The freeze drying method
Freeze drying specimen preparation reduces the distortion and shrinkage effects that occur when a wet specimen dries by normal evaporation. Distortion is due to the forces of surface tension that occur when going from a liquid to a vapour phase, such as from water to water vapour - the normal situation with biological specimens.
The freeze drying method overcomes this problem by careful sublimation of frozen specimens under vacuum - a process that avoids the liquid phase and thereby reduces distortion effects. The rate of sublimation is a function of temperature and vacuum, with typical drying times being several hours or longer.
To see application examples, please visit: Freeze Drying Images.
Ideally, freeze drying should be carried out at temperatures below the recrystallisation point of ice, but this would require very long drying times. In practice temperatures of -60°C have been found to give reasonable results under vacuums achievable with two-stage rotary vacuum pumps. For these applications see: K750X Peltier-Cooled EM Freeze Dryer.
For certain applications, however, it is necessary to dry at temperatures below -80°C with lower sublimation rates for delicate specimens. This requires better vacuum than can be obtained using a rotary vacuum pump alone and the lower temperatures associated with liquid nitrogen. For such applications the K775X is recommended.
The K775X Freeze Dryer achieves low temperatures by using a liquid nitrogen cold stage - fed from an integral vacuum dewar which is capable of giving several hours hold-time between ‘top ups’.
Pre-frozen specimens are loaded onto the cooled stage of the drying chamber through the lid using a specimen transfer holder, which is supplied with a convenient lock-and-locate loading tool. Two holders are provided - for TEM grids and for SEM stubs.
The K775X has controls for time and temperature and at the end of the drying period the stage may be heated prior to specimen removal.
The system also has facilities for purging with nitrogen gas.
A microprocessor-controlled 10-segment sequence allows 10 time periods and 10 temperature settings to be programmed to achieve a range of drying protocols. Up to 10 different protocols can be stored for future use.
This product is for Research Use Only.