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Department of Engineering, ICT and Technologies for Energy and Transport Patent Title Method and apparatus for mixing of fine and ultrafine powders. Ref. CNR 10401 Assignee (s): CNR CNR Institute: IRC Main Inventor: Paola Ammendola Countries: IT Priority date: 17/11/2015 Abstract The present invention deals with a method aiming to the mixing of fine and ultrafine cohesive powders, namely micro- and nano-particles (<30mm), based on the sound assisted fluidization technology. Since these particles are always agglomerated due to their large interparticle forces (van der Waals, capillary and coulombic), a first de-agglomeration step, followed by an efficient dispersion of the different particles of one species into the others, is necessary for obtaining a good mixing quality. The application of acoustic fields of proper intensity (125-150dB) and frequency (20-300Hz) is capable of promoting an efficient aggregates breakup mechanism and particle dispersion and, in turn, an efficient mixing of powders. In particular, under the best operating conditions the mixing index is always very high (about 1) and the characteristic mixing time relatively small (<40min). Background Commercially available mixing techniques, classified in wet and dry mixing methods, deal primarily with large, non-cohesive, spherical particles (mean particle sizes greater than 30µm), i.e. when the interparticle forces are small compared to the particle weight, and their role in mixing can be neglected. On the whole, all these technological alternatives suffer from different disadvantages, thus leading to a poor mixing quality, when applied to fine and ultrafine particles, since they are always agglomerated. These technical issues represent the object of the present invention. Technology The proposed sound assisted fluidization technology makes it possible to mix to fine and ultrafine powders in a simple and efficient way. In particular, particle aggregates undergo a continuous break-up and re- aggregation mechanism during sound assisted fluidization, due to the viscous and inertial forces generated by the application of the acoustic field. This leads to the formation of hybrid aggregates, i.e. made of different powders, and, therefore, to the mixing of the powders. Advantages and Applications The proposed technology is not intrusive (neither additional equipment nor materials must be inserted), it does not alter the particle properties, it is economic and user-friendly. Besides, the powders do not need to have any peculiar property. Potentially interested industries are those dealing with the manufacture of cosmetics, medicines, food, plastics, catalysts, biomaterials, metal foams, metal mixtures, microelectronic- mechanical systems (MEMS) and coating. Development stage The effectiveness of the sound assisted fluidization in promoting the mixing of cohesive powders has been proved at a laboratory scale by means of a fluidized bed reactor (40mm ID) equipped with a system for the generation of acoustic fields. The Scanning Electron Microscopy with X-ray microanalysis (SEM/EDS) has been performed on samples of fluidized materials in order to obtain the time dependence of the mixing index and 69 the mixing characteristic time.