Surface Analysis of ZrN Endmills After a Sodium Hydroxide Bath

As some of you might have seen, I am testing some Carbide3D ZrN single flute endmills and ran my 1/8” one too hard and got it gummed up with aluminum on the surface. With the naked eye, it just looked gray, almost like the coating wore off, but with closer inspection, it was aluminum coated onto the surface.

I decided to do some research on how to remove the aluminum and knowing that sodium hydroxide (NaOH) reacts with aluminum to form water soluble sodium aluminate ( and hydrogen gas. Some people online were concerned about it reacting with the ZrN coating but a few different sources I found mentioned that this reaction won’t occur until 500C. ( &

As such, I went ahead and taped the endmill to the side of a beaker where the ZrN part was in a 1M NaOH solution. I left if for 30 min and returned to find it nearly entirely cleaned! The largest piece of aluminum was still stuck on, albeit much smaller. All the rest was nearly gone.

However, it was not without its costs. It looks like the aluminum that was stuck pitted the surface and left it slightly damaged, however still looking remarkably better than before. There also looked to be some small remnants on the surface that may react with more time. I have yet to test how well it cut again, I would imagine fairly well (certainly better than it did with aluminum coating the surface), but I did notice I broke the tip, which will impact performance.

(I also figured out how to make the entire image in focus so these pictures are better)

New 1/8" ZrN coated single flute endmill from Carbide3D

Pitting on the Surface

I recommend you give this a try to clean ZrN endmills covered in aluminum, it won’t return them perfectly to their former glory but you should be able to get a few more uses out of them.


That was really interesting, thanks for posting.

A couple of the mills I’ve been abusing have turned silver. I guessed the coating wore off. Maybe I’ll try giving them a bath :smiley:.

I see sodium hydroxide is available on Amazon. What mix ratio did you use? With water, distilled water?

From the description a 1M (i.e. 1 molar) NaOH solution, which is one mole of NaOH in a solution totaling 1L. Since this application isn’t very sensitive to concentrations, you can just measure one liter of distilled water and slowly add one mole of sodium hydroxide (40 grams), stirring to dissolve. (Scale the ratio down for less solution, of course, unless you want a whole liter.)

Of course, as any chemistry student can tell you, always (slowly) add the chemical to the water so you gradually increase the concentration as it dissolves. (Adding water to a pile of sodium hydroxide would definitely be educational.) Also, dissolving NaOH in water is rather exothermic, but this is just a 1M solution.


@The_real_janderson Cool analysis! I use purple degreaser. I wonder if purple causes the same reactions as NaOH.

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Thank you sir. Wasn’t sure how to convert M to something I have the means to measure. Now I know.

Used to deal a lot with metalorganics for compound semiconductor production so very familiar with exothermic reactions!

Absolutely! It was fun to run the experiment.

Like @ClayJar mentioned, it is a 1 molar solution of sodium hydroxide (NaOH). 1 mole of NaOH is 40 grams so a 1 molar solution is 40 g/L. Scale down to whatever you want (I used 2 grams in a 50mL beaker of water). And yes, it is exothermic but it takes a couple minutes to dissolve and it’s a weak solution so don’t worry about it boiling or being too hot.

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Most degreasers are alkaline owing to their ability to react with oils/greases and form emulsifying agents (basically making soap through a saponification reaction). I read of some people doing the exact same thing, it’s just easier and cheaper for me to get sodium hydroxide than purple degreaser. I imagine the purple degreaser is weaker in strength so you probably toss your endmills in and leave them overnight.


very cool photos!

i wonder if the pitting is the byproduct of the reaction?

Interesting. The areas without aluminum did not show any pitting in the NaOH bath so I didn’t see a reason to trace the pitting back to that.

idk, just a thought.

i pictured it much like the way an ultrasonic cleaner works, tiny bubble explosions.
but chemical things and tiny chemical created craters

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I like the image it shows in my mind of tiny explosions on the surface, sadly, it’s much more like sugar dissolving into water gradually with little bubbles of hydrogen streaming up during the process.

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When I looked at the “pitting” photo again, it looked more like there was still aluminum on the surface. Might be because it’s late, though.

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In the first pitting photo, the only aluminum I saw left was the glob on the far left. Otherwise they looked like tiny craters on the surface where aluminum used to be.

I tend to avoid dangerous chemicals. I found out that aluminum will slowly get eaten by white vinegar, it turns black and will detach itself from the flutes in the process.

I was able to remove the big chunks of aluminum stuck to it over a 24h period, however I’m curious to see closely how it’s like, what kind of magnyfying glass you are using if you don’t mind sharing?

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What do you do with these solutions when you’re done with them, asks the guy that drinks Lake Michigan water?

Vinegar (acetic acid) works differently than sodium hydroxide (NaOH), since NaOH is a base, rather than an acid. Acids will corrode the tungsten carbide over time so I chose not to pursue that. You can also use concentrated degreasers as they rely on bases to turn the greases and oils into soap to be able to remove them.

I am using a Keyence VHX-5000 digital microscope to view these. They are out of the range of consumers ($15,000+) so you’d be better off with a different setup to view them. I’ve seen folks get good results out of 10x, 15x, or 20x loupes with their smartphone taking pictures.

EDIT: I mention below that acetic acid (vinegar) should be no issue for corrosion of carbide or ZrN coatings.

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I only drink the purest Mississippi water myself so I understand you. I neutralize the NaOH solution with citric acid, forming sodium citrate and water. Sodium citrate is a food additive with no environmental hazards so I just pour it down the drain.

For people at home, just use vinegar to neutralize it. To see if it is neutralized, add some baking soda. If it fizzes, it’s neutralized and if it doesn’t, add more vinegar.

Ah damn I’ll try that with my smartphone, considering the quality of the magnifyed pictures I was expecting such prices.

Regarding vinegar, I did research before hand and I’m pretty sure some people said it was fine for tungsten carbide, but I may have read wrong, thought vinegar is not a strong acid, would it have enough times to corrode the tungsten ?

That could be an interesting experiment to do if you ever find yourself some free time and a piece of carbide laying around, absolutely not suggesting lol

Curious about the specifics of the types of cutting this endmill did. Chiploads ect

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Was wondering about correct disposal, thanks.

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