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The compaction of magnesium carbonate

Compaction is essentially a two-stage process. As pressure is applied, re-arrangement of powder particles takes place within the die, so that large voids are filled and interparticulate friction may be sufficient to cause fragmentation of the weaker particles. Further increase in pressure is believed to cause elastic and plastic deformation of the particles, which results in the particles being brought into close physical contact ; this in turn may permit interparticulate bonding by a “cold welding” mechanism (cf. Higuchi, Rao & others, 1953 ; Armstrong & Griffiths, 1970). We have observed that compacts of magnesium carbonate, when placed in water, disintegrated rapidly into their component particles, presumably due to breakdown of interparticulate bonds by a liquid of high dielectric constant. We therefore considered that if particles of known size were compressed and then allowed to disintegrate, evidence of fragmentation or interparticulate bonding might be obtained.