To study thermal desulfurization of pyrite (FeS2), we conducted in situ neutron diffraction experiments in the temperature range 298–1073 K. On heating, pyrite remained stable up to 773 K, at which it started to decompose into pyrrhotite (Fe1−xS) and S2 gas. Rietveld analysis of the neutron data from 298 to 773 K allowed determination of the thermal expansion coefficient of pyrite (space group Pa$\bar 3$) to be αV = 3.7456 × 10−5 K−1, which largely results from the expansion of the Fe–S bond. With further increase in temperature to 1073 K, all the pyrite transformed to pyrrhotite (Fe1−xS) at 873 K. Unit-cell parameters of Fe1−xS (space group P63/mmc) increase on heating and decrease on cooling. However, the rates in cell expansion are larger than those in contraction. This hysteresis behavior can be attributed to continuous desulfurization of pyrrhotite (i.e., x in Fe1−xS decreases) with increasing temperature until the stoichiometric troilite (FeS) was formed at 1073 K. On cooling, troilite underwent a magnetic transition to an orthorhombic structure (space group Pnma) between 473 and 573 K. In addition, using differential thermal analysis (DTA) and thermogravimetric analysis (TGA) implemented with a differential scanning calorimeter, we performed kinetic measurements of pyrite decomposition. Detailed peak profile and Arrhenius (k = A exp(−Ea/RT)) analyses yielded an activation energy Ea of 302.3 ± 28.6 kJ/mol (based on DTA data) or 302.5 ± 26.4 kJ/mol (based on TGA data) and a ln(A) of 35.3 ± 0.1.

In this work, flavonoids in Polygonum cuspidatum Sieb. et Zucc. were extracted by ultrasound-assisted methodology and determined by ultraviolet–visible spectrophotometry. After that, extraction conditions were optimized by the single fact investigation, the central composite design, and response surface methodology (RSM) in turn. The results showed the optimal values of ethanol concentration, solid–liquid ratio, extraction temperature, extraction time, ultrasonic power, and number of extraction times were 60%, 1:20 (g/mL), 45 °C, 34 min; 80 W, and 5, respectively. The extraction ratio of flavonoids could be as high as 94.50%. The influence order of each factor was ultrasonic power > extraction time > extraction temperature > ethanol concentration. The results also showed that the experimental value was close to the predicted value (94.49%) of the established model by RSM, which proved that the established model was reasonable. The thermodynamic results showed that the extraction process was endothermic and could proceed spontaneously.

In this work, a novel shape-stabilized phase change material, composed of n-octadecane, expanded graphite (EG), and sodium chloride (NaCl), was prepared by a convenient method. In the composite, EG was used as the matrix material and NaCl served as the nucleating agent. Effects of the additional amount of NaCl on the thermal properties of the composite were investigated by DSC and TG. The melting and crystallization enthalpies of the composite are −160.23 J/g and 162.80 J/g, respectively; the supercooling degree of the composite decreased to 3.77 °C when compared to 7.58 °C of the pure n-octadecane. Furthermore, the thermal cycling performances became better, and the thermal decomposition temperature improved to 150 °C. The composite exhibited high latent heat, low supercooling degree, good thermal cycling performance, and enhanced thermal stability, making it a potential material for the thermal energy storage application in the field of thermal regulation.

Surface molecularly imprinted polymer of solanesol (SA-SMIP) was prepared by reversed phase suspension polymerization using modified titanium dioxide (TiO2) as carrier, and operation conditions were investigated and optimized. Structures of modified TiO2 and SA-SMIP obtained at optimal conditions were characterized by Fourier transform infrared spectrometer adopting original TiO2 and non-surface molecularly imprinted polymer as reference. The SA-SMIP synthesized under optimal conditions displayed an excellent recognition of SA from the mixture of SA and triacontanol. The maximum separation degree of SA was 2.90. Finally, the adsorption kinetics and isotherm were investigated and analyzed. Adsorption kinetics results indicated that the adsorption of SA-SMIP to SA was a pseudo-second order process, and the adsorption of beginning and later stages was controlled by homogeneous particle diffusion and adsorption reaction process, respectively. Adsorption isotherm results documented hereby were two sorts of bonding sites, complete imprinted cavities and defective imprinted cavities. The adsorption for two bonding sites could be well lined up with the Langmuir model.

Enthalpy increments, $\Delta _{298}^T{H^0}$, for highly nonstoichiometric SrFeO3−δ (δ = 0.18–0.41) were obtained between 373 and 1273 K in air using drop calorimetry. The analysis of the $\Delta _{298}^T{H^0}\left( T \right)$ dependence at lower temperatures allowed evaluating the enthalpy of tetragonal to cubic ${{I4} / {mmm}} \,{\tf="TeX CM Bold Maths Symbols"\char33}\, Pm\bar{3}m$ phase transition at 560 K, 1.57 kJ/mol, and the Maier–Kelley function for $\Delta _{298}^T{H^0}\left( T \right)$ of tetragonal SrFeO3−δ (space group ${{I4} / {mmm}}$). Combined investigation of oxygen nonstoichiometry $\bolddelta \left( T \right)$ dependence, measured by thermogravimetry, and higher-temperature $\Delta _{298}^T{H^0}\left( T \right)$ of cubic SrFeO3−δ (space group $Pm\bar{3}m$) yielded the temperature-dependent reduction (oxygen release) enthalpy, $\Delta H_{{\rm{red}}}^{\rm{0}}$. Calorimetrically-determined $\Delta H_{{\rm{red}}}^{\rm{0}}$ of SrFeO3−δ increases from 65 ± 7 kJ/mol O at 873–973 K to 84 ± 7 kJ/mol O at 1073–1273 K, which may indicate that the short-range vacancy ordering in SrFeO3−δ is hampered at higher temperatures.

While rhenium has proven to be an ideal material in fast-cycling high-temperature applications such as rocket nozzles, its prohibitive cost limits its continued use and motivates a search for viable cost-effective substitutes. We show that a simple design principle that trades off average valence electron count and cost considerations proves helpful in identifying a promising pool of candidate substitute alloys: The Mo–Ru–Ta–W quaternary system. We demonstrate how this picture can be combined with a computational thermodynamic model of phase stability, based on high-throughput ab initio calculations, to further narrow down the search and deliver alloys that maintain rhenium’s desirable hcp crystal structure. This thermodynamic model is validated with comparisons to known binary phase diagram sections and corroborated by experimental synthesis and structural characterization demonstrating multiprinciple-element hcp solid-solution samples selected from a promising composition range.

The thermodynamic properties of ZnxMn3−xO4 and Mg1−zCuzCr2O4 spinel solid solutions have been studied using high-temperature oxide melt solution calorimetry. Except for MgCr2O4 spinel, which possesses cubic structure, the other three end-members are tetragonal. The enthalpies of mixing are small endothermic and fit subregular solution behavior. The main contribution to the energetics of mixing of both spinel systems comes from the difference in the crystal structure between the end-members: a change in the tetragonal distortion for ZnxMn3−xO4 solid solutions and a transition from cubic to tetragonal for the Mg1−zCuzCr2O4 system. If all Mg1−zCuzCr2O4 spinels possessed the same structure, the mixing enthalpies would be close to zero. Because both series have normal cation distributions, the entropies of mixing are equal to the configurational entropies of mixing of Zn2+ and Mn2+ and of Mg2+ and Cu2+ on tetrahedral sites, and the activities would follow Raoult’s law. The calculated Gibbs energy of mixing confirms the absence of solvus at any temperature for both systems.

The defect fluorite titanium-doped yttrium niobate samples Y3Nb1−xTixO7−δ have been synthesized and investigated by the means of high-temperature X-ray diffraction, dilatometry, and thermogravimetry. Thermal expansion coefficients (TECs) as well as chemical expansion coefficients for material with 5, 10, and 15 mol% of titanium were determined. All investigated samples exhibit chemical contraction caused by Ti doping. The values of TECs obtained by two different methods show similar results, which suggests the isotropy of the polycrystalline ceramic. Thermogravimetric studies have shown that all of the compositions exhibit a mass increase upon being exposed to a humid air atmosphere. The total proton concentration calculated on the basis of these results was in the range of 0.1 mol%. Moreover, titanium content influences chemical expansion coefficient, water uptake, and protonic defects concentration, whereas it does not significantly affect the values of TECs.

Enthalpies of water adsorption on amorphous and crystalline oxides and peroxides of uranium are reported. Despite substantial structural and computational research on reactions between actinides and water, understanding their surface interactions from the energetic perspective remains incomplete. Direct calorimetric measurements of hydration energetics of nano-sized, bulk-sized UO2, U3O8, anhydrous γ-UO3, amorphous UO3, and U2O7 were carried out, and their integral adsorption enthalpies were determined to be −67.0, −70.2, −73.0, −84.1, −61.6, and −83.6 kJ/mol water, with corresponding water coverages of 4.6, 4.5, 4.1, 5.2, 4.4, and 4.1 H2O per nm2, respectively. These energetic constraints are important for understanding the interfacial phenomena between water and U-containing phases. Additionally, this set of data also helps predict the absorption and desorption behavior of water from nuclear waste forms or used nuclear fuels under repository conditions. There are also underlying relations for water coverage among different U compounds. These experimentally determined data can be used as benchmark values for future computational investigations.

Using the data obtained by Knudsen effusion mass spectrometry, the standard formation thermodynamic properties of La2Hf2O7, Nd2Hf2O7, and Gd2Hf2O7 were calculated in the present study at high temperatures. Based on the results obtained, it was shown that the standard formation Gibbs energies of La2Hf2O7, Nd2Hf2O7, and Gd2Hf2O7 from the elements at the temperature 2445 K were consistent with the empirical rule concerning decrease of stability of pyrochlore hafnate phase with decrease in lanthanoid ionic radius. The La2Hf2O7 and Gd2Hf2O7 heat capacities were obtained in the present study by differential scanning calorimetry. These data were used along with those found earlier to evaluate the standard formation Gibbs energies of La2Hf2O7 and Gd2Hf2O7 from the elements at the temperature 298 K, which equal (−3937 ± 10) kJ/mol and (−3895 ± 10) kJ/mol, respectively. The thermodynamic properties of La2Hf2O7, Nd2Hf2O7, and Gd2Hf2O7 estimated in a wide temperature range allowed consideration of reliability of data available in the literature.

The BaNd2O4 compound and the BaO–Nd2O3 system are of interest for electroceramics. In this work, we synthesized BaNd2O4 by solid-state reaction, measured its heat capacity from 573 to 1273 K by differential scanning calorimetry, and determined its enthalpy of formation from component oxides at 298 K by high-temperature oxide melt solution calorimetry to be −43.75 ± 4.68 kJ/mol. Our newly determined values and available literature data were employed to assess the phase equilibria in the BaO–Nd2O3 system using CALPHAD methodology. A self-consistent thermodynamic database and the calculated phase diagram of the BaO–Nd2O3 system are provided. The optimized thermodynamic parameters are in good agreement with available experimental data. BaNd2O4 is calculated to melt incongruently at 2177 K. This thermodynamic analysis is essential for the optimization of synthesis conditions for materials and for the evaluation of their stability under appropriate technological operating conditions.

Enthalpies of formation and heat capacities are key parameters for thermodynamic assessments using the CALPHAD method and were determined in this work in the ZrO2–Y0.5Ta0.5O2 quasibinary system. ZrxY0.5−x/2Ta0.5−x/2O2 samples with compositions in the monoclinic and tetragonal ZrO2-based solid solutions (0.65 ≤ x ≤ 1) as well as the two monoclinic (M′ and M) polymorphs of the Y0.5Ta0.5O2-based solid solutions (0 ≤ x ≤ 0.2) were investigated. The enthalpies of the two monoclinic polymorphs M′ and M are essentially the same within experimental uncertainty and have significant energetic stability (enthalpies of formation near −45 kJ/mol) relative to their component oxides. The monoclinic and tetragonal zirconia-rich solid solutions have little energetic stability with respect to ZrO2, Ta2O5, and Y2O3 and presumably owe their existence to the configurational entropy. The heat capacities of M′ and M phase are similar and can be estimated from their constituent oxides using the Neumann–Kopp rule.

Oxide inclusions such as gray spots are the main defects caused by rail flash butt welding (FBW). An appropriate temperature field and upsetting process are essential for the extrusion of joint impurities. This study constructed a thermomechanical coupling model for the solid-state upsetting process of rail FBW through a combination of finite element simulation and experiment. Subsequently, the effects of different temperature fields and upsetting parameters on the extrusion behavior of impurities were studied. The results show that when the lateral deformation of the joint is not considered, selecting the appropriate upsetting length and increasing the width of the high-temperature plastic zone are beneficial for the extrusion of harmful impurities. Moreover, using variable speed upsetting or increasing the speed of the early upsetting facilitates the extrusion of impurities. However, the impurities in the deeper areas of the rail are difficult to move, and they easily form gray spot defects if the oxide inclusions remain.

Using ethanol adsorption calorimetry, the surface energetics of two carbon substrates and two products in microwave-assisted carbon nanotube (CNT) growth was studied. In this study, the ethanol adsorption enthalpies of the two graphene-based samples at 25 °C were measured successfully. Specifically, the near-zero differential enthalpies of ethanol adsorption are −75.7 kJ/mol for graphene and −63.4 kJ/mol for CNT-grafted graphene. Subsequently, the differential enthalpy curve of each sample becomes less exothermic until reaching a plateau, −55.8 kJ/mol for graphene and −49.7 kJ/mol for CNT-grafted graphene, suggesting favorable adsorbate–adsorbent binding. Moreover, the authors interpreted and discussed the partial molar entropy and chemical potential of adsorption as the ethanol surface coverage (loading) increases. Due to the low surface areas of carbon black–based samples, adsorption calorimetry could not be performed. This model study demonstrates that using adsorption calorimetry as a fundamental tool and ethanol as the molecular probe, the overall surface energetics of high–surface area carbon materials can be estimated.

The system GeO2–TiO2 was studied experimentally at high pressure and temperature to measure the miscibility of the two components and to test its applicability as a temperature sensor in high-pressure experiments. Significant solubility between the two end-members was found, with two coexisting solid solutions at high pressure exhibiting mutual solubility that increases with temperature along a solvus. The two solid solution compositions at the solvus can be distinguished readily by X-ray diffraction. At higher temperatures, a complete solid solution exists between the two end-members. The complete solution occurs above a critical line in P–T space (a critical point at each pressure). The critical point is located near 1630 °C and mole fraction ${X_{{\rm{Ti}}{{\rm{O}}_{\rm{2}}}}} = 0.57$ at 6.6 GPa and changes by 60 ± 5° per GPa in the region from 4 to 7 GPa. A model for the shape of the solvus is developed using X-ray diffraction data points from a series of quench experiments and an in situ experiment, and the model is used to estimate the thermal gradients in a Kawai-type multianvil assembly.

Carbonate glasses can be formed routinely in the system K2CO3–MgCO3. The enthalpy of formation for one such 0.55K2CO3–0.45MgCO3 glass was determined at 298 K to be 115.00 ± 1.21 kJ/mol by drop solution calorimetry in molten sodium molybdate (3Na2O·MoO3) at 975 K. The corresponding heat of formation from oxides at 298 K was −261.12 ± 3.02 kJ/mol. This ternary glass is shown to be slightly metastable with respect to binary crystalline components (K2CO3 and MgCO3) and may be further stabilized by entropy terms arising from cation disorder and carbonate group distortions. This high degree of disorder is confirmed by 13C MAS NMR measurement of the average chemical shift tensor values, which show asymmetry of the carbonate anion to be significantly larger than previously reported values. Molecular dynamics simulations show that the structure of this carbonate glass reflects the strong interaction between the oxygen atoms in distorted carbonate anions and potassium cations.