Molten KOH + NaNO3 resistant materials

[50AE]

Hi folks,

I hope you're doing well! Life gets so different for many of us.

Here's a tricky question. What common materials would be suitable to resist a molten quite dangerous mixture of KOH + NaNO3 at around 300C?

I'm using this mixture to clear off the grade 2 enamel insulation of the wires of my coils. I've been prototyping, designing, winding and selling audio transformers for 4 years now.

Due to extremely little time on my hands, I've been using stainless steel solder pots, but these gets corroded one year after approximately.

One idea is to get these ceramic chemistry pots and build a custom heater;

What do you guys think?

Edited March 10, 2021 by 50AE

[Arthur]

Most of the clays will eventually dissolve in molten KOH, machined graphite may be a possible alternative.

[a_bab]

Nickel crucible is the answer. It is basically immune to molten lye.
Quite possibly - monel would also resist corrosion.

Some stainless steel grades may also work.

 

Good to see you back

Edited March 11, 2021 by a_bab

[sefrez]

Nickel crucible is the answer. It is basically immune to molten lye.

Quite possibly - monel would also resist corrosion.

Some stainless steel grades may also work.

 

Good to see you back

What about hot water containing alkali hydroxide? I seem to remember heating NaOH to dryness and causing a little corrosion on nickel. I suppose that could be different in a similar way it is with aluminium. Aqueous NaOH attacts aluminum violently, but molten NaOH without traces of water doesn't appear to.

[Richtee]

Hi folks,

 

I hope you're doing well! Life gets so different for many of us.

 

Here's a tricky question. What common materials would be suitable to resist a molten quite dangerous mixture of KOH + NaNO3 at around 300C?

 

I'm using this mixture to clear off the grade 2 enamel insulation of the wires of my coils. I've been prototyping, designing, winding and selling audio transformers for 4 years now.

 

I am doing well, thank you and good to see ya.

 

How interesting... tube amp applications I assume...

 

Anyway, what you cleaning off the insulation for? Just the solder connections? Surely some 220 grit sandpaper... or is there something I’m not understanding here?

[50AE]

Hey, hey!

In the beginning I used stainless steel cups, but their "nickel" content seemed to be dissolving, the melt turning in a green color. A standard 0.5mm thickness cup would last for approximately 6 months before getting drilled from corrosion.

The main contribution to corrosion though was the hygroscopic nature of the contents, thus taking in water from air, which would then aggressively attack the main iron content and turning it into rust. But mild steel doesn't seem much bothered from the melt alone.

So I turned to the idea of using simple, narrow and tall pots. If it has to be mild steel, then why not steel plumbing? At least they're cheap and easy to find. And a narrow tube is much easier to plug and protect the chemicals from taking in water.

Richtee, good guess! For mostly tube amps. In fact I posted a video recently on my new channel.

The sandpaper method or utility knife both work. But when you need to produce a transformer with +30 lead wires to clean and you need to work efficiently, this method is a no-go. You can imagine how dipping the whole bunch of wires all together into the melt turns a 10 minute procedure into a 10 second one.

Here we're talking about grade 2 enamel polyimide wire, which has a Kapton kind of strength and it's extremely hard to get off. Friends chemists help me test it thoroughly with many kinds of chemicals inside a lab. Only heated hydrazine managed to cope with the speed of molten KOH + NaNO3, but I prefer working with the later And you can't remove it with solder. Edited March 13, 2021 by 50AE

[Richtee]

You got a helluva lot more patience than I, Gunga Din I have wound transformers years ago. Nothing that complex, simple primary/secondary ones. It’s painstaking work.

[sefrez]

I am not qualified to offer this as a suggestion (and am somewhat doubtful that it would even work,) but being a member of pyro form, I couldn't help but be curious as to what molten sodium chlorate would do? If there is glass content in the coating it wont be dissolved like is probably the case with your solution, but organics may be broken down. Obviously such a setup would be quite hazardous, and the chlorate may even decompose too quickly at melt temperature (just under 500F) if it is something that is left in that state as you work. There could be many other hazards along with it and so again, I'm not suggesting it. It was just on my mind and if anyone knows anything better maybe they could comment.

[50AE]

Some years later, I managed to dig up an MSDS of a substance called Strip ISO-VERRE that removes the lacquer of Class 2 enamel (polyimide-imide). It contains Methylene chloride, Phenol, formic acid and hydrofluoric acid.

Distributors in Europe seem not to return my emails, so I'll try recreating it.

P.S. A chlorate molten bath would probably decompose too quickly?

Edited August 17, 2022 by 50AE

[WSM]

Some years later, I managed to dig up an MSDS of a substance called Strip ISO-VERRE that removes the lacquer of Class 2 enamel (polyimide-imide). It contains Methylene chloride, Phenol, formic acid and hydrofluoric acid.

Distributors in Europe seem not to return my emails, so I'll try recreating it.

P.S. A chlorate molten bath would probably decompose too quickly?

 

 

Yeah, possibly BOOM !!!

 

Please, do be careful. (Watch out for HF, too! Read the SDS.)

 

WSM

Edited August 19, 2022 by WSM