Solder as a heat transfer agent to aluminum without sticking?

I need to quickly, precisely, briefly heat small aluminum parts to temperatures in the 300 °C to 400 °C range. Maybe a solder pot would work? I’d need a solder (or other alloy) that did NOT wet or stick to aluminum, and did not leave any deposits on it either. I think I also need the solder to not form a scummy film on the surface that would cling to the parts, interfere with heating them, and contaminate them.

The parts are a bit smaller than pushpins. I want to heat them for, say, a second to a minute. I plan to leave a precise thermometer in the pot, too. Perhaps I need to use stainless tweezers or tongs to hold the parts and maybe swirl them around, so perhaps I need the solder not to wet stainless as well, but maybe this isn’t needed.

Any thoughts?


Good thinking. I think I vaguely remember concluding something, that I was trying to solder and the solder just beaded up on, was aluminum. Same with stainless steel. It sounds to me like it should work. Dross forming on top could be a problem, but it shouldn’t stick either. I won’t argue with somebody that tried it and it didn’t work.

Do you think small steel shot or sand would work? Slower transfer but definitely less hassle. If you use metal make sure you don’t expose yourself to the fumes.

Tin-lead solders won’t wet aluminum (at least, not without a very aggressive flux). However, all solders will form a dross unless they are heated in an inert atmosphere.

Type 710 silicone oil can go to 300 C if that would be enough.

unfluxed solder should work.

you could keep skimming the surface.

you could put a gentle nitrogen gas flow over the top.

What about regular vegetable oil from a supermarket?

Peanut oil has a smoke point of around 400°F, or 204C.
Avocado oil has a smoke point of 520°F, 270C, but is really expensive.

OK, I didn’t see that he needed 300 degrees Celsius, and I’m accustomed to Fahrenheit temperatures.

Thanks! I think all points are useful except the misfires on lower temps, but thanks for those anyway.

I just heard that some solder pots have a skimmer for wiping the dross off the top just before immersion. That could sure help. I also like the nitrogen blanket idea. But the pot is hot and will heat the nitrogen and make it convect. In fact, it will about double the nitrogen’s absolute temperature and halve its density, so this should be pretty vigorous. However, if I get a vapor that is at room temperature more than twice the density of air, it ought to still pool down in the pot even at this high temperature. Maybe a dash of Freon or xenon. Where is the radon, when you finally have a use for some? How about uranium hexafluoride - don’t they want to get rid of what Iran has?

Find yourself a high-temperature mineral oil, and you won’t have to use Nitrogen. You won’t get any crap forming on the top, either. It will leave an oil film on your parts when you remove them, however. That can be easily removed after the fact with some sort of solvent, if that will still fulfill your needs.

ETA: I’ve seen ones that can take in the 500C range, but you will have to search for them yourself. I haven’t used anything like this in ages, and don’t know where to buy it, because I used them in a chem lab that I didn’t buy the supplies for.

Forget the UF6. Highly reactive. You wouldn’t like the results.

Air acts like a gas with a molecular weight of about 29, just over the 28 for N2. CO2 is 44. You don’t need a big flow to blanket a small pot.

labdude, CO2 at 600 K is about 20% lighter than room temperature air.

Cheshire, thanks, but oil clinging to the parts would ruin them. They have a certain… complicating detail. Besides, what can handle 500 ºC? When I’ve looked for oils and polymers for high temperature I have not found anything that can even stay at 400 ºC for all that long. The highest temp wire insulation I’ve found, for example, is only rated for 250 ºC, though it survives 350 ºC for a few minutes. You sure you don’t mean ºF?

OK Napier you are telling me the air over the pot stays at 72 degrees F? A small stream of CO2 over a 300 degree C pot would be expanding and rising, sweeping the air away.

No, I did mean C, it was a chem lab. We measured everything in metric. I may, however, be misremembering how high it went, but we were using it for finding melting points of stuff, and some of them were in the 400s. Try a chemistry supply place. But then, if oil causes problems, you’ve got no reason to bother.

labdude, what I was getting at was that heavy enough gas could still pool in the pot even though it was twice as hot as the surrounding air. If air higher than, but near, the pot is at room temp, it could displace CO2 that was twice as hot and somewhat lighter than the air. So the CO2 would be rising. But something much denser than CO2 wouldn’t. It would circulate inside the pot, and there’d be some mixing and loss at its top, and to the extent that it transferred heat to the air above it then that air would rise away, but it could still make a decent temporary heavier-than-air blanket. That’s what sounded so good to me.