52014

Passivation of Titanium  

April 28, 2009

Hi,
I work in the orthopaedic medical device industry.
We currently passivate all products - this includes non stainless steel products such as Titanium. I know the chemistry about removal of free iron and formation of an oxide layer, the later of which will not happen on Ti.
Bassically does anyone have any info on passivation of non ferrous metals in the medical device industry. Does it need to be done? Know any standards?What is it for?
I ask as our products are plasma coated and are shot blasted, cleaned, passivated and then coated. I am looking to change the passivation to before shot blasting - or getting rid of altogether on Ti products.
I think one reason is that if any ferrous tooling is used by mistake - the passivation will remove any iron contamination - whhich would mean it is OK to passivate before shot blasting. Another reason may be any iron impurity bought to the surface of the Ti by shot blasting will be removed, in which case its not OK to passivate before shot blasting.
I have never been able to detect any free iron on the surface of Ti using copper sulphate.
Can anyone help?

Cheers
Jim

Jim Baker
Validation manager at medical device manufacturer - Gloucester, UK

Considering that Ti will oxidize with time in air, I would be a bit surprised if a strong oxidizing acid would not give at least a minor coating.
If you are shot blasting with steel shot, passivation before blasting would be a waste of time. I would find the use of steel shot a bit disturbing.

James Watts
- FL

Review the applicable ASTM standards. You will see that talk of the "passivation" of Ti and its alloys is something of a misnomer.

Acid processing of Ti is more oriented to the removal of undesirable "alpha case" and surface contaminants, as opposed to the use of the term "passivation" in the context of stainless steels.

Dave Wichern - The Bronx, New York

Dave, I always thought that removal of "alpha case" required a fluoride containing acid.
It seems to me that there have been letters in the past where "passivation" of Ti was required. It sure seemed to me that it was NOT the normal use of the word "passivation".

James Watts
- FL

Yes, it absolutely does require the use of HF, or NH4HF2.

The topic of 'what does passivation mean?' has been debated ad nauseum on the site here. Some seem to think it means the formation of an enhanced layer of passive oxides on a stainless steel surface. This is the nitric acid faction.

Others seem to believe that it is simply the removal of iron rich surface smears and foreign contaminants. This is the citric acid faction.

Which is right? I don't pretend to know. But neither applies to Ti and its alloys, which spontanteously form nicely passive oxides on simple exposure to air.

Dave Wichern - The Bronx, New York