14 replies to this topic

[BlackSky]

I'd like to give a useful information. Actually, I already posted this previously in my friend Stuart's forum but I would like to re-post it here too.

Do you know From where these numbers came from for the BP ratio ? I mean 75:15:10 .

Well, I will explain in detail.

1st , As we all know that the BP reaction is as following:

2KNO3 + S + 3C => K2S + N2 + 3CO2

We need to calculate the atomic wieght for each part in the reaction to find the exact wieght needed to complete the reaction .
From the periodic table we have these atomic wieghts:
K=39
N=14
O=16
S=32
C=12

Now , we have to start calculating the atomic wieght for each part of the left hand side of the equation :
2KNO3 = 2*(39+14+3*16) = 202
S = 32
3C = 3*12 = 36

The total wieght for the left side = 202+32+36 = 270
So, the percentage of each part will be its wieght devided by the total wieght as following :
KNO3 = 202/270 = 74.8 ( We can Say it is 75 )
S = 32/270 = 11.85 ( We can Say it is 12 )
C = 36/270 = 13.3 (We can Say it is 13 )

So, It will be 75:12:13 / KNO3:S:C
This ratio is the optimum to complete the recation , But sometimes we have to increase the C and reduce the S to be 75:15:10/KNO3:C:S to make the reaction slower to be used in rockets, But the best that should to be used in explosives is the exact ratio above 75:13:12 .

I hope that I gave a useful info.

Edited by BlackSky, 12 September 2004 - 06:17 PM.

[BigG]

Fully agreed - this theory have nothing to do with reality.

First, as Daniel pointed out, there is no such thing as a perfect reaction, even when the reaction is a simple mix of two chemicals. Second, and even more important, - when those ratios were reached, there was no way to measure atomic weight. It was just a matter of trail an error.

Think of 75:15:10 to be a mark of history. There are mixtures that are a bit more optimal, but this has proved itself for so long, that it is an agreed number.

Still, some manufacturers do not use 75:15:10 (for example Estates, the makers of black powder rocket engine), but a ratio that is slightly different. 75:15:10 is easy to remember and produces great results.

[HighTemp]

And 1 little mistake:
3C = 3*16 = 36
I think it should be 3*12

[Richard H]

As far as I know the exact reaction is unknown, as there are many variables. The composition of charcoal and the volatiles it contains is somewhat complex.

[Stuart]

It is impossible for there to be an exact equation for the reaction, only a possible one based on the ease that different chemicals bond. One bit of BP will be different from the next and this is the same with most other chemical reactions.

The method BlackSky used to work out the ratios is valid to an extent, you need a lot of Potassium Nitrate to produce the oxygen required to burn all of the Charcoal and Sulphur.

I know this was not how it was worked out in the previous centuries and they did stumble across it by trial and error but the 75:15:10 is a very good ratio because it is almost stoichiometricly balanced for the most likely products of deflagration.

Carbon Dioxide will be formed as the Oxygen is the only real element there that will react with it well. Potassium Sulphide is formed as the Oxygen will be taken up by the Carbon and Nitrogen is a relatively inert chemical hence it forms mostly Nitrogen Gas leaving Potassium and Sulphur to do what it want.

Of course though, you will get lot of other products, if not hundreds along with the Potassium Sulphide, Carbon Dioxide and Nitrogen.

[lord_dranack]

Here's an approximate equation given in "The chemistry of Firerworks" from the RSC:

74KNO3 + 96C + 30S + 16H2O => 32N2 + 56CO2 + 14CO + 3CH4
+ 2H2S + 4H2 + 19K2CO3 + 7K2SO4
+ 8K2S2O3 + 2K2S + 2KSCN
+ (NH4)2CO3 + C + S
This is for 75.7% salpeter, 11.7% charcoal, 9.7% sulfur and 2.9% moisture.

It certanly gives some idea of how complex the burning is in reality, which as has been said is very complex.

[BlackSky]

Woooow

Too many replies

Anyway, I started posing that chemical equation as for a closed system reaction for a BP burning neglecting the external atmosphere effects (I mean this is an ideal reaction for the BP burning). As we know that the effect of the external materials like H2O has no much effect to the reaction if it in a closed case.
Mine was 75:15:10 while lord_dranack's was 75.7:11.7:9.7 +(2.9 for H2O vaipour).
If you are burning the BP in a closed system like inside a b**b case or a rocket case there will be no H2O vapour in that much to be within the reaction. So, The reaction will be almost ideal. I agree that there will be a little H2O and some other gases but their will be neglected as they exist in too small quantities and will not effect the huge amount of the main reaction materials like the C,S and KNO3.

May I ask a question ?
Why do you make simple things to be tooooooo complex ?

Thanks HighTemp, I've corrected the mistake. It was a typing mistake and you can see that the result was right.

Thanks Stuart for the details.

Thank you all for your useful info.s.

Regards to all of you.

Edited by BlackSky, 11 September 2004 - 01:22 AM.

[Stuart]

Doesn't matter if there is water in it or not, the actual reaction will still be a hell of a lot more complicated than that. To list a few products, you would get Nitrous Oxide, Nitrogen Oxide, Nitrogen Dioxide, Potassium Sulphate, Potassium Oxide, Sulphur Dioxide, Potassium Sulphite, Potassium Sulphide, Potassium Carbide, Potassium Carbonate, Potassium Thiocyanide, Carbon Monoxide, Carbon Dioxide to name some. There would be more products and probably some really strange ones where hotspots are formed.

Edited by Stuart, 11 September 2004 - 06:41 AM.

[BlackSky]

Moreover , if you did not fine the components of the BP then some of C and S will not react leaving some KNO3 and may notice that sometimes a white material left after burning the BP because of over oxidizing even if the ratio is mesured 100%. Also, if you burn it in an open air and the O2 in the atmosphere will be another oxidizing agent and you will notice this white material.
Truly , the reaction is much much complex if we want it to be complex but it also so simple if we don't bother ourselfs calculating everything !

I did not say that there is a water in the reaction sine the closed system reaction will prevent the water to enter the reaction. Do you believe that there is more than 2% of water in the reaction? I thing the reaction will be too bad and the rocket will stay at the ground looking for you and saying "Do you really want me to fly and my BP is wet !?".
As Mr.Daniel Scott said , if there is alittle wet in the BP the burn rate will be too slow.
Do you see that slowness of burning while you are launching your rockets or burning a dried BP ? This will answer the question if the water is exist in high percentage or not. One or two drops of water over the BP will kill your BP efficiency and I think one or two drops means less than 1% of 100 grams of BP. You can weight it to be sure. So, what about 2 or 2.9% . Do you think that it will be good ?!

Edited by BlackSky, 11 September 2004 - 06:06 PM.

[alany]

Hey you started this thread!

BP composition had been refined by experiments long before stociometry was devised.

Water /is/ the "magic ingredient" in BP, dry grinding and pressing produces a terriable product, and bone-dry BP is quite a bit slower than BP containing a bit less than 2% water. Charcoal is far from pure carbon, and the sulfur/carbon/potassium nitrate system is very complicated, with lots of lower order pathways that are crucial to the overall effect.

You sound like you have little experence with actually making and using BP. Please don't claim to understand BP, the truth is nobody really does, that is what makes it so special!

I've got several years experence with it and it still suprises me on a regular basis. It seems to do counter intutitive things all the time, especially when your charcoal feedstock varies as much as mine does.

[BlackSky]

Hay alany,

Did you see that I mentioned charcoal in any of my posts ?
I say C that is mean pure carbon.
Can you read well or need me to read for you. I said this is an ideal BP bruning and this means that we have pure components in a closed system ! And closed system means that therer is no external components allowed to be in the reaction except the main ingredients.

I've got several years experence with it and it still suprises me on a regular basis. It seems to do counter intutitive things all the time, especially when your charcoal feedstock varies as much as mine does.

There is no doubt to take several years for you to understand the BP and to be surprised when you don't know the principles of the BP. Please analy, Don't take it personally I was joking with you.

When using water as a binder then it should be dried completely since water is used to dissolve the KNO3 and then reach all the parts of the ration and also organize the structure of the components of the BP and the mission of water is then ended.

Regards

Edited by BlackSky, 12 September 2004 - 12:39 PM.

[BigG]

Blacksky - I think the main problem is that you titled the thread "Do you know why BP is 75:15:10?", and then suggested that the reason is because people modify the proportions to get a slower burning mixture. You presented it is the reason for which BP is 75:15:10, and that is simply wrong. IF you titled the thread - optimal BP ratio, and revised some of your post to suggest that there more optimal compositions then 75:15:10, you would have found that people are willing to take on the discussion.

[BlackSky]

Thanks BigG. I think you and Stuart the only two who understand what I am aiming to.
Well, I will change the title to be as you said.

Regards