Martin-christ Alpha 2-4 LSCplus User Manual download pdf (Page 115)

ALPHA 1-4 LSC&

ALPHA 2-4 LSC&

12 Glossary

Version 01/2011, Rev. 1.5 of 16/12/2013 • sb

115

Translation of the original operating manual

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.

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