Composite Propellants

[BigBang]

I really just depends on who you ask. Believe it or not, a high vacuum is NOT desired because it can deteriorate the strength of the propellant. A food sealer would be fine, but *might* not hold a vacuum long enough.

 

Th easiest think to do would be find an old pump on ebay or something of that nature.

 

One thing I should mention. It is necessary to vacuum process with high solid loading, that is to say, above 80% solids. You can usually get away with out for those under 80.

[Boomer]

Simply from common sense: You want to get the bubbles out, you do NOT want to get to 0.001mm Hg resulting in the binder to start boilling at room temp.

 

From that, the easiest thing would be an old fridge compressor. They go to approx. (!) 25 mbar, even if yours is half as good that's still 95% vacuum. Rotary types can go much lower but the cheap ones all have pistons with a dead space. If you don't distill acids or solvents with it, it should last a long time. Catch the oil that comes out.

 

Or the good old water ass pirator.

[ActionTekJackson]

One thing I should mention. It is necessary to vacuum process with high solid loading, that is to say, above 80% solids. You can usually get away with out for those under 80.

I know this is pretty old stuff here, but what exactly does this mean?

 

Also, I found an old military misile motor design manual which is a polyurethane bound CP, the formula is supposedly as follows:

 

73% - AP

15% - Al (mesh not specified)

12.8% - PolyUrethane

 

Is it odd that a military formula would call for a 100.8% composition? Also, has anyone tried this or similar? I know there's been some work with Polyurethane compositions, but most of that was earlier work from me or not related to rockets.

[ActionTekJackson]

Bump... *points up*

[TheSidewinder]

Solid loading basically means "the percentage of solids versus liquids".

 

The ammonium perc, Al, Zinc Oxide (in composite smokes), etc are the solids. The epoxy and its catalyst, plus any plasticisers, are the liquids.

 

As to percentages, you know what they say: There's The Right Way, The Wrong Way, and The Army Way.

[ActionTekJackson]

Solid loading basically means "the percentage of solids versus liquids".

 

The ammonium perc, Al, Zinc Oxide (in composite smokes), etc are the solids. The epoxy and its catalyst, plus any plasticisers, are the liquids.

 

As to percentages, you know what they say: There's The Right Way, The Wrong Way, and The Army Way.

ok, that makes sense now, thanks :-) So I spose I'll try the army way and let y'alls know. *yes... I am from Idaho where we use y'all, and no, I'm not a hillbillly ;-)*

[BigBang]

Urethane propellants were used in the early hobby composite motors. I wanna say vulcan, but it was probably the manufacturer before them.

 

Did we talk about urethane propellants a year or 2 ago?

 

If you need any help, shoot me an IM or PM

[ActionTekJackson]

Urethane propellants were used in the early hobby composite motors. I wanna say vulcan, but it was probably the manufacturer before them.

 

Did we talk about urethane propellants a year or 2 ago?

 

If you need any help, shoot me an IM or PM

Yea we did, I just have the tools now that I might be able to do something finally, except a damn press lol... *sigh*

[BigBang]

The great thing about composites is you don't need one.

[ActionTekJackson]

I almost put this in the sugar rocket thread, but my question is not really specific to sugar rockets. I'm wanting to do Composite rockets in the kitchen. I've since moved and don't really have a garage or anyplace to make rockets like I used to unless I wanna drive to my friends parents or my parents. My fiance wouldn't like me being gone that much. My idea is KNO3 composite, but what else is a good fuel for that but sugar? Ok, so are there any sugar based binders? The only thing I can think of is commercially or home made inverted sugar. That mostly water though and probably very similar to recrystallizing. This is an option I am considering but requires use of the oven, obviously this poses a higher safety risk by performing that procedure in the kitchen of my condo. So the goal is some sort of mostly non-toxic composite that does not require the use of the oven for production, that I can easily clean to minimize extended time periods of pyro clutter in the kitchen (for my safety).

 

Some information on Inverted sugar.

 

"Invert sugar

Sucrose can be split into its two component sugars (glucose and fructose). This process is called inversion, and the product is called invert sugar. Commercial invert sugar is a liquid product that contains equal amounts of glucose and fructose. Because fructose is sweeter than either glucose or sucrose, invert sugar is sweeter than white sugar. Commercial liquid invert sugars are prepared as different mixtures of sucrose and invert sugar. For example total invert sugar is half glucose and half fructose, while 50% invert sugar (half of the sucrose has been inverted) is one-half sucrose, one-quarter glucose and one-quarter fructose. Invert sugar is used mainly by food manufacturers to retard the crystallization of sugar and to retain moisture in the packaged food. Which particular invert sugar is used is determined by which function – retarding crystallization or retaining moisture – is required.

 

Home cooks make invert sugar whenever a recipe calls for a sugar to be boiled gently in a mixture of water and lemon juice."

 

Information provided by LEGAL © 2007 The Sugar Association, Inc.: All rights reserved

[Seymour]

My idea is KNO3 composite, but what else is a good fuel for that but sugar?

 

People have been doing catalysed Potassium nitrate/epoxy for a while...

 

It does not quite fit the bill for being non toxic, but the oven and press are not needed!

[psyco_1322]

You might be interested in this composite.

 

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

[Swede]

Urethane propellants were used in the early hobby composite motors. I wanna say vulcan, but it was probably the manufacturer before them.

 

Did we talk about urethane propellants a year or 2 ago?

 

Well, we did the poly glue experiments and there's no doubt it can be energetic. But the huge problem with poly glue for a binder in a rocket is going to be the inevitable voids. No doubt melting some LDPE might be a better option. Experiment VERY small to ensure the molten PE does not self ignite upon contact with the oxidizer; OR....

 

Research PE polymerization and execute the linking in-situ, once the tube is loaded.

 

Take everything ^^^ said with a huge grain of salt. I know very little about composite propellants; these are just random and perhaps very dangerous thoughts. Polymer chemistry has really advanced, and I suspect we can do better at home than epoxy as a fuel. Something that can pour, vacuum if needed, and cure in place.

[Mumbles]

So you want to bind a rocket using something that has a gaseous feed stock huh? PE is done by a radical mechanism. You're looking at around 300C, and 2000bar to get it to go. I'd go with a water/alcohol/solvent soluble polymer. Perhaps polystyrene or Polyvinyl alcohol. Just a little bit of solvent to slightly moisten it, with most of the work being done by mechanical pressure. That or a crosslinking polymer. Perhaps bakelite. Most of the others I know well are UV initiated.

[Mumbles]

Have you actually gotten them to strobe? I've heard many people say that they could only get a big mess or simply blue stars.

[Swede]

So you want to bind a rocket using something that has a gaseous feed stock huh? PE is done by a radical mechanism. You're looking at around 300C, and 2000bar to get it to go. I'd go with a water/alcohol/solvent soluble polymer. Perhaps polystyrene or Polyvinyl alcohol. Just a little bit of solvent to slightly moisten it, with most of the work being done by mechanical pressure. That or a crosslinking polymer. Perhaps bakelite. Most of the others I know well are UV initiated.

 

If that was directed at me and my PE comments, then I deserve that... as I mentioned, polymer chemistry is not a strength of mine.

 

There are those castable urethanes (Alumilite and similar) that might work. The problem with many of them is the ultra-fast cure, on the order of less than a minute. The good part about them is that they tend to NOT gas too much, and the resultant grain would probably be pretty uniform.

[BigBang]

I would imagine there would be some urethane polymers which do not outgas or outgas in a way wich a cured grain can attain decent density.

 

As for what you're saying, Swede, I'd say that would be an amazing idea, but it isn't a new one. You could avoid the creep with low solid loads. I wonder if a UV set up polymer would be good, I'd like to look into that some day. Just so you know, the ARCAS (check it out on google) used a melt cast grain with PVC. Meltcast is one of the few ways you can get 90% solids and have it work. (if anyone doesn't know what solids loading is, it's the amount of solids in the mix (like metals or oxidizer, the other stuff is a liquid until it's cured. generally, higher solids, higher performance)

[Swede]

I know if I keep pondering high-powered rocketry, I'll get sucked into it, and it appears to be a big black hole!

 

On the "grains" or whatever you call the fuel that gets reloaded... would it be possible to create a set of steel dies, and create grains that are nearly 100% solids under great pressure? We press BP into amazingly strong pucks with just a few % of dextrin or red gum... I'm picturing a press and a die set rather than casting the fuel.

[TheSidewinder]

Well, if it's liquid enough to cast I don't see how putting it under pressure will make a difference. You normally can't compress a liquid, even a very thick one, and dry ingredients (such as BP) have air voids that pressing eliminates, or at least reduces greatly.

 

Unless I'm missing something here.....

[Aquarius]

I've been thinking the same Swede. Had a look at Nakkas site today, where he uses West Systems epoxy for casting a KN/Epoxy grain.

Could a KNSU grain be coldpressed, and then heattreaded while still in the mold?

Or maybe using epoxy and pressed, like you said?

If one could do that, it might be a easy and "safe" way of making up quick BATES grains ( a full length would probably be too long anyway.)

[BigBang]

If you have a liquid resin system you "don't need" pressure. However, some binders aren't curable for us ametuers. In this case, you can press grains. If you want an example, go to Nakka's website and look for ammonium nitrate propellant. He pressed his grains.

 

Oh and, you shouldn't really need to press KNSU. I mean, it's really easy to use the recrystallized method. Plus, if you pressed it, it would probably still be crumbly and go boom.

Edited February 18, 2009 by BigBang

[Aquarius]

@BigBang: No, I think you got me wrong on the KNSU. What I tried to explain was if one could press KNSU in dry form, and then heat them to a molten state in a oven and let them cool down?

I just hate the whole process with melting KNSU, I find it a lot of work, cleaning etc. Maybe I'll get som sorbitol, hear that KNSB is easier to pour into molds.

[Swede]

TheSidewinder, my thought there was going with a relatively dry mix, say 98% solids, 2% binder, perhaps rubber of some sort, and enough acetone or MEK to activate the binder, so the propellant mix would look and handle like a vaguely clumpy powder. This known volume gets scooped into the steel die, and pressed with an experimentally-derived pressure. The die is opened, and you've turned the powder into a solid grain. Using non-aqueous solvents would allow it to dry in a day or less, as opposed to becoming permanently damp internally. A Bates grain would dry very quickly using acetone or MEK, I'm guessing.

 

It's just a thought from someone with zero experience with this sort of thing.

[TheSidewinder]

Ah, ok, I see what you're getting at.

 

In Mason City (I think) someone gave me a composite formula that I have yet to try. But it's one that uses VERY little binder (HTPB or PBAN), no catalyst (you'll see why), you thin the epoxy with one of several common solvents, and you rice the comp after getting it all thoroughly mixed. Once riced, you let it dry until the epoxy thinner you've used evaporates, then you press it exactly as you describe.

 

With no catalyst, no curing is needed (so no outgassing or thermal reactions will occur). The resin doesn't need any additional drying after pressing, either, so you can shoot them immediately, as well.

 

If you want the formula, let me know. I'll track it down.

[derekroolz]

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?

 

 

How do you guys get these chemicals? Do you order them where it is still legal or do you buy like drugs. Becasue i cant find these chems anywhere!!!

(saying this in the most politfull way possible)