THE BRIQUETTING OF GRAPHITE*

Natural-graphite and finely ground artificial-graphite powders have been subjected to improved compacting ( “Shape”) techniques, developed by the National Coal Board, in an attempt to produce strong, dense materials suitable for use in atomic reactors. The densities of the natural-graphite and artificial-graphite compacts were 2.18 and 2.06 g/ml, respectively; the strengths were ∼2000 Ib/in2in each case. Whereas “Shape” techniques improved the compact quality of briquettable materials (e.g. artificial graphite ground to 12 μ dia.), non-briquettable materials (e.g. +350 B.S. mesh artificial graphite) could not be satisfactorily compacted by any means.Compact quality was very sensitive to particle size and size distribution in the sub-sieve range. On the whole, compact density decreased with decreasing particle size, whereas the strength increased. An empirical relationship S = KA 5/2,between the strength (S) and the specific surface area (A) of the powder, was obtained for electro-graphite powder compacted at 10 tons/in2Annealing these compacts at 800°C reduced their density by 1-2% but increased their strength by ∼30%.The compacts were extremely anisotropic and experiments which were aimed at reducing this anisotropy are described.