Sciencemadness Discussion Board - Flash powder peak pressure and propellant use?

Flash powder peak pressure and propellant use?

testimento - 1-1-2014 at 18:39

I was trying to find data for ClO3/4 + Al based flash powder compositions and their peak overpressure statistics, but I couldnt't find any relevant data. What I'm looking for is a comparison between black powder, flash powder and nitrocellulose. I'm aware that chlorate fuel oil compositions and ANFO have 50-100kbar peaks and high explosives like ETN PETN RDX go for 350kbar.

I heard a source that chlorate flash compositions and black powder wouldn't actually other than rarely and in large amounts cross 1kbar threshold. Therefore, even common flash power could be used as a limited use substitute for propellant. I'd be interested to test out a microscale mortar to find out what'd it do.

Ral123 - 1-1-2014 at 20:32

ANFO 50-100kbars? More like 10 I'd say. I believe the flash would generate high peak pressures at first, but the Al2O3 will condense down the barrel and the pressure would drop.

Praxichys - 2-1-2014 at 09:37

Both black powder and flash powder vary wildly in performance based on the concentration, particle size, and powder density of each compound. It is therefore difficult to classify one over the other in terms of peak pressure.

However, what RAL says is true in that black powder will likely outperform flash powder for use as a propellant simply because the flash powder has no gaseous reaction products at ambient temperature.

Pure ANFO comes in at 20-25kbar and 3000-4400m/s depending on prill density.

Performance characteristics are also highly dependant on the explosive's form factor and how it is initiated. Consider modern double-base smokeless powder, made of nitrocellulose and nitroglycerin, both of which come in at over 200kbar. However, the SAAMI pressure for a typical rifle cartridge is around 4kbar.

Also consider the application. A spritz of hairspray can throw a potato 50m while staying under the 0.2kbar burst pressure of the PVC pipe, and having about the same energy as a 9x19 pistol bullet which launches with 170 times the pressure.

Ral123 - 2-1-2014 at 10:10

I'm not saying the flash is weak, I'm saying it would put unnecessary strain and wear to the barrel and chamber and still not deliver much of an improvement. And who wants a blinding flash on each shot. They are investing a lot in developing propellants to be flashless and smokeless.

DubaiAmateurRocketry - 2-1-2014 at 10:41

Flash powder as a propellant ? Never try that, even propellant with binders can explode, flash powder will just destroy the engine.

Bert - 2-1-2014 at 15:09

70:30 flash powder tends to destroy fireworks mortars and/or rocket casings. Pressure rise is too fast, and permanent gas usually too small for what you say you want to do. If you seriously want an Aluminum fueled rocket, you might try Manganese dioxide-Aluminum.

Stage concussion mortars are very well made, and use flashpowders carefully tailored NOT to destroy them- fuel & oxidizer materials and particle sizes, oxidizer:fuel ratios are different than those you'd use for an aerial or ground salute.

Ral123 - 2-1-2014 at 15:39

Happy to see Bert not criticising us for even thinking such a thing.
Is there such a thing as a non aluminium fuelled rocket, except the most amateur sugar/BP?

Bert - 2-1-2014 at 17:58

I've seen very long burn time end burners made with ammonium nitrate/Magnesium. Coat the Mg appropriately and don't try to store them long.

You can make composite fuel engines with amorphous Boron instead of Aluminum, if you're well funded- Or without if you're willing to lower performance.

Zinc/Sulfur has been used- Kind of dangerous and fairly low Isp though.

If you include hybrids, using slug of cellulose as a fuel grain with nitrous oxide has decent Isp.

I'm sure we can come up with other combinations, but you'll have to settle for 2 out of 3: cheap, easy or stable...

Ral123 - 2-1-2014 at 20:10

What's so dangerous in zinc/sulphur? What improvement will Mg give over Al? I didn't know you can make stable rocket fuel with AN.

Turner - 2-1-2014 at 20:13

I've never been able to ignite a Nitrate salt and Al mix. Nitrates and Mg can burn though.

Ral123 - 2-1-2014 at 20:14

And I've heard they do it on their own

testimento - 2-1-2014 at 21:16

Hmm.. I see.

How about chlorate/perchlorate + charcoal? Any good common mixture that gives a nice kick to a bulk from a pipe or barrel without destroying it all.

And this is just mostly hypothetical question for mortar type device.

You need to remember that I'm the guy who lives in a country where there are no chemical, pyrotechnic or any other shops that deliver even common chemicals, because everything is highly illegal in here.

[Edited on 3-1-2014 by testimento]

Bert - 3-1-2014 at 08:48

Quote: Originally posted by Ral123

And I've heard they do it on their own

Lots of fireworks factories and munitions plants have been destroyed by careless use of Mg.

If you coat the Mg with linseed oil and allow it to dry, it is somewhat protected and may be used in nitrate mixes. The Mg mixes usually don't store very long even with the polymerized oil coating, and the oil coating is not sufficient for protecting the metal in a perchlorate mix. Also, when oils polymerize (dry) they develop heat- so this must be done in thin layers, well spread out.

Adding Mg or high Mg alloys to a hot Potassium dichromate solution will coat the metal with a dichromate layer, this is good enough protection for ammonium perchlorate mixes MADE WITHOUT WATER DURING PROCESSING. Ammonium perchlorate/sulfate/Magnesium strobe stars bound with nitrocellulose lacquer can be made this way. Dichromate is hexavalent chrome, a carcinogen, toxic, environmental hazard. Not to be done carelessly.

Quote: Originally posted by testimento

Hmm.. I see.

How about chlorate/perchlorate + charcoal? Any good common mixture that gives a nice kick to a bulk from a pipe or barrel without destroying it all.

Chlorate analogues of black powder were tried as propellants as soon as these chemicals were available. There was a famous accident with several fatalities at the French royal powder mill at Essone in the 1700's from the attempt by Berthelot to use Potassium chlorate for black powder manufacture in a stamp mill...

Chlorate or perchlorate with charcoal have been used as BURST CHARGES in a LOT of oriental fireworks shells. The Isp is higher than nitrate versions but the pressure exponent is also higher, these tend to destroy mortars too. I have used the perchlorate version in stage concussion mortars, the chlorate version was popular in the 1800's for large firecrackers before Aluminum powder became cheaply available.

A rocket propellant made from potassium perchlorate and asphalt (called Galcit) was used by the USA during WWII in weapons.

http://www.nakka-rocketry.net/propel.html

If you're trying to make a gun propellant with higher Isp than Potassium or Sodium nitrate black powder, Ammonium nitrate/charcoal (amonpulver) has similar performance of smokeless powder. But the nitrate undergoes a change in crystal form (and crystal SIZE) at 32 C, cycling the storage temperature across this point will cause your fuel grain to crumble, increasing the surface area/burn speed and most likely leading to a catastrophic failure of rocket casing or gun barrel...

Are you yet getting the idea that there's a good reason the most commonly used propellants are formulated as they are? I remember very well learning these things the HARD WAY as a teenager back before the Internet made it easier to get pyrotechnic texts.

Having to make your own chemicals from "over the counter" consumer goods will take longer but cause you to learn far more about chemistry and lab techniques than just buying finished goods. It may be frustrating, but you will be a better technician for the experience.

Sent from my iPhone
(Christ. Do you have any idea how long that took on a smart phone?!)

[Edited on 3-1-2014 by Bert]

Ral123 - 3-1-2014 at 11:42

So the stable organic nitrates are as safe to be mixed with metals as KNO3, AN etc?

Bert - 3-1-2014 at 12:05

Quote: Originally posted by Ral123

So the stable organic nitrates are as safe to be mixed with metals as KNO3, AN etc?

You can't make a blanket statement on that. Way too many possibilities.

And safety of fuels mixed with inorganic nitrates has way too many variables to be assumed as "safe" either- You need to proceed case by case. Treatment of the mixture as water binding, resulting ph of mixture etc. will vary safety yet again.

Get a good referance such as Takeo Shimizu's Fireworks: The art, Science & Technique or Alexander Hardt's Pyrotechnics. And keep any experiments small...

Ral123 - 3-1-2014 at 12:30

I guess high quality stabilised PETN/NC/RDX/DEGDN can be mixed with Al/Ti. But I'm still far from trusting such mixtures.

testimento - 3-1-2014 at 21:21

So what would be the balanced equation with KClO4 + C? With black powder it'b be following:

10KNO3 (s) + 3S (s) + 8C (s) → 2KCO3 (s) + 3K2SO4 (s) + 6CO2 (g) + 5N2 (g)

I suppose that the C would burn to CO2 so that it'd be so:

KClO4 + 2C = KCl + 2 CO2

So it'd be at 138.5 grams of KClO4 and 24 grams of charcoal to produce 74.5 grams of KCl and 88 grams of CO2. That is, in volume 44 liters of CO2, and the mixture volume would be around 100mL, the volumetric increase would be 440 times.

Or them I made a mistake and everything above is BS.

Bert - 4-1-2014 at 06:52

Balanced equations frequently do not represent either optimal performance in pyrotechnics and propellants OR real world results. For example, you may have better propellant performance (higher velocity) from a larger volume of CO and a little less heat than from a smaller volume of CO2 and a little more heat-

The analyzed result of burning black powder is somewhat different from your equation, there are a bunch of side reactions going on. And the ballance shifts, depending on the degree of confinement the powder was burned at as well.

55.91% solid products (in decending order of quantities)
K2CO3, K2SO4, K2S, S, KNO3, KSCN, C, NH4CO3,

42.98% gaseous products (in decending order of quantities)
CO2, N2, CO, H2S, H2, CH4, H2O

Common ratios used for BURST POWDERS from Shimizu:

Potassium chlorate bursting charge, H3

Potassium chlorate 75%
Hemp coal (or Pawlownia coal) 25%
Glutinous rice starch +2% (Additional percent) (I have substituted dextrine)
(Or a ratio of chlorate to hemp coal of 10:3 is also popular)

Potassium perchlorate bursting charge, KP

Potassium perchlorate 70%
Hemp coal (or Paulownia coal) 18%
Sulphur 12%
Glutinous rice starch +2% (Additional percent)