Pressure-transmitting Fluid Research Articles

Compression heating influence of pressure transmitting fluids on bacteria inactivation during high pressure processing

Compression heating characteristics of different pressure transmitting fluids [three different concentrations (75:25, 50:50, 25:75) of water–glycol mix and sodium benzoate (2%) solutions] and their influence on inactivation of spores of Bacillus subtilis in phosphate buffer (0.067 M, pH 7.0) during high pressure processing (HPP) were studied. Experiments were conducted using a pilot scale food processor. Pressure transmitting fluids containing highest percentage of glycol (25:75 water–glycol mix) showed highest temperature increase while 2% sodium benzoate solution showed least temperature increase during high pressure processing. The target pressure, holding time, compressibility, initial temperature, and the rate of heat loss to the surroundings primarily influenced the apparent temperature increase of pressure transmitting fluid in a vessel during HPP. The temperature change was further influenced by the fluid properties such as viscosity, specific heat and thermal conductivity. Use of sodium benzoate solution as pressure-transmitting fluid resulted in highest inactivation of B. subtilis spores. Change in pressure transmitting fluid temperature as a result of compression heating and subsequent heat transfer should be considered in inactivation of bacterial spores by HPP.

Raman Investigation of Fullerene [60] Under hydrostatic Pressure

ABSTRACTWe report the results of a study of adsorption of small molecules on the surface of buckminsterfullerene, C60. The pressure dependence of the Raman spectrum was investigated over the range 0–10 GPa in methanol-water mixtures that were used as the pressure transmitting fluid (PTF) in a diamond anvil cell. It is found that the spectral shift and its pressure derivative are sensitive to both the applied pressure and to the composition of the PTF. These observations are consistent with an explanation that involves preferential adsorption onto the surface of the C60. In particular, the notion of C60 collapse needs not be invoked to explain the observations.

Vibrational Spectroscopy of GaN:Mg Under Pressure

AbstractThe microscopic structure of Mg-H complexes in GaN has been a subject of intense theoretical and experimental investigation. In order to probe the Mg-H structure, we have studied the effect of hydrostatic pressure on the local vibrational mode (LVM) frequency. At ambient pressure, the LVM frequency is 3125 cm-1, which corresponds to a N-H stretching mode. In this study, Fourier-transform spectroscopy was performed on free-standing GaN:Mg,H samples in a diamond-anvil cell, with nitrogen as a pressure-transmitting fluid. The samples had been removed from their sapphire substrate by the laser-liftoff technique. The LVM frequency was measured, at liquid helium temperatures, for pressures ranging from 0 to 5 GPa. The pressure dependence of the frequency is nonlinear: first it decreases with pressure, then it increases. Comparison with first-principles calculations allows us to derive information about the microscopic structure of the Mg-H complex. The calculated stable configuration indeed gives rise to a frequency shift consistent with experiment. Based on the comparison between theory and experiment, we can exclude the bond-center configuration, which would result in a much larger pressure derivative than experimentally observed.

Effect of viscosity of the pressure-transmitting fluid on the metrological characterization of the piston gauge up to 1 GPa

A systematic theoretical investigation has been carried out to study the effect of viscosity of the pressure-transmitting fluids on the measurement of pressure up to 1 GPa using piston gauges. The fluid flow equation is modified to determine the fall rate (v) with pressure (P), taking the pressure-dependent viscosityη(P) and clearance between piston and cylinder [H(P)] terms into account. Above 0.4 GPa, the fall rate curve shows the tendency to be pressure independent. The near-constancy ofv withP can be avoided with less viscous fluid or by increasingH(P). Finally. the initial clearance obtained from the experimental data of fall rate, shows a weak dependence of pressure, although theoretically it is assumed to be independent of pressure. This weak pressure dependence is attributed to the effect of viscosity of the pressure transmitting fluid.

The mechanical properties of PVC under high pressure

The deformation properties of PVC have been studied under high pressure. Craze initiation and yield criteria have been proposed. The brittle-to-ductile transition was observed between 1×107 and 2×107 Pa, which is a relatively low transition pressure compared to polystyrene. Deformation in the post-yield region occurred by neck formation and subsequent drawing to produce chain orientation. When PVC was exposed to the pressure-transmitting fluid, silicon oil, a strong environmental stress cracking effect was observed.

The mechanical behaviour of polystyrene under pressure

Tensile deformation of polystyrene carried out under pressure up to 4 kbar has shown that the pressure-transmitting fluid (silicon oil) acts as a stress crazing and cracking agent. Unsealed specimens showed a brittle-to-ductile transition at 2.95 kbar, while specimens sealed with Teflon tape and rubber showed the same transition at only 0.35 kbar. Analysis of the stress-strain curves for the sealed specimens indicated that the pressure dependency of the craze initiation stress differs from that of shear band initiation stress. The brittle-to-ductile transition occurs when the initiation stresses of both processes become equal. The principal stress for craze initiation showed almost no pressure dependency, suggesting that crazes initiate when the principal stress level of the tensile specimen reaches a critical value irrespective of the applied hydrostatic pressure. Similarly, no pressure dependency was observed for the principal ductile fracture stress. The pressure dependency of yield stress agreed well with a non-linear pressure dependent von Mises yield criterion.

Gold capsules for high pressure experiments

The exceptional ductility and corrosion resistance of gold are utilised in the study of chemical reactions at very high pressures. To isolate the reactants from the pressure-transmitting fluid they are enclosed in sealed capsules which are constructed from thin-walled gold tubing.

Charge Mobility of Organic Semiconductors under High Pressure. Anthracene

Abstract The charge mobilities of anthracene single crystals were measured under high pressures up to 7.4 kbar. An experimental apparatus like Kepler’s was used. A sample holder was attached in a Drickamer-type high-pressure photocell, with kerosene employed as the pressure-transmitting fluid. The electron mobilities along the a and b crystal axes increased as the pressure applied increased; the values of the charge drift mobility at 7 kbar were 1.7 times as large as those at atmospheric pressure. The electron mobility along the c′ axis was nearly constant. The hole mobility, however, could not be measured, because the tail of the pulse signal, observed on the oscilloscope, was deformed.

Hydrothermal Crystallization of Yttrium‐Iron Garnet on a Seed

Yttrium‐iron garnet has been shown to be the stable solid phase, congruently saturating, and not subject to reduction in 50 wt% NaOH between 350° and 425°C at pressures from 200 to 1350 atm. Substantial diffusivity of hydrogen through platinum and gold has been shown to lead to the formation of Fe3O4 in garnet syntheses attempted in platinum or gold capsules where water was the pressure‐transmitting fluid. Yttrium‐iron garnet has been grown on a seed crystal under the following conditions: crystallization temperature, 370°C; dissolving temperature, 420°C; pressure, 200 atm; and solvent, 50 wt% NaOH. The rate of crystallization was 0.08 mm per day in the (111) direction.