Controlling hydrolysis and dispersion of AlN powders in aqueous media


Aqueous suspensions of aluminum nitride (AIN) powders have been prepared in the presence of different surface-active agents, namely, H3PO4 and an anionic surfactant, to avoid the hydrolysis of AIN powders and to enhance dispersion. The most determinant parameters to the hydrolysis process (DeltapH and time of contact) and the stabilization of AIN particles in water (surface crystallinity, surface chemical modification, and surface ionic charge) were seen to be strongly dependent on the acidic agent. The H3PO4 treatment was effective against hydrolysis of AIN due to the formation of a phosphate-based protection layer on the particles' surface, and, although it keeps the pH of the suspension below 4. it does not guarantee a good dispersion. The individual adsorption of the anionic surfactant at the surface of AIN particles did not completely suppress the hydrolysis but it did enhance the degree of dispersion. A proper combination of the two types of surface-active agents enabled the preparation of AIN aqueous suspensions of relatively low viscosity and high AIN concentration, which can be a good starting point for aqueous-based colloidal shaping techniques or for freeze granulation or spray drying to obtain suitable granulate powder characteristics for dry-pressing technologies. An adsorption mechanism of the surface-active agents onto the particles' surface is proposed and supported by NMR and FT-IR analyses. (C) 2003 Elsevier Science (USA). All rights reserved.






Oliveira, M; Olhero, S; Rocha, J; Ferreira, JMF

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