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3D-Printed Ceramics Could Help Build Hypersonic Planes ( 80

An anonymous reader writes: Researchers have used a 3-D printer to make specialized ceramic parts that have overcome one of the biggest problems with ceramic objects: their tendency to crack. This new method is 100 to 1,000 times faster than previous 3D-ceramic-printing techniques, the researchers said. Furthermore, electron microscopy of the end products detected none of the porosity or surface cracks that normally weaken ceramics; indeed, these silicon carbide materials were 10 times stronger than commercially available ceramic foams of similar density, the scientists noted. "If you go very fast, about 10 times speed of sound within the atmosphere, then any vehicle will heat up tremendously because of air friction," said Tobias Schaedler, senior scientist at HRL Laboratories in Malibu, Calif. "People want to build hypersonic vehicles and you need ceramics for the whole shell of the vehicle."
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3D-Printed Ceramics Could Help Build Hypersonic Planes

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  • Tell that to my coffee mug.
    • by Rei ( 128717 ) on Sunday January 03, 2016 @06:44PM (#51232227) Homepage

      When was the last time your coffee mug melted?

      The point isn't to stop them from getting hot - the point is to not melt or weaken when they do. Ceramics are the best materials in existence for this. For example, hafnium nitride carbide melts at 4126C. Iron boils at 2826C. And this is more meaningful than it sounds - because the only ways during reentry that one can get rid of heat are storage, ablation, and radiation. Depending on the Cp scaling factor, ablation and storage are proprortional to the temperature to the 1-2 power while radiation is proportional to the fourth power of the temperature. So being able to tolerate a given amount of higher temperatures translates to being able to dissipate far greater amounts of reentry heating.

      The fact that their first material was silicon oxynitride I find interesting. I don't know how thick their layers are and whether they're able to get any transparency out of them, but thin films of silicon oxynitride are sometimes used for gradient-indexed optics - by changing the ratio of oxygen and nitrogen you can greatly change the refraction index, and thus make things like perfectly flat, thin transparent objects that function as lenses - like a fresnel lens but without roughness or distortion. And when you dope silicon oxynitride you can make phosphors of various colours. So depending on what blend of powder they lay down with the print head they may be able to use it as a rather nifty optics-printer. And since they're using UV to solidify the substance they're basically doing photolithography, aka they should be able to do very fine details. And it's a dielectric with good thermal conductivity. See where I'm going with this? Literally printing your own displays.

  • by Brett Buck ( 811747 ) on Sunday January 03, 2016 @06:11PM (#51232071)

    The heating is largely from compression heating the air, not "friction" in the usual sense.

    • I'm kinda hoping that a scientist working in the field knows about this, and just figured that "compression" was too big a word for most laymen (and, increasingly, most reporters).

    • by Rei ( 128717 ) on Sunday January 03, 2016 @06:56PM (#51232279) Homepage

      It's not even that simple.... in the exosphere, it's more like individual particle collisions than like dealing with a bulk gas. And then when you get deeper you get into the atmosphere, it still doesn't behave like a normal gas - the dense compression shocks of air that you've built up in front of you that are so hot that you actually lose some of the heating energy to endothermic chemical reactions - there's a different equilibrium there than at lower temperatures. While there's enough time to reach the new equlibrium in the shocks in front of the spacecraft, in the sidestream the gas moves past so fast that it doesn't have time to reach its new equilibrium as it cools ("frozen reactions") - the reactions happen at a point well behind the spacecraft, releasing the energy there. So the spacecraft actually gets away with bypassing part of the energy it's losing to the atmosphere.

      On the other side, these frozen reactions have downsides too - it's part of what makes scramjets so difficult (the desired combustion being "frozen" to past the end of the craft due to insufficient reaction time). In fact, if this didn't happen, you could potentially make spacecraft that propel themselves in the outer reaches of the atmoshere/low Earth orbit (anywhere over 100km really) without need for onboard propellant by recombining the free oxygen radicals that dominate there. (technically you still probably could, but it would require a long spacecraft indeed)

    • Lol... I came here to say exactly this. Why any reporter would type anything these days without fact-checking it blows my.... wait... I retract my previous statement.

  • by turkeydance ( 1266624 ) on Sunday January 03, 2016 @06:15PM (#51232099)
    in the shape of an ashtray
  • "People want to build hypersonic vehicles and you need ceramics for the whole shell of the vehicle."

    Only the military wants hypersonic vehicles like this - unlike ICBMs, these would be harder to detect until they reach their targets. This will be a destabilizing factor between the east and west - and you can be damn sure China will build similar vehicles.

    • by fnj ( 64210 )

      Only the military wants hypersonic vehicles like this

      It seems to me that a few people might be interested in flying 12,087 km from Los Angeles to Sydney in 3.8 hours at Mach 3 or 2.3 hours at Mach 5, rather than 13.4 hours at Mach 0.85. Like maybe just about everybody who flies that route or a comparable route.

      • It would probably be cheaper to just send them by sub-orbital ballistic craft. No fighting air resistance for most of the flight.
        • The problem with that is it's going to make many people nervous, particularly those manning a nation's "early warning system" or "strategic rocket forces". It is hard to tell whether that flight is a business trip or a nuclear attack. Long range hypersonic or sub-orbital weapons face about the same problem.

          • by ceoyoyo ( 59147 )

            The generation that was really paranoid about those things is starting to die off. I wouldn't be surprised if, in the next twenty or thirty years, we get over that particular fear entirely. If you wanted to launch a sneak attack you could put nukes on regular airliners... there's no reason for them to go fast if they're disguised. Ballistic airliners would still be easily distinguished from ballistic missiles: they'd fly trajectories that didn't spill the rich peoples' drinks. Finally, there's not much p

            • You know that it's getting easier to track submarines ... eventually they will not be immune to a preemptive first strike. Plus there are ABM systems, which are improving.
          • by Rei ( 128717 )

            Unless people start making ballistic missiles that look like airplanes, they're going to have very different radar signatures.

            If a country doesn't trust another to not hide their missiles as aircraft, then they won't allow ballistic aircraft transit with that country. The US could still allow ballistic aircraft with, say, Britain while not allowing it with, say, Russia. To get permission to launch, every flyover state would have to give permission - which they wouldn't give if they had fears of a conceale

    • I would very much want ECONOMICAL hypersonic transportation. Unfortunately I think it is a real long shot. This technology might be a minor help for one of the many problems that would need to be solved.

    • by LWATCDR ( 28044 )

      Ahhh. No
      This is also useful for space flight aka scramjet to orbit and also possibly for gas turbine blades as well as other high temp objects.
      Hypersonic strategic weapons will not have a destabilizing effect at all. Just as today SLBMs will be the final deterrent.

      • by Rei ( 128717 )

        Scramjets are rather difficult to orbit. But they are rather interesting for high speed suborbital flight. They let you go through some very thin, high air, very fast. It's also possible to use them for launching into even higher parabolas where they can't fly steady-state, but just drift with nearly no resistance on their way to the destination.

        • by LWATCDR ( 28044 )

          Scramjets can get very close to orbital speeds so all that is needed is a small booster to put you into a stable orbit.
          Yea people want this for any number of devices. The fear on Slashdot at times borders on the level of fear of Trump supporters.

  • Basically part of what the ceramics are doing is insulating components underneath from the heat and friction.

    If the ceramic compound is less porous, there's less air space in there. Which means less thermal isolation.

    So the ceramic compound goes from being a thermal insulator to a thermal mass.

    You REALLY don't want that kind of thing on a hypersonic vehicle.

"If you lived today as if it were your last, you'd buy up a box of rockets and fire them all off, wouldn't you?" -- Garrison Keillor