PURPOSE: To efficiently obtain hollow acicular calcium fluoride by bringing an acicular material having a two-layer structure of a calcium fluoride surface layer and a calcium carbonate inner layer into contact with a selective dissolving agent to dissolve and remove the calcium carbonate.
CONSTITUTION: Hydrofluoric acid is added to acicular calcium carbonate which is, if necessary, dispersed in a dispersion medium, in such a manner that the molar ratio of HF/CaCO3 is 1 to 1.5, so as to convert the surface layer of the acicular calcium carbonate into calcium fluoride. Thus, an acicular material having a two-layer structure of a surface calcium fluoride layer and an inner calcium carbonate layer is obtd. This acicular material is brought into contact with a dissolving agent to dissolve and remove the calcium carbonate without dissolving the calcium fluoride to obtain hollow acicular calcium fluoride having 1-5μm diameter and 10-100μm length.
INUI SABURO
IWASHITA TETSUSHI
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