Reaction between Aluminum Sulfide and Bleach?

  1. Hello. I have recently decided to create the silicon dioxide thermite reaction for a monitored school project. It is my understanding that the heat produced by this reaction per mole is less than the activation energy for the reaction per mole, and so I must mix in sulfur in order to encourage the process. I would like to have a globule of silicon as a souvenir for the reaction, but since the side reaction that creates the needed propagation energy produces Aluminum Sulfide, my silicon metal will likely release foul and toxic Hydrogen Sulfide whenever it is damp.

    I read in an unreliable internet source that the silicon product can be soaked in bleach in order to eliminate the foul aluminum sulfide. My question is four-fold:

    Will this work?

    If so, what reaction takes place between the hypochlorite and Aluminum sulfide?

    Can this reaction be lit with Magnesium like a standard thermite process?

    Are there any additional risks associated with thsi thermite reaction that are not present in standard thermite reactions?

    Thank you in advance for any help or advice.

    Please do not lock this thread. This reaction is considerably safer than any other thermite process that I am aware of. Also, I am asking specifically how to handle the products, not how to make the reaction occur. I am in no way holding PF liable for any accidents that occur because of this reaction.
    Last edited: Jun 20, 2009
  2. jcsd
  3. chemisttree

    chemisttree 3,723
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    Better to say what reaction takes place between the hydrolysis product of aluminum sulfide and hypochlorite.

    Really? Then why do you ask:

    So, now we know that you are asking about how to use this mixture (How do I light it?) and that you are ignorant of additional risks associated with this thermite formulation! How do you sqare that with your statement, "This reaction is considerably safer than any other thermite process that I am aware of."?

    You'll put your eye out!
  4. mrjeffy321

    mrjeffy321 882
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    As seen in the link provided by “chemisttree”, the bleach (Sodium Hypochlorite) should oxidize the sulfide into sulfate, thus illuminating the smell. However, this may not be a perfect solution to the problem.

    Liquid bleach is an aqueous NaOCl solution. Water will react with the Al2S3 to produce the smelly hydrogen sulfide gas. Also, the sodium sulfate which is produced by the NaCl + Al2S3 reaction is water soluble. The problem comes when one realizes that the Aluminum sulfide is not just a surface coating on the silicon, or only located in one pocket. It is everywhere. There are small deposits of aluminum sulfide throughout the elemental silicon sample which is produced. So if you dump this in a bucket of bleach and let it react for a while you will eventually erode away your silicon lump into a bunch of silicon powder. The conversion of solid Al2S3 into gaseous H2S and dissolved Na2SO4 will break apart the solid silicon lump.

    Perhaps it is possible only to do this treatment for a brief time and hope that you can react all of the Al2S3 on the surface and that the stuff you miss which is located farther into the volume of the silicon lump is sufficiently protected that you cannot smell it.
    Actually, as long as you keep your sample fairly dry after an initial cleaning the smell is not that bad, you generally have to hold it right up to your nose (though doing so is not recommended) before you can tell its there.

    Yes, magnesium ribbon can be used to light the sulfur-boosted SiO2 thermite reaction.

    If I had to rank the danger of sulfur-boosted SiO2 thermite relative to other thermites (for example Iron Oxide thermite), I would probably say that the SiO2 thermite is more dangerous due to the sulfur content and the Al2S3 / H2S problem.
    Still, though, I would argue that thermite reactions (when pursued responsibly with a mind towards safety) are excellent chemistry demonstrations which do not pose an unreasonable danger.

    Although “wil3” may not yet be an expert on thermite reactions he has shown in this instance that he is thinking about the possible dangers of the reaction ahead of time and attempting to find solutions which will mitigate their effects (for example, neutralizing the sulfides produced in the reaction). He is seeking advice from people more knowledgeable than himself, but at the same time keeping a skeptical eye on the information he receives from the internet since he realizes it may not be 100% reliable, and thus tried to find corroborating sources.
  5. chemisttree

    chemisttree 3,723
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    It is also likely that any silicon produced will also be reactive toward bleach since there will be a strongly alkaline solution of sodium hydroxide present as well. The strong alkali in bleach will dissolve any passivating silica exposing the underlying silicon and it's (the NaOH) progressive removal should enhance the reactivity of the hypochlorite (if much less than bucket quantities of bleach are used) which will expose more silicon which will react with more alkali which will enhance the reactivity of the remaining hypochlorite... oh dear!

    Expect hydrogen bubbles, bad smells, lots of heat but hope for a mild reaction.
  6. mrjeffy321

    mrjeffy321 882
    Science Advisor

    What I usually due to clean the Al2S3 from my silicon lumps is to submerge them in water (perhaps with a small amount of a weak acid) for a few minutes. This will get a lot of the sulfide off the surface without damaging the silicon lump too badly, but the smell will remain.
    It will bubble and smell while it is in the water and while it is drying. What you might do is bubble the gasses given off through a bleach solution so as to neutralize the fumes.

    Another thing I forgot to mention before…
    There are other ways to boost thermite reactions without using sulfur. One way would be to use potassium chlorate. But in doing this you must make sure to use a coarse-grain aluminum powder to slow it down and prevent a flash-reaction. My friend did some good work on developing ways to boost SiO2 and TiO2 thermite reactions with KClO3, and even Calcium Sulfate,
    Helpful Information:
  7. chemisttree- You are absolutely right that my question had an inherent logical fallacy. I have not done this reaction before, I based the claim that the reaction was less vigorous entirely off of hearsay and grainy Youtube videos. Sorry for the misunderstanding. Thank you for the link to the paper- I find the authors' analysis of the first order differential rate law for the reaction very interesting. Also, thank you very much for warning me about the reaction involving the silicon and the basic solution. I will definitely alter my approach to the "souveneir" based on that information.

    mrjeffy321- It's clear that you have a bit of experience with this sort of reaction. Excellent idea of compromising between stench and sample by only reacting the surface coating of Aluminum Sulfide. I will definitely test that out. Your first link was actually the "sketchy web source" I noted in my first post- I had considered his potassium chlorate approach, I just decided that sulfur would be less of a hassle to obtain. The Amazing Rust site is amazing- I actually emailed the site operator with a few questions about the mesh sizes for the reactants, and he had a very nice response.

    Thank you both for some incredible answers. I was worried that my post would garner no responses, and so I really appreciate the long and comprehensive answers that both of you gave. Thank you very much!
  8. berkeman

    Staff: Mentor

    I think it's time to lock this thread. A little too much info on how to boost thermite reactions...
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