52087

Testing trivalent chromate by testing for cobalt  

May 2, 2009

Since the process for trivalent blue passivation utilizes a cobalt compound, could you suggest a testing method to determine if the cobalt was present?

Wayne Koppe
QA Director - Liberty, SC, USA

Wayne:

First let me say only some trivalent chromates contain cobalt. Second, why do you want to test for it? Are you trying to determine if a chromate was applied? the type of chromate? Or???

Generally, unless you specify a specific chromate for your contractor to apply, specification for chromate only list the requisite corrosion resistance, color and if required ROHS compatibility. The requirement that a finisher use a cobalt containing material would be your specific spec.

I suppose that you could dissolve the coating and check it with a properly equipped instrumental analytic laboratory but you would probably be measuring something under 1 ppm (part per million).

Again I ask why do you want to do this?

Gene Packman
- Great Neck, NY

Cobalt is added only to enhance the corrosion inhibiting property of the trivalent chromate coating.If the requirement of Salt spray resistance is met then Co concentration need not be looked into.Cr+3 and Co must be in adequate concentration to offer a good corrosion resistance.

S.Ramajayam

Subramanian Ramajayam     plating chemist Bangalore, Karnataka, India