No registration or passwords; no pop-up ads -- just aloha, fun, & answers.
(as an eBay Partner & Amazon Affiliate earns from qualifying purchases).
Home /
T.O.C.
Fun
FAQs
Good
Books
Ref.
Libr.
Advertise
 
Help
Wanted
Current
Q&A's
Site 🔍
Search
pub  Where the
world gathers for metal finishing
Q&As since 1989



-----

Passivating titanium - chemical equation




When passivating Ti6-4 as per ASTM B600 [affil link] (HF &: nitric acid), can someone supply a balanced chemical equation for the basic chemical reaction which takes place?

Cheers

Peta Wingrove
medical equipment - Sydney, NSW, Australia
2003



2003

The basic equations look like this:

Ti --> Ti4+ + 4e-

Ti4+ + 2H2O --> TiO2 + 4H+

Now, this is highly simplified. Due to the presence of HF, another reaction that takes place is the following:

Ti + mHF + nHNO3 => oTiF4 + pH2O + qNO

Sorry, I don't have the balanced equation for above. The F from HF is slowly consumed by the formation of fluoro and oxofluoro complexes with the Ti4+ from the first reaction. Also, TiO2 is not the only oxide species that is formed. The oxide layer is actually composed of TiO near the Ti substrate, then Ti2O3, and then TiO2 at the surface.

HF is a reducing acid, and therefore promotes more aggressive attack of the titanium surface. HNO3 is an oxidizing acid, and therefore promotes the formation of a stable, passive film. The ratio needs to be a minimum 7:1 (HNO3:HF) in order to limit the uptake of hydrogen into the titanium.

More information on this subject can be obtain from the following references:

"The behaviour of titanium in nitric-hydrofluoric acid solutions", Corrosion Science Volume 30, Issues 4-5 , 1990 , Pages 461-476. (Available from Elsevier/Science Direct) http://www.nsc.co.jp/gikai/en/contenthtml/n85/8512.pdf http://www.timet.com/pdfs/corrosion.pdf

Toby Padfield
Automotive supplier - Michigan


adv.
ti anodizing  russamer labs banner




(No "dead threads" here! If this page isn't currently on the Hotline your Q, A, or Comment will restore it)

Q, A, or Comment on THIS thread -or- Start a NEW Thread

Disclaimer: It's not possible to fully 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 might be harmful.

If you are seeking a product or service related to metal finishing, please check these Directories:

 
Jobshops
Capital
Equipment
Chemicals &
Consumables
Consult'g, Train'g
& Software


About/Contact  -  Privacy Policy  -  ©1995-2024 finishing.com, Pine Beach, New Jersey, USA  -  about "affil links"