再结晶石墨的形成机制

用高温高压温度梯度法作为实验手段来生长优质宝石级金刚石单晶。发现在金刚石合成的稳定区内(人造石墨碳源已完整为金刚石,而且籽晶上有宝石级金刚石单晶的持续生长),结晶性完整的亚稳态再结晶石墨更容易在相对低压高温区出现,其成核驱动力小于金刚石。本文还首次从过剩溶解度角度讨论了再结晶石墨的形成过程。研究表明:在金属触媒溶液中由高温端扩散下来的大量碳源处于过饱和状态时,再结晶石墨是作为一种中间相首先出现,当压力、温度合适时,再结晶石墨会再次成核为金刚石单晶,否则,再结晶石墨就会稳定保留下来。

Formation mechanism of re-grown graphite

Large synthetic diamond was grown by temperature gradient method(TGM) under HPHT.It was found that,in the diamond-stable region,where the man-made graphite has been completely transformed into diamond and the gem diamonds are continuously growing on the seed crystals,the re-grown graphite is easier to appear at lower pressure and higher temperature.The driving force for the nucleation of re-grown graphite is smaller than that for diamond crystals.The formation mechanism of re-grown graphite is explained from the point of super-concentration of carbon(diamond or graphite) in the metal solvent.It is suggested that the re-grown graphite appears as the transitional phase first.Then if the P-T condition is suitable the re-grown graphite will re-nucleate into diamond crystals.Otherwise,the re-grown graphite will be retained stably.