2227.     MCCARTNEY, J. T., AND ANDERSON, R. B.  Crystalline Aggregation of Cobalt Powder.  Jour. Appl. Phys., vol. 18, 1947, pp. 902-903; Chem. Abs., vol. 42, 1948, p. 805.

        In electron-microscopic studies of Fisher-Tropsch catalysts, an interesting phenomenon was observed in Co metal powder, reduced from cobaltous oxide.  The oxide particles sintered into larger smooth droplets of Co that were aggregated into thin, hexagonal platelets.  X-ray diffraction analysis showed the presence of the hexagonal crystal phase of Co.  A possible explanation is that the aggregates are formed by forces similar to those operating in normal crystal formation, but of reduced magnitude insufficient to destroy the identity of the component particles.  It is not evident why this phenomenon has been observed only in Co.