Knudsen Effusion Mass Spectrometric Method Research Articles

Mass Spectrometry Study of the Thermodynamic Properties of Spinel Solid Solutions

The partial pressure values of vapor species over spinel solid solutions and the boundary of the solid spinel solutions in the MgAl2O4 (solid solution) + Al2O3 region are determined on the basis of the data obtained by Knudsen effusion mass spectrometric method in the temperature range 2000–2200 K. The obtained thermodynamic information is compared to the information available in the literature. The values of oxide activities, Gibbs energies, enthalpies and entropies of formation of solid solutions show a slightly negative deviations from ideality.

Synthesis, vaporization and thermodynamic properties of superfine yttrium aluminum garnet

The study of high temperature behavior of Y3Al5O12 is urgently required for development of high temperature materials of the new generation including ultra-high temperature ceramics. The superfine Y3Al5O12 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 Y3Al5O12 as well as of the melts in the Y2O3-Al2O3 system were studied at temperatures higher than 2270 K. The simultaneous transition to the gaseous phase of both Al2O3 and Y2O3 from the melt under study was observed during isothermal keeping of the Y3Al5O12 sample at the temperature 2675 K with the predominant alumina removal. Analysis of the values of the thermodynamic properties obtained in the Y2O3-Al2O3 system showed negative deviations from ideal behavior despite the possibility of existence of the miscibility gap at the temperature 2675 K.

Vaporization and thermodynamics of ceramics based on the La2 O3 -Y2 O3 -HfO2 system studied by the high-temperature mass spectrometric method.

Materials based on the La2 O3 -Y2 O3 -HfO2 system are promising for the production of highly refractory ceramics, e.g., thermal barrier coatings and molds for casting of elements of gas turbine engines. When these ceramics are synthesized or used at high temperatures, selective vaporization of components may take place, resulting in changes in the physicochemical properties of the materials. Consequently, development of materials based on the La2 O3 -Y2 O3 -HfO2 system requires information on vaporization in this system as well as on its thermodynamics, without which prediction and modeling of their physicochemical properties are impossible. Vaporization processes and thermodynamic properties in the La2 O3 -Y2 O3 -HfO2 system were studied by the high-temperature Knudsen effusion mass spectrometric method using a MS-1301 mass spectrometer. Electron ionization of vapor species was employed at an ionization energy of 25eV. The samples under study and reference substances were vaporized from a tungsten twin effusion cell. At 2337K the main vapor species over samples in the La2 O3 -Y2 O3 -HfO2 system were shown to be LaO, YO and O. The partial pressures of the vapor species mentioned and the La2 O3 and Y2 O3 activities in the samples were obtained at 2337K. The Gibbs energies of mixing and excess Gibbs energies were found in the solid solution of this system. Vaporization of ceramics based on the La2 O3 -Y2 O3 -HfO2 system at 2337K led to selective transition of La2 O3 and Y2 O3 to the gaseous phase, with the La2 O3 vaporization rate being higher than that of Y2 O3 . The directions of composition changes of samples due to their vaporization at 2337K were determined. In the solid solution of this system negative deviations from ideal behavior were found. The ability to estimate the excess Gibbs energies in the solid solution of the La2 O3 -Y2 O3 -HfO2 system by the Kohler method was shown.

Synthesis, vaporization and thermodynamics of ceramic powders based on the Y2O3–ZrO2–HfO2 system

Nano-particles of refractory oxides based on the Y2O3–ZrO2–HfO2 system (cubic phase) were synthesized using the glycol-citrate method. The dependence of the morphology and fineness of the powder obtained on the heat treatment conditions was considered. Vaporization processes and thermodynamic properties of ceramic powder in the Y2O3–ZrO2–HfO2 system were studied by the Knudsen effusion mass spectrometric method in the temperature range 2700–2925 K. It was found that at the temperature (2773 ± 40) K the ceramic powder containing Y2O3:ZrO2:HfO2 as 0.15:0.60:0.25 mol fractions underwent a congruent sublimation. The phenomenon observed was confirmed during ten hours vaporization under conditions intermediate to the equilibrium state and the evaporation from the exposed surface. This experimental observation may be successfully used for the development of advanced high temperature coatings based on the ceramics of the Y2O3–ZrO2–HfO2 system.

Application of the Barker lattice theory to modeling of thermodynamic properties of PbO–B2O3–SiO2 melts

The purpose of the present study was to apply the generalized lattice theory of the associated solutions to modeling of thermodynamic properties of melts in the PbO–B2O3–SiO2 system. Values of PbO activity used for simulation were obtained by the high temperature mass spectrometric Knudsen effusion method at the temperature 1100K for twenty-four compositions in the glass-forming region of the system studied. Thermodynamic data calculated for the PbO–B2O3–SiO2 melts were in agreement no worse than 40% with the experimental ones. In the frame of the model used the relative numbers of bonds of various types as a function of the melt composition were found when the second coordination sphere was taken into account. It allowed to discuss the concentration changes of Gibbs energy of formation in the melts considered in relation to the formation of various types of chemical bonds. Thermodynamic functions in PbO–B2O3–SiO2 melts found in the present study were compared also with the corresponding data calculated using the semi-empirical Kohler method using the data for the binary systems.

The solubility and diffusion coefficient of helium in uranium dioxide

The solubility and diffusion coefficient of helium in the single-crystal UO 2 samples were determined by a Knudsen-effusion mass-spectrometric method. The measured helium solubilities were found to lie within the scatter of the available data, but to be much lower than those for the polycrystalline samples. The diffusion analysis was conducted based on a hypothetical equivalent sphere model and the simple Fick’s law. The helium diffusion coefficient was determined by using the pre-exponential factor and activation energy as the fitting parameters for the measured and calculated fractional releases of helium. The optimized diffusion coefficients were in good agreement with those obtained by a nuclear reaction method reported in the past. It was also found that the pre-exponential factors of the determined diffusion coefficients were much lower than those analyzed in terms of a simple interstitial diffusion mechanism.

High-temperature mass spectrometric study of the vaporization processes of V2 O3 and vanadium-containing slags

A Knudsen effusion mass spectrometric method was used to study the vaporization processes and thermodynamic properties of pure V(2)O(3) and 14 samples of vanadium-containing slags in the CaO-MgO-Al(2)O(3)-SiO(2) system in the temperature range 1875-2625 K. The system was calibrated using gold in the liquid state as the standard. Vaporization was carried out from double tungsten effusion cells. First it was shown that, in vapor over V(2)O(3) and the vanadium-containing slags in the temperature range 1875-2100 K, the following vapor species were present: VO(2), VO, O, WO(3) and WO(2), with the latter two species being formed as a result of interaction with the tungsten crucibles. The temperature dependencies of the partial pressures of these vapor species were obtained over V(2)O(3) and the slags. The ion current comparison method was used for the determination of the V(2)O(3) activities in slags as a function of temperature with solid V(2)O(3) as a reference state. The V(2)O(3) activity coefficients in the slags under investigation indicated positive deviations from ideality at 1900 K and a tendency to ideal behavior at 2100 K. It was shown that the V(2)O(3) activity as a function of the slag basicity decreased at 1900 K and 2000 K and was practically constant in the slag melts at 2100 K. The results are expected to be valuable in the optimization of slag composition in high-alloy steelmaking processes as well as for their environmental implications.

Vapor Pressure Measurements by Mass Loss Transpiration Method with a Thermogravimetric Apparatus

Thermobalances are used for equilibrium vapor pressure measurements based on both effusion and transpiration methods. In the case of the transpiration method, however, despite the numerous advantages a thermogravimetric apparatus can offer, it is not as widely used as is the conventional apparatus. In this paper, the difference that can exist in the vapor phase compositions in an effusion cell and in a transpiration cell is shown first with two examples. Subsequently, how a commercial thermobalance was utilized to perform transpiration experiments that conform to the basic principle of the transpiration method and yield vapor pressures consistent with the Knudsen effusion mass spectrometric method is described. The three systems investigated are CsI(s), TeO(2)(s), and Te(s), each known to vaporize congruently, but in different manner. A critical analysis was performed on the information available in the literature on transpiration measurements using thermogravimetric apparatuses, and the salient findings are discussed. Smaller plateau regions than with conventional transpiration apparatuses and the lack of evidence for perfect transpiration conditions in some transpiration thermogravimetric investigations are shown with a few examples. A recommendation is made for the use of the rate of mass loss versus flow rate plot to ascertain that the usual apparent vapor pressure versus flow rate plot corresponds to a meaningful transpiration experiment.

Thermodynamics and nonstoichiometry in the D0 3 compound Ni 3Sb

The thermodynamic activity of antimony was determined for nickel–antimony alloys in the composition range between 20 and 52 at% Sb by means of a Knudsen Effusion Mass Spectrometric (KEMS) method. The experimental data in the homogeneity range of the hexagonal γ-NiSb phase (B8-type) were compared with the literature data obtained by a different method. For the activity values in the nonstoichiometric compound Ni 3Sb (D0 3-type), a statistical-thermodynamic model was applied which uses the energies of formation of the six different types of point defects, obtained from ab initio calculations, as parameters. According to these formation energies, the most prominent point defects in nonstoichiometric Ni 3Sb are nickel vacancies. It was found that the inclusion of a full volume relaxation in the ab initio calculations improves the fit of the theoretical curve considerably.

Mass Spectrometric Measurements of the Gas Phase Composition over Mould Powder Samples in Vacuum Conditions at 50‐1550°C

Heating and melting of mould powders in a steel caster may lead to harmful gaseous emissions into the atmosphere. In the present work the volatility of commercial mould powders used in continuous casting processes was studied by the mass spectrometric Knudsen effusion method. Partial pressures of the vapour phase components were measured under vacuum conditions in the temperature range 50‐1550°C at a heating rate of 100°C/hour. In the temperature interval 50‐600°C gas phase is formed by H2O and CO2. At higher temperatures the principle vapour species are Na, NaF, Na2F2, KF, SiF4, SiF2, SiO, CaF2, and CO. Gaseous AIF3, MgF2 and AIOF were identified less reliably. A preliminary decarburised sample exhibited a noticeably different vaporisation pattern. HF was not detected. Under plant conditions SiF4 was pointed out as the most probable air polluting vapour component.

Mass Spectrometric Study of the Thermodynamic Properties of Melts in the Cs2O-B2O3 System

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.

Vaporization and thermodynamic properties of melts in the Na2O-B2O3-SiO2 system

The vapor composition, partial pressures of the molecular species of the vapor, and activities of the melt components in the Na2O–B2O3–SiO2 system at temperatures of 1300 and 1350 K are studied using the Knudsen effusion mass-spectrometric method. It is shown that the vapor composition depends on the concentration ratio of sodium and boron oxides in the condensed phase. When the content of boron oxide is larger than the content of sodium oxide in the condensed phase, the vapor contains NaBO2, (NaBO2)2, and B2O3 molecules. At the ratio [Na2O] : [B2O3] > 1, the gas phase contains atomic sodium. The activities obtained for NaBO2 and B2O3 indicate substantial negative deviations from an ideal behavior.

Thermodynamic study of the gaseous molecules Al2N, AlN, and Al2N2 by Knudsen cell mass spectrometry

The Knudsen effusion mass spectrometric method has been employed to measure the equilibrium partial pressures of the Al2N molecule over the AlN–Au–graphite system. Theoretical computations were carried out to determine the structure, molecular parameters, and thermodynamic properties of Al2N. The partial pressures have been combined with the calculated thermal functions to determine the atomization enthalpy, ΔaH0o, and enthalpy of formation, ΔfH298.15o, in kJ mol−1, of 783.2±15 and 342.7±15 for Al2N, respectively. Upper values for the dissociation energy of AlN, D0o(AlN,g)⩽368±15 kJ mol−1, and for the atomization enthalpy of Al2N2, ΔaH0o(Al2N2,g)⩽1402 kJ mol−1 have been obtained. These results are discussed and compared with recent theoretical literature values.

Vaporization properties of Cs 2U 4O 12 in LWR severe accident simulating conditions

Vaporization behaviors of Cs 2U 4O 12 were studied by using the Knudsen effusion mass spectrometric method at temperatures from 1273 to 1573 K. To clarify vaporization properties of Cs 2U 4O 12 in case of severe accident conditions of light water reactors, partial pressure measurements were made in D 2O/D 2 mixtures. The D 2O/D 2 environments were established in the Knudsen cell by introducing D 2(g) or D 2(g) + O 2(g) gas into the cell through a fine platinum tube attached to the bottom of the cell. Cesium vapor Cs(g) was found as the dominant vapor species over the compound either in vacuum or in the simulated atmospheres. In this study, the average temperature applied was 1423 K, the pressure of Cs(g) over the specimen in vacuum was 1.97 Pa while the oxygen potential measured was −148.2 kJ/mol. The pressure of Cs(g) increased moderately to 2.26 Pa after the introduction of the D 2(g), and it decreased slightly to 1.56 Pa with the admission of D 2(g)+O 2(g).

A high temperature mass spectrometric study of the thermodynamic properties of Cu-Mg solid alloys

Vapor pressures over Cu–Mg alloys containing 0.1–0.8 atomic fraction Mg were measured by the mass spectrometric Knudsen effusion method in the temperature range 590–860 K. Corresponding values of Cu and Mg activities in this concentration range and ΔHof, ΔGof, for Cu2Mg and CuMg2 were assessed. © 1998 John Wiley & Sons, Ltd.

Thermodynamic investigation of small germanium–tin clusters with a mass spectrometer

The partial pressures of GeSn, Ge2Sn, GeSn2, and Ge3Sn have been measured above a mixture of tin, silicon, and germanium using the Knudsen effusion mass spectrometric method. Partial pressures and estimated thermal functions yield the atomization enthalpies, ΔHa,0, in kJ mol−1, of: 230±13 (GeSn), 490±22 (GeSn2), and 559±27 (Ge2Sn). For the molecules Ge3Sn, Ge4Sn, and SnC upper limits (for the atomization enthalpy) have been obtained as: 996±32, 1389±42, and 452±14, respectively.

Thermodynamic study of the vaporization of Cs 2UO 4 by high temperature mass spectrometry

With regard to the behavior of high radioactivity fission products in the case of accidents, the thermochemical behavior of Cs 2UO 4 at high temperature is not completely known. A study of the vaporization of Cs 2UO 4 was carried out from 873 to 1373 K using the Knudsen effusion mass spectrometric method. To simulate some LWR accident atmospheres, a D 2/D 2O environment was established by introducing D 2(g) and/or D 2O(g) gas into the Knudsen cell, separately or as a mixed gas. Thus, the influence of the input of D 2/D 2O on the vaporization of Cs 2UO 4 was investigated quantitatively.

Vaporization features of oxide systems studied by high-temperature mass spectrometry

Vaporization processes of the binary phosphate, borate, silicate and zirconate systems, obtained by the Knudsen effusion mass spectrometric method are summarized according to the position of oxide-modifiers in the periodic table of the atoms. The polymerization and association processes as a result of vaporization of borate and phosphate systems are predominant. The association and the dissociation of the oxide components during vaporization are the characteristic of silicate systems. In the zirconate systems studied mainly the dissociative vaporization processes of oxides at high temperatures were mentioned. The main factors for the prediction of the relative volatility of the binary systems are considered.

Thermodynamic Study of Small Silicon Carbide Clusters with a Mass Spectrometer

The Knudsen effusion mass spectrometric method has been used to measure the equilibrium partial pressures of SiC2, Si2C, Si2C2, and Si3C above the SiC−graphite system at temperatures between 1750 and 2000 K. New thermal functions have been calculated for these molecules from recent literature experimental and theoretical molecular parameters and combined with the measured partial pressures to obtain the atomization enthalpies, ΔHa,0, in kJ mol-1: 1247 ± 8 (SiC2), 1052 ± 10 (Si2C), 1652 ± 14 (Si2C2), and 1437 ± 14 (Si3C). The derived enthalpies of formation, ΔHf,298, in kJ mol-1, are 633 ± 9 (SiC2), 566 ± 11 (Si2C), 678 ± 15 (Si2C2), and 632 ± 15 (Si3C).

Thermodynamic properties of FeCl 3-graphite intercalation compounds by mass-spectrometric Knudsen effusion method

A mass spectrometric Knudsen effusion method has been used for the determination of thermodynamic properties of stage 1 FeCl3-graphite intercalation compound (GIC). Enthalpies of the transformation of stage 1 to stage 2 FeCl3-GIC by the vaporization of FeCl3 (g) and Fe2Cl6 (g), and enthalpy of the reduction of FeCl3 to FeCl2 in the stage 1 FeCl3-GIC have been determined to be 170.5±5.4, 188.2±5.4 and 144.5±4.9 kJ mol-1, respectively, from the equilibrium partial pressures over the GIC. Activities of FeCl3 and FeCl2 components in. the stage 1 FeCl3-GIC together with the activity coefficient of FeCl3 have been also evaluated. The activity coefficient of FeCl3 in the stage 1 FeCl3-GIC is found to be larger than that in the stage 2 FeCl3-GIC, indicating that the stage 1 FeCl3-GIC is thermodynamically less stable than the stage 2 FeCl3-GIC.