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Analytical Chemistry

X-Ray Vision For Mechanochemical Mills

Chemists use X-ray diffraction to monitor chemical milling reactions in real time

by Jyllian Kemsley
December 3, 2012 | APPEARED IN VOLUME 90, ISSUE 49

MILLOMETER
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Credit: Nat. Chem.
A powder X-ray diffraction set-up to monitor chemical milling reactions includes a gold-colored X-ray collimating tube (left) and two sample holders for milling jars (right). The detector (not shown) sits opposite the collimator.
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Credit: Nat. Chem.
A powder X-ray diffraction set-up to monitor chemical milling reactions includes a gold-colored X-ray collimating tube (left) and two sample holders for milling jars (right). The detector (not shown) sits opposite the collimator.

Applying mechanical force, such as grinding in a ball mill, is one way to carry out a chemical transformation. But it’s tough to monitor such mechanochemical reactions in real time. Researchers led by Tomislav Friščić of McGill University, in Montreal, have now found a way to do it by in situ powder X-ray diffraction of mixtures in operating chemical milling reactors (Nat. Chem., DOI: 10.1038/nchem.1505). In the past, scientists’ main recourse was to stop the mill periodically to sample material for study. That approach is known to change reactions, Friščić says. Friščić and his colleagues overcame that limitation by turning to an X-ray source at the European Synchrotron Radiation Facility in France to get a beam strong enough to penetrate milling jars with 3-mm-thick walls of steel, aluminum, or poly(methyl methacrylate). To prove the utility of their powder diffraction technique, the researchers followed known methods to produce zeolitic imidazolate frameworks from zinc oxide. They were surprised to see in real time how quickly the reactions take place, Friščić tells C&EN. The researchers further discovered they can measure particle sizes, allowing them to correlate that property to reactivity.

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