Knudsen Effusion Mass Spectrometry Research Articles

Vaporisation thermodynamic studies over and biphasic regions of U-Sn system using high temperature mass spectrometry

High-temperature vaporisation thermodynamic studies over <U3Sn7(cr) + USn2(cr)> and <USn2(cr) + USn(cr)> two-phase regions were carried out by employing Knudsen Effusion Mass Spectrometry (KEMS) in the temperature range 1148–1465 and 1222–1471 K, respectively. Sn(g) was the only species observed in the mass spectra of the equilibrium vapour phase over both the biphasic regions. The partial pressure-temperature relations of Sn(g) were deduced aslog(pSn/Pa) = (−15,737 ± 73)/(T/K)) + (9.52 ± 0.06) (1148–1465 K) <U3Sn7(cr) + USn2(cr)> andlog(pSn/Pa) = (−16,151 ± 67)/(T/K)) + (9.70 ± 0.05) (1222–1471 K) <USn2(cr) + USn(cr)>Using p-T relations, the enthalpies of the following heterogeneous reaction equilibria were evaluated by the second law method: U3Sn7(cr) = 3USn2(cr) + Sn(g) and USn2(cr) = USn(cr) + Sn(g). Subsequently, the Gibbs energies of the formation of U3Sn7(cr) and USn2(cr) were derived. Knudsen effusion mass spectrometric studies over these two biphasic regions are being reported for the first time.

Thermodynamics of gaseous strontium and calcium cerates studied by Knudsen effusion mass spectrometry and estimation of relative electron ionization cross-section for CeO2(g).

Ceria-based systems are of great interest because of their unique properties. Such systems may be used as anode materials for SOFCs or in oxygen sensors. Theexploitation of these materials often requires high temperatures. In such conditions, the partial or complete evaporation of materials is possible. Therefore, knowledge of the values of partial pressures and thermodynamic properties is essential to predict and/or prevent possible consequences and accidents. Knudsen effusion mass spectrometry was used to determine partial pressures of vapor species over the SrO-CeO2 and CaO-CeO2 systems. Measurements of partial pressures were performed with a MS-1301 mass spectrometer. Vaporization was carried out using molybdenum or tungsten effusion cells. A theoretical study of gaseous strontium and calcium cerates was performed by several quantum chemical methods: density functional theory (DFT) M06, DFT PBE0, and MP2. The minimum value of relative electron ionization cross-section for CeO2 was estimated. In the temperature range of 2218-2249 K above the SrO-CeO2 system and of 2128-2208 K above the CaO-CeO2 system, gaseous M, MO, MO, CeO2, O, O2 and MCeO3 (M = Sr, Ca) were found. Energetically favorable structures of gaseous SrCeO3 and CaCeO3 were found, and vibrational frequencies were evaluated in the "rigid rotor-harmonic oscillator" approximation. On the basis of the equilibrium constants of gaseous reaction MO + CeO2 = MCeO3, the standard formation enthalpy of gaseous SrCeO3 (-913 ± 26 kJ/mol) and of gaseous CaCeO3 (-917 ± 26 kJ/mol) at 298 K were determined. The estimated value of relative electron ionization cross-section for CeO2 is in agreement with the general rule applicable for dioxides. The stability of SrCeO3 and CaCeO3 gaseous species was confirmed by KEMS. Gas-phase reactions involving gaseous SrO (CaO) and CeO2 with gaseous SrCeO3(CaCeO3) were studied. Enthalpy of formation reaction of gaseous SrCeO3(CaCeO3) from gaseous SrO (CaO) were evaluated theoretically, and the obtained value is in agreement with the experimental one.

Thermodynamic study of tin tetraiodide (SnI4) sublimation by effusion techniques

This study presents the first investigation of the sublimation behavior of tin tetraiodide, SnI4, using effusion-based techniques, within a low temperature range (313–340) K. The temperature range covered in the experiments was lower than in previously reported studies based on static methods. Knudsen Effusion Mass Loss (KEML) measurements were performed in the range of (317.1–339.6) K using effusion cells with different orifice sizes. The vapor pressures were measured in the range (0.13–1.13) Pa and were found to be independent of the orifice size. The standard molar enthalpy and Gibbs energy of sublimation at 298.15 K obtained by the Clarke and Glew fit of experimental data are (88.1 ± 0.9) kJ⋅mol−1 and (38.96 ± 0.08) kJ⋅mol−1, respectively. Knudsen Effusion Mass Spectrometry (KEMS) experiments were also performed in the range (313.3–331.7) K, resulting in a sublimation enthalpy value in good agreement with the KEML values and not negligibly higher vapor pressure values. KEMS vapor pressure data were also analyzed by the third-law method. A comparison of our experimental results with the literature data available for both sublimation and evaporation properties of SnI4 is reported. Additionally, ancillary DFT and ab initio calculations were performed to estimate the molecular properties of SnI4(g) and the extent of the gas-phase dissociation to SnI2 and I2.

Knudsen effusion mass spectrometry: Current and future approaches.

Knudsen effusion mass spectrometry (KEMS) has been a powerful tool in physical chemistry since 1954. There are many excellent reviews of the basic principles of KEMS in the literature. In this review, we focus on the current status and potential growth areas for this instrumental technique. We discuss (1) instrumentation, (2) measurement techniques, and (3) selected novel applications of the technique. Improved heating methods and temperature measurement allow for better control of the Knudsen cell effusive source. Accurate computer models of the effusive beam and its introduction to the ionizer allow optimization of such parameters as sensitivity and removal of background signals. Computer models of the ionizer allow for optimized sensitivity and resolution. Additionally, data acquisition systems specifically tailored to a KEMS system permit improved quantity and quality of data. KEMS is traditionally utilized for thermodynamic measurements of pure compounds and solutions. These measurements can now be strengthened using first principles and model-based computational thermochemistry. First principles can be used to calculate accurate Gibbs energy functions (gefs) for improving third law calculations. Calculated enthalpies of formation and dissociation energies from ab initio methods can be compared to those measured using KEMS. For model-based thermochemistry, solution parameters can be derived from measured thermochemical data on metallic and nonmetallic solutions. Beyond thermodynamic measurements, KEMS has been used for many specific applications. We select examples for discussion: measurements of phase changes, measurement/control of low-oxygen potential systems, thermochemistry of ultrahigh-temperature ceramics, geological applications, nuclear applications, applications to organic and organometallic compounds, and thermochemistry of functional room temperature materials, such as lithium ion batteries. We present an overview of the current status of KEMS and discuss ideas for improving KEMS instrumentation and measurements. We discuss selected KEMS studies to illustrate future directions of KEMS.

First Sublimation Thermodynamics and First Gas‐Phase Experimental Molecular Structure of Heteroporphyrins: 5,10,15,20‐Tetraphenyl‐21‐X, 23‐Y‐Porphyrins (X=O or S; Y=N or S)

AbstractFirst sublimation enthalpies of heteroporphyrins: 10,15,20‐tetraphenyl‐21‐oxa‐ (HOPP), 5,10,15,20‐tetraphenyl‐21‐thia‐ (HSPP) and 5,10,15,20‐tetraphenyl‐21,23‐dithia‐ (S2PP) were measured by Knudsen effusion mass spectrometry: ΔsublH (T)=209±2 (561 K), 224±2 (552 K) and 219±2 (577 K) kJ/mol, respectively. Geometry and force field of a free molecule of HSPP was studied by quantum chemistry, and first gas‐phase experimental molecular structure of heteroporphyrins was derived by gas‐phase electron diffraction. Theoretically observed changes of the coordination cavity geometries due to heteroatomic intracavity substitution were experimentally confirmed with good agreement. Molecular structures of the dimeric associates of the heteroporphyrins were tested simulated to reveal tendencies in sublimation thermodynamics.

Enthalpy of Formation of Calcium and Magnesium Oxide Obtained by Knudsen Effusion Mass Spectrometry

Calcium and magnesium oxide are important components of metallurgical slag systems. However, the literature values for the standard enthalpy of formation ΔfH298∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{\\Delta }_{f}H}_{298}^{^\\circ }$$\\end{document} of both oxides exhibit large variations in some cases. Since ΔfH298∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{\\Delta }_{f}H}_{298}^{^\\circ }$$\\end{document} is crucial for the modeling and prediction of equilibrium states and, thus, also for process optimization; it was determined by Knudsen effusion mass spectrometry (KEMS). Pure CaO as well as MgO were investigated in an iridium Knudsen cell. For this purpose, the intensities of the main species present in the gas phase were recorded in a temperature range between 1825 K to 2125 K and 1675 K to 2075 K, respectively, and their partial pressures were obtained. It was observed that CaO and MgO evaporated congruently with the main species in the gas phase, Ca, Mg, O, and O2. The experimental vapor pressures of the gas species in the study of MgO are in good agreement with the calculated values using FactSageTM 7.3 and the FactPS database, while those for the evaporation of CaO show significant differences. These calculations are based on available thermodynamic information, including the Gibbs energy functions of CaO(s), Ca(g), MgO(s), Mg(g), O(g), and O2(g). After calculating the partial pressures and equilibrium constants of reactions, an average formation enthalpy of ΔfH298∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{\\Delta }_{f}H}_{298}^{^\\circ }$$\\end{document} = − 624.5 ± 3.5 kJ/mol for CaO(s) and ΔfH298∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{\\Delta }_{f}H}_{298}^{^\\circ }$$\\end{document} = − 598 ± 10 kJ/mol for MgO(s) based on the third law method of thermodynamics were obtained. The deviation of ΔfH298∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{\\Delta }_{f}H}_{298}^{^\\circ }$$\\end{document} for MgO from the previous literature values can be attributed to the use of different ionization cross sections, temperature calibration, and variation of tabulated Gibbs energy functions.

Thermodynamic properties of indoline and benzoxazine based spiropyrans studied by Knudsen effusion mass spectrometry

An approach including thermal analysis and Knudsen effusion mass spectrometry was used to investigate the thermal stability range and the thermodynamic properties of sublimation for four indoline and benzoxazine based spiropyrans: 1,3,3-trimethyl-6′- (tert-butyl) −8′-formyl-spiro [indoline-2,2′-2H-chromene] (1), 1,3,3,8′-tetramethyl-6′-formyl-spiro [indoline-2,2′-2H-chromene] (4), 1,3,3-trimethyl-8′-methoxy-6′-formyl-spiro [indoline-2,2′-2H-chromene] (7), and 3-methyl-6′-methoxy-8′-formyl-spiro [1,3-benzoxazin-4-one-2,2′-2H-chromene] (9). The melting and decomposition temperatures as well as the melting enthalpies were obtained by thermal analysis. The electron ionization mass spectra as well as the ionization efficiency curves were measured. Schemes of the formation of the main ions in the mass spectra were suggested. The temperature dependencies of vapor pressures were used to obtain the sublimation enthalpies. All data were obtained for the first time.

Potential of Knudsen Effusion Mass Spectrometry (KEMS) for Energy Materials Science

The determination of valuable thermodynamic data for materials at elevated temperatures is a very important issue in Materials Science. This can be achieved by the elucidation of vaporization processes with mass spectrometric techniques.Knudsen Effusion Mass Spectrometry provides the identification of gaseous species present above condensed phases and permits the determination of their partial pressures up to a total pressure of 200 Pa.The key for establishing model calculations using DG minimization tools like among others FactSage, Pandat or Thermocalc is the knowledge of the thermodynamic data of molecules and compounds. This includes the partial pressures of gaseous species, the standard enthalpies and entropies of formation of gaseous and condensed phases as well as their enthalpies and entropies of mixing and the knowledge of phases and chemical compounds which are formed upon reactions.The method will be described and examples and an insight will be given how basic thermodynamic data are derived with the above mentioned method for the incorporation into thermodynamic databases. Examples of investigations carried out in our lab will be given.The number of groups worldwide using this advanced technology has been shrinking during the last decades. Therefore, we are pleased to announce the setup of a completely new designed instrument in our laboratory which can determine data with higher precision and better resolution.The new set up will be presented as well.

Thermodynamic properties of refractory Mo-Nb-V-Ti high entropy alloys (HEAs)

High entropy alloys (HEAs) are solid solution alloys containing at least 5 elements in equiatomic or near-equiatomic composition. In the present study we report on an alloy design route for refractory HEAs based on Mo-Nb-V-xTi alloys (x denotes mole per cent of Ti, x = 5, 10, 15, 20, 25, the mole per cents of Mo, Nb, and V are equal). The thermodynamic activities of Ti and V were determined by Knudsen effusion mass spectrometry and the measured data were compared to the calculated data obtained by CALPHAD method.

Assessment of thermal stability of two N-ethoxyethyl-N-methylpiperidinium borate ionic liquids by non-Arrhenian incremental kinetic method

Thermal stability of two borate-based ionic liquids (ILs) recently proposed as effective additive for high voltage batteries, N-ethoxyethyl-N-methylpiperidinium bis(oxalato)borate (BOB) and N-ethoxyethyl-N-methylpiperidinium difluoro(oxalato)borate (DFOB), was investigated. Thermogravimetry–differential thermal analysis measurements performed under nitrogen at 1, 2, 4, and 7 °C min−1 show gradual mass loss above 220 °C for both compounds. The TG curves were processed by isoconversional kinetic analysis under the assumption of non-Arrhenian behavior. The outcome of the analysis suggests that even the initial decomposition stages occur by a complex mechanism, probably via competing evaporation–decomposition paths with relative contributions varying with the heating rate. The service lifetimes estimated by the kinetic analysis result in a stability of DFOB up to 10-times higher than that of BOB in the 25–125 °C range. Further experiments were carried out by the Knudsen effusion mass spectrometry (KEMS) in order to get information on the composition of the vapor phase produced upon heating under effusion conditions. The mass spectra of the vapor phase showed a rapid onset of decomposition at 110 °C and 130 °C for BOB and DFOB, respectively, with a large release of the ion species with m/q = 98. This decomposition path dominates the simple evaporation to neutral ion pairs, which was nonetheless observed at m/q = 172 (integer cation). All the results seem to point toward a higher stability of DFOB compared to BOB, most probably due to the charge-stabilizing inductive effect of fluorine atoms.

Determination of activities and condensation temperatures of GaO1.5 and InO1.5 in anorthite-diopside eutectic melts by Knudsen Effusion Mass Spectrometry

The group 13 elements Ga and In are overabundant in bulk silicate Earth (BSE) when compared to lithophile elements of similar 50% nebular condensation temperature Tc50. To understand whether evaporation from silicate melts provides a more accurate description of volatility during the later stages of planetary accretion, namely, at higher temperatures and oxygen fugacities than in the solar nebula, knowledge of the activities of GaO1.5 and InO1.5 in silicate melts and their stable gaseous species are required. To this end, we doped anorthite-diopside (An-Di) eutectic glasses with ∼1000 and ∼10,000 ppm of Ga and In and determined their equilibrium partial pressures above the silicate liquid by Knudsen Effusion Mass Spectrometry (KEMS) using Ir cells at 1550–1740 K over the log(fO2) range ΔIW+1.5 to ΔIW+2.5 (IW = iron-wüstite buffer). We detect Ga0 and In0 as the dominant vapour species and determine activity coefficients of γ(GaO1.5) = 0.036(6) at 1700 K and of γ(InO1.5) = 0.017(12) at 1674 K. Using these activity coefficients, we calculate partial pressures of Ga and In, together with those of similarly volatile elements, K and Zn and show that their relative volatilities from An-Di eutectic melts are in the in order Ga > K ∼ In > Zn, different from those predicted from their Tc50 under nebular conditions but in line with their relative abundances in the BSE. This substantiates the view that the abundances of volatiles in BSE, such as Ga and In, may have been set by evaporation from silicate melts under oxidising conditions at later stages of planetary accretion. Moreover, chondrules likely never underwent significant evaporation during melting and their volatile-depleted nature is likely inherited from the earliest solid condensates.

Sublimation behavior of AlN in nitrogen and argon at conditions used for high-temperature annealing

High-temperature annealing (HTA) is one of the most promising techniques to produce high-quality, cost-efficient AlN templates for further epitaxial growth of AlGaN devices. Unfortunately, the yield of this process seems to be limited due to the restricting face-to-face configuration that is typically used, in which contaminations of the template surface can occur easily. A high yield is crucial for process transfer into industry. Indeed, templates that are annealed in open-face configuration suffer from surface degradation due to excessive AlN evaporation during the course of the annealing process. To highlight the physics that are restricting the open-face approach of the process, sublimation behavior of AlN at temperatures and atmospheres typically used in HTA processes has to be examined. In this study, we use the Knudsen effusion mass spectrometry technique to confirm the previously published results on equilibrium partial pressures of species above AlN. Based on the experimentally determined data and further AlN sublimation experiments, the apparent sublimation coefficient of AlN in N2 and Ar atmospheres at HTA process conditions can be derived. Despite N2 having a stabilizing effect on AlN during HTA, the still high decomposition rates of several hundred nanometers per hour can explain the excessive damage that is typically observed if AlN/sapphire templates are annealed in an open-face configuration. Finally, based on theoretical considerations, a strategy to reduce the sublimation of AlN during HTA in open-face configuration is suggested.

Vapor Composition and Vaporization Thermodynamics of 1-Ethyl-3-methylimidazolium Hexafluorophosphate Ionic Liquid

The processes of the sublimation and thermal decomposition of the 1-ethyl-3-methylimidazolium hexafluorophosphate ionic liquid (EMImPF6) were studied by a complex approach including Knudsen effusion mass spectrometry, IR and NMR spectroscopy, and quantum chemical calculations. It was established that the vapor over the liquid phase primarily consists of decomposition products under equilibrium conditions. Otherwise, the neutral ion pairs are the only vapor components under Langmuir conditions. To identify the nature of the decomposition products, an experiment on the distillation of the ionic liquid was performed and the collected distillate was analyzed. It was revealed by the IR and NMR spectroscopy that EMImPF6 decomposes to substituted imidazole-2-ylidene (C6N2H10PF5) and HF. The measured vapor pressure of C6N2H10PF5 reveals a very low activity of the decomposition products (&lt;10−4) in the liquid phase. The absence of a significant accumulation of decomposition products in the condensed phase makes it possible to determine the enthalpy of sublimation of the ionic liquid assuming its unchanged activity. The thermodynamics of the EMImPF6 sublimation was studied by Knudsen effusion mass spectrometry. The formation enthalpy of EMImPF6 in the ideal gas state was found from a combination of the sublimation enthalpy and formation enthalpy of the ionic liquid in the condensed state. The obtained value is in good agreement with those calculated by quantum chemical methods.

Determination of thermochemical properties of stainless steels type D-9 and T-91 using Knudsen Effusion Mass Spectrometry

High temperature vaporisation thermodynamic studies over D-9 and T-91 stainless steel samples were carried out in the temperature range 1202–1529 K and 1232–1530 K respectively, by using Knudsen Effusion Mass Spectrometry (KEMS). These studies revealed that both the alloys undergo incongruent vaporisation. Cr(g), Mn(g), Fe(g) and Ni(g) were the neutral vapour species observed over the D-9 alloy. Cr(g), Mn(g) and Fe(g) were the neutral vapour species observed over the T-91alloy. Partial pressure-Temperature relations were derived using KEMS for the first time. Apparent enthalpies of vaporisation data were deduced by second law method. Chemical activities of all the major metallic elements (Fe, Cr, Ni and Mn) in the commercial grade D-9 austenitic stainless steel were determined in the temperature range of 1202–1529 K. In case of T-91 ferritic steel, chemical activities of Fe, Cr and Mn were determined in the temperature range of 1232 -1530 K.

Thermodynamic properties of the Na2O-BaO-B2O3 glasses and melts

The glass formation region in the system Na2O-BaO-B2O3 has been established. Thermodynamic properties for this system were derived. It is found that the lower border of glass formation region is limited to composition containing 10–30 mol.% Na2O, 10–30 mol.% BaO and 60 mol.% B2O3. A region with partial crystallization has been found inside the glass formation region. This region is limited to compounds 5 Na2O-20 BaO-75 B2O3 mol.% and 10 Na2O-20 BaO-75 B2O3 mol.%. The vaporization processes and thermodynamic properties of the Na2O-BaO-B2O3 melts were investigated by the Knudsen effusion mass spectrometry in the temperature range 1290–1750 K. The values of the component activities, Gibbs energies and excess Gibbs energies were derived from experimental data. It was shown that the studied system is characterized by a negative deviation from the ideal behavior.

Evaporation/Decomposition Behavior of 1-Butyl-3-Methylimidazolium Chloride (BMImCL) Investigated through Effusion and Thermal Analysis Techniques

The evaporation/decomposition behavior of the ionic liquid 1-butyl-3-methylimidazolium chloride (BMImCl) was studied with various techniques, such as thermogravimetry (TG), Knudsen effusion mass loss (KEML), and Knudsen effusion mass spectrometry (KEMS), in order to investigate the competition between the simple evaporation of the liquid as gaseous ion pairs (NIP: neutral ion pair) and the thermal decomposition releasing volatile species. TG/DSC experiments were carried out from 293 to 823 K under both He and N2 flowing atmospheres on BMImCl as well as on BMImNTf2 (NTf2: bis(trifluoromethylsulfonyl)imide). Both ionic liquids were found undergoing a single step of mass loss in the temperature range investigated. However, while the BMImNTf2 mass loss was found to occur in different temperature ranges, depending on the inert gas used, the TG curves of BMImCl under helium and nitrogen flow were practically superimposable, thus suggesting the occurrence of thermal decomposition. Furthermore, KEML experiments on BMImCl (in the range between 398 and 481 K) indicated a clear dependence of the unit area mass loss rate on the effusion hole diameter, an effect not observed for the ILs with NTf2 anion. Finally, KEMS measurements in the 416–474 K range allowed us to identify the most abundant species in the vapor phase, which resulted in methyl chloride, butylimidazole, butyl chloride, and methylimidazole, which most probably formed from the decomposition of the liquid.

Evaporation thermodynamics of 1‐butyl‐3‐methylimidazolium tetrafluoroborate ionic liquid

Thermodynamic properties of evaporation of 1‐butyl‐3‐methylimidazolium tetrafluoroborate (BMImBF4) ionic liquid (IL) were determined by Knudsen effusion mass spectrometry. Heating of this compound is accompanied by competing evaporation and decomposition. Interpretation of mass spectrum was carried out by the analysis of data obtained for different evaporation conditions: i) Knudsen cell with a small effusion orifice, ii) open Knudsen cell, and iii) open surface of IL. It was revealed that at non-equilibrium Langmuir conditions BMImBF4 IL evaporates congruently practically only in the form of neutral ion pairs (NIPs). In equilibrium conditions, decomposition products prevail in vapor with only about 7 % vapor fraction of NIPs. The main route of IL decomposition is the formation of substituted imidazole‐2‐ylidene (C8N2H14BF3) and hydrofluoric acid (HF). The mass spectrum of C8N2H14BF3 was obtained by the analysis of a distillate collected during evaporation in the Knudsen cell. The decomposition products, due to their high volatility, do not accumulate practically in the liquid phase and hence the activity of IL may be considered to be 1. This circumstance makes it possible to perform the thermodynamic calculations for the IL evaporation reaction. The temperature dependence of the NIPs’ vapor pressure, ln(p/Pa) = (–13.806 ± 0.252)∙103/T + (23.443 ± 0.519), was used to obtain the vaporization enthalpy, ΔvH°(298.15 K) = 138 ± 5 kJ·mol−1, by the methods of the second and third laws. The formation enthalpy of BMImBF4 NIPs, ΔfH°(298.15 K) = −1084 ± 15 kJ·mol−1, was found from combination of the vaporization enthalpy and the formation enthalpy of IL. The vapor composition over BMImBF4 under equilibrium conditions was computed. It was demonstrated that decomposition of IL is kinetically hindered so the studied system is characterized by a partial equilibrium.

Comparative study of fission product release of homogeneous and heterogeneous high-burn up MOX fuel by Knudsen Effusion Mass Spectrometry supported by EPMA, SEM/TEM and thermal diffusivity investigations

The fission product release of two irradiated mixed oxide (MOX) fuel variants from the high burn-up disk irradiation test IFA-655 in the Halden reactor was investigated by Knudsen Effusion Mass Spectrometry (KEMS). The fresh samples were provided and characterised within the NFIR11NFIR: https://www.epri.com/portfolio/programs/108031 program. Both fresh fuel variants contained 16 wt.% plutonium but differed principally by the distribution of the plutonium: in one it was heterogeneously dispersed, in the other one homogeneously. The fission products release (Kr, Xe, I, Cs, Te, Sr, Nd) measured by KEMS as a function of annealing temperature is reported. The gas release (including helium) has been measured quantitatively. The interpretation of the release measurements is supported by microstructure and elemental analyses (SEM, TEM, EPMA). A correlation has been made with results from thermal diffusivity measurements obtained on the same fuels.

Quantification of thermodynamic properties for vaporisation reactions above solid Ga2O3 and In2O3 by Knudsen Effusion Mass Spectrometry

Even though Ga2O3 and In2O3 are broadly used as semi-conductors, thermodynamic data for their vaporisation reactions exhibit a large spread. Therefore, the vaporisation behaviour of solid Ga2O3 and In2O3 was determined by means of Knudsen Effusion Mass Spectrometry (KEMS). Ga2O3 and In2O3 were studied in an iridium Knudsen cell and heated over a temperature range of 1200–1750 K in order to identify the species present in the vapour phase, and determine their partial pressures. We find that M2O (where M = Ga or In) is the most abundant gas species above the solid oxide, followed by M and MO, in accord with tabulated data. Following the calculation of partial pressures and equilibrium constants, we propose ΔfH298,3rdoGa2Og = −68966 ± 7442 Jmol-1 and ΔfH298,3rdoIn2Og = −22245 ± 964 Jmol-1 from the 3rd law method. Deviations in ΔfH298,3rdoi relative to literature KEMS measurements are generally within ∼2% relative, and can be ascribed to the use of different ionisation cross sections, Knudsen cell material, temperature calibrations, as well as tabulated Gibbs energy functions. However, comparison with ab initio studies suggests the data reported in this work is more accurate than in previous studies, given that the ΔfH298,3rdoInOg = 157744 ± 3681 Jmol-1 deviates by only ∼0.2% from the theoretical value.

Quantum chemical and experimental thermodynamic studies of HfO(g).

Hafnium dioxide vaporizes primarily to HfO(g) in a reducing environment. The thermochemistry of HfO(g) is calculated from quantum methods and measured via Knudsen effusion mass spectrometry. For the computations, all-electron and relativistic effective core potential calculations are used. The calculation of an accurate dissociation energy and an entire potential energy curve is reported. These calculations lead to ΔfH°(298) = 63.19 ± 10 kJ/mol, S°(298) = 235.52 J/mol K, and Cp(298-2500K) = (2.741 × 10-9)T3 - (9.853 × 10-6)T2 + (1.295 × 10-2)T + 2.761 × 10-1 J/mol K. Experimentally, HfO(g) is generated from the reaction of Hf(s) and HfO2(s) in a specially made Hf Knudsen cell. A third law treatment of the data leads to ΔfH°(298) of 58.4 ± 12.3 kJ/mol, in good agreement with the calculated value.