Diamond vitreous bond

Fig. 8. (a) Synthetic diamond grit for resinoid or vitreous bond (free-cutting) abrasive wheels, and (b) synthetic diamond grit for metal bond abrasive... 

The bond systems used with cBN are the same as those with diamond— resin, vitreous, metal, and single layer (electroplated or brazed)—but the relative prevalence is different. The most popnlar bond systems with cBN are vitreous and single layer, the reverse of the sitnation with diamond. In many cases the lifetime, finish, and grinding efficiency of vit-leons bond cBN wheels are superior to those of corresponding resin bond wheels. Factors contribntmg to the performance of vitreous bonds are hardness, thermal conductivity and stability, and higher porosity (which simplifies wheel surface conditioning) than resin bonds. 

Amorphous carbon is a general term that covers non-crystalline forms of carbon such as coal, coke, charcoal, carbon black (soot), activated carbon, vitreous carbon, glassy carbon, carbon fiber, carbon nanotubes, and carbon onions, which are important materials and widely used in industry. The arrangements of the carbon atoms in amorphous carbon are different from those in diamond, graphite, and fullerenes, but the bond types of carbon atoms are the same as in these three crystalline allotropes. Most forms of amorphous carbon consist of graphite scraps in irregularly packing. 

It is interesting to note in passing that many other tetrahedrally bonded crystals have a similar negative expansion coefficient at low temperatures, for example germanium (< 48 °K), silicon (materials like vitreous silica (Collins White, 1964). This behaviour is thus apparently a feature of this type of bonding structure, rather than being a peculiarity of ice itself. 

It has been suggested that the structure of vitreous carbon includes, in addition to the graphitic sp (trigonal) bonds, some sp (tetragonaQ bonds which are characteristic of diamond bonding. This would possibly contribute to the isotropy, the high strength, and the hardness of the material (see Ch. 2, Sec. 3.0).i ii The presence of the diamond structure in a similar material, diamond-like carbon, is well established (see Ch. 14). 

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