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The 6 Alloy Families: Indium - Part 1

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  • Eric Bastow: Today we're going to be talking about this really awesome metal called Indium. It's so awesome there's a whole company named after it. Indium melts at a 157 degrees C, which is 315 degrees Fahrenheit. It's a really, really strong, but it's not as strong as I am. Actually, no. It's really, really soft metal, much softer than lead. Because it is so soft, when used as a solder, it's actually very good for high CTE-mismatch applications, where you have two dissimilar materials that are expanding and contracting at different rates. If they're soldered together with indium – indium or an alloy of indium – it can help to absorb some of those stresses.
    Because it is so soft, it also works very well in compression seals. If you have two surfaces, two flanges, you're trying to make a seal of some sort, you can put a piece of indium in there. When you bolt it together, the indium is so soft it'll fill in any air gaps and seal it off. It also is very useful in thermal interface applications, because it is so soft so that when you put it between two surfaces that you want to thermally link together, it makes really good contact, because it is so soft it will conform to those surfaces.
    Indium also has really low vapor pressure, and that's very useful when making a seal on a vacuum system. The other soft metals, like lead, have a high vapor pressure, and they would actually contaminate that high-vacuum system. Indium is so soft, and one of the unique properties of Indium is it remains soft even at cryogenic temperatures. There's actually a report that the Air Force did, where they took an alloy of indium, they took it down to liquid helium temperatures, which is 4 degrees Kelvin, and the material still remained compliant. If you try to do that with something like a tin-based alloy, or tin itself, it will just turn to powder.
    Indium has really, really good thermal conductivity and that's another attribute that makes it very useful as a thermal interface material. The thermal conductivity is 86 Watts per meter degree K. We have this awesome metal. A whole company is named after it. If you'd like more information on it, please contact us at


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