Sucrose crystal growth

Figure 4-15 Projection of a Sucrose Crystal Along the a Axis. Source From B.M. Smythe, Sucrose Crystal Growth, Sugar Technol. Rev., Vol. 1, pp. 191-231, 1971.

Smythe, B.M. (1967) Sucrose crystal growth. Australian Journal of Chemistry, 20, 1087, 1097, 1115. 

Mantovani, G., Vaccari, G., Accorsi, C.A., Aquilano, D. and Rubbo, M., 1983. Twin growth of sucrose crystals. Journal of Crystal Growth, 62, 595-602. 

The face-by-face (R,a ) Isotherms on sucrose crystals growing from pure solutions allow us to determine the activation energies and, to some degree, the growth mechanisms for each of the F faces. 

Figure 16.5. Supersaturation behavior, (a) Schematic plot of the Gibbs energy of a solid solute and solvent mixture at a fixed temperature. The true equilibrium compositions are given by points b and e, the limits of metastability by the inflection points c and d. For a salt-water system, point d virtually coincides with the 100% salt point e, with water contents of the order of 10-6 mol fraction with common salts, (b) Effects of supersaturation and temperature on the linear growth rate of sucrose crystals [data of Smythe (1967) analyzed by Ohara and Reid, 1973],...

Fig. 1. 28.1. DTA measurement of a 10% sucrose-10% NaCI solution during slow rewarming after quick (200 °C/min) freezing. 1, Glass transition at = 93 °C 2, crystal growth (exothermic) at -65 °C 3, significant exothermic event, crystallization of NaCI at =44 °C 4, eutectic melting at =22 °C ...

Factors that influence growth of sucrose crystals have been listed by Smythe (1971). They include supersaturation of the solution, temperature, relative velocity of crystal and solution, nature and concentration of impurities, and nature of the crystal surface. Crystal growth of sucrose consists of two steps (1) the mass transfer of sucrose molecules to the surface of the crystal, which is a first-order process and (2) the incorporation of the molecules in the crystal surface, a second-order process. Under usual conditions, overall growth rate is a function of the rate of both processes, with neither being rate-controlling. The effect of impurities can be of two kinds. Viscosity can increase, thus reducing the rate of mass transfer, or impurities can involve adsorption on specific surfaces of the crystal, thereby reducing the rate of surface incorporation. 

Bennett, M. C. Fentiman, Y. L., Growth Rate of Sucrose Crystals Related to Krypton Surface of Seeds. In Industrial Crystallization The Institute of Chemical Engineers London, U.K. 1969, pp. 217-226. 

After the juice has settled, the scum is removed and sent to the fermenting tank in the still house. The clear juice runs to evaporators, its sucrose content being about 14 per cent. In the first evaporation, it is concentrated to about 50 per cent sucrose. Further concentration is carried on until the desired point for proper crystal growth has been reached. The mass in the pan, then called massecuite, contains a total of 82 per cent sucrose and perhaps 8 per cent water. Of the total sugar in the hot massecuite 56 per cent is in crystals and 44 per cent is in solution after cooling 65 per cent has crystallized and 35 per cent remains in solution. 

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