Home / Documents & Brochures / Technical Briefs / Freeze Drying:

2 (b). Freezing Considerations

Table of Contents:

1. Introduction
2. Principle
(a) Sublimation Considerations
(b) Freezing Considerations
3. Practice

The presentation and nature of a specimen prior to freeze-drying depends on the user and the application. Irrespective of this, however, there is a pre-requisite for good (FAST) freezing, this is probably the most singularly influential factor on the final result, within the limitations previously considered of the drying routine.

A range of cryogens and freezing techniques are being applied to the freezing of specimens, the understanding of the mechanisms of which, are still at an early stage.

However, with exceptions, (Hyperbaric freezing containment of ice crystals is generally less than 20 micrometers from the surface, and Liquid Nitrogen (LN2) usually readily available and unsophisticated in its application, should be satisfactory for a range of specimen freezing. The technique for its application is that of plunge freezing by hand or mechanical device. It is more valid when used in its sub-cooled state (Slushy Nitrogen at Triple Point temperature of -210oC), as this reduced the effect of an insulating gas layer being formed (Lieden effect) around the specimen during the passage into the cryogen.

 Page 4 of 5: 1 2 3 4 5