Crystals agglomeration

Hostomsky, J., 1987. Particle size distribution of agglomerated crystal product from a continuous crystallizer. Collection of Czechoslovakian Chemical Communications, 52, 1186-1197. 

Sugar-boiling for proper crystallization is done in the metastable and intermediate phase below the metastable zone, crystals dissolve and inefficiencies result above the intermediate phase, uncontrolled false grain or extra, small, and agglomerated crystals form, resulting in poor-quality crystals. When the syrup is in the metastable phase, it is seeded that is, a predetermined amount... 

Crystal agglomeration (crystals sticking together) normally occurs in the crystal separator and/or dryer. Ammonium chloride and borax can form agglomerates in the crystallizer depending on the type and amount of impurities present as well as the level of supersaturation. 

It is important to note that unlike in precipitation method, both polar solvent, such as acetone, and nonpolar solvents, such as diethyl ether and hexane, produced needlelike crystals of ibuprofen when saturated solutions were cooled to 5°C over 120 min. Dichloromethane produced cubic, whereas acetonitrile produced spherical agglomerated crystals by this method. Solvent evaporation of ethanol gave platy... 

Development of agglomerated crystals of ascorbic acid by the spherical crystallization technique for direct tabletting and evaluation of their compactibiUties ... 

Parameters determining the agglomeration behavior and the micromeritic properties of spherically agglomerated crystals prepared by the spherical crystallization technique with miscible solvent systems ... 

Fig. 6.2-92 Scanning electron micrographs of 1) external appearance, 2) cross section of a) ESM, b) SA agglomerated crystals of ascorbic acid [6.2.3.2]...

Fig. 6.2-93 Scanning electron micrographs of a) spherically agglomerated crystals of a drug b) sample of the same product, showing its uniformity (courtesy AstraZeneca R D, Molndal, Sweden)...

Fig. 6.2-97 Scanning electron micrographs of single dry crystals of acebutolol hydrochloride and of spherically agglomerated crystals [6.2.3.4]...

Many investigators have studied models of the von Foerster type (see Trucco (4) for several references and properties), which belong to the general population balance category used in kinetic theory, particle agglomerization, crystallization, etc. (see Himmelblau and Bischoff (5) for a textbook treatment). We will use the model of Rubinow (6) for reasons discussed below. 

A typical experiment normally yields several well-faceted single crystals of (SN)X ranging in size from 0.5 to 1.5 mm these represent approximately 10% of the total mass. The remainder consists of less perfect crystals and also polycrystalline agglomerates. Crystals up to 4-5 mm in length have been obtained by this method. 

Crystals generally contain foreign impurities, solid, liquid or gas, and the pockets of impurity are called inclusions . The term occlusion has also been used in this connection, but it has also been applied to the surface fluid that becomes trapped between agglomerated crystals and left behind after filtration. For this reason, the term inclusion is preferred because it tends to emphasize the entrapment of impurity inside a crystal. 

Kawashima Y, Cui F, Takeuchi H, Niwa T, Hino T, Kiuchi K Improved static compression behaviors and tablettabilities of spherically agglomerated crystals produced by the spherical crystallization technique with a two-solvent system. Pharma. Res. 1995 12, 1040-4. 

Kawashima Y, Imai M, Takeuchi H, Yamamoto H, Kamiya K, Hino T. Improved flowability and compactibility of spherically agglomerated crystals of ascorbic acid for direct tabletting designed by spherical crystallization process. Powder Technol. 2003 130,... 

Kawashima Y, Lin SY, Oj wa M, Handa T, Takenaka H. Prep>arations of agglomerated crystals of polymorphic mixtures and a new complex of indomethacm-epirizole by the spherical crystallization technique. J. Pharm. Sci. 1985 74,1152-6. 

Kawashima Y, Takeuchi H, Niwa T, Hino T, Yamakoshi M, Krhara K. Preparation of spherically agglomerated crystals of an antibacterial drug for direct tabletting by a novel spherical crystallization technique. Congr. Int. Technol. Pharm. 1989 5, 228-34. 

Sano, A., Kuriki T., Kawashima Y., Takeuchi H., Hino T., and Niwa T. (1992). Particle design of tolbutamide by spherical crystallization technique. V. Improvement of dissolution and bioavailability of direct compressed tablets prepjared using tolbutamide agglomerated crystals. Chemical and Pharmaceutical. Bulletin, 40, 3030-3035. 

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