65. Terbium: The Joy of Tedium

For more than one reason, element 65 makes the short list of “most annoying elements.”

Featured above: Sitting for portraits could take a very long time, but Mosander didn’t mind.

Show Notes

If you enjoy the program, it would mean a great deal if you were to nominate it for a People’s Choice Podcast Award. There’s a post that walks you through the process right here.

I really hate when I learn some new bit after I’ve already recorded and edited an episode. In this case, I hadn’t even thought of learning why Terfenol-D is called Terfenol-D. Truly an oversight on my part.

Turns out it’s named for its constituent elements. (Literally, the elements.) Terbium, iron (ferrum), and the -D stands for dysprosium. As for the “nol”? That’s Naval Ordnance Lab, where it was originally developed.

We’ve seen this schema before. In episode 22, we learned about nitinol — nickel, titanium, Naval Ordnance Lab.

Supposedly, some foreign exchange students performed a little extracurricular research to learn exactly how Terfenol-D is made. Someone who was very pleased with themselves gave that story the headline, PRC Espionage Leads To ‘Terf’ War.

At one point in time, terbium was considered for use in a fake enamel material or dentures. Apparently this makes the teeth look more natural — possibly only when subject to ultraviolet light? I wasn’t entirely clear on that bit. The idea was it would allow for the creation of dentures that didn’t use radioactive uranium (!!!), but it never really took off.

Finally, those promised fluorescent crystals, as demonstrated by a video that has a real throwback vibe, like the chemistry videos I used to watch in high school. (Or Look Around You, which… surely I must have mentioned Look Around You on some episode or another before now.)

Episode Script

In the 1970s, scientists found that including a little terbium in x-ray machines made that equipment far more sensitive than it was before. This was a pretty significant advance in public health — it meant that patients receiving x-rays could be exposed to far lower doses of radiation and still wind up with useful medical images. That was especially a boon for people who require frequent x-rays for medical conditions. This meant they didn’t have to worry so much about the harm being caused by their medical treatment.1 2

Scientists had found a unique use for the rare earth, something that made laboratory procedures quicker and less unpleasant — a use for terbium that actually improved people’s lives. It’s a gleaming moment in terbium’s history — and, as we will see today, the exact opposite of everything else that’s ever involved terbium.

You’re listening to The Episodic Table Of Elements, and I’m T. R. Appleton. Each episode, we take a look at the fascinating true stories behind one element on the periodic table.

Today, we’re bugging out over terbium.

You know the deal by now: A grey metal, with a grey personality, which proves that just because a metal is called “rare,” that doesn’t make it precious. And as you already know, it’s part of the legion of elements that originate from Sweden’s little Ytterby.

We’ve been wading through the lanthanides for a while now, so you could be forgiven for thinking that this is all starting to feel a little repetitive, or a little tedious, or even a little repetitive. Most people would. But one person who didn’t was Carl Gustaf Mosander, and that’s what made him so special.

Mosander was born in Sweden toward the end of the 18th century, which was cosmically good luck for someone with an interest in chemistry. He was in exactly the right place at exactly the right time to study under the tutelage of Jons Jakob Berzelius. Mosander was a painfully slow experimenter, often to his mentor’s frustration, but he more than made up for his slow speed3 with the fine precision of his results. Ultimately, Berzelius hand-picked Mosander as his successor as the Karolinska Institute’s professor of chemistry and pharmacy.4

Those were some impossibly large shoes to fill. Berzelius was legendary in his own lifetime. He discovered two elements and was the first to isolate two more; he coined basic chemical terms like isomer, allotrope, and catalysis; he invented the system of chemical notation that the modern periodic table displays. His birthday is a national holiday in Sweden.

Talk about a tough act to follow.

Admirably, Mosander did not resign himself to languish in the shadow of “the Father of Swedish Chemistry”… but neither did he seek to surpass his achievements. Instead, he simply set out to be the best possible Mosander he could be.

And once again, he was extremely fortunate to be in the right place at the right time. The world didn’t need another Berzelius after he retired. There was a whole family of new elements waiting to be discovered, but they weren’t going to be found via electrolysis, the process so theatrical that it made Humphry Davy look like a madman and bestowed several injuries to match. Nor would they be cerebral puzzles, like technetium, which Emilio Segre realized Ernest Lawrence had accidentally synthesized in his lab, then got Lawrence to unwittingly send it to him.

No, isolating the lanthanides was much more straightforward than that. All it required was a sample of ore — something from that mine in Ytterby would probably do the trick. The ore was then dissolved in acid, producing a liquid mixture of mineral salts. Then, very carefully, very slowly, this solution was brought to the exact temperature that would cause one, and only one, of the elements in the solution to crystallize, removing that element and leaving the rest. It’s an effective technique, but not perfectly efficient, so the chemist would repeat the procedure. And they would repeat it again. And again… hundreds or even thousands of times.5

It’s the kind of work that demands a scientist who possesses more patience than brilliance. Davy would have thrown down his electrodes in frustration; Segre probably wouldn’t have bothered in the first place. Carl Gustaf Mosander, however, was exactly the right person for the job. He wasn’t just up to the task — he truly reveled in it. He was motivated not by a desire to push scientific boundaries, but to conduct experiments and record measurements with the utmost possible precision. It was actually a source of great pride for him that he didn’t even need to understand the theoretical underpinnings of the process in order to execute it properly.6 7

Thus, through the power of good old-fashioned elbow grease and gumption, Mosander ran through the lanthanides. He separated lanthanum from cerium, then showed that there were even more elements hiding within that cerium, and from yttria he distilled terbium and erbium.

Scientific progress is often portrayed as something that requires intelligence so vast as to be entirely inaccessible to the common folk, unique insights that geniuses, in their kindness and grace, bestow upon humanity in their grace. And sure, Einstein is great, but he wasn’t some divine being. By reinforcing that narrative, perhaps we end up discouraging participation in the sciences by those who possess other, equally valuable gifts.

More often than not, scientific progress is driven not by polymaths who won the intellectual lottery of life, but by those who are simply willing to do the hard work.

Now the element collectors are the ones being called upon to perform some hard work, because I’m afraid terbium is not one of those elements that’s part of our daily lives. Even the textbook example of a common application for terbium seems out of reach for the average chemical enthusiast.

When talking about how terbium is used, all the popular literature mentions a little device called the SoundBug. It’s a little doodad — technical term — about the size of your palm. It has a suction cup so it can be attached to a flat surface, like a window, or a wall, and it turns that surface into a flat resonance panel — a speaker.8 9

It’s a pretty neat trick that can fill a room with sound without any visible speakers. It does this through the clever use of Terfenol-D, which, despite its name, is not a highly lethal pesticide. Rather, it’s an alloy of terbium, dysprosium, and iron that exhibits a rare behavior: When subjected to an electromagnetic field, the metal will change its shape and size. Feed an electrical signal to a piece of Terfenol-D and it will pump those good vibrations through any flat surface you like.

It’s a phenomenon called magnetostriction. You might have noticed that several of the lanthanides possess notable and strange magnetic properties. That’s thanks to the high number of unpaired electrons they all have, as we discussed in episode 60, Neodymium.

That’s all well and good, but there’s only one problem: Nowhere does the SoundBug actually appear to be for sale. It seems that no one’s even mentioned the thing since about 2004.

It all starts to add up after a quick glance at the copyright pages of the aforementioned literature. The authoritative sources were all written or last updated around 2010. The SoundBug was already old news then, and there’s a solid decade between then and the recording of this podcast. Simply put, things have changed.

The company that manufactured the SoundBug is actually still around. They’re called FeONIC, and they seem to have abandoned consumer electronics to instead provide this technology to retailers. They don’t publish the prizes of their products; instead, interested parties need to request a tech demo from their sales department.

Their flagship product is called, somewhat ominously, “Whispering Window,” and it’s essentially a souped-up SoundBug that’s tailored for the retail environment. Specifically, it turns large display windows into speakers, quietly and invisibly suggesting that passers-by should go in that store to buy things they don’t need. “Turn pedestrians into customers,” their website promises.10

You can tell that we’re living through late capitalism because our brightest minds are finding new, innovative ways to convert literally every possible surface into ubiquitous multimedia advertising machines.

For the record, if you happen to spy a Whispering Window device out in the wild, this program is certainly not recommending that you quickly abscond with the device to add terbium to your element collection and bring a single, brief moment’s peace into this unrelenting world.

No, you’ll have to make do with an old TV screen, or fluorescent light bulbs, or lasers, or some other such device that, frankly, we’ve seen several times before.

Or you could set up your own fractional crystallization rig and isolate a few grams of pure terbium from some easy-to-find feldspar rocks! If Mosander had the technology to do it 200 years ago, you can certainly do the same thing today. Just be aware that you’ll be stuck in the chem lab for a very, very long time.

Thanks for listening to The Episodic Table of Elements. Music is by Kai Engel. To learn how to turn your terbium metal into fluorescent green crystals, visit episodic table dot com slash T b.

Last call to nominate the show for a People’s Choice Podcast award! The top ten programs in each category advance to the next stage of the awards process, and in the Science & Medicine category, there are only fifteen contestants this year. Your vote can really make a difference here! I’ll include instructions on how to vote again in today’s show notes.

Next time, we’ll meet a jack of all trades, master of none with dysprosium.

Until then, this is T. R. Appleton, reminding you that Brawndo’s got what plants crave! It’s got electrolytes!



  1. Rare Earth Phosphors For X-Ray Conversion Screens, US Patent US3725704A.
  2. Radiation Physics, X-Ray Exposure Reduction Using Rare-Earth Oxysulfide Intensifying Screens. Robert A. Buchanan, Solon I. Finkelstein, Kenneth A. Wickersheim, October 1, 1972.
  3. deep owls
  4. Episodes From The History Of Rare Earth Elements, p. 50-51. Edited by C. H. Evans, 2012.
  5. Episodes From The History Of The Rare Earth Elements, p. xvii-xviii. C. H. Evans, 2012.
  6. Svenskt Biografiskt Lexikon, p. 739-732. Anders Lundgren, 1985-1987.
  7. The Chemical Industry In Europe: Industrial Growth, Pollution, And Professionalization, p. 75. Ernst Homburg, Anthony S. Travis, Harm G. Schröter, 2013.
  8. BBC News SCI/TECH, Bug Sets Windows Shaking. Ivan Noble, March 18, 2002.
  9. ZDNet, Soundbug. Rupert Goodwins, April 24, 2002.
  10. Straight from the source!

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