Effect of pyrogallol additive on the growth rate and the habit of hydroquinone crystals

Hydroquinone crystals, obtained batch-wise by cooling from unseeded aqueous solutions, changed in shape from rodlike to prismatic by the presence of pyrogallol as an additive. The additive pyrogallol worked as a crystal habit modifier. The metastable zone width determined for unseeded solutions was increased by the addition of pyrogallol. This suggests that primary nucleation was also reduced by the presence of pyrogallol. Experiments on the hydroquinone crystal growth using a fluidized bed crystallizer showed that the longitudinal growth rate was much decreased by the presence of the additive pyrogallol, while the lateral growth rate was not affected by the additive. The effect of the additive on the longitudinal growth rate was reasonably explained by the Kubota-Mullin model [J. Cryst. Growth 1995, 152, 203-208], and the crystal habits (aspect ratios) estimated from longitudinal and lateral growth rates were in good agreement with the experimental values.