Dissolution in HCl of hematite particles with different morphologies l
ed to sigmoidal dissolution vs. time curves. The rate of dissolution w
as directly proportional to the sample surface area and independent of
crystal morphology. Hematites produced by heating goethite at 600 or
800-degrees-C dissolved more rapidly per unit area than did hematites
grown from solution. TEM showed that some platy crystals developed cen
tral holes after prolonged acid attack; the hole formation was attribu
ted to enhanced dissolution at screw dislocations present on the (001)
faces of the crystals. Except where particularly susceptible regions
involving strained areas or dislocations were present, there appeared
to be no preferential acid attack at any particular crystal face. The
original morphology was usually maintained during the reaction.