Composite Propellants

[firetech]

Google the chems you want and look for a distributor. Otherwise go to skylighter.com. You can't find them anywhere because they have been taken off the immediate market by the government. Yeah, it sucks, but it's for safety purposes.

[TheSidewinder]

Firefox still sells a Composite Propellant kit. A good one, too.

 

http://firefox-fx.com/rocketry.htm

 

About 3/4 down the page.

 

Be sure and order extra Ammonium Perchlorate. When I bought this kit, I got 30 lbs extra: 15 lbs each of 90 and 200 micron.

 

The less expensive kit works just as well as the one costing $7.00 more, but I *think* the curing process takes more work. Read up on it.

[al93535]

Just testing some new propellant.....

[firetech]

That seems to burn remarkably slow for a propellant. How is APCP so efficient then?

[TheSidewinder]

Could be a burn without much nozzle confinement. And it was a short test, but looked good.

 

Can you share the formula, Al?

[dagabu]

Could be a burn without much nozzle confinement. And it was a short test, but looked good.

 

Can you share the formula, Al?

 

I used RC-Candy fuel almost exclusively but I used APCP from time to time also, we used Ammonium Perchlorate, aluminum 425 and 300 spherical, PVC, and Hydroxyl-terminated polybutadiene as the binder. My notes don't have the quantities, I will have to dig out my old hard drive if you want that.

 

D

[al93535]

I am trying 5 different formulations at the moment. I will have static tests and measure the thrust of them all within a month or so. When I have the best performer I will post the results.

[Yafmot]

If pressing of fuels with polymeric binders was such a hot idea, GD, Aerojet, Raytheon, Thiokol and everyone else would be doing it. It's not only unnecessary, but could be dangerous. CTPB is a lot less toxic than HTPB, and outgassing is one of the reasons they dont press it. A hard vacuum will densify this type of propellant and remove voids far better than pressure. I talked to a couple of old timers the other day. One was at China Lake in the old days. The other was at JPL & then Rocketdyne in the '50s and '60s. I also talked to an acquaintance of mine out at Aerojet. To a man, they scratched their heads & asked "Why the hell would anyone do that?" What I'm getting at is, don't try to reinvent the square wheel.

 

As for catalytically cured binders, if you're not satisfied with epoxies, I would suggest a vinylester system, such as the Dow "Derakane" series. One of the main reasons it is rarely used in aircraft primary structures is its flammability. Once the stuff gets going, it's difficult to extinguish. It would likely result in a more reactive fuel, albeit a little more expensive. You might also want to try Polyester. I don't mean Bondo. It's too thick to mix a lot of dry stuff in it. I mean the laminating/casting resin you get at the fiberglass supply. (Don't try to use it with Carbon fiber, by the way: It's too brittle to be a matrix for anything but glass.) This would also give a more reactive fuel than epoxy.

 

Many epoxy systems won't even burn on their own. They're formulated not to support combustion. In the case of vinylesters, make sure there is no flame retardant or other combustion inhibitor in it, for obvious reasons. Polyester, as stated above, is somewhat brittle, but there are tougheners that will help keep it from slivering.

 

And a word of warning. Almost all catalyzed systems are exothermic to some degree. Some extremely so. Hysol 9396, for instance, comes with a warning not to mix more than about a pound, or a fire will probably result. Every composites fabrication operation has its own litany of incidents where some idiot mixed too much, or loaded both monomer and catalyst into one side of the RTM machine & caused a disaster. Needless to say, too big a batch of propellant, or too much catalyst, and you're running a real risk of real trouble.

[gregkdc1]

If you don't mind I am going to bring up an old thread and would like to discuss vacuum degassing composite propellants. I recently attempted to make some swamp gas propellant and although I didn't calculate the density the grains were full of voids, so much so I don't dare put them in a motor. I then attempted to make a vacuum chamber out of the bottom of a plastic pressure cooker and a see through Pyrex lid. The problem I am having is that my compressor isn't powerful enough to operate my Harbor Freight venturi pump and it will only pull a pressure down to 21" Hg. How much of a vacuum do you need? I am going to try working with the propellant when it is hot (around 140 F) so that it is less viscous in hopes of it being pourable. This would also get the water in the propellant closer to its boiling point without a complete vacuum. I need a stronger pump but I am torn (the wife is getting irritated) with the price of buying a powered vacuum pump or a hand pump. Any ideas? The hand pumps seem to be able to pull a decent vacuum but their reviews indicate that they don't last more than a few times, or you can buy a decent hand pump for the same price as a low end powered pump. At what point do you over vacuum a propellant? I would hate to suck all of the DOA or something similar out of the propellant. Right now I am leaning toward buying this aspirator off of amazon. http://www.amazon.com/dp/B003OBYNBO/ref=dra_a_cs_ss_hn_it_P1400_1000?tag=dradis-20

There is a guy on you tube using one to boil water here

it seems strong enough. I cast in my back yard and have a pressurized irrigation system that has higher pressure and flow compared to most faucets, and the waste water can water the lawn. Last should there be a problem it would be nice to have a running hose handy. Any thoughts? Thanks Greg

[goldwingnut54]

Try Craigslist vacuum pumps. Try the following syntax

site:craigslist.org robinair no spaces until after the.org which makes it a nationwide search. 100 bucks or less oughta get you in to the 29+ inches of mercury range. You'll find a several tonight even.

 

The only drawback to this search is date of posting hiccups.

 

You might be able to borrow one from a farmer, to see if you can meet your parameters before throwing down a C-note. I have a Robinair 1550 you could borrow, if shipping weren't so high. They are fairly HEAVY.

 

Stan

Edited July 1, 2013 by goldwingnut54

[dangerousamateur]

25 Ammonium Perchlorate 90 micron down

45 Ammonium Perchlorate 200 micron

20 MgAl -200 mesh

3 Potassium Dichromate (not used as a "coating" in this case)

7 Barium Carbonate

--------------------------------------------------

100 parts total.

 

 

One question:

Why are sometimes two different mesh sizes of AP being used?

[Mumbles]

It allows some control of the burn rate.

[goldwingnut54]

Higher solids loading also. Image a gallon jar full of golf balls. Couldn't you load another 50 or 100 marbles? Then you could pour in hundreds more BB's, right?

 

Higher solids loading to binder ratio results in higher specific impulse. (More juice)

Edited July 10, 2013 by goldwingnut54

[dangerousamateur]

Higher solids loading also. Image a gallon jar full of golf balls. Couldn't you load another 50 or 100 marbles? Then you could pour in hundreds more BB's, right?

 

I agree. But how about leaving the golf balls out and only use the small stuff?

Wouldn't that have the same bulk density or am i making a mistake here?

[goldwingnut54]

No, not really a mistake, because the physics are counterintuitive.

 

Bigger granules = more weight.

 

Sometimes exaggerating the concept clears up matters. Let's say you could chisel out a perfectly shaped cube of Ammonium Perchlorate 12" X 12" X 12" and weight it. Then compare that weight to an identical volume of small granules (or any size granules for that matter). Which would weigh more?

 

Bigger granules weigh more than smaller granules, and that's a fact. It is what I call a barnyard physics lesson.

 

 

 

Here is a real-life barnyard physics example:

 

A bushel of wheat is a measure of volume, and the benchmark is 60 pounds per bushel (of Hard Red Winter Wheat). 60# per Bushel is like "Par" in golf. Wheat (individual berries) vary in size by year, mostly because of the weather conditions. And we're talking small amounts of variation here. It might take a second look by a city boy to tell the difference, but that second look will do. A bushel of 57# wheat is below par, and will cost the farmer. (Guess how I know?) Bigger BERRIES make for heavier bushels, E.V.E.R.Y single time...so long as berry size is the only variable. As a curious kid, I didn't believe it, but I was wrong.

 

When I used to run the farm, we had a variety of wheat called Early Premium (or Early Triumph) that had BIG fat berries that we always wanted to cut first, partly because would lay down in strong winds, but mostly because it might weigh up to 65 or even 66 pounds per bushel, which was a LOT more $$ in our pockets. But it did poorly once the rains came on that standing, fully ripened wheat. In other words you wanted to get it out of the field, ASAP, and harvest might last a couple of weeks or more. The rain "bleached" the reddish color of the berries a little and probably shrivelled them slightly, but once it rained it wouldn't go 65 pounds any longer. Our smaller berries of other various varieties might weigh only 60 or 61 lbs. Shriveled wheat on years or in fields that had some issue would weigh MUCH less.

 

Bigger berries = fewer berries per given volume, which resulted in heavier weight per bushel.

 

...EVERY time....

 

Back to propulsion: The particulates in a composite fuel formula is much more complicated than my simple example due to 1) having to actually MANAGE the physical mixing of the composition, 2) what Mumbles alluded to--"managing burn rate" which is complicated and has a lot of "rocket science" already settled, and 3) other considerations well beyond the scope of this forum.

 

And we are just talking about oxydizer here, there are also particulate considerations for fuel and burn rate modifiers. But it is a balancing act to get maximum solids loading (weight) and a managable mix. 2 or more particle sizes allow for filling up of the innerstices (empty spaces) left by the larger particles.

Edited July 12, 2013 by goldwingnut54

[gregkdc1]

Just a quick update about my vacuum degassing chamber. I bought the aspirator from Amazon, in spite of the fact that it is a piece of plastic that cost about $25 with shipping bugs me I am happy with it's simplicity and think it should last a long time as there aren't any moving parts to wear out.

Yesterday I hooked it up to my irrigation hose to see what kind of vacuum it would pull, and it only went to 23" of mercury. "WTH?" I thought, when it occurred to me that I should do some test to see if my gauge is working properly.

First I placed a warm cup of water in the chamber, pulled a vacuum and within minutes it was boiling. Great at least I should be able to vacuum hot propellant.

Next I placed some of the cold water coming out of the hose into the chamber. It took a little longer but the water did start to boil slowly. The temperature of the cold water was 67 degrees Fahrenheit. It has been a long time since any chemistry classes so calculating the pressure at this temp seemed daunting but luckily for me there are online calculators. If they are correct the pressure should have been around ½ psi or -28 inches of mercury. Is this correct? All the while the gauge never went above 22 inches when the water was boiling.

[FrankRizzo]

A water aspirator will only draw a vacuum to the point that the feed water begins to boil. Colder water will give you a stronger vacuum. It does sound like your gauge is incorrect though.

[dangerousamateur]

@goldwingnut54:

 

Thank you for your answer

Seems logical.

 

 

Say, these composite fuels, is it possible to get them to a consistency where casting (like it is possible with sorbitol) is feasible?

Sure would simplify the whole process a lot...

[boule]

Well, cast composite fuels are pretty much the standard in high power rocketry but not really feasibly for pyro. If you employ a cast mix in a cardboard casing, it needs to be elastic enough to actually expand witih the casing or it will crack with a resulting cato. Most APCP formulations require so much binder that they will not actually burn unconfined or in a low pressure environment like our pyro supplies. Generally speaking if you use something with a lot of binder analog to APCP you will either end up with a road flare or, if you have the mix right and confine it sufficiently, you get a really good pressure buildup that blows the tube to kingdom come. All the people that I have talked to who had "successfully" employed composite propellants ended up with either a significant failure rate or had reinforced their tubes, either with a little bit of fibreglass or by actually soaking the tube in resin.

I've tried going the route with cast propellants that contain solvents..... don't do it. Other than that, some other binders tend to be more promising, including bakelite, urea formaldehyde resins and certain types of sillicone but I have had a hard time obtaining sufficient quantities for more than a few tests at reasonable costs. Thus the research is not yet finished and I would recommend right now to work with rocket candy for economy and reliability reasons.

[Seymour]

In my experience, pressing composites with solvent still there in to cardboard cases results in funny hydraulics focusing the energy somewhere with the really scary result of the tube breaking. Since the compressed fuel is behaving as a fluid. it don't just split, it seems to explode as the "fluid" comes out of the hole with a bit of a bang.

 

I don't like my rockets making a "bang" noise under the press. Bad for ones nerves.

 

Pressing APCP with a dry fuel works fantastically. Just add a little wax for a binder, or press dry, just like whistle or BP. Sure, you never get optimum conditions for APCP to work with a paper case and a pressed fuel, but you can still get very good performance if you compare it to typical firework rockets rather that optimum high power performance, and of course APCP can be so easily coloured!\

 

Phenolic resin powders like resinox seem to work superbly as 1/1 replacements for traditional binders such as HTPB.

 

Most APCP formulations require so much binder that they will not actually burn unconfined or in a low pressure environment like our pyro supplies

 

This may be true for some APCP but I highly doubt it's true most of the time. For example, I have never ever come across APCP that won't burn at atmospheric pressure, though I'm sure it exists. Many times I've seen it burn unstably and go out, and for sure most of the time it burns much slower than it would at pressure (most of the time...)

 

But the majority of the stuff I've seen... a wide range of formulas, catalysts and binders, has burned at atmospheric pressure reliably with no issues.

 

That said, making AP based firework rockets is not as straightforward as making more traditional firework types such as whistle and BP. However I'd put that down to lack of information. There are many thousands of us who make whistle and BP rockets in paper casings, so getting data on what works perfectly can be easy and cross reference-able.

 

I've yet to play with these AP firework mixes enough to be able to confidently promote ideal dimensions, but I've had a good haul of very good successes along with the usual interesting launches that you get with very much experimental rockets.

 

Successful core burning rockets have been made in the ½” size using a core 30mm deep and 4mm diameter. I've made bigger too but not enough to bother publishing the results, other than my optimism.

 

Green

50% AP

30% BN

14% Resinox

5% MgAl

1% Fe2O3

 

Cerice

54% AP

25% SrN

16% Resinox

4% MgAl

1% CuO

 

Yellow

44% AP

22% BN

14% SrN

14% Resinox

5% MgAl

1% Fe2O3

 

Red

47% AP

32% SrN

15% Resinox

5% MgAl

1% Fe2O3

 

There be a few mixes I've had work well. Each probably has an ideal core size and shape but really, they all work as is, and the surface area changing from a 4mm dia core to a 12.5mm ID tube is pretty huge. somehow they still take off with gusto and don't blow up at the end. Amazing ability to handle abuse I think.

[experienced]

Does anyone have any information on an Ammonium Nitrate/Urethane Propellant? I found this on Nakka's website, but he didn't actually have any information listed, only that he'd had experience with it. I e-mailed him about it the other day, and am waiting for a reply. I just wanted to see if anyone here had any knowledge about it, preparation, ratios, special safety precautions. I'm ultimately curious because Urethane is extremely easy to obtain here in the US, unlike PBAN or HTPB.

Well i shy away from ammonium nitrate formulas, since i had a detonation with it once. And once was enough, to convince me to not use it any more. so i switched to using, tri or di-nitrocellulose. by nitrating plain, news print. which can be easily rolled into tubes, with or without a core. but you have to compensate, with a thicker tube with the higher pressure. cause they tend to go, really supersonic. but high grade 98% nitric acid, has become harder to get. but can compensate, by adding a little more sulfuric acid than the formula requires.

[experienced]

Just a quick update about my vacuum degassing chamber. I bought the aspirator from Amazon, in spite of the fact that it is a piece of plastic that cost about $25 with shipping bugs me I am happy with it's simplicity and think it should last a long time as there aren't any moving parts to wear out.

Yesterday I hooked it up to my irrigation hose to see what kind of vacuum it would pull, and it only went to 23" of mercury. "WTH?" I thought, when it occurred to me that I should do some test to see if my gauge is working properly.

First I placed a warm cup of water in the chamber, pulled a vacuum and within minutes it was boiling. Great at least I should be able to vacuum hot propellant.

Next I placed some of the cold water coming out of the hose into the chamber. It took a little longer but the water did start to boil slowly. The temperature of the cold water was 67 degrees Fahrenheit. It has been a long time since any chemistry classes so calculating the pressure at this temp seemed daunting but luckily for me there are online calculators. If they are correct the pressure should have been around ½ psi or -28 inches of mercury. Is this correct? All the while the gauge never went above 22 inches when the water was boiling.

Well with a suction aspirator, water pressure also becomes a critical factor. The higher the water pressure, the greater the suction. You might want to check, what is your water pressure. And if you have a pressure regulator, you can increase it. But make sure you do not exceed, the pressure of your plumbing where generally 55 or 60 psi is about max.

 

But on ebay, i bought a excellent 10lpm diaphragm vacuum pump 28torr for $25 - not including shipping of course. And i have bought several on ebay, and have never been disappointed. Even a small 1.5 liter per min, 22 tor vacuum pump - for $23.50 including shipping. But if you do buy a diaphragm pump, you want to make sure it is compatible with any solvent being used.

Edited October 7, 2013 by experienced

[dema]

for me the composite propellant is very good but it is difficult to use two formulations in one motor so i prefer thermoplastic composite propellant

[ddewees]

In my experience, pressing composites with solvent still there in to cardboard cases results in funny hydraulics focusing the energy somewhere with the really scary result of the tube breaking. Since the compressed fuel is behaving as a fluid. it don't just split, it seems to explode as the "fluid" comes out of the hole with a bit of a bang.

 

I don't like my rockets making a "bang" noise under the press. Bad for ones nerves.

 

Pressing APCP with a dry fuel works fantastically. Just add a little wax for a binder, or press dry, just like whistle or BP. Sure, you never get optimum conditions for APCP to work with a paper case and a pressed fuel, but you can still get very good performance if you compare it to typical firework rockets rather that optimum high power performance, and of course APCP can be so easily coloured!\

 

Phenolic resin powders like resinox seem to work superbly as 1/1 replacements for traditional binders such as HTPB.

 

 

 

This may be true for some APCP but I highly doubt it's true most of the time. For example, I have never ever come across APCP that won't burn at atmospheric pressure, though I'm sure it exists. Many times I've seen it burn unstably and go out, and for sure most of the time it burns much slower than it would at pressure (most of the time...)

 

But the majority of the stuff I've seen... a wide range of formulas, catalysts and binders, has burned at atmospheric pressure reliably with no issues.

 

That said, making AP based firework rockets is not as straightforward as making more traditional firework types such as whistle and BP. However I'd put that down to lack of information. There are many thousands of us who make whistle and BP rockets in paper casings, so getting data on what works perfectly can be easy and cross reference-able.

 

I've yet to play with these AP firework mixes enough to be able to confidently promote ideal dimensions, but I've had a good haul of very good successes along with the usual interesting launches that you get with very much experimental rockets.

 

Successful core burning rockets have been made in the ½ size using a core 30mm deep and 4mm diameter. I've made bigger too but not enough to bother publishing the results, other than my optimism.

 

Green

50% AP

30% BN

14% Resinox

5% MgAl

1% Fe2O3

 

Cerice

54% AP

25% SrN

16% Resinox

4% MgAl

1% CuO

 

Yellow

44% AP

22% BN

14% SrN

14% Resinox

5% MgAl

1% Fe2O3

 

Red

47% AP

32% SrN

15% Resinox

5% MgAl

1% Fe2O3

 

There be a few mixes I've had work well. Each probably has an ideal core size and shape but really, they all work as is, and the surface area changing from a 4mm dia core to a 12.5mm ID tube is pretty huge. somehow they still take off with gusto and don't blow up at the end. Amazing ability to handle abuse I think.

Seymour,

 

Can these formulas be mixed with Vaseline/lacquer thinner and riced... or will the resin become too hard to effectively press?

Edited November 20, 2013 by ddewees

[Seymour]

To be honest I am not sure how Resinox behaves with alkanes, but doing that very thing with wax is on my to-do list. I think it is definitely worth trying!

 

Basically I cannot be fully confident in a "yes", but I suspect you can