Vapours

About: Vapours is a research topic. Over the lifetime, 1153 publications have been published within this topic receiving 15022 citations.

Theoretical aspects of the growth of a non-Kossel crystal from vapours: the role of advacancies.

Abstract: The growth of an arbitrary multicomponent non-Kossel crystal via the Burton-Cabrera-Frank mechanism is studied, considering the effect of advacancies and their recombination with adatoms on the surface. An analysis is carried out for two cases: growth due to vapours and growth due to chemical reactions. The analytical expressions are found for the rate of advancement of a group of equidistant steps and the crystal growth rate considering the properties of all the species involved in the growth process. Gallium nitride is used as an example to show that the effect is stronger at higher temperatures and in the presence of dopants that may increase the vacancy concentration. The impact of applied mechanical stress on the growth rate and mechanisms of its influence on the growth kinetics are discussed. It is demonstrated that the contribution of the vacancies to the total mass transfer depends on the type of applied stress. Tensile stresses increase the concentration of advacancies and total recombination rate, whereas compressive stresses lead to the opposite result. Some effects inherent to the multicomponent systems being considered are discussed.

The Thermal Properties and Heats of Adsorption of Films on Vitreous Silica

Abstract: As a contribution to the few existing data of sufficient accuracy for the calculation of heats of adsorption and other thermal properties of films on adsorbents simpler than charcoal, a series of measurements has been made of the adsorption of the vapours of benzene, acetone, and methyl alcohol on vitreous silica at temperatures between 70 and 25° C Previous experience with this adsorbent (Palmer and Clark 1935; Palmer 1937) showed that it was well suited for the purpose, particularly in respect to the very rapid attainment of equilibrium Complete isothermals at 25° for these vapours up to saturation pressures have already been investigated and recorded (Palmer 1937) The use of vapours rather than gases not only admits of experimental simplicity, but has the further advantage that the free energy of adsorption (or adsorption potential) is immediately calculable from the relative pressure at equilibrium It is hoped that the selection of substances is representative, in that they are respectively non-polar but polarizable, polar but non-associated, polar and associated These molecular distinctions appear prominently in the properties of the adsorption films Experimental The preparation of the silica adsorbent, manipulation, and methods of measurement were in principle the same as those previously described, with the following modifications The volumenometric portion of the apparatus, including the manometer bulbs b 1 and b 2 (fig 1; cf Palmer 1937, fig 1) was housed in an air thermostat T 1 regulated to 42·5°, and the horizontal adsorption tube A immersed in a water thermostat T 2 that could be set at temperatures ranging from 70 to 20° Connecting tubes were kept at 43° by means of electrically heated wrapping wire Since there was a maximum temperature difference of only about 20° along the tube t (of 1 mm bore) and a pressure of vapour never less than about 1 mm, no correction for thermal pressure difference was necessary (see also below, p 194) The powdered adsorbent weighed about 15 g and exposed about 7 sq m of surface; its exact specific surface was determined by the rate of solution in hydrofluoric acid, as previously described (Palmer and Clark 1935)

Process and apparatus for purifying an exhaust gas laden with vapours of a foreign substance with recovery of the foreign substance

Abstract: In a process for purifying exhaust air laden with petrol vapours with recovery of the petrol, which process is based on condensing out the petrol by cooling the exhaust air, to achieve the low temperatures required for a virtually complete separation, the refrigerant medium provided for a heat exchanger 6 serving for separation is liquid nitrogen 17. To avoid the atmospheric oxygen condensing out and the formation of explosive mixtures connected with this and to create a sufficient refrigeration capacity with discontinuous feed of exhaust air, the heat exchange with the exhaust air is exclusively carried out via a buffer medium which has a transition between a solid and a liquid phase at a transformation temperature at or below the condensation temperature of the petrol vapours, but above the condensation temperature of the atmospheric oxygen, the buffer medium being cooled by the liquid nitrogen precisely to the conversion to the solid phase.