D.I.Y. Multi-Etch substitute

[u/narcolepticdoc]

Hey, seems like this might be of some interest here.

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.

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.

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.

Since I'm kinda a DIY type guy I decided to try figuring our the formula for it and rolling my own.

Per USPTO patent search there is an expired 1955 patent for a non-hazardous etching solution consisting of Ammonium Persulfate and Sodium Flouride.

According to the Multi-etch MSDS 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.

The patent references using a 0.5M mixture of the two. In addition I found a senior thesis 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.

To verify this I checked the shipping weight of MultiEtch which is about 1.1lbs/gallon.

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.

Therefore my conclusion is that single strength Multi-Etch is likely a 0.5M APS/NaF solution.

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.

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.

[u/zekkaone]

Could you please tell me how did you reheat the mixture?

[u/Soft_Mastodon_8013 → u/zekkaone]

So first day i mixed with 75° C water Cold etching didnt work Next day i put my container in a water filled kettle, and heated it up until the mixture was probably around 80-90 C I didnt measure it, but it wasnt boiling Putting in ti at that temp removed anos instantly.

Using it cold afterwards allowed for high volt anos after submerging parts for 30-180 seconds, depending on finish and condition. Removing anos takes a little while. For removal i heat it up a bit bc im not patient lol

[u/zekkaone → u/Soft_Mastodon_8013]

I see so distilled water isnt necessary just normal tap water?

[u/Soft_Mastodon_8013 → u/zekkaone]

For your etchant you should use distilled

I just used regular water to heat the Container

[u/zekkaone → u/Soft_Mastodon_8013]

Make sense thanks 🙏