High-temperature Mass Spectrometry Research Articles

Determination of the saturation vapor pressure of silicon by Knudsen cell mass spectrometry

Silicon evaporation has been investigated by high-temperature mass spectrometry, and the saturation vapor pressure of silicon over its melt has been determined over the temperature range from 1739 and 2326 K. The saturation vapor pressure data obtained via silicon evaporation from Knudsen cells made of molybdenum, tungsten, molybdenum disilicide-lined molybdenum, and graphite silicided by the gas-phase method are compared. Among these materials, silicided graphite is the most inert toward silicon vapor. The silicon partial pressures measured in the silicided graphite cell are close to the recommended values.

Determination of Suitable Column Geometries by Means of van Deemter and Kinetic Plots for Isothermal and Isocratic Method Development in High-Temperature Liquid Chromatography Isotope Ratio Mass Spectrometry

The method of high-temperature liquid chromatography isotope ratio mass spectrometry (HTLC-IRMS) is used to determine the origin or authenticity of compounds. Currently, the drawback of this hyphenation is the interface which causes pronounced band broadening due to a large extra-column volume. Therefore, the aim of this study is to determine suitable column geometries and particle sizes at different temperature and to study the effect of extra-column band broadening. The tools to assess the efficiency of columns are van Deemter and kinetic plots. By comparison of different column geometries and particle sizes, it could be shown that 3.0 mm ID columns achieve a higher performance than 2.1 mm ID columns and a particle size of 1.7 μm is advantageous over 3.5 and 5.0 μm particles when the injection volume is adjusted to 2 μL and the temperature is higher than 60 °C. Because water was the mobile phase, the retention factor could not be kept constant at different column temperatures. The lower retention factor at elevated temperatures leads to a decrease of the plate number, because of the relatively larger contribution to extra-column band broadening at lower retention factors. This is the reason why 3.0 mm ID columns should be preferred for the HTLC-IRMS hyphenation when the separation is carried out under isothermal and isocratic conditions.

Investigation of thermal properties of the volatile carbonyl compounds of rhenium Re2(CO)10 and Re(CO)3(C5H5)

The present work deals with the investigation of the thermal properties of two volatile rhenium compounds Re2(CO)10 and Re(CO)3(C5H5). The thermal behaviour of Re(CO)3(C5H5) in the condensed phase is studied by means of thermogravimetry and differential scanning calorimetry. Thermal decomposition of the vapour of Re2(CO)10 and Re(CO)3(C5H5) is studied in vacuum and in the presence of hydrogen and water vapour by means of insitu high-temperature mass spectrometry. The routes of vapour decomposition on a heated surface are proposed. Using Knudsen’s effusion method with mass spectrometric registration of the composition of the gas phase, and the flow method, temperature dependences of saturated vapour pressure were measured; thermodynamic parameters of the sublimation of complexes were calculated. For Re2(CO)10 we specified the data on the saturated vapour pressure using two independent methods within the temperature range below the phase transformations of the compound and the start of decomposition of complex vapour: ΔHTaver∘=(95.5±2.3)kJ·mol−1, ΔSTaver∘=(188.3±7.0)J·mol−1·K−1 (effusion method), ΔHTaver∘=(93.6±1.7)kJ·mol−1, ΔSTaver∘=(187.5±5.0)J·mol−1·K−1 (flow method). For Re(CO)3(C5H5) the thermodynamic characteristics were determined for the first time: ΔHTaver∘=(85.2±1.0)kJ·mol−1, ΔSTaver∘=(173.6±2.7)J·mol−1·K−1 (flow method).

Composition of saturated vapor over Ytterbium bromides

The vaporization process of ytterbium di- and tribromide was studied using high-temperature mass spectrometry over the temperature range of 850 to 1300 K. It was ascertained that, at the early vaporization stages, the vapor contained molecules YbBr3, YbBr2, YbBr, Br2, Yb2Br2, Yb2Br3, Yb2Br4, Yb2Br5, Yb2Br6, and atoms Yb and Br. The partial pressures of all components of saturated vapor were calculated. It was found that vapor composition reflected the course of the reactions of decomposition of tribromide and disproportionation of dibromide in the condensed phase. It was concluded that vaporization of di- and tribromide was incongruent at the initial stages; vaporization of both agents acquired a congruent character with the Yb: Br = 1.0: 1.9±0.2 ratio with time.

Mass-spectrometric examination of vaporization of sodium nitrite and sodium and potassium nitrates

Vaporization of sodium nitrite and sodium and potassium nitrates was examined by high-temperature mass spectrometry. The inverse temperature dependences of the vapor pressure logarithm for these compounds were presented. Enthalpies of vaporization and standard enthalpies of formation of gaseous NaNO2, NaNO3, and KNO3 were determined.

Vapor formation and thermodynamic properties of the gallium-lead system melts

A vapor composition and thermodynamic properties of melts of the gallium-lead system were studied by high-temperature mass-spectrometry. It was shown on the basis of thermodynamic calculations that Ga1−xPbx melts are characterized by an appreciable positive deviation from the ideal behavior in the temperature range 780–1170 K.

Mass-spectrometric study of molecular and ionic sublimation of gadolinium and terbium tribromides in Knudsen and Langmuir modes

Molecular and ionic sublimation of gadolinium and terbium tribromides in Knudsen and Langmuire modes was studied by the method of high-temperature mass-spectrometry. On the basis of obtained enthalpies of sublimation and ion-molecule reactions the enthalpies of formation of LnBr3 and Ln2Br6 molecules and LnBr4− and Ln2Br7− negative ions were determined. For the first time the electron work function for crystals of the studied tribromides was calculated.

Mass spectrometric investigation of vaporization in the Bi2O3-Fe2O3 system

The thermodynamics of vaporization in the Bi2O3-Fe2O3 quasibinary system was studied by high-temperature mass-spectrometry. The partial pressures of the constituents of a saturated vapor over the system at 1100 K were determined. Based on the experimental data, the following parameters were calculated: the activities of the components of the Bi2O3-Fe2O3 system condensed phase, the standard enthalpies of some heterogeneous reactions, and standard enthalpies of formation and enthalpies of formation for crystalline BiFeO3 and Bi2Fe4O9 from individual oxides. An optimal temperature for the solid-phase synthesis of bismuth ferrites from simple oxides is recommended.

Simulation of thermodynamic properties of borosilicate melts containing alkaline-earth metal oxides

The possibility for simulation of thermodynamic parameters of MO-B2O3-SiO2 melts (M = Ca, Sr, Ba) in terms of the UNIQUAC associated solution theory was demonstrated using the experimental data obtained previously by high-temperature mass spectrometry (1650–1800 K). The calculated numbers of different bonds formed in the examined melts were found to correlate with the deviations of their thermodynamic parameters from ideality.

Thermodynamic properties of silicate glasses and melts: VII. System MgO-B2O3-SiO2

Processes of evaporation and thermodynamic properties of glasses and melts of the system MgO-B2O3-SiO2 in the range of 1550–1800 K were studied for the first time by high-temperature mass-spectrometry. The resulting activities and Gibbs energies of components and also corresponding excess values point to negative deviations from ideal behavior and to the absence of immiscibility fields in glasses and melts of the system under study in the studied temperatures and concentration intervals.

Retention, Recovery and Recycling of Metal Values from High Alloyed Steel Slags

Retention, Recovery and Recycling of Metal Values from High Alloyed Steel SlagsThe work was carried out in four parallel directions. The thermodynamic activities of oxides of Cr in steel slags were determined by slag-gas equilibration technique. The ratio of Cr2+/Cr3+in CaO-MgO(-FeO)-AlO3-SiO2-CrO×system slags was measured by X-ray absorption near edge spectra (XANES). High-temperature mass spectrometry method was also used to obtain the distribution of chromium oxides. A mathematical correlation was established for estimating the ratio of Cr2+/Cr3+as a function of temperature, partial pressure of oxygen and slag basicity. Laboratory investigations of the decarburization of high alloy steels under controlled oxygen potentials have been carried out to retain Cr in the steel phase. A mathematical model has been developed for the decarburization process with controlled oxygen partial pressure. Experimental and theoretical investigations have been carried out in optimizing the Mo-additions to steel in the EAF practice in Uddeholm Tooling AB. Substantial saving of Mo as well as less emissions of Mo-bearing dust are indicated in the study. A salt extraction process was developed to extract the metal values from steel slags. Successful extractions, followed by electrolysis indicate that this could be a viable route towards recovery of metals from metallurgical slags.

Thermodynamic study of the uranium–vanadium system

Temperatures of solid/liquid transitions and vanadium thermodynamic activity data are measured in the U–V system to improve the thermodynamic description of the U–V and C–U–V systems. Binary alloys are synthesized from the pure metals in a high vacuum furnace. With that apparatus, both liquidus temperatures and vanadium activities are measured for each sample. During the experiments, the temperature of the samples is monitored with an optical pyrometer. In parallel, the activity of vanadium referred to pure vanadium is measured for x V = 0.18, 0.40 and 0.62 in the (1850 to 2090) K temperature range using high temperature mass spectrometry coupled to a multiple Knudsen cell system. The quenched microstructure of the alloys is analysed by electron microscopy. These new data together with the few ones from the literature are finally used to obtain a consistent set of thermodynamic parameters for the U–V system using the Calphad method.

Thermal analysis of monument patina containing hydrated calcium oxalates

This work describes the thermal transformation of patina samples formed on the surface of dolomitic rocks used to build the Romanesque Torme's Church (Burgos, Spain). Analyses were performed using a combination of high-temperature XRD, simultaneous TG/DTA and gas mass spectrometry. The XRD analysis revealed the presence of hydrated calcium oxalates. The following three steps were proposed for the thermal transformation of the raw material: dehydration of weddellite/whewellite to form calcium oxalate, transformation of calcium oxalate to calcium carbonate, and formation of calcium oxide produced via decomposition of the calcite. DTA/TG and mass spectrometry analyses confirmed this mechanism. In addition, a high proportion of organic compounds was detected and was possibly formed via degradation of products applied for the building's conservation by the action of microorganisms attack. Mass spectrometry analysis revealed CO (and CO 2) gas evolved during the transformation of CaC 2O 4 to CaCO 3. The CO 2 gas also appears at 765 °C due to the decomposition of calcium carbonate, and it appears over a large range of temperatures due to the decomposition of organic compounds. The TG analyses performed in a CO 2 atmosphere were used to determine the percentages of Ca and Mg contained in dolomite, and the calcium carbonate formed by oxalate decomposition. DRIFTS and mass spectrometry results revealed the presence of several aliphatic and/or aromatic compounds containing C O groups.

Characterization of Rapeseed (Brassica napus) Oils by Bulk C, O, H, and Fatty Acid C Stable Isotope Analyses

Rapeseed ( Brassica napus ) oils differing in cultivar, sites of growth, and harvest year were characterized by fatty acid concentrations and carbon, hydrogen, and oxygen stable isotope analyses of bulk oils (delta(13)C(bulk), delta(2)H(bulk), delta(18)O(bulk) values) and individual fatty acids (delta(13)C(FA)). The delta(13)C(bulk), delta(2)H(bulk), and delta(18)O(bulk) values were determined by continuous flow combustion and high-temperature conversion elemental analyzer-isotope ratio mass spectrometry (EA/IRMS, TC-EA/IRMS). The delta(13)C(FA) values were determined using gas chromatography--combustion-isotope ratio mass spectrometry (GC/C/IRMS). For comparison, other C(3) vegetable oils rich in linolenic acid (flax and false flax oils) and rich in linoleic acid (poppy, sunflower, and safflower oils) were submitted to the same chemical and isotopic analyses. The bulk and molecular delta(13)C values were typical for C(3) plants. The delta(13)C value of palmitic acid (delta(13)C(16:0)) and n-3 alpha-linolenic acid (delta(13)C(18:3n-3)) differed (p < 0.001) between rape, flax, and poppy oils. Also within species, significant differences of delta(13)C(FA) were observed (p < 0.01). The hydrogen and oxygen isotope compositions of rape oil differed between cultivars (p < 0.05). Major differences in the individual delta(13)C(FA) values were found. A plant-specific carbon isotope fractionation occurs during the biosynthesis of the fatty acids and particularly during desaturation of C(18) acids in rape and flax. Bulk oil and specific fatty acid stable isotope analysis might be useful in tracing dietary lipids differing in their origin.

Thermodynamics of sodium molybdate evaporation

High-temperature mass-spectrometry is used to study the evaporation of Na2MoO4(l) at 1050–1300 K. Na2MoO4(g) molecules are found to be present in the vapor. The partial pressure of Na2MoO4(g) is determined to be logp = 13794/T + 6.19. The enthalpy of sublimation Δ s H 0 ∘ (Na2MoO4 (s)) = 352 ± 20 kJ/mol is determined using the third law of thermodynamics. The atomization energy of the Na2MoO4(g) molecules is calculated to be Δ at H 0 ∘ (Na2MoO4(g)) = 2960 ± 40 kJ/mol.

Estimations of Electrical Conductivities in Molten Slag Systems

In order to optimize the metallurgical processes it is necessary to improve the understandings of the industrial slag properties, which include thermophysical and thermochemical properties. In the present study Mass Triangle Model was applied to predict these properties. According to the model formula, a program was developed in Visual C++ environment to calculate different properties in limited solubility ternary system. Successful applications of this model in predicting viscosity, surface tension, and density have been demonstrated in the case of a number of ternary slags in liquid state, as for example, RExOy-CaF2-SiO2 (RE refer to rare earth metal), MnO-TiO2-SiO2, CaO-Al2O3-SiO2, BaO-FeO-Fe2O3, CaO-MnO-SiO2 etc. In addition, the method has also been extended to predict electrical conductivities and sulphide capacities, which is first attempt to compute properties. Furthermore, an extension of this model has also been performed in the present study to obtain the corresponding properties in a homogeneous ternary system. Good agreement between model calculation and literature values had demonstrated that mass triangle model offers a powerful and efficient tool for estimations of various properties of molten system only based on limited experimental information.Knowledge of the thermodynamic properties of chromium oxides-containing slags is of great importance to chromium retention in stainless steel production, in view of chromium impacts on economic costs and environmental protection. Thus, the oxidation states of chromium in slags as well as sulphide capacity of CrOx-containing slag have been studied. In the studies of oxidation state of chromium in slags, gas/slag equilibrium technique was used for CaO-SiO2-CrOx system and the ratio of Cr2+/Cr3+ in multicomponent slags was measured by X-ray absorption near edge spectra (XANES). High-temperature mass spectrometry method was also used to obtain the distribution of chromium oxides in CaO-MgO(-FeO)-Al2O3-SiO2-CrOx system. It is to be noted that the present work is probably the first to employ Knudsen cell-mass spectrometry as an effective way to estimate chromium valences through vapor species. Utilizing the data obtained in present study as well as those reported in literature, a mathematical correlation was established for estimating the ratio of Cr2+/Cr3+ as a function of temperature, partial pressure of oxygen and slag basicity. The comparison between experimental valence ratio values and estimated ones presents a satisfactory agreement.The sulphide capacities of CaO-SiO2-CrOx pseudo-ternary slags were measured using the gas-slag equilibration technique in the temperature range 1823–1923 K under two different oxygen partial pressures 9.80×10-3 and 9.88×10-4 Pa. The results showed that log10Cs varied linearly with the reciprocal temperature, and the slope was higher than the corresponding value reported in the case of the binary CaO-SiO2 of corresponding composition. By using the equation developed as part of this project relating Cr2+/Cr3+ with basicity, oxygen partial pressure and temperature, it was possible to understand the effect of CrO on the sulphide capacities; viz. the sulphide capacity shows a decreasing trend as Cr2+ replaces Ca2+ in the slag. With further increase of Cr2+ content, there are indications of the occurrence of a minimum point beyond which the sulphide capacities show a slight increasing trend. The latter is attributed to the increasing extent of the polymerization reaction releasing oxygen ions for sulphide reactions in the metasilicate region. The behavior of CrO in the slag was found to be analogous to FeO.Estimation of liquidus and solidus temperature of slag was also carried out in the present study. The results indicated that it is possible to get a reasonable idea of the solidus temperature from X-ray radiography while DSC would indicate the liquidus temperature of slag

Thermodynamic properties of the system MgO-B2O3 melts

Vaporization processes of melts of the system MgO-B2O3 at 1640 K were studied by high-temperature mass spectrometry, and thermodynamic properties (activity, chemical potentials of MgO and B2O3, and also the corresponding excess values) were determined. Considerable negative deviations from the ideal behavior in the melts of the studied system are observed. The termodynamic properties of the system MgO-B2O3 can be calculated within the framework of the lattice theory of associated solutions.

Thermodynamic parameters of vaporization of EuBr2

The vaporization process of europium dibromide was studied using high-temperature mass spectrometry. It was ascertained that saturated vapor in temperature range of 1049–1261 K was represented mainly by EuBr2 molecules; the fraction of dimer molecules Eu2Br4 was less than 1%. Heat capacities of solid and liquid europium dibromide, as well as the melting enthalpy were measured by means of differential scanning calorimetry in temperature range 300–1100 K; using these data thermodynamic functions for EuBr2 in condensed state were calculated. For all experimental data, including the literature data, thermodynamic characteristics of the vaporization of europium dibromide were determined using a unified set of thermodynamic functions according to the methods of the second and third laws of thermodynamics. The value of ΔsHo(298.15 K) = 354 ± 5 kJ/mol was recommended for the reaction of sublimation of EuBr2(cr.) = EuBr2.

10.1007/s11176-008-1001-6

Vapor composition and thermodynamic properties of melts of the In-Pb system were studied by high-temperature mass spectrometry. In the temperature range 780–1170 K, the In1−x Pb x melts feature an appreciable positive deviation from the ideal behavior.

High Temperature Interaction Between UO2 and Carbon: Application to TRISO Particles for Very High Temperature Reactors

For very high temperature reactors, the high level operating temperature of the fuel materials in normal and accidental conditions requires studying the possible chemical interaction between the UO2 fuel kernel and the surrounding structural materials (C, SiC) that could damage the tristructural isotropic particle. The partial pressures of the gaseous carbon oxides formed at the fuel (UO2)-buffer (C) interface leading to the build up of the internal pressure in the particle have to be predicted. A good knowledge of the phase diagram and thermodynamic properties of the uranium-carbon-oxygen (UCO) system is also required to optimize the fabrication process of “UCO” kernels made of a mixture of UO2 and UC2. Thermodynamic calculations using the FUELBASE database dedicated to Generation IV fuels (Guéneau, Chatain, Gossé, Rado, Rapaud, Lechelle, Dumas, and Chatillon, 2005, “A Thermodynamic Approach for Advanced Fuels of Gas Cooled Reactors,” J. Nucl. Mater., 344, pp. 191–197) allow predicting the phase equilibria involving carbide and/or oxycarbide phases at high temperature. Very high levels of CO(g) and CO2(g) equilibrium pressures are obtained above the UO2±x fuel in equilibrium with carbon that could lead to the failure of the particle in case of high oxygen stoichiometry of the uranium dioxide. To determine the deviation from thermodynamic equilibrium, measurements of the partial pressures of CO(g) and CO2(g) resulting from the UO2/C interaction have been performed by high temperature mass spectrometry on two types of samples: (i) pellets made of a mixture of UO2 and C powders or (ii) UO2 kernels embedded in carbon powder. Kinetics of the CO(g) and CO2(g) as a function of time and temperature was determined. The measured pressures are significantly lower than the equilibrium ones predicted by thermodynamic calculations. The major gaseous product is always CO(g), which starts to be released at 1473 K. From the analysis of the partial pressure profiles as a function of time and temperature, rates of CO(g) formation have been assessed. The influence of the different geometries of the samples is shown. The factors that limit the gas release can be related to interface or diffusion processes as a function of the type of sample. The present results show the utmost importance of kinetic factors that govern the UO2/C interaction.