Natural polycrystalline diamond

Although the first natural polycrystalline diamond was discovered in the 19th century, it was only investigated on a scientific basis during the 1970s, and was classified into two broad types Carbonado and Balias [139]. 

Carbonado is a porous, randomly polycrystalline diamond aggregate [140]. Balias on the other hand is defined as polycrystalline diamond of oriented globular growth . Its crystallites have (110) directions oriented radially. 

Experiments so far have clearly indicated that these natural forms of sintered diamond are truly polycrystalline ceramics, exhibiting transgranular fracture as a result of diamond to diamond bonding. 

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A wide range of cutting-tool materials is available. Properties, performance capabilities, and cost vary widely (2,7). Various steels (see Steel) cast cobalt alloys (see Cobalt and cobalt alloys) cemented, cast, and coated carbides (qv) ceramics (qv), sintered polycrystalline cubic boron nitride (cBN) (see Boron compounds) and sintered polycrystalline diamond tbin diamond coatings on cemented carbides and ceramics and single-crystal natural diamond (see Carbon) are all used as tool materials. Most tool materials used in the 1990s were developed during the twentieth century. The tool materials of the 1990s... 

Natural diamonds used for jewellery and for industrial purposes have been mined for centuries. The principal diamond mining centres are in Zaire, Russia, The Republic of South Africa, and Botswana. Synthetic diamonds are made by dissolving graphite in metals and crystallising diamonds at high pressure (12-15 GPa) and temperatures in the range 1500-2000 K [6] see section 3. More recently, polycrystalline diamond films have been made at low pressures by... 

The term PDC is defined as polycrystalline diamond compact. The term TSP is defined as thermally stable polycrystalline diamond. TSP materials are composed of manufactured polycrystalline diamond which has the thermal stability of natural diamond. This is accomplished through the removal of trace impurities and in some cases the filling of lattice structure pore spaces with a material of compatible thermal expansion coefficient. 

The section describes the first lADC standardized system for dull grading natural diamond, PDC, and TSP (thermally stable polycrystalline diamond) bits, otherwise known as fixed cutter bits [55]. The new system is consistent with the recently revised dull grading system for roller bits. It describes the condition of the cutting structure, the primary (with location) and secondary dull characteristics, the gage condition, and the reason the bit was pulled. 

In the diamond stmcture, carbon atoms are present in sp hybridization, with a tetrahedral stereochemistry and a face-centered cubic stmcture that is shown in Fig. 2.1. Besides natural diamond, synthetic diamond has been produced since General Electric first announced its successful high-pressure synthesis in 1955. Sintered polycrystalline diamond, different types of diamond films, and diamondlike carbon are other types of diamond-related synthetic materials, some of which are noncrystalline [13, 19] these solids have their own terminology [10, 20]. Unhke other carbonaceous solids, diamond has a rather limited and specific relevance to adsorption. Indeed, ever since the publication of a pioneering work... 

Apart from naturally occurring diamond there is by now a variety of artificial carbon materials that feature diamond structure as well. These include the synthetic diamond generated by high pressure and temperature, but also films, polycrystalline materials resembling the carbonados (Section 1.3.2) and the so-called... 

GE reported the discovery of natural semiconducting diamond in 1952 [31]. Presently, hot filament CVD and microwave plasma assisted CVD (MPACVD) produce polycrystalline or diamond carbon (DLC) films at 1-10 pm/h on a variety of substrates. However, true epitaxial growth presently is not routinely achievable at this time. Diamond substrates also are not readily available making large area lattice matched depositions a problem. Typieal substrates are Si, sapphire and even copper. Boron is an effective p-type dopant, but there is no successful n-type dopant, although As, Li, O, P and Sb have been tried. 

Sintered Diamond. A natural polycrystalline form of diamond called carbonado is known. It is much tougher... 

Carbon in the structural form of diamond is the only element used industrially as a hard material. Each year about ten tons of natural diamond and about twenty tons of synthetic diamond (produced via high temperature high pressure synthesis) are marketed as hard materials. While pure diamond is transparent, a yellow tint results from the replacement of some carbon atoms by nitrogen, and a blue, yellow, or even green tint through substitution of carbon by boron atoms. Polycrystalline diamond with impurities, used as an abrasive, is often black. 

Ceo and C70 have been found to occur in nature, but are known to degrade in the presence of light and air (presence of ozone). Ceo is the softest form of carbon but when compressed to below 70% of its original volume, it is reputed to be harder than diamond. It can be transformed into diamond by rapid compression (1.52 MPa in less than one second) to yield polycrystalline diamond in a carbon matrix. Ceo has remarkable impact strength, being able to withstand a collision when impacted at 24,135 km h onto a stainless steel plate, and just bouncing back. 

In addition, electron diffraction patterns of polycrystalline diamond are similar to those of basal-plane oriented polycrystalline graphite and, when analyzing mixtures of the two, it may be difficuitto separate one pattern from the other. Unfortunately, mixed graphite-carbon-diamond aggregates eire common in natural and synthetic materials. 

SlimDril drill bils are manufaclured from polycrystalline vi/ith natural diamonds on the face of the bit for oil and natural gas drilling. 

Diamond is obtained as a polycrystalline material by CVD with properties similar to these of natural diamond. Efforts to produce single crystal thin films have so far been largely unsuccessful. 

There are two types of internal textures seen in natural diamond crystals that show conditional changes. Although Dana [9], [10] and Orlov [11] distinguished between single crystals and polycrystalline aggregates, they did not put crystals that had experienced the two conditions into different categories. 

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