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Dynamic Synthesis of Diamonds

#KR-864


Numerical Simulation and Experimental Tests of Phase Transitions in Carbon at Moderate Dynamic Conditions of Loading

Tech Area / Field

  • MAT-SYN/Materials Synthesis and Processing/Materials
  • CHE-THE/Physical and Theoretical Chemistry/Chemistry

Status
3 Approved without Funding

Registration date
28.03.2002

Leading Institute
Kyrgyz-Russian Slavonic University, Kyrgyzstan, Bishkek

Collaborators

  • University of Nebraska / Department of Chemical Engineering, USA, NE, Lincoln\nKumamoto University / Shock Wave and Condensed Matter Research Center, Japan, Kumamoto

Project summary

The main objective of the project is to investigate the dynamic synthesis of diamonds at moderate and low pressure. These findings can be juxtaposed to conventional methods of super-high pressures. To accelerate the kinetics of phase transition from hexagonal graphite to diamond under these milder conditions, preliminary treatment of initial components is required. Treatments include mechanical activation, dynamic compaction etc. Special emphasis will be placed on mechanochemistry, because lowering of activation energies by lattice distortion, elastic or plastic in nature, is still considered an underexplored area in science. High priority will also be given to research on and selection of the most effective catalysts for phase transitions in graphite.

Another important goal of the project is to lengthen the exposure time of the reacting species to extreme conditions (i.e. pressure, temperature, dynamic effects). An increase in exposure time of the system leads to larger crystals and higher yield. To increase the exposure time, it is proposed to use a combination of high-velocity processes (impact and explosion), accompanied by SHS chemical reactions (Self-Propagation High-Temperature Synthesis). New experimental systems should be developed on a basis of the ballistic launcher facility that is currently available, with the help of numerical calculations.

Some preliminary experimental results have been obtained. Initial velocities of the projectile were 700-1200 m/s, diameter of Cu-C specimen was of 40-60 mm, content of graphite in the mixture was of 8-16%, content of synthesized diamond was of 3.5-19%, sizes of crystals - up to 300 мm and more. The experiments demonstrate the possibility to obtain diamonds under moderate pressure using preliminary treatment and a catalyst.

The experimental data alone do not provide sufficient information to reveal all the details of the dynamics of the process and to optimize the process for synthesis of artificial diamonds. The modern engineering approach is to use detailed numerical models to describe the behavior of the condensed medium under extreme conditions of loading. High-performance computers allow one to conduct large-scale computing experiments with high level of reliability, in other words, the models provide not merely qualitative, but actual quantitative data on the process. Thus it becomes a design tool that can assist in the selection of optimum conditions of the process and design of experiments.

A mathematical model for high-velocity processes was developed. A model of porous medium was used in the computations. It is characterized by the possibility of void formation, growth, and annihilation. The mathematical model of the problem includes, within the framework of mechanics of deformable solids, the equations of mass, momentum and energy. This set of equations is closed by the equation of state of Mie-Gruneisen type and governing equations for the elastic-plastic behavior of the continuum under conditions of shock-wave loading are used. The model takes into account the influence of temperature effects on macrokinetics of phase and chemical transformations.

In preliminary numerical studies, the behavior of the Cu-C mixture under shock wave loading was investigated. The numerical simulations were carried out in axisymmetrical statement by the finite element method. Initial velocity of the projectile (aluminum cylinder, 30 mm in diameter, 40 mm long) was of 800 m/s. The ampoule with external diameter of 40 mm and 80 mm long contained the pressed mixture Cu-C (d0 = 36 mm, с0=6.8 g/cm3, the initial porosity was 6 %, T0=1100 K). The width of the lateral steel wall of the ampoule was 2 mm. On the back side of the ampoule a rigid wall was placed. The results of the computations illustrate the process of propagation of a shock wave along the ampoule accompanied by a decrease in the amplitude of pressure, because of a lateral unloading wave. Later, at a stage of steady penetration of the projectile into the ampoule, the amplitude of pressure has become approximately 0.5 GPa.

For development of the research within the framework of the given project it is proposed to implement the following tasks:

1. Development of mathematical models of the process. Adaptation of a computer code to the problems. Increase of efficiency of the numerical scheme.

2. Computation of processes of preliminary treatment of components of a mixture.

3. Computation of the combined effects of high-velocity impact, explosion, chemical SHS-reaction on the synthesis of artificial diamonds.

4. Computation of the effect of catalysts on phase transitions.

5. Calculation and improvement of parameters of the experimental equipment for verification of the numerical simulation.

6. Experimental tests. The microanalysis of the received samples.

7. Summarizing of obtained results, description of a technique of synthesis of diamonds in moderate dynamic conditions and application for the patent.

The research team has wide experience in materials science and in theoretical and experimental study of processes of high velocity loading of deformable solids that confirms by papers in scientific journals, active participation in international symposia and conferences on mechanics, physics, and chemistry. At disposal of the team there are numerical codes for successful fulfillment of the project tasks. The agreement on use of the experimental equipment located in Tomsk (Russia) is achieved.

The work plan consists of the following tasks:

1. Development of the mathematical models of the process and the subsequent numerical codes;

2. Do a systematic numerical study of the processes of mechanical activation, dynamic compaction, and the influence of phase transitions;

3. Investigate the effects of impact velocity, explosion, chemical SHS-reactions on yield;

4. Design experimental equipment on the basis of the numerical results;

5. Build experimental set-up and perform experiments to validate the numerical results.

Major results of the project will be new knowledge of fundamental features of phase transitions in carbon at moderate dynamic conditions of loading with formation of a cubic phase. Another result will be the development of a new technique, designed by computer and verified in the laboratory, for the synthesis of artificial diamond. The successful completion of the project will enable the research team to do further research on synthesis of other materials. It will also bring valuable lessons in patent filing, intellectual property handling and licensing agreements.

The role of the foreign collaborators will consist of the refinement and coordination of the plan of activities, exchange of the scientific information, participation in achieving the various research goals of the project, providing comments on the reports on the project, assist with intellectual property handling and help to disseminate results. Prof. Hendrik J. Viljoen (USA) will provide input on the development of mathematical models of the process, and Prof. Kazuyuki Hokamoto (Japan) on the experimental aspects of the research.

The project will promote recovery and strengthening of links between CIS scientists and integration of Kyrgyz scientists into the international scientific community. If the project is funded, the objectives of the research will be met and it will lead to a new technology. Scientists will get valuable lessons in patents, licensing and technology transfer that will motivate them further to develop industrially valuable processes and acquire economic independence.


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