Shock synthesis

Shock Synthesis. When graphite is strongly compressed and heated by the shock produced by an explosive charge, some (up to 10%) diamond may form (26,27). These crystaUite diamonds are small (on the order of 1 llm) and appear as a black powder. The peak pressures and temperatures, which are maintained for a few microseconds, are estimated to be about 30 GPa (300 kbar) and 1000 K. It is beheved that the diamonds found in certain meteorites were produced by similar shock compression processes that occurred upon impact (5). 

For shock-synthesis and processing experiments, less precise systems are typically employed. These systems use commercial explosives that may be used to accelerate plates or to compress samples in the form of a tube. These systems are suitable for establishing nominal shock conditions for materials processing experiments, but are generally not suitable for careful characterization of materials response [87G02, 88M01]. 

Shock-synthesis experiments were carried out over a range of peak shock pressures and a range of mean-bulk temperatures. The shock conditions are summarized in Fig. 8.1, in which a marker is indicated at each pressure-temperature pair at which an experiment has been conducted with the Sandia shock-recovery system. In each case the driving explosive is indicated, as the initial incident pressure depends upon explosive. It should be observed that pressures were varied from 7.5 to 27 GPa with the use of different fixtures and different driving explosives. Mean-bulk temperatures were varied from 50 to 700 °C with the use of powder compact densities of from 35% to 65% of solid density. In furnace-synthesis experiments, reaction is incipient at about 550 °C. The melt temperatures of zinc oxide and hematite are >1800 and 1.565 °C, respectively. Under high pressure conditions, it is expected that the melt temperatures will substantially Increase. Thus, the shock conditions are not expected to result in reactant melting phenomena, but overlap the furnace synthesis conditions. 

Shockley diode equation, 22 243, 246 Shockley equation, 74 838-839 Shock synthesis of diamonds, 3 536 Shock treatment... 

Chyba, C. F. and Sagan, C. (1992). Endogenous production, exogenous delivery and impact-shock synthesis of organic molelcules an inventory for the origin of life. Nature, 355, 125-32. 

Wolffe, A.P., l.F. Glover and J.R. Tata. Culture shock synthesis of heat-shock-like proteins in fresh primary cell cultures. Exp. Cell Res. 154 581-590, 1984. 

Figure 5.13 Scheme of the diamond production by shock synthesis according to the DuPont method. 

Figure 5.14 HRTEM-image of diamond particles generated by shock synthesis in a laboratory scale reactor ( Elsevier 1998).

By shock synthesis A carbon material is converted into diamond by the action of a shock wave generated, for example, by a detonation or a projectile. This procedure is employed, for instance, to prepare polycrystalline microdiamond with primary particles measuring in the range of nanometers. 

The synthesis of a novel 7-813X4 phase with a cubic spinel structure (see Figure 2.1c) was carried out under high pressure (15 G Pa) and at temperatures above 1920 ° C in a laser-heated diamond cell [22]. Today, many different processing techniques for y-813X4 synthesis are available, the most common being the diamond anvil cell (DAC) synthesis (G. 8erghiou, et al., unpublished results), the multianvil pressure apparatus (MAP) synthesis [23], and the shock synthesis [24]. 

Batsanov SS, Egorov VA, Khvostov YuB (1976) Shock synthesis of difluorides of lantanides. Pioc Acad Sci USSR Dokl Chem 227 251-252... 

Diamond and cBN powders produced by milling are essentially monocrystalline and dominate the market. However, polycrystalline diamond powder can also be produced by shock synthesis. Under suitable conditions, shock waves produced by explosively driven projectiles can produce HPHT conditions in confined volumes for a sufficient duration to achieve partial conversion of graphite into nanometer-sized diamond grains which can also sinter into micrometer-sized, polycrystalline partieles." This process was commercialized by DuPont to produce a polycrystalline DMP (trade name Mypolex ) that is more friable than monocrystalline DMP and is well suited to fine polishing applications. Hexagonal (graphite-hke) BN will also react under shock-synthesis conditions, but the dense, nanometersized particles that are produced are of the wurtzite phase (wBN) rather than the cubic phase. So far, nano-wBN has not achieved much commercial importance. 

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