Surface Analysis of ZrN Endmills After a Sodium Hydroxide Bath

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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Yep, absolutely. They were gummed up and I mentioned them in this post (Need help testing cutters). I was really deep for 1/8" endmills and you commented that I was probably deflecting and fighting that.

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Right, I would like to revise my previous statement. Strong acids like hydrochloric and sulfuric will damage them. Acetic acid (vinegar) should be just fine. I wouldn’t worry about it and now I am curious to give it a try myself.

I just need to gum up another endmill now…

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No worries, it always comes when you either don’t want it or don’t expect it lol.

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