Low-pressure Treatment Research Articles

The Alkoxylation of Aerosil Silica with C1–C4 Alcohols

Abstract The Aerosil surface was treated with C1–C4 alcohols under both high-pressure and low-pressure conditions. The high-pressure treatment was carried out at various temperatures up to 250 °C using an autoclave, while the low-pressure treatment was done at 280 °C under vapor pressure at room temperature. The surface changes were followed by IR spectroscopy, and the carbon content was determined. The degrees of alkoxylation (OR groups/100 Å2) of the Aerosils treated sufficiently under low pressures were 1.3–1.6, approximately equal to the amount of OH isolated before the treatment, while the values under high pressures reached 2.3–3.4, equal or near to the amount of the total OH. The values for methoxylation were particularly higher, while those for t-butoxylation were quite low. These results, in addition to the observation of the IR spectra, indicate that the isolated OH groups are predominantly esterified under low pressures, while under high pressures the vicinal OH groups are esterified as well, and the opening of the siloxane bonds occurs easily in the case of methoxylation. The stability of the alkyl groups on the Aerosil against heating decreased in the order of: primary>secondary>tertiary.

�ber den einflu� des hydrostatischen druckes auf die ultrastrukturen von zellen und geweben. V. Die bedeutung der druckdauer f�r die druckresistenz der membran-, filament- und mikrotubulisysteme in Zellen mariner Tiere

Interactions between period and degree of pressure have been investigated in membrane and filament systems of gill tissue, skin, and muscles of Modiolus modiolus, Mytilus edulis (Baltic and North Seas) and Branchiostoma lanceolatum (Pallas) at the ultrastructural level. The results show the importance of time for the degree of structural disintegration at constant pressure. Destruction already occurs after 2 min of low-pressure treatment at 300 atm. After 10 min continued pressure at the same level, no further structural dis-organization (qualitative or quantitative) occurs, even when the time period is prolonged. For some organelles (i.e., cilia and microvilli), better structural preservation is apparent after 30-min pressure compared to 10-min treatment at the same pressure level. This is a so-called “acclimatisation” to pressure.

Bipropellant droplet combustion in the vicinity of the critical point

Droplet conditions during high-pressure combustion were examined both experimentally and theoretically. Measurements were made of steady burning temperatures and the pressures required for the supercritical combustion of n -octane and n -decane droplets burning in air. The measurements were made under zero gravity conditions in order to eliminate convection and to prevent the droplet from falling due to reduced surface tension near the critical point. Theoretical results were obtained with the conventional low-pressure treatment of phase equilibrium at the droplet surface as well as with high-pressure models which allowed for real gas effects as well as finite ambient gas solubility. A variable-property gas-phase model was employed in the analysis which allowed for the diffusion of dissolved gases along with the fuel. The high-pressure models yielded reasonably good predictions of the measured conditions required for supercritical burning (on the order of 2-2.5 times the critical pressure of the pure fuel for n -octane and n -decane droplets burning in air). The low-pressure model was not satisfactory, predicting supercritical burning pressures roughly one-half the measured values. The concentration of dissolved gas becomes quite high as the supercritical burning condition is approached (20–40% for paraffins heavier than n -octane). The calculations also indicated conditions where water should condense on the droplet surface, both during heat-up and steady burning, for the n -paraffin hydrocarbons.