Compound physical and mechanical effects stimulating metastable diamond formation

Abstract

Purpose. To synthesize diamond polycrystals in a thermodynamically stable region, and to grow up a single crystal shell under conditions of thermodynamic metastability. To investigate some physical properties and features of the internal structure for synthesized single crystals for the development of new models and hypotheses regarding the issue of diamond genesis. Methodology. Experimental studies using shock-wave effects on a metal alloy containing non-diamond carbon. Methods of infrared and ultraviolet spectroscopy, X-ray phase analysis, electron paramagnetic resonance, isotope analysis, differential thermal analysis, electron microscopy, and others are used. The synthesis of nanocrystalline diamond particles as nuclei for growing single crystals is carried out by the shock-wave method using profiled shock waves. Findings. A complex of physicochemical methods for studying the grown diamond monocrystals has been carried out. The reasons for the discrete growth of diamond and the retention of the central inclusion (a polycrystalline diamond of shock-wave origin) in the process of growth have been established and analyzed. It is shown that the discreteness of diamond formation is characteristic only for thermodynamically metastable conditions. The results of the experiments give grounds to make an assumption about the metastable growth, including of diamonds from primary deposits. Originality. The hypothesis has been developed concerning the origin of diamond nanoparticles in interstellar carbon clouds which refer exclusively to central polycrystalline inclusions in a monocrystal diamond shell. The hypothesis eliminates the scientific contradiction that arises in all cases when attempts are made to interpret the natural discreteness of diamond formation based on the regularities of the graphite-diamond state diagram. Possible causes of discrete diamond formation in nature and the scenario of the formation of diamond nanocrystals in an interstellar cloud of atomic carbon have been considered. Practical value. The value of the experimental research results refers to the development of a non-energy-intensive technology for the growing large diamond monocrystals at temperatures of 5001400 K, and pressures of 105107 Pa.