Surface passivation of MgAl2O4 spinel powder by chemisorbing H3PO4 for easy aqueous processing


A stoichiometric MgAl2O4 spinel (MAS) powder was synthesized by heat treating at 1400 degrees C for 2 h a compacted mixture of alpha-Al2O3 and calcined caustic MgO, followed by crushing and milling. The surface of this powder was then passivated against hydrolysis with H3PO4 and Al(H2PO4)(3) in an ethanol solution. The as-passivated powder could then be dispersed in water using tetramethylammonium hydroxide (TMAH) and an ammonium salt of poly(acrylic acid) (Duramax D-3005) as dispersing agents and gelcast to form green consolidates with relatively high strength (> 15 MPa). The good dispersing behavior of the passivated powder in water was confirmed by the low viscosity of its suspension containing 41-45 vol % solids, demonstrating the viability of replacing organic solvents by water in colloidal processing of MAS-based ceramics. The Fourier transform infrared (FT-IR), X-ray diffraction (XRD), and energy dispersive X-ray (EDAX) studies revealed that only negligible amounts of phosphate ions at the Surface are required to effectively protect the powder from reacting with water.



subject category

Chemistry; Materials Science


Olhero, SM; Ganesh, I; Torres, PMC; Ferreira, JMF

our authors


S.M.O. wishes to thank the Foundation for Science and Technology (FCT) of Portugal for the financial support under Grant SFRH/BPD/27013/2006. I.G. thanks SERC-DST (Government of India) for the awarded BOYSCAST fellowship (SR/BY/E-04/06). The financial support of CICECO is also acknowledged.

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