Hi,
I have a porous NiTi (Nitinol) sample, after heat treatment a blue oxide layer was formed on it.
I try to remove it by electropolishing it in 79% acetic acid and 21% percholeric acid but it was useless.
Do you know any other method to get rid of that bluish oxide layer?
Thank you so much
The oxide layer on nitinol should easily dissolve in dilute (5-10%) hydrofluoric acid (you cannot keep the metal in acid for too long, otherwise not only the oxide will dissolve, but also the titanium from the alloy!). Instead of dilute hydrofluoric acid, you can use concentrated (37%) hydrochloric acid or hot (60-80°C) 40% sulfuric acid.
The blue oxide layer on nitinol will dissolve in dilute (5-10%) hydrofluoric acid, rather than going for hydrochloric or sulphuric acids, it is better to use Hydrofluoric acid, Because the HCL and H2So4 will leave residues on the surface and also slightly the surface properties will get altered.
Hydrofluoric acid may be used to remove blue oxide layer Arun K V
I confess that I have no experience on Nitinol, only on alpha + beta alloys, but I suggest to use purely mechanical ways. If the layer of oxide is blue and transparent, it means that it is just some micron thick. If you apply an acid (an etchant) apart all the problems you can have with the usage of strong acids, and HF is particularly dangeous, you can have hydrogen Pickup in Titanium, which is avid of Hydrogen, plus a bad surface (orange peel). If the sample is porous I would definetly use an acid, becouse I think it will be practically impossible to remove completely the residuals of the etchant. If the sample is for biomedical applications, this could be extremely dangerous. A thin layer of oxide could be abraded away with abrasives like carborundum, Zirconia or Alumina. This is of course true only on the outer surface. Inside the pores it is another story. I hope this helps.
Thank you all Vadim Verlotski Marco CostanziManickam Ravichandran for your very useful answers. Arun K V actually after removal of oxide layer I want to do anodization procedure and the final application of sample is biomedical
I wanted to say that in case of biomedical usage I would NOT use an acid, sorry for the missing "not" (I am becoming old)
Marco Costanzi Thanks a billion for your update, you are still very young and very smart, wish you a successful, happy, healthy and long life
Can you grind your alloy on a very fine paper to remove the layer?
Hi,
NiTi (nitinol) samples by sandblasting and electrochemical method are useful to remove that bluish oxide layer. Used to remove a layered oxide for different materials.
Please see my previous reply. Take into account that there has been a company producing prosthetic devices that was closed by the amount of claims due simply to the fact that they used a detergent to clean the parts, a detergent that was chlorinated. Despite deep rinsing the tiny amount of Halogens left onto the parts caused corrosion fatigue cracking.
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