back to article Boffins use inkjets to print explosives

As anybody who's emerged from a car crash in good shape can tell you, it's good to have some explosives around - they pop modern vehicles' air bags. Of course explosives are also hard to manufacture and handle, which is why researchers at Purdue University in the US tried to print them. The boffins believe they've cracked the …

  1. Sampler

    Not usually one for pedantry

    But isn't thermite an incendiary, not an explosive (ie, it burns very hot, very well, but doesn't actually explode)?

    1. frank ly

      Re: Not usually one for pedantry

      You're probably right. I'm wondering why they use copper oxide instead of iron oxide, which is usual for bulk thermite. I assume it makes a better/easier printing 'ink' or sticks to the substrate better, or something.

      1. Anonymous Coward
        Anonymous Coward

        Re: Not usually one for pedantry

        No, the copper produces a more vigorous reaction than Rust.

        Bigger "bang" for your buck.

    2. Mark 85 Silver badge

      Re: Not usually one for pedantry

      Indeed it is an incendiary. From my military days, we were told it won't go boom because while it burns hot, it doesn't burn fast enough to go "boom". There might be some explosives that use thermite as a starter though but I'm not sure.

    3. Anonymous Coward Silver badge
      Mushroom

      Re: Not usually one for pedantry

      Explosives are triggered by pressure (which may be generated by rapid heat expansion) - it's the shock wave that makes the rest of the explosive go boom.

      Thermite doesn't do that.

      C4 famously burns quite nicely when set fire to, but explodes when detonated - very different behaviours.

      1. DJO Silver badge

        Re: Not usually one for pedantry

        Presumably the higher surface area to volume ratio will allow the thermite to burn a lot faster than normal lumpy thermite.

        1. Peter2 Silver badge

          Re: Not usually one for pedantry

          Presumably the higher surface area to volume ratio will allow the thermite to burn a lot faster than normal lumpy thermite.

          Yes, but I think the issue is controllability. Using a lump of thermite to set off the airbag in the steering column of your car would seem to risk igniting the airbag, and potentially depositing a burning lump of thermite on the lap of the driver having burnt it's way through the intervening material. If you can control the laydown to the micron level discussed then i'd imagine that it opens up the safe, controlled use of thermite for things that it hasn't been safely useable for previously.

        2. Weiss_von_Nichts
          Flame

          Re: Not usually one for pedantry

          Maybe. Nonetheless not even two horses would get me into a car with thermite-fueled airbags. Sounds more like a Napalm-bag to me.

          1. Tom 7 Silver badge

            Re: Not usually one for pedantry

            Gunpowder is an explosive and that burns rather than detonates. Contain it and it definitely goes bang - which is good enough for me. Containing thermite would probably achieve the same result.

            1. Weiss_von_Nichts

              Re: Not usually one for pedantry

              "Containing thermite would probably achieve the same result."

              No. It definitely won't. Thermite will melt or burn practically any container except a ceramic one. And it combusts by no means as rapidly as gunpowder or any real explosive.

            2. Kevin McMurtrie Silver badge

              Re: Not usually one for pedantry

              Thermite isn't an explosive because it doesn't expand when it burns. It just sits there and makes a blinding-hot puddle of metal. It would need to be mixed with something else that vaporizes.

      2. Peter2 Silver badge

        Re: Not usually one for pedantry

        Black Powder (ie gunpowder) isin't triggered by pressure, but would be triggered by thermite, or any spark in it's vicinity.

        At this point there is some argument about if that explodes or just burns really fast, which I shall forestall by pointing out that it's internationally reconised as being an explosive, and this happens when you blow up a ton of it. https://youtu.be/zI9WMJX85Eg?t=52m27s

      3. The First Dave

        Re: Not usually one for pedantry

        "Explosives are triggered by pressure"

        That is fundamentally the difference between "an explosive" and a "High Explosive" - the latter detonates, while the former burns rapidly. Shock alone will not set off Gunpowder (unless it generates heat on contact), while most kinds of Plastic explosive will burn safely.

        1. Anonymous Coward
          Anonymous Coward

          Re: Not usually one for pedantry

          "the latter [high explosives] detonates"

          This seems to be the key difference; a low-explosive, like gunpowder, actually burns in a similar way to paper or wood, with a clearly defined flame-front, progressively and subsonically, whereas a high-explosive detonates when and as a supersonic shock wave passes through it. The energy (and gas) release occurs far more quickly - supersonically vs. subsonically - with a high-explosive than with a low-explosive.

          1. Charles 9 Silver badge

            Re: Not usually one for pedantry

            Then what do you class triacetone triperoxide and other unstable compounds that can react to more than just pressure yet do perform chemical supersonic detonations when they DO go off?

  2. Phil Kingston

    "the only sacrifice at this point of development is that the nanothermite" and a warranty

  3. jake Silver badge

    I can't be the only one ...

    ... who has long thought that mixing thermite and inkjet printers is good idea.

    1. Tom 7 Silver badge

      Re: I can't be the only one ...

      No - theres not enough 'mass' in a printer to make it more entertaining than just thermite itself.

      Now mixing a printer with an airbag could be fun...

    2. I ain't Spartacus Gold badge

      Re: I can't be the only one ...

      I approve of blowing up printers, and / or hitting them with big hammers.

      What I'm not so sure about is giving them control of explosives. Printers are mischievous, if not actuallly evil, and should not be trusted with such power.

      it'll all end in tears terminators. You mark my words!

    3. John Brown (no body) Silver badge

      Re: I can't be the only one ...

      "... who has long thought that mixing thermite and inkjet printers is good idea."

      The White Rabbit Project, starring the Mythbusters B team, had Grant Imhara demonstrate what happens when an unmodified inkjet printer has it's inks replaced with accelerates. The heat used in the normal inkjet printing process is enough to set the whole thing on fire.

  4. Anonymous Coward
    Anonymous Coward

    Burning 200K cooler is a 'sacrifice'?

    Tell that to the people with burns on their face from when their airbag deployed. Granted that's better that not having a face behind it impacted the steering column at 75 mph, but airbags that don't burn you would be a nice improvement.

    1. Tom 7 Silver badge

      Re: Burning 200K cooler is a 'sacrifice'?

      I thought the burns from airbags were not thermal burns but 'carpet' burns from the material dragging across your face.

      AI could be introduced to punish bad drivers though so a choice of explosives could help moderate drivers.

      1. Hans Neeson-Bumpsadese

        Re: Burning 200K cooler is a 'sacrifice'?

        I thought the burns from airbags were not thermal burns but 'carpet' burns from the material dragging across your face.

        Correct, I believe, so deserving of an upvote, but..

        AI could be introduced to punish bad drivers though so a choice of explosives could help moderate drivers.

        Worthy of a downvote for referring to AI. What you;'re described is a simple algorithm.

        Sorry, but it really boils my p*** that these days everything is getting caught up in the hype about AI. If all you're talking about is getting a machine of some sort to just do a thing, you are describing an algorithm.

      2. Anonymous Coward
        Anonymous Coward

        Re: Burning 200K cooler is a 'sacrifice'?

        AI could be introduced to punish bad drivers though so a choice of explosives could help moderate drivers.

        Nice idea. Maybe have arse airbags in the seat, and use tintawn as the seat material. If the register <Driver behaviour> equals the value "complete tit" or "aggressive moron", then when the car comes to a halt, the moment the ignition is switched off, the arse airbags fire.

  5. Anonymous Coward
    Anonymous Coward

    Airbags...

    Don't use thermite.

    No napalm either.

  6. Paul Woodhouse

    hmm... air bag explosives are dangerous enough, plenty of vids on youtube of morons possibly getting non-posthumous Darwin awards by sitting on seats with airbags under them and setting them off..

    while we're on about printers, laser toner itself is pretty damn explosive given the right environment as me and an old colleague once found out during a very boring overtime session one Saturday.

    1. Tom 7 Silver badge

      @ Paul Woodhouse.

      Under no circumstances should you connect a 32' length of 6' plastic drain pipe vertically to the side of a building, light a candle at the bottom and then pour a cup of toner down it.

      Or alternatively lie the pipe on a slope and pour the toner in the top and roll the pipe so the toner is evenly distributed down the length and throw in a lit banger and RLF. This is because you will be running backwards so you dont miss the fun and that could be dangerous!

      1. Paul Woodhouse

        Re: @ Paul Woodhouse.

        heh, ours involved a shit load of the stuff and one of those old metal dusty bins... it set off a few car alarms and we could deffo feel the shockwave even though we were hiding behind one of those big industrial bin thingies...

      2. Pen-y-gors Silver badge

        Re: @ Paul Woodhouse.

        6' drainpipe is bloody big drainpipe

        <spinal tap>

    2. Pen-y-gors Silver badge

      Making amateur bangs is not a good idea.

      Scene: St Andrews, late 1974. A University residence Ball.

      After the cabaret everyone goes out into the courtyard for fireworks - not the official sort, these had been made by a chemistry student, in coke cans. Some were quite pretty, a few exploded (no injuries).

      Everyone goes back to the drinking.

      Shortly after there is a nee-naw and blue lights, and the fuzz arrive. Warden then spends some hours down at the Police Station arranging bail for the Senior Student (still dressed as a little schoolboy after the Cabaret) and various others. Unamused Bomb Squad arrives from miles away. I suppose doing this a few days after the Birmingham pub bombings might, in hindsight, have been a mistake.

      1. CrazyOldCatMan

        Some were quite pretty, a few exploded (no injuries).

        Everyone goes back to the drinking.

        Shortly after there is a nee-naw and blue lights

        Much like a friend and I playing with crow scarer fireworks (along the lines of open up, scrape out all the black powder, put into empty baked bean can, put in magnesium strip, light strip, run) in Hadley Woods in Barnet in the late 70's..

        We were not to know that it was only about 100ft away from a Conservative ministers back garden fence..

        Cue a somewhat embarrasing episode involving a slipper after the police made house-to-house enquiries and my dad putting two and two together (the other two being the empty box of old crow scarer fireworks in the garage..) I was (maybe) 10 at the time.

    3. CrazyOldCatMan

      laser toner itself is pretty damn explosive given the right environment

      Any fine particulate that can be oxidised rapidly is going to be dangerous in the (wrong) environment. Sawdust, coal dust and fine sugar have all caused major fires when mixed into a sufficient volume of air while a heat source is present..

      1. Pen-y-gors Silver badge

        Sawdust, coal dust and fine sugar have all caused major fires when mixed into a sufficient volume of air while a heat source is present.

        And flour, I believe. And not just fires - explodes impressively at the right concentrations.

        Cue Sir Pterry and "Monstrous Regiment" - but happens in real life as well.

        1. Claptrap314 Silver badge

          Not just flour. The dust that happens when you pile a lot of wheat (or sorghum) into a grain elevator also does well. There have been a number of explosions, with varying numbers of dead humans, throughout the US, especially in the Midwest. I don't seem to hear about them as much any more--which is hopeful.

          1. Charles 9 Silver badge

            I believe insurance companies demand regular housecleaning in order for silo owners to keep their policies. The risk of a YOYO after the next silo explosion probably makes for a good motivator.

            If you think dust explosions are intense, you should see what happens when you switch out dust for fuel mist (the end result is a nightmare called a Fuel-Air Explosive).

        2. jake Silver badge

          Flour.

          Can demo this. Take a six foot length of 4" PVC pipe. Drill four 3/4" holes around the circumference of one end, about 2" from that end. Place a votive candle on the ground, and put the pipe over it. Light the candle through one of the holes. Dump about a 3 tablespoons of sifted[0] flour into the open end. On a calm day, the minor explosion[1] can be fairly loud, and the resulting smoke-ring can rise & expand far more than you might think. All sizes are approximate. I've never actually measured anything when doing this, yet it always works despite my lack of care and attention.

          NOTE! While I've never had an issue playing with this toy, nor have I ever heard of anybody getting hurt or doing damage to anything, this may be illegal in your jurisdiction. Most such toys tend to get lawmakers upset, probably because they are always vaguely afraid that somebody, somewhere, is having fun.

          [0] If you don't sift it, it might fall as a clump & extinguish the candle.

          [1] Depending on pipe size, hole size & number, grind of flour, and other variations, the noise can range from a mild "pop" to a dull "thud" to a deep "bang".

  7. Tom 7 Silver badge

    Shaped Charge Tats!

    Could catch on...

  8. Herbert Meyer
    Mushroom

    instead of a Suicide Vest

    They will have a Suicide Tee Shirt. With graphics.

  9. Pen-y-gors Silver badge

    This might not bode well

    This is clever, but - and I hesitate to ask this question as it may be mis-interpreted by certain organisations - how difficult is it to make normal thermite in large quantities? Not that I want a detailed recipe, you understand, but is it kitchen-table chemistry or major-industrial-plant chemistry?

    Interesting possibilities for booby-trapped 3D-printed stuff though...

    1. Hans Neeson-Bumpsadese

      Re: This might not bode well

      I think it falls into the shed-tech / kitchen table end of things. I seem to recall one of those popular let's-blow-stuff-up-and-pass-it-off-as-science programmes on the tellybox, where they mixed up a batch on table (although they obscured some details so you couldn't just copy the recipe yourself)

    2. handleoclast

      Re: This might not bode well

      how difficult is it to make normal thermite in large quantities?

      Take quantity X of finely-powdered ingredient A and mix thoroughly with quantity Y of finely-powdered ingredient B. Piece of piss.

      It's not hard to find out what the ingredients are. Actually, there are several variations, but one is cheaper than the others.

      It's not hard to work out the appropriate quantities.

      Mixing is dead easy.

      Getting the ingredients in finely-powdered form is more work.

      You can't ignite it easily. A match won't do it. You need a higher temperature than you can get from a match.

      Even so, it's not beyond the bounds of your average terrorist. Well, apart from the intelligence required to figure out some of the steps. And having a mind-set that relies on facts and logic rather than belief in fairy tales.

      That said, thermite isn't explosive. So not of much interest to terrorists. There are possible terrorist applications but the terrorists don't seem to have thought of them.

      1. Anonymous Coward
        Anonymous Coward

        Re: This might not bode well

        1kg of fine aluminium powder, apx 15 quid. Ebay

        1kg of fine ferric oxide, apx 10 quid. Ebay

        Small bottle of potassium permanganate and glycerine (pet shop and chemist) apx 5 quid.

        Instructions for quantities and igniting all over internet.

        But thermite isn't particularly "explosive". But by god, it burns like fury!!

        Mainly used for welding train tracks and fucking up large calibre weapons.

        1. Mike 16 Silver badge

          Ebay, or Amazon? Re: This might not bode well

          A friend ordered some fine Al powder for use in paint, and Amazon popped up that "People who bought this item also bought" Fine iron oxide powder. (They also suggested glassine envelopes and blue rock candy when he bought a hazmat suit just before All Souls day...)

        2. Farnet

          Re: This might not bode well

          Please don't post any recipes for anything dangerous here as someone will try it.

          From experience, as a (lapsed) member of the pyrotechnics society, as a member we were heavily coerced into rapidly understanding the difference between detonation and deflagration within mixtures, and although BP is classified as an explosive it will only explode in a confined environment that gets breached by a pressure build up (as per some of the clever clogs above comments).

          The danger of Thermite is once the reaction starts you cannot stop in, as it generates the gases required itself to continue the reaction during the burn process (and pouring water on it is a REALLY bad idea), but it will not explode, there is a way to do it in open air but like I said I'm not explaining it here.

          H.E. is a whole different ball game and something that's hard to comment on as H.E. covers a very wide spectrum of mixtures.

    3. CrazyOldCatMan

      Re: This might not bode well

      how difficult is it to make normal thermite in large quantities

      Pretty easy - we did it in O-level chemisty. We had a slightly mad lab-tech who had a favourite phrase: "put a bit more in"..

      We melted the suspended ceiling tiles. Apparently, we were supposed to use the smallest size of crucible and not the largest..

  10. Red Ted Silver badge
    Pint

    Four PhD Supervisors?

    Ms Murray has my sympathies, all the students I knew with two supervisors spent signifiant amounts of time with one contradicting the other.

    I predict an exponential increase in this problem with each extra supervisor! She may need a bunch of this --->

    Thermite is one of my favourites as a civilian application of explosives, for example welding railway rails together.

    1. I ain't Spartacus Gold badge
      Happy

      Re: Four PhD Supervisors?

      Ah well. She may have had trouble with multiple PHD supervisors. But now she can print a letter or t-shirt that will burn your face off - so they'll probably be a lot nicer to her in future...

      1. Swarthy
        Thumb Up

        Re: Four PhD Supervisors?

        So she just invented Explosive Runes?

  11. david 136

    I'm for this 1000% if they use it to make it easier to open blister packs.

    1. Tom 7 Silver badge

      RE: Blister packs???

      So you could package bacon in such way that, not only could you get the package open on a blurry sunday morning, it would be piping hot too!

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