The inhibition of dicalcium phosphate dihydrate crystal growth by polycarboxylic acids

Abstract

The constant composition method has been used to study the influence of polycarboxylic acid, viz., benzene hexacarboxylic acid (mellitic acid), citric acid, tricarballylic acid, and polyacrylic acid (mol wt 2100), on the kinetics of crystal growth of dicalcium phosphate dihydrate (DCPD) on DCPD seed crystals at pH 6.00 and 37°C. Among the polycarboxylic acids, only the addition of mellitic and polyacrylic acids to the calcium phosphate supersaturated solutions has a significant inhibitory influence upon the crystal growth of DCPD. In the case of mellitic acid, this effect is interpreted in terms of adsorption, following the Langmuir isotherm, of mellitate ions at the active crystal growth sites. The order, in terms of decreasing effectiveness on the rate of DCPD crystal growth, of various polycarboxylic acids studied is as follows: polyacrylic acid ⪢ mellitic acid > citric acid = tricarballylic acid = no inhibitor