Determination Of Vapor Pressure Research Articles

Thermochemical investigations in the system Cd–Gd

Vapour pressure measurements were performed in terms of a non-isothermal isopiestic method to determine vapour pressures of Cd in the system Cd–Gd between 693 and 1045K. From these results thermodynamic activities of Cd were derived as a function of temperature for the composition range 52–86at.% Cd. By employing an adapted Gibbs–Helmholtz equation, partial molar enthalpies of mixing of Cd were obtained for the corresponding composition range, which were used to convert the activity values of Cd to a common average sample temperature of 773K. The relatively large variation of the activity across the homogeneity ranges of the phases Cd2Gd and Cd45Gd11 indicates that they probably belong to the most stable intermetallic compounds in this system.An activity value of Gd for the two phase field Cd6Gd+L was available from literature and served as an integration constant for a Gibbs–Duhem integration. Integral Gibbs energies are presented between 51 and 100at.% Cd at 773K, referred to Cd(l) and α-Gd(s) as standard states. Gibbs energies of formation for the exact stoichiometric compositions of the phases Cd58Gd13, Cd45Gd11, Cd3Gd and Cd2Gd were obtained at 773K as about −19.9, −21.1, −24.8, and −30.0kJgatom−1, respectively.

Determination of Vapor Pressures for Organophosphate Esters

Organophosphate compounds are ubiquitous in the environment and to better understand and predict their environmental transport and fate, well-defined physical-chemical properties are needed. The subcooled liquid-phase vapor pressures at 298.15 K (p298) were determined for 11 chlorinated and nonchlorinated phosphate flame retardants (PFRs) by the capillary gas chromatography retention time method (GC-RT). Values of log (p298/Pa) ranged from −5.22 to −1.32 and enthalpies of vaporization (ΔlgH/kJ·mol–1) ranged from 82.0 to 109. Log (p298/Pa) by GC-RT showed good overall agreement with estimates using the Modified Grain Method (EpiSuite) and with the mean of experimental and in silico literature values, whereas values for the chlorinated PFRs appeared to be overestimated. SPARC modeling seriously underestimated p298, especially for the less volatile compounds. The Junge–Pankow adsorption model at 288.15 K predicted that most of the PFRs would be predominantly in the particulate phase in urban air and distributed between the particulate and gaseous phases in background air.

A new approach to determine vapor pressures of compounds in multicomponent systems by comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry

A method is described to determine vapor pressures of compounds in multicomponent systems simultaneously. The method is based on temperature-gradient analysis by comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GCxGC-TOFMS). Vapor pressures are determined with the aid of known vapor pressure values of reference compounds eluting before and after the analytes. Reference compounds with the same functionalities as the analytes are preferred, but when these are not available, the alkane series can be utilized. The number of compounds whose vapor pressures can be determined is limited only by the peak capacity of the chromatographic system. Although the lowest subcooled vapor pressure determined was 0.006Pa, for tetrahydroaraucarolone in an atmospheric aerosol sample, vapor pressures as low as 10−6Pa can be measured with the described set-up. Even lower values can be measured with higher GC temperatures and longer analysis times. Since only a few picograms of compound is required, in a mixture of any complexity, the GCxGC-TOFMS method offers unique sensitivity, rapidity, and comprehensiveness.

A new approach to determine vapour pressures and hygroscopicities of aqueous aerosols containing semi-volatile organic compounds

We present a new approach to study the equilibrium gas-particle partitioning of volatile and semi-volatile organic components in aqueous aerosol, deriving a correlational analysis method that examines and interprets simultaneous and correlated fluctuations in particle size and composition. From this approach, changes in particle size driven by organic component evaporation can be clearly resolved from size changes driven by hygroscopicity and fluctuations in environmental conditions. The approach is used to interpret measurements of the evaporation of semi-volatile organic components from binary aqueous/organic aerosol and the hygroscopic growth of involatile inorganic aerosol. The measurements have been made by the aerosol optical tweezers technique, which allows the simultaneous retrieval of particle size and refractive index with high accuracy. We suggest that this approach will be particularly valuable for investigating the thermodynamic behaviour of mixed component aqueous aerosol and will allow the accurate derivation of solution phase equilibrium properties that are prone to large uncertainties when measurements are made simply of the change in particle size with gas phase relative humidity.

Determination of Vapor Pressure of Liquid Copper by Carrier Gas Method

The relationship between the vapor pressure of liquid copper and the flow rate of carrier gas argon was discussed, when the carrier gas method was used to determine the vapor pressure of liquid copper at 1892 K. The proper argon flow rate range obtained was 150–500 mL/min and enough evidence was provided to verify the vapor pressure-flow rate of carrier gas relationship at the target temperature. Based on the proper flow rate range, the vapor pressure of liquid copper was measured at 1609–1892 K. The relationship of vapor pressure–temperature obtained by the method of regression analysis can be expressed as: ln(p/Pa) = (25.470 ± 0.903) − (39099.8 ± 1574.5)/T. Further, the thermodynamic properties including the heat of vaporization and the Gibbs free energy of the Cu (l) = Cu (g) reaction were calculated by the vapor pressure obtained over the temperature range covered.

Gas chromatographic vapor pressure determination of atmospherically relevant oxidation products of β-caryophyllene and α-pinene

Vapor pressures (subcooled liquid, pliquid) of atmospherically relevant oxidation products of β-caryophyllene (β-caryophyllene aldehyde 0.18 ± 0.03 Pa and β-nocaryophyllene aldehyde 0.17 ± 0.03 Pa), and α-pinene (pinonaldehyde 16.8 ± 0.20 Pa, cis-pinic acid 0.12 ± 0.06 Pa, and cis-pinonic acid 0.99 ± 0.19 Pa) at 298 K were obtained by gas chromatography with flame ionization detection (FID) and mass spectrometric (MS) detection. The effects of stationary phase polarity and column film thickness on the vapor pressure values were investigated. Increase in stationary phase polarity provided smaller values, while increase in film thickness gave slightly higher values. Values for vapor pressure were at least two orders of magnitude lower when obtained by a method utilizing vaporization enthalpy (determined by gas chromatography–mass spectrometry) than by retention index method. Finally, the results were compared with values calculated by group contribution theory. For the β-caryophyllene oxidation products, the values measured by gas chromatography were slightly lower than those obtained by theoretical calculations. The opposite trend was observed for the α-pinene oxidation products. The methods based on gas chromatography are concluded to be highly useful for the determination of vapor pressures of semi-volatile compounds. Except for the most polar pinic and pinonic acids, differences between vapor pressure values obtained by GC–FID and GC–MS were small. Since GC–MS provides structural information simultaneously, the use of GC–MS is recommended.

Hole Transport Materials Based Thin Films: Topographic Structures and Phase Transition Thermodynamics of Triphenylamine Derivatives

The topographic structural analysis of thin films of triphenylamine (TPA) derivatives, obtained by vacuum deposition, is presented. The topology of the films is highly dependent on the number of phenyl rings as well on the presence of methyl groups. The glass transition temperatures can be predicted from the melting temperatures, according to the molecular symmetry, flexibility, and molecular size of the amorphous nonplanar materials suitable for long-time use in OLED based devices. A phase transition thermodynamics study, including vapor pressure and heat capacity determinations of some hole transport materials based triphenylamine derivatives (DDP, p-TTP, TPB, TPD, TDAB, and m-MTDAB) is presented. Analysis of the enthalpic and entropic contributions provides an understanding of the fusion temperature differentiation, which results in higher melting points for TDB and TDAB and lower values for TPD and m-MTDAB, due to the presence of meta-CH3 groups. The thermodynamic parameters of sublimation were used to explain the slightly higher volatility of solid DDP relative to p-TTP and the similarity between the volatilities of solids TPB and TDAB.

In Situ Direct Measurement of Vapor Pressures and Thermodynamic Parameters of Volatile Organic Materials in the Vapor Phase: Benzoic Acid, Ferrocene, and Naphthalene

We report the direct determination of vapor pressures and optical and thermodynamic parameters of powders of low-volatile materials in their vapor phase using a commercial UV/Vis spectrometer. This methodology is based on the linear proportionality between the density of the saturated gas of the material and the absorbance of the gas at different temperatures. The vapor pressure values determined for benzoic acid and ferrocene are in good agreement with those reported in the literature with ∼2-7 % uncertainty. Thermodynamic parameters of benzoic acid, ferrocene, and naphthalene are determined in situ at temperatures below their melting points. The sublimation enthalpies of the investigated organic molecules are in excellent agreement with the ICTAC recommended values (less than 1 % difference). This method has been used to measure vapor pressures and thermodynamic parameters of organic volatile materials with vapor pressures of ∼0.5-355 Pa in the 50-100 °C temperature range.

Vapor pressure of 1-octanol below 5 kPa using DSC

American Society for Testing and Materials (ASTM) Method E 1782-08, Standard Test Method for Determining Vapor Pressure by Thermal Analysis recommends use of hermetic-type sealable sample pans with a single 50–75μm pinhole in the lid for pressures between 5kPa and 2MPa. At pressures below 5kPa using the recommended pinhole range, boiling endotherms become increasingly broad. Earlier studies demonstrated qualitative improvement in endotherm sharpness with use of larger pinholes (up to 350μm) at pressures below 5kPa. In the current work, the vapor pressure of 1-octanol was determined in accordance with ASTM E 1782-08 using pinholes ranging from 75 to 350μm from atmospheric pressure down to 0.197kPa. These results clearly indicate that vapor pressure data in good agreement with the literature can be produced for 1-octanol at pressures as low as 0.2kPa if pinhole sizes up to 350μm are used; the results are comparable to those generated using the current ASTM-recommended pressure and pinhole parameters.

Spectroscopic determination of enthalpies of sublimation of organic materials in the vapor phase: Benzoic acid, ferrocene, and naphthalene

Techniques for determining the enthalpies of sublimation of low volatile materials in the vapor phase are quite rare. Although benzoic acid, ferrocene, and naphthalene are used as reference materials for indirect determination of vapor pressure of volatile materials, the discrepancy of the values of their enthalpies of sublimation is considerably large (∼10–15kJ/mol). In this work, the enthalpies of sublimation of vapors of these materials are determined using absorbance spectroscopy in the ultraviolet region of the electromagnetic spectrum. This methodology is based on the linear proportionality between the density of the saturated gas of the material and the absorbance of the gas. The determined values of enthalpies of sublimation are in excellent agreement with the mean value of those reported in literature and those recommended by the ICTAC. This method is shown to be accurate and rapid.

A dynamic, luminescent and entangled MOF as a qualitative sensor for volatile organic solvents and a quantitative monitor for acetonitrile vapour

A new luminescent entangled (srs nets with two-fold interpenetration, linked via short Cu⋯Cu distances of ca. 2.8 Å) MOF, namely, [(CuCN)3L·(guest)x]n (L = 2,6-bis((3,5-dimethyl-1H-pyrazol-4-yl)methyl)pyridine; x = 1 or 2), which contains microporous channels, is synthesized. This MOF material shows structural dynamics upon adsorption of various volatile organic solvent molecules, accompanied by reversible guest responsive colour changes of the fluorescence emission that are discernible by the naked eyes. The vacuated form of this material can also exhibit qualitative solvate-optical sensing behaviours toward various mixed solvents. Moreover, a quantitative real-time monitoring device is constructed that implements the determination of acetonitrile vapour pressure through optical response, which causes a drastic emission change from blue to yellow. The detailed structural elucidation provides structure–property understanding for the host–guest responsive dynamics.

Vaporation characteristics of low-melting nitrocompounds by isothermal thermogravimetry

Determination of vapor pressure is critical for accurate detection of trace volatile hazardous materials, ensuring human health and environmental security. 2,4,6-Trinitrotoluene (TNT), 3,4-Dinitrofurazanfuroxan (DNTF), and 2,4-Dinitroanisole (DNAN) are an important class of volatile low-melting nitrocompounds which are widely used in military, aerospace, and defense industry. In this study, the sublimation and evaporation characteristics of these three nitrocompounds were investigated for the first time by using isothermal thermogravimetry (TG) undergoing zero order, non-activated evaporation processes, analyzed with the Antoine and Langmuir equations, and confirmed with benzoic acid as a calibration material. The Clausius–Clapeyron equations of TNT, DNTF, and DNAN at both sublimation and evaporation processes are established using the temperature dependence of vapor pressure. The enthalpies of sublimation and evaporation are determined. The results of TNT are well consistent with literatures, proving that the isothermal TG for determination of vapor pressure is eligible and accurate. This work lays the foundation for further study of the reliable trace detection of hazardous low-melting nitrocompounds.

Vapor pressure curve determination of α-lipoic acid raw material and capsules by dynamic thermogravimetric method

α-Lipoic acid (ALA) has been described as a potent biological antioxidant and detoxification agent. ALA has become a common ingredient in multivitamin formulas and anti-aging supplements. Vapor pressure determination by thermogravimetric method has been used to characterize drugs and pharmaceutical preparations. The aim of this study was to determinate the vapor pressure of ALA raw materials and capsules using thermogravimetric method. TG curves of ALA were determined by the TA Instruments model SDT Q600 TG/DSC Thermal Analyzer. The TG curves of ALA displayed a single mass loss in the temperature range (from 227.16 to 319.29°C), at a heating rate of 10.0°Cmin−1. ALA showed zero order kinetic reaction for all heating rates (10.0, 20.0, 40.0, 60.0 and 80.0°Cmin−1). The vapor pressure curves were constructed from the Langmuir equation. This work suggests that thermogravimetry can be utilized as a rapid and effective technique for the estimating of ALA vaporization characteristics.

Determination of Vapor Pressures of Fe-Oxides in Humid Atmospheres

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Determination of Vapor Pressure of Chemical Compounds: A Group Contribution Model for an Extremely Large Database

In the present study, a group contribution model is developed for determination of the vapor pressure of pure chemical compounds at temperatures from 55 to 3040 K. About 42 000 vapor pressure values belonging to around 1400 chemical compounds (mostly organic ones) at different temperatures are treated to propose a reliable and predictive model. A three-layer artificial neural network is optimized using the Levenberg–Marquardt (LM) optimization algorithm to establish the final relationship between the functional groups and the vapor pressure values. The obtained results indicate the average absolute relative deviation (AARD%) of the calculations/estimations from the applied data to be about 6% and a squared correlation coefficient of 0.994. Furthermore, the outliers of the model are detected using the leverage value statistics method.

Indirect Determination of Vapor Pressures by Capillary Gas–Liquid Chromatography: Analysis of the Reference Vapor-Pressure Data and Their Treatment

Knowledge of low vapor pressures p0 is indispensible for modeling the fate of chemicals in the environment as well as for other important applications. The indirect determination of vapor pressures by the capillary gas–liquid chromatography–relative retention time (GLC–RT) technique has attracted the attention of many research groups, and two review papers devoted to this topic have already been published. To complement these reviews, the quality of the literature vapor pressures for reference compounds is analyzed, along with the influence of the equations used for the temperature dependence of p0 and the effects of the extrapolation interval applied. Since the GLC–RT techniques yield p0 of subcooled liquid even in the case of solid samples, different approaches employed for the recalculation of solid vapor pressures for reference compounds to the values for subcooled liquids are discussed. It is shown that a selection and/or application of the physicochemical properties of the reference compounds can si...

Evidence of an odd–even effect on the thermodynamic parameters of odd fluorotelomer alcohols

A phase transition study, including vapour pressure determinations of odd fluorotelomer alcohols {oFTOH; CF3(CF2)nCH2OH, with n=5 to 9}, is reported in order to explore the effect of the successive introduction of –CF2– groups into the molecule on the thermodynamic properties related to (solid+liquid, solid+gas, and liquid+gas) equilibria. An odd–even effect on the thermodynamic parameters of fusion and sublimation was observed in the homologous series of odd fluorotelomer alcohols indicating an increase of the stability in the crystal packing for the members with an odd number of carbon atoms. The vaporization parameters of o-FTOH were compared with the literature data for their alkane analogues and the results showed a higher volatility of liquid fluorotelomer alcohols than their congeners. The higher molecular conformation restriction of perfluorinated alcohols and/or the higher molar mass seems to contribute to their higher entropy of vaporization which drives the volatility of the 1H,1H-perfluorinated alcohols.

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.

Simple Method for Determining the Vapor Pressure of Materials Using UV-Absorbance Spectroscopy

Accurate thermodynamic parameters of thin films of materials are crucial in understanding their behavior in the nanometer scale. A new and simple method for determining the vapor pressure and thermodynamic properties of nanometer thick films of materials was developed based on UV-absorbance spectroscopy. Well-characterized benzoic acid was used to calibrate the spectrometer and the experimental conditions. The thermodynamic properties of pentaerythritol tetranitrate (PETN) were determined to validate the use of this new method. The estimated values of the thermodynamic parameters of PETN are in excellent agreement with the values reported using the most widely used Knudsen effusion method for determining vapor pressure lower than 1 pascal. The elegance of this method is its simplicity. The results indicate that UV-absorbance spectroscopy is a model-free and powerful technique in determining thermodynamic parameters in the nanoscale.

Surface Tension and Bubbles

From a molecular perspective, we described the origin of surface tension. Surface tension is exceptionally good at rounding things out, such as bubbles can produce in surfactant solution , also in liquid or vapor-liquid phase transition. Through the experiment of determination of saturated vapor pressure of pure liquids, maybe we can conclude that almost all the bubbles were generated as result of the breakup of the gas-liquid interface.