Stoichiometry and optimum ratio of reactants

[Pyrophoric]

Having recently made KClO3 quite successfully by electrolysis (another story) I was looking around for some basic compositions on the PFP that would give results indeed proving that I had made KClO3....I found three charcoal/sulfur/chlorate mixtures listed - all with quite different reactant ratios. I simply chose one, specifically KClO3:60% S:30% C:10% I was quite unimpressed by the burn rate of this comp produced by mixing the reactants that had beforehand been crushed by a spoon. The mix also had much residue left over after burning, however it did explode when given a firm whack with a hammer. I decided that this mixture could be improved.

So in an effort to optimise the mixture I assumed the greatest amount of energy would be released when the products of the reaction consisted of CO, KCl, SO2 - that is species with the highest possible inter-atomic bond strength. [Not knowing the exact bond enthalpies I may be wrong! Can someone correct me on this?]
Using this information I came up with a few equations describing the mass ratio of the reactants required to produce only the before mentioned products (not in any particular ratio though). Below is a table of selected values taken from the graph generated from the equations. An infinite number of combinations are possible by basically varying the ratio of carbon to sulfur. X is just an arbitrary value used to define different mole ratios. Ratios are expressed as a fraction of unity.

graph can be found here (http://www.geocities.com/pyrophoric_me/KClO3z.gif) (right click and save as)

Equation(s):
(18x-36)/(79x+12)=y (1)
(48)/(79x+12)=y (2)
(61*x)/(79x+12)=y (3)


x.............Carbon....Sulfur.....KClO3
---------------------------------------------
2.0..........0...........0.28235..0.71765
3.0..........0.07229..0.19277..0.73494
4.0..........0.10976..0.14634..0.7439
5.0..........0.13268..0.11794..0.74939
6.0..........0.14815..0.09877 0.75309
7.0..........0.15929..0.08496..0.75575 <=chosen mix
8.0..........0.1677....0.07453..0.75776
9.0......... 0.17427..0.06639..0.75934
10.0........0.17955...0.05985..0.7606
11.0........0.18388...0.05448..0.76163
12.0........0.1875.....0.05.......0.7625
13.0........0.19057...0.0462....0.76323
14.0........0.1932.....0.04293 0.76386
15.0........0.19549...0.0401....0.76441
---------------------------------------------

You can see the mix ranges from zero carbon and a large quantity of sulfur, to (when x = infinity) zero sulfur and a large proportion of carbon. Change in enthalpy is going to be increasing as x increases due to a greater proportion of the fuel being in the form of carbon. I simply picked one result which "looked" like it still had enough sulfur to catalyse the reaction, while still maintaining a large portion of carbon - which is going to release more energy per atom of oxygen than sulfur. This assumption had to be made as there is no other way, other than by experiment to determine which is the optimum tradoff between reaction rate and change in reaction entahlpy. The measured reactants were crushed up with the back of a spoon and mixed. The resulting meal powder burnt MANY times faster than the original comp (couldn't get a quantitative measurement as only was a 2 gram sample) it infact flashed like fine grain commercial black powder and left very little residue (just a thin white coating). Surprisingly this mixture, despite it's fierce burn rate, failed to explode when struck with a hammer - only quietly deflagrated - probably due to comparatively low sulfur content. If I ever get around to it I might measure the burn rates of some other points on the graph to find the optimal value. Both test mixtures were made from the same batch of chemicals and all reactants were measured down to 1/10mg.

After the success of my method of analysis I then tried it on KNO3/S/C mix (black powder)

Graph here (http://www.geocities.com/pyrophoric_me/KNO3z.gif) (right click and save as)

Equation(s):
(30x-72)/(131x+24)=y (1)
(96)/(131x+24)=y (2)
(101x)/(131x+24)=y (3)

x...........Carbon.....Sulfur......KNO3
--------------------------------------------
3.0.........0.04317..0.23022..0.72662
4.0.........0.08759..0.17518..0.73723
5.0.........0.11487..0.14138..0.74374
6.0.........0.13333..0.11852..0.74815
7.0.........0.14665..0.10202..0.75133 <=common formulation :D
8.0.........0.15672..0.08955..0.75373
9.0.........0.16459..0.0798....0.75561
10.0.......0.17091..0.07196...0.75712
11.0.......0.17611..0.06553...0.75836
12.0.......0.18045..0.06015...0.7594
13.0.......0.18413..0.05559...0.76028
14.0.......0.1873....0.05167...0.76103
15.0.......0.19005..0.04827...0.76169
---------------------------------------------

To my surprise one of my datapoints matched very closely to the common 75:15:10 mix.

Now you may be asking what the purpose of all these graphs were? Well if you had a composition from a database that could not be fitted to graph generated for that mixture you would know that the products of the reaction cannot be solely the products with the highest possible bond enthalpies used to generate the graph. Hence the mixture is not optimised, as some of the energy generated during the reaction would be going into decomposing/vaporising material that would not add to the energy produced during the reaction. We can see that a common formulation for blackpowder agrees very well with the graph and therefore it must be close to optimal. These graphs would also simplify the task of finding the optimal ratio as only one vaiable has to be changed - namely x. The original composition pulled from the PFP database does not even approximate the graph at any point and therefore it must be quite far from optimal.
It would be interesting to see how the overall change in enthapy ranges as the mixture varies (need data for that).
Now all we need is a way to predict rate of reaction and we could predict the optimum mix for any reactants!

Apologies if this was all a waste of time.

[Bert]

1. What do you intend to DO with the mix. If you're making a chlorate "gunpowder" for small shell burst, firecrackers or end burner rocket fuel, you're on the right track. Stars are tuned for the visual effect, not the optimum ingredient ballance for maximum gas generation with fastest burn rate. Guns don't do well with chlorate propellants, don't go there!

2. Ever heard of triangle diagrams? These are a quicker, more intuitive way to apprehend the effective zone for a 3 part composition such as you're playing with.

[T_Pyro]

What are the advantages of a chlorate "BP" over the conventional BP, if any? I'd guess that it'd be more energetic, but also more dangerous! I remember reading somewhere that chlorate-based rocket fuels only work for very strong-walled rocket motors, because they tend to explode if they aren't strong enough.

It's just my personal opinion, but I'd save my chlorate for coloured stars, since (having to prepare it by electrolysis,) I value it more than potassium nitrate.

[Guerilla]

H3 is noticeably more powerful than BP as far as the burn rate is concerned and compared to good BP it takes minimum effort to prepare. It is also one of the least sensitive chlorate burst comps out there..

As for rockets, I've had better results with using a liquid binder/fuel (such as Epoxy) and preferably launched soon after casted to prevent fuel cracks. Still, most of the chlorate rockets I've tried have blown into pieces right after ignition..something I don't enjoy seeing after spending weeks electrolyzing chlorate.

[poor man]

H3 is noticeably more powerful than BP as far as the burn rate is concerned and compared to good BP it takes minimum effort to prepare. It is also one of the least sensitive chlorate burst comps out there..


H3, I also find to not need very intimate mixing, and even when only rolled together by the diaper method, burst quite fast. But while it is one of the least sensitive Chlorate burst comps, it is still quite sensitive to shock and friction. A friend, a while ago, not being well informed of the dangers of chlorate mixes, ground very pure ingredients of KClO3 and Charcoal in a mortar and pestle. It was OK for a few minutes, but as soon as he felt safe with it, he ground it like he would any insensitive composition. It went up in his face engulfing his head. Sure he was OK after a week or so, but I hate to think of adding sulfur to the mix! H3 is a fast burning comp on its own, unless for gaseous output, the sulfur is not really necessary, and will cause the compostion to become very sensitive to friction.

[markgollum]

Well, if you are finding that your chlorate compositions aren’t burning as fast as you expected them to, it might be because your chlorate isn’t very pure.
The first few times I made potassium chlorate, it was of pretty poor quality, it would burn a lot slower than BP, and leave considerable residue, so my opinion of it wasn’t very high. But then one day, I decided that I wanted to do some impact sensitivity tests with it, and recrystalized it from boiling water. Then I made up a little 75/25 KClO3/sucrose mix and lit it, well, it burnt a lot faster than it had ever burnt before, (pretty close to my BP) and now I have a much higher opinion of it.
By the way, mixing a chlorate and sulfur together is dangerous IIRC.

PS When I can dig a hole in the ground (its frozen right now), I am going to do some tests in which I attempt to detonate a mixture of potassium chlorate, and a fuel(s) in which the fuel is not a nitrated organic compound.

[nesler]

I have some doubts about being able to detonate a chlorate-based mix, but I perhaps that doubt might be mitigated by the fuel that you'll be using. What were you planning on using as a fuel?

[kingspaz]

if he uses a detonator then the chlorate/fuel mix will be detonable if very finely powdered. if he attempts to detonate it with a fuse then it will be a simple deflagration.

[markgollum]

Well, the reason that my tests will be done withought nitro compounds is that I can no longer get battery electrolyte, due to the fact that the battery businesses around here have been fined for selling it, and have been told that it is illegal for them to sell it anymore. :( :mad:
And yes, I will preform the tests with a home-made detonator (usually 2.5g of pressed HMTD in a slurpee straw).
As far as the composition go, the ones that I am considering are as follows:

(1) KClO3/ C12H22O11 (75% chlorate)
(2) KClO3/C12H22O11/CH3OH (I am hoping that the methanol will desensitise it a bit)
(3) KClO3/CH4N2O(urea)
(4) KClO3/ C12H22O11/either ethylene glycol or glycerol

I haven’t yet decided what I am going to set the OB at, so that’s why I haven’t included the ratios (OB will probably be slightly negative for power IIRC).

The reasons that I chose these fuels, is that according to my calculations (bond energies were used for urea) they exhibited one or more of these two things.

(1) An exceptionably large amount of thermal energy output per oxygen used to combust them, for a non-metal (especially the urea and methanol, 223.17kJ and 225kJ per ½ O2 respectively).

(2) An exceptionably large number of moles of gas produced per oxygen used to combust them (especially the sucrose).

[Marvin]

Pyrophoric,

Using chlorates and sulphur together is suicidal, and I'm very surprised Bert didnt mention this. There are long term stability problems. Some star compositions together with antacids are more stable, but as a rule, if you are going to use chlorates you should not use sulphur.

Chlorate+Carbon, as in H3 is pretty stable, much faster than gunpowder and about as safe as chlorate mixtures get. One fact often overlooked is becuase it is only a 2 componant mixture, it is a lot less sensitive to the processing than BP, and so people instantly achieve an improvement with little effort. The optimum ratio of Potassium chlorate to carbon is neerly stoichiometric for CO, neer enough what you expected. The mathematical goal isnt complete combustion or maximum bond energy, its maximum total energy released for a given amount of mixture.

Crushing the ingrediants with a spoon and mixing them will get you nowhere. The key to good blackpowder is the processing.

Additionally Id be very suspect of any method that got you the classic 75:15:10 mixture for blackpowder as optimum. Throughout the ages the mixture has gradually moved towards this ratio and we are left to assume by the textbooks it took 500 years for the right mix to be 'discovered'. In fact at each stage in history the mix used was optimum for the degree of processing and the quality of ingredients used. 75:15:10 almost certainly isnt optimum for most peoples home made black powder. The poorer the processing the more the mix leans towards fuel rich for best performance.

Making good BP, and also making decent BP easily, has been covered in detail, so its not worth my repeating information here.