Nucleation control and growth kinetics of ammonium hydrogen tartrate single crystals in silica gels

A detailed study of the variation in the nucleation density and growth of ammonium hydrogen tartrate (AHT) single crystals as a function of the concentration of the feed solution, the gel density, the gel pH, the gel aging time and the temperature is presented. Whereas opaque crystals were produced from high density high pH gels, good quality transparent single crystals were obtained in low density low pH gels. The use of intermediate neutral gel column and gel aging times considerably reduces the number of nucleation sites. The nucleation density decreases as the temperature increases. A simple procedure to control nucleation sites in gels was adopted and resulted in a dramatic increase in the size of the crystals. Kinetics studies of the nucleation and growth of AHT needle crystals showed that these crystals grow by a one-dimensional diffusion-controlled reaction between ammonium chloride and tartaric acid. The implications of this behaviour are discussed.