Determination Of Vapor Pressure Research Articles

Vapor pressure determination for several polychlorodioxins by two gas saturation methods

Vapor pressures of several individual chlorodioxins are determined by two gas saturation methods, one using 2 – 3 mg of unlabelled material with GC-FID analysis (Method 1), and the other, 10 – 100 ug of 14C-compounds (Method 2). Values from Method 1 can be used for calculation of thermodynamic parameters, but those from method 2 are adequate for environmental modelling. The temperature ranges were chosen (a) Method 1: to allow extrapolation of vapor pressures over a wide temperature range, and (b) Method 2: for environmental relevance.

Measurement of low vapour pressures according to the Knudsen effusion method

The exact measurement of low vapour pressures during recent years has become increasingly important, particularly for environmental problems caused by organic chemicals. Not only for this but for many other fields information about the phase transition solid - gas and liquid - gas is of great scientific interest. In this work a brief survey of the determination of vapour pressures with thermo-analytical methods is made. In particular the thermo-gravimetric vapour pressure measurements by means of a Knudsen cell and a newly developed vapour pressure balance for exact measurement of very low vapour pressures are described. Applications for organic materials (fungicides, benzoic acid, oils) are discussed.

Determination of vapor pressures for chloroguaiacols, chloroveratroles, and nonylphenol by gas chromatography

Vapor pressures of six chlorinated phenols were measured by capillary gas chromatography using a 1.0-m BP-1 bonded phase column. GC-determined vapor pressures (P GC) were correlated with known liquid-phase vapor pressures (P L) by the equation: Log P GC = 1.026 Log P L — 0.132, r 2 = 0.975 (vapor pressures in pascals). This relationship was used to estimate P L for chloroguaiacols, chloroveratroles, and 4-nonylphenol from their experimental P GC.

Determination of amphetamine, cocaine, and heroin vapour pressures using a dynamic gas blending system and gas chromatographic analysis

A dynamic gas blending system was used to generate controlled vapour concentrations of amphetamine, cocaine, or heroin. An adsorption – thermal desorption – gas chromatographic procedure was developed and used to measure the output vapour concentrations. The vapour pressure of amphetamine at 20 °C was determined, and vapour pressures as a function of temperature have been measured for cocaine and heroin.

Temperature variation of sodium and mercury partial pressures over sodium amalgams

The partial pressures of Na, Na2, Hg over sodium amalgams are described for sodium mole fractions 0.55-1.00 over the range 700-1300 K. These data are extrapolated from some recently published results of the determination of the total vapour pressure over sodium amalgams and the activity of sodium in the liquid amalgams. The data are essential for calculation of the total vapour pressure and vapour phase composition above sodium amalgams in discharge lamps where the dose is partially evaporated.

Eine einfache Methode zur Bestimmung von Dampfdrücken

AbstractQuantitative headspace analysis represents a simple method for the determination of vapor pressures. The method is based on the measurement of the substance concentration in the saturated vapor phase (headspace) which stays in equilibrium with the condensed phase. During the procedure the total amount of substance being present in a defined volume of vapor is collected on an adsorbent and quantified either by gravimetry or, after desorption from the carrier, by chromatography. The presented method delivers good results in a wide range of vapor pressures between 1 · 10−5 and 1 · 104 Pa.

Determination of vapour pressures down to 0.01 Pa by headspace gas-chromatography

The application of automated headspace gaschromatography for the determination of vapour pressures is described. The vapour pressures determined at different temperatures for 1-chloronaphthalene, anthracene, γ-hexachlorocyclohexane and hexachlorobenzene agree well with the data from literature. The lower limit of applicability of the method is in the range of 0.01 Pa.

The determination of vapour pressures from relative volatilization rates

Relative volatilization loss rates for several different chemicals, mostly pesticides, in binary mixtures were determined in a temperature controlled cabinet. In some cases the loss rates were affected by the other chemical in the pair; this occurred with mixtures of liquids and solids and with mixtures of chemicals whose vapour pressures differed by more than a factor of ten. These effects can readily be avoided and the results indicate that the measurement of relative volatilization rates can be used to determine vapour pressures to within a factor of 3 in the range 10 −4 to 0.2 Pa. The loss rates measured for certain chemicals in different experiments were consistent to within 11% suggesting that under the controlled conditions used the reference compound does not need to be present in a mixture and the chemicals could be exposed singly if this were preferable.

Vapor pressure determination of arsenic activity in a molten Cu-Fe-S matte

The activity of As in a molten copper smelting matte of composition 35.0 mass pct Cu, 35.8 mass pct Fe, and 29.9 mass pct S has been derived from vapor pressure measurements at 1336 K. The initial As doping level was 1.6 mass pct. Mass spectrometry showed the principal vapor phase species to be As2; smaller amounts of AsS and S2 were also present. The activity coefficient of As in the matte, γ (As), was found to have the value 0.7 ±0.2 (mole fraction)-1 in the composition range studied. Activity values found in the present study were an order of magnitude smaller than those determined by an isopiestic method, and were about two orders of magnitude greater than those derived from measurements of As distribution between copper and white metal. The vapor pressure method is believed to be more direct and reliable; sources of error in the various methods are discussed.

An apparatus for precise measurement of gas solubility and vapor pressure of mixed solvents.

An apparatus and procedures are described for accurate determination of both gas solubility and vapor pressure of mixed solvents. A degassing process in which a mixed solvent is degassed thoroughly while keeping the composition unchanged is examined carefully. Measurement of the vapor pressure of the solvent is made before the introduction of the gas component, which increases the reliability of gas-solubih''ty data determined later. Experimental data are presented for the vapor pressures and nitrogen solubilities of binary mixtures of cyclohexane and benzene at 25°C. Reproducibilities are ±10 Pa and ±0.1% for the vapor pressures and the solubilities, respectively.

Contribution to the methodology of optimization and in-process control of some physical properties of pharmaceutical bulk substances and granulates

Many experts consider drug analysis exclusively as a chemical measuring technique. In the pharmaceutical industry, physical and physico-chemical parameters form an integrated part of the quality specification, because they play an essential role both in quality assurance and in the technical and economic aspects of production on the commercial scale. Such physical and physico-chemical properties are analysed by special, non-chemical methods. In their programme of systematic research in this field, the authors have elaborated new methods to test some essential properties of powders and granulates used in the production of compressed tablets. The following test and production methods have been developed: (i) the determination of flowing-sliding characteristics of granulates based on the measurement of the mass-flow (g s(-1)) and mass-flow density (g s(-1) cm(-2)); (ii) the determination of optimum granulometric parameters with regard to tablet diameter; (iii) the direct determination of the temperature-dependent equilibrium vapour pressure; and (iv) the compression of tablets under controlled temperature.

The mechanism and kinetics of evaporation from laser irradiated UO2 surfaces

A theoretical analysis of laser evaporation experiments for the determination of the high temperture saturated vapor pressure of uranium dioxide is presented. The interaction of laser radation with the condensed phase is discussed and the timescales involved in the energy equilibration processes are given. The mechanism of evaporation is described within the framework of the Terrace–Ledge–Kink model, where it is shown that by using symmetry properties of ionic crystal lattices, the surface Madelung potentials and binding energies of ions and neutral ionic units may be determined. Results are presented for NaCl, CsCl, and UO2 surfaces. Based on these calculations, general conclusions are drawn on the nature of the evaporating species. In addition, it is shown that the multispecies evaporation from uranium dioxide is fundamentally related to the amount of atomic and electronic disorder in the surface layer. The effects of the kinetics of surface reactions on the rate of evaporation are investigated. Parallel reaction paths such as direct evaporation from kink sites are treated in addition to surface diffusion followed by desorption series reactions. Finally, the possibility of producing superheated metastable surface layers under pulsed laser heating conditions is investigated using models for the kinetics of atomic and electronic disorder in the condensed phase.

A method for determining the volatility of active ingredients used in plant protection. Part III: The temperature relationship between vapour pressure and evaporation rate

AbstractHitherto it has been possible to determine vapour pressures only at a temperature of 20°C when using the method previously described for measuring the evaporation rate. The scope of application of the method has now been extended to temperatures of 30, 40, 50 and 60°C; because of the known temperature dependence of the vapour pressure, the vapour pressures at all the intermediate temperatures can then be calculated from these values.

Determination of vapour pressures of nine organic chemicals adsorbed on silicagel

The vapour pressures of nine organic chemicals adsorbed on silicagel were determined by a method which can be standardized. They were compared with those of the non-absorbed, free compounds (range 6 × 10 −3 – 7 × 10 4 Pa).

Application of a simple automatic null method for vapor pressure measurements by the torsion-Knudsen effusion-recoil technique

A description is given for a null method apparatus for continuous determination of vapor pressure by the ’’Torsion-Knudsen Effusion-Recoil’’ technique. The compensation system can be operated manually or automatically and is based on an industrial core-magnet moving-coil galvanometer with two windings (10 and 4000 ohms). The significant advantages of the method are: (a) there is constant sensitivity over the entire pressure range of Knudsen effusion conditions; (b) there is negligible mass load of the torsion element (max. 0.5 g); (c) it is possible to switch the integrated damping on or off at any time desired; (d) system oscillations can be initiated by current pulses; and (e) calibration of the torsion element can be done under high vacuum with improved accuracy. Precision of torsion calibration attained is 0.1%. Resolution is limited by the current measurement and is about 0.6%–0.9% of the picoammeter range.

Sublimation Behavior of Tris(2,2,6,6-tetramethyl-3,5-heptanedionato)lanthanoid(III)

Abstract Two fundamental experiments (to determine vapor pressures and vacuum sublimation-recrystallizing temperature zones) were undertaken on a series of remarkably volatile and thermally stable lanthanoid(III) chelates of 2,2,6,6-tetramethyl-3,5-heptanedione (Ln(thd)3) in order to obtain information about their sublimation behavior. Vapor pressures of these chelates were measured from 100 to 150 °C by means of a modified Knudsen effusion technique. Vacuum sublimation-recrystallizing temperatures were determined by using a sublimation apparatus with a continuous temperature gradient along its sublimation tube. The obtained enthalpies of sublimation were classified into three groups (La to Gd, Tb and Dy, and Ho to Lu), and the vacuum sublimation-recrystallizing temperature zones were divided into two sets (La to Tb, and Dy to Lu). The Tb and Dy chelates were also found to change thermally from a dimeric form to a monomeric form at a definite temperature. These results are explained in terms of the two different crystallizing forms of Ln(thd)3 chelates. Furthermore, the regularity in their sublimation behavior is discussed as a function of the atomic numbers of the lanthanoid metals, using thermochemical considerations.

A new technique for the determination of vapour pressures by the Knudsen effusion method

A description of a new technique-PENKER (Pendulum electronically balanced Knudsen-effusion recoil)-for vapour pressure measurements based on the Knudsen effusion method is given. The determination of vapour pressures by means of the suggested method is based on the recoil momentum of the evaporating species: the displacement of a pendulum, caused by the recoil of the escaping molecular beam, is automatically counteracted by an electromagnetic compensation system which is electronically controlled. The suggested method has clear advantages over the TORKER technique. It shows better mechanical stability, no oscillations, symmetrical furnace-cell configurations are possible, and there are no problems with electromagnetically induced cell rotations.

The Determination of mean vapour pressure from thermohygrograph charts

An expression is derived relating the mean vapour pressure to the mean values of temperature and relative humidity. After examining a number of typical thermohygrograph charts it is concluded that only a small error will normally be introduced by assuming that the mean vapour pressure is equal to the mean relative humidity multipliedby the saturated vapour pressure at the mean temperature. The situations where the use of correction factors will give a slight improvement in accuracy are also discussed. The mean vapour pressure may thus be determined from quantities readily obtained using a planimeter. This allows a very considerable saving in time and effort compared with obtaining a mean from vapour pressures calculated at several points on the chart from pairs of temperature and relative humidity readings.

Low vapor pressure determination by the radiotracer transpiration method

Low vapor pressure determination by the radiotracer transpiration method

On the vapor pressure of sulfuric acid

The vapor pressure of H2SO4 over 98.01 mass‐% sulfuric acid solution has been determined experimentally over the temperature interval 338 to 445 K. Values of the enthalpy and entropy changes upon vaporization deduced from the data accord well with other estimates available in the literature. Extrapolation to 99.0 mass‐% and 296.15 K allows us to confirm another recent vapor pressure determination, thereby supporting the conclusion that the vapor pressures most often used in nucleation calculations in the past are as much as an order of magnitude high.