摘要
在Fe-Ni-C体系中高温高压生长金刚石单晶,通过对触媒和金属包覆膜的物相结构表征、相图分析以及热力学计算等方法探讨金刚石形核长大的碳源供给。研究发现:在金刚石形核的初期,由于石墨的不断熔入,触媒熔体会迅速形成对碳的过饱和溶液,并析出初生渗碳体。金刚石单晶合成之后触媒和金属包覆膜的组织与物相均以渗碳体为主。相图分析发现,金刚石的形核长大伴随有渗碳体的分解。热力学计算表明,在金刚石稳定生长区域,渗碳体向金刚石转变的相变自由能比石墨-金刚石的相变自由能更负。由此说明,Fe-Ni-C体系高温高压生长金刚石单晶的直接碳源并非石墨,而是渗碳体,即金刚石单晶来源于渗碳体高温高压的金刚石化而不是石墨的直接转化。
Diamond synthesis experiments were carried out in the Fe-Ni-C system under high temperature and high pressure （HTHP）. The real carbon source forming diamond was investigated by characterizing the structure and phase of the catalyst and the metal surrounding the carbon films, by analyzing the phase diagram and by ther- modynamic calculations. These show that the catalyst and metal are composed mainly of cementite and the catalysts rapidly become supersaturated by absorbing carbon from the graphite and separate out as cementite （Fe3 C or Fe2C： Fe） when diamond begins to form a nucleus. According to the phase diagram, the diamond nucleation and growth are accompanied by the decomposition of the cementite. Thermodynamic calculations indicate that the phase transformation free energy of Fe3 C to diamond and ^-Fe is more negative than that of graphite to diamond in the stable diamond growth region. All of these results indicate that the real carbon source for diamond growth in the Fe-Ni-C system under HTHP is cementite, and not graphite.
出处
《新型炭材料》
SCIE
EI
CAS
CSCD
北大核心
2010年第2期119-123,共5页
New Carbon Materials
基金
国家自然科学基金(50772060)~~
关键词
人造金刚石
碳源供给
铁基触媒
高温高压
Synthetic diamond
Carbon source supply
Iron-based catalysts
HTHP
