Meet Uncle Tungsten's hard-living brother, Tungsten Carbide

I have a new ring that I like to play with and show to people. I wanted tungsten but I ended up with tungsten carbide. Read on.

For many years I wore two rings--a plain silver band on my right hand and my plain platinum wedding band on my left. I'm a materials scientist by trade, so occasionally I would pass these around at conferences and challenge people to identify the metals.

People are used to the relative heft of aluminum and steel; steel is three times as dense as aluminum. Materials scientists play with a lot of different metals, but one of them thought the silver ring was aluminum and the platinum ring was steel, simply because of their weights. (Never mind how absurd it would be to wear aluminum and steel rings. Materials scientists sometimes come up short in the social graces.) Platinum is indeed twice as dense as silver. But the thing is, silver is even denser than steel. Platinum is seriously heavy stuff. Lacking a known reference, the weigh-it-in-your-hand judgement can be way off.

A year or two ago I started seeing rings with dark gray inlaid bands. I found out this was tungsten - and immediately wanted it. In addition to being almost as dense as platinum, tungsten has the highest melting point of any pure metal. (So when spontaneous human combustion catches up with me, they'll be able to salvage my jewelry.)

This month I got my chance. It was near my birthday, and my wife brought me to a jewelry store to show me a diamond ring. Which, it turned out, cost half what my car did. But they also had a heap of plain metal bands. One was polished and dark grey - not just a tungsten inset, but all tungsten. Happy birthday to me! When I got it home I happened to see writing inside it and found that it's really tungsten carbide, but I don't feel too badly about that. Tungsten carbide is the material used to cut other metals: it makes up machine tool cutting bits that reach 1000 degrees C and suffer tremendous forces. These tools (and probably my ring) are actually tungsten carbide powder cemented together with about 5 volume percent cobalt, but I'm not complaining. So my new ring is essentially unscratchable. I'm unlikely to grab anything harder than it is.

I'm no longer wearing the silver band, though maybe I should be. There were other interesting rings in that heap, and I'm tempted to start wearing a metallurgical display case on my hands. The titanium rings were super-light (density less than half that of silver) and actually rather pretty. Some had a rainbow oxide treatment. Titanium is a great lightweight structural metal (turbine engine blades, etc) but it gives a lousy friction and wear surface. So I'm OK with tungsten carbide for the time being.