Nonequilibrium Phase Diagrams of C-H-O and Other Ternary Systems

Abstract

Since 1986 a great upsurge in research on activated low-pressure diamond growth from the vapor phase has unfolded throughout the world. Many scientists coming from different academic fields have joined in this research and research papers have increased very quickly. At the early stage, the gas sources of carbon were mainly a CH4-H2 mixture, and other hydrocarbons in a hydrogen mixture. The general expression could be written as C x H y -H2. A little later alcohol-H2, methanol-H2, acetone-H2, ether-H2, and other oxygen-containing organic compounds in a hydrogen mixture were also used as reaction sources. The CH4-H2 mixture together with direct addition of a little oxygen was also used for diamond growth. It was observed that the addition of oxygen in the reaction sources is often favorable to get diamond thin films with higher quality and to lower the temperature for diamond growth. In the oxygen—acetylene torch combustion process for diamond thin film growth oxygen plays a more important role. Although as pointed out in the last chapter a C-H-O system with a fixed ratio between oxygen and hydrogen or consisting of two reactants can be treated as a binary or pseudobinary system, from the viewpoint of thermodynamic analysis, these systems are C-H-O ternary systems. It is well known that a ternary system has two independent component variables, which may be denoted by X 1 and X 2. The change of composition of the system may be illustrated by a plane triangular phase diagram.