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

2. Principle

Table of Contents:

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

At normal temperatures and pressures the water in the specimen would dry by evaporation and would experience forces due to the effects of surface tension between the liquid and vapour interface, however, at pressures below the Triple Point, the solid phase can be changed to the vapour phase at a rate depending on temperature, without the liquid phase being present.

In the case of a frozen Biological Specimen where we are considering water (H20) from solid to vapour phase the Triple Point pressure is a relative vacuum.

There are notable exceptions such as Carbon Dioxide (C02) where the Triple Point is higher than atmospheric pressure.

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