Papers by Keyword: Hydrostatic Pressure

Abstract: Electrical measurements under increasing hydrostatic pressure (1–4000 [bar]) have shown that electrical conductivity is closely related to the iodine doping rate (0–14%) of polyacetylene (PA) films. In pristine PA, conductivity increases with pressure while in 14% iodinedoped PA it decreases. A most important result is noticed for an intermediate doping rate (1.5%). In fact, for sweeping of the range of pressure, conductivity decreases in the beginning and then increases with pressure augmentation. This change is located at a critical pressure Pc. An empirical formula was proposed to describe this behaviour. The aim of this work is to contribute to the greater understanding of the pressure effect on the transport mechanism and/or the nature of charge carriers.

Abstract: Creation and transformation of defects in single crystalline (001) oriented Si-Ge with about 5.6 at. % Ge content, containing oxygen interstitials, Oi’s, at 9x1017cm-3 level, were investigated, after processing for 5 h at up to 1400 K (HT) under Ar pressure to 1.1 GPa (HP), by X-ray, synchrotron, infrared and photoluminescence methods. To create nucleation centres for Oi’s precipitation, some samples were pre-annealed for 10 h at 1000 K under 105 Pa. HT-HP treatment at 1230/1400 K results in improved sample homogeneity and crystallographic perfection. HT-HP induced changes in Si-Ge are related mainly to HP-stimulated diffusivity of Ge.

Abstract: In this paper, length of grain-to-grain contact, number of contacts per grain and ratios between the length of contacts and geometric characteristics of grains in heterogeneous Berea sandstone and Indiana limestone are studied. It is shown how hydrostatic pressure up to 40 MPa influences these grain boundary parameters. Observations show that there are different types of influence of hydrostatic pressure on grain boundary parameters in the studied sandstone and limestone.

Abstract: Natural tissue, especially autologous tissue is one of ideal materials for tissue regeneration. Decellularized tissue could be assumed as a second choice because the structure and the mechanical properties are well maintained. Decellularized human tissues, for instance, heart valve, blood vessel, and corium, have already been developed and applied clinically. Nowadays, decellularized porcine tissues are also investigated. These decellularized tissues were prepared by detergent treatment. The detergent washing is easy but sometime it has problems. We have developed the novel decellularization method, which applied the high-hydrostatic pressure (HHP). As the tissue set in the pressurizing chamber is treated uniformly, the effect of the high-hydrostatic pressurization does not depend on the size of tissue. We have reported the HHP decellularization of heart valve, blood vessel, bone, and cornea. Furthermore, HHP treatments are reported to have the ability of the extinction of bacillus and the inactivation of virus. So, the HHP treatment is also expected as the sterilization method. We are investigating efficient processes of decellularization and recellularization of biological tissues to have bioscaffolds keeping intact structure and biomechanical properties. Our recent studies on tissue engineering using HHP decellularized tissue will be reported here.

Abstract: We report studies of defects in electron-irradiated Czochralski-grown silicon (Cz-Si) subjected to thermal treatments at 1000oC and 1130oC with or without the application of high hydrostatic pressure of ~ 11 Kbars, prior to irradiation. The work is primarily focused on the impact of the pre-treatments on the production rate of the VO defect and its conversion to the VO2 defect. To this end, IR spectroscopy measurements were carried out and the amplitudes of the VO band (830 cm-1) and the VO2 band (888 cm-1) were monitored in the course of an isochronal anneal sequence up to ~ 550oC. Thermal treatments at 1000oC result in a reduction of the production rate of the VO defect. This rate however increases when pressure is applied during the treatment. The opposite behavior is observed for thermal treatments at 1130oC. The production rate of the VO increases slightly in heat treated samples but decreases substantially when high pressure is applied. Similar trends show the conversion of the VO to the VO2 defect for the corresponding treatments. The results are discussed taking into account the oxygen precipitates formed at the various treatments and their impact on the amount of primary defects available during irradiation which affects the production of the vacancy-oxygen defects.

Abstract: An analytical model describing the deformation behaviour of copper during the high-pressure torsion (HPT) processing is presented. The model was developed on the microstructural basis where the material is partitioned in two ‘phases’, the dislocation densities in cell walls and the dislocation densities cell interior, entering the model as scalar internal variables. The resulting ’phase mixture’ model is combined with strain gradient theory to account for strain non-uniformity inherent in SPD. It was demonstrated that gradient plasticity model is capable of describing the experimentally observed trends and accounting for a homogenisation of the accumulated shear strain across the HPT sample. The predictions of the model with respect to the ultrafine grain size produced by HPT and evolution of dislocation densities are in good agreement with experimental results reported by other research groups.

Abstract: Fast neutron irradiations on pre-treated Cz-grown silicon were carried out. The pretreatments involved thermal anneals at 450 oC and 650 oC under high hydrostatic pressure. We mainly examined, by means of IR spectroscopy, the effect of pre-treatments on the production of the oxygen-vacancy (VO) pair. The amplitude of the VO band was found independent on the 450 oC treatment although the amplitudes of the TDs bands were reduced. On the other hand, the amplitude of the VO band was found lower in the samples treated at 650 oC, indicating an influence on the production of the oxygen-vacancy defects. The results are discussed and explanations are suggested concerning possible interactions between thermal and radiation defects.

Abstract: It is established that some superplastic materials undergo significant cavitation during deformation. Cavitation not only limits the superplastic ductility of the material, but also reduces the service properties and the fatigue performance of the formed parts. Experimental results have shown that an effective method to eliminate cavitation is the application of hydrostatic pressure during deformation. In this work, finite element simulations are carried out to study the effects of hydrostatic pressure on damage evolution during SPF. The analysis is conducted for the superplastic copper based alloy Coronze-638 at 550 °C. The results clearly demonstrate the effectiveness of the superimposition of hydrostatic pressure in reducing the amount of cavities generated during SPF and improving the integrity of the formed part.

Abstract: Transformations of the SiGe/Si superlattice structures, either annealed at high pressure, or irradiated by high energy ions and subjected to post-implantation annealing, were studied and compared. Both types of treatments were found to lead to the formation of recharged defects clusters, resulting in the appearance of peaks on C-V characteristics, shrinkage of Ge profiles registered by SIMS technique after annealing, and disappearance of peaks in the free carrier profiles. The effects were more pronounced in the case of high energy ion implantation. The results are explained by the vacancy - assisted precipitation of Ge in SiGe layers.

Abstract: In the investigation the 3D version of the Estrin-Tóth dislocation model was used to analyze deformation behaviour of pure Cu, subjected to high pressure torsion (HPT) under pressures equal to 0.8, 2, 5, 8 GPa. As a result of the computer simulation, the nature and reasons for strain hardening are analyzed, the dislocation density evolution versus degree of SPD and graincell size versus degree of SPD curves were plotted. It is shown that the model adequately reflects the acting deformation mechanisms and structural changes during HPT at different applied pressures. It has been stated that an increase of the applied pressure at HPT leads to an increase in the activity of dislocation sources and sinks in the grain-cell walls. Misorientations between boundaries are estimated. It is revealed that an increase of the applied pressure contributes to a growth of the misorientation angles between neighbouring grain-cells.