Procedure For Cp-Determination; Right Choice Of The Reference Sample; Right Choice Of The Sample Geometry; Correct Coating - NETZSCH LFA 447 Nanoflash Operating Instructions Manual

TM
LFA 447

Procedure for cp-determination

The determination of the specific heat using LFA 447 occurs via the comparison method. Exactly
the same test conditions for sample and reference are absolutely necessary.
Please note the following indications:

Right choice of the reference sample

Reference samples are offered for each material group: metals (e.g. SRM1461); polymers,
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ceramics (e.g. Pyroceram); C-composites (Poco graphite).
Sample and reference should show similarly the same surface structure.
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Right choice of the sample geometry

Ideally the dimensions of the sample and reference should be equal → different
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dimensions are offered for all reference samples.
Different diameter or edge lengths do mostly not cause an negative effect on the
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measuring results as long as the whole bottom side of the sample is lighted and the same
aperture diameter is used (the aperture diameter must always be smaller than the
diameter of the sample plate, ratio 0.7 to 0.8).
Increase variations result if the thickness of the sample and reference is strong different,
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But: important is the distance between the surface of the sample and IR-detector, viz:
through balancing of the difference of level good measuring results can be achieved, it is
recommended to balancing the difference of level from thickness differences of more
than 0.5 mm.

Correct coating

The coating with graphite spray is used on the one hand for an increase of the emission
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ratio and the absorptance of the samples so that the signal-to-noise ratio is improved
and otherwise to a homogenization of the surface (similar and homogenize energy input
for sample and reference).
Coat 2 to 3 thin layers (Shake the can and hold it approximately 30 cm from the samples),
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clean the sample with alcohol – This must be done before each measurement!

Other checks

Check if the windows are clean before each measurement (Borofloat-glass between
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furnace and flash lamp as well as the 4 sapphire windows of the furnace lid).
Check that nothing stands between the flash lamp and the sample (connecting cable or
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similar, especial for sample position 1 and 3), if necessary remove the front cover, take
out the Borofloat-glass, loose the cable connection and correct the position.
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Operating the Instrument
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