-- The Home Page of the Finishing Industry
A website for Serious Education, promoting Aloha,
& the most FUN smiley you can have in metal finishing

on this site
current topics
topic 0287

The Chemical Mechanism of Sulfuric Acid Anodizing?

A discussion started in 1996 and continuing through 2008.
Add your Q. or A. to restore it to the "Current Topics" discussions.


I am trying to understand the chemical mechanism of sulfuric acid anodizing. Specifically, to determine the amount (if any) of aluminum sulfate produced. Is there any reference that discusses this issue. The MA State Form S requires the accounting of all listed chemicals and I do not have any information on the rate of formation. Any hints would be appreciated.

Art Sanders

Lowenheim's Electroplating, McGraw Hill, says that some part of the anodic coating is sulfate, and Langford and Parker's "Analysis of Electroplating and Related Solutions" [linked by editor to info about book at AbeBooks] gives an analysis for aluminum in anodizing solutions. But I believe that the amount of dissolved aluminum in these baths is insignificant when compared to the amounts found in other solutions such as in etching.

If you must get some value of the aluminum, I think the best way is by analysis, since you probably drag in more dissolved aluminum than you make in the bath. What is the threshold reporting value for aluminum sulfate in MA form S?

tom pullizzi monitor
Tom Pullizzi
Falls Township,


The reporting threshold for MA Form S is 25,000 lbs of Alum produced. I would like to gain an understanding of the chemical mechanism of sulfuric acid anodizing. I have searched different material but can not seem to find one that specifically addresses the subject. Could you suggest any articles of reference books that would be helpful?

Art Sanders

November 15, 2008

Hi, Art. I'd be pretty confident that the reactions are explained in exhaustive detail in Surface Finishing and Treatment of Aluminum and its Alloys, by Wernick, Pinner & Sheasby because everything about anodizing is :-)

But the principle reaction is fairly simple. The aluminum is made anodic, which causes oxidation of the aluminum and generation of oxygen, and the aluminum is converted to Al2O3. There is some hydrolysis, so the reaction product also involves aluminum hydroxide rather than pure aluminum oxide, but I don't think sulfur plays a significant part in the reaction.


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

This public forum has 60,000 threads. If you have a question in mind which seems off topic to this thread, you might prefer to Search the Site

ADD a Comment to THIS thread START a NEW threadView CURRENT TOPICS

Disclaimer: It's not possible to diagnose a finishing problem or the hazards of an operation via these pages. All information presented is for general reference and does not represent a professional opinion nor the policy of an author's employer. The internet is largely anonymous & unvetted; some names may be fictitious and some recommendations may be deliberately harmful.

  If you need a product/service, please check these Directories:

JobshopsCapital Equip. & Install'nChemicals & Consumables Consult'g, Train'g, SoftwareEnvironmental ComplianceTesting Svcs. & Devices

©1995-2018, Inc., Pine Beach, NJ   -   About   -  Privacy Policy
How Google uses data when you visit this site.