coexisting curves for varying the values of the interspecies contact energy, ε*, the relative indentation size, λ, and the sphere-to-cube size ratio, ζ. By starting from a known coexistence point with ε* > 0 and λ = 0 (no indentation), it is found that increasing λ (at fixed ε* and ζ) reduces the free-energy and pressure of the C* phase at coexistence, indicative of stronger entropic bonding. Remarkably, it is demonstrated that a purely athermal C* phase (i.e., with ε* = 0) can be formed for λ ≥ 0.7 and suitable choices of ζ. A metric of nonadditive (excess) volume of mixing is also suggested as an approximate predictor of athermal C* phase stability. The principles used to engineer selective entropic bonds and compounds with congruent melting are expected to be applicable to other particle shapes and crystalline phases.

Melting curve and phase diagram of ammonia monohydrate at high pressure and temperature.

The phase diagram and melting behavior of the equimolar water-ammonia mixture have been investigated by Raman spectroscopy, x-ray diffraction, and visual observations from 295 K to 675 K and up to 9 GPa. Our results show non-congruent melting behavior of ammonia monohydrate (AMH) solid below 324 K and congruent melting at higher temperatures. The congruent melting is associated with the stability of a previously unobserved solid phase of AMH, which we named AMH-VII. Another, presumably water-rich, hydrate has also been detected in the range 4 GPa-7 GPa at 295 K on decompression of the high pressure disordered ionico-molecular alloy (DIMA) phase. Comparing our melting data to the literature suggests that non-congruent melting extends from 220 K to 324 K and that the solid phase that borders the fluid between 220 K and 270 K, called AMH-III, is not a proper phase of AMH but a solid solution of ammonia hemihydrate and ice. These results allow us to propose a revised and extended experimental phase diagram of AMH.

Physicochemical Interactions in the GeSb2Te4–PbSb2Te4 System

For the first time, the GeSb2Te4–PbSb2Te4 section of the GeTe–Sb2Te3–PbTe quasi-ternary system is investigated by complex methods of physicochemical analysis (differential thermal, microstructural, and X-ray phase analysis with microhardness measurement and density determination) and the phase diagram is constructed. It is established that the section is a partially quasi-binary section of the GeTe–Sb2Te3–PbTe quasi-ternary system. The GeSb2Te4-based region of the solid solution (15 mol % PbSb2Te4) is revealed. The congruently melting compound GePbSb4Te8 is formed with the ratio of the initial components 1:1. Single crystals of the GePbSb4Te8 quaternary compound are formed by the method of chemical transport reactions. The unit-cell parameters of the GePbSb4Te8 compound, which crystallizes in the orthorhombic crystal system, are determined: a = 5.06 A, b = 9.94 A, an c = 11.62 A. It is established by investigation of the temperature dependences of certain electrical parameters of the GePbSb4Te8 compound and (GeSb2Te4)x(PbSb2Te4)1 – x solid solution that the alloys have p-type conductivity.

Lightning-induced weathering of Cascadian volcanic peaks

The process of meteorological lightning-induced modification of coherent volcanic rocks is examined by geochemical, textural, and experimental analysis of fulgurites from South Sister volcano, Oregon Cascades, USA. Lightning's effects on volcanic target rocks was simulated with an arc-welding device in order to reproduce the geochemical and textural features of natural fulgurites and to constrain temperatures of melting and devolatilization behavior during lightning strikes. Melting of volcanic target rocks produces melts of exceptional compositional diversity, ranging from those with pure mineral compositions (e.g., diopside and plagioclase), resulting from congruent melting reactions, to those that are highly mixed and compositionally identical to the target rock. Geochemical and textural observations on fulgurites suggest that melting proceeds rapidly, by an in situ modal batch process whereby individual crystals melt and contribute small aliquots to a larger batch that is then mixed by viscous flow. Hydrous species remaining in the glasses are trace (OH≪0.1 wt.%), and consistent with partial equilibration to high temperature (>2000°C) supra-liquidus, 1-atm conditions. Lightning also induces physical weathering, in that the target rocks may be vapourized to form channels through the rock, representing injection of elemental components to the atmosphere. Finally, lightning acts as a multi-faceted producer of dry, chemically equivalent volcanic glass, which may be subject to long-term hydration by environmental waters at surface conditions. These re-hydration signatures contrast those of volcanic glasses, which have both magmatic and meteoric components, and are used herein to examine the post-lightning environmental history of these glasses, including age dating lightning events by diffusion chronometry. Our study of volcanic fulgurites illustrates the potential to use their hydration signatures to date paleoweather events at decadal to centuries scale. Because the lightning strike is in and of itself so effective at devolatilizing melts in an instant, the resultant fulgurites are a unique earth material that record individual weather events (i.e., a thunderstorm), and also longer-term paleoweather intervals.

Fabrication and thermal conductivity of CeO2–Ce3Si2 composite

Various compositions of CeO2–Ce3Si2 (0, 10, 30, 50, and 100 wt%Ce3Si2) composites were fabricated using conventional sintering and spark plasma sintering. Lower relative density, enhanced interdiffusion of oxygen and silicon, and silicide agglomerations from the congruent melting of Ce3Si2 at 1390 °C were only observed from conventionally-sintered pellets. Thermal conductivity of spark plasma sintered CeO2–Ce3Si2 composites was calculated from the measured thermal diffusivity, specific heat, and density, which exhibited dense (>90 %TD) and homogeneous microstructure. The composite with 50 wt%Ce3Si2 exhibited 55% higher thermal conductivity than CeO2 at 500 °C, and 81% higher at 1000 °C.

Mechanical Properties of Rapidly Solidified Ni₃Ge and Ni5Ge₃ Intermetallic Compounds.

The congruently melting, single phase, intermetallic compounds β-Ni₃Ge and ε-Ni5Ge₃ were produced by arc melt. Each was subject to rapid solidification via drop-tube processing. Each compound remained fully single phase (either β-Ni₃Ge or ε-Ni5Ge₃) irrespective of the imposed cooling rate. In the investigation of β-Ni₃Ge compound, droplets spanning the size range ≥850 to ≤38 μm diameter particles, with corresponding cooling rates of <700 to >54500 K s-1, were subject to microstructural investigation using SEM. Six dominant solidification morphologies were identified with increasing cooling rate, namely; (i) spherulites, (ii) mixed spherulites and dendrites, (iii) dendrites-orthogonal, (iv) dendrites-non-orthogonal, (v) recrystallized, and (vi) dendritic seaweed, are observed imbedded within a featureless matrix. For the ε-Ni5Ge₃ compound, four dominant solidification morphologies were observed, namely; (i) partial plate and lath, (ii) plate and lath microstructure (iii) isolated hexagonal crystallites, and (iv) single crystal imbedded within a featureless matrix. Micro-Vickers hardness test result of both compounds showed a complex dependence of micro hardness upon cooling rate. At 700 K s-1 the hardness was significantly lower in both compounds than the reported equilibrium value, although in both cases this subsequently increased with further increases in cooling rate. Moreover, in both cases, microstructural transition, such as change in growth direction, led to abrupt drops in hardness. The micro-Vickers hardness results confirmed that the ε-Ni5Ge₃ is significantly harder (maximum 1021 Hv0.01) than the β-Ni₃Ge compound (maximum 526 Hv0.01).

Detection of Intermediate Phases in Metal Alloys

In addition to property anomalies, a distinguishing feature of the intermediate phase is the qualitative change of the crystallization or recrystallization interval (Q∆LS) that occurs at congruent and incongruent melting phases, at eutectic or eutectoid points, at the ends of eutectic or eutectoid horizontals, and also at any nonmonotonicity of the liquidus, since the solidus or solidoid is a horizontal in eutectic or eutectoid systems. A technique has been developed that allows us to associate anomalies in the properties of industrial alloys with state diagrams based on the first established criterion - a qualitative change (length in temperature) of the crystallization (recrystallization) interval (Q∆LS), as well as with a difference in the structural heredity (genealogy) of the component atoms that make up dual system. A joint analysis of the anomalies in the properties of binary alloys with state diagrams (based on the established criterion (Q∆LS)) allows us to relate the latter to the presence of intermediate phases in Al − Si, Fe − C, Al − Cu systems. The intermediate phases AnBm-Q∆LS explaining the anomalies of properties are declared: ~Al7Si, Al41Cu9 − correspond to the eutectic point; Fe24C − eutectoid point; Al11Si, AlSi6 − the bend of the liquidus; Fe42C − bending liquidoid; Al49Cu, Al98.5Si1.5 − the end of the eutectic horizontal; Cu4Al, Cu7Al3 − to the ends of the eutectoid horizontal.

Determination of Low-Melting Alloys in the Ternary Systems NaCl–NaI–Na2WO4 and KCl–KI–K2WO4

The ternary systems with a common cation, NaCl–NaI–Na2WO4 and KCl–KI–K2WO4, were studied by differential thermal analysis. The composition point of the congruently melting compound NaCl ⋅ Na2WO4 formed in the NaCl–Na2WO4 system divides the NaI–NaCl–Na2WO4 system into two triangles, in each of which there is a ternary eutectic. The characteristics of invariant points were determined, and phase equilibria in the studied systems were described.

Congruent melting of tungsten phosphide at 5 GPa and 3200 °C for growing its large single crystals**Project supported by the National Key Research and Development Program of China (Grant Nos. 2016YFA0401503 and 2018YFA0305700), the National Natural Science Foundation of China (Grant No. 11575288), the Youth Innovation Promotion Association of Chinese Academy of Sciences (Grant No. 2016006). the Key Research Platforms

As one of important members of refractory materials, tungsten phosphide (WP) holds great potential for fundamental study and industrial applications in many fields of science and technology, due to its excellent properties such as superconductivity and as-predicted topological band structure. However, synthesis of high-quality WP crystals is still a challenge by using tradition synthetic methods, because the synthesis temperature for growing its large crystals is very stringently required to be as high as 3000 °C, which is far beyond the temperature capability of most laboratory-based devices for crystal growth. In addition, high temperature often induces the decomposition of metal phosphides, leading to off-stoichiometric samples based on which the materials’ intrinsic properties cannot be explored. In this work, we report a high-pressure synthesis of single-crystal WP through a direct crystallization from cooling the congruent W–P melts at 5 GPa and ∼ 3200 °C. In combination of x-ray diffraction, electron microscope, and thermal analysis, the crystal structure, morphology, and stability of recovered sample are well investigated. The final product is phase-pure and nearly stoichiometric WP in a single-crystal form with a large grain size, in excess of one millimeter, thus making it feasible to implement most experimental measurements, especially, for the case where a large crystal is required. Success in synthesis of high-quality WP crystals at high pressure can offer great opportunities for determining their intrinsic properties and also making more efforts to study the family of transition-metal phosphides.

Growth and the Actual Compositions of Cation‐Deficient Sodium‐Gadolinium Molybdate Single Crystals

AbstractThe concentration series of sodium‐gadolinium molybdate (NGM) crystals have been grown by Czochralski technique from stoichiometric Na0,5Gd0,5MoO4 melt, and from seven different nonstoichiometric melts in various atmospheres. The actual cation compositions of the crystals are measured by microprobe analysis. The location of the congruently melting composition is found for this compound, and the homogeneity field is evaluated. The unit cell parameters of the crystals have been calculated from X‐ray diffraction (XRD) analysis results. Hydrostatic densities of the crystals are measured. Based on these results, the actual molar weights of the samples are calculated that allows more precise determination of the crystals compositions. The studied crystals are shown to contain substantial sodium deficiency and excess of gadolinium compared to stoichiometry. The amount of cation vacancies occurs in both sublattices along with increase of Gd2O3/Na2O molar ratio in the crystals.

Synthesis, Crystal Growth, and Transport Properties of van der Waals Tetrel Pnictide GeAs2

Bulk GeAs2 was synthesized utilizing a vapor transport reaction with iodine. Thermal stability tests under dynamic conditions show that GeAs2 decomposes below 700 K, in contrast to the reported congruent melting at 1029 K measured at saturated As vapor pressure. GeAs2 is a p-type narrow bandgap (∼0.4 eV) semiconductor. From a thermoelectric standpoint, GeAs2 outperforms previous computational predictions in thermopower and thermal conductivity. However, electrical resistivity is significantly higher than predicted values, resulting in the low overall thermoelectric figure of merit. Aliovalent doping strategies for GeAs2 should be developed to achieve reasonable thermoelectric performance.

Model for the Calculation of the Dissociation Rate of Nitride Fuel at High Temperatures

A simple theoretical model is proposed in this paper based on an analysis of the experimental data available in the available literature. It describes the rate of mass loss during the dissociation of uranium nitride in a vacuum and in a gas atmosphere due to the evaporation of substances from the surface of materials. The proposed model can be used to assess the degree of dissociation of uranium nitride, which is one of the main causes of fuel destruction, since congruent melting is observed only at high nitrogen pressures.

Growth, Compositions, and Mechanical Characteristics of Sodium–Gadolinium Molybdate Single Crystals

A concentration series of sodium–gadolinium molybdate single crystals have been grown by the Czochralski method from melts of stoichiometric and some nonstoichiometric compositions in atmospheres with different oxygen contents. The actual compositions, microhardness, and crack resistance of the grown crystals have been investigated. All crystals are characterized by a significant sodium deficit with respect to stoichiometry and a large number of vacancies in the (Na + Gd) sublattice. The range of congruent melting is determined for this compound, and its homogeneity range is estimated to extend (on the scale of atomic concentration ratios Gd/Na) at least from 1.10 to 1.75. It is found that the microhardness of sodium– gadolinium molybdate crystals is significantly anisotropic, whereas the degree of crack resistance anisotropy does not exceed the measurement error. At the same time, neither microhardness nor crack resistance exhibit any significant dependence on the growth charge composition and the synthesis conditions in the investigated range of variation in these parameters.

Heat capacity measurement of C14–ZrMn2 and thermodynamic re-assessment of the Mn–Zr system

The CALPHAD approach was used to derive thermodynamic parameters of the Mn–Zr system based on experimental results and critical evaluation of available data. Novel ab-initio calculations as well as experimental data on enthalpy of formation and heat capacity measurements for the C14–ZrMn2 Laves phase were taken into account. The congruent melting point of the C14–ZrMn2 Laves phase was determined using differential thermal analysis (DTA) at 1765 K. Data on heat capacity for the C14–ZrMn2 phase were extended to high temperature range up to 980 K using differential scanning calorimetry (DSC). Standard entropy for C14–ZrMn2 was calculated using an extended Einstein model based on newly obtained results. Additionally, the sublattice model based on antisite substitution in the C14–ZrMn2 Laves phase has been used in order to describe its homogeneity range. Based on the currently obtained results and novel literature data, thermodynamic parameters for the Mn–Zr system were re-optimized. The self-consistent thermodynamic description derived in the present work reproduces all experimental data well.

The influence of the size effect on the transition of Au-Cu alloy nanoparticles to the dynamic amorphous state

In this paper, the effect of size on the Au-Cu diagram for nanoparticles with a diameter of 1.5–20 nm is discussed. The first goal of the study is to obtain this phase diagram including the size-region of ultrasmall nanoparticles of Au–Cu alloy. It was found that the congruent melting point decreases with decreasing particle size. The second goal is to study the dependence of the critical diameter of nanoparticles and the critical temperature on the alloy composition. The thermodynamic conditions of the transition of ultra-small Au-Cu nanoparticles to the dynamic state were studied for the first time. It is shown that their critical diameter strongly depends on the alloy composition. The dependence of the critical diameter and critical temperature of nanoparticles on the alloy composition has a minimum due to congruent melting. The minimum critical diameter of the alloy nanoparticles is achieved at 1.5 nm approximately. The minimum critical temperature is about 390 K.

Thermodynamic and thermophysical properties of Cu-Si liquid alloys

The Cu-Si system is of primary interest for many industrial applications, especially for waste applications. Due to eutectic reactions and the congruent melting of intermetallic phases, these binary alloys exhibit specific behaviors as a function of temperature and composition. A complete investigation of the thermodynamic and thermophysical properties of such liquid metals that may form is required to optimize such a process at the industrial scale. To better predict the thermophysical properties of these metallic alloys, measurements of the surface tension are carried out for bulk mole fractions of up to 32%at Si. These experiments were conducted by means of the oscillating drop technique using the electromagnetic levitation method [1]. To better predict the thermodynamics of such liquids during the experiments, these tests were complemented by chemical activity calculations using the Calphad method. The experimental results obtained from the electromagnetic technique are compared and discussed taking into consideration the Egry model [2], the most suitable one in case of formation of high-temperature intermetallic compounds.

A coupled phase diagram experimental study and thermodynamic optimization of the Li2O-CaO-Al2O3 and Li2O-CaO-SiO2 systems, and prediction of the phase diagrams of the Li2O-CaO-Al2O3-SiO2 system

A coupled experimental phase diagram study and thermodynamic modeling of the Li2O-CaO-Al2O3 and Li2O-CaO-SiO2 systems was conducted at 1 atm total pressure. Differential scanning calorimetry (DSC) measurements were performed in the Li2O-CaO-Al2O3 and Li2O-CaO-SiO2 systems. In addition, the phase relations in the Li2O-CaO-Al2O3 system were determined by equilibration/quenching experiments at 1643 and 1743 K, and the phases were characterized with X-ray diffraction (XRD) and Electron-probe micro analysis-wavelength dispersive spectroscopy (EPMA-WDS). The absence of ternary compounds or solid solutions was confirmed. Congruent melting of Li2CaSiO4 compound in the Li2O-CaO-SiO2 system was determined at 1350 ± 5 K. Thermodynamic optimization of the Li2O-CaO-Al2O3 and Li2O-CaO-SiO2 systems was carried out based on new phase diagram experiments and critically evaluated literature data. The phase diagrams of the quaternary Li2O-CaO-Al2O3-SiO2 system were predicted using the thermodynamic models with optimized model parameters.

T-x-диаграмма системы Ga – Se в диапазоне составов 48.0 – 61.5 мол. % Se по данным термического анализа

Целью настоящей работы было термографическое исследование T-x диаграммы системы Ga – Se в диапазоне температур от 500 до 1100 °С и в диапазоне составов от 48.0 до 61.5 mol % Se. Методом исследования являлся дифференциальный термический анализ c компьютерной регистрацией данных. Получены свидетельства о наличии ретроградного солидуса фазы g-GaSe со стороны селена (с областью гомогенности в несколько десятых mol % при температурах выше эвтектической) и о независимом существовании близких по составу фаз e-GaSe и g-GaSe. При этом более богатая галлием фаза e-GaSe испытывает перитектический распад с образованием расплава (L2) и g-GaSe. Для темпера-туры предполагаемой перитектической реакции получено значение 921 ±2 °С. Вместе стем, на данном этапе работ не получено никаких данных в пользу существования ожидавшейся (по аналогии с системой Ga – S) высокотемпературной модификации, близкой по составу к сесквиселениду галлия (Ga2S3). Другие результаты, полученные в настоящей работе (характер и температуры плавления промежуточных фаз, температуры эвтектического и монотектического превращений, а также координата эвтектического состава), хорошо согласуются с литературными данными по исследованной системе&#x0D; &#x0D; &#x0D; &#x0D; &#x0D; ЛИТЕРАТУРА1. Kainzbauer P., Richter K. W., Ipser H. The binary Bi-Rh phase diagram: stable and metastable phases //J. Phase Equilibria and Diffusion, 2018, v. 39(1), pp. 17– 34. DOI: https://doi.org/10.1007/s11669-017-0600-52. Dolyniuk J.-A., Kaseman D. C., Sen S., Zhao J., Osterloh F. E., Kovnir K. mP-BaP3: A new phase froman old binary system // Chem. Eur. J., 2014, v. 20, pp. 10829–10837, DOI: https://doi.org/10.1002/chem.2013050783. Березин С. С., Завражнов А. Ю., Наумов А. В., Некрылов И. Н., Брежнев Н. Ю. Фазовая диаграммасистемы Ga–S в области 48.0–60.7 мол. % S // Конденсированные среды и межфазные границы, 2017,т. 19(3), с. 321–335. DOI: https://doi.org/10.17308/kcmf.2017.19/2084. Волков В. В., Сидей В. И., Наумов А. В., Некрылов И. Н., Брежнев Н. Ю., Малыгина Е. Н., Завражнов А. Ю. Высокотемпературная кубическая модификация сульфида галлия (Xs = 59 мол. %) и Т, х-диаграмма системы Ga – S // Конденсированные среды и межфазные границы, 2019, т. 21(1), с. 37–50.DOI: https://doi.org/10.17308/kcmf.2019.21/7155. Zavrazhnov A., Berezin S., Kosyakov A., Naumov A., Berezina M., Brezhnev N. J. The phase diagramof the Ga–S system in the concentration range of 48.0–60.7 mol % S // Thermal Analysis and Calorimetry,2018, v. 134(1), pp. 483–492. DOI: https://doi.org/10.1007/s10973-018-7124-z6. Okamoto H. Ga–Se (Gallium-Selenium) // J. Phase Equilibria and Diffusion, 2009, v. 30, p. 658. DOI:https://doi.org/10.1007/s11669-009-9601-37. Dieleman J., Sanders F. H. M. Phase diagram of the Ga-Se system // Phillips J. Res., 1982, v. 37(4),pp. 204 – 229.8. Zavrazhnov A. Yu. Turchen D. N., Goncharov Eu. G., Zlomanov V. P. Manometric method for thestudy of P-T-x diagrams // J. Phase Equilibria and Diffusion, 2001, v. 22(4), pp. 482–490. DOI: https://doi.org/10.1361/1054971017703330639. Shtanov V. I, Komov A. A, Tamm M. E., Atrashenko D. V., Zlomanov V. P. Gallium-selenium systemphase diagram and photoluminescence spectra of GaSe crystals // Doklady Akademii nauk SSSR, 1998, v. 361(3),pp. 357–361. (in Russ.)10. Glazov V. M., Pavlova L. M. Semiconductor and metal binary systems. Phase equilibria and chemicalthermodynamics. Springer, 1989, 327 p. DOI: https://doi.org/10.1007/978-1-4684-1680-011. Ider M. Pankajavalli R., Zhuang W. Thermochemistry of the Ga–Se System. J. Solid State Scienceand Techn., 2015, v. 4(5), Q51–Q60 DOI: https://doi.org/10.1149/2.0011507jss12. Zavrazhnov A., Naumov A., Sidey V., Pervov V. Composition control of low-volatile solids throughchemical vapor transport reactions. III. The example of gallium monoselenide: Control of the polytypicstructure, non-stoichiometry and properties // Thermochimica Acta, 2012, v. 527, pp. 118–124. DOI:https://doi.org/10.1016/j.tca.2011.10.012

Thermal analysis of cesium hafnium chloride using DSC–TG under vacuum, nitrogen atmosphere, and in enclosed system

This paper reports on the preparation of undoped cesium hafnium chloride (Cs2HfCl6) and study of its thermal properties. The Cs2HfCl6 is considered, due to its excellent scintillation properties, as a promising candidate for cost-effective radiation detectors with potential to replace traditional halide scintillators, e.g., NaI:Tl and CsI:Tl. The Cs2HfCl6 material was successfully synthesized from a cesium chloride and a hafnium chloride mixed together in stoichiometric ratio. The presence of only one crystalline phase of the Cs2HfCl6 in the material was confirmed by the X-ray diffraction analysis. The simultaneous non-isothermal differential scanning calorimetry and thermogravimetry (DSC–TG) of the synthesized material under nitrogen atmosphere, vacuum, and in enclosed system was performed. The Cs2HfCl6 decomposition and melting of CsCl–Cs2HfCl6 mixture under nitrogen and vacuum were observed. On the contrary, the DSC measurement of the cesium hafnium chloride in enclosed system showed only one endothermic peak related to the congruent melting point. Furthermore, the repeated DSC–TG measurements to investigate the materials’ stability in enclosed system were carried out as well.