One of the most important developments in man-made diamond synthesis is CVD (Chemical Vapor Deposition) Diamond. CVD diamond is higher harness, wear resistance and thermal resistance than PCD (Polycrystalline Diamond) made by high pressure and high temperature method. There are many advantages for CVD diamond product that derives from the unique hardness, excellent toughness, high abrasive resistance, high thermal conductivity, low coefficient of thermal expansion and electrical properties of diamond. Comparing to natural diamond, CVD diamond overcomes the inherent shortcoming of single crystal cleavage, reaches better adherence to functional substrates, and offers higher uniformity and homogeneity of the coatings over large areas; another benefit for CVD polycrystalline diamond characters the best randomly oriented structure. With those properties, CVD diamond can be ideal for using as superabrasive product for a board rang of applications by engineering CVD diamond structure and CVD process.
CVD DIAMOND GROWTH
The growth of CVD diamond involves series of gas phases, surface chemical reactions and microstructure evolution. Activated methane, which is decomposed at high temperature in a plasma, is a diamond carbon source. In the presence of hydrogen the carbon is deposited on the substrate and then converted to the diamond film with sp3 bonding, carbon allotrope diamond. Hydrogen is used to promote diamond growth by stabilizing the thermodynamically metastable diamond and preferentially etching non-diamond carbon deposits. Another gas, such as argon, is required for protecting the Cathode that generates plasma.
|CVD DIAMOND PROPERTIES|
|Thermal Diffusivity||2.3 - 9.2||cm2/s|
|Hardness||1 x 104||Kg/mm2|
|Refractive Index||2.38||- - -|
|Dielectric Constant||5.7||- - -|
|Loss Tangent||< 4 x 10-4||- - -|
|Thermal Expansion Coefficient||1.0 x 10-6 (300℃)||- - -|
|Resistivity||Up to 1016||Ω - cm|
|Dielectric Strength||1 x 107||V/m|
|Poisson's Ratio||0.07||- - -|