Nanocomposites and nanomaterials

Effect of expanded graphite particle size on the physical properties of compacted powders
Revo S.L.1, Melnichenko M.M.1, Avramenko T.G.1, Ivanenko K.O.1, Hamamda S.2
1 Taras Shevchenko National University of Kyiv, 64/13, Volodymyrska Street, 01601 Kyiv, Ukraine.
E-mail: s_revo@i.ua
2 Laboratory of Thermodynamics and Surface Treatment of Materials, University of Constantine 1, Constantine, Algeria.

The influence of dispersity of ground expanded graphite (EG) on the structure and microhardness of compacted samples is considered in this work. The processing criteria for powders of different fractions have been specified to achieve the uniform distribution of particles in the cell and to optimize the practically important characteristics of such samples.
It was shown, that mechanical grinding and separation of EG powder allow predicting the morphology of particles and effect on the physical characteristics of compacted powders. In particular, it was found that particles with a dispersion of 260 μ are characterized by a complex morphological structure, which effects on their ability to distribution, lamination and stacking under compaction and on the microhardness of resulting compacts. These samples are characterized by a more anisotropic and macrolayered structure vs. the samples with the average cross-sectional dimension of powder 50 μ. Significantly, with an increase in the particles dispersity and the approximation of their shape to the equiaxial anisotropy of the resistivity of compacted samples decreases by 30%.
In addition, it was shown that the accumulation of internal stresses in the particles structure, which occurs under grinding, directly increases the microhardness of the compacted samples. The particles with an average cross-sectional dimension of 120 μ have maximum microstresses. The microhardness varies from 0.117 to 0.044 GPa with a change in the load on the indenter in the range from 20 to 80 g for such samples. The more isotropic distribution of the microhardness have been observed for the fraction of 50 μ due to the more equiaxed shape of the particles, which makes it possible to predict the technological aspects of obtaining materials with predetermined characteristics.