D. Tefelski

Pressure-induced phase transition in soy oil

Following the earlier works [R.M. Siegoczyński, Reports of the Institute of Physics. No. 46, Publishing House of the Warsaw University of Technology (1998). R.M. Siegoczyński, J. Je¸drzejewski and R. Wiśniewski, High Pressure Res. 1 225–301 (1989).] on the investigation of oily liquids such as oleic and triolein, authors predicted the occurrence of a phase transition in the wide class of commercial oils containing oils with double carbon bonds. Those predictions have been confirmed by the observation of the phase transition in rapeseed oil [A.J. Rostocki, R. Wiśniewski and T. Wilczyńska, in press]. The present article shows further confirmation of those predictions presenting first-order phase transition in soy oil. The measurements performed in the range up to 1 GPa have shown pressure-related discontinuity of permittivity and volume.

Monte Carlo simulations for optimization of neutron shielding concrete

Concrete is one of the main materials used for gamma and neutron shielding. While in case of gamma rays an increase in density is usually efficient enough, protection against neutrons is more complex. The aim of this paper is to show the possibility of using the Monte Carlo codes for evaluation and optimization of concrete mix to reach better neutron shielding. Two codes (MCNPX and SPOT — written by authors) were used to simulate neutron transport through a wall made of different concretes. It is showed that concrete of higher compressive strength attenuates neutrons more effectively. The advantage of heavyweight concrete (with barite aggregate), usually used for gamma shielding, over the ordinary concrete was not so clear. Neutron shielding depends on many factors e.g. neutron energy, barrier thickness and atomic composition. All this makes a proper design of concrete as a very important issue for nuclear power plant safety assurance.

Compressibility studies of some vegetable oils up to 1 GPa

The paper presents compressibility studies of some vegetable oils within the range of 1 GPa. The measurements of the volume were done for rapeseed oil, soy oil, sunflower oil and linseed oil at constant temperature. On this basis, the modified Tait equation coefficients were evaluated. In the case of rapeseed oil, soy oil and sunflower oil, the discontinuity of P–V characteristics for phase transition has been observed. The value of Tait coefficients for the pressure above the phase transition suggests that the high-pressure phase is solidified. The experiment was conducted with a computer-based data acquisition system with software written in National Instruments LabVIEW™ graphical programming language. Piston displacement was measured by electronic digital calliper with RS232 interface.

Temperature effect upon the pressure-induced phase transformation in oleic acid

We present the results of the experimental study of transmitted and scattered light in oleic acid under carefully selected rates of pressure changes automatically exerted at different ambient temperatures. When the temperature of the investigated sample exceeded 60 °C, the phenomenon of very strong light scattering related to the increase of the sizes of scattering centres formed by groups of interacting molecules disappears, leading to a conclusion that at temperatures higher than 60 °C the new phase induced by pressure ceases to exist.

Certain physico-chemical properties of triolein and methyl alcohol–triolein mixture under pressure

The article discusses further research of the new high-pressure phase in triolein and in triolein mixed with methyl alcohol. The transformation from the initial isotropic state of liquid to the high-pressure phase in case of the mixture of triolein–alcohol was observed by us for the first time. In this study, we compare the phase transformation under pressure, both for oil and for oil–alcohol mixture. Spectra of Raman and UV–VIS absorption show that the application of pressure to triolein leads to partial irreversibility of the observed processes. That partial irreversibility is important for the food conservation methods based on high-pressure technology since triolein is a good model of the most of vegetable oils components.

Observation of pressure-induced phase transitions in rapeseed oil with methyl alcohol mixtures

A high-pressure research on rapeseed oil and mixtures of rapeseed oil with methyl alcohol has been made. In all cases, at least one occurrence of the first order phase transition similar to that in castor oil was noticed [R.M. Siegoczyński, Reports of the Institute of Physics. No. 46, Publishing House of the Warsaw University of Technology (1998)]. Experiments were performed in a cylindrical chamber with a simple piston system, working together with 20 ton hydraulic laboratory press. The pressure in those experiments was approaching 1 GPa. Changes of pressure, volume, temperature and capacitance were recorded using an advanced data acquisition system. In this article, the changes of the relative electric permittivity ϵr as function of pressure and also the compressibility of investigated liquids have been presented. Abnormal rise of the dielectric constant in the mixture of rapeseed oil with methyl alcohol was observed. These results suggest the occurrence of a new phase transition apart from the one observed earlier in rapeseed oil [A.J. Rostocki, R. Wiśniewski and T. Wilczyńska, J. Mol. Liq., in press].

Changes of liquid structure under pressure in oleic acid

In this study, we show that in the case of oleic acid, the transition to the high-pressure phase, strong scattering of light phase is observed. Before this state is reached, the investigated liquid goes into a stable intermediate state at lower pressures showing weaker light scattering. Molecules of the liquid in the high-pressure states are more ordered and the time to reach these states is relatively long. On the basis of measurements of the changes of permittivity, the intensity of the transmitted light and temperature in oleic acid as a function of time after the application of pressure, this paper presents an analysis of changes of the structure of the investigated liquid during its transformation. †Presented at the 42nd EHPRG conference, Lausanne, September 1–4, 2004.

A study of the high pressure phase transition of diacylglycerol oil by means of light transmission and scattering

A sample of diacylglycerol (DAG) oil, being a mixture of DAGs and triacylglycerols with a ratio of 82% and 18%, respectively, and with a vestigial content of monoacylglycerols and free fatty acids, has been researched in high pressure conditions. As a result of dynamically applied pressure, a discontinuous (first-order) phase transition of the DAG sample has been observed. After the threshold value of the pressure for the phase change was determined, a number of further measurements were performed. The aim of the measurements was to pressurise the DAG sample with different rates of compression. During the measurements, the following parameters were recorded: the intensities of beams both transmitted and scattered at the angle of 90°, and the temperature of the sample. The obtained data may prove useful for an introductory description of the phase change kinetics induced by dynamically applied pressure.

Molecular collapse – modification of the liquid structure induced by pressure in oleic acid

Recently we showed that in case of the oleic acid (C 18 H 34 O 2), the transition to the high-pressure, strong scattering of light phase is quite complicated. This article presents further analysis of structure changes of the investigated liquid during its transformations. The basis of the analysis are measurements of the transmitted and scattered light intensity and temperature changes as a function of time after the application of pressure. During the decompression and the return to the initial state, the intensity of the scattered light increases several times. The automatic pressure system allowed us to observe six pressure regions of the liquid structure modification during the pressure rise. In the fourth region of applied pressure, the molecules spontaneously draw onto themselves, enlarging the available free volume that causes the further volume reduction with compression and does not produce a pressure change. We called the phenomenon a molecular collapse.

The investigation of the dynamics of the phase transformation in triolein and oleic acid under pressure

An aim of our work is the understanding of processes happening during phase transformations under the pressure in triglycerides and unsaturated fatty acids. Particles of investigated liquids possess the double bond between carbon atoms, which causes the bended shape of the particle and makes its free rotation impossible. This property causes low temperatures of melting point and high temperatures of boiling and also investigated by us phase transformations. For study of the dynamics of phase transformation in these liquids we measured light transmission and light scattering at 90 degrees angle, temperature, permittivity and internal pressure versus time. We applied pressure using computer controlled pump with a stepping motor, which makes increase of the pressure steady. The phase transformation in oleic acid lasts several seconds, in triolein it lasts several minutes. We think that the elongated time of phase transformation is caused by a hooked shape of particles of triolein and the dynamics of that process is determined by the tangling of particles. We checked the influence of smaller particles of oleic acid on the phase transformation by investigating the mixture of these liquids.