Single crystals and other reasons my job rocks

The post about metal rings got me thinking about my job. As a materials scientist, I get to melt stuff. A friend once told me "you don't have to scratch a chemist very deep to find a pyromaniac." It's no coincidence he was a chemist. Melting stuff is fun. No, it's not fun, it's AWESOME.

The other day I mentioned that tungsten has the highest melting point of any pure metal. I once had the great privilege to handle several single crystals of tungsten, each the size of a thick toothpick. Here's where I school you a little.

The metals you see around you every day are crystalline, just like diamonds. The difference is that jewelry gemstones are single crystals, whereas metal crystals are small and so well bonded together that you don't notice them. In a crystal, all the atoms are lined up in three dimensions, packed in closely like freshly racked billiard balls. By contrast, in a glassy material, the atoms are positioned randomly.

You can make single crystals of many materials by a technique called Czochralski growth, where basically you melt a bowl of the material, bring a cold "seed crystal" down in contact with its surface, and slowly pull upwards while keeping the seed cool. The molten material will solidify onto the seed in perfect alignment with the atoms that are already there. This is how the computer industry makes silicon "boules" twelve inches in diameter, later to be made into microprocessors.

At this point your scalp may be starting to sweat as you contemplate the possibility of twelve-inch diamonds. Relax: there is no such thing as molten diamond. It goes straight from solid to gas, like moth balls and dry ice. There's a similar problem with tungsten: the only kind of bowl you can melt tungsten in would be either diamond (expensive) or, well, cold tungsten. Instead, they use a different technique. They make a rod of ordinary tungsten, and then melt a little section in the middle. They move this molten section slowly along the length of the rod, and usually eventually one of the solidifying crystals will get bigger until it fills the whole width of the rod. This is quite difficult at 6200 degrees Fahrenheit.

In my current job, I use a similar technique--a quartz tube with a moving heater around it and an alloy inside--to make nearly perfect crystals of my material. There are usually at least two or three crystals at any point along the length of the thing, but still: it's a two pound metal crystal, an inch around and eight inches long. It gives me a gut thrill every time I handle one, and I think of the perfect crystalline order of tens of millions of atoms standing in a line.

It's a coincidence, probably, that these objects are shaped like metallurgical phallic symbols. Alloy furnaces are the hairy ball sacks of materials science. It's complete command over nature, a triumph of empirical rationalism, and it gives me a hardon once in a while.

That might seem perverse, but I think it's common. Accountants and MBAs get a hardon for large sums of money. Engineers, for metals and big power and, well, big engines. Military guys, for big weapons, probably. HU-AH.

Other amazing things I have held in my hands: a fist-sized chunk of "machinable tungsten" (really tungsten powder cemented together with rhenium) which was astonishingly heavy; a fuel injector plunger coated with "near-frictionless carbon", which provides a sliding friction coefficient of 0.001 in dry air; a four-inch-wide disc of boron carbide, one of the hardest materials known; and more.