abstract
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.
keywords
HYDROLYSIS; CERAMICS; BEHAVIOR; OXIDES
subject category
Chemistry; Materials Science
authors
Olhero, SM; Ganesh, I; Torres, PMC; Ferreira, JMF
our authors
José Maria da Fonte Ferreira
Retired Professor
Paula Maria da Costa Torres
Assistant Researcher
Susana Maria Henriques Olhero
Assistant Professoracknowledgements
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.