Evolution of phases and habit during the crystallization of freeze-dried lactose/salt mixtures in humid air RID A-8162-2012

Author:

Barham, A. Shawqi  Omar, A. M. Elmonsef  Roos, Yrjo H.  Hodnett, B. K.  

Journal:

CRYSTAL GROWTH & DESIGN

Issue Date:

2006

Abstract(summary):

Phase compositions, transient phases, and morphology of the crystallization of freeze-dried lactose/salt mixtures in humid air were estimated by in situ X-ray diffraction analysis complemented by ex situ scanning electron microscopy, powder diffraction, and analysis of the solid state alpha/beta anomeric ratios by gas-liquid chromatography. The salts studied are calcium chloride (CaCl2), magnesium chloride (MgCl2), potassium chloride (KCl), and sodium chloride (NaCl) with lactose/salt molar ratios of 2: 1, 4: 1, and 9: 1 mol/mol. Following an induction period during which water is sorbed, crystallization is rapid and the predominant phases observed using the in situ method in freeze-dried lactose/magnesium chloride (MgCl2), sodium chloride (NaCl), and potassium chloride (KCl) are mixtures of alpha-lactose monohydrate and beta-lactose. In general, the alpha/beta ratio of the solid state as measured by gas-liquid chromatography was similar to the crystalline phase composition as measured by X-ray diffraction. A transient phase appears in lactose/KCl (4: 1 and 9: 1 mol/mol), lactose/ MgCl2 (9: 1 mol/mol), and lactose/ NaCl (9: 1 mol/mol), namely, alpha/beta mixed phase. Another transient effect observed with nearly all the lactose-salt mixtures was the observation of a subtle shift in the lattice parameters of alpha-lactose from a = 8.006 angstrom, b = 21.562 angstrom and c = 4.800 angstrom for short crystallization times to a = 7.982 angstrom, b = 21.562 angstrom, and c = 4.824 angstrom for longer times. The transient effects, namely, the observation of the alpha/beta mixed phase and the distortion in alpha-lactose monohydrate lattice parameters, are explained in terms of stresses induced during the rapid onset of crystallization.

Page:

1975---1982