The influence of processing temperature on the structure and properties of mesophase-based polygranular graphites

Two polygranular graphites were prepared by sintering a coal-tar pitch based mesophase and a naphthalene-based mesophase. The influence of temperature on the structural ( density, porosity and light texture), mechanical (flexural strength) and electrical ( electrical resistivity) properties of the carbons was studied at different stages of carbonization/graphitization (400 - 2600 degreesC). The results show that the density of the materials increases continuously with temperature, pores mainly appearing below 800 degreesC, during the low-sintering phase and at the initial stages of the solid-sintering process. Above this temperature, porosity decreases due to the densification of the materials. Densification is clearly evidenced by a reduction in interlayer spacing and an increase in crystallite size. Flexural strength and electrical resistivity follow a different trend depending on the temperature range. Thus, flexural strength reaches its maximum value at 1000 degreesC, while electrical resistivity decreases continuously with temperature. Any variation in these properties is mainly related with porosity and crystallographic order. The different composition of the raw materials causes structural, mechanical and electrical changes to occur to different extent in both materials. (C) 2004 Kluwer Academic Publishers.