Influence of Equivalence Ratio, Velocity Gradient, and Surface Roughness of Substrate on the Combustion Synthesis of Diamond Films Using a Flat Flame Burner.

Abstract

An experimental study to synthesize diamond films has been conducted under a well-defined flow field to make clear the mechanism of combustion synthesis of diamond films. Using a flat flame burner, the homogeneous diamond films are synthesized on substrates, above which flat, premixed acetylene/hydrogen/oxygen flames are established. The effect of equivalence ratio and velocity gradient is examined on the growth rates of diamond films, crystal sizes, and their morphology. It is found that not only the maximum growth rate but also the maximum crystal size can be obtained when the equivalence ratio is about 2.50, and that the growth rate, crystal size, and/or morphology are nearly the same when the velocity gradient is kept constant. These results are confirmed by a conical flame with a welding torch. In addition, the scratching treatment for the substrates by diamond powder is unnecessary, the maximum growth rate of diamond films can be obtained when the surface roughness is about 0.11 μm, and the nuclei of diamond appear in scratches on the substrates.