Daniel

Topic: Trivalent chromium removal from hexavalent chromium bath

Actually i´m doing the old school  method to convert some trivalent chromium to hexavalent chromium.

Using small cathodes and large anode area to achive  high CD on cathodes low CD on anodes.

what is the correct appereance of the cathodes after the procces is done what is supposed to be seen on the cathodes ?

what is the correct amount of time or how many times i have to do this treatment if my bath is highly contaminated?


Thanks

yes i know i have to practice more with my cell phone about the pictures i take. sorry


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Last edited by Daniel (10/20/2009 - 03:23 AM)

DustinGebhardt

Re: Trivalent chromium removal from hexavalent chromium bath

The anodes should be made from lead and the color should be "chocolate brown" to black.  This indicates a good layer of lead oxide, which is the material that actually oxidizes the tri-chrome back to hex-chrome.  The color of the anodes will vary from a bright-blue standard chrome color to a dark, spongy gray to even black, depending upon the current density.  


The amount of time required will vary depending on the level of contamination.  What is your percent tri-chrome?


If you are seeing buildup of tri-chome in your bath, I would suggest that you increase your anode area.  A typical decorative application calls for an anode to cathode ratio from 1.2:1 to 2:1

-Dustin Gebhardt, CEF

Advanced Manufacturing/Finishing Engineer

Moen

Sanford, NC

Daniel

Re: Trivalent chromium removal from hexavalent chromium bath

Thanks!

is there a way to know when the treatment is done, for example cathodes not spongy at certain current density, anodes blue and shiny etc.?

DustinGebhardt

Re: Trivalent chromium removal from hexavalent chromium bath

In a properly operating chrome plating bath, the anodes should always be brown in color.  Once you turn the power off, the lead oxide begins to dissolve away, so if the bath has been idle for some time, you may not see the color.  Also, certain anode shapes (scalloped or wavy being the most common) can sometimes inhibit the proper formation of the oxide layer.  It is for this reason that I personally normally only recommend smooth round anodes. 


The look of the piece at the cathode will change depending upon the current density as per normal chrome plating.  If you are applying the normal current density, the cathode will look like normal chrome plating.  High current density = burned and spongy.  Low current density = no plating.


They sell an optical test kit which tells you how much tri-chrome you have in your bath.  Check with your chemical vendor or equipment vendor for this tester.

-Dustin Gebhardt, CEF

Advanced Manufacturing/Finishing Engineer

Moen

Sanford, NC