Diamond characteristics

The choice of solvent/catalyst alloy for synthetic diamond growth not only has an influence on nitrogen content, but also on other diamond characteristics such as morphology, color, and inclusion content. The dependence of some of these diamond characteristics on solvent/catalyst typically used for research and commercial production by institutes and companies such as De Beers, Sumitomo, General Electric, and NIRIM, amongst others, are summarized in Table I. 

Diamond Characteristics. It is generally accepted that, for a material to be recognized as diamond, it must have the following characteristics ... 

Hardness on the Mohs scale is often above 8 and sometimes approaches 10 (diamond). These properties commend nitrides for use as crucibles, high-temperature reaction vessels, thermocouple sheaths and related applications. Several metal nitrides are also used as heterogeneous catalysts, notably the iron nitrides in the Fischer-Tropsch hydriding of carbonyls. Few chemical reactions of metal nitrides have been studied the most characteristic (often extremely slow but occasionally rapid) is hydrolysis to give ammonia or nitrogen ... 

Figure 29.1 Crystal structures of ZnS. (a) Zinc blende, consisting of two, interpenetrating, cep lattices of Zn and S atoms displaced with respect to each other so that the atoms of each achieve 4-coordination (Zn-S = 235 pm) by occupying tetrahedral sites of the other lattice. The face-centred cube, characteristic of the cep lattice, can be seen — in this case composed of S atoms, but an extended diagram would reveal the same arrangement of Zn atoms. Note that if all the atoms of this structure were C, the structure would be that of diamond (p. 275). (b) Wurtzite. As with zinc blende, tetrahedral coordination of both Zn and S is achieved (Zn-S = 236 pm) but this time the interpenetrating lattices are hexagonal, rather than cubic, close-packed.

Figure 4-162 shows a natural diamond drill bit which has a long outer taper and medium inner cone, radial flow fluid courses, and five to six stones per carat (spc) diamonds set with a medium placement density. Using the definitions in Figures 4-156, 4-158, 4-159, and 4-160, the characteristics of this bit are coded D 2 R 5 as follows ... 

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. 

The positive displacement motor whose performance characteristics are given in Table 4-115 is a 5 6 lobe profile motor. This lobe profile design is usually used for straight hole drilling with roller rock bits, or for deviation control operations where high torque polycrystalline diamond compact bit or diamond bits are used for deviation control operations. 

Figure 15-20. Currenl versus voltage characteristics of the lTO/MEH-PPV/C Au device in the dark (diamonds) and upon illumination wilh the 514.5 nm line of argon-ion laser of 1 mW/cm2 (triangles) (reproduced by permission of the American Institute of Physics from Ref. 1891).

Cubic boron nitride (c-BN) is a different material altogether from h-BN, with a structure similar to that of diamond, which is characterized by extremely high hardness (second to diamond) and high thermal conductivity.As such, it is a material of great interest and a potential competitor to diamond, particularly for cutting and grinding applications. Its characteristics and properties are shown in Table 10.3... 

Chemical Resistance. C-BN is essentially inert to all reagents at room temperature. It does not react with carbide formers such as Fe, Co, Ni, Al, Ta, and B at approximately 1000°C (while diamond does) this is a useful characteristic in machining and grinding applications. However, it reacts with aluminum at 1050°C and with Fe and Ni alloys containing Al above 1250°C.P4]... 

There are more than a million known carbon compounds, of which thousands are vital to life processes. The carbon atom s unique and characteristic ability to form long stable chains makes carbon-based life possible. Elemental carbon is found free in nature in three allotropic forms amorphous carbon, graphite, and diamond. Graphite is a very soft material, whereas diamond is well known for its hardness. Curiosities in nature, the amounts of elemental carbon on Earth are insignificant in a treatment of the... 

Two types of species have been detected in the /rSR spectrum of Ceo- One shows an unreacted or meta-stable muonium state which may well correspond to an internal state, muonium is trapped inside the cage Mu Ceo in the current notation [2]. This may be compared with normal muonium (Mu ) in diamond and many other elemental and compound semi-conductors, where the trapping site is in one of the cavities of tetrahedral symmetry. This state of CeoMu is not discussed here, but it does exhibit all the characteristics expected of the internal chemistry of Ceo-The anomalous muonium state. Mu, observed in semi-conductors and generally accepted to arise from muonium being trapped within one of the chemical bonds of the crystal, is unknown in molecules [5,6]. The constraints of the crystal lattice are necessary for the bond-centred state to be stable. 

In the course of the PP calculations of these quantities for Si [10] and Ge [11], a characteristic local pattern which reflects position, shape and size of a specific atom in the crystal is observed on the contour map of the valence electron A(r)-function. The atom is one of the two atoms in the unit cell of diamond structure. It seems as... 

A number of chemical elements, mainly oxygen and carbon but also others, such as tin, phosphorus, and sulfur, occur naturally in more than one form. The various forms differ from one another in their physical properties and also, less frequently, in some of their chemical properties. The characteristic of some elements to exist in two or more modifications is known as allotropy, and the different modifications of each element are known as its allotropes. The phenomenon of allotropy is generally attributed to dissimilarities in the way the component atoms bond to each other in each allotrope either variation in the number of atoms bonded to form a molecule, as in the allotropes oxygen and ozone, or to differences in the crystal structure of solids such as graphite and diamond, the allotropes of carbon. 

Like graphite, C60 can be transformed into diamond, but the process requires less stringent conditions. It has also been found that Cso becomes a superconductor at low temperature. Another interesting characteristic of Cso is that when it is prepared in the presence of certain metals, the Cso cage can enclose a metal atom. In some cases, other materials can be enclosed within the C60 cage in a "shrink wrapped" manner to form "complexes" that are described as endohedral. It has also been possible to prepare metal complexes of Cso that contain metal-carbon bonds. A compound of this type is (C6H5P)2PtC60. 

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