Rosalind Franklin coined terms still used for carbon

Person: Rosalind Franklin
Lived: 1920–1958
Field: X-ray crystallography
From: British

The story

Rosalind Franklin ended the Second World War as an expert on what she called the holes in coal. She had studied its porosity for the British Coal Utilisation Research Association and earned a Cambridge PhD in 1945. Looking for her next post, she asked her friend Adrienne Weill, a French physicist and former student of Marie Curie, to let her know of openings. At a conference in 1946 Weill introduced her to Marcel Mathieu, a director of France's national research organisation, the CNRS.

This led to a post with the crystallographer Jacques Mering at the Laboratoire Central des Services Chimiques de l'État in Paris, where she started on 14 February 1947 as one of fifteen researchers. Mering applied X-ray diffraction, firing X-rays at a material and working out its atomic arrangement from the pattern of scattered rays to substances with little regular order. He taught Franklin the practical side of this difficult art, and she became an accomplished X-ray crystallographer.

She applied the technique to carbons, materials that are notoriously hard to study because their atoms are only partly ordered, and in particular to the changes in their atomic arrangement when they are heated and converted to graphite, the ordered form of carbon found in pencil lead. In a 1951 paper in the Proceedings of the Royal Society, refereed by J. D. Bernal and Dorothy Hodgkin, she showed that carbons fall into two families. Graphitising carbons turn into crystalline graphite when heated to about 3,000 °C. Non-graphitising carbons never do, however hot they get. She named the two classes. Later work showed that in the second family, cross-links between tiny crystallites lock the structure in place and block the change to graphite.

The classification proved lasting. Graphitising carbons, made from materials such as petroleum coke, tend to be soft and non-porous, while non-graphitising carbons, such as chars and glassy carbon made from substances like sucrose, are hard and low in density. Later researchers refined her structural picture, but the distinction itself remains part of the mainstream physics and chemistry of carbon, and her work is covered in the long-running textbook series Chemistry and Physics of Carbon.

Franklin kept up her interest in carbons for the rest of her career, publishing on their structure almost every year. Her years in Paris also gave her the skill in X-ray diffraction of imperfectly ordered matter that led John Randall to recruit her to King's College London in 1951 to work on DNA.

Why it matters

Franklin's classification of carbons is still used by materials scientists to understand why some carbons become graphite and others stay hard and porous.

About Rosalind Franklin

London-born Jewish chemist whose X-ray images of DNA, including Photograph 51, were crucial to the double helix; she also pioneered the structure of viruses and coal.

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Rosalind Franklin

1920–1958 · X-ray crystallography

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