Sciencemadness Discussion Board

Dry Si+KMnO4=?

Conure - 23-4-2023 at 06:41

Does anyone know the equation for a dry reaction of Si+KMnO4?

The equation below gives a stoich ratio of 7.5 which gives a weak and incomplete reaction. This indicates that there is too much KMnO4.
3 Si + 4 KMnO4 = 3 SiO2 + 4 MnO2 + 2 K2O

Using a ratio of 3 gives a nice firey reaction and using a ratio 1 gives a slower reaction that can melt through steel.

[Edited on 23-4-2023 by Conure]

Admagistr - 23-4-2023 at 07:51

Quote: Originally posted by Conure  
Does anyone know the equation for a dry reaction of Si+KMnO4?

The equation below gives a stoich ratio of 7.5 which gives a weak and incomplete reaction. This indicates that there is too much KMnO4.
3 Si + 4 KMnO4 = 3 SiO2 + 4 MnO2 + 2 K2O

Using a ratio of 3 gives a nice firey reaction and using a ratio 1 gives a slower reaction that can melt through steel.

[Edited on 23-4-2023 by Conure]


May be: 4 KMnO4+5Si=K2SiO3+4 MnSiO3+ K2O







[Edited on 23-4-2023 by Admagistr]

B(a)P - 23-4-2023 at 14:02

Can you test the properties of your reaction products?

Hey Buddy - 23-4-2023 at 19:43

If the reaction products are known, you can determine exactly the highest energy possible by using Jains pyrotechnic valence method. It works by addressing each element in fuel and oxidizer according to the valence number of its final product, post reaction. Then from that, the optimum mixture can be exactly calculated, for highest possible energy. It's very accurate. It was developed for use in the petroleum industry to analyze fuel combustion mixtures but works so well it can be applied to anything. Formulations like ANFO and black powder are replicated exactly. I have run patent pyrotechnic mixtures through the equation and many times the patent ratios they file for are precisely the calculated percentages.
Mn is the tough one, I'm not exactly sure what its final valence would be or I would just calculate it for you. This is probably one where testing the old fashioned way is best.
Antimony and KMnO4 64%/36% is used as delay mixture in firing trains. I find Si produces a slag easily if that's desirable.

There's also the shaw thermite tables in the thermite thread. Cant recall if KMnO4 is in the tables as oxidizers, it might be in there.

Regardless, pyro valence technique is described in "Chemistry of Pyrotechnics", John Conkling pretty straight forward. I highly recommend. It makes mixes easy and works with covalent explosives and binder mixtures too. It starts on page 32 on this pdf.


Attachment: Chemistry_of_Pyrotechnics_Conkling.pdf (3.6MB)
This file has been downloaded 321 times

Conure - 24-4-2023 at 11:05

Quote: Originally posted by B(a)P  
Can you test the properties of your reaction products?

I dont have any lab equipment so it would have to be very simple tests, if you have any ideas. Btw the end products look like black glass. Perhaps it's SiO2 mixed with MnO2.

metalresearcher - 24-4-2023 at 12:32

Si 'metal' can easliy be made from mixing finely divided silica sand with Mg powder :

2Mg + SiO2 => Si + 2MgO
48.6 60

Use a 48:60 == 4:5 stoichiometric mixture.

Igniting with a simple small propane torch works. The reaction proceeds rather slowly but gets very hot. The result can be dissolved in aqueous HCl which dissolves the MgO, leaving black or dark gray Si behind. That can be used to react with KMnO4. Interesting to try it out.

Laboratory of Liptakov - 24-4-2023 at 12:59

Very interesting methode for preparation Silicon. Thanks for sharing....:cool:
Silicagel is relatively pure SiO2, it should by works.

[Edited on 24-4-2023 by Laboratory of Liptakov]

Admagistr - 24-4-2023 at 13:14

Quote: Originally posted by Laboratory of Liptakov  
Very interesting methode for preparation Silicon. Thanks for sharing....:cool:
Silicagel is relatively pure SiO2, it should by works.

[Edited on 24-4-2023 by Laboratory of Liptakov]


The production of silicon from SiO2 by reduction of Mg is a very well-known and old procedure, I have a German book from the period of World War II and it is already described there...It is not a specialty, but rather the silicon obtained in this way is not very pure,it does not matter for the mentioned purpose...;)

Conure - 24-4-2023 at 23:14

This is not a thread about extracting silicon you roly-pollies! :mad:

Admagistr - 25-4-2023 at 10:33

Quote: Originally posted by Conure  
This is not a thread about extracting silicon you roly-pollies! :mad:


It's a thread about realizing the reaction you filmed on YT and that includes getting silicon powder...Not everyone is going to buy expensive silicon powder from a semiconductor manufacture,but people want to get silicon as cheaply as possible and preferably by themselves when they are doing practical chemistry. So don't insult anyone unnecessarily and don't bring emotions into the discussion on the Forum,which will do no good to anyone.It's counterproductive and will only provoke the same negative reaction in others...

Silicon Powder

MadHatter - 25-4-2023 at 13:29

I bought silicon powder for $9 per pound from my favorite pyrotechnics supplier.
It's -200 mesh and costs less than most other fuels.
https://www.fireworkscookbook.com


[Edited on 2023/4/25 by MadHatter]

B(a)P - 25-4-2023 at 13:45

Quote: Originally posted by Conure  
Quote: Originally posted by B(a)P  
Can you test the properties of your reaction products?

I dont have any lab equipment so it would have to be very simple tests, if you have any ideas. Btw the end products look like black glass. Perhaps it's SiO2 mixed with MnO2.


You could react it with hydrochloric acid and estimate how much MnO2 is present by observing the evolved chlorine gas. Try taking a small sample (sub gram) and grinding it finely, then slowly add HCl to your sample if it bubbles and you see a yellow gas then you know you have a decent quantity of MnO2 in your product. If you have peroxide you could do a similar test with that (add peroxide to a ground sample of your product), as MnO2 will decompose peroxide into water and oxygen. Try the peroxide test first if you have it, oxygen is obviously a lot friendlier than chlorine.

Admagistr - 25-4-2023 at 14:00

If the seller doesn't import it from China and possibly checks the purity,it's a perfect source,at least for members from the USA.A few days ago one of our new members wrote to me on U2U that he bought fake molybdenum oxide MoO3 on Aliexpress...It doesn't melt even at temperatures close to 1200C.I'll have X-ray spectrometry done,I wonder what it really is...

[Edited on 25-4-2023 by Admagistr]

Conure - 25-4-2023 at 20:40

Quote: Originally posted by B(a)P  
Quote: Originally posted by Conure  
Quote: Originally posted by B(a)P  
Can you test the properties of your reaction products?

I dont have any lab equipment so it would have to be very simple tests, if you have any ideas. Btw the end products look like black glass. Perhaps it's SiO2 mixed with MnO2.


You could react it with hydrochloric acid and estimate how much MnO2 is present by observing the evolved chlorine gas. Try taking a small sample (sub gram) and grinding it finely, then slowly add HCl to your sample if it bubbles and you see a yellow gas then you know you have a decent quantity of MnO2 in your product. If you have peroxide you could do a similar test with that (add peroxide to a ground sample of your product), as MnO2 will decompose peroxide into water and oxygen. Try the peroxide test first if you have it, oxygen is obviously a lot friendlier than chlorine.

The only H2O2 I have access to is 12%, would that be enough?

Herr Haber - 26-4-2023 at 04:44

Quote: Originally posted by MadHatter  
I bought silicon powder for $9 per pound from my favorite pyrotechnics supplier.
It's -200 mesh and costs less than most other fuels.
https://www.fireworkscookbook.com


[Edited on 2023/4/25 by MadHatter]


I have yet to find any "cons" to Si powder. I mostly used it as primer in colored compositions with Parlon as a binder. I found that most composition using acetone as a solvent are very dense (without pressing) and hard to ignite.
Si + KClO4 is just as good as a Mg ribbon in contact of the composition.

Many other fuels either dont give you the slag you desire when using Si or react to water, solvents or other components in the mixture.
Metallic fuels such as Al, Mg and apparently MgAl can react depending on the condition. Titanium and Zirconium seem less problematic.
I tried BKNO3 bound in NC on top of a composition. Besides the nice flame I've got nothing special to report. Besides , boron has it's own issues with oxygen.
The issue with metallic fuels is that even though they have superior heat output their reaction products have a low molecular weight and end up in the air, not in direct contact with the composition as I (wrongly maybe) imagine molten SiO2 used as a primer adhering to the falling star / crossette / etc.

May I ask OP, why chose KMnO4 as the oxydizer ?

Conure - 26-4-2023 at 08:03

Quote: Originally posted by Herr Haber  

May I ask OP, why chose KMnO4 as the oxydizer ?

Because I wanted to see how Si and KMnO4 react... This thread is not about pyrotechnics.

[Edited on 26-4-2023 by Conure]

Hey Buddy - 26-4-2023 at 08:23

Quote: Originally posted by Herr Haber  


Si + KClO4 is just as good as a Mg ribbon in contact of the composition.

Many other fuels either dont give you the slag you desire when using Si or react to water, solvents or other components in the mixture.


This is also what I find. Si/KClO4 is very hot and produces slag. If less slag/hotter conditions are needed, I've found TiH2/KClO4 makes a very hot incendiary with little slag. Id imagine Ti would be similar. It seems to fire out reaction products that ignite anything combustible around, but it doesnt gather slag at the reaction zone.

Si/CaSO4 from 30-70% Si is apparently also a decent delay composition.

woelen - 26-4-2023 at 10:31

The OP wants to discuss the specific reaction between KMnO4 and Si, let's try to stay close to this subject.

I myself think that the observed reaction strongly depends on the ratio at which KmNo4 and Si are mixed, and I even think that many different reactions occur at the same time. Solid-solid reactions seldomly are just a single reaction.

The manganese can end up in many different oxidation states, most likely +4 and 0. Maybe +2 and +3 as well. If a large amount of Si is used, then it may go down to 0.
In order to find plausible reaction equations, just work with pure oxides and Mn, so use K2O, MnO, Mn2O3, MnO2 and SiO2 as reaction products. K2O will combine with SiO2 to K2SiO3 (silicate), with MnO2 to K2MnO3 (manganite) and with Mn2O3 to KMnO2 or K3MnO3. The mix will be a complicated one.

Admagistr - 26-4-2023 at 10:56

Quote: Originally posted by woelen  
The OP wants to discuss the specific reaction between KMnO4 and Si, let's try to stay close to this subject.

I myself think that the observed reaction strongly depends on the ratio at which KmNo4 and Si are mixed, and I even think that many different reactions occur at the same time. Solid-solid reactions seldomly are just a single reaction.

The manganese can end up in many different oxidation states, most likely +4 and 0. Maybe +2 and +3 as well. If a large amount of Si is used, then it may go down to 0.
In order to find plausible reaction equations, just work with pure oxides and Mn, so use K2O, MnO, Mn2O3, MnO2 and SiO2 as reaction products. K2O will combine with SiO2 to K2SiO3 (silicate), with MnO2 to K2MnO3 (manganite) and with Mn2O3 to KMnO2 or K3MnO3. The mix will be a complicated one.


Hi Woelen,what do you personally think of the equation I suggested above:
4 KMnO4+5Si=K2SiO3+4 MnSiO3+ K2O
Could this be one of the reaction branches of this reaction?Surely K2MnSiO4 would also be formed if it is stable under the given conditions,that's why I preferred to write MnSiO3 and K2O separately in the equation,but in practice there will be a lot of products including various manganese oxides,manganates,...

Hey Buddy - 26-4-2023 at 14:31

Quote: Originally posted by woelen  

I myself think that the observed reaction strongly depends on the ratio at which KmNo4 and Si are mixed, and I even think that many different reactions occur at the same time. Solid-solid reactions seldomly are just a single reaction.

The manganese can end up in many different oxidation states, most likely +4 and 0. Maybe +2 and +3 as well. If a large amount of Si is used, then it may go down to 0.


This is correct and it is likely there will be parallel reactions going on with one taking the lead depending on how intense the reaction is. --This is why it's difficult to speculate the valence of Mn with accuracy. I believe you would have to determine this by measuring products to be exact.
--In terms of a narrowing it down, I can only say with certainty that Si itself becomes SiO2 in oxidation under thermitic conditions. With a final valence of +4. Other materials that share this state of oxidation in the same thermitic conditions are: S, Ti, and Zr. If you cant find a measured reaction from Si/KMnO4 in literature, you may find a KMnO4 oxidized reaction with one of those other materials. The pathway would likely be analogous because their final valences are equal.

B(a)P - 27-4-2023 at 02:00

Quote: Originally posted by Conure  
Quote: Originally posted by B(a)P  
Quote: Originally posted by Conure  
Quote: Originally posted by B(a)P  
Can you test the properties of your reaction products?

I dont have any lab equipment so it would have to be very simple tests, if you have any ideas. Btw the end products look like black glass. Perhaps it's SiO2 mixed with MnO2.


You could react it with hydrochloric acid and estimate how much MnO2 is present by observing the evolved chlorine gas. Try taking a small sample (sub gram) and grinding it finely, then slowly add HCl to your sample if it bubbles and you see a yellow gas then you know you have a decent quantity of MnO2 in your product. If you have peroxide you could do a similar test with that (add peroxide to a ground sample of your product), as MnO2 will decompose peroxide into water and oxygen. Try the peroxide test first if you have it, oxygen is obviously a lot friendlier than chlorine.

The only H2O2 I have access to is 12%, would that be enough?


Yes MnO2 will decompose 12% peroxide.

woelen - 29-4-2023 at 09:57

Quote: Originally posted by Admagistr  

Hi Woelen,what do you personally think of the equation I suggested above:
4 KMnO4+5Si=K2SiO3+4 MnSiO3+ K2O
Could this be one of the reaction branches of this reaction?Surely K2MnSiO4 would also be formed if it is stable under the given conditions,that's why I preferred to write MnSiO3 and K2O separately in the equation,but in practice there will be a lot of products including various manganese oxides,manganates,...

This could be one of the possible outcomes of the reaction. Whether you get K2MnSiO4 or K2O + MnSiO3 hardly is relevant in this kind of solid-solid reactions. How clear is the distinction between K2O+MnSiO3 and K2MnSiO4? There may even be different crystal lattices corresponding to the same empirical formula, depending on the temperature of formation. Really hard to say in this kind of reactions.

Admagistr - 29-4-2023 at 11:25

Quote: Originally posted by woelen  
Quote: Originally posted by Admagistr  

Hi Woelen,what do you personally think of the equation I suggested above:
4 KMnO4+5Si=K2SiO3+4 MnSiO3+ K2O
Could this be one of the reaction branches of this reaction?Surely K2MnSiO4 would also be formed if it is stable under the given conditions,that's why I preferred to write MnSiO3 and K2O separately in the equation,but in practice there will be a lot of products including various manganese oxides,manganates,...

This could be one of the possible outcomes of the reaction. Whether you get K2MnSiO4 or K2O + MnSiO3 hardly is relevant in this kind of solid-solid reactions. How clear is the distinction between K2O+MnSiO3 and K2MnSiO4? There may even be different crystal lattices corresponding to the same empirical formula, depending on the temperature of formation. Really hard to say in this kind of reactions.


Thanks for the answer.You are right,it makes no sense to distinguish in a solid phase reaction how the K2O is incorporated into the crystalline lattice of the silicate and whether it is fully or partially incorporated and what the modification of the resulting compound will be.It has no effect on the equation to find the best ratio of reactants and the K2O will be present anyway...

clearly_not_atara - 29-4-2023 at 12:58

The most vigorous reaction is most likely:

2Si + 4KMnO4 >> 4MnO2 + 2K2SiO3 + O2

Further reduction of MnO2 likely is rather sluggish. Decomposition of KMnO4 in an acidic rxn mixture at high temperatures is very likely to evolve some oxygen.

woelen - 1-5-2023 at 05:26

I agree that there is a good chance that some oxygen is formed, but this is a loss of energy. Oxygen is quite energetic and I personally think that among the most energetic reactions one will find the following:

3 Si + 4 KMnO4 --> 4 MnO2 + 2 K2SiO3 + SiO2

At places, where there is no perfect mixing, and some KMnO4 is present without nearby Si, certainly some O2 will be formed, but this loss of O2 makes the reaction less energetic. If mixing would be really perfect and no O2 would be formed at all, then the reaction would be even more energetic.



[Edited on 1-5-23 by woelen]

Conure - 23-5-2023 at 02:29

Quote: Originally posted by B(a)P  
Quote: Originally posted by Conure  
Quote: Originally posted by B(a)P  
Quote: Originally posted by Conure  
Quote: Originally posted by B(a)P  
Can you test the properties of your reaction products?

I dont have any lab equipment so it would have to be very simple tests, if you have any ideas. Btw the end products look like black glass. Perhaps it's SiO2 mixed with MnO2.


You could react it with hydrochloric acid and estimate how much MnO2 is present by observing the evolved chlorine gas. Try taking a small sample (sub gram) and grinding it finely, then slowly add HCl to your sample if it bubbles and you see a yellow gas then you know you have a decent quantity of MnO2 in your product. If you have peroxide you could do a similar test with that (add peroxide to a ground sample of your product), as MnO2 will decompose peroxide into water and oxygen. Try the peroxide test first if you have it, oxygen is obviously a lot friendlier than chlorine.

The only H2O2 I have access to is 12%, would that be enough?


Yes MnO2 will decompose 12% peroxide.

I dripped some H2O2 on the products and started bubbling. (but that also happened when the luquid hit the steel plate beneth it.) The products left some brown foam after the bubbling.