Control of polymorphism and crystal size of L-glutamic acid in the absence of additives

• Published in: Journal of crystal growth 2004-12, Vol.273 (1), p.258-265
• Main Authors: Cashell, C., Corcoran, D., Hodnett, B.K.
• Format: Article
• Language: English
• Subjects: A1. Crystal morphology; A1. Polymorphism; A2. Growth from solution; B1. Organic compound; B2. L-Glutamic acid; Condensed matter: structure, mechanical and thermal properties; Crystalline state (including molecular motions in solids); Crystallographic aspects of phase transformations; pressure effects; Equations of state, phase equilibria, and phase transitions; Exact sciences and technology; General studies of phase transitions; Nucleation; Physics; Structure of solids and liquids; crystallography
• ISSN: 0022-0248; 1873-5002
• DOI: 10.1016/j.jcrysgro.2004.08.020

Slow cooling of a supersaturated solution of L-glutamic acid, with continuous or pulsed agitation during cooling, is sufficient to stabilise the α-polymorph for crystallisation times of 24 h at 45 °C. Rapid cooling with agitation or slow cooling without agitation favours formation of the stable β-polymorph. A reduction in average particle size and crystal quality of the α-crystals was observed following agitation and there was a marked absence of β-inclusions on the surface of and inside the α-crystals under these conditions. Two hypotheses are presented to explain the stabilisation of the α-polymorph namely, (i) that agitation is sufficient to disrupt nucleation of the β-crystals on the surface of the α-crystals and (ii) that α-crystals formed with agitation during slow cooling are small and poorly formed and lack the necessary well-formed crystallographic facets on which the β-form can nucleate. That the β-polymorph is favoured during rapid cooling with agitation can be explained in terms of the reduced period of agitation.