| 초록 |
Graphite nanometer particles are typically prepared in liquids by vibration ball mills. However, it is known that the wet process takes long periods of grinding time like 24 hours or more and requires a series of subsequent high energy operations such as de-watering, drying, regrinding and classification. On the other hand, there would be numerous advantages if fine grinding could be done effectively in dry atmosphere. However, since crystalline graphite has a layered structure giving a high lubrication property, its dry grinding, especially when obtaining nanometer particles, is extremely difficult. The shape of the graphite particles is also important for its utilization since particles with flaky shape can maintain relatively high electrical and thermal conductance as well as lubrication ability. Therefore, it would be necessary to reduce the size of graphite particles into fines with flaky shape while grinding proceeds. Also, some studies on the fabrication of sub-micron-sized graphite particle powders were performed under various degrees of low atmospheric pressure using an attrition mill. These attempts to reduce the size of natural crystalline graphite to nano-scale thickness via a method that uses an attrition mill have not been effective. The objective of this research described in this paper was to investigate the size reduction and the exfoliation model of a platelet-like natural crystalline graphite with low expansion via the attrition mill system. The size reduction efficiency of the low-level expanded graphite according to the grinding time revealed a stairway-type decreasing pattern. This is believed to have been because the size reduction process involves repeated expansion and exfoliation of the units of clusters and/or stacks. A new size reduction model with respect to such phenomenon was suggested. Nano-platelet-type graphite powder with an average particle size of 3 µm and a thickness of 20-50 nanometers was fabricated. |
