Mechanochemical methods offer unprecedented academic and industrial opportunities for solvent‐free synthesis of novel materials. The need to study mechanochemical mechanisms is growing, and has led to the development of real‐time in situ X‐ray powder diffraction techniques (RI‐XRPD). However, despite the power of RI‐XRPD methods, there remain immense challenges. In the present contribution, many of these challenges are highlighted, and their effect on the interpretation of RI‐XRPD data considered. A novel data processing technique is introduced for RI‐XRPD, through which the solvent‐free mechanochemical synthesis of an organic salt is followed as a case study. These are compared to ex situ studies, where notable differences are observed. The process is monitored over a range of milling frequencies, and a nonlinear correlation between milling parameters and reaction rate is observed. Kinetic analysis of RI‐XRPD allows, for the first time, observation of a mechanistic shift over the course of mechanical treatment, resulting from time evolving conditions within the mechanoreactor.
We describe an experiment in a special device, which permits to quantify the energy input into a solid sample and to follow the products of mechanochemical synthesis step by step. The application of the device is tested on the ''glycine-oxalic acid dihydrate'' system, in which two products are formed concomitantly on co-grinding.Mechanochemical synthesis has been known for at least a century, 1 but the interest in it has grown enormously during the last decade, 2 in particular, in relation to obtaining new organic compounds, salts, and co-crystals. 3 Many examples of successful synthesis achieved on co-grinding a powder mixture in a mortar or in a mill have been described. However, the mechanisms of these transformations remain far from being understood, although several approaches and models have been proposed. The latter are based on considering eutectic melting, 4 dissolution in a small amount of liquid added on cogrinding or present in the reagents as a crystal solvent, 5 a gas-solid reaction resulting from the sublimation of one or more components, 6 and direct solid-state interdiffusion of the components. 2,7 One of the major problems which is intrinsic to the mechanochemical reactions is that a sample is treated not continuously, but in mechanical pulses. As a result, the total time of the mechanical treatment in a mill, or in another mechanical device, differs from the actual time, during which the sample was subjected to mechanical pulses. 2,4b,5a,8 The energy of pulses, their duration, the shape of a pulse, and the time between the pulses are the parameters, which are very important for the reaction outcome. However, it is practically impossible to control them, when either a manual grinding or the treatment in a commonly used mechanical device (a mill, an attritor, an automatic mortar, etc.) is considered. 2,4b,5a,8 In the present communication we describe a model experiment accomplished in a special device designed and manufactured for the detailed studies of mechanochemical reactions in one-or multi-component systems, which enable to treat a sample by individual mechanical pulses of variable and controllable energy, duration, and frequency. 9 This device has been tested on a model system ''glycine-oxalic acid dihydrate'' 10 and allowed us to follow the products of co-grinding formed at the different steps of the transformation.
The effects of milling ball mass, size and material are isolated for a model mechanochemical co-crystallisation.
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