CONSTANT COMPOSITION STUDY OF CRYSTAL-GROWTH OF CALCIUM-FLUORIDE - INFLUENCE OF POLY(CARBOXYLIC ACIDS), POLYPHOSHATES, PHOSPHONATES, AND PHYTATE

The constant composition technique has been used to study the crystal growth of calcium fluoride on calcium fluoride seed crystals at sustained supersaturation, 37-degrees-C, in the presence of inhibitors of varying functional groups. The inhibitors investigated include (1) poly(carboxylic acids) (benzenehexacarboxylic acid, mellitic acid, MA; benzene-1,3,5-tricarboxylic acid, trimesic acid, TMA; poly(acrylic acid), PAA mol wt 5100; citric acid, CA), (2) polyphosphates (pyrophosphate, PYP, hexametaphosphate, HMP; phytic acid, PA), and (3) phosphonocarboxylic acid (2-phosphono-1,2,4-butanetricarboxylic acid, PCA). The effect of these inhibitors on the growth kinetics has been studied at several inhibitor concentrations. The retarding effect of these inhibitors is interpreted in terms of adsorption, following the Langmuir isotherm, of inhibitor ions at the active crystal growth sites. The order, in terms of decreasing effectiveness on the rate of CaF2 crystal growth, of various inhibitors studied is as follows: PAA >> PCA > MA > HMP > PYP > PA > CA > TMA.