Sciencemadness Discussion Board - Chromate/Dichromate thermite

Chromate/Dichromate thermite

garphield - 2-8-2020 at 19:48

I have a decent amount of sodium dichromate and would like to make thermite using it, aluminium powder, and some calcium fluoride as flux. I do want to get some decently sized pieces of chromium metal, but im not gonna reduce it to Cr2O3 because I want to know what it will be like and I cant find any sources online, and I can get the dichromate for $6/lb so will be ok with a lower yield. Would a 3:1 ratio of thermite to flux be ok? I'm worried that without flux it would just act like flash powder, and although its not gonna be confined that would mean I would get no yield and it would still be kinda dangerous. Sodium dichromate is sorta deliquescent and forms hydrates, but since I am gonna dry it before doing anything with it and use the thermite within a few hours of manufacture it should be fine. Im planning on doing this at a 50 gram scale because my Al powder is made from just putting foil in a blender and I'm using KMnO4/ethylene glycol as my initiator so im worried that at a smaller scale it either won't burn well or the metal will have more manganese than chromium in it.

fdnjj6 - 2-8-2020 at 20:03

Just going to put this here:
https://www.fishersci.com/store/msds?partNumber=S2583&pr...

If you have a potential flash powder mix I seriously hope you know what you're doing. A 4 for the health rating, a confirmed and potent carcinogen, and a very low LD50 is pretty fucking bad and not something I'd make potentially explosive mixtures out of. You'll need a proper testing area. Don't do this anywhere where the unreacted materials could be exposed to others and do not let that stuff get into the soil.

I almost ordered some dichromates for my lab which has pretty advanced glassware and good safety in place, but decided against it due to the toxicity. Please be responsible and safe.

garphield - 2-8-2020 at 20:13

Yeah it might not be the best idea to do this, if it exploded it would be extremely bad (on small scales and unconfined probably not enough to maim me if im wearing face shield+safety glasses but still), and although the dermal LD50 is ~20 times larger than the oral one because it doesnt go through skin very well that would change if i was breathing it in/had lots of open wounds. If I do it, I will bring a spray bottle with a sodium sulfite solution to neutralize anything that gets out, I'm not just gonna dump large amounts of hexavalent chromium into the environment.

JJay - 3-8-2020 at 03:41

Potassium dichromate is better for thermite because it is not hygroscopic. As I recall, it's typically used for starting less energetic chromium thermites for preparing elemental chromium.

You should have some idea of what you are doing with chromium salts ince they are potentially dangerous and bad for the environment, and they are carcinogenic. If you just want fire and explosions, I would suggest different oxidizers.

Whathappensif - 3-8-2020 at 04:03

I would second not using chromium as your oxidizer in the thermite, because of its carcinogenicity. Use iron oxide or even copper oxide (less good for the environment).

Beware though, CuO and Al thermites are explosive, the smaller the particle size the more so.

Also unless your thermite is well contained, you will be sputtering around unreacted reactants and products, which if they are toxic, will pose problems later.

Herr Haber - 3-8-2020 at 06:12

The Gayest Person on Youtube videos on thermites would be a good start for this kind of project.

I wouldnt have bet a penny on many of his experiments. Sincerely amazing.

Tsjerk - 3-8-2020 at 06:38

Quote: Originally posted by fdnjj6

I almost ordered some dichromates for my lab which has pretty advanced glassware and good safety in place, but decided against it due to the toxicity. Please be responsible and safe.

Really? You didn't order it because it is toxic? I would understand you being careful not to ingest any because you know it is toxic... but not buying it is another extreme.

During the first practical course of biology students at my old university they are told to weigh potassium dichromate, some random amount, and make a solution out of it. They are told it is toxic and to be careful not to spill. We all know they will spill all over, and show them by wiping the place down with a wet piece of white paper. They are all shocked when we show them the orange paper and tell them it is carcinogenic... Maybe they will pay a little more attention next time we tell them something is toxic.

Quote: Originally posted by Whathappensif

I would second not using chromium as your oxidizer in the thermite, because of its carcinogenicity. Use iron oxide or even copper oxide (less good for the environment).

That would beat the goal of producing chromium.... not?

garphield - 3-8-2020 at 07:21

yeah im gonna be doing it on a large concrete thing and will bring a bottle of sodium sulfite to reduce any dust that comes out to Cr(III), im not gonna be eating it and will be wearing ppe. main thing im worried about is if it will act like flash powder and explode when im handling it, i will be mixing it on site by pouring both reagents into one plastic bag before rolling it around inside the bag so no sparks are generated to make sure there's no way it accidentally ignites but if there's a good chance of it exploding when lit i wont be doing it anyways

Cr(iii) isn't that bad for the environment, copper is def worse than that.

Syn the Sizer - 3-8-2020 at 07:26

I agree, not getting something as a chemist because it is toxic will limit your projects. Just be careful with it, I was pissed off in O-Chem course when our instructor took the section of a lab out using chromic acid because of its risks. We should learn how to safely use it before entering the field where employers expect us to know how to use stuff safely.

I am planning on getting 500g of dichromate because it is a strong oxidizer, almost as strong as KMn04 but cheaper and easier to find. You can use it to turn primary alcohols into aldehydes or further into carboxilic acids, and secondary alcohols into ketones, among many other things.

I am also getting N,N-dimethylaniline to synthesize a few of the methyl dyes, also very toxic but I will be safe in using it.

We walk down the streets breathing auto exhaust, smoke from smokers, all sorts of toxins daily, as long as we are safe using reagents, they are the least of our worries.

garphield - 3-8-2020 at 07:45

It would still be nice to know if anyone has done this before, or failing that if you think it will burn at a reasonably slow rate or just act like flash powder.

Whathappensif - 3-8-2020 at 09:27

Quote: Originally posted by Tsjerk

That would beat the goal of producing chromium.... not?

Sorry, I didn't see the bit about him wanting chromium.

Personally I don't mind so much working with with alkylating agents, oleum, fuming nitric acid....but get nervous around lead, mercury or chromium compounds.

Syn the Sizer - 3-8-2020 at 09:38

Mercury is the one that I am nervous about.

Syn the Sizer - 3-8-2020 at 10:24

Sorry, we all kind of derailed your thread. My thoughts are if you are unsure and not getting any definitive answers here (I personally have no experience), maybe try it on a super small scale and see how it turns out.

Metacelsus - 3-8-2020 at 10:32

If you just want chromium metal, you should reduce the dichromate to Cr2O3 first. The reaction will be safer, and also higher yielding because less aluminum will be needed.

garphield - 3-8-2020 at 11:29

lmao i was making aluminium powder with a coffee grinder and the plastic part with the blades just broke so im not gonna be able to make any until the replacement parts arrive. it was really old tho so that might have been the reason it broke, but i will put in less stuff at once next time so theres no chance of it jamming. good thing the replacement part is really cheap lol

JJay - 3-8-2020 at 14:44

Offhand, I see Schlessinger's Inorganic Laboratory Preparations in the Sciencemadness library contains this preparation:

I see another prep in Walton's Inorganic Preparations that doesn't use barium... it uses chromium trioxide, saying that a small amount of chromic oxide thermite is insufficient to melt alumina. There is at least one other chromium prep in the SM library that I remember seeing.

If you are going to use sodium dichromate, it will have to be thoroughly dried and protected from air, or the mixture will be hard to ignite and will tend to blow apart prematurely before everything is reacted if it is ignited. Sodium dichromate is usually sold as a dihidrate, and it is deliquescent.

You should not store chromium-aluminum thermites. The should be prepared immediately before use, and while I don't think they will spontaneously combust, I'm not so sure about that with sodium dichromate. Also, they should be treated gently (don't mix in a mortar or blender, and don't hit with a hammer or anything like that).

garphield - 3-8-2020 at 15:09

Quote: Originally posted by JJay

...if you are going to use sodium dichromate, it will have to be thoroughly dried and protected from air, or the mixture will be hard to ignite and will tend to blow apart prematurely before everything is reacted if it is ignited. Sodium dichromate is usually sold as a dihidrate, and it is deliquescent.

You should not store chromium-aluminum thermites. The should be prepared immediately before use, and while I don't think they will spontaneously combust, I'm not so sure about that with sodium dichromate. Also, they should be treated gently (don't mix in a mortar or blender, and don't hit with a hammer or anything like that).

yeah when I do it I will dry out the dichromate, grind it with the flux in a mortar and pestle, then immediately put it into a ziploc bag. then at the site i will use it at right before use i will get a premeasured amount of aluminium powder into the bag, close it, and gently shake/rotate the bag to mix the two powders. water especially could be a concern as if it gets wet the dissolved dichromate might react with the aluminium powder vigorously enough to start the reaction right there.

fdnjj6 - 3-8-2020 at 22:11

Yes, I refuse to bring anything into my home lab that has a health rating of 4 on the NFPA diamond. Nitric acid is the only exception only because I know it inside and out and have lots of experience with it and it's decomposition products. It would've been 1/4 pound of dichromates. I don't have proper disposal for chromium products. The reaction should work with KMnO4 anyway, but yea I refuse to do high risk experiments in my home lab.

Nitrosio - 4-8-2020 at 05:17

https://www.researchgate.net/publication/236556739_Theoretic...

JJay - 4-8-2020 at 05:34

Quote: Originally posted by Nitrosio

https://www.researchgate.net/publication/236556739_Theoretic...

It doesn't seem to contain data for any phosphates, but that looks like a good reference.

Tsjerk - 4-8-2020 at 06:50

Quote: Originally posted by fdnjj6

Yes, I refuse to bring anything into my home lab that has a health rating of 4 on the NFPA diamond. Nitric acid is the only exception only because I know it inside and out and have lots of experience with it and it's decomposition products. It would've been 1/4 pound of dichromates. I don't have proper disposal for chromium products. The reaction should work with KMnO4 anyway, but yea I refuse to do high risk experiments in my home lab.

That is perfectly fine, but you don't have to tell everyone every time you see someone talking about something toxic. Unless someone wants to make dimethyl mercury or clearly doesn't know what they are dealing with, it is fine to assume they will not eat or inhale the stuff.

symboom - 4-8-2020 at 12:11

This might be a little bit of topic but it is a dichomate kinda thermite
caesium dichromate can be reacted with zirconium to produce pure caesium metal

Tsjerk - 4-8-2020 at 13:12

Do you have a source for that?

symboom - 4-8-2020 at 13:34

Well Wikipedia states it due to ceasium and it low boiling point I know it seems like that reaction should not be possible but if is driven forward and zicronium has a high boiling point so that helps. This is similar in the process to obtain potassium metal from a reaction of lithium and potassium chloride also works with ceasium chloride
https://en.m.wikipedia.org/wiki/Caesium
Cs2Cr2O7 + 2 Zr → 2 Cs + 2 ZrO2+ Cr2O3

[Edited on 5-8-2020 by symboom]

fdnjj6 - 4-8-2020 at 20:27

Quote: Originally posted by Tsjerk

Quote: Originally posted by fdnjj6

I didn't mention it everytime. I mention it here because um, I'm not sure if you read his post, but he is making a potentially explosive mix. So, while you won't see it under my fdnjj6 profile, I used to be heavily into energetics and I can tell you that when things go boom unconfined, it tends to send shit everywhere, making it very easy to inhale and expose yourself to it and expose the entire area around you to it. While I know this place isn't super good on safety, this was something that definitely needed a good word of caution. And to be blatant, there are a LOT of people, especially kids, on here who do not know what they are doing. So it's fair to assume so.

He also commented on me saying that I just refused to order the dichromate so I figured I'd elaborate.

I help people out all the time with toxic stuff. Mainly on Reddit, however I felt like dropping the MSDS and a good warning was very appropriate. Not sure why you felt the need to say what you said, it was unnecessary.

[Edited on 5-8-2020 by fdnjj6]

symboom - 5-8-2020 at 10:08

Oh I see what you mean I just saw dichromate and did not put two and two together chromium thermite uses chromium 3 oxide. The reaction I stated uses zicronium so I suppose it is a slow reaction to form ceasium in a vacuum

[Edited on 5-8-2020 by symboom]

garphield - 16-9-2020 at 09:16

I did this using sodium chromate and 1/3rd of the weight of the chromate+aluminium of CaF2 as flux. When I was drying out the chromate in a beaker I put in the CaF2 since I thought that would lead to better mixing, but this led to it forming a cement-like thing that cracked the beaker when it dried and required breaking with a hammer and then grinding for quite a while in a mortar and pestle to grind up. It still had some large chunks left. When I ignited the thermite, it burnt very bright but you could still see yellow from the chromate on the surface of the slag when it cooled and there were many bubbles from escaping gases (guessing water vapor). I crushed up the slag with a hammer, then soaked it in water which dissolved a large portion of it, as the slag is mostly sodium aluminate. However, there was still maybe half of it left from the CaF2 and maybe some calcium aluminates that formed. The chromium had a lot of slag stuck on it still which was pretty much impossible to get off unless you were willing to smash up the globs of chromium metal (it is pretty brittle). Might try this again in the future with no flux at all since the sodium from the Na2CrO4 will act as one too, and this way the whole thing can dissolve in water.