From: REMOVE_THISdwilkins@means.net (Don Wilkins)
Newsgroups: rec.crafts.metalworking
Subject: Re: SELL - Iodide Zirconium Rods 30$ / kg, Zr > 99.8%
Date: Sat, 07 Feb 1998 16:18:46 GMT

On 3 Feb 1998 21:57:31 -0500, kinsler@froggy.frognet.net (Mark
Kinsler) wrote:

>Does anybody know what the heck "iodide zirconium" is?

Yup it is zirconium metal produced by the iodide method. I suspect
that you might like to know more.

Cheap (and not pure) zirconium is produced by adding gaseous zirconium
tetrachloride to molten magnesium metal. (In the absence of air of
course) The end product is always contaminated with magnesium and it
doesn't take much magnesium to make it brittle, etc.

Now long ago someone discovered that at one temperature iodine would
react with zirconium metal to form zirconium tetraiodide and that at a
higher temperature the tetraiodide would decompose to zirconium metal
and free iodine. Now since the tetraiodide is a gas at these
temperatures it would appear that one could move zirconium from one
place to another using the iodine to do the transporting. In fact this
is exactly what happens . The "hottest zone" usually starts as a
tungsten filament. So you put some impure zirconium metal in a vacuum
system with a tad of iodine, create your temperature differential, and
let your iodine run back and forth between the hot impure stuff and
the hotter filament. It goes in one direction as zirconium tetraiodide
and returns as elemental iodine. Fortunately magnesium (a major
contaminant) and a lot of other junk don't participate in this cycle.

The resulting zirconium is high purity and ductile. The rods which
come out of the process are a mass of fairly large single crystals
(beautiful stuff). One of the processes is called the van Arkel
method.

The high purity zirconium was used extensively for containing nuclear
fuel in reactors. Some of the best sonar transducers are made of
lead-zirconium-titanium oxides. Zirconium oxide is (or was) added to
the ceramic in spark plugs to reduce the coefficient of expansion and
increase the dielectric strength.

So that is why it is called iodide zirconium. Probably more than you
ever wanted to know.

Titanium and a few other metals can be produced in high purity by
similar techniques.