Vapor Pressure Measurements Research Articles

Enthalpies of formation of 5,6-dihydro-5-methyluracil and 5,6-dihydro-6-methyluracil

The standard (p°=0.1MPa) molar enthalpy of combustion, ΔcHm°, of two crystalline compounds, 5,6-dihydro-5-methyluracil and 5,6-dihydro-6-methyluracil, were determined, at T=298.15K, using a static bomb combustion calorimeter. The vapor pressures as a function of the temperature were measured for those compounds, by the Knudsen effusion technique, and the standard molar enthalpies of sublimation at the mean temperature of the vapor pressure measurements were derived from the Clausius–Clapeyron equation, and corrected to T=298.15K using an estimated value for ΔcrgCp,m°. These values were used to derive the standard molar enthalpies of formation of the two compounds studied, in the condensed and gaseous phases. Some considerations about the relative stability of the two isomers were made and compared with similar compounds.

A new way of phase identification, of AgGaGeS4∙nGeS2 crystals

The phase identification of AgGaGeS4·nGeS2 (n=0–4) crystals grown by vertical Bridgman–Stockbarger technique was carried out to find the boundary value n between a homogeneous solid solution and its mixture with GeS2. To obtain reliable results, the conventional methods of X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDX) were completed by less common vapor pressure measurement in a closed volume and precise density measurements, which are very sensitive to the detection of small amounts of crystalline and glassy GeS2 and heterogeneous state of the crystals. The boundary value n=1.5 at 1045 K and the coexistence of the solid solution AgGaGeS4·1.5GeS2 with the β-GeS2 phase for n>1.5 was found. Glassy GeS2 (~2 mol%) was revealed by vapor pressure measurement and XRD studies in all the crystals. This is discussed in terms of the supersaturated solid solution decomposition upon temperature decreasing and the microphase separation of overcooled melt near the melting point under non-equilibrium crystallization. For the first time, the p–T dependence for glassy GeS2 was measured by the vapor pressure measurements.

A Fairly Common Error in Processing the Results of Knudsen Effusion Mass Spectrometry: Sublimation Enthalpy of Vanadium as an Example

It has been shown in this paper, that a fairly common approach of Knudsen effusion mass spectrometry based on the so called “self-calibration” for the instrument sensitivity (combination of single measurement for absolute vapor pressure by Knudsen method with the mass spectrometry for its temperature dependence) leads to a very large uncertainty for the enthalpy of sublimation for the substance under investigation. The uncertainty may not be less than the uncertainty of initial single measurement for vapor pressure, and so, the array of data obtained by its combination with the mass spectral data is not the array of independent measurements. The difference between the uncertainties for two approaches (considered and criticized) may be near one order of magnitude for vapor pressure. There are presented the results of 13 measurements of vapor pressure for vanadium in the paper (1). Formal statistical treating of these results leads to sublimation enthalpy with the uncertainty less than ±1 kJ·mol-1, although the uncertainty of the calibration experiments (2 experiments) amounts near ±13 kJ·mol-1.

Combination of Thermal Analysis and Knudsen Effusion Mass Spectrometry for Study of Metal Materials on Macro- and Nano-Scale

The study of metal materials could not be possible without the use of sophisticated techniques often enabling us to do precise experiments of various types by means of multifunction equipments. One of these is an apparatus combining thermal analysis (TA) with Knudsen effusion mass spectrometry (KEMS). In the Netzsch STA 409 CD/3/403/5/G apparatus, a specially-adapted type of the commercial STA 409 CD – QMS 403/5 Skimmer Coupling Instrument, the holder for differential scanning calorimetry (DSC) or differential thermal analysis (DTA) can be replaced by another one with alumina Knudsen cell for vapour pressure measurement of activities of components. The instrument capabilities are demonstrated on several examples of TA and effusion measurements of bulk metal materials and nano-powders.

Liquid/Gas and Liquid/Liquid Phase Equilibria of the System Water/Bovine Serum Albumin

The thermodynamic behavior of the system H2O/BSA was studied at 25 °C within the entire composition range: vapor pressure measurements via head space sampling gas chromatography demonstrate that the attainment of equilibria takes more than one week. A miscibility gap was detected via turbidity and the coexisting phases were analyzed. At 6 °C the two phase region extends from ca. 34 to 40 wt % BSA; it shrinks upon heating. The polymer rich phase is locally ordered, as can be seen under the optical microscope using crossed polarizers. The Flory-Huggins theory turns out to be inappropriate for the modeling of experimental results. A phenomenological expression is employed which uses three adjustable parameters and describes the vapor pressures quantitatively; it also forecasts the existence of a miscibility gap.

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.

The role of biotic interactions for the early establishment of oak seedlings in coastal dune forest communities

Although forest managers are aware of the need to adapt forest management to climate change, this task is still challenging due to the difficulty for predicting local species and communities responses to climate change. The aim of this paper is to focus on the adaptation of sylvicultural techniques to changes in interactions between tree recruitment and understory species due to climate change. A space-for-time design was used in coastal dune forest communities from the south west of France. The study area is a 240km-long sand strip covered by forest communities with minimal variation in soil conditions along a natural gradient of increasing water stress. We transplanted seedlings of three oak species of contrasting strategies at both the wet and dry ends of the climate gradient, both in forest and gap plots and with and without understory shrubs. We measured Vapor Pressure Deficit in all treatment conditions. We found strong canopy and climate conditions effects on interactions between understory shrubs and oak transplants. Competition was dominant in the forest plots of the wettest site and facilitation in the gap plots of the driest site. Oak survival without shrubs (but not with shrubs) was strongly related to VPD values, which suggests that the positive effect of shrubs in the most stressful conditions was due to decreased atmospheric stress below their canopy. In contrast, we found that understory shrubs/oak seedlings interactions were weakly affected by oak species functional strategies. Our results provide evidence that future oak regeneration management should take into account changes in interactions with understory shrubs due to climate change. In particular, we recommend conserving understory shrubs in the most stressful sites in order to maintain a sufficient oak regeneration for the long term dynamics of coastal oak forest communities under changing climate.

Et3GeN(SiMe3)2 and Et3SnN(SiMe3)2: New precursors for chemical vapor deposition processes

We have synthesized the germanium- and tin-containing organosilicon compounds Et3GeN(SiMe3)2 and Et3SnN(SiMe3)2 as new precursors for the preparation of materials by chemical vapor deposition. The compounds were characterized by NMR, IR and UV spectroscopies and thermal analysis. Using vapor pressure measurements, we obtained temperature dependences of their saturated vapor pressure. We assessed their thermal stability and calculated the thermodynamic characteristics of vaporization of the organosilicon compounds.

Thermodynamic surface properties of [BMIm][NTf2] or [EMIm][NTf2] binary mixtures with tetrahydrofuran, acetonitrile or dimethylsulfoxide

The surface tension, σ, of binary mixtures of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [BMIm][NTf2] with tetrahydrofuran (oxolane, thf), acetonitrile, dimethylsulfoxide ((methylsufinyl)methane, dmso) and of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide [EMIm][NTf2] with dimethylsufoxide was measured between (293.15 and 313.15)K using the pendant drop method. On the basis of experimental σ values and activity coefficients of solutes in their solutions with ionic liquid obtained from vapor pressure measurement, Gibbs excess surface concentrations of thf, acetonitrile or dmso in mixtures with [BMIm][NTf2] or [EMIm][NTf2] were determined. The results are discussed in terms of possible interactions between ILs and aprotic polar substances.

Accuracy of high-temperature mass spectrometry measurements of vapor pressure

Accuracy of high-temperature mass spectrometry measurements of vapor pressure

Vapour pressure measurements on lanthanum polyphosphate and ultraphosphate by the transpiration method

The vapour pressure of P4O10 produced by decomposition of LaP3O9 and LaP5O14 (LaP3O9→LaPO4+1/2 P4O10; LaP5O14→LaP3O9+1/2 P4O10) was measured by the transpiration method over the temperature ranges (1123 to 1323)K and (923 to 1173)K, respectively. The standard thermodynamic quantities of LaP3O9 and LaP5O14 were derived by the use of second-law method and Neumann–Kopp rule. The derived thermodynamic quantities are consistent with the phase equilibria in the (La2O3+P2O5) system reported previously. There is a significant discrepancy between the present results and the literature data for LaP3O9 at T=298.15K, possibly due to the lack of accurate thermodynamic values of LaPO4 in the past. The thermal and chemical stabilities of LaP3O9 and LaP5O14 were analysed toward their proposed use as proton-conducting solid electrolytes in fuel cells. LaP3O9 is considered more promising from the viewpoint of proton conductivity and thermal stability. In the presence of water vapour or hydrogen gas, the decomposition of LaP3O9 and LaP5O14 would be accelerated significantly.

Predicting Temperature-Dependent Solid Vapor Pressures of Explosives and Related Compounds Using a Quantum Mechanical Continuum Solvation Model

Temperature-dependent vapor pressures of solid explosives and their byproducts are calculated to an accuracy of 0.32 log units using a modified form of the conductor-like screening model for real solvents (COSMO-RS). Accurate predictions for solids within COSMO-RS require correction for the free energy of fusion as well as other effects such as van der Waals interactions. Limited experimental data on explosives is available to determine these corrections, and thus we have extended the COSMO-RS model by introducing a quantitative structure-property relationship to estimate a lumped correction factor using only information from standard quantum chemistry calculations. This modification improves the COSMO-RS estimate of ambient vapor pressure by more than 1 order of magnitude for a range of nitrogen-rich explosives and their derivatives, bringing the theoretical predictions to within typical experimental error bars for vapor pressure measurements. The estimated temperature dependence of these vapor pressures also agrees well with available experimental data, which is particularly important for estimating environmental transport and gas evolution for buried explosives or environmentally contaminated locations. This technique is then used to predict vapor pressures for a number of explosives and degradation products for which experimental data is not readily available.

Measurement of Heavy Oil and Bitumen Vapor Pressure for Fluid Characterization

The prediction of heavy oil phase behavior, particularly with solvents, is sensitive to the characterization of the middle and heavy boiling point components of the oil. These components are typically characterized based on an extrapolation of distillation data. One method to test the extrapolated characterization is to model the vapor pressures of these fractions or residues containing these fractions. Unfortunately, the vapor pressures are too low to be reliably measured with conventional techniques. A new high vacuum static apparatus was designed and constructed for the measurement of vapor pressure of heavy oil and bitumen samples. The apparatus is capable of measuring pressures from 100 down to 0.1 Pa and temperatures in the range of 293.15–473.15 K. New procedures were developed to degas samples and obtain accurate vapor pressures at vacuum conditions. The apparatus was tested on n-hexadecane and naphthalene at temperatures between 303.15 and 363.15 K. The measured vapor pressures were, on average, all within 13% of the literature data. The vapor pressures of a Western Canadian bitumen sample (WC_BIT_B1) and three of its fractions were measured using the apparatus. The WC_BIT_B1 bitumen was modeled using the Advanced Peng–Robinson equation of state using a Gaussian extrapolation of its distillation curve for the maltene fraction and a Gamma molecular distribution for its asphaltene fraction. The measured vapor pressures were all predicted to within 3.5%.

Vapor pressures of aqueous blended-amine solutions containing (TEA/AMP/MDEA) + (DEA/MEA/PZ) at temperatures (303.15–343.15) K

In this study, a new set of data on the vapor pressure of aqueous blends of the most industrially important amines monoethanolamine (MEA), diethanolamine (DEA), triethanolamine (TEA), methyldiethanolamine (MDEA), 2-amino-2-methyl-1-propanol (AMP), and piperazine (PZ) were presented. The blended-amines systems are mixtures of (TEA/AMP/MDEA)+(MEA/DEA/PZ), at total amine concentration=30wt% (10wt% amine 1+20wt% amine 2). Experimental data were obtained at atmospheric pressure and temperatures (303.15–343.15)K using a vapor pressure measurement apparatus. The apparatus consisted mainly of a degassing system and a vapor pressure measurement setup where the equilibrium experiment was performed. The vapor pressures of aqueous solutions of each of the six single-amine systems were also presented. Results showed that the addition of amine in water lead to the lowering of the vapor pressure. The vapor pressure increased with increasing temperature, and decreased with increasing mole fraction of amine in the solution. The vapor pressure data were correlated with temperature using the reliable Antoine equation, which yield an average absolute deviation of 0.09% for the aqueous single-amine systems, and 0.13% for the aqueous blended amine systems. The results presented in this work can be applied in engineering design calculations to have reliable vapor pressure estimates for the investigated amine systems in the temperature range (303.15–343.15)K.

Thermodynamic study of selected monoterpenes

A thermodynamic study of important biogenic compounds, (–)-α-pinene, (–)-β-pinene, (–)-cis-verbenol, and (–)-verbenone, is presented in this work. The vapor pressure measurements were performed using the static method over the environmentally important temperature range from 238 to 313K. The sublimation and vaporization enthalpies were derived from these measurements as well as directly determined by a Calvet high temperature microcalorimeter. Heat capacities of condensed phases were measured by Calvet and drop calorimetry in the temperature interval from 273 to 355K. The thermodynamic properties of the ideal-gas state were calculated by combining statistical thermodynamics and density functional theory (DFT) calculations. The trends in thermodynamic properties within the group of compounds possessing similar molecular structures are discussed.

Non-canonical mass laws in equilibrium isotopic fractionations: Evidence from the vapor pressure isotope effect of SF6

We report experimental observations of the vapor pressure isotope effect, including 33S/32S and 34S/32S ratios, for SF6 ice between 137 and 173K. The temporal evolution of observed fractionations, mass-balance of reactants and products, and reversal of the fractionation at one temperature (155K) are consistent with a subset of our experiments having reached or closely approached thermodynamic equilibrium. That equilibrium involves a reversed vapor pressure isotope effect; i.e., vapor is between 2‰ and 3‰ higher in 34S/32S than co-existing ice, with the difference increasing with decreasing temperature. At the explored temperatures, the apparent equilibrium fractionation of 33S/32S ratios is 0.551±0.010 times that for 34S/32S ratios—higher than the canonical ratio expected for mass dependent thermodynamic fractionations (∼0.515). Two experiments examining exchange between adsorbed and vapor SF6 suggest the sorbate–vapor fractionation at 180–188K is similar to that for ice–vapor at ∼150K. In contrast, the liquid–vapor fractionation at 228–300K is negligibly small (∼0.1‰ for 34S/32S; the mass law is ill defined due to the low amplitude of fractionation). We hypothesize that the observed vapor pressure isotope for SF6 ice and sorbate is controlled by commonly understood effects of isotopic substitution on vibrational energies of molecules, but leads to both an exotic mass law and reversed fractionation due to the competition between isotope effects on intramolecular vibrations, which promote heavy isotope enrichment in vapor, and isotope effects on intermolecular (lattice) vibrations, which promote heavy isotope enrichment in ice. This explanation implies that a variety of naturally important compounds having diverse modes of vibration (i.e., varying greatly in frequency and particularly, reduced mass) could potentially exhibit similarly non-canonical mass laws for S and O isotope fractionations. We examined this hypothesis using a density function model of SF6 vapor and lattice dynamic model of SF6(ice). These models support the direction of the measured vapor pressure isotope effect, but do not quantitatively agree with the magnitude of the fractionation and poorly match the phonon spectrum of SF6 ice. A strict test of our hypothesis must await a more sophisticated model of the isotopic dependence of the phonon spectrum of SF6 ice.

Estimation of precipitable water vapour using vapour pressure and air temperature in an arid region in central Saudi Arabia

Precipitable water vapour (PWV) is an important component of the atmosphere and significantly influences many atmospheric processes. It is a physical parameter that is difficult to measure with adequate spatial and time resolution under all weather conditions. In this study, radiosonde data for the city of Riyadh in central Saudi Arabia (24°43′ N; 46°40′ E, 764ma.s.l.) from 1985 to 2007 were used to model the precipitable water vapour (PWV) from the measurements of vapour pressure and air temperature. A multilinear model was essentially unbiased with a correlation coefficient (R2) of 0.81, a mean bias error (MBE) of −0.06mm, and a root mean square error (RMSE) of approximately 2.80mm. The performance of the model was tested against two independent datasets. The first dataset was four and half years of radiosonde measurements of PWV for the period 2008–March 2012, and the second set was two years of PWV data obtained from sun photometer measurements at 940nm. For both datasets, the predictability of the model was excellent, with MBE values of less than 1mm. The RMSE was 3.21mm for the first set and 2.50mm for the second set. The predictive powers of 15 empirical models from the literature were tested against the measured PWV for the period 1985 to 2007. The performances of these models varied. The proposed multilinear model from this study outperforms the overall performance of these 15 models.

Preliminary Heat Capacity and Vapor Pressure Measurements of 2D 4He on ZYX Graphite

We report preliminary heat capacity and vapor pressure measurements of the first and second layers of 4He adsorbed on ZYX graphite. ZYX is known to have much better crystallinity than Grafoil, the most commonly-used exfoliated graphite substrate, such as a ten-times larger platelet size. This allows us to distinguish different phases in 2D 4He much more clearly and may provide qualitatively different insights into this system. We found a significantly asymmetric density-dependence of the heat-capacity peak associated with the $\sqrt{3}\times\sqrt{3}$ phase formation comparing with that obtained with Grafoil. The 2nd-layer promotion density is determined as 11.8±0.3 nm−2 from the heat-capacity measurement of low density samples in the 2nd layer and vapor pressure measurement.

Comparisons between Hygroscopic Measurements and UNIFAC Model Predictions for Dicarboxylic Organic Aerosol Mixtures

Hygroscopic behavior was measured at 12°C over aqueous bulk solutions containing dicarboxylic acids, using a Baratron pressure transducer. Our experimental measurements of water activity for malonic acid solutions (0–10 mol/kg water) and glutaric acid solutions (0–5 mol/kg water) agreed to within 0.6% and 0.8% of the predictions using Peng’s modified UNIFAC model, respectively (except for the 10 mol/kg water value, which differed by 2%). However, for solutions containing mixtures of malonic/glutaric acids, malonic/succinic acids, and glutaric/succinic acids, the disagreements between the measurements and predictions using the ZSR model or Peng’s modified UNIFAC model are higher than those for the single-component cases. Measurements of the overall water vapor pressure for 50 : 50 molar mixtures of malonic/glutaric acids closely followed that for malonic acid alone. For mixtures of malonic/succinic acids and glutaric/succinic acids, the influence of a constant concentration of succinic acid on water uptake became more significant as the concentration of malonic acid or glutaric acid was increased.

Amine blends using concentrated piperazine

Blends using concentrated (25 35wt %) piperazine (PZ) were characterized as solvents for CO2 capture at typical coal flue gas conditions. The new blends are 6 m PZ/2 m hexamethylenediamine (HMDA), 6 m PZ/2 m diaminobutane (DAB), 6 m PZ/2 m bis(aminoethyl)ether (BAE), 5 m PZ/2 m aminoethylpiperazine (AEP), and 5 m PZ/2.3 m 2-amino 2-methyl-propanol (AMP). The CO2 absorption rate of the blends was measured using a wetted wall column (WWC). The CO2 vapor liquid equilibrium was measured at 20–160°C. Amine vapor pressure measurements are reported to show potential volatility at practical conditions. The rate of thermal degradation was measured from 135 to 175°C. Oxidative degradation was measured in two semi-batch experiments with different O2 rate at absorber conditions. Advanced parameters are introduced to demonstrate the overall rate and energy performance of the solvents in a real process. The performance of 7 m MEA, 8 m PZ, and six other competitive PZ blends are evaluated based on previous results and presented as basis of comparison.All of the PZ blends have better solubility window than 8 m PZ, with no precipitation at rich loading. The absorption rate of the concentrated PZ blends is similar to that of 8 m PZ and 1.5 2 times higher than 7 m MEA; the solvent capacity is about 20% lower than 8 m PZ and 15% higher than 7 m MEA. Among all of the PZ blends, 5 m PZ/5 m MDEA has the best combination of rate and capacity. Blends using HMDA, AEP, BAE, AMP, and MEA have a high heat of CO2 absorption. Blends using MEA, MDEA, and AMP are not thermally stable, while other blends have good thermal stability. The combination of high Habs and thermal stability leads to good overall energy performance, which is observed for 6 m PZ/2 m HMDA, 6 m PZ/2 m BAE and 5 m PZ/2 m AEP. AMP has relatively high volatility, whereas BAE and AEP are expected to have low volatilities. The only drawback of 6 m PZ/2 m BAE is its high oxidation rate. 6 m PZ/2 m HMDA and 6 m PZ/2 m DAB have good oxidative stability.PZ blends using low viscosity amines will have high absorption rate, and tertiary and hindered amines will contribute to high capacity. Amines with high pKa will improve the blend Habs. For thermal stability, alkanolamines should not be used together with PZ. Highly viscous blends such as 6 m PZ/2 m HMDA are expected to have 10–20% higher cost associated with cross-exchanger design and operation than solvents with low viscosity.