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topic 60690

Trivalent Chrome Electrolyte testing in lab


February 9, 2018

Q. I am trying to create a trivalent chrome electrolyte to plate onto copper at a small laboratory scale.

My main electrolyte is:

M Chromium(III) sulfate salt 1.0 Mol (referred to the metal chromium content, so .5 Mol Cr2(So4)3)
HCOOH 0.5 Mol
CO(NH2)2 0.5 Mol
Al2(SO4)3·18H2O 0.15 Mol
Na2SO4 0.3 Mol
H3BO3 0.5 Mol

I am operating at room temp or slightly above, 20 °C - 30 °C or so. I am aiming for current densities around 10-25 ASD (.1-.25 A/cm2). My anode is pure platinum foil. My cathode/substrate is copper. I am doing this is a small 50 mL bath.

However, I cannot seem to get any sort of metallic coating at all. At best I get dark/black coatings on my copper that do no adhere well. Any advice?

Adam

Adam Vitale
- Richland, Washington, USA


February 2018

? Hi Adam. Please introduce yourself, your overall goal, and where you got this formula so we can understand how best to try to help you. There is nothing wrong with you trying to do whatever you want to try to do, but we don't really know exactly what that is :-)

For example, do you already know that people generally simply buy their trivalent chromium plating solutions from specialist companies which have spent decades developing them, and the formulations are not public knowledge? Trivalent chrome often requires special apparatus like diaphragms to separate the anolyte from the catholyte, as well. Are you confident you've done proper preparation to the copper to make sure it is ready to accept chrome plating?

You may know 10 times as much about trivalent chrome plating as I'll ever know; maybe you are a chemist who has already industrialized trivalent chromium plating solutions, but we readers don't know quite where to start until you tell us :-)

Thanks & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"


February 10, 2018

Q. Apologies about that. I am a post-doc graduate working at a national lab. I am not new to electrochemistry but I am new to chrome plating, specifically. I am mostly following published papers such as
https://www.researchgate.net/publication/259866027_Chromium_electroplating_from_trivalent_chromium_baths_as_an_environmentally_friendly_alternative_to_hazardous_hexavalent_chromium_baths_comparative_study_on_advantages_and_disadvantages

The main goal at the moment is simply to deposit trivalent chrome onto copper foils at a small laboratory scale. In my experience, depositing hexavalent chrome is (very) easy, but trivalent is giving me headaches.

Adam Vitale
Pacific Northwest National Laboratory - Richland, Washington, USA


Digital version
mfg_online

(No longer published, but Elsevier hasn't yet de-commissioned the online version of the Guidebook)
Download it before it disappears.


February 2018

A. Thanks Adam. We travel in slightly different worlds, but practical industrial trivalent chrome plating has been done for decades now with proprietary formulations from companies like Atotech and MacDermid and other suppliers, with membranes to separate the anolyte from the catholyte, or with graphite anodes and no membranes. My understanding is that we still don't have practical hard chrome plating (thick plating layers) from trivalent chromium though. You might find the two chapters about chrome plating in the Metal Finishing Guidebook helpful. Good luck.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"



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