Vol 68, No 2 (2023)

Thermophysical properties of solid and liquid calcium (99.75 wt % pure) were experimentally studied with high accuracy in the temperature range 720–1290 K using dilatometer measurements, gamma-ray attenuation measurements (the gamma-ray method), high-temperature drop calorimetry, and the laser flash method. The behaviors of the density, enthalpy, and thermal conductivity of calcium in the fusion–crystallization region were studied. The enthalpy of fusion was measured as 8075 J/mol, the relative density change upon fusion as 3.3%, and the relative change in thermal conductivity upon fusion as 26%. The results were compared to the respective values in the related literature. The measurements at temperatures above 720 K either significantly amend the available literature data, or are currently unique. The constancy of the heat capacity of liquid calcium in the temperature range 1115–1290 K was verified. Fitting equations were derived, and recommended values of the investigated properties of calcium were tabulated for 720–1290 K, the temperature range where calcium is in the condensed state.

The pressure of ferrocene in the system host (organometallic framework [Zn4(dmf)(ur)2(ndc)4])–guest (ferrocene) has been measured by static method with membrane zero-manometers in the temperature range from 324 to 462 K. As a result of the study, temperature dependences of pressure have been obtained for the transition of the guest from the host framework to the gas phase, the enthalpy and entropy of this process have been determined, and the change in the Gibbs energy during ferrocene binding by the framework has been calculated. Based on this information, conclusions have been made about the nature of interactions between host and guest molecules, and the obtained results have been compared with the previously studied benzene sorption on [Zn4(dmf)(ur)2(ndc)4].

The paper presents an extension of the Voronin–Kutsenok method for joint description of both thermochemical and bulk data with combination of Planck–Einstein functions and modified Tait equation. Two approaches based on the Gibbs and Helmholtz energy descriptions were proposed. Magnesium oxide (periclase) was chosen as the test system. The parameters of the equation of state were optimized using published data over a broad range of thermodynamic variables (up to 3000 K and 145 GPa). The predictive power of both approaches was estimated.

Cs2MoO4 and Li1.9Cs0.1MoO4 crystals were grown from melt by the low-thermal-gradient Czochralski technique. The standard formation enthalpy of cesium molybdate Cs2MoO4 was measured by solution calorimetry. The heat capacity of Li1.9Cs0.1MoO4 was measured by differential scanning calorimetry (DSC) in the temperature range 320–710 K. The lattice enthalpy of Cs2MoO4 was calculated using the Born-Haber cycle. Cesium molybdate was shown to be thermodynamically stable to decomposition into constituent simple oxides (Cs2O and MoO3), which made it promising for application. Li1.9Cs0.1MoO4 experienced no phase transitions in the temperature range 320–710 K.

Previous experimental data on the vaporization and high-temperature thermodynamic properties of hafnium and rare earth oxide ceramics are considered here. The La2O3–Sm2O3 system is for the first time studied at 2323 K using Knudsen effusion mass spectrometry. As a result of this study, the vapor composition over ceramic samples under investigation is identified, and concentration dependences of the partial pressures of vapor species over the system under study and condensed-phase thermodynamic properties are determined, namely, the component activities and the excess Gibbs energy. The enthalpy of formation from oxides and excess entropy of the La2O3–Sm2O3 system at 2323 K are determined using the Wilson polynomial. The Kohler, Redlich–Kister, and Wilson semiempirical methods were used to calculate the thermodynamic properties in the La2O3–Sm2O3–Y2O3–HfO2 and La2O3–Sm2O3–ZrO2–HfO2 quaternary systems at 2330 K using the equilibrium data gained in the relevant binary systems. The results of the calculations were compared to previous semiempirical estimates of the respective quantities for the La2O3–Y2O3–ZrO2–HfO2 and Sm2O3–Y2O3–ZrO2–HfO2 systems taken as examples. Calculations by the Wilson method are shown to provide the best match with the experimentally obtained lanthanoid oxide activities in the La2O3–Sm2O3–Y2O3–HfO2 and La2O3–Sm2O3–ZrO2–HfO2 systems.

Ceramic Bi1.4Dy0.6O3 and Bi3Nb0.2Sm0.8O6.2 samples were prepared by solid-phase synthesis. The compounds have cubic structures (space group Fm3m). Their standard enthalpies of formation were determined by solution calorimetry, and their lattice enthalpies were calculated. The lattice enthalpies of Bi3Nb0.2R0.8O6.2 compounds decrease in magnitude when erbium is replaced by samarium, due to the lanthanide radius increasing from erbium to samarium. The lattice enthalpy of Bi1.4Dy0.6O3 has a greater magnitude than the lattice enthalpy of Bi1.2Gd0.8O3.

Tensimetric studies were carried out to determine temperature-dependent saturated vapor pressures and calculate thermodynamic characteristics of vaporization for R3N·BH3 (R = Me or Et) alkylamine boranes. These compounds have sufficient volatility and thermal stability to be used as precursors in vapor deposition processes to produce films based on phases of the B–C–N system. Triethylamine borane (TEAB) was used to synthesize boron carbonitride films at 773 and 873 K. The resulting layers were characterized by ellipsometry, atomic force and scanning electron microscopy, FTIR, Raman, and energy dispersive spectroscopies. The conditions for the production of continuous homogeneous films consisting of nanoparticles 20–60 nm in size aggregated into larger pseudohexagonal particles were determined. The surfaces of the films have an average and root mean square roughness, equal to 0.8 and 1.0 nm, respectively.

Solid–liquid equilibria in the system H2O–Gd(NO3)3 were measured from –20 to 70°C using the isothermal saturation method. The Pitzer–Simonson–Clegg thermodynamic model was implemented to obtain the temperature dependence of Gd(NO3)3⋅6H2O solubility constant, to calculate salt solubility and to construct a phase diagram of the system from eutectic point to hydrate melting. Thermochemical properties of gadolinium nitrate aqueous solutions, such as dilution enthalpies and heat capacities, were assessed also. The model has shown to be reliable for phase equilibria calculation from –35 to 90°C and from 0 up to ~15 mol % of salt as well as the thermodynamic properties of Gd(NO3)3 aqueous solutions at room temperature and around it.

A CVD technique has been developed for the deposition of homogeneous graphitic carbon nitride films on silicon and quartz glass substrates using melamine as a precursor. Layer-by-layer deposition at low precursor loadings makes it possible to deposit a film up to 1.4 µm thick; however, it is possible to achieve large thicknesses by multiple repetition of the experimental cycle. The effect of synthesis parameters on the surface morphology of deposited layers has been studied by scanning electron microscopy. The chemical composition and structure of graphitic carbon nitride films are confirmed by a set of spectroscopic methods and X-ray diffraction. The optical properties have been studied using diffuse reflectance spectroscopy. Scanning electron microscopy and X-ray diffraction analysis have shown that films deposited at temperatures of 550–650°C have a layered microcrystalline structure. The bandgap of the obtained samples was 2.76–2.93 eV.

High-temperature composite materials comprising single-walled carbon nanotubes embedded in a polybenzimidazole (PBI) polymer matrix with a weight percentage of nanotubes from 1 to 5% were prepared and characterized. Film composite samples were prepared by flow-coating from dispersions of nanotubes in 2% PBI solution in N-methyl-2-pyrrolidone. The temperature dependences of electrical resistance of the composites were studied in the range from room temperature to 300°C in a high vacuum at a pressure less than 1 × 10–3 Pa. The first heating cycle to 300°C gave rise to an increase in room-temperature electrical resistance of the samples due to the desorption of oxygen from the nanotubes. For the composites containing 5 and 1% nanotubes, the change was about 1.4 and 500 times, respectively. This increase was reversible: when the samples were transferred to the ambient air, the electrical resistance relaxed to its initial value. The thermal stability of the composites was proved by the repeatability of the subsequent heating cycles and by thermogravimetric analysis.

The effect of silicon dioxide nanoparticles on the formation of hydrate phases in the presence of CH4/CO2 has been studied. The theoretical experiment has been carried out by molecular dynamics methods at initial pressures in the system of 2.4 and 1.2 MPa and a temperature of 271 K for methane and carbon dioxide systems. The results showed that in the presence of silicon dioxide nanoparticles, the induction time of the methane hydrate formation decreased by 79%, and the amount of methane trapped in the hydrate cavity increased by 55.8% at a pressure of 2.4 MPa. In the presence of silicon dioxide nanoparticles, the induction time for the formation of carbon dioxide hydrate decreased by 62%, and the amount of carbon dioxide trapped in the hydrate cavity increased by 27.8% at a pressure of 1.2 MPa.