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27 lines
3.0 KiB
Markdown
Executable File
Hey, seems like this might be of some interest here.
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Since I had originally posted this elswhere, I had to convert this from message board format, so sorry if some of the links don’t work or the formatting is off.
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I'm just starting to muck about with anodizing Titanium despite having had a power supply sitting around for the better part of a decade and I've tried using Whink rust remover but I don't like playing with Hydrofluoric acid and it really seems to destroy the surface finish pretty quickly.
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I would just get some multi etch, but they supply it in gallon mix only and I don't want to mix that much up at once. Because there's no way to ensure a proper mixture of the powders if you try and divide it up before dissolving it, there really isn't a way to mix smaller amounts. Also, for those living outside the country, MultiEtch is not readily available for shipment.
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Since I'm kinda a DIY type guy I decided to try figuring our the formula for it and rolling my own.
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Per USPTO patent search there is an expired 1955 [patent](https://patents.google.com/patent/US2942954A/en) for a non-hazardous etching solution consisting of Ammonium Persulfate and Sodium Flouride.
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According to the Multi-etch [MSDS](https://static1.squarespace.com/static/5c17d54ada02bc9741cdfef6/t/5cab543beb393122e83f883f/1554732091574/MultiEtch-Safety+Data+Sheet-Dry.pdf) those are the only two components of the etchant, but the exact proportions are not required to be listed, so what is needed is the amounts of both to use.
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The patent references using a 0.5M mixture of the two. In addition I found a [senior thesis](https://web.wpi.edu/Pubs/E-project/Available/E-project-042910-083844/unrestricted/Alternatives_to_Hydrofluoric_Acid_Etching_At_Wyman_Gordon_Company.pdf) from Worchester Polytech referencing use of both 0.5M and 1.0M solutions of APS and NaF to etch titanium, so I suspect those concentrations correspond to regular and double strength Multi-Etch.
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To verify this I checked the [shipping weight](https://theringlord.com/cart/shopdisplayproducts.asp?Search=Yes&sppp=1000&page=1&Keyword=multietch&category=ALL&highprice=&lowprice=&allwords=multietch&exact=&atleast=&without=&cprice=&searchfields=) of MultiEtch which is about 1.1lbs/gallon.
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For a 1L of 0.5M etchant, one would need 114g of APS and 21g of NaF for a total of 135g of chemicals per liter. So for 4 L of etchant, one needs 540g of chemicals, or 1.19lbs. 1 gallon is about 3.785 L, so for 1 gallon of solution you need a total of 1.126 lbs of chemicals. Pretty darn close to 1.1lbs.
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Therefore my conclusion is that single strength Multi-Etch is likely a 0.5M APS/NaF solution.
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Both chemicals are readily available, and reasonably inexpensive even in non-bulk form. I paid $35 for 1kg of APS and $20 for 500g of NaF, enough to make about 2.3gallons of etchant. I'm sure you could do much better if you bought in larger quantities.
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Of course it's simpler to just buy some Multi-Etch, but if you want to mix smaller amounts or are unable to have it shipped to you, this may be a workable alternative.
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#chemistry #clipped |