Synthetic diamond coatings

Ceramic-coated disposable inserts, including silicon nitride, boron nitride, titanium nitride (TIN), titanium carbide (TIC) and sintered synthetic diamond ... 

One of such unique coatings is Diamond Like Carbon (DLC). The conventional synthesis of synthetic diamonds requires extremely high temperatures and pressures. By PECVD, Diamond Like Carbon is created under mild conditions by the decomposition of methane in H2/CH4 mixture. The applications of DLC are numerous coatings for cutting tools, optical fibres, electronic devices for reading magnetic tapes, or even protective coatings in chemical reactors. 

When a single crystal diamond (synthetic or natural) is the substrate, epitaxial growth occurs the growing diamond replicates the substrate crystal lattice and turns to single crystal film. The film thickness usually comes to a few microns however, films of 1 mm in thickness were reported. The diamond-coated area would achieve 10 cm in diameter by order for industrial applications, much larger areas (e.g. 40 by 60 cm) are covered. Samples destined for the electrochemical measurements used to have dimensions ca. 1 by 1 cm. 

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. 

OTHER COMMENTS used as a white pigment in exterior house paints, interior air-dry and baked enamels and lacquers, inks and plastics, in water paints, leather finishes, shoe whiten-ers, and ceramics rutile sand is suitable for coating welding rod materials rutile-like pigments are also useful as opacifying agents other uses include the manufacturer of cosmetics, food color additives, and synthetic diamonds. 

CVD-diamond coatings are polycrystsdiine, as opposed to natural and high-pressure synthetic diamond which are normally single crystals. This polycrystalline characteristic has important bearing on the general properties of the coatings as shown in Sec. 4.0. 

The abrasives used for coatings are diamond, aluminum oxide (corundum), silicon carbide, boron carbide, boron nitride, emery, flint (quartz), and garnet. These range in hardness and cost. Typically the superabrasives, synthetic diamond and cubic boron nitride, do not compete easily with the standard abrasives. 

A few years ago, diamond was considered as an exotic, rather expensive material that was only used as a window material in high-pressure cells (see Section 14.3). Now synthetic diamonds are becoming more available, and diamond can also be used as a coating for less chemically resistant materials with and far lower cost and superior infrared transparency. Diamond has a characteristic doublet absorbing between about 1900 and 2300 cm , but fortunately, few functional groups absorb in this region. 

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. 

Superhard materials implies the materials with Vickers hardness larger than 40 GPa. There are two kinds of super-hard materials one is the intrinsic superhard materials, another is nanostructured superhard coatings. Diamond is considered to be the hardest intrinsic material with a hardness of 70-100 GPa. Synthetic c-BN is another intrinsic superhard material with a hardness of about 48 GPa. As introduced in Section 2, ta-C coatings with the sp fraction of larger than 90 % show a superhardness of 60-70 GPa. A typical nanostructured superhard coating is the heterostructures or superlattices as introduced in Section 4. For example, TiN/VN superlattice coating can achieve a super-hardnessof56 GPa as the lattice period is 5.2 nm[101]. 

Contrary to the new carbon materials presented so far, diamond films are a product that is already being employed with many variants in large scale applications. Especially the coating of tools and fast turning parts represents a considerable market, but there are also electronic uses and synthetic optical windows on offer. Some of the important fields of appHcation are presented in more detail below. 

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