Polishing Defects - struers Tenupol-3 Gebrauchsanweisung

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Tenupol-3
Instruction Manual

2.12. Polishing Defects

2.12.1. Problem Areas
If a sufficient high quality is not obtained in electrolytic polishing it will be
necessary to alter the polishing conditions. There are five important
parameters:
 the type of electrolyte
 the flow rate of the electrolyte
 the temperature
the electrical conditions and

 the geometrical conditions
In the Tenupol-3 the geometrical conditions are fixed and can only be
altered by changing or altering certain components.
 As to the other parameters the following will apply:
 The chemical composition of the electrolyte is highly important for the
quality of the polishing. An unsuitable electrolyte will cause inferior
polishing, oxidized or etched surface , pittings or one-sided polishing,
i.e. only one side of the specimen is polished, the other is black and
oxidized. It is not at all certain that an electrolyte, which in other
apparatus (e.g. the Polectrol) will polish a certain material, will also be
suitable for thinning it on the Tenupol-3. A-2, for instance, is not
suitable for use with Tenupol-3. In the literature numerous examples
are cited of electrolytes suitable for thinning. (See e.g. l.S. Brammer
and M.A.P. Dewey: Specimen Preparation for Electron Metallography.
Blackwell Scientific Publication, Oxford 1966).
 The flow rate determines first of all whether a viscous anodic layer can
be maintained during polishing. Jet polishing tends to remove the layer.
The proper choice of flow rate is therefore mostly determined by the
material to be polished and by the electrolyte. The best flow rate differs
much from case to case and it is not possible to give general rules.
 In some cases a lower temperature will give better results. A lower
temperature slows down the polishing and provides less etching and
oxidation.
 The electrical conditions of course determined whether a polishing is at
all obtained. The right conditions will only be present within a certain
range of current densities. If a current versus voltage curve is drawn the
best polishing conditions will be found where the current is
approximately constant within a range of voltages. Moreover, some
users have found that a better polish is obtained on some materials, if
towards the end of the process the current is applied as a series of
shocks.