Why is Gold So Weird? 
by Andrew Kerr

Note: The Uzi Landman quote below was extracted from Georgia Tech press release Physicists Discover Gold Can Be Magnetic on the Nanoscale. That press release was the springing-off point for this article.

One is not supposed to judge a book by its cover, but gold, a metal that has been aesthetically admired since the dawn of time, possesses dazzling physical properties that live up to its beauty.

The latest in a long line of weird gold discoveries comes from Georgia Tech, where the Center for Computational Materals Science has found that gold, which is not magnetic when it is, say, in the form of a necklace around your neck, is magnetic on the nanoscale (in other words, when the quantity of gold is extremely tiny [nanotechnology generally focuses on stuff happening at between one billionth to ten millionths of a meter]). "It’s a very exotic thing," says Uzi Landman, who is director of that center. "Finding materials that have magnetic properties when their bulk form doesn’t have those properties is very interesting from a fundamental point of view, and may have certain future technological applications."

We have long known that gold is weird. The first useful physical property of gold that the ancients discovered is its extreme malleability and ductility (in other words, it can be bent and shaped easily without the metal breaking). In fact, gold is the most malleable and ductile metal on earth. One can hammer gold into a thickness that is way less than that of a sheet of paper. That same extreme softness demands that under certain circumstances gold must be combined with other metals to make it harder (as is often the case with jewelry). Gold karats refer to the ratio of gold to other substances in such combinations on a scale of 24 parts--so 24 karat gold is 100% gold.

But counterintuitively, when one thinks of other soft things (like Nerf footballs), gold is also extremely heavy is due to its incredible density.

The ancients also quickly figured out that gold does not corrode over time (rust is an example of a common type of corrosion). So, if you put together gold's malleability and its resistance to corrosion you can see why, in the 15th century, people began using gold for fillings in teeth.

Shaping gold into stuff was about all people could do with it for centuries, though those typically superstitious medieval folks tried eating it, reckoning that something so rare and pretty must also be great for the body. Even today's filthy rich sometimes eat or drink things with gold flakes in them. But the same properties that make gold so resistent to corrosion also guarantee that it reacts to nothing in the human body whatsoever; like an introvert walking through a party without making eye-contact with anyone, metallic gold will er, "pass through" the body unaltered. This same resistance to interactivity with other elements is also why pure gold has no taste when put in your mouth--so there's no flavor enhancement to be gained from adding it to your chocolate candies.

With the development of research into electricity in the early 19th century, new gold weirdness was uncovered. It was found that gold is a poorer conducter of heat and electricity than copper and silver, but gold remains conductive longer than those other metals due to that same resistance to corrosion.

Gold is also highly reflective, making it an ideal coating for astronaut visors. it can be pounded thin enough to be mainly transparent while still casting the glare of the sun back out into space.

So when you consider all these strange properties of gold, one can better understand why Georgia Tech's discovery about gold's magnetic properties on the nanoscale could prove very useful in the construction of various nanodevices. And since there's not a lot of gold around, finding a "nano" application for the stuff might be a very good idea! :-)



Some related links:

American Museum of Natural History page on properties of gold
Ye olde Wikipedia entry on gold
A look at the history of dentistry, which mentions gold