Table 1 - uploaded by Eckard Bich
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Results of new relative measurements on the vapor of acetic acid are reported. The measurements were based on a single calibration at room temperature with a theoretically calculated viscosity value of argon. Nineteen isochoric series, differing in density, were performed in an all-quartz oscillating-disk viscometer from 298 to 598 K and for densit...
Citations
... Although in the HT experiment the temperature was not very high (457 K), the decomposition could be stimulated by brass surfaces along the rather long channel of the used evaporator [8]. Earlier even in an all-quartz apparatus for viscosity measurements thermal decomposition of AA was detected at about 480 K and low densities of the substance [28], which resembles our experimental conditions. Parameters of AA determined from both data sets and the corresponding best theoretical values are collected in Table 3. ...
We have designed and constructed a combined experimental setup for synchronous measurements of electron diffraction patterns and mass-spectra of gas samples. Test measurements have been performed for acetic acid at two temperatures, 296 and 457 K, respectively. Electron diffraction data have been analysed taking into account mass spectra measured in the same experiments. From the diffraction intensities molecular structures and mole fractions of the acetic acid monomer and dimer have been refined. The obtained results demonstrate the importance of measuring mass spectra in gas electron diffraction experiments. In particular, it is possible to detect the sample decomposition, which can be used for the optimization of experimental conditions and for the data interpretation. The determined in this work length of the hydrogen bond in the acetic acid dimer, re(O<sup>...</sup>H) = 1.657(9) Å, is in good agreement with modern theoretical predictions. We recommend to measure diffraction patterns of acetic acid for the calibration of the sample pressure in the diffraction point.<br
Low-density viscosity measurements on eight gaseous and vapor mixtures between 297 K and 638 K, originally performed using oscillating-disk viscometers, were re-evaluated after improved re-calibration. The relative combined expanded (\(k=2\)) uncertainty of the re-evaluated data are 0.2 % near room temperature and increases to 0.3 % at higher temperatures. The re-evaluated data were converted into quasi-isothermal viscosity data. Those for carbon dioxide–ethane, propane–isobutane, and methanol–triethylamine could be used to determine the zero-density and initial density viscosities, \(\eta _\text{mix}^{(0)}\) and \(\eta _\text{mix}^{(1)}\). The \(\eta _\text{mix}^{(0)}\) data for carbon dioxide–ethane agree almost perfectly with viscosity values theoretically computed for the nonspherical potential of the intermolecular interaction. Three procedures were applied to determine the interaction viscosity, \(\eta _{ij}^{(0)}\), and the product of molar density and diffusion, \((\rho D_{ij})^{(0)}\), both in the limit of zero density. In a first procedure only applicable for the three mentioned mixtures, \(\eta _{ij}^{(0)}\) values were derived from the \(\eta _\text{mix}^{(0)}\) data additionally requiring \(A_{ij}^*\) values (ratio between effective cross sections of viscosity and diffusion). This procedure should provide the best results when it is possible to use \(A_{ij}^*\) values computed for the nonspherical potential. This was only feasible for carbon dioxide–ethane, for which the experimentally based \(\eta _{ij}^{(0)}\) and \((\rho D_{ij})^{(0)}\) data perfectly agree with theoretically calculated values. For the seven other mixtures, the resulting data represent only preliminary ones. The second and third procedures were applied to the six vapor mixtures methanol with triethylamine, benzene, and cyclohexane and benzene with toluene, p-xylene, and phenol. The resulting data showed a density dependence and were extrapolated to zero density.
Previously published experimental viscosity data at low density, originally obtained using all-quartz oscillating-disk viscometers for R134a and six vapors of aromatic hydrocarbons in the temperature range between 297 K and 631 K at most, were re-evaluated after an improved re-calibration. The relative combined expanded ( $$k=2$$ k = 2 ) uncertainty of the re-evaluated data are 0.2 % near room temperature and increases to 0.3 % at higher temperatures. The re-evaluated data for R134a as well as for the vapors of mesitylene, durene, diphenyl, fluorobenzene, chlorobenzene, and p -dichlorobenzene were arranged in approximately isothermal groups and converted into quasi-isothermal viscosity data using a first-order Taylor series in temperature. Then, the data for R134a were evaluated by means of a series expansion truncated at first order to obtain the zero density and initial density viscosity coefficients, $$\eta ^{(0)}$$ η ( 0 ) and $$\eta ^{(1)}$$ η ( 1 ) . For the six aromatic vapors, the Rainwater–Friend theory for the initial density dependence of the viscosity was used to derive $$\eta ^{(0)}$$ η ( 0 ) values. Finally, reliable $$\eta ^{(0)}$$ η ( 0 ) and also $$\eta ^{(1)}$$ η ( 1 ) values for R134a were selected as reference values in the measured temperature range to be applied when generating a new viscosity formulation.
Previously published experimental viscosity data at low density, originally obtained using all-quartz oscillating-disk viscometers for 12 gases and vapors in the temperature range between 297 K and 691 K, were re-evaluated after an improved re-calibration. The relative combined expanded (k = 2) uncertainty of the re-evaluated data is 0.2% near room temperature and increases to 0.3% at higher temperatures. The re-evaluated data for sulfur hexafluoride, methanol, n-pentane, n-hexane, n-heptane, neopentane, cyclohexane, benzene, toluene, p-xylene, phenol, and triethylamine were arranged in approximately isothermal groups and converted into quasi-isothermal viscosity data using a first-order Taylor series in temperature. Then, they were evaluated by means of a series expansion truncated at first order to obtain the zero-density and initial density viscosity coefficients, η⁽⁰⁾ and η⁽¹⁾. When the number of isothermal data or their quality was not adequate, the Rainwater–Friend theory for the initial density dependence of the viscosity was additionally used to derive η⁽⁰⁾ and η⁽¹⁾ values. Finally, reliable η⁽⁰⁾ and η⁽¹⁾ values, preferably obtained from the isotherms, were recommended as reference values for the 12 gases and vapors in the measured temperature range to be applied when generating any new viscosity formulation.
We have designed and constructed a combined experimental setup for synchronous measurements of electron diffraction patterns and mass-spectra of gas samples. Test measurements have been performed for acetic acid at two temperatures, 296 K and 457 K. Electron diffraction data have been analyzed taking into account mass spectra measured in the same experiments. From the diffraction intensities, molecular structures and mole fractions of the acetic acid monomer and dimer have been refined. The obtained results demonstrate the importance of measuring mass spectra in gas electron diffraction experiments. In particular, it is possible to detect the sample decomposition, which can be used for the optimization of experimental conditions and for the data interpretation. The length of the hydrogen bond in the acetic acid dimer determined in this work, re(O⋯H) = 1.657(9) Å, is in good agreement with modern theoretical predictions. We recommend measuring the diffraction patterns of acetic acid for the calibration of the sample pressure in the diffraction volume.
