Crystal habit modification

The morphological theory of Hartman and Perdok (1955) considers the bond energies involved in the integration of growth units into the lattice. In this 

If no PBC exists within a layer, dhkh the face is called a kinked or K-face, which needs no nucleation for growth since it corresponds to a generalized type 

The Hartman-Perdok approach is applied by making projections of the crystal structure parallel to a PBC and tabulating all the bonds. The packing of the chains determines the F-faces, provided that the chains are bonded by strong bonds. Sometimes it is easier to recognize the slices, and in that case the PBC may be found as the intersection of two slices. 

Some reported examples of the use of PBC analysis to predict crystal morphology include hexamethylenetetramine (Hartman and Perdok, 1955), calcium sulphate (gypsum) (van Rosmalen, Marchee and Bennema, 1976), anthracene (Hartman, 1980), magnesium hydrogenphosphate (newberyite) (Boistelle and Abbona, 1981), sodium sulphite and potassium sulphate (Follner and Schwarz, 1982), succinic acid (Davey, Mullin and Whiting, 1982), sucrose (Aquilano et al, 1983). 

The adsorption of an impurity on a crystal face can have a similar effect to a change of solvent. Since adsorption reduces the interfacial tension, it will also reduce the a-factor and consequently roughen the surface. If adsorption is selective, i.e. only on to specific faces of the crystal, or to different extents on different faces, any significant change from the smooth to rough condition could lead to faster growth on those faces and hence to a habit change. 

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WHETSTONE, J. Trans. Faraday. Soc. 51 (1955) 973-80 and 1142-53. The crystal habit modification of inorganic salts with dyes (in two parts). 

Y.N. Tsuchiya, Crystal Habit Modification of Ammonium Nitrate. III. Application to Ammonium Nitrate-Fuel Oil Explosives , KKK 23, 78-83 (1962) (in Engl) CA 58,... 

In actual production, effective additive bisPEA is a by-product of the racemization step, and racemized PEA containing enough bisPEA to produce crystal habit modification is recycled to the next resolution step as part of the raw material (7 S)-PEA (Figure 17). 

Since this new methodology has been applied in an actual production process, optical purity of enantiopure PEA has been well stabilized. Detailed crystal habit modification mechanisms of the phenomenon35"38 and its application to other compounds39 are reported in the literature. 

Crystal habit modification. Several crystal habits have been reported in the open and patent literature for zeolite omega. Elongated hexagonal rods (15,16) or fibres (17) have been reported when the zeolite resulted from the recrystallization of another zeolite, Y (15) or S (17), or of clays (16). Moreover the natural counterpart of zeolite omega, mazzite, appears as bundles of needle-shaped particles (18). All these solids have been grown at low supersaturation levels, hence under conditions in which our results show that the growth in the direction <001> prevails on the growth normal to the c-axis (Fig.8). 

The term crystal habit is often used to describe the relative sizes of the faces of a crystal. Crystal habit is readily modified by conditions of nucleation and growth, and it is rather difficult to prepare ciystals with all faces of the same form equally developed (M2). Small amounts of soluble impurities, especially dyes, which may be adsorbed selectively on the different faces of a crystal, cause these faces to be suppressed in favor of others. This can alter the external geometry of a crystal completely, except for its interfacial angles. Many examples of crystal habit modification are reported in the literature (B8), and in some commercial... 

All of these changes in ciystal habit caused by kinetic factors are drastically effected by the presence of impurities that adsorb specifically to one or another face of a growing ciystal. The first example of crystal habit modification was described in 1783 by Rome de Lisle [77], in which urine was added to a saturated solution d NaCl changing the crystal habit from cubes to octahedra. A similar discovery was made by Leblanc [78] in 1788 when alum cubes were changed to octahedra by the addition of urine. Buckley [65] studied the effect of organic impurities on the growth of inoiganic crystals from aqueous solution, and in Mullin s book [66] he discusses the industrial importance of this practice. 

Whatever the details of the kinetic mechanism, impurities cause crystal habit modification. Buckley [65] has classified many impurity effects on different crystal habit modifications. In most cases, impurities decrease the growth rate of specific crystal faces, which lead to a change in the crystal habit because the slowest growing faces will dictate the crystal morphology. In some exceptional cases, impurities can increase the growth rate of a particular crystal face. For example, 1% Fe added... 

Garekani, H.A. Sadeghi, F. Badiee, A. Mostafa, S.A. Rajabi-Siahboomi, A.R. Crystal habit modifications of ibuprofen and their physicochemical characteristics. Drug. Dev. Ind. Pharm. 2001, 27 (8), 803-809. 

Whetstone, J. Crystal habit modification of inorganic salts with dyes. II. Relationship between the structure of crystals and habit-modifying dyes. Trans. Faraday Soc. 1955, 51, 1142-1153. 

Venkataram, S. Khohlokwane, M. Microencapsulation of an iron chelator for sustained release and crystal habit modification. J. Microencapsulation 1996, 13 (5), 519-525. 

Phase transfer and crystallisation This occurs when the suspension particles have a limited solubility in the oil phase. Small suspension particles which are more soluble than their larger counterparts (due to curvature efiects) may dissolve in the oil phase and then recrystaUize onto the larger suspension particles (this is a form of Ostwald ripening). Large and sometimes needle-shaped crystals may be produced as a result of crystal habit modification (this sometimes occurs with Ostwald ripening). 

On storage, the smaller particles will dissolve in the oil and recrystaUize on any larger particles which may be in the vicinity of the O/W interface. Some crystal habit modification may be produced and large plates or needles are formed which... 

Boistelle, R. (1976) Survey of crystal habit modification in solution. In Industrial Crystallization (6th Symposium, Usti nad Labem), J.W. MuUin (ed.), 203 214, Plenum Press, New York. 

Mullin, J.W., Amatavivadhana, A. and Chakraborty, M. (1970) Crystal habit modification studies with ADP and KDP. Journal of Applied Chemistry, 20, 153-158. 

Van Rosmalen, G.M. and Bennema, P. (1990) Characterization of additive performance on crystallization habit modification. Journal of Crystal Growth, 99, 1053-1060. 

Whetstone, J. (1949b) The effect of crystal habit modification on the setting of inorganic... 

Crystal Growth Modification. As a practical example of crystal habit modification, one can consider the growth of ice crystals in ice cream. If the crystals grow too large or attain certain shapes, the organoleptic or perceived quality of the product will be reduced significantly—the ice cream becomes sandy. In practice, the crystallization phenomenon is controlled by the addition of various natural gums (e.g., locust bean gum) that presumably adsorb on specific crystal faces and retard or prevent further deposition of water molecules. 

Bolstelle, R. Survey of crystal habit modification in solution. In ... 

Growth mechanisms of sucrose from face-by-face kinetics and crystal habit modifications from Impuntles effect. In Industrial Crystallization 84 (eds. Jancic, S.J., de Jong, E.J.), p. 91, Elsevier, Amstardam 1984... 

Khamskll, E.V. Zhur. Prlkl. Khlm. 32 (1959) 948 (642J Khamskll. E.V. Some problems of crystal habit modification. In Industrial CrystalUzaUon (ed. MuHln, J.W.). p. 215, Plenum Press, New York 1976... 

Clydesdale, G., Hammond, R. B., and Roberts, K. J. 2003. Molecular modeling of bulk impurity segregation and impurity-mediated crystal habit modification of naphthalene and phenanthrene in the presence of heteroimpurity species. J. Phys. Chem. B 107 4826. 

Traditional uses of the alkyldiphenyl oxide disulfonates include (1) emulsion polymerization to yield faster run times with less reactor waste and smaller particle size (2) acid dyeing of nylon carpet fiber as leveling agents to promote an even distribution of dye, (3) crystal habit modification to alter crystal shape and size and (4) cleaning formnlations to provide solubilization in strongly acidic, caustic, and bleach environments. 

FIG. 2 Polymorphism in ammonium nitrate (top) and effect of additives on crystal habit modifications (bottom). 

Depending upon the nature of additives, the process of crystal habit modification can be initiated at various stages of crystal phase changes, e.g., I... 

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