Capacitance Diaphragm Manometer Research Articles

Phase Transitions Equilibria of Five Dichlorinated Substituted Benzenes

This work reports an experimental study aiming to determine the thermodynamic properties of five chlorinated compounds with environmental impact. The vapor pressures of the crystalline phases of three isomers of dichlorobenzoic acid (2,4-, 2,5-, and 2,6-) and 2,6-dichlorobenzonitrile were measured at several temperatures using the Knudsen effusion technique. Another technique (a static method based on capacitance diaphragm manometers) allowed the measurement of the vapor pressures of both the crystalline and liquid phases of 2,4-dichlorobenzonitrile between 303.0 and 380.0 K. This latter technique also enabled the measurement of sublimation vapor pressures of 2,6-dichlorobenzonitrile over a larger range interval of temperatures, T = 328.7 and 391.8 K. The standard molar enthalpy, entropy, and Gibbs energy of sublimation (for all the compounds studied) and vaporization (for 2,4-dichlorobenzonitrile) were derived, at reference temperatures, from the experimental vapor pressure results. The temperatures and enthalpies of fusion and the isobaric heat capacities of the five crystalline-substituted benzenes were determined using differential scanning calorimetry. The contributions of the three substituents (-COOH, -CN, and -Cl) to the sublimation thermodynamic properties of the compounds studied were discussed.

Study on the volatility of four benzaldehydes

This work reports the experimental determination of relevant thermodynamic properties of four benzaldehydes. The vapor pressures of both crystalline and liquid phases (including supercooled liquid) of syringaldehyde, 3,4,5-trimethoxybenzaldehyde, 4-(dimethylamino)benzaldehyde and of the liquid phase of veratraldehyde were determined using a static method based on capacitance diaphragm manometers. Additionally, the sublimation vapor pressures of the four compounds were also determined at different temperatures, using the Knudsen mass-loss effusion method. The experimental results allowed accurate determination of the standard molar enthalpies, entropies and Gibbs energies of sublimation and of vaporization for the benzaldehydes studied, at reference temperatures, allowing phase diagram representations of the (p,T) results, in the neighborhood of the triple point of the four compounds. Their temperatures and molar enthalpies of fusion were determined using differential scanning calorimetry and were compared with the ones obtained indirectly through vapor pressure measurements. Using high-precision drop calorimetry, the standard isobaric molar heat capacities of the four crystalline benzaldehydes were determined at 298.15 K. The enthalpy of the intermolecular hydrogen bond OH…O in the crystalline phase of syringaldehyde was estimated.

Thermodynamic Stability of Fenclorim and Clopyralid.

The present work reports an experimental thermodynamic study of two nitrogen heterocyclic organic compounds, fenclorim and clopyralid, that have been used as herbicides. The sublimation vapor pressures of fenclorim (4,6-dichloro-2-phenylpyrimidine) and of clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) were measured, at different temperatures, using a Knudsen mass-loss effusion technique. The vapor pressures of both crystalline and liquid (including supercooled liquid) phases of fenclorim were also determined using a static method based on capacitance diaphragm manometers. The experimental results enabled accurate determination of the standard molar enthalpies, entropies and Gibbs energies of sublimation for both compounds and of vaporization for fenclorim, allowing a phase diagram representation of the (p,T) results, in the neighborhood of the triple point of this compound. The temperatures and molar enthalpies of fusion of the two compounds studied were determined using differential scanning calorimetry. The standard isobaric molar heat capacities of the two crystalline compounds were determined at 298.15 K, using drop calorimetry. The gas phase thermodynamic properties of the two compounds were estimated through ab initio calculations, at the G3(MP2)//B3LYP level, and their thermodynamic stability was evaluated in the gaseous and crystalline phases, considering the calculated values of the standard Gibbs energies of formation, at 298.15 K. All these data, together with other physical and chemical properties, will be useful to predict the mobility and environmental distribution of these two compounds.

Thermodynamic Properties of Moldy-Musty Contaminants of Wine

This paper reports thermodynamic properties of phase transitions of 2,4,6-trichloro and 2,4,6-tribromo anisoles and of 2,4,6-tribromophenol. The vapor pressures of both crystalline and liquid phases (including supercooled liquid) of the three compounds were measured, respectively, in the temperature ranges T = (297.1 to 368.3) K, T = (330.7 to 391.7) K, and T = (336.5 to 401.7) K, using a static method based on capacitance diaphragm manometers. Moreover, the sublimation vapor pressures of 2,4,6-tribromophenol were also measured in the temperature interval (307.2 to 329.2) K, using a Knudsen mass-loss effusion technique. The standard molar enthalpies, entropies, and Gibbs energies of sublimation and of vaporization, at reference temperatures, were derived from the experimental results as well as the (p,T) values of the triple point of each compound. The temperatures and molar enthalpies of fusion of the three benzene derivatives were determined using differential scanning calorimetry and were compared with...

Vapour pressures and thermodynamic stability of the three aminophenol isomers

The Knudsen mass-loss effusion method was used to determine the sublimation vapour pressures, at different temperatures, of ortho and para aminophenols in the temperature intervals T = (321.1 to 343.3) K and T = (337.2 to 359.2) K, respectively. The vapour pressures of crystalline meta-aminophenol were measured using the referred to above technique, between (321.4 and 343.3) K, and a static method, based on capacitance diaphragm manometers, between (354.4 and 391.8) K. The latter technique was also used to measure the liquid vapour pressures of this isomer over the temperature range T = (370.0 to 423.3) K. The experimental results enabled the determination of the standard (po = 0.1 MPa) molar enthalpies, entropies and Gibbs energies of sublimation, at T = 298.15 K, of the three compounds, and of vaporization of the meta isomer. The standard enthalpies of formation in the gaseous phase were calculated using quantum chemical calculations and also by combining literature results of enthalpies of formation in the crystalline phase with the sublimation enthalpies results determined in this work. Gas-phase absolute entropies and heat capacities of the three compounds studied were also calculated using theoretical methods. The standard Gibbs energies of formation in crystalline and gaseous phases were determined and used to evaluate the thermodynamic stability of the three isomers in standard conditions. DSC analysis enabled the determination of the temperature and molar enthalpies of fusion of the compounds studied.

Vapor Pressures and Gibbs Energies of Formation of the Three Hydroxybenzaldehydes

This work reports experimental sublimation and vaporization vapor pressures at different temperatures of the three isomers of hydroxybenzaldehyde. A static method based on capacitance diaphragm manometers was used to measure the vapor pressures of both (crystalline and liquid) condensed phases of ortho, meta, and para hydroxybenzaldehydes, through the temperature ranges T = (264.6 to 341.7) K, T = (324.9 to 419.4) K, and T = (334.9 to 429.4) K, respectively. The Knudsen mass-loss effusion technique was also used to determine the vapor pressures of crystalline meta and para isomers in the temperature intervals T = (309.1 to 331.2) K and T = (319.1 to 341.2) K, respectively. The obtained results enabled the determination of the standard molar enthalpies and entropies of sublimation and of vaporization, at chosen reference temperatures, as well as the (p,T) values of the triple point of the compounds studied. The temperatures and enthalpies of fusion were determined from differential scanning calorimetry. Th...

Vapor Pressures of Four Methyl Esters of Substituted Benzoic Acids. The Intermolecular Hydrogen Bond OH···O

This paper reports experimental vapor pressures of condensed phases of methyl p-cyano, p-formyl, p-nitro, and p-(methylamino) benzoates measured over the temperature ranges (303.9 to 393.0) K, (303.1 to 388.2) K, (319.0 to 415.8) K, and (332.9 to 392.4) K, respectively, using a static method based on capacitance diaphragm manometers. The Knudsen mass-loss effusion technique was also used to measure the vapor pressures of crystalline methyl p-(methylamino)benzoate in the temperature range (317.1 to 339.2) K. These results enabled the calculation of the standard molar enthalpies and entropies of sublimation and of vaporization, at reference temperatures as well as the (p,T) values of the triple point of each compound. The temperatures and molar enthalpies of fusion were determined using differential scanning calorimetry and were compared with the values derived indirectly from the vapor pressure measurements. The enthalpies of the intermolecular hydrogen bonds O–H···O in the crystalline phase of the parent ...

The influence of the halogen atoms and acetyl group on vapour pressures and related properties of the p-haloacetophenones

This work reports experimental vapour pressures at different temperatures of four halogenated acetophenones. The liquid phase vapour pressures of p-fluoro and p-chloro acetophenones were measured, respectively, across the temperatures ranges (255.1 to 310.2)K and (271.6 to 335.0)K, using a static method based on capacitance diaphragm manometers. This experimental technique was also used to measure the vapour pressures of both (crystalline and liquid) condensed phases of p-bromo- and p-iodoacetophenones, respectively, through the temperature intervals (295.3 to 378.4)K and (313.1 to 402.0)K. The temperatures and molar enthalpies and entropies of fusion of the four p-halogenated acetophenones were determined using differential scanning calorimetry. The standard molar enthalpies, entropies and Gibbs energies of sublimation and of vaporisation, at selected reference temperatures, were derived from the experimental results. The contributions of the acetyl group and of the constituent halogen atoms to these thermodynamic properties were also predicted through correlation equations.

Thermodynamic properties of fluoranthene: An experimental and computational study

Vapour pressures of both crystalline and liquid (including super-cooled liquid) phases of fluoranthene were measured using a pressure gauge (capacitance diaphragm manometer) over the temperature range (348.8 to 404.3)K yielding accurate determination of enthalpies and entropies of sublimation and vaporisation. Enthalpy of sublimation was also determined using Calvet microcalorimetry. The enthalpy of fusion was derived from vapour pressure results and from d.s.c. experiments. Static bomb calorimetry was used to determine the enthalpy of combustion of fluoranthene from which the standard enthalpy of formation in the crystalline phase was calculated. The enthalpy of formation in the gaseous phase was calculated combining the result derived for the crystalline phase with the enthalpy of sublimation determined from the vapour pressure measurements. Computational results of the enthalpies of formation of fluoranthene and fluorene were also calculated at the G3 and G4 levels, and compared with the experimental values.

The characterization of new VGMS (vacuum gauge metrology system) by the traceability of multi stage static expansion system

In this study, the design and characterization of vacuum gauge calibration system which was upgraded is described. A capacitance diaphragm manometer is used to characterize the system performance. 1Torr and 10Torr CDGs are available to compare the performance of VGMS system which is traceable to the static expansion system generating calibration pressures in the range of 9×10−4Pa up to 1×103Pa. The working pressure range of VGMS system is 1×10−4–1.3×105Pa. It is used a comparison method as a calibration process. After making the system description and process, the results of calibrations included uncertainty values are given to determine long term instability and show the performance of the system.

Fluorene: An extended experimental thermodynamic study

This work reports new experimental thermodynamic results on fluorene. Vapor pressures of both crystalline and liquid phases were measured using a pressure gauge (capacitance diaphragm manometer) and Knudsen effusion methods over a wide temperature range (292.20 to 412.16) K yielding accurate determination of enthalpy and entropy of sublimation and of vaporization. The enthalpy of sublimation was also determined using Calvet microcalorimetry. The enthalpy of fusion was derived from vapor pressure results and from d.s.c. experiments. Static bomb calorimetry was used to determine the enthalpy of combustion of fluorene from which the standard enthalpy of formation in the crystalline phase was calculated. The enthalpy of formation in the gaseous phase was calculated combining the result derived for the crystalline phase with the enthalpy of sublimation.

Energetic and Structural Study of Diphenylpyridine Isomers

The energetic and structural study of three diphenylpyridine isomers is presented in detail. The three isomers, 2,6-, 2,5-, and 3,5-diphenylpyridines, were synthesized via Suzuki-Miyaura methodology based on palladium catalysis, and the crystal structures of the isomers were obtained by X-ray diffraction. The relative energetic stabilities in the condensed and gaseous phases as well as volatilities and structures of the three studied isomers were evaluated, regarding the position of the phenyl groups relative to the nitrogen atom of the pyridine ring. The temperature, standard molar enthalpies, and entropies of fusion were measured and derived by differential scanning calorimetry. The vapor pressures of the considered isomers were determined by a static apparatus based on a MKS capacitance diaphragm manometer. The standard molar enthalpies, entropies, and Gibbs energies of sublimation, at T = 298.15 K, were derived, and the phase diagram near the triple point coordinates were determined for all isomers. The standard (p(o) = 0.1 MPa) molar enthalpies of combustion of all crystalline isomers were determined, at T = 298.15 K, by static bomb combustion calorimetry. The standard molar enthalpies of formation, in the crystalline and gaseous phases, at T = 298.15 K, were derived. The experimental results for the energetics in the gaseous phase of the three compounds were compared and assessed with the values obtained by ab initio calculations at different levels of theory (DFT and MP2) showing that, at this level of theory, the computational methods underestimate the energetic stability, in the gaseous phase, for these molecules. In order to understand the aromaticity in the central ring of each isomer, calculations of NICS (B3LYP/6-311G++(d,p) level of theory) values on the pyridine ring were also performed.

Zero shift in the differential capacitance diaphragm gauges due to the change in line pressure

This paper describes the results of experiments concerning the effect of line pressure on the zero stability of the differential capacitance diaphragm manometers. It is observed that in capacitance manometers with single-sided configuration, the zero shift value varies with different gases for a particular line pressure change and is directly proportional to the dielectric constant of the gases. For the four sensors studied, it is found that the zero shift is positive in nature and varies linearly with the change in line pressure. The linear relationship obtained on the basis of the experimental results is found useful in determining the zero shift values for any gas at any line pressure change. The zero shift at different line pressures with various gases in differential capacitance diaphragm manometers is of great importance for the metrological applications.

Automated system for measuring leak standards

An inexpensive, automatic measurement system for standard leaks has been developed and tested. The principal of operation is pressure rise in a measurement chamber held at a low pressure. This design minimizes temperature effects, considerably improving performance over what would be achievable using a similar technique at atmospheric pressure. Provision is made for determining working measurement volume by expansion from a calibrated reference volume incorporated in the piping. Demonstrated operating range is ∼10−8–10−4 atm cm3/s (10−13–10−9 mol/s) regardless of the gas being used. The sensing element is an industrial grade capacitance diaphragm manometer. A very inexpensive home computer performs all control and calculations. The accuracy and performance of this system have been verified through comparison to other leak calibrators.

Sensitivity of capacitance diaphragm manometers to static magnetic fields

The sensors of the two capacitance diaphragm manometers investigated in this study appear to have no significant dependence upon exposure to static magnetic fields. Subsequent use of the sensors in the near-field environment of the PDX tokamak showed the sensors could perform unshielded in a magnetic environment, however, it was found necessary to magnetically shield the associated signal-conditioning electronics.

The vapour pressure of benzoic acid

Vapour pressures of benzoic acid were measured in the temperature range 316 to 391 K with a capacitance diaphragm manometer. The results were fitted to a three-parameter equation: R 1n(p/p °) = −δG °(θ)/θ+ δH(θ)(1/θ−1/T)+δC ° p(θ){θ/T−1 +1n(T/θ)} For the mean temperature θ = 353.15 K the thermodynamic-function changes are evaluated as: ΔG o(353.15 K) = −(10151±5) J · mol −1, ΔH o(353.15 K) = (89.45±0.05) kJ · mol −1, and ΔC p o(353.15 K) = −(48.4±5.0) J · K −1 · mol −1. A review of the literature data is given.

Check on the linearity of a capacitance diaphragm manometer between 10−4 and 10−1 Torr

A procedure is outlined whereby the pressure measurement linearity of a certain class of capacitance diaphragm manometers can be evaluated. Data are presented to illustrate the technique as applied to the 10−4–10−1 Torr pressure range.

In Situ Vapor Pressure Measurement for Low Temperature Thermometry

By use of a capacitance diaphragm manometer operated at low temperatures, it is possible to measure the vapor pressure of cryogenic liquids without the uncertainties introduced by thermomolecular pressure gradients (thermal transpiration). Since the zero of this manometer is more stable at low temperature than at room temperature, useful sensitivity is increased. Because of the increased sensitivity at low pressure as well as great convenience and simplicity, this technique appears to have wide application in precise vapor pressure thermometry and similar work.