高压物理学报

Carbon Nanotube Properties under High Pressure

CHEN Liang-Chen, WANG Li-Jun, TANG Dong-Sheng, XIE Si-Shen, JIN Chang-Qing

2001, 15(1): 1-4 . doi: 10.11858/gywlxb.2001.01.001

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Abstract:
The structure and physical properties of carbon nanotubes under high pressure up to 50.7 GPa were investigated using in situ high pressure energy dispersive X-ray diffraction with synchrotron radiation. At atmospheric pressure, the structure of carbon nanotubes is similar to the hexagonal close-packed lattice of graphite with the interplanar spacing of diffraction line (002) d002=0.340 4 nm and that of line (100) d100=0.211 6 nm. According to the high pressure X-ray diffraction results, diffraction results, diffraction line (002) is broadened and weakened above 8 GPa, and carbon nanotubes became partly amorphous. When pressure of 10 GPa and 20 GPa was down to zero, the diffraction line (002) was partly recovered. But at the maximum pressure of 50.7 GPa, they entirely became amorphous and this amorphous transition is irreversible. The equation of state of Birch-Murnaghan was used to obtain the bulk modulus .

Strain Gradient Effects on the Strengthening Behaviors of Particle Reinforced Metal Matrix Composites

DAI Lan-Hong, LING Zhong, BAI Yi-Long

2001, 15(1): 5-11 . doi: 10.11858/gywlxb.2001.01.002

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Abstract:
Although much efforts have been made to understand the relationship between microstructures and deformation behaviors of particle-reinforced metal matrix composites (PRMMCs) during the past several decades, there are still some phenomena remained to be understood, one of which is size effects in PRMMCs. Recently, many experimental results demonstrate that reinforcing particle sizes have a significant influence on yield and flow stresses of PRMMCs. However, various micromechanical models which are based unpon homogenization technique for particulate composites predict particle volume fraction effects on deformation behavior of composite materials but show an independence of particle sizes. According to this observation, a strengthening-strain gradient relation for particle-reinforced metal matrix composites was developed by madding use of the concept of geometrically necessary dislocation and proposed dislocation model. A comparison with existing experimental results demonstrates that the relationpredicts a dependence of yield and flow stresses of composites on reinforcing particle sizes. From this relation, we found that the strengthening effect of mechanical behavior of composites is controlled by both characteristic microstructure geometrical parameters and strain gradient in matrix. For a given PRMMCs, the strengthening effect of the composite is completely controlled by particle size or strain gradient in the matrix. This tells us that the strain gradient in matrix may be an important factor controlling deformation and fracture behavior of heterogeneous material systems. Moreover, effects of characteristic microstructure geometrical parameters on deformation localization of PRMMCs are also discussed.

Enhancement of Both Ionic Conductivity and Permittivity of the High Polymer Film P(EO)n-CuBr2 under Hydrostatic Pressure (Ⅰ)－Discovery of Pressure Effects of Three Different Phases

SU Xiao, DAI Wei-Ping, SU Fang

2001, 15(1): 12-23 . doi: 10.11858/gywlxb.2001.01.003

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Abstract:
With the addition of different weight of CuBr2 (ratio n =[EO]/[Cu]=4, 8, 12, 16, 24) to polyethylene oxide (molecular weight 5106), a series of high polymer ionic conductors P(EO)n-CuBr2 were prepared. Both complex impedance spectra of samples in the hydrostatic pressure range from 0.1 to 350 MPa and alternating current conductivity of samples in the pressure range from 0.1 to 2 400 MPa were measured in detail. Results show that the pressure dependence of conductivity can be decomposed into four linear parts. According to the phase analysis from X-ray diffraction patterns, it is found that three of the four straight lines correspond to the pressure effects of the amorphous phase of PEO, the crystalline phase of PEO, and the new phase of CuBr2. Hence, the composition dependence of the corresponding activation volume and cutoff pressure of the three types of conductivity-pressure effects can be calculated.

A Constitutive Model for Materials under High-Temperature and Pressure

LI Mao-Sheng, CHEN Dong-Quan

2001, 15(1): 24-31 . doi: 10.11858/gywlxb.2001.01.004

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Abstract:
D.J.Steinberg, S.G.Cochran, and M.W.Guinan (SCG) presented a constitutive model for metals applicable at high strain rate in 1980. A new expression for the temperature related term in SCG model was suggested in this work. The expression gives that their moduli vanish at melting temperature, i.e., G(Tm)=0. Therefore, SCG model with the suggested expression can be used to describe material properties under high temperature. We have carried out calculations for Al and 93W, the theoretical results are in agreement with that of experiments very well.

Effects of Graphitization on the Synthesis of Ultrafine Diamond by Explosive Detonation

CHEN Peng-Wan, YUN Shou-Rong, HUANG Feng-Lei, DING Yan-Sheng, CHEN Quan

2001, 15(1): 32-38 . doi: 10.11858/gywlxb.2001.01.005

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Abstract:
Graphitization plays an important role in the synthesis of Ultrafine Diamond (UFD) during explosive detonation. Carbon phase diagram was studied and a diamond-graphite dynamic equilibrium line is introduced to study the effects of graphitization. The effects of graphitization under different charge conditions and preserving conditions were investigated numerically.

Investigation of Shock Pressure Evolution of Initiation in IHE's JB9014 at Ambient and -54 ℃

CHI Jia-Chun, LIU Yu-Sheng, GONG Yan-Qing, LI Qiang

2001, 15(1): 39-47 . doi: 10.11858/gywlxb.2001.01.006

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Abstract:
The pressure evolution of shock initiation for IHE's JB9014 at ambient and -54 ℃ was investigated experimentally using embedded manganin gauges. The pressure evolution observed in JB9014 at -54 ℃ shows homogeneous initiation mechanism, by comparison, these observed in JB9014 at ambient temperature show a combination of homogeneous and heterogeneous initiation mechanism. The results show that JB9014 at -54 ℃ becomes significantly less sensitive to shock than at ambient temperature and that JB9014 is less shock sensitive than PBX-9502 with same TATB/binder ratio at both ambient temperature and -54 ℃.

Grain Size Refinement and Homogenization of Multi-component Powders by Shock Treatment

YANG Shi-Yuan, JIN Xiao-Gang, DONG Yu-Bin

2001, 15(1): 48-53 . doi: 10.11858/gywlxb.2001.01.007

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Abstract:
The grain size refinement and homogenization of Al-C, Al-Si and Si-C powders after shock loading were studied. Experimental results show that shock wave propagation in powders resulted in significantly grain size reduction and homogenization of micron powders. The extent of grain size reduction of one component is related to its crystal structure and mechanical properties. The grain size of shock treated Si-C powder is smaller than 300 nm.

Oblique Shock Wave Propagation in Water

TANG Wen-Hui

2001, 15(1): 54-59 . doi: 10.11858/gywlxb.2001.01.008

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Abstract:
The relation among downstream Mach number, density ratio, pressure increase, shock angle and upstream Mach number are discussed based on a simple equation of state for water. A dimensionless shock polar equation is presented. The critical conditions for the turning of attached oblique shock wave to detached shock wave and the downstream flowing at the velocity of sound are discussed.

Pressure Effect on Lattice Distortions of La0.3Bi0.2Ca0.5MnO3

WANG Xin, CUI Qi-Liang, PAN Yue-Wu, ZOU Guang-Tian, LIU Jing

2001, 15(1): 60-63 . doi: 10.11858/gywlxb.2001.01.009

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Abstract:
In-situ high pressure behaviors of Jahn-Teller distortions in La0.3Bi0.2Ca0.5MnO3 were studied by energy dispersive X-ray diffraction. External pressure modified effectively local structural parameters such as the MnO bond distance and MnOMn bond angle, and brings about the competition between the distorted mode Q2 and Q3. With pressure increasing, mode Q3 becomes dominant while mode Q2 within the a-b basal plane disappears at ～1.8 GPa.

Pressure Effect on Rheological Properties of Food Gum Solutions

LI Bian-Sheng, ZENG Qing-Xiao, RUI Han-Ming, LIU Tong-Xun, CHEN Zhong, RUAN Zheng

2001, 15(1): 64-69 . doi: 10.11858/gywlxb.2001.01.010

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Abstract:
The rheological properties of food gum solutions (carrageenan, agar, high methoxyl pectin, sodium alginate, xanthan and guar gums) after high pressure treat were investigated. After the treatment, the viscosity of the solutions changes very differently. The viscosity of carrageenan and agar solutions increases, that of high methoxyl pectin, sodium alginate and guar gum solutions dose not change very much, and that of xanthan gum solutions decreases. Experimental results show that the storage moduli (G) of carrageenan and agar solutions became smaller and their G are smaller than their G after the treatment. The loss tangents (tan =G/G) of high methoxyl pectin, sodium alginate and guar gum solutions after the treatment are almost the same as that before the treatment. All the results above indicate that the pressure effects on the solutions depend on gum structures. The possible reasons were discussed in the paper.

Flyer Velocity Measurement Using Double-Sensitivity VISAR

CHEN Guang-Hua, LI Ze-Ren, LIU Yuan-Kun, MA Ru-Chao, LIU Jun

2001, 15(1): 70-74 . doi: 10.11858/gywlxb.2001.01.011

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Abstract:
A double-sensitivity VISAR was used to measure flyer velocity. Through comparing two velocity histories and combining with physical consideration, it is possible to guess how many fringes were lost due to bandwidth limitation of VISAR.

Li3N Function in BN Synthesis

XU Xiao-Wei, LIU Zhi-Fu, LIN Qian-Shao, LI Yu-Ping

2001, 15(1): 75-79 . doi: 10.11858/gywlxb.2001.01.012

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Abstract:
Li3N functions in the reactions between B4C and nitrogen containing compounds were investigated under high temperature. Experimental results showed that no hBN formed from the reaction between B4C and Si3N4, and only small amount of hBN formed from the reaction between B4C and NH4Cl. After Li3N was added into starting materials, the amount of hBN formed from both reactions increased obviously. The reaction between Li3N and B4C did not form hBN. All the results gave the conclusion that Li3N acted as catalyst in the reaction between B4C and nitrogen containing compounds. No hBN or cBN was obtained from B4C-Si3N4-Li3N system after a high temperature and high pressure treatment. The rule of choosing B source and N source for cBN synthesis at lower pressure also is discussed.

2001 Vol. 15, No. 1

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