finishing.com -- The Home Page of the Finishing Industry

HomeFAQsSuggested
Books
Help
Wanteds
Advertise
on this site
FORUM
current topics
The world's most popular metal finishing site, and the internet's friendliest corner

topic 17947

Chemical Composition of Anodized Aluminum


2002

A simple question, that I can't seem to find an answer to: what is the chemical composition of an anodized aluminum coating? I understand that it is usually an aluminum oxide, but with the different processes and different types of anodize, does the composition vary at all? Specifically, I am wondering if a black, hard anodized coating will have a significant amount fluorine or carbon, detectable via SEM-EDX.

Thanks,

Fong Liu
- San Jose, California, USA


2002

One reference book list the ingredients of an anodic coating as: Aluminum Oxide 80%, Aluminum Sulfate 18% (but this varies as a function of the "dissolved aluminum" in the bath, Water as 2%, and the rest is the alloying ingredients of the particular alloy that have become occluded during the film formation.

After sealing, the aluminum oxide in the 500 pores per square inch has been converted to "Hydrated aluminum oxide" which is larger molecule and literally "plugs" the pores.

If there is any fluorine or fluoride present then it came either from using tap water or from a proprietary low temperature sealing compound (which is poor sealing at best).

Carbon is everywhere, and EDAX would probably find some, however there is no theoretical reason for any carbon presence in clear anodizing. Black anodizing, if the color came from organic dye, yes, would show carbon on the EDAX. If the black came from the natural color (from the alloying ingredients) of hard coat, then there should be NO carbon.

robert probert
Robert H Probert
Robert H Probert Technical Services
supporting advertiser
Garner, North Carolina


2002

I don't know for certain, and it would depend on how the parts were made black, but ... if an organic dye was used it might well contain carbon in the final coating.

Jim Gorsich
Accurate Anodizing Inc.
supporting advertiser
Compton, California, USA
accurate anodizing banner


2002

Fong, when I've examined hard anodize in the SEM, I get a sulfur peak from the EDS. Of course, all of my hard anodizing is done in a sulfuric acid bath. I've never gotten additional peaks of fluorine or carbon.

Good luck!

lee gearhart Lee Gearhart
metallurgist - E. Aurora, New York


2002

Fluorides are used in cold sealing processes that lock in the dyed color, in your case black, without reducing the abrasion resistance because it's done at near room temperature as opposed to nickel or cobalt acetate which operate at elevated temperatures.

As far as what is the composition of anodize, nearly anything that it touches after anodizing as the porous structure adsorbs anything it's immersed in or touches until such time that it is sealed. Sealing can occur over time by picking up moisture from the air or oils from ones hands. Typically hardcoat isn't sealed so that the abrasion resistance isn't compromised.

milt stevenson jr.
Milt Stevenson, Jr.
Anoplate Corporation
supporting advertiser 
Syracuse, New York

Anoplate banner

Q, A, or Comment on THIS thread SEARCH for Threads about ... My Topic Not Found: Start NEW Thread

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


©1995-2019 finishing.com, Inc., Pine Beach, NJ   -   About finishing.com   -  Privacy Policy
How Google uses data when you visit this site.