Detonation synthesis

The generation of high pressures by means of a detonahon in a confined container has been known for long. As early as in the 1960s it has been employed by soviet scientists to prepare nanodiamond, and by now the controlled detonation of explosives is performed even on a large scale. 

In principle, there are two procedures that differ in the kind of starting material used. In the first process, the explosive is detonated mixed with a graphitic substance. Two things happen simultaneously then Firstly, a direct conversion of the already existing elemental carbon, and secondly, a condensation of carbon from the explosive. Together they result in the formation of a polycrystalline diamond product with particle dimensions almost idenhcal to those of the starting material. Hence, an at least partially martensitic process can be assumed for the mechanism of formation. The yield is about 17% relative to the carbon employed or, relative 

Sometimes also methane, ammonia, and nitric oxides form in addition to the products given in Eq. (5.1). At the same time the substances present are coupled to each other by several equilibria (Eq. 5.2(a)-(c)). 

In a first step, the carbon atoms released from the decomposition of the explosive coalesce to form small clusters. These keep on growing then by diffusion. From a certain particle size on, the growth of diamond particles takes place also at the expense of smaller clusters. It ceases completely, however, once the pressure has dropped. The time-window for diamond formation is very short due to the detonation character of the synthesis, so particles can only be formed up to a certain size in the first place. Considering further that the markedly smaller 

Usually, several detonations are performed in a chamber before the soot is removed. Apart from the coolant chosen, the product quality is also influenced by the reactor geometry as it is decisive for the fast heat dissipation. The detonation soot is purified in an autoclave under elevated pressure and at high temperatures 

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Dolmatov VY (2001) Detonation synthesis uitradispersed diamonds properties and applications. Uspekhi Khimii 70(7) 687-708, in Russian... 

Dolmatov VY (2003) Ultradisperse diamonds of detonation synthesis production, properties and applications. State Polytechnical University, St. Petersburg... 

Vereschagin, A.L. Sakovich, G.V. Komarov, V.F. Petrov, E.A. Properties of ultrafine diamond clusters from detonation synthesis. Diamond Relat. Mater 1993, 3, 160-162. 

Today there are several other ways of diamond synthesis besides the HPHT method. For example, it is possible to utilize the pressure of a shock-wave generated in an explosion. This process mostly yields powdery products with particle sizes in the range of micrometers (1 mm at max.) that may be employed for industrial purposes as well. Moreover, very small diamonds (5-20 nm) can be made by reacting explosives in confined containers. Diamond films are produced on various substrates by chemical vapor deposition (CVD method using methane as a carbon source. Detonation synthesis and vapor deposition will be described in detail in Chapters 5 and 6. 

Figure 5.11 Structural formulae of the two explosives most commonly employed for detonation synthesis.

Figure 5.12 Industrial scale installation for the detonation synthesis of diamond at the Alit Corp. in Zhitomir (Ukraine). The reactor s volume is about 100m ( Alit Corp.).

Figure 5.18 IR-spectra of nanodiamond from different sources (a) detonation synthesis with water as coolant, (b) with CO2 as coolant. Due to the wet-chemical processing both spectra show strong signals of adsorbed water (dotted lines).

Dolmatov VY. Detonation synthesis ultradispersed diamonds properties and apphca-tions. Rnss Chem Rev 2001 70 607. 

Hence the volume of a mixture of heterogenous molecules interacting by the vdW mechanism exceeds the additive value, and according to the Le Chatelier principle such mixture under high pressure will be separated. It follows that the diamond cluster size depends on the separation extent of components of the detonation cloud. In this context, it seemed reasonable to perform a detonation synthesis of c-BN under similar conditions (in a large chamber). No attempt in this direction has been... 

Therefore, successful realization of detonation-induced /t-BN -> c-BN phase transition requires that the hydrolysis of BN is suppressed, but detonation gases usually contain water vapour (see above) at high temperature. However, using the hydrogen-free explosive benzotrifuroxan, CeNeOe (and thus excluding water in the detonation cloud) we have achieved the detonation synthesis of c-BN with a 80 % yield [266]. 

V yskubenko BA, Danilenko V V, Lin EE et al (1992) The effect of the scale factors on the size and yield of diamonds during detonation synthesis. Fizika Gorenia i Vztyva 28(2) 108-109... 

Batsanov SS (2009) Thermodynamic reason for delamination of molecular mixtures under pressure and detonation synthesis of diamond. Russ J Phys Chem A 83 1419-1421 Ree FH (1986) Supercritical fluid phase separations— implications for detonation properties of condensed explosives. J Chem Phys 84 5845-5856... 

Gavrilkin SM, Batsanov SS, Gordopolov YA, Smirnov AS (2009) Effective detonation synthesis of cubic boron nitride. Propellants Explos Pyrotech 34 469-471 Schlosser H, Ferrante J (1993) High-pressure equation of state for ptirtially ionic solids. Phys Rev B 48 6646-6649... 

The most frequently employed starting explosives in indnstrial-scale production of diamond by detonation synthesis are, as a rnle, trinitrotoluene (TNT) and hexogen (also called RDX = Research Department Explosive), with detonation performed in a water medium to reach a higher productivity. The most complicated stage in the industrial process is chemical isolation of NC diamond from the detonation carbon prodnced in an explosion, which is actually a mixture of micro- and nanoparticles of graphite, varions forms of sp -hybridized carbon and impurities originally contained in the explosive itself, and construction materials of the synthesis vessel. For details of the technology used in detonation diamond synthesis, the reader can be referred to Ref. 19 and Section 9.23.2 for the structure of the detonation diamond particles, their properties, and applications. 

Note that pilot production of diamond micrometer-sized powders by detonation synthesis was started by Dupont in the late 1970s, and in the Soviet Union, at the Institute of Problems in Chemical Physics, in 1982-1983, with graphite used as starting material in both cases. 

One major feature of the detonation synthesis of NDs is that it does not require graphite or any other additional source of carbon to support it It is the explosives themselves initiating the shock wave that acts as the source of the carbon to form diamond nanocrystals. For this purpose, their composition is chosen such as to ensure formation of free carbon in the chemical reactions running in the shock wave. This condition defines the so-called negative oxygen balance of the explosive composition. The explosive composition customarily used in detonation synthesis of diamond is the TNTRDX mixture taken in the 40 60-70 30 ratio. ... 

Selection of the optimum medium needed to sustain detonation synthesis of ND is governed by the need to prevent oxidation of the detonation products that can occur in contact with atmospheric oxygen, as well as to provide the maximum possible rate of cooling of the ND formed to preclude transition of the diamond to graphite. In industrial-scale production of detonation ND, the explosive charges are placed in carbon dioxide, water, or solid carbon dioxide ( dry ice ). ... 

Depending on the used medium, the side products (detonation carbon) produced in detonation synthesis contain 20-70 wt% diamond. The remainder is a mixture of various structural forms of ip -carbon, the state of hybridized electronic orbitals characteristic of graphite. The yield of the diamond phase is the highest with carbon dioxide in the solid state, and the lowest, when it is in gaseous form. The medium most frequently used in industrial synthesis is water. 

The shell is formed in the process of reverse diamond-to-graphite transition in the concluding stages of detonation synthesis, after the shock wave has passed and the pressure has dropped below the limit of thermodynamic stability of diamond. The thickness of the shell is largely determined by the conditions of the DND synthesis and in the course of DND isolation from detonation carbon, the thickness of the shell decreases. In the strongest regimes of i p -oxidation, the shell can be ranoved completely, except for separate single-layer 5p2 caj-, Q j islands, which result, as shown by calculations, from natural reconstruction of the free surface of diamond nanoparticles. 

As follows from elanental analysis, the main impurities in the structure of a DND particle are nitrogen (about 2 -w %) and hydrogen (about 1 wt%), which are assigned to the high concentration of these elements in the starting reagents employed in the detonation synthesis. 

V. Y. Dohnatov, Ultradisperse Diarrwnds of Detonation Synthesis Production, Properties and Applications, State Polytechnical University, SL Petersburg, 2003. 

Dolmatov VY (2007) Detonation-synthesis nanodiamonds synthesis, structure, properties and application. Russ Chem Rev 76(4) 339-360... 

In Chapter 2, the development of composite materials based on improved nanodiamonds is reported by P. Ya Detkov, V. A. Popov, V. G. Kuhchikhin and S. I. Chukhaeva. The authors describe methods for improving the quality of diamond nanopowders obtained by detonation synthesis, as well as some commercial applications of nanodiamonds. The authors prove that the synthetic detonation diamond is a promising material that can be used in many fields. Of special interest are its applications in compos ite materials both with a metal and polymer matrix. Commercial production of ultradisperse diamonds (or nanodiamonds) has been developed, and it is synthesized on a scale sufficient for particular industries. 

This chapter describes the methods of improving the quality of diamond nanopowders obtained by detonation synthesis, and some commercial applications of nanodiamonds that have been developed. 

In the latter case, transition of the carbon of an explosive into the diamond phase occurs as a result of explosive transformation of the explosive, that is, in the detonation wave. The method was called detonation synthesis. Diamonds are also formed in the degradation of some inert (nonexplosive) organic substances in the detonation wave, if they are used as additives to potent explosives. An attractive feature of detonation synthesis of diamonds is that it uses charges from explosives obtained in the disposal of weapons. Thus, the detonation synthesis of diamonds can help utilize explosives obtained in weapons dismantlement. 

Diamond particles formed in the detonation synthesis ate 2-6 nm in size. Particles of detonation diamond have a cubic lattice with lattice parameter a = 0.3575 nm (in natural diamond, a = 0.3566 nm). Due to the small size of particles, the detonation diamonds are called ultradisperse diamonds (UDD) or nanodiamonds. 

Besides the diamond phase, the condensed products of explosion recovered from the armored chamber after the explosion of a charge contain the nondiamond modifications of carbon and metal impurities. Depending on the method of synthesis, the diamond phase in the condensed carbon products of explosion is 30 to 75% of the weight of these products. Optimization of the detonation synthesis by the ratio of trinitrotoluene and hexogen in the mixture, by the ratio of the weight of exploded charge and the volume of the chamber and also the use of special coolants enables a stable 75% yield of the diamond phase in the condensed products of explosion. 

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