INFLUENCE OF POLYELECTROLYTES ON THE CRYSTAL-GROWTH OF CALCIUM-SULFATE DIHYDRATE

A seeded growth technique has been used to study the influence of polyelectrolytes on the crystallization of calcium sulfate dihydrate CaSO//4 19 2H//2O from stable supersaturated solution at temperatures ranging from 25 to 45 degree C. The results indicate that the crystallization in the presence of polyelectrolytes is preceded by an induction period following which crystal growth of CaSO//4 multiplied by (times) 2H//2O proceeds with a rate close to that in pure supersaturated solution. Temperature changes, polyelectrolyte concentration, molecular weight, and polyelectrolyte composition greatly affect the duration of induction period. The observed induction periods for the growth of CaSO//4 multiplied by (times) 2H//2O in the presence of polyelectrolytes strongly suggest that the polyelectrolyte is incorporated into the crystal lattice as the crystal grows.