Composite Propellants

[BigBang]

Composite Propellants are simply compositions containing an “Oxidizer”, a “Fuel”, and a rubbery, elastic “Binder”. This type of Propellant was first tested "in the Old Days" and used KClO4 as the Oxidizer and Tar as the Fuel/Binder. The problem with this Propellant was that, when it would burn, the Fuel Grain would be compacted due to the pressure, but when the pressure dropped, the Fuel Grain wouldn't take its original shape back.

 

Some common Oxidizers are NH4ClO4, NH4NO3, and KClO4. You all know what these do, so I won't go into detail on them.

 

There are many Binders, but the two most common are PBAN and HTPB. PBAN, when uncured, is a thick, sticky, stinky substance. It is hard to mix and takes a few days, at elevated temperatures, to cure. It is the Binder used in the Space Shuttle's SRB’s. HTPB, however, is thinner than PBAN, doesn't smell nearly as bad, and isn't as sticky. It can be cured faster at room temperatures and cures within a day. With the addition of DBTDL, the Propellant can be fully cured and ready for flight the next day.

 

Metal powders are sometimes added to increase performance of the motor. They act as a Fuel and increase the flame temperature. This increased “Candle Power” produces a higher Burn Rate. The increased Burn Rate increases the Chamber Pressure, thus increasing Propellant Flow Rate, thus producing higher Thrust. What a wonderful chain of events, eh? The most common Metals used are Al, Mg, and Be, believe it or not. Mg must be used with AN motors, because Al causes the Motor to “Chuff”, and no Metals gives a Low-Grade Propellant.

 

Burn Rate Catalysts can be added to speed up your Propellant. A few catalysts can be used, such as Ammonium Dichromate, Chromium Oxide, Black Copper Oxide, Iron Oxide (red or black) are the most common. Other, more exotic, Catalysts are Copper Chromite and the most powerful I have heard of is Catocene, which is Iron-based. CuO is favorable, due to the fact that it imparts a nice blue coloration to the flame.

 

Different effects can be achieved, by the addition of certain substances. By adding 20-40% Zinc Dust, massive amounts of black smoke can be produced. Anyone familiar with HPR, this is the “Blackjack” or “Smokey Sam” effect. Barium Salts can be added to give a green flame and Strontium Salts can be added to produce a red color . . . think “Green Gorilla” and “Redline”. Titanium can be added to produce the “Skidmark” effect, which happens to be my favorite. I have heard that coarse “Magnalium” is what is used in the “Skidmark Squirrel” motors, made by Animal Motor Works.

 

Sometimes, a “Structural Effect” is wanted. HX-878, also known as Tepanol, is used to provide greater cross-linking between the HTPB chains. This is a must, when Motors are used in high performance rockets. Some can pull well over 100 G’s of acceleration. Stress on the Fuel Grain can be so great as to tear it, causing a “CATO”. The cross-linking Tepanol produces strengthens the grain, so it can handle such stresses. Thermal stresses are also troublesome. To help keep heat transfer from running out of control, about 2 drops of Silicon Oil should be added per kilogram of Propellant. A massive amount of UV Radiation is produced in these Motors and, because some Propellants are semi-transparent, something must be added to stop these rays from penetrating into the Fuel Grain. If you don't, the Fuel Grain could burn all at once, resulting in a “CATO”. To prevent such occurrences, .5% Lampblack should be added to block the UV Light Ray Infiltration.

 

Fuel Grain configuration is one issue that can affect your Motor the most. An “End-Burner” is probably the simplest, of all. It is just a solid piece, which burns from one end to the other with a Slow Burn Rate. There are “Core-Burners”, which have a Moderate Burn Rate. This type burns from the center or “Core”, outward until it has spent all of its Fuel. The “Bates Grain” configuration is similar to the “Core-Burner”, in that it has a central, circular shape. The main difference from the “Core-Burner” is that it is segmented, burning from more than just the “Core”. You can stack these Fuel Grains in your Casing to achieve the desired result. There is also a “C-Slot” configuration, which is a long slice through the Fuel Grain that forms a thin rectangle. It extends from the Core to the Case Wall. A “D-Slot” is a slice down a chord of the propellant, removing a “D-shaped” piece of Propellant. “Moon-Burners” are “Core-Burners” with the Core off-center in the Fuel Grain. The final type is the “Star Grain”. This is the most variable type of Core that produces the highest Thrust. It can look like a Star, a Cross, or a Hexagon, with segments extending out from the vertices.

 

Now, once you have everything worked out, you can cast your Fuel Grain. First, weigh out your Binder into a suitable container. Once you do this, add your Metal Powder. Mix this up, coating your Metal with the Binder. Add all of your other “Solids” which ARE NOT “Oxidizers” and mix it until a homologous mass is formed. Next, add your “Oxidizer”. When you stir this in, it will become very hard to mix. To make it easier to mix, 5% of the Oxidizer can be substituted for a “Plasticizer”. If any more is added, the finished Fuel Grain will be brittle and unusable. The final chemical to add is your Curing Agent. To determine how much to use, you can use this formula:

 

Curing ratio = .80 x ( Equivalent weight of Curing Agent ) / ( Equivalent weight of Binder )

 

Once you mix in the Curing Agent, it is a “race against the clock” to pack your Fuel Grain. If you use a “Cure Catalyst”, you have even less time! Take little balls of the “dough-like” Propellant and lightly pack them into your Tube. If you are using a Core, you must pack around this. Once packed, you simply have to wait until it hardens. You should also put your Propellant under Vacuum, to remove all the Gas Bubbles. I typically overlook this step for smaller motors. If you are using HTPB, you only have a day’s wait.

 

I did a small “Test Batch”, today, of a “Sparky Propellant”. Its Composition is as follows:

 

NH4ClO4 68%

R-45M (HTPB) 14%

Aluminum, India Blackhead 13%

Titanium Flakes 5%

PAPI 98 +2% (should be 1.9, rounds to 2)

Small Drop of DBTDL

 

Mixed in a small “Tupperware” container, this was a 50 gram Test Batch. Because it uses Black Aluminum, no Lampblack was needed for UV protection. It burns with a Bright, Yellow-White flame, through sparks like a little “Gerb”. It produces almost no visible smoke.

 

Pics.

http://www.apcforum.net/files/sparksreceding.jpg

http://www.apcforum.net/files/fewsparks.jpg

 

Video

www.apcforum.net/files/sparkytest.wmv

 

The video is of about 3 grams of this Propellant burning in that “Tupperware” container. It isn’t a solid mass. Rather, it is just a coating on the inside of the container. It wasn’t cured yet, but this shows that it WILL burn easily when it isn’t hard yet. As a reference, the Bicycle Tire in the background is 26” in diameter. I loaded up a Tube with this and, once cured, will cut it to make a “D-slot grain”. I’ll add to this thread, once I have gone forward with actual Motor Construction.

 

Now, I also hope to discuss here, alternative Fuels or Oxidizers, an example of which is Hydrazinium Nitroformate, coupled with Glycidyl Azide Polymer as the Binder / Fuel. It is said to be much more powerful than APCP and doesn’t give off Cl, as a byproduct of combustion.

 

What are everyone else’s experiences with these Propellants if any? Any ideas that could improve it, give new effects, or anything else worthwhile to contribute?

PROPELLANT_THERMOCHEMISTRY_PROGRAM_for_sparky_test.doc

[TheSidewinder]

I'm at the very beginning of my experimentation with APCP rockets. I bought the Firefox kit last season (and am happy with it), then bought extra oxidizer as needed.

 

Someone at the PGI last year gave me a formula that uses PBAN or HTPB, take your pick, but WITHOUT a catalyst. The key is to use very little of the binder. And while it's not as "hot" as a standard APCP mix, it is a HELL of a lot easier to handle, and just tame enough that you can use a slightly modified nozzle mix, instead of needing a (expensive!) machined graphite nozzle.

 

YOU ALSO NEED AN INDUSTRIAL-RATED MIXER.

Cheap kitchen mixers can't handle it. I have a Kitchenaid Professional 600.

 

Formula in parts (by weight):

 

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.

 

THEN, an additional:

5 Red Gum

0.5 Stearic Acid

5 PBAN or HTPB

 

Solvent: Any hydrocarbon solvent that is compatible with PBAN or HTPB can be used. I forget what he said he personally used (I was hastily scribbling notes here, sorry) so I'll be using Acetone, Mineral Spirits, or Turpentine after I figure out which one dissolves the binder best.

 

Mix PBAN and the solvent of your choice until binder and solvent are fully integrated. Blend in the Stearic Acid, Red Gum, Potassium Dichromate, and Barium Carbonate. Mix until fully blended, adding additional solvent as necessary to keep it "mixable" in the bowl.

 

Add the 90 micron AP, mix, then add the 200 micron AP while still mixing. At this point it will start to really stick together. Add JUST enough solvent to keep it manageable.

 

Spread out as thin as you can get it on some surface that it won't stick to, such as plastic wrap on a tabletop, INERT metallic surface (stainless, aluminum, etc) whatever. Lay this out in the sun on a good hot, bright day to evaporate the solvent.

 

When enough hydrocarbon solvent has evaporated to allow screening, screen it through a 10-20 mesh screen into granules. Let these dry further, until the tackiness is ALMOST gone.

 

Use an arbor press with a standard BP, cored, set of rocket tooling, and press hard!

 

You may need some sort of mold release on the spindle, but probably not if it's good and smooth.

 

The Stearic Acid can be increased to a maximum of 1% (1 part), but my notes don't say WHY no more than that. IIRC, he said it will change the burn rate enough to be a problem.

 

The clay mixture for the nozzle is not a standard BP nozzle mix, but it's close, AND will work well enough for pyrotechnic use. This isn't an "Amateur Rocket" motor, where you're trying for great height. It's pyro! The nozzle only has to last as long as the burn, you aren't gonna reuse it.

 

4 parts Bentonite

1 part Graphite

1 part Grog

 

He also said that, if your propellant mix is chuffing even though you followed the directions exactly, you can add 1-2 parts of PRECOATED Magnesium to increase pressure and eliminate it.

 

BUT BEWARE! Doing so increases the pressure, and the risk of a CATO. Experiment safely until you get the mix dialed in.

 

Note: the 3 parts of Potassium Dichromate in the main formula will NOT protect added Mg! Pretreat it!

 

I will be trying the above formula this Summer. I already tried a "standard" APCP formula and it was a unholy mess trying to load 8oz (1/2") tubes with it. I'll use that one in some 1-3 pounders with carbon-cloth lined tubes and a machined graphite nozzle. But for small rockets, this sounds like a good method.

 

Enjoy.

 

M

[BigBang]

I personally like these propellant because of their castability. It is easier for me just because I haven't made a press yet. Also, if you happen to drop it from a good height, the grain won't fracture due to its elasticity.

 

The potassium dichromate works as a catalyst, just as ammonium dichromate does. That's why it isn't used to coat the magnalium.

 

You don't need machined graphite nozzles for all motors, it is just one of the best materials, that can be used for multiple launches. Durhams water putty works well for most motors. Most commercial motors single use motors, aerotech for instance, use glassed phenolic for their nozzles.

 

Here is another video of my propellant burning, and a better one than before. It is a "plug" of propellant I cut off of the main grain. It is 18mm in diameter and .25" in height. It contained about 2.5 grams of propellant.

 

http://www.apcforum.net/files/sparkyplugvid.wmv

[Exerd]

Had to bring this back up...

 

Has anyone out there experimented with the combination mentioned of Hydrazinium Nitroformate/Glycidyl Azide Polymer?

 

I use AP composite propellants on a regular basis, I also prefer them due to their castability and elastic properties. I must say I don't think I'll ever go back to blackpowder. But, I am very curious about the above mentioned propellant.

 

I'm curious as to what Isp's have been achieved from this stuff? What about flame appearence?

 

There doesn't seem to be much info on the propellant, although I read something about long crystals forming at the production plants in the propellant which were vital to the end volumetric loading percentage.

[DeAdFX]

HNF/GAP/Al is suppose to have an ISP around ~300ish+. If I remember correctly in order to cure GAP needs BF3 or some other sort of nasty hard to get chemical. I am doubtful anyone in the amature(sp) world of rocketry would have GAP. It might be possible that someone has HNF. Hydrazine and Trinitromethane can be made from OTC ingredients.

 

HNF's has a very fast burn rate and its burn rate is also influenced greatly by the pressure in the motor. Other than that I don't know much about this new "enviroment friendly" propellant. To be honest I am surprised that this propellant is considered to be enviromentally friendly. Trinitromethane is zillions of times more toxic than hydrochloric acid and Ammonium Perchlorate. .

[BigBang]

The products of the popellant are what is considered more "enviromentally friendly" than those from APCP. You are right about the nasties the actual propellant is made up of. GAP is very, very toxic, and so is its partner in this mix. It does, however, have an extremely high Isp, which is why I would like to be able to experiment with it. I have most of the information on how to produce both the HNF and GAP. What scares me is the volatile precursors, and my lack of experience with them.

 

I have seen a few videos of test launches using this propellant, but am not sure from where. It is a rather fast burning propellant. No smoke-trail was produced. You could see only a small, "clear" flame spouting from the nozzle.

 

What the common chemist need to find, is a propellant with such a high Isp as HNF/GAP, but with easily obtained or manufactured ingredients. A propellant like this could have the potential to be a new workhorse for high performance and altitude projects.

 

Any ideas?

[DeAdFX]

Some ideas...

 

I have read a couple of threads posted by Boomer that mention the use of an Ammonium Nitrate/other ionic Nitrates as a eutectic rocket propellant. To bad these eutectics melt at to high of a temperature 90C+. I doubt you could add any magnesium to mix without it exploding/burning.

 

Or you could just neturalize trinitroform with ammonia instead. Ammonia happens to be a lot more common than hydrazine and probably cheaper too[assuming you don't have to go through a bunch of hoops because of meth producers].

 

 

I find it backwards ass that the enviromentally concious are trying to replace a moderatly toxic composite propellant with an incredibly toxic propellant and then label it "enviromentally friendly". The only oxidizer that is green for explosives and rocketry is Ammonium/Potassium/most other ionic Nitrates unless you are an aquatic life form. Then in that case you are fucked.

[ActionTekJackson]

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.

[ActionTekJackson]

Well, I'm working on a new kind of Composite. Styrene bound, the formula is as follows.

 

KClO4 - 70

Styrene - 15

Aluminum (fine) - 15

 

My issue is how to get the styrene (styrofoam is the closest I have) in a state that it will mix with the Perchlorate and Al. I tried dissolving the styrofoam with gasoline (wanted to use acetone but didn't have any at the time), and mixed it that way, but this was rather messy to press and the grain shrunk upon drying, so there were cracks in it. My other idea is to try melting it, now stryofoam melts at rought 250F, so this worries me on a safety standpoint... any suggestions? Below is a stat sheet of projected performance.

KP_StyrAl.txt

[Mumbles]

The main problem is that the styrene is not the same as polystyrene. Styrene is a liquid. If you must use Polystryene, I would do the same thing with the gas(preferably acetone because it's cleaner actually). Only don't press it. Let it evaporate and powder it. It can then be pressed, or redampened to an appropriate level.

 

Out of anything I do think the biggest problem is inproper materials. I mean it'd be like me trying to make BP, but running out of charcoal, so I used chopped up cellulose instead, and expecting it to work.

[ActionTekJackson]

The main problem is that the styrene is not the same as polystyrene.  Styrene is a liquid.  If you must use Polystryene, I would do the same thing with the gas(preferably acetone because it's cleaner actually).  Only don't press it.  Let it evaporate and powder it.  It can then be pressed, or redampened to an appropriate level. 

 

Out of anything I do think the biggest problem is inproper materials.  I mean it'd be like me trying to make BP, but running out of charcoal, so I used chopped up cellulose instead, and expecting it to work.

You pose a good point, I wouldn't even be considering it, except the grain that I did make, that cracked, burned extremely well, and did in fact explode when the flame entered the crack in the grain. So I will try your idea, I didn't think about that. On a side note, any ideas where I can get styrene, and does it ever "dry out" or harden. I haven't tried searching for this yet, but I will... Thanks for the input mumbles!

 

*edit* ok so this program actually had polystyrene as an option, and the ratios are actually the same, so it doesn't make alotta difference whether I use Styrene or Polystyrene. Below is that stat sheet for KP-PolystyrenAl (like the name? ) Oh, also, changing the KClO4 for NH4ClO4 seriously increases performance and the ratio (according to this) should stay about the same. *edit*

KP_PolyStyrenAl.txt

[Mumbles]

I actually just came across a source the other day looking for polycarbonate. I know there are a few more I've seen, i just can't remember where. Not sure the process as for polymersation.

 

http://www.tapplastics.com/shop/product.php?pid=41

[DeAdFX]

I made some Polystyrene propellant before. Here are some tips. Instead of using acetone use Xylene/toluene/benzene. These are much better solvents.

 

 

I first added 6mL of Xylene to 10grams Potassium Chlorate. I stirred the slush around to evenly mix the xylene. I added 3 grams worth of polystyrene(PS). AFter the first gram or so of PS the mix became very difficult to stir. The viscosity is close to that of PBAN. I then added 2grams of Aluminum powder and stirred until I got a grey colored blob.

 

USing any less xylene will make the mix difficult to mix while using to much will cause the propellant to take longer to dry. 6mL works pretty darn nicely. I tried using acetone but I found it much more of a pain to work with. Acetone is nice in the sense that it is low toxicity but sometimes the nasty stuff is the "only" way to go.

 

As the propellant dries it goes from viscous gel to a brittle solid. I believe the addition of plasticizers is neccessary for the propellant to be of any use. The propellant also burns very smokey. I might of had to much polystyrene though.

 

 

 

Another possibility for composite propellant.... Awhile ago I mixed Golden powder with Triethanol amine(TEA) and Peanut butter)PB). I dissolved 12grams KNO3, 6 grams VitC, ~10mL TEA and a gram of PB in ~20ml water. What I got was a mass with a silly putty like consistancy. The mix didnt burn for crap because the OB was deep in the negative. I think If i were to make an OB positive mix of Golden powder, pulverize it, and add it to a smaller portion of TEA and PB I could get a propellant that actually burns....

 

The purpose of the PB was to act as a plasticizing agent and the TEA was used to form an emulsion.

[pa_pyro]

If you need a source of aluminum for composite rockets.

 

http://cgi.ebay.com/5-Pounds-Atomized-Alum...1QQcmdZViewItem

[fizeau]

At last I succeeded in teaching the weed remover how to fly. No CATO so far

(let´s see what the future brings). Videos:

http://www.youtube.com/watch?v=EgUwZzzu9Po

http://www.youtube.com/watch?v=Eif_42Ihpn0

 

I´m also pleased with my nitrate rockets. Please be indulgent on the fact

that I didn´t put a report on it. The indulgence of my neighbours

regarding bangs is limited.

Video: http://www.youtube.com/watch?v=DhNmErbVVXU

Some time ago I purchased a 100 pound bag of NH4NO3... I´ve read here in the forum that some members are using it successfully in rocketry. I would like to do so too. But I can´t take the usual way of using polyurethane, it is not available in my country just as chromates and dichromates. Someone

mentioned CuO as a catalyst. This chemical as well as MnO2 I could get.

So I would like to ask two questions: First, are there any risks in using

MnO2 with Mg grit and NH4NO3. Second, has anyone personal experience

with other synthetics usable as binder for AN propellants. Any advice would be appreciated - it would spare me weeks of work in the fumes of solvents until I could find an alternative to polyurethane.

[asilentbob]

http://www.fiberglasssupply.com/

My dad and I got styrene monomer, MEKP catalyst, and a foam core blank from here when we made a surfboard. (a great project BTW) As you can see they have a nice assortment of epoxys and fillers too.

 

I have a good ammount of styrene monomer and catalyst left and i should be getting some ammonium perchlorate in a month or so. I might attempt making a little composite propellant, however the ammonium perchlorate is mostly for stars.

[cplmac]

I've been wanting to sit down and thoroughly read this thread for a while now. Good stuff every one thanks. Got a question though, to these high powered composite rockets require high strength casings suck as machined aluminum or steel?

[TheSidewinder]

If you're talking rocketry as applied to the Pyrotechnic field (and we should be, in this forum) then, in a word, NO.

 

We NEVER use a metallic casing of ANY kind.

 

IIRC, our Guild actually prohibits pyro devices with metal components (unless it's part of a genuine Class C item maybe??) and someone please correct me if I'm wrong, but I'm fairly certain that's true at the PGI as well. And it's only common sense after all.

 

Now, if you're talking the Amateur Rocketry field then, in a word, YES.

 

I forget the site, but you can purchase motors (which use propellant reloads) that are made out of precisely machined Aluminum or other metals. High-strength Fiberglass or Phenolic is used also, but usually for one-shot disposable motors. I've visited these sites and drooled a bit myself, but I'm more of a hobby rocketeer. Was launching Estes rockets when I was a pre-teen.

 

I'm no expert in the Amateur Rocketry field. My knowledge is strictly pyro. But I'm playing with APCP Composites, so I've researched a bit.

 

If you get your hands on some genuine New England Paper brand tubes I'm almost certain they will work as-is, AND they don't violate the "no-metal" rule.

 

You may end up, after experimenting with them, having to line the casing with Carbon cloth to prevent burnthru, but that's easily done on a 1-pounder or bigger. And again, it doesn't violate the rule.

 

I've seen nozzle formulas that use only Graphite, Bentonite, and Grog which claim to work acceptably (but you still get noticeable erosion). You can machine nozzles out of graphite blocks as well, but that's beyond me at this time.

 

That said, using any "home-made" metallic case is inviting disaster, as far as I can see. Unless you are both a skilled Machinist and skilled Propulsion Engineer.

 

The metallic motors you can purchase for Amatuer uses are designed specifically for their own reloads, so the pressures are already well-considered by the time you purchase them. I've seen kits that call for your own home-made propellants, but I'd be very wary of them personally.

 

Hope that helped...

 

M

[cplmac]

I was speaking specifically to the formulas that were mentioned in this thread. Fortunately I have NEPT tubes available, but I wanted to know if the composite fuels generated to much pressure. Also the nozzle is a concern. I have been considering picking up some PBAN but I want to get my head around what will be required first.

[TheSidewinder]

Im almost certain NEPT tubes will do the trick. Like I said, you may end up having to line the casing to prevent burn-thru, if you're using a traditional APCP formula. (A Carbon Cloth lining would also strengthen the tube considerably.)

 

As to nozzles? I'm still working on that. I hope the Graphite/Bentonite/Grog mix I was given will work and not just erode completely through, halfway up. I'll find out this Summer.

 

If you have a friend with a metalworking Lathe or Mill, he could machine Graphite block nozzles for you. This would need to be epoxied in place and allowed to fully cure before loading, though.

 

 

M

[cplmac]

I have a lathe in the shop, just don't have any graphite blocks. Thanks sidewinder!

[DeAdFX]

hmmm. Question..

 

I was wondering how could I degass a composite propellant such as ammonium perchlorate/PBAN/Aluminum Powder/combustion catalyst?

 

Is it as simple as putting your composite mixture in a sealed device and applying a vacuum for a certain period of time?

 

or is degassing unnecessary for the amateur?

[BigBang]

It is just that simple. Apply a vacuum for about 5 minutes.

 

Generally, it is not needed, but it lack thereof will cause a lack in performance, albeit minor.

[asilentbob]

I've had that same question in the back of my mind for some time too... Thanks.

[Mumbles]

BigBang, since you probably have the most experience in this field, I was wondering what they used to create the vacuum. Do they use a full scientific vacuum pump, or a venturi pump or a vacuum food sealer or something?