高压物理学报

Explosive Shock Synthesis of Wurtzite Type Boron Nitride

TAN Hua, HAN Jun-Wan, WANG Xiao-Jiang, SU Lin-Xiang, LIU Li, LIU Jiang, CUI Ling

1991, 5(4): 241-253 . doi: 10.11858/gywlxb.1991.04.001

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Abstract:
Reported in the paper are techniques of wurtzite type boron nitride (wBN) synthesis from graphite type BN (gBN) by means of shock compressions created via explosive detonation. Recovered samples after shock processing are treated with molten alkalis and hydrochloric acid. Despite that the domestic gBN materials we used are far inferior, both in the crystallinities and particle sizes, to those used in foreign countries for the purpose of shock synthesis of wBN, the yield of our wBN reaches 11 to 12 g per shot, with a convertion ratio over 50%; X-ray diffraction and x-ray fluorescence spectrometry analyses reveal that the total impurity content of this chemically extracted wurtzite type boron nitride product is less than 0.5%. Four different starting gBN from different manufacturers were used in the experiments to synthesis wBN under the same conditions of shock compressions. It is found that the yield of wBN is closely related to the crystallinity of the starting gBN materials. Specific area measurements and XRD analysis indicate that our wBN is a polycrystal super-fine powder material with average particle size of 0.1 m, which consists of many primary crystallites of 17.5 nm in dimension. Thermal stability of our wBN powder is characterized by the emergence of an exothermic peak in the atmospheric gas condition from DTA analysis. Initial temperature of this exothermic reaction is about 1 055 K and peak temperature 1 238 K.

Pressure Induced fcc-hcp Phase Transition of Fe62Ni27Mn11 (wt%) Alloy at Room Temperature

YANG Hai-Bin, ZOU Guang-Tian, LI Ming-Hui

1991, 5(4): 254-262 . doi: 10.11858/gywlxb.1991.04.002

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Abstract:
By using Mao-Bell type diamond anvil cell (DAC) and an in situ high pressure powder X-ray diffraction method, the pressure induced phase transition and the isothermal compression of Fe62Ni27Mn11 (wt%) alloy were investigated at room temperature and high pressure up to 43.2 GPa. The crystal structure of this alloy is the fcc structure below 19.4 GPa. The pressure induced fcchcp phase transition occurs at 19.4 GPa, and then the fcc phase and the hcp phase coexisted up to 43.2 GPa with the same molar volume. The ratio of the lattice parameters of the hcp phase, c/a, keeps essentially a constant value of 1.6300.006 in the present high pressure range of the experiments. In the course of unloading, the hcp phase will remain its existence down to 5.8 GPa, and then transforms completely to the fcc structure as it is release to atmospheric pressure. The Murnaghan isothermal equation of state for this alloy was fitted with the parameters B0=(16612) GPa, B0'=5.20.5 by using the least-square method. A model for this pressure induced fcchcp phase transition is presented and the reason why it has so wide a two-phase-coexistence pressure region is also discussed.

The Relationship of the Electronic Structure and EOS of LiH with the Ion Radius Ratio

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

1991, 5(4): 263-266 . doi: 10.11858/gywlxb.1991.04.003

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Abstract:
The computational results of ion crystal LiH at different WS radius ratios by using LMTO energy band method are presented. The compressibility is from =1.0 to =2.5. The effects on electronic structure, electronic occupation number and zero-temperature equation of state are examined. It is shown that if the WS radius ratio R(Li)/R(H) is too small the calculation will yield wrong results; if the ratio is in a reasonable range, different values of radius ratios will affect the electronic structure and electronic occupation number, but affect little the overall properties of the crystals, such as, the EOS, phase transformation and so on. The above effects will be weakened at high pressures.

A Study on Sintering Behavior of Silicon Nitride Si3N4 Micro-Powder under High Pressures

SHEN Zhong-Yi, SUN Ji-Rong, LIU Shi-Chao, LIU Yong, HUANG Zhen-Kun

1991, 5(4): 267-274 . doi: 10.11858/gywlxb.1991.04.004

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Abstract:
Silicon nitride (Si3N4) is a series of ceramic material with outstanding technological properties and has been widely investigated for various engineering applications. On the other hand, these kinds of ceramics are of covalent bounding and are very difficult to sinter. This investigation was conducted for understanding the high pressure sintering behavior of Si3N4 micro-powder samples. Sintering was performed at high pressures ranging from 3 to 7 GPa and temperatures in a range of 800~2 000 ℃. The sintering samples are composed of Si3N4 and AlN, Al2O3 and La2O3 additives. The sintering compacts were characterized with the aid of X-ray diffraction, scanning electron microscopy and density measurement methods. The obtained results shows that the conversion of Si3N4 phase is greatly promoted by highly compression and the powder samples could be sintered at quite lower temperatures. Additionally, the high pressure sintering process is observed to be consisting of two stages: at moderate temperatures the sintering process consists of only the joining of the composited particles, while at high enough temperatures, the solid state reactions between the composite powders can be greatly proceeded and resuled in a fully sintered compacts.

Study of Wurtzite-Type Boron Nitride and Its Applications (Ⅰ)Shock Wave Synthesis of Wurtzite-Type Boron Nitride

CHI Yuan-Bin, WANG Li-Zhong, XU Hong-Shan, LI Ming-Hui, CHEN Li-Xue, LI Shu-Qing, CHEN Yu-Fei

1991, 5(4): 275-285 . doi: 10.11858/gywlxb.1991.04.005

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Abstract:
Two kinds of hBN (hexagonal boron nitride) powder were used as raw material for synthesizing superhard BN by shock compression. Our explosive experimental assembly was similar to that of Japan Nippon Oil and Fast Company Ltd. After shock treatment the recovered mixture of BN and iron powders was immersed in HCl solution to dissolve the iron material. The residue was refined by caustic fusion. By observing X-ray diffraction pattern, we found that all refined BN was wBN (wurtzite-type boron nitride) and that zBN (zinc blende-type boron nitride) did not exist in the refined BN. The purity of refined wBN approached 99% and the impurities were Cr, Fe, Ti, Mn and Ca. We think the impurities to come from the stainless steel capsule used in caustic fusion, except the Ca originated in the raw material hBN. Using Scherrer line-broadening equation D=57.3K/(b-b0)cos , the crystallite sizes of the wBN were estimated at 24 nm, It was also noted that the sizes of wBN transformed from abovementioned two kinds of the raw material were no obvious difference. The DTA result manifests that the wBN started endothermal reaction at 1 127 K and the absorptive peak of heat was at 1 260 K. This shows the wBN to be more thermostable than diamond but less than zBN.

A New Method for Polishing Sintered Diamond

XU Ji-An

1991, 5(4): 286-287 . doi: 10.11858/gywlxb.1991.04.006

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Abstract:
A smooth, fine and easy polishing method for sintered diamond with iron metal is reported in this paper.

Relative Electrical Resistance of Tungsten under High Pressure

PU Feng-Nian, BI Xiao-Qun, DING Yu-Zhen, GOU Qing-Quan

1991, 5(4): 288-290 . doi: 10.11858/gywlxb.1991.04.007

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Abstract:
The pressure dependence of relative electrical resistance of tungsten is measured in the DAC by our established method under the pressure from 0.8 GPa to 30.8 GPa. The measurement below 10 GPa is in good agreement with that of Bridgman. In the pressure range from 10 to 30.8 GPa, the relative electrical resistance of tungsten decreases smoothly with the increasing pressure. The data above 10 GPa have not ben reported to our knowledge so far.

The Experimental Research of Heat Resistance of Octahedral Boron-Skinned Diamond

ZHANG Qing-Fu, GOU Qing-Quan, LIU Lü-Hua, ZHANG Hui-Ping

1991, 5(4): 291-295 . doi: 10.11858/gywlxb.1991.04.008

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Abstract:
This paper presents the experiment results on the boron atom permeated into the surface of natural octahedral diamond to form boron skin with ion implantation method. Analysis was done to find whether its heat resistance is the best. The XPS analysis and TGA analysis were carried out on octahedral B-skinned diamond with four energies (2.0, 5.5, 7.0 and 8.5 keV). XPS analysis showed that B-skin was formed on the surface of diamond. TGA analysis proved that the onset oxidation temperature of octahedral B-skinned diamond is over 1 000 ℃. Results show that {111} plane of octahedral B-skinned diamond has the best anti-oxidization resistance, and this property is not dependent on the depth of B atoms implanted into the diamond.

Sintering of Diamond-Tungsten Carbide Composite under High Pressure and High Temperature

LI Ying, ZOU Guang-Tian

1991, 5(4): 296-300 . doi: 10.11858/gywlxb.1991.04.009

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Abstract:
With small amount of TiH2 and other elements as the cement, a high quality diamond-tungsten carbide composite has been sintered at high pressure and high temperature with DS-029A type cubic press. In the experiment, dehydrogenation of TiH2 and purification of diamond powder were carried out simultaneously at high vacuum and high temperature to get active Ti with stronger compendiousness to sinter diamond powder as well as diamond powder-tungsten carbide base. The relations between abrasive resistance and microstructure of the composite and between abrasive resistance and experimental conditions were investigated in detail. The thermostability of the composite was measured. Results show that the abrasive resistance of the composite changes little with temperature up to 850 ℃.

Approximate Calculations of Shock Adiabats for Porous Materials

LI Xiao-Jie

1991, 5(4): 301-306 . doi: 10.11858/gywlxb.1991.04.010

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Abstract:
In this paper, it is assumed that the linear relationship of shock adiabat, D=a+bu is valid for dense materials having different specific internal energies at zero-pressure. On the basis of this assumption and by using the thermal expansion relation at normal pressure, equations for calculating shock adiabats and isentropic for porous materials are derived. The calculated shock adiabats for porous aluminum, copper, and iron, are in accord with the measured data given in Ref. [1].

1991 Vol. 5, No. 4

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