MRS-BA-defsi-0410 118
5 Determining moisture levels
The MRS 120-3 moisture analyzer is used as a quick and reliable
means of determining the moisture content in powders and liquids
by the thermogravimetric process.
5.1 Fundamental principles
The term moisture does not just relate to water, it also
encompasses all substances which evaporate when they are
heated. Alongside water, they also include
–
fats
–
oils
– alcohol
– solvents
– etc...
There are different techniques for determining the moisture of a
material.
Thermogravimetry is the technique used in the MRS 120-3. In this
technique, the sample is weighed before and after heating so as to
determine the moisture content from the difference.
The conventional drying oven technique works on the same
principle except that, the measurement takes much longer. In the
drying oven technique, the sample is heated from the outside
inwards by a stream of hot air so as to draw out the moisture.
In the case of the halogen radiation used in the MRS 120-3, the
radiation mainly penetrates into the sample where it is converted
into heat energy, heating the sample from the inside out. A small
portion of the halogen radiation is reflected by the sample; this
reflection is lower in dark samples than in light samples. The
penetration depth of the halogen radiation depends on the
permeability of the sample. In the case of low-permeability
samples, the halogen radiation only penetrates into the upper
layers of the sample, which may lead to incomplete drying, charring
or combustion. Consequently, the sample preparation is extremely
important.
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