高压物理学报

Free Volume Theory of High Pressure Melting

CHEN Dong-Quan, LI Mao-Sheng, CAI Ling-Cang

2001, 15(2): 81-86 . doi: 10.11858/gywlxb.2001.02.001

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Abstract:
An integral melting equation was derived according to free volume theory. Because free volume, Vf is much smaller than cell volume V (Vf/V0.005～0.01) at melting temperature, a simplified formula was obtained to be the same as Lindemann equation. The immanent physics of Lindemann law is discussed briefly.

Pressure-Induced Phase Transitions of Layered Perovskite-Like Manganates Ca3Mn2O7

ZHU Jia-Lin, CHEN Liang-Chen, YU Ri-Cheng, LI Feng-Ying, LIU Jing, JIN Chang-Qing

2001, 15(2): 87-90 . doi: 10.11858/gywlxb.2001.02.002

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Abstract:
In situ energy dispersive X-ray diffraction measurements on layered perovskite like manganates Ca3Mn2O7 under pressure up to 35 GPa were performed by using diamond anvil cell with synchrotron radiation. The results show that two phase transitions occured in layered perovskite-like manganates Ca3Mn2O7 under pressures in the range of 0～35 GPa. The crystal structure changes from tetragonal to orthorhombic at about 1.3 GPa, and then from orthorhombic to tetragonal at about 9.5 GPa, respectively.

Investigations of Explosion Characteristics of Lead Shield Mild Detonating Fuse

ZHAO Guo-Min, ZHANG Ruo-Qi, CHEN Gang, WANG Cheng-Hong

2001, 15(2): 91-96 . doi: 10.11858/gywlxb.2001.02.003

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Abstract:
The exploding characteristics of lead shield Mild Detonating Fuse (MDF) with a diameter of 2 mm were studied experimentally. The detonation velocity of the MDF is DJ=(6.950.06) km/s. The fragment sizes of lead shield after MDF explosion were very small, and the mass of the fragments, which were smaller than 5 m in size, was about 40 percent of the whole mass of the shell. The scatter velocity of the fragment produced by MDF exploding and the MDF impulse were also measured.

Numerical Study on the Damaging of Wolfram Balls Flying in Gases

CAO Ju-Zhen, LI En-Zheng, WANG Zheng

2001, 15(2): 97-102 . doi: 10.11858/gywlxb.2001.02.004

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Abstract:
The damage of different ball with the diameters of 6 mm (W and Fe) and 8.5 mm (W) flying in a gas with different velocity was studied. The damaging threshold velocities of different balls were obtained. The investigation showed that the damage degree of balls depends on the material, velocity and the size of the balls. The perforating ability of damaged balls to 6 mm thick steel targets was also studied.

The State Equations of Plasma Produced by Pulse Discharge in Water

LU Xin-Pei, PAN Yuan, LIU Ke-Fu, LIU Ming-Hai

2001, 15(2): 103-110 . doi: 10.11858/gywlxb.2001.02.005

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Abstract:
The temperature of plasma produced by pulse discharge in water (PPDW) is about 2104 K to 5104 K, and the max pressure of PPDW reaches 1～10 GPa. So the PPDW should not be treated as an ideal gas. In this work, the corrections to the ionization potentials in an equilibrium equation of PPDW, and the pressure from the degeneracy of electrons, the effect among charged particles and perturbations of energy eigenvalue of atoms were calculated. The calculation results show that: (1) When the total density n of H, O, H+, O+ and O2+ is about 1029 m-3, the electron density, ne increases by about 70% considering the correction of ionization potential; (2) The degeneracy of electrons has little effects on the pressure of PPDW; (3) The effects among charged particles makes the pressure of PPDW decreased at higher temperature, by no more than 10%; (4) When n=1029 m-3 and T2104 K, the pressure goes up by about 30% for the perturbation of atom energy level.

Effect of the Treatment under High-Temperature and High-Pressure on YNi2B2C Grain Boundary

XIONG Han, YAO Yu-Shu, YAN Qi-Wei, NI Yong-Ming, JIN Chang-Qing, ZHAO Zhong-Xian

2001, 15(2): 111-116 . doi: 10.11858/gywlxb.2001.02.006

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Abstract:
Near critical temperature a negative peak in the field-cooled measured-upon-warming magnetization curve was observed in YNi2B2C superconductor, which was prepared by melting in an arc furnace then treated under high pressure. The study of effect of high-temperature and high-pressure treatment on the magnetization curves of bulk and powder samples measured at zero-field cooled and field cooled conditions shows that the negative magnetic peak in the field cooled magnetization comes from the grain boundary that leads a week link, but not from magnetic phase transition or the coexistence of superconductivity and magnetism. The result also demonstrates that the preparation and crystal growth of the material can be taken under high temperature and high pressure.

Sound Speed of a Kind of Porous Iron at High Pressures

LI Xi-Jun, ZHOU Xian-Ming, JING Fu-Qian

2001, 15(2): 117-121 . doi: 10.11858/gywlxb.2001.02.007

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Abstract:
Four sound speed measurement experiments were conducted on porous iron samples and its bulk sound speed was calculated from its Hugoniot equation of state. The results indicate that the shock melting of the porous iron occurs in the pressure range of 121 to 157 GPa.

Hydrostatic Pressure-Induced Ferroelectric-Antiferroelectric Phase Transformation in PbLa(Zr,Sn,Ti)O3 Ceramics

XU Zhuo, FENG Yu-Jun, ZHENG Shu-Guang, JIN An, WANG Fang-Lin, YAO Xi

2001, 15(2): 122-126 . doi: 10.11858/gywlxb.2001.02.008

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Abstract:
Hydrostatic pressure-induced ferroelectric-antiferroelectric phase transformation and dielectric properties in PbLa(Zr,Sn,Ti)O3 ceramics were investigated experimentally. Experimental results show that the dielectric properties of the samples versus hydrostatic pressure suggest that diffuse phase transition and frequency dispersion.

Numerical Simulations of Blast Flow-fields in Closed Blast-Resistant Containers

CAO Yu-Zhong, LU Ze-Sheng, GUAN Huai-An, ZHANG You-Ping

2001, 15(2): 127-133 . doi: 10.11858/gywlxb.2001.02.009

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Abstract:
Numerical results of the time-dependent behaviors of blast flows in a closed blast-resistant container with hemisphere roof and cylinder wall are presented. Results obtained using a total variation diminishing (TVD) scheme are compared to experimental results. The numerical results are in good agreements with experimental results.

Study of Thermal Relaxation at CHBr3/NaCl Interface under Shock Compression

HU Jin-Biao, LIU Ji-Ping, TAN Hua, YANG Jia-Ling, TANG Zhi-Ping

2001, 15(2): 134-140 . doi: 10.11858/gywlxb.2001.02.010

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Abstract:
Shock temperature measurement of opaque materials is through measuring the optical radiation at sample/window interface. So the research of optical radiation history at sample/window is fundament of shock temperature measurement of opaque materials. But this research is not easily realized because of the mixture of temperature changing at the interface caused by thermal diffusion and wave reflecting because of mismatching of shock impedance between sample and window material. In this paper a special experiment system was proposed for researching the thermal relaxation process. The experimental results at two shock pressure points show that the thermal relaxation time is about nano-second, which agrees with the theoretical result calculated by Grover et al.

Surface Velocity Measurement Using All-Fiber VISAR

PENG Qi-Xian, TAN Hua, WANG Wei, LI Xue-Mei, WANG Wu, HU Li; YE Kun-Zhen, LIU Guo-Xiang, ZHENG Sheng-Cai

2001, 15(2): 141-145 . doi: 10.11858/gywlxb.2001.02.011

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Abstract:
A new kind of VISAR called all-fiber white light velocity interfermetic system for any reflector is introduced. The system was used to measure the free surface velocities of samples under dynamic loading. Experimental results show that the system works well for low velocity (10 m/s). It seems that the system needs to be improved for higher velocity.

The Influence of Temperature and Strain Rate on the Flow Stress of Tantalum

PENG Jian-Xiang, LI Da-Hong

2001, 15(2): 146-150 . doi: 10.11858/gywlxb.2001.02.012

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Abstract:
The influence of temperature and strain rate on the flow stress of tantalum under temperature range from -100 ℃ to 400 ℃ and strain rate from 10-5 s-1 to 5103 s-1 was studied. The results showed that the flow stress of tantalum was very sensitive to the changes of temperature and strain rate. Two theoretical methods were compared, and Zerilli-Armstrong model was found to be more satisfactory to describe the dependence of the flow stress on temperature and strain rate.

Investigation of Structures and Heat of Formation for RDX and Its Decomposition Products Using Molecular Orbital Method

CHENG Xin-Lu, WANG Kai-Ming, HU Dong

2001, 15(2): 151-154 . doi: 10.11858/gywlxb.2001.02.013

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Abstract:
The molecular structure and the heat of formation of explosive RDX and its decomposition products, such as C3H6N5O4, C3H6N4O2, H2CNCH2NCH2, CH2=NNO, were studied using molecular orbital method. The heat of formation obtained by PM3 method was very close to experimental results.

Discussion on the Physics Base of a Volumetric Equation of State

LI Xin-Zhu, WU Qiang

2001, 15(2): 155-160 . doi: 10.11858/gywlxb.2001.02.014

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Abstract:
A new equation of state v-vc=(R/p)(h-hc) with the assumption R=R(p) (where v, p, h are specific volume, pressure and specific enthalpy respectively, R is substance parameter, the subscript c refers to the state not depending temperature), has been used in the study of the shock compression of porous materials, since it was developed by Qiang Wu et al. However, this EOS was on the basis of the assumption that the specific heat at constant pressure cp remains constant, so its physics base about the EOS has not been proved and the concert form was not got. In this paper, a proof to the N-EOS was finished with solid physics and statistical mechanics, and the normal formula of substance parameters was obtained in microphysics. We also proved that the physics base of the N-EOS with R=R(p) is in correspondence with the law of states of the Debye theory and its validity is not limited by the assumption which the cp remains constant. In addition, the calculation results of R with experimental data under normal pressure shows that R=R(p) is not very accurate approximation. A tentative discussion about the problem of =(v) approximation of the Gruneisen EOS was done.

2001 Vol. 15, No. 2

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