Chemists : Suitable material for vessel to melt sodium hydroxide in? - Page 1
Forum section: electronics / general

author: Chris Wilson
author_rank: Super Contributor
timestamp: June 24, 2017, 09:40:21 am
content: I need to melt some sodium hydroxide (caustic soda) and have already done some permanent damage to one of the wife's Pyrex dishes. What material will remain unaffected by melted (by heat) caustic soda that I might have about? Thanks.

author: TheAmmoniacal
author_rank: Unknown
timestamp: June 24, 2017, 10:07:21 am
content: What we use in the lab is a nickel crucible, but I think steel should be fine too.Molten sodium hydroxide dissolves glass.

author: MagicSmoker
author_rank: Super Contributor
timestamp: June 24, 2017, 10:08:53 am
content: IANAC, but...Clean, oil-free cast iron (the oil-free part is really important) or pretty much any stainless steel alloy should work. All of the silicates (which is to say, all glasses and most ceramics) will dissolve in molten NaOH.

author: jpanhalt
author_rank: Super Contributor
timestamp: June 24, 2017, 10:35:18 am
content: Agree with IANAC. I have also used mild steel for melted salt baths. Mine were various mixtures of KOH, NaOH, and sodium nitrate to strip insulation from magnet wire.Mild steel was more available and easier to machine. Hear's my little "hot pot":John

author: Chris Wilson
author_rank: Super Contributor
timestamp: June 24, 2017, 11:06:50 am
content: OK, I have a turned mild steel disc about 3/4 inch deep lying on the bench I made as a form tool, so I will turn a recess in it for the caustic soda. It was the only stuff i have tried that was able to strip some antique Litz!Thanks guys.

author: MagicSmoker
author_rank: Super Contributor
timestamp: June 24, 2017, 11:11:46 am
content: Quote from: jpanhalt on June 24, 2017, 10:35:18 amHow did that work out? A few years ago I looked into making my own molten salt "dip stripper" with an old solder pot (indeed, that's how I knew that it was ok to use cast iron or stainless steel to melt NaOH), but ended up replacing all of my magnet wire with lower-temp insulation that can be stripped by dipping into solder directly.

author: jpanhalt
author_rank: Super Contributor
timestamp: June 24, 2017, 12:07:04 pm
content: Quote from: MagicSmoker on June 24, 2017, 11:11:46 amWorked well. I found a ratio of NaNO3 to KOH of 1:3 to 1:5 at 292°C to 320°C to work best. Increasing NaNO3 caused more blackening and faster insulation removal. Substituting NaOH seemed to be a bit slower and required a higher temperature. There is some fizzing with NaNO3, so don't fill the pot full. Be sure to rinse wire after removal.My Litz wire was all solderable, so I didn't test it. Should be OK for that purpose, though.John

author: TerraHertz
author_rank: Super Contributor
timestamp: June 24, 2017, 04:32:42 pm
content: Quote from: Chris Wilson on June 24, 2017, 09:40:21 amBtw, is that 'Pyrex' of recent manufacture? Possibly by a mob calling themselves 'World Kitchen'?If so, it isn't actual pyrex. World Kitchen bought the trademark, and promptly started whacking it on crappy soda-lime glass products. Some of the 'pyrex' I see in shops is even quite greenish (high iron content soda-lime glass.) There have been many serious injuries due to people buying fake 'pyrex' ovenware, and having it shatter while full of very hot food on removal from ovens, etc.https://en.wikipedia.org/wiki/Pyrex

author: Gyro
author_rank: Super Contributor
timestamp: June 24, 2017, 05:33:15 pm
content: From the article it looks as if it's only a US problem, the rest of the world gets proper Pyrex Borosilicate glass. Worth keeping an eye on the PYREX vs pyrex trademark though.

author: Ampera
author_rank: Super Contributor
timestamp: June 24, 2017, 05:46:17 pm
content: I warn everybody I meet that their pyrex isn't actually PYREX. I hate the assholes who push this shit on people. My mom never baked with it again because a dish blew up in the oven spreading glass everywhere. The people who make it are terrible people, and I hope someone actually comes to make proper borosilicate so we don't have to buy that shit.

author: IanB
author_rank: Super Contributor
timestamp: June 24, 2017, 05:53:42 pm
content: It probably should be mentioned that melting sodium hydroxide is very dangerous. If it spits or splashes the flying hot droplets could do serious damage to your eyes or do nasty things to your skin. Enclosed safety glasses, gloves and protective lab coat/overalls are very necessary.

author: Chris Wilson
author_rank: Super Contributor
timestamp: June 24, 2017, 05:57:53 pm
content: Some great info and safety tips, thanks everyone!

author: jpanhalt
author_rank: Super Contributor
timestamp: June 24, 2017, 06:06:06 pm
content: Arcuisine sold on Amazon claims to be borosilicate glass:https://www.amazon.com/Arcuisine-Borosilicate-Glass-Bakeware-Storage/dp/B013XAAPDAAnchor brand appears appears to just be tempered soda-limeTarget lists several products as being "borosilicate" glass, but the brands are "Pyrex" and "Anchor." So, I would not trust that advertising (see attachment).John

author: SeanB
author_rank: Super Contributor
timestamp: June 24, 2017, 06:57:47 pm
content: Mild steel, graphite or even stainless steel will work, just do not use anything galvanised. Guy, it probably was the new Fakerex, you only get the old real borosilicate glass as either old units at flea markets or as garage sale items, I have seen the new ones shatter as well, and the shards are big and nasty, along with also having a significant amount of small glass shards and spalls as well in there, just from placing hot onto a heat resistant counter top holder.Even the borosilicate glass is workable with a decent MAPP torch, I have repaired a few measuring cylinders with chipped tops by simply using heat to rework the rim to a smooth even shape, and reforming the spout in the hot glass with some pliers before flame polishing it all, then leaving to cool slowly. Soda glass you need to anneal carefully, it will shatter with the heat at the one point, unlike the borosil glass.

author: MK14
author_rank: Super Contributor
timestamp: June 24, 2017, 07:11:43 pm
content: Quote from: IanB on June 24, 2017, 05:53:42 pmIf they are so hot, can't they melt straight through (cheap/normal) safety stuff, and still cause terrible injuries ?E.g. Plastic eye protection goggles.

author: alm
author_rank: Super Contributor
timestamp: June 24, 2017, 07:30:36 pm
content: Due to limited heat capacity, I would not be too worried about penetrating plastic safety glasses. Just like drops of solder are not very likely to burn through anything. I would not trust latex/nitrile gloves to offer much protection, so wearing something more substantial like leather gloves over them might be warranted. Plus ideally a fume hood.

author: TerraHertz
author_rank: Super Contributor
timestamp: June 24, 2017, 11:05:03 pm
content: Quote from: Gyro on June 24, 2017, 05:33:15 pmI put that down to the 'Wiki fuzz' effect. In Australia glassware marketed as 'pyrex' seems to be universally NOT borosilicate. And the company in question presumably calls themselves 'World kitchen' for a reason.

author: Halcyon
author_rank: Unknown
timestamp: June 25, 2017, 01:43:56 am
content: Quote from: TerraHertz on June 24, 2017, 11:05:03 pmYou can get both 'forumlations' of Pyrex kitchenware in Australia; Soda-lime glass and borosilicate, the latter being low expansion and more resistant to breakage during extreme temperature changes. You just have to read carefully on what is on the box. You'll find a lot of those discount shops just sell the soda-lime stuff (although still technically genuine "Pyrex"), thankfully most of the big supermarkets here sell the proper borosilicate Pyrex and it's not really that much more expensive.For my everyday cooking (measuring liquids or preparing stocks using boiling water) I just use laboratory beakers made from borosilicate. They also look nifty.

author: Ampera
author_rank: Super Contributor
timestamp: June 25, 2017, 02:16:34 am
content: Quote from: Halcyon on June 25, 2017, 01:43:56 amMan, I would love to see the inside of your house, especially your kitchen. You've hinted at having a lot of unique and interesting kit in there. The most interesting thing in my house is an electric smoker.

author: David Hess
author_rank: Super Contributor
timestamp: June 25, 2017, 04:15:24 am
content: Quote from: TerraHertz on June 24, 2017, 04:32:42 pmWow, that is slimy. I hope everybody involved in making that decision and everybody who supported it goes to the special hell.I had one of these "new" Pyrex dishes explode not long ago and now I know why.Quote from: TwoOfFive on June 25, 2017, 02:16:34 amMy roommates walked in once when I was cooking candy fudge using my Tektronix DMM916 multimeter with a thermocouple probe to accurately gauge soft ball stage. After seeing that, they lost all interest in my cooking.