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[Display omitted] • Evaporation of [BuMIm+][Cl-](l) is accompanied by thermolysis and C2-methylation to form in situ new ion pairs. • At a low rate of thermolysis the pressures and the enthalpy of evaporation of [BuMIm+][Cl-] ion pairs are determined. • The suppression of [BuMIm+][Cl-] evaporation is a consequence of an increase involvement of ion pairs in side reactions. • The priority and possible directions of reactions involving ion pairs were revealed using quantum chemical calculations. The evaporation and thermal decomposition (thermolysis) of 1-butyl-3-methylimidazolium chloride ionic liquid, [BuMIm][Cl](l), were studied in the temperature range of 373–463 K by thermogravimetry–mass spectrometry (TG–MS) and Knudsen cell mass spectrometry (KCMS) methods. The saturated vapor pressures and the enthalpy of vaporization of [BuMIm][Cl](l) were determined within 373–398 K, where the thermolysis of this ionic liquid occurs via the S N 2 mechanism at a low rate. With increasing temperature, the thermolysis becomes more extensive, which is accompanied by the C2-methylation of [BuMIm][Cl](l). The resulting ion pairs [BuMMIm+][Cl-] are thermally unstable and decomposed. A decrease in the vapor pressure of the ion pairs [BuMIm+][Cl-] at a constant temperature takes place due to side reactions, resulting in the suppression of the evaporation. Complex ionic compounds were found in the thermolysis/evaporation residues using atmospheric pressure chemical ionization (APCI) and matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS) methods. The priority and possible pathways of reactions involving ion pairs and the thermolysis products were established by quantum chemical calculations. [ABSTRACT FROM AUTHOR]

[Display omitted] • Evaporation and thermolysis of the studied methanesulfonates proceed independently. • Vapor pressures and enthalpies of vaporization of ionic liquids are determined. • Thermolysis proceeds with formation of gaseous products with IL activity equal to 1. • The kinetics of [EtMIm][CH 3 SO 3 ](l) thermolysis reactions is described in two ways. • Thermolysis rate is determined by product flux and expressed by IL concentration. Knudsen cell mass spectrometry was used to study the evaporation of two ionic liquids, 1-ethyl-3-methylimidazolium methanesulfonate ([EtMIm][MS], MS = CH 3 SO 3) and 1-butyl-3-methylimidazolium methanesulfonate ([BuMIm][MS]), accompanied by thermal decomposition (thermolysis). The independent occurrence of evaporation and thermolysis reactions made it possible to determine their thermodynamic and kinetic characteristics under identical experimental conditions. The saturated vapor pressures were measured and the standard enthalpies of vaporization of [EtMIm][MS](l) and [BuMIm][MS](l) were obtained. The standard thermodynamic functions of formation in the liquid and gaseous states at 298.15 K were estimated from the available experimental data and the results of quantum chemical calculations. The gaseous decomposition products of ionic liquids were identified and the pressures of the thermolysis products of [EtMIm][MS](l) were determined. According to the experimental data and quantum chemical calculations, the thermolysis of [EtMIm][MS](l) occurs through heterogeneous reactions far from the equilibrium state. The kinetics of the reactions is described in two ways. When the degree of sample conversion is used as a variable, the constant reaction rates at the initial stage of thermolysis correspond to a pseudo -zero order reaction with a monotonic increase in the degree of conversion. In the proposed alternative approach, the reaction rates are estimated from the fluxes of thermolysis products and are expressed in terms of ionic liquid concentration. [ABSTRACT FROM AUTHOR]

This study investigates interactions between methylglyoxal (MGL) and 29 different samples, such as clays, proxies and natural dusts from the arid regions of the planet. Initial and quasi steady state uptake coefficients (ɣ 0 and ɣ qss) of MGL are determined using a Knudsen cell at concentration of 70 ppb, under dry conditions. Remarkably high ɣ 0 values for MGL, ranging from 0.05 to 0.67, are determined, close to those of radical species, suggesting a high affinity for dusts. ɣ 0 is evidenced to be linearly correlated with the Al/Si ratio of dust samples, indicating a specific initial affinity of MGL with aluminum surface sites. Ɣ qss , determined after 40 min of exposure, ranges from 2.9 × 10−7 to 5.9 × 10−6. Ɣ qss is linearly correlated with Ti/Si ratio, highlighting specific affinity of MGL with titanium. The impact of concentration on ɣ qss is investigated on Gobi dust with MGL concentrations ranging from 0.1 ppt to 2.2 ppm. Ɣ qss increases when MGL concentration decreases. Under typical dust storm conditions, MGL uptake competes with gas phase removal by OH radicals or photolysis. In addition, the maximum storage capacity of MGL by samples is determined at 2 ppm with Knudsen cell. MGL uptake does not exceed a compact monolayer on natural dust samples, whereas on some surrogates multilayer uptake is reached. Comparison of ɣ 0 and ɣ qss of glyoxal and MGL shows that MGL generally exhibits higher affinity with samples. The maximum number of molecules taken up by Gobi dust (N max) of MGL is compared with those for isoprene, isopropanol and acetic acid retrieved from literature. It points at the dependance of N max on chemical functionality of VOCs: oxygenated compounds exhibit higher interactions with dust. Data are available to increase the representativeness of modeling. • Uptake coefficient of methylglyoxal on mineral surfaces is high and irreversible. • Dust composition (Al/Si and Ti/Si ratios) is corelated with methylglyoxal uptake. • On gobi dust, steady state uptake coefficient depends on methylglyoxal concentration. • Mineral dust can be a significant sink of methylglyoxal leading to SOA formation. • This work provides kinetic data to improve model simulations. [ABSTRACT FROM AUTHOR]

[Display omitted] • The reactivity of a biodiesel soot was investigated using a Knudsen flow reactor. • Biodiesel soot (soybean/palm) is oxidized more quickly than other soot samples. • Reaction mechanisms of soot with NO 2 and trifluoroacetic acid are proposed. • The reaction with TFA indicate the high presence of basic oxides on the surface. • IR bands attributable to PAHs and carbonyls are detected. The characteristics and atmospheric reactivity of soot generated from an alternative fuel (soybean/palm biodiesel) have been investigated for the first time using a Knudsen flow reactor with a mass spectrometer as detector for gaseous species. The heterogeneous reactions with nitrogen dioxide (NO 2) and trifluoroacetic acid (CF 3 COOH, TFA) have been investigated. Uptake coefficients calculated for the reaction of NO 2 (γ 0 = (3.85 ± 0.70) ∙10–3) are one order of magnitude higher than the corresponding TFA reactions (γ 0 = (6.06 ± 0.24) ∙10–4). NO is the only product observed in the gas phase. Knudsen cell reactor has also been used in the characterization of chemical functions on the surface since NO 2 can be used to identify reducing groups, while TFA is used to evaluate basic sites. Compared to other soot samples, biodiesel soot shows higher reactivity with NO 2 which has implications in the regeneration process of the diesel particulate filter (DPF). IR bands attributable to polycyclic aromatic compounds have been observed by Diffuse Reflectance Infrared Fourier Transform spectroscopy (DRIFTs). Bands of carbonyl compounds are also clearly observed. Thermogravimetric analysis/ differential scanning calorimetry-mass spectrometry (TGA/DSC-MS) is used to obtain more information about the volatile organic compounds present on the soot surface. Scanning Electron Microscopy/Energy Dispersive Spectroscopy (SEM/EDS) analysis indicates a particle size in the range 14–40 nm and carbon as the major element (92 %). According to the obtained results, a mechanism of processes occurring at the surface has been proposed. [ABSTRACT FROM AUTHOR]

The heterogeneous reactions of nitrogen dioxide (NO 2 ) and trifluoroacetic acid (CF 3 COOH) with soot produced by diesel and GTL (gas-to-liquid) fuels were investigated using a Knudsen flow reactor with mass spectrometry as a detection system for gas phase species. Soot was generated with a 4 cylinder diesel engine working under steady-state like urban operation mode. Heterogeneous reaction of the mentioned gases with a commercial carbon, Printex U, used as reference, was also analyzed. The initial and the steady-state uptake coefficients, γ 0 and γ ss , respectively, were measured indicating that GTL soot reacts faster than diesel soot and Printex U carbon for NO 2 gas reactant. According to the number of reacted molecules on the surface, Printex U soot presents more reducing sites than diesel and GTL soot. Initial uptake coefficients for GTL and diesel soot for the reaction with CF 3 COOH gas reactant are very similar and no clear conclusions can be obtained related to the initial reactivity. The number of reacted molecules calculated for CF 3 COOH reactions shows values two orders of magnitude higher than the corresponding to NO 2 reactions, indicating a greater presence of basic functionalities in the soot surfaces. More information of the surface composition has been obtained using Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) before and after the reaction of soot samples with gas reactants. As conclusion, the interface of diesel and GTL soot before reaction mainly consists of polycyclic aromatic hydrocarbons (PAHs), nitro-compounds as well as ether functionalities. After reaction with gas reactant, it was observed that PAHs and nitro-compounds remain on the soot surface and new spectral bands such as carbonyl groups (carboxylic acids, aldehydes, esters and ketones) are observed. Physical properties of soot from both fuels studied such as BET surface isotherm and SEM analysis were also developed and related to the observed reactivity. [ABSTRACT FROM AUTHOR]

[Display omitted] • The thermal decomposition (thermolysis) of 1-ethyl-3-methylimidazolium chloride dominates upon its Knudsen evaporation. • The evaporation and thermolysis were quantitatively characterized experimentally and by the quantum chemical calculations. • The pressures P([Emim][Cl]) were measured, and the enthalpies of vaporization were obtained by the "3rd law" procedure. • The rate constants of two parallel heterogeneous reactions of the [EtMIm][Cl](l) thermal decomposition were evaluated. The use of ionic liquids (IL) at elevated temperatures has revealed interest in the study of evaporation and thermal decomposition (thermolysis) processes that determine the thermal stability of IL. In this work the evaporation of 1-ethyl-3-methyl-imidazolium chloride ([EtMIm][Cl]), which is accompanied by the significant thermal decomposition, was studied by the Knudsen cell mass spectrometry. The composition of gas phase over [EtMIm][Cl] and its change in time were established in the temperature range of 403–449 K. The saturated vapor pressures, vaporization enthalpy and rate constants of thermolysis reactions were determined. The equilibrium and rate constants for gas-phase thermolysis reactions of [EtMIm][Cl] were calculated by the quantum chemical methods. Based on the results of experiments and calculations, the processes responsible for mass loss – thermolysis and evaporation – were quantitatively described. [ABSTRACT FROM AUTHOR]

Chondrules, igneous objects of ∼1 mm in diameter, formed in the earliest solar system via a transient heating event, are divided into two types: main (type I, FeO-poor) and minor (type II, FeO-rich). Using various chondritic materials for different redox conditions and grain sizes, chondrule reproduction experiments were carried out at IW-2 to IW-3.8, with cooling rates mainly ∼100°C/h, with peak temperatures mainly at 1450 °C, and mainly at 100 Pa in a Knudsen cell providing near chemical equilibrium between the charge and the surrounding gas at the peak temperatures. Vapor pressures in the capsule were controlled using solid buffers. After and during the significant evaporation of the iron component from the metallic iron-poor starting materials in near equilibrium, crystallization occurred. This resulted in the formation of a product similar to the type I chondrules. Dusty olivine grains occurred in charges that had precursor type II chondrules containing coarse ferroan olivine, but such grains are not common in type I chondrules. Therefore fine-grained ferroan matrices rather than type II chondrules are main precursor for type I chondrules. The type I chondrules would have evolved via evaporation and condensation in the similar conditions to the present experimental system. Residual gas, which escaped in experiments, could have condensed to form matrices, leading to complementary compositions. Clusters of matrices and primordial chondrules could have been recycled to form main-generation chondrules originated from the shock heating. [ABSTRACT FROM AUTHOR]

One of the main chemical forms of cesium in the gas phase during severe light-water reactor accidents is expected to be cesium metaborate, CsBO 2 , according to thermodynamic equilibrium calculations considering its reaction with boron. However, the accuracy of the thermodynamic data of the gaseous metaborate, CsBO 2 (g), has been judged as poor. Thus, Knudsen effusion mass spectrometric measurements of CsBO 2 were carried out to obtain reliable thermodynamic data. The evaluated values of the standard enthalpy of formation of CsBO 2 (g), obtained by the 2nd and 3rd-law treatments, are −700.7 ± 10.7 kJ/mol and −697.0 ± 10.6 kJ/mol, respectively, and agree with each other within the experimental errors, which indicates that our data are reliable. Furthermore, it was found that the existing data of the Gibbs energy function and the standard enthalpy of formation agreed well with the values evaluated in this study, which indicates that the existing thermodynamic data are also reliable. [ABSTRACT FROM AUTHOR]

In this study, the temperature dependence of the heterogeneous uptake of acrylic acid on Arizona test dust (ATD) has been investigated within a temperature range of 255-315 K using a Knudsen cell reactor. Combined with diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) experiment, it was found that acrylic acid could adsorb on ATD via surface OH groups and convert to carboxylate on the particle surface. The kinetics study suggests that the initial true uptake coefficient (γt) of acrylic acid on ATD decreases from (4.02 ± 0.12) x 10- 5 to (1.73 ± 0.05) x 10- 5 with a temperature increase from 255 to 315 K. According to the temperature dependence of uptake coefficients, the enthalpy (ΔHobs) and entropy (ΔSobs) of uptake processes were determined to be -(9.60 ± 0.38) KJ/mol and -(121.55 ± 1.33) J•K/mol, respectively. The activation energy for desorption (Edes) was calculated to be (14.57 ± 0.60) KJ/mol. These results indicated that the heterogeneous uptake of acrylic acid on ATD surface was sensitive to temperature. The heterogeneous uptake on ATD could affect the concentration of acrylic acid in the atmosphere, especially at low temperature. [ABSTRACT FROM AUTHOR]

Fabrication of the Pd-PdBa secondary-emission cathodes is considered. The parameters of the physicochemical processes responsible for restructuring the surface of the field-emission cathode's working edges upon activation of the secondary-emission cathodes are determined. It is demonstrated that emission from cathodes initiates generation in magnetrons with a nonincandescent launch. [ABSTRACT FROM AUTHOR]

The uptake of HNO 3 , H 2 O, NO 2 and NO was studied on meteoric smoke particle analogues using a low-pressure Knudsen cell operating at 295 K. The analogues used were olivine (MgFeSiO 4 ) and a haematite/goethite (Fe 2 O 3 /FeO(OH)) mixture synthesised by the sol–gel process. For uptake on MgFeSiO 4 , the following uptake coefficients were obtained: γ (HNO 3 )=(1.8±0.3)×10 −3 , γ (H 2 O)=(4.0±1.3)×10 −3 , γ (NO 2 )=(5.7±0.2)×10 −4 and γ (NO)<3×10 −4 . γ (HNO 3 ) did not show a dependence on the mass of MgFeSiO 4 in the Knudsen cell (when varied by a factor of 6) implying that, because of relatively efficient uptake, HNO 3 is removed only by near-surface particles. This was corroborated by application of a surface uptake model. Saturating the MgFeSiO 4 particles with water vapour before exposing them to NO 2 increased γ (NO 2 ) to (2.1±0.7)×10 −3 , but had a very small effect on γ (HNO 3 ). For uptake on Fe 2 O 3 /FeO(OH), γ (HNO 3 )=(1.5±0.2)×10 −3 . These results were then included in a whole atmosphere chemistry–climate model, which shows that the heterogeneous removal on meteoric smoke particles in the winter polar vortex between 30 and 60 km appears to provide an important sink for HNO 3 . [ABSTRACT FROM AUTHOR]

Ultrathin Parylene-N (PPXN) films were prepared by using a home-made Knudsen Cell (KC). The PPXN films were identified by infrared (IR) spectra. The morphology and insulativity of PPXN films were measured by atomic force microscope (AFM) and current density versus voltage ( j – V ) characteristics. Well controlled 1-nm-thick PPXN thin films were inserted at different locations in the N′-bis(naphthalene-1-yl)-N, N′-bis(phenyl) benzidine (NPB) layers of organic light emitting diodes (OLEDs) with the structure of ITO/NPB/tris (8-hydroxyquinolato) aluminum (Alq 3 )/LiF/Al. For an optimized PPXN inserted structure, current efficiency of 6.27 cd/A was achieved, 11% higher than the 5.64 cd/A of the control one with 1-nm-thick PPXN buffer inserted at the anode interface. The device current efficiency improvement is due to the electron blocking of PPXN buffers, and the current density variation of devices under operation was explained by tunneling barrier reduction. [ABSTRACT FROM AUTHOR]

Highlights: [•] Vapour pressure measurements performed at high temperatures on (U,Pu) oxide samples. [•] Experimental facility consisted of a Knudsen cell coupled with a mass spectrometer. [•] Partial pressures of gaseous species were assessed from ionisation efficiency curves. [•] Vapour pressure was calculated using a thermochemical model for the ternary system. [ABSTRACT FROM AUTHOR]

Abstract: The high temperature vaporization of (SiC-SiO2) powders mixtures has been studied under vacuum using the Knudsen Cell Mass Spectrometric method in order to determine their vapor pressures as a function of their composition and to check their morphology change with time during the heat treatment. Various characterization methods – grain size distribution analysis, XRD, Raman spectra and Scanning Electron Microscopy – were used before and after heat treatment in the mass spectrometer in order to observe the growth of any possible links between SiC grains. The present study showed that as long as silica was present, links growth could not be observed. Lower SiO(g) and CO(g) partial pressures than equilibrium were observed and the evaporation coefficients have been determined. Then the origin of such low pressures was related to the control of the vaporization by oxygen diffusion in the silica layer existing at the surface of the SiC grains. [Copyright &y& Elsevier]

Abstract: Knudsen effusion mass spectrometry (KEMS) was used to determine the equilibrium vapour pressures of sodium over five selected compositions in different solid two-phase regions of the Na2O–Nb2O5 system at 1100–1470K. The results were then used to determine the standard thermodynamic functions of five solid compounds: Na3NbO4, NaNbO3, Na2Nb4O11, NaNb3O8 and NaNb13O33. These data were then incorporated into the IVTANTHERMO database to perform equilibrium calculations under real conditions relevant to the high temperature stability of sodium niobate, which is an important end member of the alkali niobate-based lead-free piezoelectric ceramics. [Copyright &y& Elsevier]

Abstract: Vapour pressure measurements at high temperatures have been performed on plutonium oxide samples using a Knudsen cell coupled with a mass spectrometer. Different experimental conditions were applied for the derivation of the solid–gas phase relations for three composition in the Pu–O phase diagram: the (Pu2O3–PuO2− x ) two-phase domain, the congruent vapourisation composition and near stoichiometric PuO2.00. The partial pressures of the gaseous species PuO2, PuO, and Pu were assessed from ionisation efficiency curves recorded at constant temperature. The vapour pressure results for different phase fields were discussed together with all the available literature data. [Copyright &y& Elsevier]

Abstract: Knudsen cell high temperature mass spectrometric measurements have been performed on neptunium dioxide. Several samples have been analysed for vaporisation in vacuum and oxidative conditions and different behaviours have been observed. The results for the vapour pressure of pure neptunium dioxide samples are discussed together with the data on americium dioxide and plutonium–americium mixed oxide samples that contained very small amounts of neptunium, in which neptunium is produced by alpha-decay from americium. In the view of extreme dilution of neptunium in the sample, Raoult’s law has been applied. The ionisation efficiency curves for Np+, NpO+, and were recorded for constant temperature. The dissociative ionisation contribution was evaluated with respect to the composition of the gaseous phase which under Knudsen conditions is in equilibrium with the condensed phase. [ABSTRACT FROM AUTHOR]

1,2-Dimethyl-3-(1′,1′,3′,3′-tetramethyl-3′-phenyldisiloxanyl)methylimidazolium bis(trifluoromethanesulfonyl)amide ([PhC 5 OSi 2 MMIm + ][Tf 2 N − ]) is the first silicon-containing ionic liquid which was characterized with the vaporization enthalpy, (138.5 ± 1.8) kJ mol −1 , and saturated vapor pressure, ln( p / Pa ) = −(16656 ± 219)/( T / K ) + (30.69 ± 0.92). This compound is a unique ionic liquid giving ions, retaining both cationic and anionic portions, in the electron impact ionization (EI) mass spectrum. [ABSTRACT FROM AUTHOR]

Abstract: The development of an ALD process, which is based on the sequential self-limiting surface reactions from generally two gaseous precursors, requires knowledge of the reactions mechanisms. Most of the studies of ALD modeling have been focused on the surface reactions. However, the most common use of organometallic molecule as gaseous precursors which are generally thermally unstable at temperatures close to the deposition one requires also an understanding of the gas-phase chemical reactions, as for the usual CVD processes. This presentation describes specific examples of the application of mass spectrometry to the determination of the thermal stability and behavior of organometallic precursors used for the ALD deposition of TaN and ZrO2 ultra thin layers. [Copyright &y& Elsevier]

Abstract: Thermodynamic properties of B2O3 in the (Al2O3 +B2O3) binary system were investigated by vapor pressure measurement of B2O3 in equilibrium with (Al2O3 +B2O3) compounds or melts using double Knudsen cell mass spectrometry. The Gibbs free energy change of formation of Al18B4O33 (9Al2O3·2B2O3) was estimated from the vapor pressure in equilibrium with a mixture of Al18B4O33 and Al2O3 at 1573K to 1673K. And activities of B2O3 in the two-phase region Al18B4O33 and B2O3-rich liquid, and (Al2O3 +B2O3) melts were obtained at 1373K to 1423K by vapor pressure measurements. [Copyright &y& Elsevier]

Abstract: l-tyrosine (L-Tyr) films with an oblique columnar structure were prepared by the Knudsen cell effusion method. The L-Tyr films were formed at a Knudsen cell temperature that was sufficiently lower than the decomposition temperature of L-Tyr. As the heating rate controlled by DC current is increased, the molecular network constructed of hydrogen bonds tends to collapse, and the film density and surface hydrophobicity tend to decrease. Higher DC currents are likely to induce a decarboxylation reaction. L-Tyr films prepared at a higher heating rate have enhanced gas sorption capabilities for a wide range of volatile organic compounds (VOCs). The sorption capabilities are particularly enhanced for linear hydrocarbons. The gas sorption characteristics for VOCs suggest that the adsorption in the vicinity of the film surface is dominant rather than diffusion into the film, which corresponds with the densified surface morphology. [Copyright &y& Elsevier]

The heterogeneous reactions of trace gases in the atmosphere on atmospheric particles could greatly affect the nitrogen, sulfur, ozone, and photochemical oxidant cycles. The uptake coefficient is an important kinetic parameter for atmospheric models to assess the role of heterogeneous reaction in the global cycles of trace gases. In this study, the heterogeneous uptake coefficients of carbonyl sulfide (OCS) on Al2O3 have been measured using a Knudsen cell reactor at 300K. Hydrogen sulfide (H2S) and carbon dioxide (CO2) were found to be the gaseous products. The reaction mechanism of OCS on Al2O3 was confirmed based on previous work and this study. The true initial uptake coefficient and steady-state uptake coefficient of OCS on α-Al2O3 were (3.8±0.8)×10−7 and (6.5±2.49)×10−8, and the corresponding uptake coefficients on γ-Al2O3 were (7.0±0.7)×10−8 and (1.8±0.4)×10−8, respectively. The annual flux of OCS due to heterogeneous reaction on α-Al2O3 was calculated to be 0.11–0.63Tgyr−1 based on the initial uptake coefficient and the steady-state uptake coefficient. When the fraction of Al2O3 in authentic atmospheric particles is taken into account, the annual flux of OCS due to heterogeneous reaction on atmospheric particles in the troposphere should be 0.02–0.10Tgyr−1. [Copyright &y& Elsevier]

Abstract: The studies on absolute partial pressure measurements of ionic components of the high temperature vapors over inorganic fluorides by means of Knudsen cell mass spectrometry are summarized. The problems arising when the ions are extracted directly from the effusion cell with electric field are discussed. The conditions for correct determination of the equilibrium constants for gaseous reactions, involving both positive and negative ions, are established. [Copyright &y& Elsevier]

Abstract: The volatility of pentakis(dimethylamido) tantalum (PDMAT) has been studied in the temperature range from −15 to 60 °C. A special Knudsen cell reactor coupled to a high temperature mass spectrometer, was specifically designed for the study of organometallic precursors. It is composed of an evaporation/sublimation chamber (−30 to 200 °C), which can be tight closed – like a vacuum chamber – in order to protect the precursors which are likely to be very unstable vs. moisture and atmospheric components. This chamber can be independently weighted for calibration purpose of the mass spectrometric experiments. During experiments, the effusion orifice is externally opened for direct mass spectrometric measurements of saturated vapour pressures. The device has been tested using the well-known mercury vapour pressure. First results obtained for the vaporization of PDMAT are presented. [Copyright &y& Elsevier]

Abstract: The vaporisation of a liquid Cu–In–Sn system has been investigated between 1273 and 1473K using Knudsen effusion mass spectrometry (KEMS) and the data obtained fitted to a Redlich–Kister sub-regular solution model. We examined 23 different compositions at four fixed indium concentrations: x In =0.20, 0.25, 0.29, 0.30 and 0.40 and evaluate the thermodynamic activities of all three components, not by applying the standard KEMS pressure calibration procedure, but from the measured ion intensity ratios of Cu+ to Sn+ using a recently published mathematical regression technique. The intermediate data obtained directly from the regression technique are the Redlich–Kister ternary L-parameters that are, as a function of temperature, as follows: L 0 =(−59473±7057)+(726.8±42.3)·T −(89.0±5.1)·T·ln(T); L 1 =(156840±5.2E−9)−(80±3.3E−11)·T −(5.57E−11±4E−12)·T·ln(T); L 2 =(−137168±8819)+(592.4±52.9)·T −(70.6±6.4)·T·ln(T). By using these values together with binary parameters taken from the literature, we were able to calculate several other thermodynamic functions of mixing. In particular, the partial heat of mixing of indium and its activity, which we evaluated and compared with the measured values along the Cu/Sn=1 isopleths. We obtained a good agreement between the calculated and measured values for partial heats while in the case of activity a good agreement between the two data sets is limited to a lower mole fraction of indium. [Copyright &y& Elsevier]

Abstract: One hydrocarbon-based and two fluorocarbon-based magnetic fluid samples were tested under four different vacuum levels. The weight losses of the samples were measured and the evaporation rates calculated. It was found that under higher vacuum levels (lower pressure levels) the evaporation rate of each sample was significantly higher than under atmospheric conditions, gradually reaching a saturated level while the vacuum level kept increasing. The Langmuir equation is modified to theoretically explain this phenomenon. It was also found that the fluorocarbon-based magnetic fluids are more suitable for ultra-high-vacuum applications. [Copyright &y& Elsevier]

After atmospheric aging and processing, mineral dust particles are often coated with nitrates, sulfates, and organics. In this study, laboratory experiments were done to simulate possible changes in the reactivity of mineral dust particles after being processed or aged in the atmosphere. Initial uptake coefficients of ozone on processed and unprocessed dust were measured with a Knudsen cell reactor and the relative reactivities are compared. In particular, the reactive uptake of ozone with mineral oxide particles that had been pretreated by exposure to nitric acid, sulfur dioxide, and organics are compared to particles that had not been pretreated. In some cases, it was found that the reactivity of ozone with pretreated particles was significantly reduced whereas in other cases the reactivity was enhanced. For example, the reactive uptake of ozone decreased by approximately 70% for α-Al2O3 particles coated with a layer of nitrate from reaction with nitric acid compared to particles that did not have a nitrate coating, whereas pretreatment of α-Al2O3 with sulfur dioxide showed a 33% enhancement toward ozone reactivity. For organic coatings, it was determined that SiO2 particles functionalized with a C8-alkene displayed enhanced reactivity toward ozone by 40% relative to untreated SiO2, while SiO2 particles functionalized with a C8-alkane exhibited decreased reactivity by approximately 40% relative to untreated SiO2 particles. The reaction mechanism of ozone uptake with these particles is discussed, as well as the impact on the chemistry of ozone on coated mineral dust aerosol in the troposphere. [Copyright &y& Elsevier]

A Nier-type mass spectrometer coupled with a Knudsen cell was used for the ionisation cross-section measurements of Ba, BaO, BaF2 and BaI2, using appropriate internal standards with known ionisation cross-sections. The vapour pressure ratio of standard to investigated compound, needed for calculation was obtained via the chemical analysis of the effusate. The use of this approach eliminated several sources of uncertainties. The problems concerning the preferential loss of fragment ions was also discussed and partly eliminated. The results obtained were compared with predictions, usually used in the field of high temperature mass spectrometry and a more recent approach using a model for ionisation cross-sections of high temperature molecules (MCM). [Copyright &y& Elsevier]

A Knudsen cell apparatus was used to measure the heterogeneous reactive uptake of ozone on mineral oxide powders at 296 K. Commercially available powders including α-Al2O3, α-Fe2O3, SiO2 and kaolinite were investigated as well as two different authentic mineral dusts, China loess and Saharan sand. Initial reactive uptake coefficients, γo,BET, for the purchased powders were measured as 1.2±0.4×10−4 for α-Al2O3, 2.0±0.3×10−4 for α-Fe2O3, 6.3±0.9×10−5 for SiO2 and 3±1×10−5 for kaolinite. Authentic dust samples were found to have γο,BET values of 2.7±0.8×10−5 for China loess and 6±2×10−5 for ground Saharan sand. Pressure dependence studies of this reaction on α-Al2O3 and α-Fe2O3 suggest that the initial uptake of ozone on these mineral oxides is a first-order process. Furthermore, under conditions of this study, these powders exhibit catalytic behavior toward the decomposition of ozone, and have turnover rates greater than one. Additionally, the reactive uptake of ozone on α-Al2O3 showed a small temperature dependence over a range of temperatures from 250 to 330 K, consistent with reports of low energies of activation (∼5–10 kJ mol−1) for ozone destruction on oxide powders. [Copyright &y& Elsevier]

This high temperature mass spectrometric study is aimed at the quantitative vaporization of powder beds of SiC–Al2O3 and related triphasic SiC–Al2O3–C and SiC–Al2O3-Si powder mixtures. The quantitative evaluation of reaction enthalpies showed that the different vaporization processes are not equilibrium processes and all the vaporization reactions are kinetically hindered. The multiple Knudsen cell method is used to determine directly the condensation coefficients of the Al(g), Al2O(g), CO(g) and SiO(g) species. Further, the comparison with previous equilibrium pressures calculated using thermodynamics allows the calculation of the evaporation coefficients of these species from the condensation coefficients and the measured mass spectrometric pressures. Supersaturated or undersaturated resultant pressures for each species are used as a criteria in the choice of suitable powder beds. [ABSTRACT FROM AUTHOR]

The properties of atmospheric particles are important to public health, radiative forcing of the atmosphere and to elucidating the chemical reactivity of atmospheric particles. We have constructed a Knudsen cell to study the uptake of organic compounds on soot. This article describes the construction and validation of the instrument, and our results on commercial soot concerning the uptake coefficient of ethanol, acetone, 1-butanol and diethoxymethane. First, a technical description of the instrument is presented. Next, its performance is validated by measuring the uptake of NO2 on hexane soot. Finally, the uptake coefficients of four oxygenated hydrocarbons on commercial soot are presented. The objective is to contribute to the understanding of the formation of particles in motor vehicle exhaust. A Knudsen cell is used to measure the uptake of specific gas-surface systems. A quadrupole mass spectrometer is used to determine the decay rate of a pulse of reagent gas in the reaction chamber. The BET surface area of the commercial soot was 12.6 m2/g. The uptake coefficient (γ) has been determined for ethanol (γ0,BET=7.7+-4.8×10−8), 1-butanol (γ0,BET= 1.4±0.54×10−7), acetone (γ0,BET=1-5±0.15×10−7) and diethoxymethane (γ0,BET=2.6±0.61×10−7). These results are characteristic of the specific soot sample used. The ordering of the uptake coefficients, ethanol < 1-butanol ∼ acetone < diethoxymethane, can be ascribed to a combination of physical (size and mass) and chemical effects. In addition, the initial uptake coefficient for NO2 on fresh hexane soot was determined to be γ0,BET= 1.7±1.1×10−4. In conclusion, we demonstrate that this instrument is able to measure uptake coefficients that are in agreement with accepted literature values. New data is presented concerning four light oxygenated hydrocarbons. A large amount of detailed information concerning individual heterogeneous reactions is necessary in order to model the composition of motor vehicle emissions. We look forward to increasing the size of this database. Results for a series of alcohols and alkanes will be presented in a forthcoming publication. [ABSTRACT FROM AUTHOR]

The effect of Acorus calamus products on insects is reviewed briefly. A sudden, dramatic drop occurs in the insecticidal, gaseous phase activity of calamus oil on stored-product pests, when the exposure temperature is lowered from 30° to 25°C. In an attempt to explain this finding, the vapor pressure of the main constituent of Indian Acorus calamus essential oil, β-asarone, was determined by three methods: (i) extrapolation with a gas-chromatographic method according to Jensen and Schall; (ii) calculation from boiling points with the Clausius-Clapeyron equation; and (iii) direct measurement with the Knudsen cell. The values of vapor pressure of β-asarone at 30°C according to these three methods were 3.3 x 10, 3.7 x 10 and 9.8 x 10 Torr, respectively. The volatility of β-asarone under the conditions of the fumigant experiments mentioned above was assayed by determining the weight loss from 50 mg asarone allowed to evaporate at 30°C from a filter paper disk into a 400 ml hermetically closed glass vessel. The weight loss was approximately 0.75 mg/400 ml receptacle space (≈1.9 mg/l) for every 10 days from day 0 to day 40. [ABSTRACT FROM AUTHOR]