CRYSTAL-GROWTH OF CALCIUM-FLUORIDE IN THE PRESENCE OF SOME METAL-IONS

The crystal growth of calcium fluoride seed crystals has been investigated in aqueous solution at 25-degrees-C by a constant composition method, in which the supersaturation and ionic strength were maintained constant by the addition of mixed titrant solutions containing lattice ions and controlled by a specific fluoride ion electrode. Over a range of relative supersaturation, 0.20-0.62, the crystallization reaction appears to be controlled by a surface process which, in contrast to a bulk diffusion reaction, is markedly inhibited by the presence of additives. The influence of a number of metal ions on the rate of reactions has been investigated. The reduction in growth rate can be interpreted in terms of a Langmuir-type adsorption isotherm. Direct adsorption experiments have also been done by using magnesium ion.