Martin Christ Beta 2-8 LSCplus - Manual (Page 115)

Beta 1-8 LSC&
Beta 2-8 LSC&
12 Glossary
Version 04/2013, Rev. 1.1 of 16/12/2013 • sb
115
Translation of the original operating manual
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12 Glossary
Desorption
Desorption (from Latin de-sorbere, sorbere = sup up, suck in) describes a
phenomenon whereby molecules are released from the surface of a solid.
In order to be able to desorb, the particle must have, or be provided with, a
sufficient amount of energy in order to overcome the binding energy.
Eutectic point
The eutectic point is the point at which a homogenous mixture (e.g. a
eutectic alloy) passes directly from the liquid to the solid phase without the
formation of a crystal mixture that consists of different phases.
Pressure increase test
The pressure increase test can only be carried out with double-chamber
method. During the pressure increase test, the intermediate valve prevents
the flow of steam from the drying chamber to the ice condenser so that the
water vapour of the sublimation cannot flow off. The result is a more or
less distinct pressure increase that is measured in the product chamber.
When the product has been completely dried, the vacuum does not
decrease at all or only to a slight extent.
The pressure increase test is often used as a criterion for the automatic
switching from the main drying phase to the final drying phase as well as
for identifying the end of the process.
Single-chamber method
At the single-chamber method, the freezing as well as the subsequent
drying of the product are both performed in the ice condenser chamber.
The sample is frozen as a result of the low temperature of the ice
condenser
(–55°C in the case of one-stage systems or –85°C in the case of two-stage
systems). The inside of the chamber can be cooled to approximately –20°C
or –40°C. The moderate supply of the frozen sample with energy, which is
necessary during the main drying phase, is ensured by heatable shelves on
which the product is placed.
Double-chamber method
Drying on shelves outside the ice condenser chamber is referred to as a
double-chamber system. The advantage compared to the single-
chamber method is the considerably higher product capacity. In addition,
the product chamber can be isolated from the ice condenser chamber by
an intermediate valve in order to perform a so-called pressure increase
test for determining the end of the drying process. In freeze-dryers without
an active shelf cooling, the samples need to be pre-frozen externally, e.g. in
a deep-freeze or freezer cabinet. After the transfer of the product into the
freeze-dryer, the actual sublimation is started.