Surface modification of silica particles by dry coating: Characterization and powder ageing

Abstract

International audienceIn this study the dry coating experiments were performed with two different processes using a high energy impact coater “Hybridizer” (Nara) and a high shear mixer “Cyclomix” (Hosokawa). Silica gel particles (d50 = 55µm) were coated with fine particles of magnesium stearate (d50 = 4.6µm) at two different weight ratio of magnesium stearate, 5% and 15%. Several methods of characterization were used to study the effect of dry coating of the silica gel powder. The uncoated and coated silica gel particles were observed by environmental scanning electron microscopy (ESEM). The images have shown that a more uniform coating was obtained in the case of Hybridizer. The flowability of the different samples obtained with Hybridizer and Cyclomix have been characterized by measurements of the tapped and aerated densities. It has been shown that the flowability of silica gel treated in Hybridizer was not significantly affected whereas the flowability was reduced after treatment in the Cyclomix. The wettability of silica gel was determined by measurements of the contact angle between a water drop and a powder bed prepared for each sample. The results obtained have shown that the coating of silica gel powder by hydrophobic magnesium stearate in the two different devices, Hybridizer and Cyclomix, can improve its hydrophobic properties. The results of the different characterizations have been compared with those concerning the simple mixtures prepared by using a Turbula mixer. To investigate the stability and the ageing of silica gel particles after coating, three samples of silica gel coated with 15% (w/w) of magnesium stearate in the Hybridizer device have been stored under different relative humidities (RH). The temporal evolution of the contact angle and the volume of the drop water on the surface of the bed powder have been determined after 10 days or 36 days storage. The results have shown the influence of the relative humidity on the evolution of the coated silica gel particles. The surface of the host particles recovers its hydrophilic nature after 10 or 36 days storage under different relative humidity. No significant variations of the contact angle and the volume of the drop were recorded for the sample stored under dry atmosphere (RH < 12%). The ESEM observations of the different samples confirmed the results. A mechanism that can explain these ageing effects is proposed

Modeling the mean interaction forces between powder particles. Application to silica gel–magnesium stearate mixtures

“…The ESEM images revealed that greater MS coverage can be observed on the surface of SG particles as the MS mass ratio w increased [25].…”

Surface Analysis of Silica Gel Particles after Mechanical Dry Coating with Magnesium Stearate

“…Our recent work is related to the modification of the flowability and the wettability properties of silica gel particles coated with different weight ratios of magnesium stearate by using a high energy impact coater Hybridizer from Nara Machinery 3) and a high shear mixer Cyclomix from Hosokawa 4) . For example, the flowability of the silica gel powder was significantly decreased after treatment in the Cyclomix mixer with 15% of MgSt2.…”

Effect of Organo-Functionalized Silica Particles on the Mechanical Properties of PU

“…Silica nanoparticles are by far the most popular inorganic material due to their easy preparation and functionality, chemical inertia, high thermal stability and unusual mechanical properties [4,5]. Thus, they present a wide range of application such as catalysts support, pigments, polishing material, hybrid composite materials, humidity sensors and thermal insulators [6][7][8][9].…”