摘要
利用热力学中经典的ΔG<0判定法,探讨了Fe基触媒合成金刚石晶体生长中的碳源问题,在计算中考虑了各物相的体积随温度和压力的变化。结果表明:在金刚石形成之前,就有大量Fe3C形成,而在触媒法合成金刚石的温度和压力范围内,Fe3CC(金刚石)+3-γFe反应自由能和石墨金刚石相变自由能均为负值,但前者比后者的绝对值更大,这说明前者更容易发生。因此,从热力学角度看,Fe3C的形成降低了石墨转变为金刚石所要越过的势垒,使用Fe基触媒合成金刚石单晶的生长来源于Fe3C的分解而不是石墨的直接转化。同时推导出在1200 K以上石墨-金刚石的平衡p-T关系:peq(GPa)=1.036+0.00236T(K),与F.P.Bundy的平衡线非常接近,证明了本热力学计算方法的可行性。
The diamond growth with Fe-based catalyst at high pressure and high temperature（HPHT） was analyzed with the determinant method of △G〈0 in thermodynamics theory,and the changes of volume with temperature and pressure were involved in the calculation. The results show that the Fe3 C phases have been formed before diamond nucleation; at the temperature and pressure range of the diamond synthesis with catalyst,the Gibbs free energies of Fe3 C→C（diamond）＋37-Fe and graphite→ diamond are all negative, but the former＇s absolute value is much larger than the latter＇s,which means the former will take place more easily. Therefore,from the viewpoint of thermodynamics the formation of Fe3C reduces the potential energy,of the transformation from graphite to diamond,and the diamond crystal growth with Fe based catalyst comes from the decomposition of Fe3C instead of the direct transformation from graphite. Moreover, the p-T （Pressure-Temperature） equilibrium of peq （GPa） = 1. 036＋0. 002 36T（K） was gained,which was closer to that presented by F. P. Bundy. Thereby the thermodynamic calculation used in this paper is feasible.
出处
《高压物理学报》
EI
CAS
CSCD
北大核心
2009年第3期189-195,共7页
Chinese Journal of High Pressure Physics
基金
国家自然科学基金(50772060)
山东省自然科学基金(Y2007F11)
关键词
高温高压
金刚石生长
触媒
碳源
热力学
HPHT
diamond growth
catalyst
carbon source
thermodynamics
