Freeze-drying of cephalothin sodium: granularly agglomerated crystallization during freezing. II.

The mechanism of granularly agglomerated crystallization during freezing of cephalothin sodium (CET-Na) in aqueous solution has been discussed. Our previous report noted that strict control of the following is important in order to obtain crystalline granular agglomerates of CET-Na: (1) thermal history of the solution before receiving freezing, (2) cooling rate in freezing, and (3) aging temperature level in the crystal growth step. In order to clarify the physico/chemical meanings of the individual controls, further investigations have been made: 1) with varying thermal history, aqueous 30-% CET-Na solutions were prepared for storage, first at 0 degrees C with its supersaturation and secondly at 25 degrees C, in an unsaturated state for observing any structural changes by viscosimetry, refractometry, and surface tensiometry; 2) morphological changes in ice crystals during freezing at varying cooling rates, as well as those during the crystal growth step, were observed by polarized-light cryomicroscopy and scanning electron microscopy; 3) melting, as well as crystal growth, at several aging temperature levels were observed by electrical conductometry and also by the above-mentioned techniques.(ABSTRACT TRUNCATED AT 250 WORDS)