Moissanite: a boy’s best friend

Mar 27, 2019
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After writing about Bunsen the other day – probably the most famous person on my academic family tree – I thought that some of the other members of the tree deserved a little more attention. One of the best things about academic family trees is the branches (unless you’re Paul from ChemBark and you’re trying to make a very fancy one for your boss’s birthday) – thanks to things like wars and multiple influences, the tree can branch in a few directions. Two of my branches end up including Bunsen, while another two include Gay-Lussac and Liebig, respectively.

And it’s the Gay-Lussac line that features one of the three Nobel laureates in my tree, about whom I’m going to blog today: Henri Moissan. Who? Exactly. Unlike Bunsen, he’s not much of a household name, although I think he’s better known in his native France than elsewhere.

Moissan definitely falls in the category of ‘chemists from Bunsen’s era whose achievements are overlooked’, which I mentioned last time. I first heard of Henri Moissan thanks to a Newscripts article in C&EN, in which Bob Wolke mentions that he bought his wife a ring and earrings with ‘moissanite’ gemstones. As Bob says, moissanite is “every bit as beautiful as diamond and at a fraction of the price”, thanks to its higher refractive index (more brilliance) and dispersion (fire) and lack of heavy marketing (price)! Moissanite is a silicon carbide mineral named after Moissan, who discovered it in fragments of a meteorite in Arizona. (Now there’s a marketing line for moissanite – ‘with the fire of meteorites!’)

But that’s not the only link that Moissan has to gemstones (a subject currently dear to the hearts – and wallets! – of fellow editor Gav and I, whose marital statuses have both recently shifted). After his invention of the electric-arc furnace, he made significant attempts to create diamonds in the lab. It’s not entirely clear whether he was succesful: although some reproductions of his technique worked, others didn’t. Kathleen Lonsdale argues “probably not” in this letter to Nature in 1962, and I’m not going to argue with a Dame who worked out the structure of benzene in 1929.

But none of this is what Henri Moissan was awarded the Nobel Prize for, nor why he is most known in the history books (apart from the furnace – it’s mentioned in the Nobel citation. Can you imagine that nowadays?!). It was for the isolation of elemental fluorine. If there’s one thing any chemist knows about fluorine it’s that it’s reactive. Really reactive. Which is why, in spite of fluorite minerals being known since 1530, it took 74 years of effort by the ‘fluorine martyrs’ of the 19th century to isolate it, defeating Davy, Ampère, Gay-Lussac and Faraday along the way (check out the fact box in this Angewandte Chemie article about Moissan).

How did Moissan do it? If you’re faint-hearted, look away now. He just electrolysed a solution of KHF2 in HF – being careful to keep the evolving hydrogen gas away from the fluorine gas, of course. Ampere had suggested the electrolysis of HF decades before, but its poor conductivity meant it didn’t work – Moissan’s addition of KHF2 was the crucial insight. And this method is still pretty much how it’s produced today.

Tragically, Moissan died fairly young at the age of 54, just a year after receiving the 1906 Nobel prize – he was just the sixth recipient. According to this rather picturesque article from Nature in 1931, there’s a plaque commemorating him on the school he attended as a boy in Meaux (where brie was born and where Henry V died). It’s interesting and somewhat inspiring to see that he didn’t excel at school, failing to achieve the grade needed for university and only passing it a few years later. So if you’re a keen but failing student at school – don’t give up! You might win a Nobel Prize one day…

Neil

Neil Withers (Associate Editor, Nature Chemistry)


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