Synthetic diamond powders

Dandekar, A. R. Baker, and M. Vannice, Characterization of activated carbon, graphi-tized carbon fibers and synthetic diamond powder using TPD and DRIFTS. Carbon. 1998,36(12), 1821-1831. 

Figure 14. Nitrogen concentration in diamond versus the cobalt content of iron + cobalt solvent. The diamonds were grown with 1.5 weight-% titanium addition using (a) high-purity graphite and (b) synthetic diamond powder [67].

In 2001, Tarasevich and his collaborators reported a comparison between electrocatalysts for oxygen reduction prepared using a disperse synthetic diamond powder promoted with CoTMPP and its pyropolymers . Two types of diamond powders with specific area of 5.8 and 170 m /g were used as catalyst supports and the activity of the catalysts obtained with the diamond supports was compared to that obtained with the same CoTMPP precursor loaded on acetylene black. In all cases, the loading was one monolayer of CoTMPP. These authors found a much lower activity for the electrocatalysts prepared on synthetic diamonds than for that catalyst prepared on acetylene black. The kinetic mechanisms of ORR was, however, the same for both supports. 

Koc] Kocherzhinski, Yu.A., Kulik, O.G., Equilibrium Phase Diagrams and Manufacture of Synthetic Diamond , Powder Metall. Met. Cer., 35(7-8), 470-483 (1996) (Experimental, Phase Relations, 37)... 

Martynova and Gatilova have studied the effect of adsorption of ethanolamines on the dispersability of synthetic diamond powder in various solvents. They found that triethanolamine was adsorbed from acetone solutions but negatively adsorbed from water or ethanol, though in one paper they reported that triethanolamine was positively adsorbed from ethanol at concentrations above 0.4 m. Monoethanolamine was found to be the most effective in dispersing diamond powder in acetone. The adsorption of poly(ethylene polyamine) on diamond was also studied, but the solvent used is not mentioned in the abstract. 

PCD (polycrystalline diamond) is obtained by sintering synthetic diamond powder in the presence of a metal binder (Co, Ni or Fe a low percentage by volume), at 1,350-1,500°C imder 5 GPa pressure. One may also sinter a layer of diamonds (0.5 mm thick) on a sintered hard metal substrate, the cobalt of the substrate thus participating in the sintering of the diamond and the adherence of the PCD on the substrate. Inserts up to 72 mm diameter and hardness of 5,000 to 8,000 HV may thus be attained. 

Annual production of powdered BN is ca 180—200 metric tons per year and its cost is 50—250/kg, depending on purity and density. The price of cubic boron nitride is similar to that of synthetic diamond bort. Hot-pressed, dense BN parts are 3—10 times more expensive than reaction-sintered parts. 

The high elastic modulus, compressive strength, and wear resistance of cemented carbides make them ideal candidates for use in boring bars, long shafts, and plungers, where reduction in deflection, chatter, and vibration are concerns. Metal, ceramic, and carbide powder-compacting dies and punches are generahy made of 6 wt % and 11 wt % Co ahoys, respectively. Another apphcation area for carbides is the synthetic diamond industry where carbides are used for dies and pistons (see Carbon). 

For many years the studies of surface modifications of synthetic diamond nanopowders have been conducted at the Institute for Superhard Materials. Our findings show that highly dispersed modified diamond powders hold a considerable promise in applications as adsorbents and catalysts of the oxidation and electrochemical catalysis [1-4], This promise is based on the following special features of the material ... 

As early as the 1850s, scientists tried to convert graphite into diamonds. It wasn t until 1954 that researchers produced the first synthetic diamonds by compressing carbon under extremely high pressure and heat. Scientists converted graphite powder into tiny diamond crystals using pressure of more than 68,000 atm, and a temperature of about 1,700°C for about 16 hours. 

The cubic structure is the dominant crystal structure in both natural and synthetic diamond since the staggered conformation is more stable than the eclipsed due to the slightly lower energy (0.1-0.2 eV per carbon atom). Diamond polytypes and carbyne phases form only during the homogeneous nucleation and growth of diamond powder,... 

Perhaps the first representative of a new carbon is (i) glassy carbon (GC) powder, tested first in the mid-1990s [37] and forming fine microspheres that may also have a specially treated surface. The second newly appearing carbonaceous material was (ii) diamond powder [61] applicable in both natural and synthetic forms as chemically pure, that is, undoped. (Reportedly - see [5] and a discussion inside - a certain conductivity of this otherwise totally insulating material was ensured by the presence of unspecified trace impurities.)... 

Natural and synthetic diamonds have been used for many years to true up and dress abrasive wheels. These are held in a holder of the required shape by vacuum brazing or held in a powder metal matrix and can be single point tools, multi-point grit tools, blade tools or cluster tools depending on the application (see Fig. 10.10). 

A wide variety of materials have been classified with the TrtboClassifier with positive results. These include separation of natural from synthetic diamonds, classification of electroluminescent powder, removal of dust from dolomite, removal of irregular shapes from bronze cut wire, removal of Irregular shapes from granules of hard alloys, size classification of calcium carbonate, fly ash, copper particles etc. 

The tenn size reduction is applied to all the ways in which particles of solids are cut or broken into smaller pieces. Throughout the process industries solids are reduced by different methods for different purposes. Chunks of crude ore arc crushed to workable size synthetic chemicals are ground into powder sheets of plastic are cut into tiny cubes or diamonds. Commercial products must often meet stringent specifications regarding the size and sometimes the shape of the particles they contain. Reducing the particle size also increases the reactivity of solids it permits separation of unwanted ingredients by mechanical methods it reduces the bulk of fibrous materials for easier handling and for waste disposal. 

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