With the lingering debate over the reliability of new, lead-free solders dictated by RoHS regulations, the story of Napoleon’s buttons has been making its rounds again in engineering circles.
As the story is told to many introductory chemistry class students, the tin buttons on the coats of Napoleon’s troops literally crumbled to powder after exposure to the frigid cold of a Russian winter. A metastable material, pure tin undergoes a radical structural transformation at temperatures below 0C, essentially decomposing into dust. This transformation, called tin pest, can be avoided by combining tin with other elements like, you know, lead.
The idea of Napoleon’s troops suffering a wardrobe failure of Janet-Jackson-like proportions got me wondering if there is any shred of truth to the story. Or is it one of those apocryphal tales that serves to warn about the potentially dire consequences of ignoring certain chemical properties of materials?
To answer the question of whether this tale of an unfortunate sartorial choice is fact or fiction, I asked Peny LeCouteur, co-author of the book book “Napoleon’s Buttons” How 17 Molecules Changed History,” a highly entertaining look at chemical compounds and their impact on the course of history.
“It’s a story that virtually every chemistry student has heard, but we don’t really know if Napoleon’s army actually had buttons made of tin,” she says. Though the section on Napoleon’s wardrobe is a mere couple of pages, LeCouteur, a former chemistry professor and now administrator at Capilano College, says that while she was researching the book she was struck by photos of old tin vessels that are now in museums. “What amazed me was that they no longer had that sharp outline to their geometries, which made sense because these objects were exposed to the frigid winters in northern Europe. Victims of tin pest, the outer layers simply turned to powder and sloughed off. ”
While it is possible, Lecouteur says, that the same thing could have happened to Napoleon’s buttons. But she says that there is simply not enough evidence to conclude that it did. “There were eyewitness accounts of the weather and you do see paintings that were made of Napoleon and his troops at that time holding old carpets and blankets around themselves to keep warm, so we do know something about the kind of cold they had to endure. But buttons made out of pure tin would have been quite expensive compared to wood or bone. And chemically, tin pest is a very slow process.”
So slow, in fact, that it’s likely Napoleon’s troops would have had to endure some hellishly long winters before their buttons disintegrated. And as one reader shrewdly pointed out, that means they would have had to worry about other things falling off well in advance of their buttons!
1. Although steels are metastable at room temp it takes dry ice temperatures to induce phase change. "Tin pest" disease proceeds slowly at first at 10 centigrade. Im never saw any reference in military journals that Napoleon or his officers attributed loss of buttons as significant.
2. Group 5 and group 6 alloys: bismuth, antimony, arsenic, tellurium, selenium, etc.; accelerate tin pest. Copper, Silver, Cadmium, Indium etc. alloys reduce tin phase change. Copper and Silver as intermetallic compounds Cu3Sn and Ag3Sn. Lead does not not form a solution in solid Tin, so it does not prevent tin phase change. However 50:50 Pb:Sn will leave a Lead matrix behind.
4. Pure Tin was unlikely a button material as it was too soft to hold the coats closed. More likely a Pewter Tin-Antimony-Lead alloy.
4. Russians had a Tin coin few years back. They wrestled with the Tin pest problem.
5. Tin whisker formation is proportional to Tin content of solder. Tin-Lead Solder is usually reflowed which reduces surface stress but Bright Tin plating is not reflowed.
6. Although Lead causes neural issues in young mammals in infinitessimal amounts, Silver is much more toxic to adult humans.
Karen, beta tin (white tin) is stable at room temperature, not metastable. Alpha tin (gray tin) becomes the stable phase below about 56°F. So below 56°F, beta tin is metastable - it is no longer the lowest energy state, but there is still an activation energy associated with the phase transformation.
I think the term you wanted to use is "allotropic," not "metastable."
It's interesting how non-committal Le Couteur is about the historical veracity of the "Napoleon's buttons" story, given that it's the title of her book (although the story itself is actually only mentioned briefly in the introduction).
When people talk about "pure tin" in electronics applications, they mean that it is 97% pure or more. However, I believe this still leaves enough room for alloying additions (antimony, bismuth, or lead) to suppress alpha tin formation.
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