In London for dinner—with an Australian ceramic rocket

Oct 16, 2012
In London for dinner—with an Australian ceramic rocket
A simulation of a hypersonic vehicle in the upper atmosphere. Credit: Professor Michael Smart, Professor John Drennan, David Yu, The University of Queensland

(—Melbourne researchers are literally doing rocket science with clay. They have developed a cheaper and more efficient way of making the complex, heat-resistant, ceramic parts needed to build tomorrow's rockets and hypersonic airliners.

Using clever chemistry to modify a standard method of casting ceramics in a mould, they have developed an alternative to the traditional technique of forming these ceramics as blocks at high temperatures and pressures. And their new method, a form of slip casting, allows them to generate ultra-high-temparture ceramic components at lower temperatures and pressures, which do not require extensive machining, hence saving time and energy.

"The ceramic pieces we have made are stronger and will survive to higher temperatures than those used on the ," says Dr Carolina Tallon, who is developing the processing techniques with Prof George Franks of the Department of Chemical and Biomolecular Engineering at the University of Melbourne. Their work is part of the propulsion program of the Defence Materials Technology Centre to develop manufacturing capabilities of within Australia.

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Hypersonic vehicle in the upper atmosphere travelling at Mach 8

Hypersonic flight will allow passengers to travel at up to five times faster than the speed of sound (Mach 5). A flight  between Melbourne and London would take about two hours. Jets have already been built that can achieve these speeds for a few seconds, but maintaining those conditions for an entire flight remains a challenge: and it's partly a materials challenge.

"In order to lengthen the duration of the , we need to find a perfect match between and the materials able to survive what that design entails," Carolina says. "At Mach 5, for instance, several of the components of the vehicle will be at temperatures of above 3000 °C. At these temperatures, most of the materials typically used in the will already have melted or if they have not, their properties will be severely damaged and they will not perform correctly. "

Ultra-high-temparture ceramics are a potential solution since they can survive such extreme conditions. But finding the right material is not the end of the story. The actual components to be used in the vehicle have to be formed into complex shapes.

With traditional processing techniques, the nose of a rocket, for example, would be manufactured using very and pressures to produce a very simple geometry such as a solid cylinder, which would then require extensive and costly machining. The new slip casting technique simply requires a mould into which a low viscosity slurry of a particular chemistry can be poured. The ceramic particles then pack efficiently into the required shape as the solvent is removed.

"Using these techniques, I can manufacture components, that already resemble their final shape without machining. This can all be done at lower temperatures and pressures—and the end products are stronger than those made in the traditional manner. The preliminary tests showed that the components we made were able to survive temperatures above 3400 °C while keeping their shape and mechanical integrity," Carolina says. "This technique is so versatile that we can fabricate anything from hip replacements to turbine rotors ."

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4 / 5 (1) Oct 16, 2012
What about crack propagation? Always a problem with ceramic materials.
5 / 5 (2) Oct 16, 2012
What about crack propagation? Always a problem with ceramic materials.

These aren't really the kind of ceramics you might be thinking of. Some of them are even made with combinations of finely powered metals (nano-sized particles of things like aluminum, copper, etc. can be mixed into the 'ceramic' mixture). One of the companies my father worked for (Ecka Granules) is in that business. They provide finely powered metals for production of things such as aircraft turbine fans. The 'ceramic' mixtures of these finely powdered materials allow you to produce the equivalent of an alloy composed of materials that normally do not combine to form an alloy. For example, you can't form an iron/alluminum alloy, but you can press them together in a well-mixed powder form. Note, most metals powdered this finely have explosive properties when exposed to things like air or water. Really cool stuff.
5 / 5 (1) Oct 16, 2012

That's actually a really cool area of research and applied technology that's relatively young in development. Materials can and usually do have surprisingly different properties when you break them down to nano-sized bits. The exact size and shape of the bits is also important, for example, round balls versus flat flakes or jagged crystals. The color-changing 20 symbol on the newer US $20 bill is made of nano powdered aluminum, for example, and so is the symbol on the side of the Bush beer cans that changes color with it is cold. We have really just begun to scratch the surface of what this field of technology might be able to do.
not rated yet Oct 16, 2012
For example, you can't form an iron/alluminum alloy, but you can press them together in a well-mixed powder form. Note, most metals powdered this finely have explosive properties when exposed to things like air or water.

One would think such a composite would also have at least deflagrating properties when exposed to air or water, seeing how oxidized iron reacts with aluminium.
not rated yet Oct 17, 2012
One would think such a composite would also have at least deflagrating properties when exposed to air or water, seeing how oxidized iron reacts with aluminium.

I wasn't using a real world example when I used iron and aluminum. I'm not sure anyone would actually want to do that, but who knows, maybe someone is.

In the plants where they produce these materials they keep the powder in sealed systems. It is transported through pipes with nitrogen, and all the equipment like forklifts and tools are anti-static. The lightbulbs are specical too.

One of the companies my father worked at in Kentucky had a machine malfunction. It was a 4 story tall tower with a 20 foot square base. Something set off an explosion in the powdered alluminum they were making. There wasn't anything left but the concrete slab. They didn't even find pieces of the machine around. Nobody was there, luckily.
not rated yet Oct 17, 2012
Here's some neat trivia:

One of the shades of metallic gold that Nissan uses is actually the native color of oxidized alluminum powder. It's one of the longest lasting colors of auto paint in the world because it's essentially pre-faded.

Oh, and that color-changing symbol on the 20 dollar bills is the same pigment in the auto paint that changes colors. Because of that, the pigment is a federally controlled substance. That's why that type of car paint is so expensive.

The tech that goes into making powders for pigments is the same as the tech they are using to make these new ceramic aviation materials.

You can't carry a ball point pen into a plant where they make those because there's a risk the ball will get into the aircraft part. Since such a ball wouldn't be x-ray detectable in quality control, it wouldn't be noticed until the fan blade came apart in flight. That would suck.

Coincidentally, I can't have regular pens at this bakery for the same reason. Not metaldetecta