48490

Citric or Nitric for medical implant passivation [Tennessee] 

April 12, 2008

I work for a large corporation that manufactures surgical instrumentation.We currently use citric acid to passivate because the instruments are not implants.We validated the citric on every type of stainless that we use (17-4,420,465,455,316 and 317)and had no failure with a boil test or immersion test.We are about to start making implants out of cobalt chrome and from previous experience I think we have to use nitric acid to passivate.If this is true what percentage should we use and what would the specific gravity be for that percentage? If I use nitric how do I know when it is spent or when does it need to be changed?

Billy McCulley
Supervisor manufacturing - Bartlett, TN, United States

Citric acid based passivation can and is used for implants as well as instruments. It is also used on many non ferrous alloys just as it is with stainless steel.

On what basis do you expect you must use nitric? If you refer to ASTM F-86 spec on implants, there is a clause there that allows any effective treatment as long as you document it. If your customer is specifically requiring nitric, it may be worth the effort to convince them of the benefits in allowing you to use citric.

If you still go with nitric acid, you can refer to a stainless passivation spec such as ASTM A967 and follow the formula and procedure recommended for 316 SS.

Let us know if we can be of help.

Ray Kremer Stellar Solutions, Inc. Algonquin, IL, USA