Yamato Scientific DC800 Freeze Dryers - Manual (Page 15)

11
Operation Method
Pre-freezing
At pre-freezing process, quickly and completely freeze to the inside at sufficient lower
temperature than the eutectic (crystal) point
* of the sample. Make the ice layer as thin as
possible because thick ice layer might be easily melted by drying. Moreover, keep in mind that
it becomes easy to receive the heat of external temperature, and it may cause melting-ice if it
freezes widely on the container surface when the eutectic point of the sample is low.
Keep in mind that if there are too many throughput, or if the eutectic point of the sample is low,
a melting-ice phenomenon arises and this may cause bumping or scattering of the sample.
When installing the container and starting freeze-drying after pre-freezing process, set 3-4
minutes’ interval till next sample drying starts. (This differs depending on the container and
sample types.)
Melting-ice may be caused if the interval is too short.
Eutectic (Crystal) Point
ƒ
Although pure water is frozen at 0 Celsius degree, solution is not frozen immediately below 0
Celsius degree, and the solution becomes soft ice condition because the frozen pure water and
the concentration solution that is not frozen are mixed.
Furthermore, if freezing is continued, all the solution will freeze uniformly under containing
its solutes, and will become solid ice in whole.
This temperature is called as the eutectic (crystal) point of the solution.