Shapes of Meso-Carbon Microbeads

Abstract

Quinoline-soluble coal-tar pitch, coal-tar pitch containing 3.4% free-carbon (quinolineinsoluble particles) and petroleum asphalt containing 5.4% sulphur were heat-treated for 120 min., 90 min. and 60 min. at 430°C respectively. Formation of mesophase spherules was observed by using a polarized-light microscope.The mesophase spherules were separated by solvent extraction from heat-treated pitches. The separated mesophase spherules were named meso-carbon microbeads and classified into type C, type M and type P according to above mentioned raw pitches. The shapes of meso-carbon microbeads were studied with a scanning electron microscope.The shapes of type C and type P can be divided into two classes, that is, the shapes of meso-carbon microbeads having larger size than about 5μm are approximately true spheres and those having smaller size than about 3μm are lemon-like spheroid. It is not obvious that the meso-carbon microbeads showing lemon-like shapes have the same lamellae structure as those larger than about 5μm, because the sensitive-tint technique can not be used for the meso-carbon microbeads smaller than about 3μm according to the resolving power of optical microscope.The shapes of type M are irregular, although their sizes are almost the same, and the free-carbon smaller than about 1μm are retained over the surface of mesophase.