Dynamic decomposition products of adamantane

The decomposition of organic compounds under high pressure and temperature conditions may produce diamond as well as graphite [1, 2]. The formation of diamond from non-elemental carbonaceous materials such as carbon monofluoride [3] and n-heptadecane [4] has been reported in dynamic methods and from organic compounds under static high pressure conditions [1]. The dynamic formation of diamond includes various processes such as nucleation and growth via solid-liquid-solid or solid-liquid-vapoursolid as well as martensitic and reconstructive transformations via solid-solid. In the case of hydrocarbons, the melting points are relatively low and the formation of radicals is substantial at shock pressures below 10 GPa [5, 6]. The observed opacity increases of organic liquids near 10 GPa [7] were interpreted to be the formation of solid carbon particles during shock compression. This letter reports results on the dynamic decomposition of adamantane (tricyclo[3.3.l.13'V]decane) of which the molecule possesses a carbon structure similar to diamond. In the crystal, the molecules lie at the corners and the face centres of a cubic unit cell to give a closely packed arrangement with a density of 1.08gcm -3. The melting point of adamantane is 270 ° C in a sealed platinum tube. According to pyrolysis experiments on adamantane at 15 GPa and 2000 ° C [1], diamond was the only crystalline phase. Setaka [8] made an attempt to synthesize diamond from adamantane, but failed to recover samples after shock treatments. Less than 0.5% of amorphous carbon was obtained in a large amount of unchanged adamantane up to a shock pressure of 20 GPa [9]. Experimental shock results on various organic materials have been summarized and adamantane is described as unchanged or decomposed at 18 to 20GPa [10]. The adamantane employed (Wako Chemical Co.) had a purity more than 99% and was mixed in an agate