Nanotech Foils Aid Metal-to-Ceramic Joining

mekkab writes "No longer promising commercial applications "in the future", Reactive NanoTechnologies has new nano-tech that they are actually selling a foil of alternating layers of atoms to join dissimilar materials. This joining method is unique in that the foil provides all the energy needed to melt the solder or braze, eliminating the need to heat the components with a furnace, torch, or laser. This simplifies and speeds the joining process, in many cases cutting the cost of joints in half or possibly more. The Baltimore company believes that a sheet of foil, made of alternating layers of aluminum and nickel only a few atoms thick, can revolutionize the manufacture of everything from computer chips to airline engine components."

Comments

Re:typical press release?

[The_Laughing_God]

Currently, the total bond area in many metal-ceramic joints is limited to about 1 sq inch, which is a significant limitation for most objects. The surface of a ceramic piston sleeve in a metal engine can be 100 sq in or more. (I don't think this particular example is very promising for this new nanotech, it's just a size example)

The termal stress is reduced because the two dissimilar metals are not heated very much, the brazing or solder material is heated to the high required melting temp (from the inside of the joint, outwards, rather than from the outside in). Since the dissimilar materials are not heated as much, they will not expand as much, and hence will not contract as much wehn cooled. It is the absolute change in size (relative to the intramolecular bonds of the joint) that is most relevant to joint cracking

More details

[jspey]

Jeez, I have a busy day at work and as a result have to wait utill tomorrow to find out my advisor's company has been slashdotted :-]

The foils work like this:

When two elements mix together they will all either give off energy or suck up energy. If two elements give off energy when they mix then they mix exothermically. In the case of solids, it's usually not possible to take advantage of this energy because it's very difficult to get to chunks of differnet elements to mix together on the atomic level. However advances in computer chip fabrication methods have made this energy accessible.

The energy of mixing is made available by creating very thin alternating layers of two materials with a very high heat of mixing. Right now work working with a thickness of 50nm per two layers (that's 50nm for one layer of material A plus one layer of material B). When the layers are that thick, it's possible for atoms of the two layers to actually diffuse into each other due thermal diffusion when they get hot enough.

Right now we're using a 30V spark to get them hot. The spark will get a very small section of the foil hot enough to have the two layers diffuse into each other. When this happens a lot of heat is released (since they mix very exothermically). This heat energy is enough to make the atoms all around the sparked area start to interdiffuse, which gives off heat, which causes more atoms to interdiffuse, etc. The reaction moves through the foil very quickly (around 1 m/sec) and generates enough heat to get the foil up to very high temperatures (our current system gets to around 1200 deg C). As you can see, all the heat actually does come from inside the foil. This rapidly generated heat can be used to melt a strong, high temperature solder known as a braize that's attached to the two parts you are joining. Normally the only way to melt this braize is to put it in an oven at 800 deg C or higher, which is what leads to the high thermal mismatch of metal-ceramic joins. If the foil is used to join the two materials, they won't get hotter than ~100 deg C, resulting in very low thermal mismatch. And thanks to all the work from the IC industry the technology to make these foils, which expensive to buy, is very cheap and easy to operate, allowing us to make the foils inexpensively.

I'm sure I could have done a better job of explaining the foil, but at least I have more info than the blurb. BTW, there's a better version of the article here.

Mr. Spey