Carl writes:

... ... ...


There are lots of other things besides sodium chloride to make "salt"
baths from :-). See
https://en.wikipedia.org/wiki/List_of_cooling_baths for one list, and
look at reference 2 and the reference pdf in ref 2
(https://www.larkinweb.co.uk/science/...ng%20baths.pdf)
for a bit more info. I'd try calcium chloride hexahydrate/water
either at the ratio for -41C or a bit stronger since they say it is
difficult to reach the listed temps. You could also precool your
metal with dry ice and even add some dry ice to the salt bath while it
is cooling down, or put the salt bath in a small tub in a larger tub
with dry ice packed around it. I'd make the starting ice either from
distilled water (cheap at grocery stores) or reverse osmosis water if
you have a home system already. If having the metal dripping with wet
calcium chloride is a problem during your test put the piece in a
ziploc bag. Partially seal the bag so about an inch at one side is
still open then slowly submerge the bag in plain water while holding
that corner out of the water. The air will be forced out so you get
good contact between bag and metal for good heat transfer. Finish
sealing the bag when as much of the air as possible is removed. Just
pretend it is a steak you are about to cook sous vide :-).

--
Regards,
Carl

Stunningly good info. Thanks.

I could see what NaCl-brine-ice does for the test, knowing there's
further I could go.

Dam the ends of the Rectangular Hollow Sections to hold the brine-ice
internally = direct contact. Contained. Salt on the sample wouldn't
matter anyway.

Many thanks again.