2. Chrome-free treatments

2.1 Molybdate-based treatments

The replacement of hexavalent chromium has prompted the search for elements close to Cr. Group VI A of the periodic table contains elements capable of forming oxyanions close to chromates, such as molybdates, tungstates, permanganates and vanadates, which also have oxidizing properties towards the element zinc.

Among the elements mentioned, molybdate is certainly the most widely studied. Loughborough University has certainly been one of the major players in this field [3] .