Fast crystal growth

S.V. Stability of KH2PO4 and K(H,D)2P04 in fast crystal growth rates. J. Cryst. Growth 1995, 148, 276-292. 57. 

As discussed in Chapter 2, solvent can be occluded in the crystal lattice due to fast crystal growth and/ or excessive nucleation. To test this hypothesis, a series of experiments were conducted. The following parameters were varied ... 

Solvent molecules are frequently found in association with precipitated materials. For example, crystalline substances often form with water molecules located at specific sites, e.g. water of crystallization, held in co-ordination complexes around lattice cations. Extraneous inclusion of water molecules can occur if a co-precipitated cation carries solvation molecules with it. Massive incorporation of solvent, together with other soluble impurities can occur in random pockets (inclusions) as a result of the physical entrapment of mother liquor. Fast crystal growth, leading to growth instabilities, dendrite formation, crystal agglomeration, etc., can all contribute to this undesirable feature. An account of liquid inclusions in crystals is given in section 6.6. 

Figure 40 Left Schematic illustration of a PE crystalline lamella in which the stems are inclined by a significant angle in the plane perpendicular to the fast crystal growth axis (i.e., the b-axis). In terms of the symmetry operation, such lamella exhibits an inversion point when viewed along b. Right The unbalanced stresses generated on the lamellar surface result in a helicoidal twist of the crystal, which becomes symmetric about the mirror plane M perpendicular to the crystal growth direction and passing through the primary nucleus. With permission from Rosenthal, M. etal. Angewandte Chemie lot. Ed. 123 (2011) 9043-9047. ...

First proposed by Barrer [15] and Kerr [16,17], and later by many others [18], nucleation is the result of polymerization of aluminate-silicate-tetrahedral and possibly more complex ions in the liquid phase. When the current of nuclei exceeds a critical size, fast crystal growth starts, supplied continuously with silicate and aluminate units from gel dissolution. Aluminosilicate species found in solution by Raman and Si-NMR spectroscopy [19—21] and the possibility of obtaining zeolite directly from liquid phase, omitting gel stage [22], favor this concept. 

Crystallization and reactivity in two-dimensional (2D) and 3D crystals provide a simple route for mirror-symmetry breaking. Of particular importance are the processes of the self assembly of non-chiral molecules or a racemate that undergo fast racemization prior to crystallization, into a single crystal or small number of enantiomorphous crystals of the same handedness. Such spontaneous asymmetric transformation processes are particularly efficient in systems where the nucleation of the crystals is a slow event in comparison to the sequential step of crystal growth (Havinga, 1954 Penzien and Schmidt, 1969 Kirstein et al, 2000 Ribo et al 2001 Lauceri et al, 2002 De Feyter et al, 2001). The chiral crystals of quartz, which are composed from non-chiral Si02 molecules is an exemplary system that displays such phenomenon. 

Thus far, two types of solvent-assisted solid-to-solid transformations of a kinetically formed metastable crystalline phase into a thermodynamically stable one in a process of crystal growth, relevant to the occurrence of Preferential Enrichment, have been observed One is a relatively fast polymorphic transition noted in the case of ( )-NNMe3,18 and the other is a slow one in the case of ( )-NPMe3.18,26... 

Illustrating the formulation of mass and energy balances is simplified by restricting the analysis to systems whose crystal growth kinetics are sufficiently fast to utilize essentially all of the supersaturation provided by the crystallizer in other words, the product solution... 

Fig. 14 Binary phase diagram for C246H494 in octacosane. The top curve shows the equilibrium liquidus for extended-chain crystals, and the bottom line the metastable liquidus for once-folded crystals. Experimental dissolution temperatures are fitted to the Flory-Huggins equation with / = 0.15 (solid lines). Vertical dotted lines (a) and (b) indicate the concentrations at which the growth rates were determined as a function of Tc in [29]. Horizontal dotted lines indicate the temperatures at which the rates were determined in [45] as a function of concentration. G(c) at Tc = 106.3 °C, measured along line (c), is shown in Fig. 12. The shading indicates schematically the crystal growth rate (black = fast), and the dashed line the position of the growth rate minimum...

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