Synthetic diamond production

NATURAL AND HIGH-PRESSURE SYNTHETIC DIAMOND PRODUCTION... 

Diamond. Diamond [7782 0-3] is the hardest substance known (see Carbon, diamond, natural). It has a Knoop hardness of 78—80 kN/m (8000—8200 kgf/m ). The next hardest substance is cubic boron nitride with a Knoop value of 46 kN/m, and its inventor, Wentorf, beheves that no manufactured material will ever exceed diamond s hardness (17). In 1987 the world production of natural industrial diamonds (4) was about 110 t (1 g = 5 carats). It should be noted that whereas the United States was the leading consumer of industrial diamonds in 1987 (140 t) only 260 kg of natural industrial diamonds were consumed this is the lowest figure in 48 years (4), illustrating the impact that synthetic diamonds have made on the natural diamond abrasive market. 

Synthetic Diamond. In 1955 the General Electric Company announced the successful production of diamonds (see Carbon, diamond, synthetic) from graphite under very high pressure and temperature ia the presence of a metal catalyst. It was later reported that a Swedish company, Allmana Svenska Electriska AB (ASEA), had succeeded ia ptoduciag diamond ia 1953 (35). 

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. 

Soon after the first successful diamond synthesis by the solvent—catalyst process, a pilot plant for producing synthetic diamond was estabUshed, the efficiency of the operation was increased, production costs declined, and product performance was improved while the uses of diamond were extended. Today the price of synthesized diamond is competitive with that of natural diamonds. 

The bulk of synthetic industrial diamond production consists of the smaller crystal sizes up to 0.7-mm particle size (25 mesh). This size range has wide utihty in industry, and a significant fraction of the world s need for diamond abrasive grit is now met by synthetic production yielding thousands of kilograms per year. Because the raw materials are plentiful, synthetic production could, if necessary, supply the world demand for diamond abrasive. Development work continues in order to improve size and utility of the manufactured product and to realize the full potential of diamonds at minimum cost. An appreciable increase in performance has been obtained by coating the diamonds with a thin layer of nickel or copper, before incorporating them into wheels. The thin layer of metal apparendy improves adhesion and heat transfer. 

Figure 8.4 Phase diagram of carbon showing regions of importance for the production of synthetic diamond. ...

With the technical development achieved in the last 30 years, pressure has become a common variable in several chemical and biochemical laboratories. In addition to temperature, concentration, pH, solvent, ionic strength, etc., it helps provide a better understanding of structures and reactions in chemical, biochemical, catalytic-mechanistic studies and industrial applications. Two of the first industrial examples of the effect of pressure on reactions are the Haber process for the synthesis of ammonia and the conversion of carbon to diamond. The production of NH3 and synthetic diamonds illustrate completely different fields of use of high pressures the first application concerns reactions involving pressurized gases and the second deals with the effect of very high hydrostatic pressure on chemical reactions. High pressure analytical techniques have been developed for the majority of the physicochemical methods (spectroscopies e. g. NMR, IR, UV-visible and electrochemistry, flow methods, etc.). 

Other advances in material science have helped humans mimic nature in the production of certain materials. For example, in the last half of the twentieth century we have learned how to produce synthetic diamonds. Diamonds were first produced commercially in the 1950s by General Electric by subjecting graphite to temperatures of 2,500°C and pressures approaching 100,000 atmospheres. Currently, well over a hundred companies produce synthetic diamonds. 

New uses have also been discovered, from the synthesis of high purity synthetic diamonds to the production of the nutritive sweetener aspartame it was also used as fuel in molecular motors. The book Phosgenations - A Handbook [55] discusses in detail novel and old uses of phosgene (see Sections 1.4 and 1.5, in particular). 

Nanodiamond as such is not really a new material. Indeed, essential experiments on the production of nanoscale diamond crystallites have already been performed in the late 1950s and early 1960s. No later than 1959, DeCarh and Jamieson found that tiny diamond crystalHtes could be obtained from the action of a shock wave on graphitic material. The procedure was patented in the 1960s, and from that time on, the DuPont Corp. has been producing about 2 million karat of synthetic diamond per year in this manner (Section 5.3.2). 

Since that time, synthetic diamond films have developed into an important high-tech product employed for many purposes. In comparison to other forms of diamond, the most attractive difference is the facile generation of diamond coated workpieces in almost any desired shape. The preparation of thin layers, for example, for electronic applications, became possible as well only after the development of CVD methods. 

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