Modulation of Ice Crystal Size Distribution by High Pressure-Shift Freezing

摘要

The well-known Ostwald ripening effect is studied here in ice samples formed by high pressure-shift freezing (PSF). This novel freezing process is characterised by the induction of a high number of homogeneously spatially distributed ice nuclei that give rise to a large number of small ice crystals. Ice crystal behaviour is observed by optical cold-stage microscopy after freezing by classical and PSF methods. Specially designed cells are used for allowing observation of pressure-frozen samples, which are generated by treatment in a custom-built high pressure device. Images obtained versus time are processed by image analysis state-of-the-art methodologies to yield the recrystallisation parameters. The results obtained comparing classical and PSF point to the independence of recrystallisation parameters of the initial ice crystal size distribution. The crystal size reduction obtained by PSF is maintained after a recrystallisation period. These results are discussed in terms of the different recrystallisation theories and their application to the design of ice slurries with improved properties.