Abstract
In situ monitoring of mechanochemical reactions of soft matter is feasible by synchrotron diffraction experiments. However, so far, reactions of hard materials in existing polymer milling vessels failed due to insufficient energy input. In this study, we present the development of a suitable setup for in situ diffraction experiments at a synchrotron facility. The mechanochemical transformation of boehmite, γ-AlOOH, to corundum, α-Al2O3, was chosen as a model system. The modifications of the mill's clamping system and the vessels themselves were investigated separately. Starting from a commercially available Retsch MM 400 shakermill, the influence of the geometrical adaptation of the setup on the milling process was investigated. Simply extending the specimen holder proved to be not sufficient because changes in mechanical forces need to be accounted for in the construction of optimized extensions. Milling vessels that are suitable for diffraction experiments and also guarantee the required energy input as well as mechanical stability were developed. The vessels consist of a steel body and modular polymer/steel rings as x-ray transparent windows. In addition, the vessels are equipped with a gas inlet and outlet system that is connectable to a gas analytics setup. Based on the respective modifications, the transformation of boehmite to corundum could be observed in an optimized setup.
Highlights
During the last few decades, mechanochemistry has become a very promising alternative to conventional syntheses, especially concerning sustainability and environmental friendliness.1 Conventional solid-state reactions often require harsh reaction conditions concerning temperature and/or pressure.2,3 In the solid state, reactions are driven by diffusion that takes place at surfaces, interfaces, and/or defects
Since the mean kinetic energy of the vessel is proportional to the square of the mean velocity, the mean kinetic energy reduces approximately to 50% compared to the original setup
The IR spectra obtained from the milling vessel generation 1, whose inner surface is covered with more than 50% polymethyl methacrylate (PMMA), show already after 5 min an increase in the intensity of CO2 [Fig. 5(b)]
Summary
During the last few decades, mechanochemistry has become a very promising alternative to conventional syntheses, especially concerning sustainability and environmental friendliness. Conventional solid-state reactions often require harsh reaction conditions concerning temperature and/or pressure. In the solid state, reactions are driven by diffusion that takes place at surfaces, interfaces, and/or defects. The authors were able to investigate the influence of catalytic additives such as organic liquids or ionic species on the reaction This was the first report on using a modified shaker mill for in situ XRPD experiments.. We investigate several adaptations of a typical shaker mill (Retsch MM 400) required to allow for in situ XRPD measurements and their influence on the milling process of hard matter. Such reactions cannot be performed in polymer vessels but require milling vessels made from steel or comparable robust materials.. This study will highlight the impact of different modifications of a commercial ball mill both on the milling processes and the products
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