28 replies to this topic

[Potassium chlorate]

I'll have a stab at this, please correct me if I'm wrong!.
1. potassium nitrate , 3 oxygen atoms decomposes at 400 oc
2 potassium chlorate ,3 oxygen atoms again decomps at 400 oc, but contains chlorine.
3 potassium perchlorate, 4 oxygen atoms , decomps 600 oc, again contains chlorine
my understanding is whilst the perc as more oxygen, the oxygen from the chlorate is more readily available at a lower temp , giving a cooler flame ideal for blues

and:

4. potassium chlorate, while one oxygen atom less than potassium perchlorate, has a higher percentage of chlorine

and:

5. potassium chlorate, aside decomposing at a lower temperature, also is more chemically instable overall, which makes it more willingly to react with other chemicals.

The dangerous and infamous potassium chlorate+sulfur gives the utmost colour depth together with barium nitrate, for instance. Only barium chlorate beats it.

Edited by Pyroswede, 27 September 2010 - 09:45 PM.

[vaslop2005]

I'll have a stab at this, please correct me if I'm wrong!.
1. potassium nitrate , 3 oxygen atoms decomposes at 400 oc
2 potassium chlorate ,3 oxygen atoms again decomps at 400 oc, but contains chlorine.
3 potassium perchlorate, 4 oxygen atoms , decomps 600 oc, again contains chlorine
my understanding is whilst the perc as more oxygen, the oxygen from the chlorate is more readily available at a lower temp , giving a cooler flame ideal for blues

Can I add a bit about potassium nitrate?

That it seems like a perfect oxidiser for blues here, but infact it gives off 2.5 oxygens per mol

2KNO3-->K2O+2.5O2 (or 5 O)
This is simplified...

But also, the whole idea is to join copper and chlorine in the flame... But with the stronger potassium oxide present, all the chlorine attaches itself to that instead...

That is the short version of what goes on... But hopefully understandable enough

[dr thrust]

whilst were on about chlorine content in oxidizers.
ive never been able to find much on the subject.
i know ap has 20% but what about the rest?
k chlorate?
k perchlorate?
barium chlorate?

[digger]

Also chlorate makes its chlorine more available for the production of chlorides in the flame. Chlorine donors are not always required with chlorates.

[digger]

whilst were on about chlorine content in oxidizers.
ive never been able to find much on the subject.
i know ap has 20% but what about the rest?
k chlorate?
k perchlorate?
barium chlorate?

Thats an easy one just multiply the number of chlorine atoms in the formula by 37.45 then divide by the molecular weight and multiply by 100. e.g. for AP 37.45/117.49 x 100 = 31.87%

[vaslop2005]

I could be wrong, but i dont think that either KClO3 or KClO4 give free chlorine at all,

KClO3-->KCl+1.5O2

KClO4-->KCl+2O2

but the lowered need for chlorine donors is that at the lower temperatures formed when chlorates decompose, allow the hydroxides to form (that also give colours in flames) where as in hight temp (perchlorate) flames, they decompose...

Edited by vaslop2005, 28 September 2010 - 10:46 PM.

[digger]

There must be something more going on than that.

The overall decomposition of potassium chlotate goes thus:-

4KClO3(l) → KCl(s) + 3KClO4(l) which then continues this KClO4(l) → KCl(s) + 2O2(g)

However this is what happens when you heat it in a test tube. The chemistry of pyrotechnic flames is much complex as you are aware. The only way to tell what is going on for real, would be by the use of a spectrometer. I am sure this work has been done, however I am too tired to pick up the books (maybe tomorrow).

D

Edited by digger, 28 September 2010 - 11:00 PM.

[digger]

OK could not help myself.

Just picked up Shimizu's FAST. Potassium chlorate decomposes thus at above 600C:-

4KClO3 → K2O + Cl2 + 5/2O2

So that accounts for the colour producing abilities of chlorate

Edited by digger, 28 September 2010 - 10:55 PM.

[MDH]

That doesn't explain why potassium nitrate cannot produce colors, even in the presence of both a strong chlorine donor and sulfur to neutralize the potassium carbonate in the flame.

[helix]

I could be wrong, but i dont think that either KClO3 or KClO4 give free chlorine at all,

KClO3-->KCl+O2

KClO4-->KCl+1.5O2

but the lowered need for chlorine donors is that at the lower temperatures formed when chlorates decompose, allow the hydroxides to form (that also give colours in flames) where as in hight temp (perchlorate) flames, they decompose...

I think your right as these are the combustion reactions that release the most energy. I think they both KClO3 and KCLO4 can be made to release chlorine but the reaction is not so great as the release of energy is less, ie

4ClO4+7C-->2K2O+7CO2+4Cl but only about a third as much energy is released compared to the preferred combustion, presumably this would lead to a direct reduction in flame temperature and reduce the brightness of the flame.

[digger]

I think your right as these are the combustion reactions that release the most energy. I think they both KClO3 and KCLO4 can be made to release chlorine but the reaction is not so great as the release of energy is less, ie

4ClO4+7C-->2K2O+7CO2+4Cl but only about a third as much energy is released compared to the preferred combustion, presumably this would lead to a direct reduction in flame temperature and reduce the brightness of the flame.

See above. Dr Takeo Shimizu says it does from spectral analysis showing strontium chloride in the flame without other chlorine donors.

[digger]

That doesn't explain why potassium nitrate cannot produce colors, even in the presence of both a strong chlorine donor and sulfur to neutralize the potassium carbonate in the flame.

True. But according to Shimizu potassium nitrate cannot produce a high enough flame temperature for the formation of colour. However he notes that coloured flame can be produced with the use of magnesium in the mix to raise the flame temperature.

[dr thrust]

Just wondering about strontium chloride after seeing it a few days ago in a flame test kit , I’ve never seen any formula containing it

Edited by dr thrust, 15 September 2021 - 11:16 PM.

[BlackCat]

I've never seen a formulation using it either and, if trying, I'd be very cautious.

 

The normal form is the hexahydrate which melts at 61 deg C and begins to dehydrate. Dehydration is complete at 320 deg C. The hexahydrate is very soluble in water at 106g per 100ml of water at 0 deg C and the pH of a 5% solution is acidic at 5. The anhydrous form does exist and is stable but will absorb moisture from the air to, eventually, become the hexahydrate.

 

The high water solubility would concern me for reasonable stability over a short period of time and the acidity of an aqueous solution may cause spontaneous ignition of compositions based on perchlorates and chlorates in particular. Spontaneous ignition is likely to be even more likely if the composition contains magnalium.

 

Hope that helps.

 

Personally, I've always wondered about bromides and organobromines instead of chlorine to enhance colours but they seem to be very difficult to get hold of and very expensive.

Edited by BlackCat, 17 September 2021 - 06:32 PM.