Hot-dip galvanized coatings protect steel by providing both cathodic and barrier protection. When there are concerns with environmental and/or storage conditions to which the galvanized steel will be exposed, passivation treatments can be used to prevent the formation of wet storage stain. Passivation agents delay the formation of zinc oxides and hydroxides until such time as it is safe, as determined by environmental and/or storage conditions.

To passivate the zink in steel plates, hydrochloric acid can be used to react with the iron, present as iron chloride. This process is done in the pickling bath (also called dead bath or a dead pickling solution). To control this process, a Rhosonics 9500 analyser is used to control the concentration of hydrochloric acid. The risk of under- or overpickling will dramatically reduce as well as the consumption of acid. Special software is made for this application, see the screen dump of our analyser above.

Rhosonics can offer different types of non-drifting probes in combination of a non contacting (torrodial) conductivity sensor.

This real time measurement technology is far more accurate, robust and cost effective then direct potentiometry with fluoride selective electrodes and alkalimetric titrators (10-15 minutes analysis time!) or X-ray analysers.

Other examples of pickling baths are:

• Selectively removal of Al₂O₃ from aluminium in the chromium conversion coating process. HF and H₃PO₄ are used in the pickling bath.
• At pickling in solutions containing sulphuric acid metal sulphates develops by the reaction of acid on the iron. As the iron oxides dissolve the pickling bath is strengthened with iron sulphates while the acid proportion decreases.

In case of recycling of the pickling baths, our analysers can measure very high concentrations of slurries (Model 9600).

Attachments:

Appl Pickling v1.7

[Application Note Pickling Baths v.1,7]

1064 Kb