Electropolishing Nitinol nickel-titanium alloy
A discussion started in 1997 but continuing through 20191997
Q. I am currently working on a process to electropolish Nitinol (Ni, Ti alloy) to a highly finished surface. If you have any suggestions regarding the chemicals and equipment I should consider using, please tell me. Thanks!Jingli Wang
A. Depending on the size of your workpiece (anode) and the specifications on your rectifier, you might use phosphoric acid (quite concentrated). But beware: The current densities might be very LARGE, and you will lose weight (from your workpiece) FAST!
Regards,Jan Morten Sraker
For a first information pass, you can find in the USB Library "Electroplating Engineering Handbook" by L.Durney. It has a great chapter on electropolishing various metals and gives formulations, amp/volt functions, calculations, etc. ASM Metals Handbook also has an excellent treatise. Also the Metal Finishing Guidebook is killer. These three references should be enough to get you started. Since you're in Academia I'll give you some math: "The required current density necessary to sustain a polishing condition is inversely proportional to the boundary layer thickness." You can demonstrate this on one of Dr. Newman's RDEs. I'm currently building a medium-size EP facility in Texas. I'll be happy to discuss this further if you need.
Q. I am interested about the electropolishing, chemical polishing of Nitinol for Microstructure studies using optical microscope and scanning electron microscope.Ganesh Kumara K.
Mangalore University - Mangalore , Karnataka
A. Hi ganesh
I have been trying my own luck at EP Nitinol for optical and electron microscope studies. The idea here is to get a good surface finish which can be done with a fine diamond polish.
for EP a good solution to use would be 20% H2SO4 in methanol. You can connect it as the anode to have faster removal of the oxide and then later try to polish it at the cathode with hydrogen evolution. But you need to do a couple of trials to get your own recipe as it depends on the distance of the electrodes, surface area, current density etc.. I would suggest using low to medium voltages (around 10 V) to get a steady uniform removal. In the meantime if you have had any luck with this please do let me know as I will be interested with your progress. I have a few relevant pubs. if you are interested.
-- GuruGuruprasad Ramanathan
Case Western Reserve Univ. - Cleveland, Ohio
Q. Starting up a research scale electropolishing facility for laser processed metals and alloys. In particular I would like to know about electropolishing of platinum metal and nitinol (Ni:Ti) alloys.Alan Ryder
- National Centre for Laser Applications
Q. I am interested in getting information about electropolishing nickel-titanium (Nitinol) tubing. What kind of cleaning & preparation would be appropriate? What polishing solution do I need, and any other info for a beginner. Can you help or direct me to help?ed synder
- san jose, California
A. My experience is after electropolish you will need to do a fine diamond polish to get a mirror type finish. I was working with .032 and .045 pointed wireGreg Townsend
- Minneapolis, Minnesota
Q. Since you are specializing in electropolishing Nitinol, I would like to find out about the possibility of using Nitinol as an electrode immersed in blood, but used only as a cathode. Have there been applications in cardiac or other modes of stimulation where Nitinol served as a current carrying electrode without being corroded? It is claimed to be highly bio- and hemocompatible, but what happens when current is passed through it at low densities and in pulses, rather than continuously? Does Nitinol have a protective oxide coating as titanium or is the surface similar to the bulk of the alloy?
Thank you for any info!Peter Tarjan
- Coral Gables, Florida
Embrittlement from Electropolishing of Nitinol wires1999
My name is Emanoel R. of Almeida, and I work in a parts factory for use orthodontics. I seek information on equipment and composition of the electrolyte for polishing of Nitinol (Ni-Ti alloys). Some attempts, in laboratory equipment, presented embrittlement, probably due to nascent hydrogen. Any information is of a lot of help. Thank you advance / Best Regards.Emanoel Ribeiro de Almeida
SP - Brazil
A. Nitinol is subjected to hydrogen embrittlement. Bake after your process for 30 minutes @ 400 F. You will be ok again.Todd Huehn
- Blaine, Minnesota
Safety issues in electropolishing of nitinol2001
Q. Heh people,
I am a chemical engineer with a medical device company in Ireland. We are interested in the area of Nitinol stent production. This for us would have to include electropolishing. I understand that Nitinol electropolishing is a difficult thing to master and that very few people attempt it. I presume this is due to difficulties in electrolyte composition. I know of one recommended electrolyte which is composed of methanol and sulfuric acid. To me, this seems like a dangerous arrangement of chemicals; the methanol being organic and the acid being an oxidiser.
Could anyone who has used this arrangement please inform me of relevant safety procedures they employ. Is the solution proprietary or would we have to make it up from scratch and if so, what is the method for doing this safely. Are there any other suggested electrolytes we could use? Is the solution heated?
All help is greatly appreciated.
Best regards,John Martyn
A. In order to polish Nitinol in environmentally safe solution, you need to use special polishing equipment.
Yes, we can help you in polishing Nitinol. Please visit our home page to see some description of the process.
Q. I am encountering a surface defect related problem in some nitinol wire that I have been able to plate with first a gold strike and then platinum. I believe the plating is not the source of the problem.
I would like to try electropolishing to remove the burrs and scratches and sharp points from the wires cut end. What I need are the current/voltage settings and the bath solutions make up. I hope that this is an easy enough process to add because this is something that will have to be done in house. I have a voltage and current controllable power supply and can make up most solutions here.
Any help with this would be greatly appreciated.Larry Jansen
iSense co. - Portland, Oregon
A. Monel can be electropolished with phosphoric-sulfuric-hydrochloric type bath, US Patent 2,440,715, Battelle Development Corporation.
Nichrome can be electropolished in methyl alcohol-nitric as given in Durney's Electroplating Engineering Handbook. A literature review may turn up more.
Falls Township, Pennsylvania
Q. I'm apprentice engineer in materials and I must perform electropolishing on stent made with Nitinol. If someone could help me or give me some advice concerning cathode, electrolyte and conditions of the experiments (current density, temperatures or else).
Thank you,Stephanie Garbez
A. I do not know what stent is, but Nitinol is a titanium-nickel alloy and is a shape memory metal. I think the only way to electropolish this type of metal is to use a perchloric acid based system, but be warned this can be highly explosive, so before you do it, make sure you know EXACTLY what you are doing. A simple solution would be 750-900 mls/l acetic acid and 100-250 mls/l perchloric acid, operated at 20-100 V for between 1 and 5 minutes. There is an alternative process called tampon electropolishing; this can be done on titanium alloys using a mixture of 11 mls perchloric acid with 66 mls methanol and 24 mls butyl cellosolve. A voltage of 26-28 V is needed. I would strongly recommend you ask a chemical supply house before embarking on this project.
R&D practical scientist
Chesham, Bucks, UK
A. Hi. I would re-emphasize Trevor's warning against perchloric acid. The worst finishing shop disaster in American history -- with 17 people killed, 150 people injured, and over 100 houses suffering damage -- was the explosion of an electropolishing shop which used perchloric acid. Please see thread 9408.
Ted Mooney, P.E.
finishing.com - Pine Beach, New Jersey
Striving to live Aloha
Q. I want to polish small pieces on Nitinol (50% nickel, 50% titanium). Any suggestions on an electropolishing solution to use?
- Wilmington, Massachusetts
A. Nitinol can be electropolished in strong acid solutions, (but we do not deal with hazardous technologies) or it can be electropolished in salty bath but with special equipment. Surface needs to be prepared mechanically for about 1 micron roughness. After that we electropolish to mirror reflection. You can send us nitinol parts samples polishing.
Black substance on wire (electropolished Nitinol)2003
Q. I am electropolishing Nitinol wire and have noticed a black substance adhering to the wire after changing the etchant solution. Suspecting a contaminate in the solution I emptied and mixed another batch. SAME THING! An operator says he remembers a similar occurrence some time ago but this is the first time I've noticed it (recent hire).
The stuff adheres to the wire in globules, is sticky, varies in viscosity and is removed with very hot water. What is this stuff and where is it coming from?
Also, help on what parameters to monitor polishing solution and what equipment to perform these tasks would be helpful. This process is a hard one to manage and I love to be able to get some control out of it.Kevin Ham
medical devices - Sunnyvale, California
Can you fill in some blanks? Does the Nitinol have a dark oxide on it? Are you removing it before electropolish? With what? What is you electropolish solution and other operating parameters? Electropolish of Nitinol is a dark art.Jon Quirt
- Minneapolis, Minnesota
A. It is not so hard to electropolish Nitinol wire to a surgically clean surface if you use special high-voltage equipment. It takes a few minutes, and the solution is environmentally safe and long-lasting.
As to Nitinol stents - it is a little bit more complicated since it requires to remove laser-made melts from the inner surface.
We experiment now with two-steps process:
first conventional electropolishing (but also in environmentally safe electrolyte), an then final touch by high-voltage to obtain completely clean surface.
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