Passivation

Brocca Giuseppe

The eco-friendly surface plating company

The passivation increases the corrosion  resistance of the zinc layer and provides it with a specific colouring: usually passivations are light-blue, black, yellow, green and iridescent.
The colour request is influenced by two factors, viz. the colour and the corrosion resistance.

The research undergone with a view to replacing  CrVI, because of the latter’s toxicity, has also encompassed the passivations used on zinc-plating.
 
The threevalent passivations, i.e. those exempt from  CrVI, being used at present are constantly being improved since the properties resulting from the use of CrVI can hardly be replicated.

The advantages provided by the use of hexavalent chrome as a passivating agent of the zinc coating are as follows:

  • Range of colours  from light-blue, iridescent yellow, olive green up to Black;
  • The corrosion resistance ;
  • The self-closing up properties that ensure the integrity of the passivation coating;
  • The limited cost.

However, after coming into force of the European Directive “RoHS 2002/95/CE" dated  27th january 2003 and pursuant amendment  2005/618/CE dated 18th august  2005, all member states shall enforce that as of 1st July 2006 the parts used in several fields shall not contain:

  • lead > 0,1%;
  • mercury > 0,1%;
  • cadmium > 0,01%;
  • hexavalent chrome (CrVI) > 0,1%.

We have therefore started to industrialise the passivations to threevalent chrome.
At present we can make available the following
 CrIII passivations :

  • Passivation Type II (White);
  • Passivation Type IV (White, high resistance);
  • Passivation Type VIIS (Black sealed ).