Effect of Pressure and Holding Time during Compression Molding on Mechanical Properties and Microstructure of Coke-Pitch Carbon Blocks

Abstract

In this study, isotropic coke and coal tar pitch were subjected to compression molding while varying the compression pressure and holding time. As a result, carbon blocks were fabricated, and their mechanical properties and microstructure were analyzed, with respect to applied pressure and holding time. The compression pressure was set to 70, 100 and 130 MPa, while the holding time was set to 1, 2 and 3 min. Overall, with an increase in compression pressure, bulk density increased while porosity decreased. Increased compression pressure also led to enhanced mechanical and electrical properties. Microstructural analysis confirmed that, after compression molding granules that were larger than existing kneaded particles appeared. The formation of granules is attributed to the tendency of kneaded particles to connect and coalesce with each other under applied pressure during the compression molding process. As the compression pressure increased, the proportion of granules in the microstructure increased while the size of pores decreased. This phenomenon can be attributed to kneaded particles coming closer to each other under applied pressure. At a compression pressure of 130 MPa, both bulk density and porosity increased with a longer holding time. Some pores existed within granules, while others protruded out of granules, thereby forming long channels of connected pores around them. This microstructural change was considered to result in degraded mechanical and electrical properties.