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Solids under Ultra-High Pressure

#0812


Studies of Structural Changes of Solid State Bodies Under Ultra-High Pressure Test Explosions with Sample Preservation

Tech Area / Field

  • PHY-SSP/Solid State Physics/Physics

Status
3 Approved without Funding

Registration date
23.12.1996

Leading Institute
VNIIEF, Russia, N. Novgorod reg., Sarov

Supporting institutes

  • Science and Technology Center "Superstrengh Materials", Russia, Moscow reg., Troitsk

Project summary

Improvement of the experimental method enabling the container (ampoule, core) with the materials under study to be kept safe after it has been affected by a high pulsed pressure (P » 100-400 GPa, pressure affecting time is »5 ms), and revealing of metastable phases in different substances, as well as solid-state chemical reactions in explosive experiments.

Expected results:

Improvement of investigation methods including those with the controlled pulsed pressure range, preservation of ampoules after loading, revealing of new metastable phases in substances placed into ampoules.

This project objective is to improve the experimental method enabling the container (ampoule, core) with the samples under study to be kept safe after it has been affected by a high pulsed pressure (P » 100-400 GPa, pressure affecting time is » 5ms and the pressure has been later reduced during unloading.

The developed method is suggested to be project used for studies into property changes of different materials after loading. The container (for example, in spherical geometry) can be kept safe after the experiment, if the pressure is produced within it by exploding a thin explosive layer on its surface (the work of Bakhrakh S.M., Kovalev N.P., Nadykto B.A., Novikov S.A., Chernyshev A.K. Doklady Akademii Nauk SSSR, 1974, t.215, N5, s.1090). However, in this case the pressure affecting time and amplitude are rather low because the velocity of the substance scattering on a radius from the center is suppressed due to material strength and plasticity. The further pressure increase results in destruction of the container holding the samples under study.

The devices used in project activities make it possible to expose the studied samples to a pulsed pressure from 100 to 400 Gpa during » 5 ms. The devices are structurally similar to those described in the work of Voinov B.A., Nadykto B.A., Novikov S.A., Sinitsyna L.M., Tkachenko I.A., Yukina N.A. published in "Physics of combustion and explosion", 1991, N4, p. 109. The container and samples safety is provided by using the system of heavy and light shells as parts of the cylindrical or spherical structure, which are arranged at a greater radius compared with the container. After pressure effects have been produced, the central ampoule (container) expands during unloading, decelerates in colliding with the inside heavy shell and remains indestructed.

Thus, the technical problem consists in improving and using spherical and cylindrical explosive devices for producing high pulsed pressures in ampoules kept safe after loading Liquid or solid explosives are used in these devices. Parameters of the devices are chosen based on gas dynamics calculations. Pressure-producing devices are expendable. After having been pulsed loaded, the tested materials are studied under laboratory conditions using spectral x-ray diffraction, microstructural and other methods.

Even P.Bridgeman (USA, 1940 s) noted that the static pressure of up to 10 GPa can result in great changes in structures and properties of solids. It was shown that mobility of solid atoms increases greatly under simultaneous effects produced by balk compression and shear stresses.

These phenomena were studied in detail by Yenikolopyan N.S. and his colleagues when they carried out laboratory static experiments (USSR, 1970-1990).

Phase transitions under a high static pressure (up to 200 GPa or over) are widely studied in experiments using diamond anvils. The apparent advantage of these experiments is the possibility to make a x-ray analysis of the compressed substance. The drawback of these experiments is a very small amount of the substance affected by a high pressure.

During explosive loading of samples by converging shock waves a complex deformed state is realized in compression. Under such conditions rearrangement of the crystal substance structure or chemical solid-phase reactions can take place, if the material is a complex compound. The effects produced upon the materials by compression wave high pressures and temperatures as well as by later unloading results in their destruction, melting, and formation of new dense modifications having changed physical and chemical properties. Activities under this project will make it possible to study the processes of melting during shock compression (role of micrestructure in this phenomenon), mechanical (mixing) and chemical (formation of new compositions and new crystal modifications) interactions of contacting metals, diffusion, etc.

In explosive experiments a higher pressure is produced in the substance, which can results in phase transformations and chemical reactions not proceeding under static loading. Besides, in these experiments a much greater substance mass is affected by a high pressure, which can be important for determining some physicochemical and mechanical properties of new substances. This method seems to be a useful addition to other existing methods. In proposed explosive experiments new metastable phases of substances having useful properties can be revealed. It is known that some metastable phases (such as diamond stishovite) have unique properties.

Improvement of loading explosive devices (calculations and experimental works), selection of the material to be used for studies, explosive experiments and further laboratory investigations of materials after loading are the proposed program perfection stages.

A helpful contribution of participating foreign collaborators may consist in selecting the investigation materials, probable carrying out of studies using their own equipment as well as joint discussing of the work plan and the course of its fulfilling, participating in seminars, workshops, joint publications.

The proposed project allows the weapons specialists to redirect their knowledge and expertise towards peaceful subject matters and join the international science and technology community.

The project objective is in keeping with the ISTC objective regarding support of fundamental and applied peaceful investigations, and provides perspectives for collaboration with the world science and technology community.


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