Phase diagram for diamond growth in atmospheric oxyacetylene flames

The temperature vs. gas composition phase diagram of solid carbon deposition in atmospheric oxyacetylene flame is calculated. The phase diagram, which is composed of a diamond growth region, a gas phase region, and a non-diamond carbon growth region, is identical with the reported experimental data. So the suitable ranges of substrate temperature and O(2)/C(2)H(2) ratio for diamond synthesis in oxy acetylene flames can be theoretically predicted. When the substrate temperature is between 1000 K and 1250 K, the corresponding O(2)/C(2)H(2) ratio range is about between 0.8 and 1.1. The suitable range of substrate temperature is widest for O(2)/C(2)H(2) ratio close to unity and is narrowed rapidly when the flow ratio deviates from unity.