SINTERING OF POWDERS OF POLYAROMATIC MESOPHASE TO HIGH-STRENGTH ISOTROPIC CARBONS .2. INFLUENCES OF THE SYNTHESIS CONDITIONS OF THE MESOPHASES AND THE PREPARATION OF THE POWDERS

Mesophase pitches with mesophase contents of 22, 45, 47, and 68 vol% were produced from the Ashland A 240 pitch using a discontinuous stirred tank reactor. For synthesis of the mesophase pitch with 47 vol% mesophase ferrocene was used as a soluble catalyst precursor of iron. The mesophase pitches were milled to a particle size of d(max) less-than-or-equal-to 100 mum and afterwards extracted with tetrahydrofuran. The residues were treated at 200-degrees-C with oxygen in order to adjust their thermoplasticity for sintering. For the sintering of compacted powders the particle size of the raw powder was reduced to d(max) less-than-or-equal-to 32 mum and d(max) less-than-or-equal-to 10 mum. By optimizing the thermoplasticity and the sintering conditions, nearly equal mechanical properties were obtained after sintering at 1000-degrees-C for all mesophase powders produced from pitches with mesophase contents below 50 vol%. After the stepwise high-temperature treatment of the sintered carbons up to 2440-degrees-C, two effects were observed: (a) a strong decrease of the flexural strength between 1300 and 1800-degrees-C of such carbons obtained from the mesophase pitches produced without ferrocene; this strength decrease is caused by sulfur puffing; (b) a similar strength decrease was found between 1800 and 2440-degrees-C for the carbons obtained from the mesophase pitch produced with ferrocene. The different behaviour of this material is ascribed to the formation of iron sulfide during pyrolysis and evaporation of iron, sulfur, and/or carbon disulfide above 1800-degrees-C as a consequence of dissociation and/or reduction of the iron sulfide by carbon.