Boron Matchhead Success

[WSM]

This last weekend I attended an amateur rocket launch (rrs.org) and helped with a difficult-to-ignite rocket. This composite rocket failed to launch three times before. The propellant was mixed by volume instead of mass and had a thick rubber skin on the surface which made ignition a challenge.

 

To the rescue with a commercial ematch which had a boron-based pyrogen. The match was rolled in an ignitor (roughly 0.25" in diameter by 2" long) containing some road flare composition and strands of black match. Below is a photo of the launch with the rocket at the top of the launch rail.

 

 

The commercial match is from Martinez Specialties of upstate New York and a product they've had just five years. Hotter than normal ematches, they really do the trick when others just can't!

 

WSM

[WSM]

Also from that day are photos of a couple of the zinc/sulfur rocket launches (these are typical of the zinc/sulfur, or "micrograin" launches).

 

 

These were 2" and 2-1/2" diameter, metal framed rockets which take off like a rifle shot. Thirteen to fourty pounds of propellant are used up in 200-500 milliseconds and in less than 150 feet of the flight. The balance of the flight (usually about a mile up) is coasting. The impact downrange is usually about fourty seconds after launch, for a single stage rocket.

 

It was a fun day with about a dozen launches. All of the rest of the rockets used standard ematches for their ignition (only the tough one needed the help of the boron ignitor). Several of the rockets were made by a team of High School students with the assistance of their teacher/mentor who was in attendance, along with some of their parents.

 

WSM

Edited April 4, 2011 by WSM

[alexthegreat00]

Nice. I'm on the rocketry club at my high school. I wish we had funding to do something on that scale. The largest rockets we've made were about 2' and we used boring store bought engines. I've always been interested in Zinc-Sulfur propellent. Its not efficient, but it is worth it for the effect.

[WSM]

Nice. I'm on the rocketry club at my high school. I wish we had funding to do something on that scale. The largest rockets we've made were about 2' and we used boring store bought engines. I've always been interested in Zinc-Sulfur propellent. Its not efficient, but it is worth it for the effect.

 

Hi Alex,

 

If your high school is in Southern California, they are close enough to use our facilities. Look at the Reaction Research Society web site at: rrs.org . It's the oldest continuously operating amateur rocketry club in the US (since 1943), and we invite others to join and participate. The address on the web site isn't current; the new address is:

 

P. O. Box 90933

Los Angeles, CA 90009-0933

 

The club owns it's own property in the mojave desert (since about 1955) and we're licensed and recognized as a legal rocketry facility.

 

If anyone has any questions, I'll be happy to answer them. If I can't, I'll find out and answer later.

 

WSM

[azure]

The experimentalist in me would like to make miniature Zn/S rockets with empty CO2 cartridges but my pyro side does not agree and keeps yelling SHRAPNEL!.. Edited April 8, 2011 by azure

[WSM]

The experimentalist in me would like to make miniature Zn/S rockets with empty CO2 cartridges but my pyro side does not agree and keeps yelling SHRAPNEL!..

 

 

And don't forget that micrograin (zinc/sulfur) is pressure dependent and requires a burst disk to get the performance we are getting with our rockets. We're using micarta (sp?) disks with holes drilled to accomodate the e-match leads (we use two e-matches for redundancy).

 

I suppose a well made paper tube could work. Maybe even a NEPT tube if the nozzle could be made to withstand blow-out pressures. A decent paper disk could be added before the powdered micrograin is "bounced" in. I say "bounced" in because that's the way we load it in the large metal rockets; forward bulkhead end (bolted in place before-hand) down and pour the powder in and bounce the tube on a wooden beam in the bottom of a loading pit. The mass of the micrograin compacts itself in the rocket better than any other method tried in the past 60+ years (strange as that sounds). This process is continued in increments till the tube is filled to the point where the nozzle, burst disk and e-match assemby is bolted in place, prior to launch. As to safety, we are either in the block-house or at the concrete and steel reinforced observation area in case something goes awry (which it sometimes does). Our club has a perfect safety record because we don't take short cuts with safety, and we all watch out for each other.

 

If you try a paper version, don't forget that hotter-than-normal initiation may be required to get it to go. Try thermalite or something similar if you hand fire your rocket. Otherwise use good, hot e-matches.

 

WSM

Edited April 9, 2011 by WSM

[azure]

have you tried melting the sulfer with the zinc ?

[WSM]

have you tried melting the sulfer with the zinc ?

 

Not personally, but the discussion comes up occasionally, The main problem I ever encountered (as a youth when I did that sort of thing), IIRC is the melting point and ignition point were sort of close to each other. Without careful temperature control the sulfur may ignite and ruin the attempt (and things might get exciting at that point !!!).

 

We do the majority of our work in the field and carrying all the requisite equipment to do it safely is more of a chore than most want to tackle. Add in the challenge and expense of a proper mold for the cast grain, compatible mold release agents, etc. Bouncing the powder into the tube starts looking more attractive by the minute.

 

Thanks for the suggestion (we need to keep thinking and considering other options). I have considered the sulfur melt idea for other pyrotechnic pursuits, using the proper equipment, just not micrograin in the field.

 

WSM

[azure]

Thanks

You are the first person that i've spoken with who has actual hands on experience with this propellant type.

 

Zn/S has some very interesting properties it seems, like the fact that it has a maximum pressure of 100-140 bar (2000 psi )in a rocket engine.

So it shouldnt be very likely to cato. (if built properly).

And although the isp of Zn/S is not very high it does have pretty decent density compared to other compositions

Also the isp can be further increased by adding 10% Al (cast grain) i have read.

 

But the main reason i like it is because... well it just looks so gawddamn sexy doesnt it?

zinc_sulfur_powder_calculator_hd.zip

[WSM]

Thanks

You are the first person that i've spoken with who has actual hands on experience with this propellant type.

 

Zn/S has some very interesting properties it seems, like the fact that it has a maximum pressure of 100-140 bar (2000 psi )in a rocket engine.

So it shouldnt be very likely to cato. (if built properly).

And although the isp of Zn/S is not very high it does have pretty decent density compared to other compositions

Also the isp can be further increased by adding 10% Al (cast grain) i have read.

 

But the main reason i like it is because... well it just looks so gawddamn sexy doesnt it?

 

I've seen a series of reports where modified micrograin was characterized. It was a mix of zinc, sulfur and aluminum of various proportions (all mixtures and not cast, IIRC). The report was from the early `70's if memory serves. The tri-mix did have higher ISPand performance, but I don't remember the form or particle shape of the aluminum used.

 

If I were to duplicate the effort, I'd choose a spherical aluminum to try to standardize the whole thing (and minimize the variables). Spherical aluminum does have the lowest surface area of the various forms available and would be the easiest to calculate (not easy, just easier).

 

WSM