M.B. Ewing

The ebulliometric method of vapour-pressure measurement: vapour pressures of benzene, hexafluorobenzene, and naphthalene

Abstract Experimental details of the comparative ebulliometric method for measurement of vapour pressures, together with results of measurements on benzene, hexafluorobenzene, and naphthalene, are given. The results are compared with others in the literature, and the accuracy of the method is discussed.

The effect of initiation method on the size, monodispersity and shape of gold nanoparticles formed by the Turkevich method

The growth of gold nanoparticle (Au NP) colloids was initiated either thermally, by sonolysis, microwave (MWA) or hard ultra-violet (UVC; 254 nm) irradiation. The solutions were formulated analogous to Turkevich et al. and contained an auric acid gold source and different amounts of sodium tri-citrate reductant and stabiliser. A comparison of the initiation methods, using reagent solutions of equal concentration, was used to make gold nanoparticles. This showed marked differences in the final colloid, with variance in the monodispersity, size and shape of particles with initiation method. The physical size, shape and monodispersity of colloids formed were ascertained from transition electron microscopy (TEM) imaging. Properties such as average particle size and shape were directly related to changes in the surface plasmon resonance (SPR) band from UV-visible spectra. We demonstrate how a variety of simple initiation methods can be used to synthesise near monodisperse gold nanoparticles. More importantly, it is shown how the initiation method is fundamental to the eventual particle size of the resulting colloids; with sizes ranging from 11.0–11.9 nm in thermal reactions, 16.9–18.0 nm in sonolysis reactions, 11.3–17.2 nm in MWA reactions and 8.0–11.2 nm in UVC initiated reactions. Possible reaction pathways and mechanisms are put forward to explain these marked differences.

Thermophysical properties of alkanes from speeds of sound determined using a spherical resonator 5. 2-Methylbutane at temperatures in the range 260 K to 320 K and pressures in the range 2.8 kPa to 80.9 kPa

The speeds of sound in gaseous 2-methylpropane have been obtained at temperatures between 251 K and 320 K from measurements of the frequencies of the radial acoustic modes of a spherical cavity. Perfect-gas heat capacities and second and third acoustic virial coefficients have been determined from the results. Second and third coefficients of the virial equation of state have been calculated from the acoustic virial coefficients. We also report vibrational relaxation times for 2-methylpropane.

An apparatus based on a spherical resonator for measuring the speed of sound in gases at high pressures. Results for argon at temperatures between 255 K and 300 K and at pressures up to 7 MPa

An apparatus, based on a spherical resonator, suitable for measurements with gaseous mixtures at temperatures in the range 250 K to 350 K and pressures up to 21 MPa is described. Speeds of sound in argon at pressures below 7 MPa have been determined. These measurements have provided evidence for coupling between radial gas motion and non-radical shell motion. Second acoustic virial coefficients for argon obtained from several resonators are compared.

The room temperature formation of gold nanoparticles from the reaction of cyclohexanone and auric acid; a transition from dendritic particles to compact shapes and nanoplates

A new straightforward method for the synthesis of gold nanoparticles from addition of cyclohexanone to aqueous solutions of auric acid at room temperature is presented. By understanding this process we have discovered a new organic chemistry transformation reaction for converting cyclic ketones to α-chloro ketones and a mechanism for the nanoparticle formation. Contrary to conventional gold nanoparticle syntheses, the reaction “self-initiates” at room temperature and forms an increasingly red solution over ≈60 minutes. By studying the gold colloids formation using transmission electron microscopy it was observed that large dendritic (63 ± 21 nm diameter) structures made of clustered particles (6 ± 1 nm) were initially formed. These dendritic particles then compacted into an array of denser shapes that slowly increase in size until the reaction is complete. The most prominent shapes observed were spheres (43 ± 7 nm); other shapes included dodecahedra (39 ± 10 nm) triangular (≈50 nm in height) and hexagonal (≈70 nm wide) nanoplates. The solution was stable to precipitation for over 3 months. During this period the nanoplate structures substantially increased in size (triangular ≈ 250 nm, hexagonal ≈ 320 nm) whereas other structures showed no further growth. X-ray diffraction studies demonstrated that the gold nanoparticles were crystalline. The formation of the 2-chlorocyclohexanone by-product was observed in solution phase 1H & 13C NMR, gas phase chromatography and IR spectroscopy. A mechanism is presented to account for this by-product and the reduction of auric acid to gold.

Speeds of sound, perfect-gas heat capacities, and acoustic virial coefficients for methane determined using a spherical resonator at temperatures between 255 K and 300 K and pressures in the range 171 kPa to 7.1 MPa

The speed of sound in gaseous methane has been obtained at temperatures between 255 K and 300 K and pressures in the range 171 kPa to 7 MPa from measurements of the frequencies of the radial acoustic modes of a spherical cavity. The measurements provide further evidence for coupling between radial gas modes and non-radial shell motion. Perfect-gas heat capacities and second and third acoustic virial coefficient have been determined from the results. The expermental perfect-gas heat capacities deviate by no more than 0.002 5 · R from values obtained from spectroscopic information. The second acoustic virial coefficient differ by 0.7 6 cm 3 · mol −1 from those calculated using ( p , V m , T ) results. We also report vibrational relaxation times for methane determined from the line widths of the radial modes. The u ( T, p ) results, which we estimate are accurate to ± 10 −5 · u , are compared with values calculated from six equations of state including those of industrial importance for calculating mass-flow rate through sonic nozzles.

Vapour pressures of 2-methylbutane determined using comparative ebulliometry

The vapour pressure of 2-methylbutane between 255 K and 323 K has been obtained from comparative ebulliometric measurements. Our results have been combined with those already published to obtain a correlation for the vapour pressure from 255 K to the critical temperature.

Heat capacities and second virial coefficients for gaseous methanol determined from speed-of-sound measurements at temperatures between 280 K and 360 K and pressures from 1.03 kPa to 80.5 kPa

The speed of sound in gaseous methanol has been obtained at 12 temperatures between 260 K and 360 K at pressures in the range 1.03 kPa to 80.5 kPa from measurements of the frequencies of the radial acoustic modes of a spherioal cavity. Perfect-gas heat capacities and second acoustic virial coefficients have been determined from the results. The heat capacities at temperatures between 280 K and 320 K lie about 0.002 · C pg p , m above those calculated from spectroscopic information, while at 360 K, the worst case, the difference is 0.01 · C pg p , m . Second virial coefficients of the equation of state have been calculated from the acoustic virial coefficients. These values are compared with values reported in the literature.

The (liquid + liquid) critical state of (cyclohexane + methanol) V. Use of an asymmetric potential to represent excess volumes in the critical region

The excess molar volume of {xc-C6H12 + (1 − x)CH3OH} near its (liquid + liquid) critical state has been represented by a parametric potential that includes terms to allow for the asymmetry that exists in any real fluid. The results show that the excess volume in the range |x − xc| < 0.25 can be represented to within its experimental accuracy. The value of the system-dependent parameter a and the asymmetry parameter L11, agree with the values obtained from an analysis of the excess enthalpy in the same region to well within experimental error. In addition, it has been possible to obtain an estimate of the dependence of μ12c on pressure.