Remaining of ϵ-iron structure at atmospheric pressure and superlattice formation by shearing at high pressure

Transmission X-ray diffraction pattern of iron sheared at high pressure show rings whose interplanar spacings correspond to those of ?-iron and their integral multiple, in spite of the fact that it has been kept at atmospheric pressure for ～3 months from the shearing. This and other related phenomena suggest that the pattern corresponds to the remains of the ?-iron structure in which superlattice formed. The volume of the specimen at atmospheric pressure after elapsing ～3 months at atmospheric pressure from the shearing was 86% of that before the shearing.     

XPS study of CeTbO3+δ synthesized by high pressure and temperature method

The samples of CeTbO₃₊ synthesized by high pressure and high temperature method were studied by XPS. It was found that Tb⁴⁺ ion began to transform to Tb³⁺ at about 600° C and Ce⁴⁺ to Ce³⁺ about 800° C. Single phase compound of CeTbO₃₊ having fluorite structure was formed at 1000° C, and in the compound the Ce ions had been in mixed valence state. Existence of Ce³⁺ ions in compounds could be detected with the shift of the 888 eV peak and the change of relative intensity of it to the 882 eV peak. The duration stability of CeTbO₃₊ synthesized by high pressure and temperature method was investigated.The project supported by National Natural Science Foundation of China     

Synchrotron x-ray-diffraction study of α-cristobalite at high pressure and high temperature

Abstract

Energy-dispersive x-ray diffraction using synchrotron radiation was carried out on α-cristobalite to 3 GPa and 350°C in a cubic anvil press. A cascading structural phase transition occurred beyond 0.61 GPa at room temperature. The transition was accompanied by a splitting of most of the a-cristobalite reflections: the (111) reflection at 0.61 GPa through the (211) reflections at 2.13 GPa, with many other lines between. The pressure of this transition decreased with increasing temperature.     

New vegetable and fruit–vegetable juices treated by high pressure

The aim of this work was to find sensory suitable combinations of not commonly used vegetables, that is, cabbage, celeriac and parsnip, into mixed fruit–vegetable juices, two-species vegetable juices and vegetable juices with whey. These juices might have the potential to offer consumers new, interesting, tasty and nutritional products. Another interesting variation could be preparation of vegetable juices in combination with sweet whey. Nutritional and sensory evaluations were carried out using juices prepared in the laboratory. The total phenolic content, in addition to ascorbic acid and antioxidant activity, was determined. The developed juices with high nutritional value should increase very low fruit and vegetable consumption in the Czech population. The prepared juices were high pressure pasteurized (410 MPa). This technique retains the desired levels of important nutritional substances, while being destructive to live microbial cell structure. The germination of spores is suppressed by low pH value.     

Crystal structure of the high pressure phases of bismuth bi iii and bi iii′ by high energy synchrotron x-ray diffraction

Abstract

This paper reports the results of a synchrotron X-ray diffraction study on the crystal structures of Bi 111 and Bi 111′ which have been known to form under high pressure but have, for a long time, been unsolved. Powdered samples were compressed in a cubic-type multi-anvil press, MAXID, and diffraction data were collected using an Imaging Plate with monochromatized radiation of an energy of 49.7 keV. It was possible to identify at 3.8 GPa forty-eight reflections for Bi I11 in the sin θ / δ range from 1.6 nm^?1 to 5.6 nm^?1, which were indexed in terms of a tetragonal unit cell with a=0.8659 nm and c═ O·4238 nm (2=10). Analysis based on the observed intensities of the reflections led to a structure in which atoms form a distorted body-centered cubic lattice. It is of the same type as the structure of the high pressure phase of antimony Sb 11. When pressure was increased across the suggested transition pressure 4.3 GPa between Bi III and Bi III′ to 6.6 GPa, no change in the diffraction pattern was observed, indicating that there is no distinction between the two phases as long as the crystal structure is concerned. Discussion is given on the sequence of high pressure phase transitions in the Group Vb elements.     

Thermoelastic parameter αKT of sodium chloride at high pressure and high temperature

Two different potential models to the molecular dynamics (MD) simulations have been applied to investigate the thermoelastic parameter αK_T of sodium chloride (NaCl) under high pressure and high temperature. The first one is the shell model (SM) potential that due to the short-range interaction when pairs of ions are moved together as is the case in that polarization of a crystal due to the motion of the positive and negative ions, and the second one is the two-body rigid-ion Born–Mayer–Huggins–Fumi–Tosi (BMHFT) potential with full treatment of long-range Coulomb forces. Particular attention is paid to the comparison of the SM- and BMHFT-MD simulations with the Debye model for the first time, and this model combines with ab initio calculations within local density approximation (LDA) and generalized gradient approximation (GGA) using ultrasoft pseudopotentials and a plane-wave basis in the framework of density functional theory (DFT), and it takes into account the phononic effects within the quasi-harmonic approximation. Note that the MD calculated volumes using SM model is somewhat larger than both the DFT and experimental volumes despite not considering the temperature effect. Compared with SM potential, the MD simulated 300 K isotherm of NaCl with BMHFT potential is very successful in reproducing accurately the measured volumes and the GGA calculated volumes. Generally, it is found that there exist minor differences between the LDA and GGA computed the thermoelastic parameter αK_T of NaCl, with both average results giving good agreement with SM-MD simulations. At an extended pressure and temperature ranges, the variation of thermoelastic parameter αK_T which play a central role in the formulation of approximate equations of state has also been predicted. The properties of NaCl are summarized in the pressure range of 0–300 kbar and the temperature up to 2000 K.     

Melting and Grüneisen parameters of NaCl at high pressure

The Buckingham potential has been employed to simulate the melting and thermodynamic parameters of sodium chloride (NaCl) using the molecular dynamics (MD) method. The constant-volume heat capacity and Grüneisen parameters have been obtained in a wide range of temperatures. The calculated thermodynamic parameters are found to be in good agreement with the available experimental data. The NaCl melting simulations appear to validate the interpretation of superheating of the solid in the one-phase MD simulations. The melting curve of NaCl is compared with the experiments and other calculations at pressure 0－30GPa range.     

Effects of high hydrostatic pressure on β-glucan content,swelling power,starch damage,and pasting properties of high-β-glucan barley flour

ABSTRACT

The effects of high hydrostatic pressure (HHP) on the physicochemical properties of high-β-glucan barley flour were investigated in the present study. Dough samples were made from two types of barley flour with low and high β-glucan content, respectively, and treated with HHP (200–600?MPa) for 10?min. Although the elevation of pasting properties for the samples treated at 600?MPa was reduced to the same extent as that in wheat flour at normal atmospheric pressure, β-glucan content was maintained regardless of the pressure applied. The significant increase in starch damage of the dough samples at 550 and 600?MPa was confirmed by the results of microscopic observation, which revealed that elliptical starch granules were cracked and damaged in samples with low β-glucan at 600?MPa, and in samples with high β-glucan content at 400?MPa or more. X-ray diffraction patterns of the samples treated at 600?MPa indicated the formation of amylose-lipid complexes that were considered to inhibit the elevation of viscosity.     

Structural and electronic properties of YH 3 at high pressure – band calculation by the GW approximation

Using the GW calculation for one particle energy of electrons, we studied the pressure dependence of the band gaps in YH ₃ for controversial structures reported in experimental and theoretical studies. For some types of band structures, perturbational treatment taking only diagonal matrix elements of the self-energy into account, which is the most commonly used method in the GW calculation, fails to give band gaps. In those cases, calculations in which the non-diagonal matrix elements of the self-energy are taken into account are needed to get the band gaps. In the fcc-YH ₃, band gap disappears around 5 GPa which is much lower pressure than those reported in experimental studies for the metallization in YH ₃. The band gap by the GW calculation in the C2/m structure, which is theoretically predicted to be most probable up to around 40 GPa, survives to much higher pressures than those predicted by the generalized gradient approximation (GGA), and probably to over 60 GPa. The very recent report of metallization pressure around 70 GPa on the YH ₃ metallization by means of DC conductivity measurements suggests that some structures other than the C 2/m should appear as an intermediate structure before the fcc-YH ₃ will appear by the pressurization.     

Effect of high hydrostatic pressure on seed germination,microbial quality,anatomy–morphology and physiological characteristics of garden cress (Lepidium sativum) seedlings

High hydrostatic pressure is a non-thermal food processing technology that is found to increase the percentage of germination, decrease the germination time and improve the microbial quality of seeds. In this study, pressures of 100–400 MPa for 10 min at 30°C are used to compare the percentage of germination, the microbial quality of seeds, chlorophyll a and b, and total phenolic compounds concentrations in seedlings, and the anatomy–morphology characteristics of garden cress. Enhanced reductions of total aerobic mesophilic bacteria, total and fecal coliforms, and yeast and mould populations in seeds were observed, especially at 300 MPa. In addition, the percentage of germination, chlorophyll content and phenolic compounds concentrations, fresh and dry weights, and hypocotyl lengths of the seedlings are higher than those of all samples, where the percentage of germination is equal to controls but higher than other samples, and radicula length is lower than controls but higher than others.     

Determination of Particle Size,Core and Shell Size Distributions of Core–Shell Particles by Analytical Ultracentrifugation

In core–shell nanoparticle analysis, the determination of size distributions of the different particle parts is often complicated, especially in liquid media. Density matching is introduced as a method for analyzing core–shell nanoparticles using Analytical Ultracentrifugation (AUC), making it possible to obtain the core size distribution in liquid dispersions. For this approach, the density of the dispersion is adjusted to the density of the shell. Oil filled nanocapsules are utilized with component densities of around 1 g mL⁻¹ to demonstrate this technique. The shell size distribution is calculated supposing the particle size distribution as a convolution of the shell- and core size distributions. Finally, the distributions of core size, shell thickness, particle size, and particle density and thus particle composition are obtained. To clarify the effect of swelling, AUC measurements are combined with further size characterization methods like Particle Tracking Microscopy and Dynamic Light Scattering.     

Structural and electrical properties of Ga–Te systems under high pressure

First-principles evolutionary calculation was performed to search for all probable stable Ga–Te compounds at extreme pressure. In addition to the well-known structures of P6_3/mmc and Fm-3 m Ga Te and I4/m Ga_2 Te_5, several new structures were uncovered at high pressure, namely, orthorhombic I4/mmm GaTe_2 and monoclinic C2/m Ga Te_3, and all the Ga–Te structures stabilize up to a maximum pressure of 80 GPa. The calculation of the electronic energy band indicated that the high-pressure phases of the Ga–Te system are metallic, whereas the low-pressure phases are semiconductors. The electronic localization functions(ELFs) of the Ga–Te system were also calculated to explore the bond characteristics. The results showed that a covalent bond is formed at low pressure, however, this bond disappears at high pressure, and an ionic bond is formed at extreme pressure.     

Ultra-fine grained Nd–Fe–B by high pressure reactive milling and desorption

This paper reports on the grain refinement in dynamic hydrogenation disproportionation desorption and recombination (d-HDDR) processed Nd-rich Nd₂Fe₁₄B and stoichiometric Nd₂Fe₁₄B powders using high pressure reactive milling (HPRM) followed by a subsequent desorption and recombination. In contrast to the dynamic-HDDR processed anisotropic powder with a grain size of the Nd₂Fe₁₄B phase of 300 nm, the new approach yields a further reduction of the Nd₂Fe₁₄B₁ grain size to less than 70 nm. Nd-rich Nd₂Fe₁₄B powder produced by HPRM and subsequent desorption exhibits a coercivity μ_0iH_c=1.35 T and a remanence of 0.80 T. In the stoichiometric material, the reduction of the Nd-content leads to an increase in remanence to 0.85 T. Additionally, it is demonstrated that highly anisotropic powders can also be obtained by dynamic-HDDR processing of stoichiometric Nd₂Fe₁₄B powders.     

Ferroelectric behaviour of 30nm BaTiO3 ceramics prepared by high pressure assisted sintering

Dense nanocrystalline BaTiO3 ceramics with a homogeneous grain size of 30 nm was obtained by pressure assisted sintering. The ferroelectric behaviour of the ceramics was characterized by the dielectric peak at around 120 ℃, the P-E hysteresis loop and some ferroelectric domains. These experimental results indicate that the critical grain size for the disappearance of ferroelectricity in nanocrystalline BaTiO3 ceramics fabricated by pressure assisted sintering is below 30 nm. The ferroelectric property decreasing with decreasing grain size can be explained by the lowered tetragonality and the ＇dilution＇ effect of grain boundaries.     

Symmetry breaking and restoring under high pressure: the amazing behaviour of the “simple” alkali metals

We argue that an ionic lattice surrounded by a Fermi liquid changes phase several times under pressure, oscillating between the symmetric phase and a low-symmetry dimerized structure, as a consequence of Friedel oscillations in the pair potential. Phase oscillations explain the tendency towards dimerization which has been recently reported for the light alkali metals under high pressure. Moreover, a restoring of the symmetric phase is predicted for such elements at an even higher density. Received 17 January 2003 Published online 11 April 2003 RID="a" ID="a"e-mail: giuseppe.angilella@ct.infn.it     

Effect of the codoping of N—H—O on the growth characteristics and defects of diamonds under high temperature and high pressure

Diamond crystals were synthesized with different doping proportions of N—H—O at 5.5 GPa—7.1 GPa and 1370 °C—1450 °C. With the increase in the N—H—O doping ratio, the crystal growth rate decreased, the temperature and pressure conditions required for diamond nucleation became increasingly stringent, and the diamond crystallization process was affected. [111] became the dominant plane of diamonds; surface morphology became block-like; and growth texture, stacking faults, and etch pits increased. The diamond crystals had a two-dimensional growth habit. Increasing the doping concentration also increased the amount of N that entered the diamond crystals as confirmed via Fourier transform infrared spectroscopy. However, crystal quality gradually deteriorated as verified by the red-shifting of Raman peak positions and the widening of the Raman full width at half maximum. With the increase in the doping ratio, the photoluminescence property of the diamond crystals also drastically changed. The intensity of the N vacancy center of the diamond crystals changed, and several Ni-related defect centers, such as the NE1 and NE3 centers, appeared. Diamond synthesis in N—H—O-bearing fluid provides important information for deepening our understanding of the growth characteristics of diamonds in complex systems and the formation mechanism of natural diamonds, which are almost always N-rich and full of various defect centers. Meanwhile, this study proved that the type of defect centers in diamond crystals could be regulated by controlling the N—H—O impurity contents of the synthesis system.     

Study of the electric field and wall voltage in a high pressure ac-PDP cell by laser induced fluorescence spectroscopy

The electric field in a surface discharge type ac-PDP cell with He or He/Xe(0.1%) mixture has been measured over a wide range of pressure (5－50 kPa) using laser induced fluorescence detection. The wall voltage was estimated from the measured electric field. The Stark manifolds of triplet atomic helium Rydberg state (2s^3S) with principal quantum numbers (n=8 and 9) have been used to measure the electric field, as the lifetime of 2s^3S is longer than the single atomic helium Rydberg state (2s^1S) in high pressure discharge. Comparison of the Stark manifolds between the n=9 and n=8 shows that the measurement accuracy of electric field can be increased by 10%. The maximum electric field strength during discharge and the wall voltage at the end of pulse decreases with the increase of pressure. The comparison of He and He/Xe(0.1%) discharge at 13 kPa showed that He/Xe gas mixture discharge can accumulate more wall charge on MgO surface and the electric field was somewhat higher than those of pure helium discharge during pulse off period under the same discharge conditions.     

Fracture toughness evaluation of WC–10 wt% Co hardmetal sintered under high pressure and high temperature

This work focused on fracture toughness studies of WC–10?wt% Co hardmetal fabricated through the high pressure/high-temperature technique. A powder mixture of WC–10?wt% Co was sintered at 1500–1900°C under a pressure of 7.7?GPa for 2 and 3?min. Vickers hardness test at two different loads of 15 and 30?kgf was done and fracture toughness of the sintered bodies was measured using the indentation method to obtain the effect of sintering parameters. Structural analyses were also performed via X-ray diffraction to investigate structure-related properties. Full density was achieved for high sintering temperature along with abnormal grain growth that reduced hardness. High hardness was observed ranging from 1200 to 1670?HV and fracture toughness increased with increasing sintering temperature up to the highest value of 17.85?MPa/m^1/2.     

Effects of Mg on diamond growth and properties in Fe–C system under high pressure and high temperature condition

Diamond crystal crystallized in Fe–Mg–C system with Archimedes buoyancy as a driving force is established under high pressure and high temperature conditions. The experimental results indicate that the addition of the Mg element results in the nitrogen concentration increasing from 87 ppm to 271 ppm in the diamond structure. The occurrence of the {100}plane reveals that the surface character is remarkably changed due to the addition of Mg. Micro-Raman spectra indicate that the half width of full maximum is in a range of 3.01 cm~(-1)–3.26 cm~(-1), implying an extremely good quality of diamond specimens in crystallization.