Q: Does niobium come in tubes? (I ask because I would like to avoid a rivet in a ring if I can help it.) If so, how workable is it? For instance, could I buy a tube whose inside diameter is close to what I need and then use a ring stretcher to shrink or enlarge the tube diameter? If so, how many sizes: ½, 1, 2? Can niobium be annealed easily?
A: While I have seen niobium offered in tube form the sizes of the tubes were much smaller than needed for a ring. Reactive Metals Inc. carries, I believe, small diameter niobium tube. But the answer to your rivet problem is simply to use well-done flush rivets made of niobium wire. If the holes are chamfered, and the rivets driven tight, then they can be filed flush and won’t show as rivets. You’ll still probably see the lap joint, but maybe you can design a way so that it looks like part of the design, rather than a flaw in it—think it through.
There is almost always some way to make a limitation turn into some neat design feature. Perhaps you can think in terms of modifying the design so the rivets, perhaps now in high-karat gold, become a highly decorative addition to the design, for example. A possible other solution is to use titanium, which won’t give you quite as dense a color, but which is a little harder, a good bit cheaper, and is available in larger tubes, though not inexpensively from my experience with trying to obtain such a product earlier this year. These are industrial products, not jeweler’s ones, so the sizes will be for those uses. You’ll have to experiment to see what you can find. A major problem you’ll have is that most suppliers aren’t interested in selling you only a couple inches of titanium tube. They want to sell you hundreds of feet. You may have to do some considerable searching (and/or begging.) Try the Thomas Register for a starting point, or call Bill Seeley at Reactive Metals. Maybe he knows. (Bill Seeley, Reactive Metals Studio, Inc. PO box 890, Clarkdale, AZ 86324 firstname.lastname@example.org) Reactive is also my favorite source of niobium products, especially in small quantities.
The reactive metals gain their name primarily from the ease and aggressive way they will oxidize. They exist in our normal world as metals only because the instantly formed oxide film on their surface is quite stable and strong. Heated enough to anneal them, that is no longer the case, and oxidation procedes destructively. These metals, heated enough in the presence of oxygen, can become explosively combustible. But this is a good deal hotter than just red hot. Additionally, at annealing temps, they can also absorb other gases, such as hydrogen, to their detriment, becoming quite brittle. For these reasons, annealing Niobium or Titanium or any of the other reactive metals generally requires the ability to heat the metal under a high vacuum. Needless to say, that’s not so easy for most of us. Fortunately, the stuff work hardens only very slowly, and even the harder titanium, purchased as heavy annealed rod, can be forged into quite complex forms without ever being additionally annealed.
Rings of tubing could probably be shrunken down quite a bit easily enough, if the design were uniform. Stretching is often a good deal more iffy. Try it and see. It’s the best way to learn.
by Peter W. Rowe M.F.A., G.G.