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1.

A pulse pressure was superimposed on the melt flow resulting in melt vibration. With application of the melt vibration technology, the melt flow behavior and mechanical properties of high‐density polyethylene were studied. For vibration‐assisted extrusion (VAE) at constant vibration pressure amplitude, the viscosity decreases sharply with increasing vibration frequency, and also does so when increasing vibration pressure amplitude for VAE at constant vibration frequency. The effect of vibration field on melt rheological behavior is also related to the melt temperature; a large decease in viscosity is obtained at low melt temperature. Compared with the mechanical properties obtained by conventional injection molding (CIM), the mechanical properties for vibration‐assisted injection molding (VAIM) samples were improved by changing the vibration frequency and vibration pressure amplitude. Injected at constant low vibration pressure amplitude, the VAIM sample prepared at high vibration frequency shows large elongation at break; injected at constant low vibration frequency, the VAIM sample prepared at high vibration pressure amplitude shows greatly improved yield strength. The above two VAIM processing routes produce different VAIM samples with different fracture behaviors; a distinct layered structure for VAIM samples was observed by SEM.  相似文献   

2.
Abstract

Powdered samples of TiO0.82, TiO1.04 and TiO1.25 having the cubic rocksalt-type structure with high concentration of vacancies randomly distributed were held at combined conditions of high pressure, ranging from 1 GPa to 8 GPa, and high temperature, ranging from 973 K to 1173 K, and structural changes occurring were investigated by synchrotron radiation diffraction at the conditions and by conventional X-ray diffraction after the samples were brought back to ambient condition. Pressure has been shown to suppress formation of ordered arrangements of vacancies in all the samples and lead to precipitation of a hexagonal δ-Ti3O2 in TiO0.82 and TiO1.04 and precipitation of a corundum-type Ti2O3 in TiO1.25. Irreversible change in the lattice parameter of the remaining rocksalt-type structure has been observed which is due to partial annihilation of vacancies under pressure.  相似文献   

3.
Abstract

The aim of this communication is to study the effect of the high hydrostatic pressure on the phase diagram of an AS12UN commercial alloy by DTA. The high pressure range is 0-360 MPa. Microphotographies of the recovered samples are compared with samples produced by dynamic high pressure in a die-casting set in a 4000 T press on a industrial plant.  相似文献   

4.
Abstract

X-ray and neutron powder diffraction data obtained from samples contained within high pressure cells are generally of lower quality than data collected from samples at ambient conditions. The far smaller sample size as well as possible contamination of the pattern by the pressure cell means that Rietveld refinement techniques must be adapted to extract the maximum useful information from the data. These problems become paramount as larger structures at high pressure are attempted. Techniques such as “leBail extraction”, “soft restraints” and “rigid body refinement” will be discussed with application to analysis of high pressure neutron powder diffraction data.  相似文献   

5.
Abstract

X-ray powder diffraction measurements for YBa2Cu3O7-y and NdBa2Cu3O7-y were made at the intense synchrotron radiation source under high pressure up to 5 GPa. These samples were wrapped tightly in platinum foil to avoid deoxidizing atmosphere. The orthorhombic to tetragonal transition temperature increases with pressure in both samples. These results are discussed on the basis of the disordering of the oxygen atoms on the chain sites.  相似文献   

6.
Abstract

High purity selenium samples were melted under high pressure (≤6.4 GPa) and quenched at various rates ranging from 2 K s?1 to 500 K s?1 and the recovered material was examined by X-ray diffraction and electron microscopy. In the entire range of pressure and cooling rate, the melt was found to solidify into a polycrystalline aggregate of the trigonal phase of selenium. The samples obtained by slow cooling of the melt at 6.4 GPa contain, in addition to crystalline phase, regions which appear to be amorphous.  相似文献   

7.
Abstract

The response of suspensions of spices and spice mixtures in water to high pressure treatment was investigated. Inactivation of the microbial load–mainly aerobic and unaerobic spore formers–was strongly dependent on water activity and temperature. Samples were completely decontaminated after three pressure cycles (30 min at 80 MPa followed by 30 min at 350 MPa) at 70 °C at a minimum water activity of 0.91. Pressure treated samples were examined for sensory and chemical changes. No significant changes in odour and appearance were recognized by a trained sensory panel, nor were changes in the volatile compounds of the samples detected by static headspace gaschromatography.  相似文献   

8.
Abstract

The crystal hardness-crystal perfection correlation of polyethylene (PE) samples crystallized at high pressure from the melt (chain extended) has been studied and compared to melt crystallized samples at atmospheric pressure (chain folded). For this purpose the chain extended PE samples were analyzed by WAXS and the paracrystalline lattice distortion parameter values, g 110, were calculated. Results are discussed in the light of structural and thermodynamical predictions. Analysis of data confirm the close existing correlation, previously found for chain-folded crystals, between the crystal hardness and g 110, including now both the values for chain-folded and chain-extended crystals.  相似文献   

9.
10.
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.  相似文献   

11.
Gérard Demazeau 《高压研究》2013,33(1-6):203-212
Abstract

Pressure was developed during the 20th century. The most important illustration of the use of high pressure in Materials Science was the synthesis of diamond at the beginning of the fifties.

This contribution will describe the main scientific research axis developed these last years and based on high pressure (synthesis of new materials, stabilization of specific structures, crystal-growth, preparation of finely divided materials…).

In parallel some industrial developments will be analyzed.

In conclusion, the potential of high pressure will be sketched for the near future.  相似文献   

12.
Abstract

We report the use of microwave -hydrothermal processing to synthesize various ceramic powders. Microwave-hydrothermal processing is compared with conventional hydrothermal processing in the crystallisation of MoO2. The presence of microwave field leads to accelerated kinetics of crystallization of the finely divided molybdenum dioxide particles. Existing microwave heated pressure vessels for chemical synthesis cannot be used above 250 MPa and 270°C because they contain parts made of polymeric materials. The objective of this work is to associate a microwave source to a high pressure vessel in a way such that it might be used to carry out reactions in aqueous media at pressures around 100 MPa and temperatures above the critical point of water.  相似文献   

13.
Abstract

A DIA-type cubic-anvil high pressure apparatus (SAM-85) has been interfaced with white x-ray radiation from the superconducting wiggler port of the National Synchrotron Light Source at Brookhaven National Laboratory. Energy-dispersive x-ray diffraction measurements can be obtained for samples with dimensions of the order of 1 mm as a function of pressure and temperature utilizing x-ray energies of up to100 keV.

The sample environment is examined. Pressure is uniform in the sample chamber to within 0.1 GPa, and temperature is constant in the scattering volume to within 5°C.A method is defined for determining deviatoric stress. We find that for a sample containing NaCl and Au, the deviatoric stress increases to about 0.3 GPa as pressure increases to 1.5 GPa and then remains constant, probably reflecting the strength of the sample. Upon heating, the deviatoric stress quickly approaches zero.

Presented at the IUCr Workshop on ‘Synchrotron Radiation Instrumentation for High Pressure Crystallography’, Daresbury Laboratory 20-21 July 1991  相似文献   

14.
Abstract

Studies of matter under very high pressure at synchrotron radiation sources are mostly done using pressure cells with single-crystal diamond anvils. In some cases the available volume (≤ 10?3mm3)in such cells causes problems especially at high temperature and for crystal synthesis. To ensure sufficient homogeneity of pressure and temperature, the use of cells with large sample volumes (≥ 1 mm3) is necessary.

Existing devices for such measurements are compared with a novel setup which consists of a toroidal anvil arrangement and a lightweight (50 kg) press with 250 tonnes (2.5 MN) capacity. Preliminary tests of this instrument with synchrotron radiation are reported.

Presented at the IUCr Workshop on ‘Synchrotron Radiation Instrumentation for HighPressure Crystallography’. Daresbury Laboratory 20-21 July 1991  相似文献   

15.
《光谱学快报》2013,46(5):689-702
ABSTRACT

Raman and infrared spectra are reported for iodoform samples in diamond anvil cells at ambient temperature and at pressures up to 5 GPa (Raman) and 10 GPa (infrared). The spectra appear to evolve smoothly and no evidence of any structural phase transitions is found. The dependence on pressure of 7 Raman and 13 infrared peak wavenumbers is presented. A large increase in intermolecular bonding strengths is confirmed, together with a moderate increase in intramolecular I-C-I bending forces. Color changes in the samples at high pressures are found to be mostly reversible, but long exposure to high fluxes of visible photons causes some molecular dissociation, with the release of iodine.  相似文献   

16.

We report about recent X-ray absorption spectroscopy (XAS) measurements on solid and liquid AgI under high pressure. The structural behaviour of AgI has been investigated to pressures P~4.3 GPa at room temperature and to P~1.8 GPa at 1100 K. The high temperature/high pressure conditions have been obtained by means of a large-volume press of the Paris-Edinburgh type, coupled with a 10 mm boron/epoxy biconical gasket. The absorption spectra have been collected in transmission mode, both at the K-edge of Ag and I, and the samples have been characterized in situ by energy scanning X-ray diffraction at fixed angles. Our XAS results for solid AgI are compatible with previous X-ray diffraction measurements. For liquid AgI, we observe a slight change in the intensity and a shift in the frequency of the XAS oscillations with respect to what obtained in the case of the ambient pressure liquid.  相似文献   

17.
Abstract

Bulk, semiconducting GaxTe100-x (17 ≤ x ≤ 25) glasses are prepared by the meltingh quenching method and electrical resistivity measurements are carried out at high pressures up to 8 GPa and low temperatures down to 77 K in a Bridgman anvil system. It is found that all the GaxTe100-x, glasses exhibit metallization under pressure, with a continuous decrease in electrical resistivity and activation energy for conduction. Further, the high pressure metallic phases of GaxTe100-x samples are found to be crystalline.  相似文献   

18.
Abstract

The kinetics of crystallization of eutectic alloys Al100-xSix (χ=12, 18, 26 at.%) was investigated under pressures p=0.5, 2.5, 4.5 GPa. The values of supercooling and average grain size of silicon crystals were determined for alloys quenched from melt under different pressures with the cooling rate 103 K/s. The data obtained were used to evaluate quantitatively the pressure dependences of surface tension (between melt and crystal) and activation energy of crystal growth which, in turn, have made it possible to determine the relative change of nucleation frequency and of the rate of crystal growth with pressure.

The possibility is shown, based on the investigation of mechanical properties of the samples obtained under high pressure, for improving the strength and the plasticity of A1-Si alloys by means of high pressure-high temperature treatment.  相似文献   

19.
Abstract

The effect of pressure on circular dichroism (CD) spectra of the octahedral chiral Λ-, Δ- and (Λ, Δ)trisO, O'-bis[(+)(S)-2-methylbutyl]dithiophosphate Cr(III) complexes, have been studied in the pressure range 0-2.5GPa. Results on polycrystalline samples dispersed in nujol show a pressure-induced A to A inversion of configuration at the metal center above 1.2 GPa. The high pressure stability of the A-form is explained in terms of most favoured crystal packing among different ligand conformations of the chiral complex.  相似文献   

20.

Acid phosphatase activity was measured in whole milk, skim milk, acid and rennet wheys before and after subjecting samples to high hydrostatic pressures for 10 min. Whole and skim milks exhibited a significant drop in activity following treatment at pressures in excess of 200 MPa. While rennet whey exhibited similar characteristics, acid whey was more pressure resistant and required pressures in excess of 500 MPa before exhibiting a net loss in activity. Most of the activity was lost in the first 10 min of pressurisation.  相似文献   

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