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topic 7608

Oxalic Acid Anodizing of Aluminum


Q. Has anyone heard of "Oxalic Acid Anodizing"?

The reason I ask is that we received some parts that were anodized to this process and I am skeptical of the parts because if I put an Ohmmeter across the parts I get a reading on the meter. I know that anodize is a non-conductor and I shouldn't get a reading, but I was wondering if there were something different about this process?

Thank you for your time and any help and input you may give me.

Stan Kmiecik
- Addison, Illinois USA


A. Oxalic acid anodizing basically produces hard anodic coatings on aluminum surfaces. The anodic coatings formed in oxalic acid solutions are non-conductive if there is no further surface treatment. A light yellowish color may be observed for the anodic coatings produced by oxalic acid anodizing. You may measure the coating thickness on your samples to see if there is enough anodic coating on the surface. If the coating is so thin that it is damaged during conductivity measurement, it makes you think it is conductive.

Ling Hao
- Grand Rapids, Michigan


Q. Can anyone tell me exactly what is involved in oxalic acid only anodizing. From start to finish. Also what equipment is involved.

Patrick Joseph Ruvolo Jr.
- Santa Clara, California


A. Per se' from "Aluminum How-To" book:

Here we are not talking about oxalic as an additive, but rather using oxalic acid as the electrolyte. In over 50 years of exposure to the metal finishing industry, this author has heard of only one call for oxalic acid anodizing. It is just not popular in the U.S.A. Most work on the electrolyte has been done in Japan and Germany...

robert probert
Robert H Probert
Robert H Probert Technical Services
supporting advertiser
Garner, North Carolina
Editor's note: Mr. Probert is the author of Aluminum How-To / Aluminio El Como
and co-author of The Sulfamate Nickel How-To Guide

A. Hi. Mr. Probert's book goes on to offer the formulation and operating conditions for oxalic acid anodizing, and its advantages. For "start to finish" coverage you'll probably want to consult Wernick, Pinner, and Sheasby which has many pages on oxalic acid anodizing and its variations. Best of luck.


Ted Mooney, Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

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