NUVE NF 800 - Chemical Corrosion; Stress Corrosion; Cleaning; Electricity

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7.3.1 Chemical Corrosion
This type of corrosion is caused by chemical reactions. The electrolide liquid on the
surface of the material is the main cause of the chemical reaction. If that electrolide liquid
is allowed to stay at the surface, corrosion occurs. First, discoloration appears and then
the metal pittens. Aluminum easily reacts with the ionic solutions.
The other causes of corrosion are as follows,
 Chemical vapors in the laboratory environment which dissolve in the water on the rotor
(in refrigerated centrifuges)
 Corrosive liquids which overflow from overfilled and unsealed tubes. (the liquids which
spread out during centrifugation)
 Contaminated and non-cleaned buckets, tubes and bottles.
NOTE:
If the centrifuged samples are corrosive, only rinsing with water is not sufficient.
The residuals dissolve in the water and humidity on the rotor and in the buckets.
NOTE:
Some particles may stick to the tubes, buckets and adapters. These particles
crash and do harm to anodized surface during centrifugation and ease the
occurrence of corrosion.
7.3.2 Stress Corrosion
This type of corrosion is caused by the force of the centrifugation of the corrosive chemical
which is already in contact with the alloy. As the aluminum alloy contacts with the corrosive
chemical, the stress corrosion starts. This type of corrosion is even more dangerous than
the chemical corrosion as the effects of this corrosion are microscopic and very difficult to
observe in the course of time.
The corrosive material is pushed against the aluminum alloy by the centrifugation “g” force
during the centrifugation. This situation causes the stress corrosion to occur more quickly
than the chemical corrosion does. Microscopic cracks occur under the force of the
centrifugation.
Every centrifugation causes the aluminum rotor to be attacked by the chemical more and
more and eventually micro-cracks decrease the resistance of the rotor against the
centrifugation force. Fortunately, no crash occurs just after the first micro-cracks have
appeared as the rotors are manufactured according to the high safety limits.
The corrosion of the small amount of corrosive materials does not result in severe cracks
but weakens the mechanical resistance of the rotor in the course of time.
The rotor’s places , buckets, buckets’ edges and the base of the rotor should be checked
regularly. If needed, they must not be used until a specialist has checked them thoroughly.
7.4 CLEANING
 Disconnect the centrifuge before cleaning.
 There is no need of daily cleaning unless a tube breakage occurs or any liquid spills.