Search

Ceria-based solid solutions are important materials for high- and medium-temperature electrochemical applications. However, the stabilities of both binary and ternary ceria-based solid solutions are insufficient at elevated temperatures, which limits their application as solid electrolytes or SOFC cathodes. Data on the high-temperature stability of ceria-based ceramics are unavailable in the literature. In the present study, we report a thermodynamic stability investigation of Y2O3-CeO2 and Y2O3-ZrO2-CeO2 solid solutions. The thermal prehistories of binary and ternary systems were investigated using STA, XRD, and ESCA techniques. The vaporization processes were investigated in the temperature range of 1577–2227°С via the Knudsen effusion mass spectrometry technique. Using data on the component activity in solid-phase thermodynamic properties of Y2O3-CeO2 solid solutions, which is represented as the Gibbs energy, the excess Gibbs energy was calculated as a function of the ceria mol. %. It was shown that the reduction of Ce4+ to Ce3+ in Y2O3-CeO2 and Y2O3-ZrO2-CeO2 solid solutions corresponds to less-negative Gibbs energy compared to ZrO2-CeO2 solid solutions.

The vaporization of Ti3O5 and V2O3 is studied by high-temperature mass spectrometry. Evaporation is carried out from Knudsen effusion cell made of tungsten. It is found that these oxides pass into vapor congruently with dissociation. Equations are obtained for the dependence of the partial pressures of molecular forms of the vapor on temperature in the form log p = –A/T + B.

The ceramics based on the Y2O3-ZrO2 system is promising for development of refractory materials including ultra-high temperature ceramics. In the present study the samples of the Y2O3-ZrO2 system were synthesized by the solid-state method. The vaporization processes and thermodynamic properties of the Y2O3-ZrO2 system were studied by the Knudsen effusion mass spectrometric method. The vapor composition, the YO, ZrO, ZrO2 and O partial pressures over the samples as well as the Y2O3 and ZrO2 activities of the Y2O3-ZrO2 system were determined at the temperature 2660 K. Thermodynamic properties (i.e. excess Gibbs energies) of the Y2O3-ZrO2 system obtained in the present study can be described in terms of the subregular solution model.

The vaporization processes and thermodynamic properties of twenty samples in the Gd2O3-Y2O3-HfO2 system in a wide concentration range were studied by high-temperature Knudsen effusion mass spectrometry. At the temperature 2500 K the main vapor species were GdO, YO, and O. From the measured values of their partial pressures activities of the Gd2O3 and Y2O3 as functions of concentration were determined. The HfO2 activity was calculated by the Gibbs-Duhem integration. The resulting excess Gibbs energy function exhibited negative deviations from ideal behavior. For the optimization of the obtained thermodynamic functions of the ternary Gd2O3-Y2O3-HfO2 system the generalized Barker-Guggenheim theory of associated solutions was applied. In an alternative computing procedure the same model was used, but the optimization was based on the available literature data for the corresponding binary Gd2O3-Y2O3, Gd2O3-HfO2, and Y2O3-HfO2 systems. Thus, the Barker lattice model may be used for estimation of the thermodynamic functions of a ternary system on the basis of the data for the corresponding binary sub-systems.

Ceria-zirconia solid solutions are the important materials for the application in catalysis and the energy conversion. However, the existing data on the thermodynamic properties of ceria-zirconia solid solutions which is used to distinguish their stability is controversial. In the present work, equilibrium ceria-zirconia solid solutions with 90, 50, 24 and 9 mol.% CeO2 were manufactured using the original sol-gel reverse co-precipitation method with further prolonged thermal treatment for 5–50 h at 973–1373 K. Comprehensive characterizations of the precursor powders obtained were performed via SEM, STA, XRD, ESCA and PSD-analysis. According to XRD observations combined with Rietvield refinement and ESCA the equilibrium solid solutions without an admixture of Ce3+ in the condensed phase were obtained after the calcination of samples at 1373 K. Knudsen effusion mass spectrometry was used to study the vaporization processes and the thermodynamic properties of solid solutions in the CeO2 ZrO2 system at 2150 K. Similar dependence of the CeO2 activity on the condensed phase composition was obtained for solid solutions with various ceria contents, which ensured the equilibrium evaporation. The schematic evaporation process for xCeO2-(100-x)ZrO2 solid solutions at 2100–2500 K was suggested for the first time. It was found, that high temperature behavior of CeO2 ZrO2 system significantly differs from its behavior at lower temperatures, i.e. 873–1373 K, when Ce (IV) to Ce (III) reduction takes place.

Black soldier fly allows to efficiently convert residual biomasses into a valuable source of biomolecules, such as proteins, lipids and chitin. In this study, a new method for obtaining amorphous chitin from the black soldier fly larvae was developed with a further deacetylation step. Amorphous chitin was obtained by direct extraction using concentrated phosphoric acid. The purity of the resulting chitin was confirmed by physicochemical methods (elemental analysis, IR spectroscopy, measurement of primary amines, amino acid analysis). Crystalline chitin and high molecular weight chitosan were obtained by the standard procedure including demineralisation, deproteinisation and deacetylation steps. This method allows to extract chitosan, suitable for a wide range of applications.

The study of high temperature behavior of Y 3 Al 5 O 12 is urgently required for development of high temperature materials of the new generation including ultra-high temperature ceramics. The superfine Y 3 Al 5 O 12 powder was obtained by the glycol-citrate method; the aggregation process of the sample synthesized was investigated under calcination conditions at different temperatures. Using the Knudsen effusion mass spectrometric method vaporization processes and thermodynamic properties of Y 3 Al 5 O 12 as well as of the melts in the Y 2 O 3 -Al 2 O 3 system were studied at temperatures higher than 2270 K. The simultaneous transition to the gaseous phase of both Al 2 O 3 and Y 2 O 3 from the melt under study was observed during isothermal keeping of the Y 3 Al 5 O 12 sample at the temperature 2675 K with the predominant alumina removal. Analysis of the values of the thermodynamic properties obtained in the Y 2 O 3 -Al 2 O 3 system showed negative deviations from ideal behavior despite the possibility of existence of the miscibility gap at the temperature 2675 K.

The superfine lanthanum hafnate powder was synthesized by the glycol-citrate method. The phase transitions and the changes of microstructure of the La2Hf2O7 sample were studied under different conditions of thermal treatment (973–1673 K, 2–4 h). The vaporization processes of La2Hf2O7 were established at temperatures 2297–2500 K by the high temperature mass spectrometric method. The thermodynamic properties in the La2O3-HfO2 system were obtained at temperatures 2297 and 2445 K.

Barium cerate with additions of rare-earth or 3- d metal oxides is widely used for production of solid electrolytes, ionic, and electron–ionic conductors. Knudsen effusion mass spectrometry was used to study vaporization processes and thermodynamic properties of solid solutions in the BaO – CeO 2 system at the temperature 2000 K. Ba, BaO, CeO and CeO 2 were found as the main vapor species over the samples studied. Activity values and Gibbs energy of BaO and CeO 2 in the samples studied were calculated. The activities of barium and cerium oxides in the concentration range of the homogeneous melt (70–32 mol. % of BaO) and in the region from 32 to 5 mol % of BaO (solid solution of CeO 2 + liquid) have low negative deviations from the ideal case. The determined value of the standard formation enthalpy of solid barium cerate is equal to −1692 ± 17 kJ/mol.

Wide use of phosphates in different areas motivates interest to investigation of these compounds. Knudsen effusion mass spectrometry was used to study thermodynamic properties of gaseous lead phosphates. On the basis of the measured constants of the equilibrium of gas-phase reactions the standard formation enthalpies of PbPO2, PbPO3 and PbP2O6 have been defined. For these gaseous lead phosphates thermodynamic function were calculated by statistical thermodynamic method in “rigid rotor-harmonic oscillator” approximation. The molecular parameters obtained by different quantum chemistry method.

The formation and stability of the gaseous oxyacid salts SnB2O4 and Sn2B2O5 were studied. The gaseous SnB2O4 and Sn2B2O5 were identified in the gas phase over the SnO2–B2O3 system in the temperature range 1320–1500 K. Determination of m/z-values, isotopic patterns and appearance energies of all gaseous species was performed by means of high-temperature mass spectrometry. Thermodynamic data for the gaseous SnB2O4 and Sn2B2O5 molecules were obtained by means Knudsen effusion mass spectrometry and quantum chemistry DFT M06 and MP2 calculations.

For the first time by X-ray method two phases of the solid solutions LaCo x Ga 1−1.2 x Mg 0.2 x O 3− δ and LaCo x Ga 1−1.5 x Mg 0.5 x O 3− δ ( x = 0.01–0.10) with different structure were found – rhombohedral and orthorhombic phases. On the basis of the data on evaporation of the components a synthetic procedure was advanced allowing the losses of cobalt to be minimized. The study of magnetic characteristics of obtained solid solutions showed the formation of high nuclearity clusters containing cobalt atoms, and also magnesium and associated vacancies even in diluted solid solutions. Clusters are characterized by a competition between ferro- and antiferromagnetic exchange interactions, whereas the long order exchange is antiferromagnetic.

Polysaccharide processing by means of low-temperature Electron Beam Plasma (EBP) is a promising alternative to the time-consuming and environmentally hazardous chemical hydrolysis in oligosaccharide production. The present paper considers mechanisms of the EBP-stimulated destruction of crab shell chitin, cellulose sulfate, and microcrystalline cellulose, as well as characterization of the produced oligosaccharides. The polysaccharide powders were treated in oxygen EBP for 1–20 min at 40 °C in a mixing reactor placed in the zone of the EBP generation. The chemical structure and molecular mass of the oligosaccharides were analyzed by size exclusion and the reversed phase chromatography, FTIR-spectroscopy, XRD-, and NMR-techniques. The EBP action on original polysaccharides reduces their crystallinity index and polymerization degree. Water-soluble products with lower molecular weight chitooligosaccharides (weight-average molecular mass, Mw = 1000–2000 Da and polydispersity index 2.2) and cellulose oligosaccharides with polymerization degrees 3–10 were obtained. The 1H-NMR analysis revealed 25–40% deacetylation of the EBP-treated chitin and FTIR-spectroscopy detected an increase of carbonyl- and carboxyl-groups in the oligosaccharides produced. Possible reactions of β-1,4-glycosidic bonds’ destruction due to active oxygen species and high-energy electrons are given.

Thermal behavior of components in the La2O3-SrO-CoO system at the temperature range of 1600–2087 K has been studied in this work using high-temperature differential mass spectrometry. It has been demonstrated that the value of the cobalt oxide activity coefficient decreases with an increase of the relative content of strontium oxide and the temperature.

The zirconium oxide based ceramics with addition of rare-earth metal oxides is widely used for production of high temperature materials. Knudsen effusion mass spectrometry was used to study vaporization processes and thermodynamic properties of solid solutions in the ZrO 2 –Lu 2 O 3 system at the temperature 2700 K. The Lu, LuO, ZrO and ZrO 2 were found as the main vapor species over the samples studied. The ZrO 2 and Lu 2 O 3 activities, the Gibbs free energy of formation, the excess Gibbs free energy of formation in the samples studied were calculated. The activities of lutetium oxide in all concentration range of condensed phase have low negative deviation from ideal case whereas zirconium dioxide activities have strong negative deviation from ideal case.

The stability of gaseous species GeB2O4 and GeMo2O7 was confirmed by Knudsen effusion mass spectrometry. The gas-phase reactions involving B2O3, Mo2O6, MoO3, GeB2O4 and GeMo2O7 were studied. On the basis of equilibrium constants, the standard formation and atomization enthalpies of gaseous GeB2O4 (−1101 ± 18 kJ mol−1 and 3600 ± 20 kJ mol−1) and GeMo2O7 (−1449 ± 41 kJ mol−1 and 4810 ± 43 kJ mol−1) at 298 K were determined. To get structure parameters and vibrational frequencies of gaseous GeB2O4 and GeMo2O7 quantum chemical investigation of these molecules was undertaken. Formation enthalpies of gaseous GeTaO3, GeTiO3, GeVO3 and GePO2 were estimated.

Experimental data obtained by Knudsen Effusion Mass Spectrometry and results of quantum-chemical calculations on the structure and thermodynamic properties of gaseous oxyacid salts were systematized. A criterion of thermal stability of these compounds was offered and regularities in the atomization enthalpies were established.

A number of gaseous oxyacid salts have been identified by Knudsen effusion mass spectrometry by vaporizing Ga(2)O(3) from molybdenum and tungsten cells. The stability of gaseous molecules Ga(2)MoO(4), Ga(2)WO(4), Ga(2)Mo(2)O(7), and Ga(2)W(2)O(7) was deduced from the measurements. The structures and molecular parameters of all salts investigated were obtained using quantum chemical calculations. On the basis of equilibrium constants measured for gas-phase reactions, the standard formation enthalpies were determined to be -827 +/- 26, -843 +/- 26, -1578 +/- 32, and -1525 +/- 34 kJ.mol(-1) for Ga(2)MoO(4), Ga(2)WO(4), Ga(2)Mo(2)O(7), and Ga(2)W(2)O(7), respectively.

In the present study, the stability of gaseous barium silicates was confirmed by the high temperature mass spectrometry. On the basis of equilibrium constants measured for gas-phase reactions, the standard formation enthalpies were determined for gaseous barium silicates as (−510 ± 15) kJ · mol−1 and (−884 ± 18) kJ · mol−1 at 298 K; standard atomization enthalpies as (1637 ± 17) kJ · mol−1 and (2318 ± 20) kJ · mol−1 at 298 K for BaSiO2 and BaSiO3, respectively. Based on the results obtained the critical analysis of the literature data was carried out.

The vapor composition and thermodynamic properties of components in the BaO-SiO2 system at a temperature of 1970 K are determined using high-temperature mass spectrometry. The thermodynamic properties of melts in the BaO-SiO2 system are calculated within the framework of the vacancy variant of the generalized lattice theory of associated solutions. This made it possible to establish the relation between the thermodynamic properties and the structural features of melts in the BaO-SiO2 system.

The composition of the vapor and the activities of cesium metaborate CsBO2 in glass melts of the Cs2O-B2O3-SiO2 system at a temperature of 1020 K are determined using high-temperature mass spectrometry. The activities of the individual oxides Cs2O, B2O3, and SiO2 in glass melts of the Cs2O-B2O3-SiO2 system at a temperature of 1020 K are calculated by the Wagner method from the obtained values of the activities of CsBO2. The integral and excess Gibbs energies are determined.

A review is presented of the data available in the literature on the thermodynamic properties and structure of gaseous metaborates studied by high-temperature mass spectrometry, gas-phase electron diffraction, spectroscopy, and quantum-chemical methods. The reliability and inconsistency of the thermodynamic properties and structural data obtained by these methods for gaseous metaborates are discussed. The specific features of the application of the above methods for investigating the thermodynamic properties and structure of gaseous metaborates at high temperatures are analyzed.

The vaporization of aluminum under reducing conditions is studied by the Knudsen method with mass-spectrometric analysis of the vapor phase. It is shown that, in the presence of carbon, the relative content of Al2O in the vapor increases as compared to the vaporization under neutral conditions and the vaporization temperature of aluminum-containing molecules is reduced.

The formation of associates in the vapor phase over a mixed oxide is analyzed in relation to the difference in acid-base properties and volatility between its constituent oxides. A method is proposed for assessing the standard enthalpy of formation of gaseous oxy salts. Experimentally determined standard enthalpies of formation are presented for gaseous salts formed by CrO, CrO2, MnO, FeO, CoO, NiO, and MgO.

The vapor composition, activities of the components, and Gibbs energies of melts in the Cs2O-B2O3 system at a temperature of 1020 K are determined by the Knudsen effusion mass spectrometric method. The activities of the components and the Gibbs energies of melts in the Cs2O-B2O3 system at a temperature of 1020 are calculated in the framework of the approach based on the generalized lattice theory of associated solutions with the use of the melt model including vacancies. It is demonstrated that the calculated and experimental thermodynamic properties are in reasonable agreement.

The existence of gaseous cobaltates of alkaline-earth metals was established in the present work by high-temperature mass spectrometry. Gaseous molecules: CaCoO2, SrCoO2 and BaCoO2 have been found for the first time. On the basis of the measured constants of the equilibrium of gas-phase reactions the standard enthalpies of formation: (−149 ± 19) kJ · mol−1, (−149 ± 20) kJ · mol−1 and (−250 ± 16) kJ · mol−1; and standard atomization enthalpies: (1251 ± 22) kJ · mol−1, (1233 ± 23) kJ · mol−1 and (1353 ± 20) kJ · mol−1 for CaCoO2, SrCoO2 and BaCoO2, respectively, have been defined.

The activities of silicon dioxide and barium oxide in the BaO-TiO2-SiO2 system containing from 10 to 50 mol % SiO2 at a mole fraction ratio BaO : TiO2 = 1 and at a constant SiO2 mole fraction of 0.5 are determined using high-temperature differential mass spectrometry. It is shown that the positive deviation of the SiO2 activity and the negative deviation of the BaO activity from ideal behavior are observed at high SiO2 contents.

The vaporization and thermodynamic properties (activities of the components and Gibbs energies) of melts in the Rb2O–B2O3 system at a B2O3 content varying from 66.7 to 92.0 mol % are investigated by high-temperature differential mass spectrometry upon evaporation from molybdenum cells in the temperature range 950–1350 K.

The application of the Sanderson method to the calculation of bonding energies of oxide systems in different states of aggregation is considered. In the framework of this method, the bonding energies of different oxides and oxide glass-forming systems are calculated with the inclusion of the second coordination sphere. The reliability of the calculations performed by the Sanderson method for bonding energies of oxide glass-forming systems is illustrated by comparing the obtained results with the available experimental data and theoretical values determined by other computational techniques.

The vaporization of oxygen-containing acid salts is analyzed as a function of different factors affecting the qualitative and quantitative vapor compositions. It is shown that the character of vaporization of these salts can be predicted with a high accuracy only from the complete set of a number of criteria such as the difference between the acid–base properties of oxides forming the salt, the difference in their volatilities, the position of cation- and anion-forming elements in the periodic table, and the evaporation conditions.

This paper reports on the results of systematic investigations into the thermodynamic properties of melts lying along the joins with constant SiO2 contents of 0.5 and 0.6 mole fractions in the CaO–Al2O3–SiO2 system at mole fraction ratios CaO : Al2O3 varying from 0.25 to 4.0. The activities of SiO2 in melts of this system at a temperature of 1905 ± 10 K are determined by high-temperature mass spectrometry. It is found that, in the concentration range studied, the activity of SiO2 remains constant at SiO2 contents of 0.5 and 0.6 mole fractions.

The existence of gaseous manganese tungstates MnWO4 and MnWO3 is proved by high-temperature mass spectrometry, and the standard enthalpies of formation and atomization of these salts are determined.

The vaporization of glass-forming phosphates of the periodic table Group IVA elements is studied by high-temperature mass spectrometry. Analyses of qualitative and quantitative vapor compositions have revealed a number of regularities that allow the prediction of the character of the vaporization of polyvalent element phosphates.

MASS SPECTROMETRIC STUDY OF THE VAPORIZATION OF GALLIUM PHOSPHATES SERGEY I. LOPATIN", GERMAN A SEMENOVa, ANATOL Y F. SELEVICHb Chemical Department, St. Petersburg State University, Universitetskii pr. 2 St. Petersburg, 198904, Russiaa Institute for Physical Chemical Problems, Belarusian State University, Leningradskaya 14, Minsk, 220080, Belarusb Abstract The vaporization of gallium phosphate GaP04 was studied by high­temperature mass spectrometry. • Standard enthalpies of formation and atomization (kJ/mol) were derived for GaP03 (g) (-661±35 and 1997±36), and for GaP0

27 When stainless steel or other nickel-containing materials are exposed to oxidative conditions at high temperatures, complex oxide components, in particular, oxygen-containing salts based on nickel(II) oxide, can convert to vapor. In this context, information on the molecular forms and thermodynamic properties of oxygen-containing nickel compounds in the gas phase is of considerable interest.