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jpsmith123
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Primaryless Detonators
Attached (hopefully) is a patent wherein the inventors use a "high energy pyrotechnic" mixture, i.e., basically flash powder, instead of a primary.
If this kind of thing can work, then I can imagine taking it a step further: What about an electrical impulse fed into a CuO/Al mixture? IOW, suppose
your "bridgewire" is, say, a small paper tube with a few hundred mg of pressed in CuO/Al mixture? Now, being that CuO is a semiconductor with a
negative temperature coefficient of resistance, maybe it would be possible to get the joule heaing effect to spread out over a large enough volume of
material that you would get a reasonable shock wave out of it. (I would imagine the power supply requirements would be much less problematic than
those of a "conventional" EBW).
Attachment: 5945627.pdf (964kB)
This file has been downloaded 1023 times
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12AX7
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FYI, Cu2O (red) is a semiconductor, in fact it used to be used in "copper oxide rectifiers", which were then supplanted by selenium (cough!) and
finally germanium and silicon. (Silicon carbide is now making inroads for high speed applications, though it's still pretty expensive.) AFAIK, CuO
(black) is nonconductive, but I might have to take an ohmmeter to my jar of it just to make sure. The Al (or Mg if you prefer  ) in the comp may be conductive, as conductive lampblack or graphite in bridgeless
compositions. If the comp isn't conductive, a bridgewire might be used, or a high voltage pulse could be used instead.
Tim
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jpsmith123
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If I remember correctly, both CuO and Cu2O are p type semiconductors; CuO has a bandgap of 1.2V while the bandgap for Cu2O is 2V or something like
that.
Regards,
Joe
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Boomer
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Without giving that patent, this might have looked like those kewl "can i detonate xyz with flash?" posts. So the idiots from totse were right, you
*can* det ANFO with flash - they just overlooked you need the flash in a re-enforced cap on top of some PETN, and inside a pentolite booster... 
Joking aside, thats interestring. Reminds me of the good old times when I had all the nitric I wanted, therefore all the secondaries, but TATP was
unknown, I had no mercury, and getting silver fulminate out of fun snaps was a PITA. I came up with the same idea, but lacking perc used armstrongs on
top of the MHN. NOT safer than a primary, but they worked. Needed a thick walled tube though.
Even the other idea mentioned in the patent is not new (the flier thingie). I gave it up back then since they got cumbersome. Imagine a two-foot-long
detonator, propellant charge in one end, shooting a ball bearing into the compressed MHN at the other end. 
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jpsmith123
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Those were my thoughts as well. In fact I hesitated a bit before posting it, as I don't want to feed the "k3wls", but I don't like to withhold any
interesting info from others who share my interests in energetic materials, either.
Regards,
Joe
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quicksilver
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Just for discussion's sake what are the power requirments for conventional EBW dets? Is there a standard???? I have seen various designs and, frankly,
they seem to require vastly differing juice. (what gives?)
But thinking along the lines of "flash powder" dets I believe it was Konske writing for the American Pyrotechnics Assoc. in a series of papers on
flash itself that had done some research on the amount of electrical stimulation the standard "70/30" flash needed to fire. IIRC it was somewhere in a
tenth of a Joule (the discussion was a safety issue re: mixing flash). Thus a "flash based" cap would be a dangerous animal when compared to most
anything with a bridgewire. However I would imagine that the finer the bridgewire the greater the possibility of inducing stray electrical energy via
radio waves, etc. - That issue has always been brought up and signs in the area of a large mine where I live warn of not transmitting during blasting
(a light flashes on a dirt road, etc) but it seems that the transmitter would have to be a big one (not some 5 watt mini) to get any juice in the air
enough to pose a threat. Static electricity seems much more of a significant issue.
Do any of the higher quality multi-meters have the capacity to measure static, or is that just too fine a curve for standard electrical measurment
devices?
[Edited on 4-1-2006 by quicksilver]
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12AX7
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The standard DMM has a 10Mohm (or so) impedance. You'll find it somewhere in the manual. Most are also only rated to 1kV, so you aren't going to be
measuring much static without a voltage divider (needing a 100M for 10x, or 1Gohm for 100x reading). For example, a 100M impedance reading an object
of 100pF charged to 10kV (reasonable values for a human walking over carpet, with wool socks, in winter) will discharge it to 3.6kV in only 10
miliseconds!
Special devices have been made to measure electric field directly, with typical input impedances on the order of teraohms (or more?). 1V corresponds
to a mere 160,000 electrons per second flowing!
Of course, conduction through *air*, let alone over dirty surfaces, is going to kill that. Gigaohm resistors aren't easy to maintain...
Note: 100pF at 10kV is 5mJ. E = 1/2 * C * V^2, with C in farads, V in volts and E in joules.
Tim
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jpsmith123
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| Quote: |
But thinking along the lines of "flash powder" dets I believe it was Konske writing for the American Pyrotechnics Assoc. in a series of papers on
flash itself that had done some research on the amount of electrical stimulation the standard "70/30" flash needed to fire. IIRC it was somewhere in a
tenth of a Joule (the discussion was a safety issue re: mixing flash). Thus a "flash based" cap would be a dangerous animal when compared to most
anything with a bridgewire.
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That's partly why I suggested using CuO/Al rather than a flash composition. The thought of a blob of flash powder with antennae scares me.
| Quote: |
Do any of the higher quality multi-meters have the capacity to measure static, or is that just too fine a curve for standard electrical measurment
devices?
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You'd have to buy or build some kind of high impedance electrometer for that. Depending on exactly what you want to do, maybe you could rig something
up to deliver a certain amount of energy using a capacitor and a spark gap or a pulse transformer or something?
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Boomer
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"Just for discussion's sake what are the power requirements for conventional EBW dets? "
More or less standard are 1.5 mil gold bridge wires 40 mil long. These need at least 200 amps to deliver the 'burst action' (I^2*t integral) that
explodes the bridge and dets
(not ignites) the PETN. 400-500 amps are recommended though, and should be delivered in preferably under a microsecond.
Remember that the capacitor bank only sees the cable impedance at first. Say you have a 2kV cap and a 50 ohm cable. So a 40A pulse travels down the
cable, gets reflected at the detonator (low impedance)
and adds to the cap voltage. A 80A pulse travels towards the EBW, gets reflected and so on. The resulting current through the bridge ramps up in 40A
steps while it heats up. It must reach 200 (better 400) amps
before the bridge evaporates. This is not too bad since that 'travelling' is done at 2/3 light speed.
For home brew EBWs using TR5 fuses for bridge+housing, I succeeded at 15µF, 1.5kV, 1.5kA within 600ns. That is a power rise speed of 3 TW/s btw.
Succeeded means 100% full dets, it *starts* working
at 60% of those values. And this was with MHN, not PETN!
P.S: forget fotoflash capacitors, electrolytics are too slow! Or get thinner gold wires...
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12AX7
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I'd hate to see the inductance figures there... if you have say 10uF and a mere 100nH, that's like what 160kHz resonance, or 1.6µs quarter wave
risetime, no?
I should learn about RF and transmission line theory some time...
Tim
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jpsmith123
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Hello Boomer,
I'm wondering, what was the current rating of the fuses you used? Also, what kind of switch did you use?
Regards,
Joe
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Boomer
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It worked with between 1A and 2.5A fast action TR5. The lower values were easier to get working, but below 1A the bridge tends to rupture
when you press the secondary in. 1A were still far above the 1.5 mil used comercially (hence my higher current requirement).
And the cap bank was massively parallel. Maybe that's why current rose so fast (would indicate 30 nH). OTOH I am the anti-RF guru but I feel that
feeding current from a cap into a wire is different from shorting a cap with a coil, even if coil + cable have the same inductance.
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Marvin
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Boomer, low impedence terminations reflect with inversion, so the reflected voltage will be subtracted from, not added to, the supplied voltage. I'm
not convinced transmission line theory can or should be really be applied to this unless the pulse lengths are shorter than the cable.
It would be fair to say that the cable has an inductance that contributes to the LCR time constant that dictates the rate of rise of current.
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quicksilver
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Is there a "clean" method to disasemble a TR5? Do they come apart with a solvent or is one forced to bore a hole to access the wire material?
The use of a single amp (or there about) is much more attractive than building a multi hundred amp box that requires unique switching for long term
employment. In the original tread in E&W forum much was said about the need for unique electronics for an EBW but at 1.5+ amps the testing
equipment would be commonly available.
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Boomer
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Marvin, maybe I put that wrong. It is reflected in a way that once back at the source it doubles the current. I'm no HF guru, quite the opposite, but
I have seen the oscillograms of the current ramping up. Plus this description was taken directly from Cooper, Paul W. - Explosives Engineering.
My digital scope is too slow to show the steps for short cables, all I saw was a current ramping from zero to 1500A within 600ns.
And Quicksilver, you got that wrong. I *do* use a one-amp-fuse, but you still have to *explode* the fuse wire within a microsecond. That means *not*
the rated fuse current, but said 1500 Amps! Switching was done by simply touching two massive wires. If you need timing you could use a triggered
spark gap, but looking at the scope the current rise time varies surprisingly little with hand-switching!
P.S. The top of the plastic fuse body was simply grinded off. This leaves a cylindrical housing with the wire in the centre. Fill, seal and enjoy 
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jpsmith123
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Boomer, have you tried anything other than MHN next to the wire?
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Twospoons
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Its because the voltage reflection is inverted that the current goes up! Its like connecting two batteries together - match + to + and you
get no current, but match + to - and you get lots of current.
The applicability of transmission line theory is dependent on the speed to the switch, relative to the length of the line - if the risetime of the
pulse is shorter than the pulse return time then you need to treat the system as a transmission line.
Helicopter: "helico" -> spiral, "pter" -> with wings
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jpsmith123
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Rock Fragmentation System Using Goldschmidt Method
Here's an interesting patent related to the substance of this thread. It would have been more interesting if they'd gone into some more detail though.
Attachment: 5773750.pdf (265kB)
This file has been downloaded 727 times
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Boomer
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FPMAGEL: Absolutely no comparing this to an EBW:
- You cannot det gunpowder with an exploding wire. It would take gigawatts and a 3-inch diameter column. All you do is ignite it, *then* it explodes!
- The welder cannot deliver the required current. At some ohms for the bridge (especially at melting/evaporating), you hardly get 20 amps!
- Even if it could, the rise time is magnitudes too slow. Your wire will still lazily warm up while an EBW has already detonated the main charge!
Wonder why they use 2-5 kV capacitors?
And yes I tried RDX. No way to get it working with my system. NG works sometimes (better if absorbed) but is hard to seal. I need PE ... 
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quicksilver
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Of the material I have seen there exists little information detailing the level of current for various materials (Urbanski, etc). Do you know of any
study wherein such a gathering of material exists?
[What level of electrical energy for what material stimulates det?]
Of both GMAW & SMAW; MiG & stick, I believe that there are many welders available that operate @ 200 amps+ . The Miller (& Lincoln) stick
welders particularly operate at 200 amps at the lowest entry level stick welders. Whille the more professional models operate at an astoundingly high
level of current. That is actually the only "OTC" source of high current I could think of. However it had been mentioned that a level of 1500 amps
would be needed. Searching my memory that would be available in some of the deep cut engine driven model welders available for ship-yard work. Capable
of fusing together one inch plate in a single pass. Is that not "over-kill" for a mere wire?
When welding with a home unit of 200+ amps the stick could easly be 1/8". Would this not vaperize a fine wire?
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jpsmith123
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Quicksilver I have to say that I don't understand exactly what you are getting at here.
With a conventional *exploding* bridgewire arrangement, as others have endeavored to point out, the idea is to deposit energy in the wire at such a
high rate that it doesn't just melt or vaporize...it explodes.
Whereas a welder can produce a high average power of perhaps several kilowatts, that can easily melt the wire, the EBW power supply must at a minimum
provide literally megawatts of power, but only for a short time.
In this thread I suggested that it might be possible to make some kind of a - for lack of a better term - call it "hybrid" detonator, whereby, instead
of having to add enough energy from an external source to instantaneously vaporize a wire, the idea is to bring some finite volume of an electrically
conductive energetic mixture up to ignition temperature very rapidly...maybe something analogous to running a piece of primacord lengthwise through
some ANFO to make it more effective; i.e., the ANFO is like a power amplifier.
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Axt
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What if the wire carried its own energy. The following was actually done with a welder @ 115Amp the top is straight Aluminium foil for reference, the
bottom is 2x 0.2mm platinium wires sheathed in Al foil.
<center><img src="http://www.sciencemadness.org/scipics/axt/bridgewires.jpg"></center>
You cant really tell much from the frames, the movie host I was using is down at the moment so you'll have to wait for that.
I did pull the energy figures for this to compare to conventional explosives once, cant find the exact figures right now but the base reaction Pt + Al
-> PtAl ended up holding more energy per volume then HMX (or was that for Pd/Al vs HMX? forget, probably both).
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Marvin
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Boomer, Twospoons.
I think what must happen is from the point of view of the conductor,
1. When the switch closes it starts feeding current into the transmission line.
2. The voltage pulse travels along the line at V, while the current going into the line is determined by the impedence of the line.
3. When the voltage pulse reaches the end it hits the short termination, inverts and cancels out the line voltage.
4. The ground voltage edge travels back along the line canceling the voltage but the current is still flowing.
5. When this pulse hits the capacitor end current is still flowing but the voltage over the conductors is now 0v at full current, so the voltage over
the same impedence causes an additional current to flow in the line, ie the current doubles but the voltage pulse is now V, and travels back down
toward the EBD and when it hits it, the current through it doubles, the 0v voltage pulse after inversion goes back up the line for another step
upwards to 3x initial current.
Axt, interesting idea, but assuming you could make a bridgewire fast enough, would'nt that essentially be a primary explosive in its own right with
all the inherent disadvantages EBW's are used to avoid?
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jpsmith123
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We're on the same wavelength. That's exactly what I was getting at with the CuO/Al.
| Quote: |
What if the wire carried its own energy.
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Axt
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| Quote: | Originally posted by Axt
Pt + Al -> PtAl ended up holding more energy per volume then HMX (or was that for Pd/Al vs HMX? forget, probably both). |
It was for Pd, Pt was slightly less.
Pd + Al (2890cal/cm3)
Pt + Al (2510 cal/cm3)
3CuO + 2Al (4976 cal/cm3)
HMX (2589 cal/cm3)
CuO/Al thermite releases considerably more energy per volume, but getting it to release it instantly would be much harder then a thin wire. There
probably some issue with the energy release & when it actually comes into effect with the intermetallic wire, considering its no detonation rather
lattice energy of alloying PdAl.
| Quote: | Originally posted by Marvin
would'nt that essentially be a primary explosive in its own right with all the inherent disadvantages EBW's are used to avoid?
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I dont think so, less sensitive to heat/impact ect. then the secondary explosive your trying to initiate. Its disadvantages are more likely to lie on
the EBW side, cant just connect it to a battery, and I dont think a welder would work for actual initiating a secondary explosive, not that its
practical anyway.
The <a href="http://ww1.webtop100.net/~62552/xmovies.webtop100.net/banners/intermetallic-bridgewire.mpg">movie</a> of the frames above.
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