Preliminary Explorations For The Purification And Phase Transition Of New Diamond Under High Pressure

As a new allotrope of carbon, new diamond has attracted a lot of attention since itwas found in1991. In the past two decades, much effort has been devoted to investigatethe preparation methods of new diamond. However, the new diamond samples preparedby these methods usually present characteristics with small sizes and low yields. Also thesamples usually contain more impurities. These shortcomings seriously hinder theexploration for the structure and properties of new diamond. Although much nano-scalednew diamond samples can be prepared by nano-sized Fe catalyzed carbon black, thefactors affecting the yield of new diamond are still unclear to date. Besides, purificationof the prepared samples is significant since it laid the foundation for the structure andproperties’ investigation of new diamond. In this paper, the technological factors (i.e.various carbon sources, different mole ratio of carbon to iron, heating temperature andheating time) on the yield of new diamond, the purification of prepared samples and thephase transition of new diamond under high pressure have been investigatedsystematically. The detailed contents are as follows:(1) The influences of different carbon sources and mole ratio of carbon to iron(C:Fe), together with heating temperature (T) and heating time (t) on the yield of newdiamond have been studied. The results indicated that the highest yield of new diamondcan be obtained by using carbon black as carbon source under the condition of C:Fe=4:1, T=1100℃and t=1h.(2) Based on the new diamond samples prepared by nano-sized Fe catalyzed carbonblack, the purification of new diamond samples has been investigated through differentmethods. The results manifested that the new diamond nano powders can be well purifiedby the physical method (i.e. ultrasonic dispersion by anhydrous ethanol and stirring bymagnetic), while the samples cannot be purified via the chemical method (i. e. addingacid).(3) The phase transition of new diamond under high pressure conditions has beenstudied on the basis of the purified samples. The results indicated that new diamond can transform into diamond under room temperature with the transition pressure ranges from2~6GPa, and the transition rate ascends with the increase of pressure. Moreover, it wasfound that the new diamond is decomposed when the temperature rises to200℃and thedecomposition process finishes when the temperature rises to400℃. The new diamondtransforms into graphite when temperature reaches at800℃, and the transition processproceed completely when the temperature reaches at1200℃.