High-temperature Shock Compression Research Articles

Determination of P,T-conditions developed at high-temperature shock compression of silicon nitride in planar recovery ampoules

We performed experiments on shock compression up to pressures of 36 and 50 GPa of mixed samples of silicon nitride and potassium bromide, placed between copper plates that serve as walls of a recovery ampoule. For comparison, similar experiments were carried out by the conventional compression of a mixture of silicon nitride and copper powder. The loading of the samples was fulfilled by means of aluminum flyers accelerated by products of explosion to a few kilometers per second. The pressure profiles prior to a shock wave entering the sample and after its runout were measured with the use of manganin sensors. It is found that for the configurations of the experimental assembly used, the pressure in the samples, accumulated by circulating the shock wave, reaches the desired value before unloading. Based on estimates of the rate of heat transfer between the components, it is shown that thermal equilibrium can be set during the existence of high pressure in the mixed samples. Within the framework of the single-temperature medium model, the equations of state of the samples are derived, and the temperatures of their shock compression are calculated. Using these equations, we performed numerical simulations that showed good agreement with the experimental data.

Formation of cubic silicon nitride from the low-pressure phase by high-temperature shock compression

The effect of high-temperature shock compression conditions on the degree of transformation of silicon nitride into a cubic γ-modification at pressures of 36 and 50 GPa in planar recovery ampoules is studied. The x-ray Rietveld method is used to determine the quantitative phase composition before and after shock compression. The temperature reached during compression and the residual temperature after unloading are calculated. It is shown that the use of high-temperature shock compression at 36 GPa provides a higher transformation level compared to the classical approach based on the addition of copper powder into the samples.

Phase Transformations in High-Temperature Shock Compression of Carbon Black in Various Recovery Capsules

Cylindrical recovery capsules without a central rod are used for the first time to study the phase transformations in carbon black under shock compression. Substantial differences in the regularities of transformations under shock compression in such capsules and in annular capsules (with a central rod) are revealed (the latter we used earlier to study the phase transformations in carbon materials).

Effect of Preliminary Treatment on the Structure and Phase Transformations of Graphite Under High-Temperature Shock Compression

The effect of preliminary shock-wave treatment of graphite on its subsequent transformations into dense modifications of carbon under high-temperature shock compression is studied. It is shown that this treatment leads to higher concentration of turbostratic stacking defects, increases the extent of lattice microdeformation along the c axis, and induces the formation of twins with three-dimensional configuration of C— bonds on twin boundaries. These defects significantly but differently influence the phase transformations. Turbostratic defects inhibit phase transformations whereas microdeformation and twins accelerate them.

ОБРАЗОВАНИЕ КУБИЧЕСКОГО НИТРИДА КРЕМНИЯ ИЗ ФАЗЫ НИЗКОГО ДАВЛЕНИЯ ПРИ ВЫСОКОТЕМПЕРАТУРНОМ УДАРНОМ СЖАТИИ

ОБРАЗОВАНИЕ КУБИЧЕСКОГО НИТРИДА КРЕМНИЯ ИЗ ФАЗЫ НИЗКОГО ДАВЛЕНИЯ ПРИ ВЫСОКОТЕМПЕРАТУРНОМ УДАРНОМ СЖАТИИ

Structure formation of the superhard carbon ceramics in sintering powders of the carbon amorphous phase in a mixture with nanocrystalline diamond at high static pressures

The results have been discussed of studying the structure and hardness of polycrystals produced from nanodispersed powders of mixtures of the amorphous carbon phase and nanocrystalline diamond. The initial powders have been synthesized by high-temperature shock compression and sintered at a pressure of 13 GPa and temperatures from 1100 to 2000°C. The sintering has been accompanied by the transformation of amorphous carbon into diamond. As the diamond content of the sample has been increased from 10 to 100%, the hardness increased from 45 to 80 GPa.

Shock-wave synthesis of diamond nanofibers and their structure

Diamond nanofibers produced by high-temperature shock compression of graphite nanofibers in the presence of KCl at pressures of 25–35 GPa and temperatures of 3000–3500 K have been considered. The synthesized fibers have been shown to consist of randomly oriented nanograins of diamond with the amorphous phase impurity, whose content decreases as the impact compression pressure increases.

Phase transformations of carbon-black in high-temperature shock compression

The carbon-black transformations into diamond and amorphous carbon phase having an intermediate density of 2.9 g/cm3 in high-temperature shock compression at 20–32 GPa and 2500–3500 K have been studied. The conditions of compression that ensure the maximum yield of these phases have been defined. The transformation regularities have been analyzed under the assumption that the amorphous phase is an intermediate structure on the way to the transformation of turbostratic carbon into diamond.

Explosion energy in the synthesis of superhard phases

This article reviews works of the Institute for Problems of Materials Science evoted to the application of explosion energy for the synthesis of superhard phases (SHPs) based on phase transformations of layered structures of carbon and boron nitride at high pressures. Major attention is given to the development and application of the high-temperature shock compression method, which made it possible to synthesize a new structural form of carbon and to attain, for the first time, a 70% yield of cubic BN under shock compression. The diagram of BN phase transformations by different mechanisms is discussed, which demonstrates the dependence of the phase composition of shock compression products on the ordering degree of the starting graphite-like structure.

Formation of diamond-like BN phases under shock compression of graphite-like BN with different degree of structural ordering

The formation of diamond-like modifications of BN under high-temperature shock compression ( P = 33 GPa and T up to 3500 K) has been studied. The powders of graphite-like BN with different degree of three-dimensional ordering of structure ( D 3) were used as starting materials. To increase shock temperature and preserve dense phase formed, boron nitride powder mixed with alkali halide salt was compressed in cylindrical ampoule. The recovered samples were studied by X-ray diffraction and electron microscopy. It was revealed that the phase composition of shock compression products depends on the degree of three-dimensional ordering of initial graphite-like structure. Turbostratic BN with disordered structure ( D 3 = 0) transformed mainly into cubic cBN by diffusion mechanism, whereas highly ordered graphite-like BN ( D 3 = 0.95) transformed only into wurtzite wBN by martensitic mechanism. Both cubic and wurtzite dense modifications are formed from partly ordered initial structures (for which D 3 was 0.45 ÷ 0.7). The both diamond-like phases have nanocrystalline structure.

Structure of intermediate carbon phase formed under shock compression of ultradispersed graphite materials

We have studied the structure of the products of high-temperature shock compression of wood charcoal by x-ray diffractometry and transmission electron microscopy. We have shown that as a result of phase transformations at high pressures (30 GPa) and temperatures (above 2500 K), besides nanocrystalline diamond we see formation of an amorphous carbon phase having a density intermediate between the densities of the original charcoal and diamond. Based on comparison of the observed diffraction patterns with the patterns calculated for different models for amorphous carbon, and also considering the intermediate value of the density for the amorphous phase, we have concluded that this phase has the short-range order of the hypothetical H-6 structure, characterized by a three-dimensional framework of sp2 bonds. The amorphism of the intermediate phase is due to both the crystallographic nature of the H-6 structure and the disorder of the original structures, the regular rearrangement of which to form crystalline structures is not possible.

Development of a Method for High-Temperature Shock Compression of Powder Mixtures to Obtain Cubic Boron Nitride

We used shock compression of a mixture of boron nitride powder with an alkali halide salt as an additive to realize the phase transformation of turbostratic BN to the cubic modification. We have experimentally studied the effect of the type and amount of the additive and also the initial density of the mixture on the yield of the cubic phase of BN. We have roughly calculated the pressure and temperature arising upon shock compression of powder mixtures in an annular cylindrical storage ampul. We have shown that melting of the additive has a substantial effect on development of the phase transformation in boron nitride under shock loading conditions.

Phase transformations of disordered structures of graphite-like boron nitride under high-temperature shock compression

The pattern of phase transformations in boron nitride under high-temperature shock compression has been studied using a previously proposed method for high-temperature shock-wave synthesis of high-pressure phases followed by rapid quenching. Fine powders of turbostratic and partially ordered graphite-like BN were used as initial structures. Shock compression was carried out in ring devices at a pressure of 30 GPa and a temperature above 2500 K. A mixture of dense phases (wurtzitic and sphaleritic) was found to form from the graphite-like structures under those conditions; the total yield of those phases and the relative amount of the sphaleritic modification are considerably higher when turbostratic BN is the starting material. Both of the dense phases formed have a nanocrystalline grainstructure. The wurtzitic phase does not transform into the sphaleritic phase under those conditions, which points to cubic BN forming directly from the graphite-like structures.

Phase transformations of disordered structures of graphite-like Boron Nitride under high-temperature shock compression

Phase transformations of disordered structures of graphite-like Boron Nitride under high-temperature shock compression

Formation of B-C-N heterodiamond through high-temperature shock compression of diamond and c-BN powder mixture

Formation of B-C-N heterodiamond through high-temperature shock compression of diamond and c-BN powder mixture

Shock Synthesis of Ternary Diamond-Like Phases in the B ― C ― N System

Nanodispersed powders of the ternary graphite-like phases BC1.28N and BC2.14N have been used along with mixtures of powders of turbostratic BN and C in high-temperature shock compression followed by sharp quenching. The yield of diamond-like phases has attained 50% by volume. The excess of the graphite-like phase has been removed by treatment with molten alkalis containing nitrates and then with concentrated HClO4. The shock and chemical treatments alter the compositions of the diamond-like phases towards BCN in both of the BCxN specimens on account of the segregation of the excess carbon followed by the dissolution of it. Precision lattice-parameter measurements and line shape analysis indicate that the diamond-like phase is a BN ― C substitutional solid solution. Treatment of a mechanical mixture of the graphite-like phases of carbon and BN under the same p and T conditions led to the formation of a mixture of cubic boron nitride and diamond.

An improved high-temperature shock compression and recovery system using underwater shock wave for dynamic compaction of powders

Abstract A high-temperature shock compression system using converging underwater shock waves has been developed and the performance is under attempted improvement in the present investigation. A maximum temperature of 1100°C was obtained, and the use of PBX explosive with detonation velocity of 8.5 km s−1 gave us the higher shock pressure. Also, scaling up the size of the experimental apparatus especially in the size of explosive made possible an increase in the duration of shock pressure. Small fragments of consolidated diamond powders were recovered due to difficulty of recovery of the new system, but the sample showed very high Vickers hardness above 60 GPa.

Development of high-temperature shock compression system for consolidating powders by the use of underwater shock-wave assembly

A new system for high-temperature shock consolidation was developed using a converging underwater shock-wave assembly. The possibilities and difficulties in designing the high-temperature experimental system are pointed out, and the performance of the system is evaluated by some experiments.

Reaction of powdered superhard materials with gases during high-temperature shock compression

Reaction of powdered superhard materials with gases during high-temperature shock compression

Thermal properties of alkali metals from static and dynamic compressibilities

A detailed comparison of the isothermal compression data of Vaidya et al. on the alkali metals in the preceding article is made with high temperature shock compression data. The comparison provides evidence for strong electronic d-band effects in the equation of state of Rb at high temperatures at pressures as low as 50 kbar.