Formation of graphite single crystal from iron solution by the slow cooling method.

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Graphite single crystals with maximum dimensions of 40 mm in diameter and 0.04-mm thick were prepared from an iron solution by a slow-cooling method. The cell parameters of the product were ao=2.462±0.002 and co=6.708±0.001 Å. A flux of 200 g of electrolytical iron and 8 g of graphite were charged in the graphite crucible. The iron melt, saturated with carbon, was slowly cooled from maximum temperatures ranging between 1800 and 2500 °C to near 1150 °C at cooling rates ranging from 5 to 30 °C min−1. Large graphite single-crystal films of better quality were formed after quick cooling rather than slow cooling. Large graphite crystal films were formed at above 1850 °C; temperatures greater than 1950 °C were needed in order to grow the crystal films with good quality. From in-situ observations through a hole, the growth of the small graphite crystals was seen to occur on the surface of the melt at about 1550 °C; these were gathered in a constant direction, initiating the incorporation of small crystals. The incorporation of the small crystals was promoted at about 1700 °C and the surface of the melt was covered with a single-crystal film. For the formation mechanism of the graphite single-crystal film, a heating process was played an important role.
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