Combustion synthesis of diamond

K.F. McCarty, E. Meeks, R.J. Kee, and A.E. Lutz. Scalable Stagnation-Flow Reactors for Uniform Materials Deposition Application to Combustion Synthesis of Diamond. Appl. Phys. Lett., 63 1498-1500,1993. 

Combustion synthesis of diamond films fi om atmospheric pressure oxyacetylene flame was first reported by Hirose in 1988.This technique, as shown schematically in Fig. 2h, has been demonstrated to be a potentially very important means of growing diamond (Table 1). In Hirose s experiments, linear growth rates of100-200 pmh were achieved. The results were then confirmed by Hanssen et al.l l In Hirose s experiments and most of those that followed, the oxyacetylene torch was typically run with... 

To address the incorporation of non-cryslalline phases in polycrystalline diamond films and the morphological instabilities at high growth rates, Ravil conducted an experimental investigation of the combustion synthesis of diamond and proposed a model for the development of morphological instabilities in diamond films, as schematically depicted... 

In the combustion synthesis of diamond crystals and films on Mo substrates,by reducing the O2/C2H2 ratio in the gas mixture to 0.75... 

In the case of hot-filament CVD, refractory metal filaments (e.g., W, Ta, Re, etc.) are electrically heated to very high temperatures (between 2000 and 2700°C) to produce the necessary amount of atomic hydrogen that is necessary for the reasons mentioned above for the synthesis of diamond. Except for combustion flame CVD, hot-filament CVD is considered the simplest of all of the methods and also the most inexpensive. Plasma-jet and laser-assisted CVD methods rely on a plasma torch or laser to attain the very high temperatures that are needed to... 

In the 1950s to 1980s, two main techniques were developed for the synthesis of artificial diamond (a) high-pressure/high-temperature synthesis that yielded artificial diamond gems [18], and (b) chemical vapor deposition (CVD) [19] that made possible the synthesis of diamond in thin-film form on various substrates. Different CVD techniques have been adopted in the synthesis of diamond thin films. Three main CVD techniques include hot-filament CVD [20], plasma-assisted CVD [21], and combustion CVD [22]. There are many types of plasma-assisted CVD techniques according to the energy sources, such as the microwave plasma-assisted CVD (also... 

M. Murayama and K. Uchida. Synthesis of Uniform Diamond Films by Flat Flame Combustion of Acetylene/Hydrogen/Oxygen Mixtures. Combust. Flame, 91 239-245,1992. 

The technical synthesis of graphite, diamond and a variety of other forms of sp2 carbons (Fig. 3) is described in a review [39] and is not covered here. As the unintended formation of carbon in deactivation processes and the modification of primary carbon surfaces during chemical treatment (in catalytic service and during oxidative reactivation) and their chemical properties arc frequent problems encountered in catalytic carbon chemistry, it seems appropriate to discuss some general mechanistic ideas which mostly stem from the analysis of homogeneous combustion processes (flame chemistry) and from controlled-atmosphcre electron microscopy. 

Ravi, K.V. Koch, C.A. Olson, D. Large area diamond synthesis by the combustion flame process. 2nd International Conference on the Applications of Diamond Films and Related Materials, Japan, 1993 Yoshikawa, M., Murakawa, M., Tzeng, Y., Yarbrough, A., Eds. 491. 

Nine compositions with the diamond concentration of 3, 5, 7, 9, 10, 12, 15, 20, 25 mass % were mixed with the charge Ti-C-Mo to produce multi-layered semi-products. The ready mixtures were placed layer-by-layer into a pressform in the following order diamondless layer weighing 25,5 g 3 mass % diamond layer, weighing 10 g 5 % layer -10 g 7 % layer - 10 g 9 % layer - 9,9 g 12 % layer - 9,9 g. After densification pellets were obtained 48 mm in diameter with the thickness of the layers 5.0, 2.0, 2.0, 2.0, 2.0, 2.0 mm correspondently. Multilayered pellets with the diamond concentration from layer to layer as much as 0, 5, 10, 15, 20, 25 % mass were prepared similarly. The final pellet was placed into a reactional mold. An SHS reaction was initiated from the lateral face of the cylindrical pellet by a tungsten spiral. After accomplishment of the combustion reaction and propagation of the combustion synthesis wave, the hot SHS-products were compacted in a hydraulic press at P > 400 MPa for no more than 10 s. The time of exposure to pressure was chosen dependent on the combustion temperature and reology of the products, e.g., on their plasticity and the amount of the liquid phase formed. Usually this time is 0.5 -4 2 sec. SHS-products were cooled at the room temperature. 

In addition to the statistical nature of the interface instabilities active in diamond CVD, the orientation effect and anisotropic growth of crystals (i.e., evolutionary selection) play an important role in the observed instability phenomenon. Surface chemical reactions that occur preferentially between the growing diamond surface and oxidizing species in the combustion synthesis ambient also influence the development of the microstructure and morphology of crystals in diamond films. For example, in combustion CVD,... 

K.. L. Padyukov, E. A. Levashov, and I. P. Borovinskaya, Regularities of the behaviour of synthetic diamond in the combustion wave of self-propagating high-temperature synthesis, Eng. Phys. J. 1992, 63, 577-583. 

Feynman s vision of miniaturization and the Drexler-versus-Smalley debate on feasibility of mechanosynthetic reactions using molecular assemblers were discussed. Fullerenes are the third allotropic form of carbon. Soccer-ball-structured Cgo with a surface filled with hexagons and pentagons satisfies Euler s law. Howard patented the first generation combustion synthesis method for fullerene production. The projected price of the fullerenes has decreased from 165,000 per kg to 200 per kg in the second-generation process. Fullerenes can also be synthesized using chemical methods, a supercritical extraction method, and the electric arc process. Applications of fullerenes include high temperature superconductors, bucky onion catalysts, advanced composites and electromechanical systems, synthetic diamonds. 

Building on our experience with IGC and CVC, we have replaced the heat source by a flame in the Combustion Flame - Chemical Vapor Condensation (CF-CVC) technique. This technique offers several advantages over previous methods and has the potential to continuously generate non-agglomerated powders at high rates typical for industrial processes. These advantages have been exploited in other research and commercial flame synthesis processes for the production of diamond, carbon black, other particulates, and a variety of thin films, but not to date for the large scale production of nanoscale powders. 

Chemical Vapor Deposition (CVD) has been defined as a materials synthesis process whereby constituents of the vapor phase react chemically near or on a substrate surface to form a solid product. With these traditional processes a reaction chamber and secondary energy (heat) source are mandatory making them different from the Combustion CVD process. Numerous flame-based variations of CVD have been used to generate powders, perform spray pyrolysis, create glass forms, and form carbon films including diamond films. 

Padyukov, K. L., Levashov, E. A., Borovinskaya, I. R, and Kost, A. G., Specific features of the behavior of synthetic diamond in a self-propagating high-temperature synthesis (SHS) combustion wave. J. Eng. Phys. Thermophys., 63,1107 (1992b). 

Figure 2. Schematic diagram of various CVD techniques for diamond synthesis, (a) HFCVD (b) MW PACVD (c) ECR MW PACVD (d) DC PACVD (e) RF PACVD (0 DC thermal plasma CVD (g) RF thermal plasma CVD (h) flame (combustion) CVD.l (Reproduced with permission.)...

---