High-temperature Mass Spectrometric Method Research Articles

Mass spectrometric study and modeling of the thermodynamic properties in the Gd2 O3 -ZrO2 -HfO2 system at high temperatures.

Materials based on the Gd2 O3 -ZrO2 -HfO2 system are promising for a wide range of high-temperature technological applications, such as for obtaining thermal barrier coatings in the aviation and space industry, as well as advanced materials in nuclear power applications. Experimental studies of the ceramics based on this system by the Knudsen effusion mass spectrometric method provides such valuable information as the vapor composition over the samples and enables derivation of the thermodynamic functions. Samples of ceramics in the Gd2 O3 -ZrO2 -HfO2 system were synthesized and analyzed by X-ray fluorescence and diffraction techniques. The vaporization processes and partial pressures of the vapor species over the samples were obtained by the high-temperature mass spectrometric method using the ion current comparison method. The derived thermodynamic functions were optimized within the Generalized Lattice Theory of Associated Solutions (GLTAS) approach. At the temperature of 2600 K, the GdO, ZrO, ZrO2 , HfO, and O vapor species were found over the samples, but only for the GdO and ZrO species were accurate experimental data on the partial pressures obtained. In all the ceramic samples, the Gd2 O3 activity was determined. On this experimental basis, modeling within the GLTAS approach was performed. It allowed the evaluation of the Gd2 O3 , ZrO2 , and HfO2 activities in the system under study and a rough approximation of the excess Gibbs energy as a function of composition to be obtained. At 2600 K the Gd2 O3 -ZrO2 -HfO2 system is characterized by negative deviations of its thermodynamic properties from the ideal behavior. Consistency of the obtained modeling results indicate reasonable uniformity of the energy parameters of the lattice model derived in calculations of the hafnia-containing oxide systems, which may be used in further modeling of multicomponent systems.

High-temperature mass spectrometric study of the thermodynamic properties in the Sm2 O3 -ZrO2 -HfO2 system.

The Sm2 O3 -ZrO2 -HfO2 system is a promising base for the development of a wide spectrum of new refractory materials. Reliable data on thermodynamic properties in this system are of significant importance for planning the preparation and application of high-temperature ceramics. Especially, they can be useful for calculation of the unknown phase equilibria in this system. The thermodynamic properties of the Sm2 O3 -ZrO2 -HfO2 system were studied by the high-temperature mass spectrometric method. The samples in the system under consideration synthesized by the solid-state method were vaporized from a tungsten twin effusion cell using a MS-1301 magnetic sector mass spectrometer. Ionization of the vapor species effusing from the cell was carried out by electrons at an energy of 25 eV. It was shown that, at temperatures below 2500 K, the main vapor species over the ceramics based on the Sm2 O3 -ZrO2 -HfO2 system were SmO, Sm, and O corresponding to vapor composition over pure Sm2 O3 . The SmO, Sm, and O partial vapor pressures over the samples and the Sm2 O3 activities were obtained in the temperature range 2319-2530 K. This allowed the excess Gibbs energy values to be determined. For comparison, the excess Gibbs energies in the Sm2 O3 -ZrO2 -HfO2 system were also calculated by the semi-empirical Kohler, Toop, Redlich-Kister, and Wilson methods and optimized by the statistical thermodynamic Generalized Lattice Theory of Associated Solutions (GLTAS). The thermodynamic data calculated by the semi-empirical approaches at 2423 K were shown to be lower than the experimental values. However, the Toop and Wilson methods were found to be useful for evaluation of the excess Gibbs energy values at the Sm2 O3 mole fraction less and higher than 0.32, respectively. The self-consistent thermodynamic description of the Sm2 O3 -ZrO2 -HfO2 system was derived at high temperatures by optimization of the experimental results using the GLTAS.

Mass spectrometric study of ceramics in the Sm2 O3 -ZrO2 -HfO2 system at high temperatures.

Systems containing zirconia, hafnia, and rare earth oxides are indispensable in various areas of high-temperature technologies as a basis of ultra-high refractory ceramics. Exposure of these materials to high temperatures may result in unexpected selective vaporization of components or phase transitions in the condensed phase leading to changes in physicochemical properties. Consequently, reliable application of the ceramics based on systems such as Sm2 O3 -ZrO2 -HfO2 is impossible without data on its vaporization processes and thermodynamic properties, which may be used to predict the physicochemical characteristics of the ultra-high refractory ceramics. Ceramics based on the Sm2 O3 -ZrO2 -HfO2 system were obtained by solid-state synthesis and characterized by X-ray fluorescence and X-ray phase analyses. The vaporization and thermodynamics of the system considered were examined by the high-temperature mass spectrometric method using a MS-1301 magnetic sector mass spectrometer with a tungsten twin effusion cell. Vapor species effusing from the cell were ionized by electrons with an energy of 25 eV. The main vapor species over the Sm2 O3 -ZrO2 -HfO2 system were shown to be SmO, Sm, and O at a temperature of 2373 K, indicating selective vaporization of Sm2 O3 from the samples. The partial pressures of these vapor species and the Sm2 O3 activities were determined in the Sm2 O3 -ZrO2 -HfO2 system and allowed the excess Gibbs energies to be evaluated. These excess Gibbs energy values were compared with the results obtained by the semi-empirical and statistical thermodynamic approaches. The data obtained in this study showed negative deviations from the ideal behavior in the Sm2 O3 -ZrO2 -HfO2 system at 2373 K. The results calculated according to the semi-empirical methods and statistical thermodynamic Generalized Lattice Theory of Associated Solutions were in agreement with each other. Thus, this evidenced the desirability of further experimental investigation of the Sm2 O3 -ZrO2 -HfO2 system by the high-temperature mass spectrometric method.

Samarium zirconate: Thermodynamics and vaporization at high temperatures

The purpose of the present research was to study vaporization processes and thermodynamic properties of samarium zirconate with the pyrochlore structure. The Sm2Zr2O7 sample was synthesized by the glycol-citrate method with the confirmation of its pyrochlore structure using X-ray phase analysis, infrared spectroscopy, and scanning electron microscopy. The thermodynamic properties and vaporization processes of samarium zirconate were examined by the high temperature mass spectrometric method at temperatures 2299−2730 K. The data obtained in the present study for the first time allowed determination of the Gibbs energy of formation of samarium zirconate from the pure oxides at 2460 K, which was equal to -115.7 kJ/mol, and, as a consequence, the values of the Gibbs energy and enthalpy of formation from the pure oxides at the temperature 298.15 K, which were equal to -130.5 kJ/mol and -131.4 kJ/mol, respectively.

Vaporization and thermodynamic properties of lanthanum hafnate

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.

Vaporization and Thermodynamics of Glass-Forming Oxide Melts: Mass Spectrometric Study and Modeling

Information on the vaporization processes and thermodynamic properties of glass-forming oxide melts in the systems MgO-B2O3-SiO2, CaO-B2O3-SiO2, SrO-B2O3-SiO2, BaO-B2O3-SiO2, PbO-B2O3-SiO2, CdO-B2O3-SiO2, ZnO-B2O3-SiO2, Bi2O3-B2O3-SiO2 and Bi2O3-GeO2-SiO2 together with the earlier obtained data is discussed. These data were obtained by high-temperature mass spectrometric method. Various types of vapor species were found over oxide systems studied such as the associated, dissociated and polymerized products of vaporization. The regularities of the vaporization of the binary and multicomponent glass-forming oxide melts were illustrated and discussed from the point of view of the acid-base concept. Results on determination of thermodynamic functions in oxide systems were considered taking into account the main requirements for the confirmation of their reliability. The generalized lattice theory of associated solutions was used for the calculation of thermodynamic properties of the ternary silicate melts studied. Using this approach the different levels of deviations from the ideality in the melts under investigation were clarified. The relative numbers of bonds of various types formed in the melts considered were also calculated based on the generalized lattice theory of associated solutions.

Determination of Vanadium Valence State in CaO-MgO-Al2O3-SiO2 System By High-Temperature Mass Spectrometry

In the present study, the applicability of the high-temperature mass spectrometric method combined with Knudsen effusion cell for quantifying the valence states of V in the multicomponent system CaO-MgO-Al2O3-SiO2-VOx up to a maximum temperature of 2050 K (1777 °C) was examined. The valence ratio of V3+/V4+ in slag phase was derived from the partial pressures of VO and VO2 in the effused vapor phase. The results show good agreement with the literature values obtained by other techniques. A correlation between the valence ratio V3+/V4+ and the oxygen partial pressure as well as basicity was achieved based on the present results and accessed data in the literature. The results of the present study demonstrate that the Knudsen cell-mass spectrometric method can be a very effective tool in estimating the valence ratios for of transition metals in metallurgical slags.

High Temperature Mass Spectrometric Study of Thermodynamic Properties and Vaporization Processes of Oxide Systems: Experiment and Modeling

The unique opportunities and features of high temperature mass spectrometric method for study vaporization processes and thermodynamic properties of oxide systems and materials (glasses, ceramics and coatings) were considered. Various types of vapour species were found over oxide systems studied such as the associated, dissociated and polymerized products of vaporization. The regularities of the vaporization of the binary and multicomponent oxide systems according to the position of oxide modifier in the Periodic table of atoms were illustrated and discussed from the point of view of the acid-base concept. Results on determination of thermodynamic functions in oxide systems were considered taking into account the main requirements for the confirmation of their reliability. Thermodynamic functions of oxide systems studied showed various signs of the deviations from the ideality. The general lattice theory of associated solutions was used for the calculation of thermodynamic properties of the ternary silicate melts studied. Based on this theory the correlation between thermodynamic functions obtained in the systems under consideration and the number of various types of bonds formed in these melts was illustrated. Using this approach the different levels of deviations from the ideality in the melts studied were clarified. Examples of the practical applications of high temperature mass spectrometry for developing advanced materials were shown.

Experimental Studies on the Oxidation States of Chromium Oxides in Slag Systems

In view of the importance of the thermodynamic behavior of chromium in the slag phase as well as the serious discrepancies in the earlier reports on the valence state of chromium in slag melts, the oxidation state of chromium oxides in CaO-SiO2-CrOx and CaO-MgO-(FeO-) Al2O3-SiO2-CrOx were investigated experimentally in the present study using two different experimental techniques. The gas–slag equilibrium technique was adopted to study the CaO-SiO2-CrOx system between 1823 K (1550 °C) and 1923 K (1650 °C) and equilibrated with mixtures of CO-CO2-Ar gases corresponding to three different oxygen partial pressures (between 10−4 and 10−5 Pa). After equilibrating, the samples were quenched and subjected to analysis using the X-ray absorption near edge structure method to determine the distribution ratio of Cr2+/Cr3+ in the slags. The second technique examined the applicability of the high-temperature mass spectrometric method combined with the Knuden effusion cell for quantifying the valence states of Cr in the multicomponent system CaO-MgO-(FeO-) Al2O3-SiO2-CrOx up to a maximum temperature of 2000 K (1727 °C). The results showed that the Knudsen cell-mass spectrometric method could be used successfully to estimate the valence ratio for Cr in silicate melts. According to the present study, the Cr2+/Cr3+ ratio increased with increasing temperature and a decreasing slag basicity as well as the oxygen partial pressure prevailing in the system. A mathematical correlation of X CrO/X CrO1.5 as a function of temperature, oxygen partial pressure, and basicity was developed in the present work based on the present results as well as on those assessed from earlier data.

Thermodynamic properties and structure of ternary silicate glass-forming melts: Experimental studies and modeling

Abstract Thermodynamic properties and vaporization processes of ternary silicate glass-forming melts containing Cs2O, MgO, CaO, BaO, B2O3, Al2O3 and TiO2 obtained by high temperature mass spectrometric method at the temperatures up to 1900 K were discussed. These data were used for modeling thermodynamic properties and structure of these melts based on the vacancy model of the general lattice theory of associated solutions.

Thermodynamic Study of Gaseous Manganese Phosphates MnPO3 and MnPO2.

AbstractFor Abstract see ChemInform Abstract in Full Text.

THERMODYNAMIC STUDY OF GASEOUS MANGANESE PHOSPHATES MnPO3 and MnPO2

In the present work, the stability of gaseous manganese-containing salts was proved by the high-temperature mass spectrometric method. New previously unreported species were found, MnPO3 and MnPO2. On the basis of equilibrium constants measured for gas-phase reactions the standard formation enthalpies for MnPO3 and MnPO2 were determined as −602.0 ± 10.0 kJ/mole and −299.0 ± 11.5 kJ/mole, respectively, and the standard atomization enthalpies as 1950 ± 14 kJ/mole and 1397 ± 14 kJ/mole, respectively.

Atomization enthalpies and enthalpies of formation of Ge 3 and Ge 4 by Knudsen effusion mass spectrometry

The high-temperature mass spectrometric method was employed to measure the equilibrium partial pressures of Ge 3 and Ge 4 above liquid germanium contained in a graphite Knudsen cell. These data were combined with thermal functions for Ge 3 and Ge 4, calculated from recent theoretical and spectroscopic molecular parameters, to evaluate the atomization enthalpies and enthalpies of formation. Mass spectrometric equilibrium data for Ge 3 and Ge 4 available in literature were also re-evaluated. The following atomization enthalpies, Δ a H o 0 (Ge n ,g) and enthalpies of formation Δ f H o 298.15 (Ge n ,g), in kJ mol −1, are overall assessed values: Ge 3, 589.8±19 and 531.9±19; Ge 4, 969.4±24 and 527.7±24. The atomization energies are in very good agreement with predictions by Deutsch et al. [Chem. Phys. Lett. 270 (1997) 413] using Gaussian-2 theory.

Atomization enthalpies and enthalpies of formation of the germanium clusters, Ge5, Ge6, Ge7, and Ge8 by Knudsen effusion mass spectrometry

The high-temperature mass spectrometric method was employed to measure the equilibrium partial pressures of small germanium clusters above liquid germanium contained in a graphite Knudsen cell. These data were combined with new thermal functions, calculated from recent theoretical and spectroscopic molecular parameters, to evaluate the atomization enthalpies and enthalpies of formation of Ge5–Ge8. Mass spectrometric equilibrium data available in literature were also reevaluated. The following atomization enthalpies, ΔaH0o(Gen,g) and enthalpies of formation ΔfH298.15o(Gen,g), in kJ mol−1, have been obtained: Ge5, 1313±27 and 548±27, Ge6, 1649±33 and 583±33, Ge7, 2008±42 and 598±42, Ge8, 2359±60 and 618±60. The atomization energies are compared with available theoretical values.

Vaporization studies of oxide systems using a QMS-420 mass spectrometer

The present paper is a continuation of the systematic study of vaporization processes and thermodynamic properties of oxide systems by high temperature mass spectrometric method. The features of the vaporization of the CaOB 2O 3, B 2O 3Al 2O 3 and ZnOP 2O 5 systems, such as the association and dissociation processes, are considered from the point of view of the acid-base concept. The reliability and accuracy of thermodynamic data obtained in the present work is in agreement with the results found earlier using the exchange equilibria method in slags, high temperature mass spectrometric method and by calculated values based on various approaches. A modification of quadrupole QMS-420 mass spectrometer is suggested, that can be useful for high temperature thermodynamic studies. Arrangement of the vaporizer containing a molybdenum block with four tungsten effusion cells and heater from tungsten coil is discussed. The special rotating assembly allowed the identification of the vapour composition from the samples situated in each of four effusion cells in the same experiment up to 1900 K is described.

Thermodynamic properties of the UO 2ZrO 2 system studied by the isothermal mass spectrometric vaporization method

The Knudsen effusion high-temperature mass spectrometric method was used to study the vaporization processes and thermodynamic properties of the UO 2ZrO 2 System in the temperature range 2200–2650 K. The work was carried out with the MS 1301 mass spectrometer developed for studies of physico-chemical properties of inorganic substances at high temperatures. Vaporization of the solid solutions containing 0.02–0.45 mol fractions of U0 2 was done using tungsten cells. The vaporization processes and the chemical potentials of ZrO 2 in the U0 2Zr0 2 system and in the Y 2O 3ZrO 2, Lu 2O 3ZrO 2 and HfO 2ZrO 2 systems, available in the literature, were discussed from the point of view of the acid-base concept.

Mechanism of Thermal Decomposition of Palladium β-Diketonates Vapour on Hot surface

The processes of thermal decomposition of palladium(II) β-diketonate complexes were investigated by a high-temperature mass spectrometric method with the use of a high-temperature molecular beam source. It was established that decomposition of the palladium complexes in gas phase processes proceeds by a radical mechanism and depends on temperature. For an additional proof of the existence of the radical particles the spin trap method was applied with a mass spectrometric identification of adducts. The following order of thermal stability of the complexes in gas phase was established: Pd(hfac) 2 > Pd(tfac) 2 > Pd(dpm) 2 > Pd(acac) 2 . This order is reverse to the thermal stability in a solid state. The thermal decomposition of Pd(aa) 2 and Pd(hfa) 2 complexes in deuterium showed that the deuterium presence strongly accelerates the decomposition processes.

Thermochemical study of the molecule (CsI) 4

Abstract The sublimation of CsI(s) was studied by the high-temperature mass spectrometric method with a Knudsen cell. The (CsI) 4 equilibrium partial pressure over CsI(s) was determined as log (p( Pa )) = − (12748 ± 278) T( K ) + (9.27 ± 0.36) (748–813 K ) . Entropies and enthalpy increments of (CsI) 3 (g) and (CsI) 4 (g) resulted from estimated molecular parameters. The enthalpy changes of the reactions (CsI) i (g) ⇆z i CsI(g) and i CsI(s) ⇆ (CsI) i (g) ( i = 3, 4 >) were determined by the third-law method and discussed.

Thermochemical study of the molecule (CsI) 4

The sublimation of CsI(s) was studied by the high-temperature mass spectrometric method with a Knudsen cell. The (CsI) 4 equilibrium partial pressure over CsI(s) was determined as log(p( Pa)) = − (12748 ± 278) T( K) + (9.27 ± 0.36) (748–813 K) . Entropies and enthalpy increments of (CsI) 3(g) and (CsI) 4(g) resulted from estimated molecular parameters. The enthalpy changes of the reactions (CsI) i (g) ⇆z iCsI(g) and i CsI(s) ⇆ (CsI) i (g) ( i = 3, 4 >) were determined by the third-law method and discussed.

Mass spectrometric investigation of gas phase reactions during sublimation

The use of the high temperature mass spectrometric method for the investigation of the vaporization behavior of solids and the determination of thermodynamic properties of gaseous molecules is described. Recent results by this method are reviewed and the application as an auxiliary tool in kinetic studies of sublimation processes is illustrated. The application of high pressure mass spectrometric sampling in problems of crystal growth is projected.