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Dry coating is an interesting process for creating added value binary powders composites. The principle is to mix ‘host’ particles with ‘guest’ particles with 10 to 100 times smaller size. But, behind the apparent simplicity of the process, the implied mechanisms are very complex. As a result, it is not possible so far to predict the resulting end-use properties of the produced composite powder, even if we know the properties of the host and guest powders. This papers aims at illustrating a first step to characterize more precisely the process itself and the result of the coating, i.e. coverage, homogeneity or thickness… In this work we describe the methodology to characterize the dry coating coverage through image analysis by using Environmental Scanning Electron Microscopy. A first part of this paper gives the technical and statistical aspects of the image acquisition in the electron microscope (Philips XL 30). A second part develops the image processing methodology with Matlab Image Processing Toolbox. A third part describes a validation step of the methodology by comparing the automated procedure to a ‘manual’ derivation of the coverage. The presented results imply the coverage of ‘model’ powders: host particles of ca. 100 μm and guest particles of ca. 10 μm. This work illustrates the assets of the image analysis to quantitatively characterize the average coverage and its homogeneity in dry coating application, for example when partial breakage or attrition occurs. Further results with the application of this methodology will be published in a further paper. [ABSTRACT FROM AUTHOR]

The article presents information on a study which examined the surface properties of talc particles modified by dry coating with hydrophobic silica properties. Variables studied included the concentration of silica properties and the dry coating processing time. It describes the talc powders and their characterization. The quantification of dispersion kinetics is detailed. A discussion on the findings of the study including surface morphology and wettability measurements is detailed.

Abstract: The objective of this study is to get a better understanding of dry powder coating process using experiments and numerical methods. Materials chosen as host particles are SUGLETS® (granules mainly consisting of sugar) and as invited particles, magnesium stearate (MgSt). These two materials are introduced into a high shear mixer (Cyclomix). Operations were performed at various mixing time and rotation speed of the Cyclomix. The surface morphology analysis has confirmed that Suglet particles are coated with MgSt. The product properties such as flowability, wettability and particle size distributions were also characterized. The particle motion in the Cyclomix has been simulated by using Discrete Element Method (DEM). Both number of collisions and the collision force frequency are calculated. The simulation shows an increase of the collision number with the rotational speeds. This result indicates that choosing higher rotation speeds should be better for the dry coating process as long as the particles are not broken down. [Copyright &y& Elsevier]

Abstract: An investigation into the effects of the operating conditions on a dry particle coating process has been performed with mixtures of sugar grains (Suglet®) and magnesium stearate (MgSt) as the host and invited particles, respectively. Dry coating has been carried out in a high shear mixer (Cyclomix®) at different processing times t, rotational speeds ω, and filling ratios J, of the mixer. In order to determine the effect of the operating conditions on the properties of the products, the changes in flowability and wettability of the mixtures as a function of ω, J and the operating time t have been analyzed. The flowability is found to be improved by longer processing times. Higher speeds of rotations can improve the flowability more rapidly. However, the flowability does not seem to be sensitive to the filling ratio and it may be concluded that operating with higher filling ratios gives higher production. A method is proposed to measure the mass fraction of invited particles on the surfaces of the host particles. This fraction is linked to the product properties as the flowability and wettability. This result can be predicted by a model using a coating rate constant kc which can be used to optimize dry coating processes to give desired properties of coated particles. This coating rate constant can define and represent the efficiency of the dry coating. [Copyright &y& Elsevier]