As mechanochemistry has spread across all areas of chemistry, it’s been able to synthesize multiple materials when what’s known as the typical ‘wet chemistry’ process isn’t working. But the downside is that the characterization of the reaction mixture is far less accessible than it is in solutions. Both X-ray diffraction and Raman spectroscopy, a technique which typically provides an identification ‘fingerprint’ for molecules in chemistry, were recently used to achieve in situ observations of mechanochemical reactions.
It’s possible to track solid-state reactions during synthesis, including material transformations and phase transitions, in what’s called a ball milling jar. But, because of scattering from its walls, as the X-rays go through the jar, the diffraction patterns offer a high background. Additionally, it’s expected that the sample will present broad diffraction peaks, due to the probing of a large sample area that covers the whole jar, and an extra complexity shows up as a result of diffraction on the milling balls. This technique has gained popularity in many of the various fields of mechanochemistry, but isn’t foolproof.
The researchers, with UCL’s Institute of Condensed Matter and Nanoscience, hypothesized that the issues with the diffraction could possibly be fixed, but not by changing the technique. The team decided to try modifying the material and geometry of the ball milling jar, and decided to use 3D printing technology to make the jar, as it has a complicated geometry that would be difficult to reproduce using conventional manufacturing techniques; this is especially true at the prototyping stage.According to the abstract, “Mechanochemistry is flourishing in materials science, but a characterization of the related processes is difficult to achieve. Recently, the use of plastic jars in shaker mills has enabled in situ X-ray powder diffraction studies at high-energy beamlines. This paper describes an easy way to design and manufacture these jars by three-dimensional (3D) printing. A modified wall thickness and the use of a thin-walled sampling groove and a two-chamber design, where the milling and diffraction take place in two communicating volumes, allow for a reduced background/absorption and higher angular resolution, with the prospect for use at lower-energy beamlines. 3D-printed polylactic acid jars show good mechanical strength and they are also more resistant to solvents than jars made of polymethyl methacrylate.”
In the paper, the research team details how 3D printing was used to quickly make the ball milling jars, and optimize them to achieve improved absorption and angular resolution, and a better, less high background, for their X-ray powder diffraction experiments. As we know, 3D printing technology allows for low-cost, on-demand production of customized objects, and the UCL team’s 3D printed jars were manufactured to be more resistant to solvents, when compared to typical acrylic jars. 3D printing has been used for experiments in the growing materials science field before, and judging by the success of the UCL researchers, I’m sure other institutes will also turn to the technology for help. Discuss in the Mechanochemistry forum at 3DPB.com.
[Source: Science News]