高压物理学报

A New Criterion of Hardness for Materials with Rocksalt Structure

LIU Xiao-Yang, SU Wen-Hui, MENG Chang-Gong, HU Zhuang-Qi

1994, 8(4): 241-247 . doi: 10.11858/gywlxb.1994.04.001

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Abstract:
A new criterion of hardness is proposed based on the analysis of the bonding in fourteen rocksalt-structure solids with the aid of discrete variational Xa (DV-Xa) cluster calculations. The concept of bond density is introduced to measure the hardness of materials. And there is a good linear relation between bond density and Mohs hardness. As the calculation does not involve any empirical parameters, it can be conveniently applied to some complicated systems, for example, alloys and intermetallic compounds.

Shock Compressibility of Heavy Water

LIU Fu-Sheng, LIU Xiao-Jun, CHENG Ju-Xin, CHEN Xian-Meng, JING Fu-Qian, GOU Qing-Quan

1994, 8(4): 248-253 . doi: 10.11858/gywlxb.1994.04.002

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Abstract:
Shock compression curve for heavy water (D2O) was measured in the range of 10～43 GPa by means of a two-stage light-gas gun. Shock velocities were measured to 1.2%～1.5% accuracy using the ASM probe. Impactor velocities were measured to 0.5% accuracy using an electric pin system with nanosecond time resolution. The shock impedance-match method was employed, in which the copper was used as standard. The results showed that two linear D-u fits were used to fit these data, and there exists a discontinuity between these two fits. This phenomenon may be ascribed to the dissociation of molecules of the heavy water.

Shock Temperature Measurements for Metal (Ⅰ)－Calibration of Pyrometers and Data Reduction for the Temperature at the Interface

TAN Hua

1994, 8(4): 254-263 . doi: 10.11858/gywlxb.1994.04.003

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Abstract:
Basic experimental procedures in calibrating the pyrometers used in the shock temperature measurements of metals were discussed. Methods to obtain the energy emitted from the metal sample/window interface as well as the interface temperature via Planck radiation law were presented in the paper.

Growth of Spherical Void in Viscoplastic Medium under Tensile Dynamic Loading

WANG Ze-Ping

1994, 8(4): 264-271 . doi: 10.11858/gywlxb.1994.04.004

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Abstract:
A new evolution equation of growth of spherical voids in viscoplastic medium under dynamic tensile loading is presented in this paper. In the evolution equation, strain rate, local inertial effects and work-hardening behaviour of the material are taken into account, and the influence of these effects on the growth of voids numerically analyzed and discussed. The results of numerical analysis show that the growth of voids is highly sensitive to loading and strain rate. It is also shown that local inertial effects play an important role in the process of the void growth under high loading rate, and these effects become larger as loading rate increases. An expression of critical stress of the void growth is obtained.

Electronic Structures and Equation of State for Aluminium under High Pressure

ZHANG Chun-Bin, LI Shao-Meng, TENG Ya-Gang

1994, 8(4): 272-278 . doi: 10.11858/gywlxb.1994.04.005

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Abstract:
The study for Al up to the pressure p=10 TPa, the compression 0/=10, by using the first principle calculations is performed. The energy band structures and electronic occupation numbers of the states for a series of lattice constants are presented. It follows from the energy band structures that s band always lies below the Fermi level. As the pressure increases, the bandwidths of s, p and d increase, and then the degree of hybridization become higher. So the electronic occupation numbers of s, d orbital change continuously. The effect of above mentioned changes to pressure is continuous too. In other words, sd transition is not the reason for a break in the slope of the shock Hugoniot for Al near 0.5 TPa, as claimed by Altshuler. The equation of state at T=0 K shows that bcc structure is softer than fcc. The results calculated by LMTO are different from the semi-empirical ones given by us previously. A new correct fitting for EOS from the results of LMTO is presented.

High Pressure Measurements of the Elastic Parameters of Ultrasonic State Equation for Cubic Crystal

WU Kun-Yu, SU Fang, XIE-Bin

1994, 8(4): 279-284 . doi: 10.11858/gywlxb.1994.04.006

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Abstract:
By using the technique of ultrasonic pulse-echo overlap, the pressure variations of the natural sound velocity in cubic crystals Si and Bi12GeO20 for pure longitudinal and shear waves propagating along [100], [110] and [111] direction were measured in 0.1～500 MPa hydrostatic pressure range. Based on the finite deformation theory, the elastic parameters of the ultrasonic state equation for cubic crystals Si and Bi12GeO20 were evaluated by means of the experimental results of the pressure dependence of the natural sound velocities under hydrostatic high pressure.

Impurity and Colouration Mechanism in cBN Crystal

ZHANG Tie-Chen, GUO Wei-Li, ZOU Guang-Tian, HU En-Liang, YU Hong-Chang, LI Kai-Song

1994, 8(4): 285-289 . doi: 10.11858/gywlxb.1994.04.007

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Abstract:
cBN crystal is a material synthesized under high pressure and high temperature. The crystal always contains more or less impurities relevant to its synthetic environment. The impurities will affect the color of cBN crystal. In this paper, impurities were measured, and coloration mechanism of cBN crystals was investigated.

Study on Compressive Behavior of -Fe2SiO4 under Hydrostatic Pressure

WANG Li-Jun, Ming L C, Manghnani M H

1994, 8(4): 290-295 . doi: 10.11858/gywlxb.1994.04.008

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Abstract:
The compressive behavior of -Fe2SiO4 at high pressure up to 23 GPa and room temperature has been measured by using synchrotron radiation and in situ high pressure X-ray diffraction techniques with DAC. The p-V relationship of -Fe2SiO4 at 0～23 GPa indicated that the isothermal compression process can be divided into two steps: if K0'=4, the bulk modulus K0 =1892 GPa at 0～18 GPa, and K0=21.32 GPa at 18～23 GPa. We didn't find any imformation of the phase transformation of -Fe2SiO4 in the whole experimental process. Based on the experimental data, it seems to us that the sample was in quite good hydrostatic pressure up to 18 GPa, but was in non-hydrostatic pressure due to solidification of the liquid medium when the pressure beyond 18 GPa. Finally, the phenomenon that the sample with incorrect loading method has higher K0 in those hydrostatic pressure experiments is discussed.

Studies on High Speed Reaction Spectrum of Nitromethane under High Temperature and High Pressure

HU Dong, WANG Yong-Guo, LU Hong-Bin, SUN Zhu-Mei

1994, 8(4): 296-301 . doi: 10.11858/gywlxb.1994.04.009

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Abstract:
High speed reaction spectra ignited for the mixture of nitromethane and oxygen are successfully studied by using multi-monochromator, photoelectric system and high speed data acquisition system. Both intermediates and termination products, for example, CH3O, CH, CH2O, OH, CHO, CO, CO2, H2O, NO, NO2 and so on, are observed. It is found using spectrum measurements with time-resolution that the mechanism of high speed reaction for nitromethane in explosion shock tube is different from that of heat dissociation and shock initiation.

A Study on Calculation of the Linear Thermal Expansion Coefficients of Metals

ZHENG Wei-Tao, DING Tao, ZHONG Feng-Lan, ZHANG Jian-Min, ZHANG Rui-Lin

1994, 8(4): 302-305 . doi: 10.11858/gywlxb.1994.04.010

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Abstract:
Based on the expression of pressure at temperature T and in terms of the universal equation of state Debye model and the thermodynamic relations, a general expression for the calculation of the linear thermal expansion coefficients of metals is obtained. This formula applied to the calculation of Al, Cu, Pb. Calculated results are in good agreement with the experiments.

1994 Vol. 8, No. 4

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