MECHANICAL-PROPERTIES OF BINDERLESS CARBON MOLD PREPARED FROM HEAT-TREATED MESOPHASE PITCH OF CONTROLLED GRAIN-SIZE

The mechanical properties of binderless carbon moulds produced from the preheat-treated mesophase pitch of controlled grain sizes were investigated. The particular mesophase pitch catalytically synthesized from pure naphthalene with HF/BF3 was properly preheat-treated at 753 K for 2 hours and then ground by a jet-mill into grains of different sizes. These grains were moulded at room temperature under 170 MPa into a rectangular plate (35 mm x 40 mm x 5 mm) carbonized, calcined, and graphitized up to 2773 K to examine its texture and mechanical properties. The finest grains (average particle size: 2.4 mu m) provided a high-performance graphite artifact of the bending strength: 100 MPa, the compressive strength: 190 MPa, the total pore volume: 17 mm(3)/g, and the bulk density: 2.0 g/cm(3), with extremely high carbon yield of 92% by large shrinkage ratio of 15%. The graphitized plate from the smallest grains exhibited a highly homogeneous fine-mosaic texture of optically anisotropic units <1 mu m, which were randomly oriented. No boundary among grains was distinguishable after the carbonization, indicating that the whole grains in their mould firmly adhered to each other. A crack was not detectable over the entire region in the mould even after the graphitization, corresponding to the excellent mechanical properties. In contrast, the largest grains (average particle size: 8.0 mu m) provided a graphite plate of coarse-mosaic texture, where some cracks were induced by calcination at 1573 K. The graphitization developed the cracks, decreasing the mechanical strength. The density, homogeneous isotropy, and random orientation in the packing of mesophase pitch grains depending on the grain size appear to be key factors to achieve the high performance of the graphite artifact.