The Van Arkel-de Boer process is a simple though very costly method for obtaining crystals of very high purity for a limited number of metals. It exploits the reactivity with a halogen, typically iodine, which chemically binds only the target metal, leaving behind everything else. With this, one can toss into the reaction chamber a bit of cheap, unrefined titanium ore and receive the ultra-pure metal.

The molecule formed between the target metal and the halogen is heated into a gas and allowed to settle onto a thin tungsten wire that has been electrically heated. The gas decomposes back into the halogen while depositing the metal onto the filament which grows into an ever thicker cylindrical bar.

While it’s a method that is conceptually simple it is unfortunately much too costly and inefficient to be used for industrial refinement. The titanium bars seen here can easily take weeks to form. During its growth, the chamber where the crystal is growing must be maintained hot enough to keep the titanium iodide in gaseous form and the filament upon which it’s growing electrified. For this reason the yield is way too low to be of any commercial use and remain thus of interest only when labs need small amounts of material of extremely high purity.

That and, of course, for us element nerds too!