A Thermo-Chemical Surface Treatment of AlN Powder for the Aqueous Processing of AlN Ceramics
- PDF / 222,433 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 59 Downloads / 197 Views
S. Novak Engineering Ceramics Department, Jožef Stefan Institute, SI-1000 Ljubljana, Slovenia
M. Oliveira Department of Ceramics and Glass Engineering, CICECO, University of Aveiro, 3810-193 Aveiro, Portugal
K. Krnel and T. Kosmac Engineering Ceramics Department, Jožef Stefan Institute, SI-1000 Ljubljana, Slovenia
J.M.F. Ferreira Department of Ceramics and Glass Engineering, CICECO, University of Aveiro, 3810-193 Aveiro, Portugal (Received 22 September 2003; accepted 28 October 2003)
Dense aluminum nitride ceramics were prepared by sintering green bodies at 1750 °C for 2 h. These green bodies were prepared by aqueous slip-casting from a powder that was surface-treated to prevent hydrolysis. The surface treatment of the aluminum nitride (AlN) powder consisted of dispersing the powder in warm-water solutions of aluminum dihydrogenphosphate Al(H2PO4)3. Different treatment temperatures in the range 30–80 °C were tested. For all the tested temperatures, the surface-treated AlN powder was found to be water-resistant, even after drying and/or redispersion. Various commercial dispersants were tested for their effectiveness, and the amount of dispersant was optimized in terms of a high solids loading of the suspension and an acceptable viscosity for slip casting. Based on these studies, a stable aqueous suspension of AlN powder, treated at 60 °C, with a total solids loading of 50 vol%, was prepared using CaF2 as a sintering additive. The well-dispersed powder made it possible to prepare green samples with close particle packing and relatively high sintered densities; that is, more than 96% of the theoretical density.
AlOOH (amorph) + H2O (l) → Al(OH)3
I. INTRODUCTION
Aluminum nitride (AlN) is widely used as a substrate material for electronic packaging because of its excellent thermal conductivity and electrical resistivity.1–3 For many reasons, both economic and environmental, the processing of AlN powders into components using aqueous-based (rather than organic-based) processing methods is becoming increasingly attractive.4–7 Unfortunately, however, fabricating AlN ceramics using such methods faces a major obstacle: the well-known reactivity of AlN powders with water.4–15 The hydrolysis of AlN results in an increase of the suspension’s pH due to the following thermodynamically favorable reactions: AlN (s) + 2H2O (l) → AlOOH (amorph) + NH3 (g) , NH3 (g) + H2O (l) → NH4+ (aq) + OH− (aq) 746
http://journals.cambridge.org
,
(1) (2)
J. Mater. Res., Vol. 19, No. 3, Mar 2004 Downloaded: 14 Mar 2015
.
(3)
However, if the AlN powder could be stabilized with respect to water, it would be possible to handle and store AlN powder in humid atmospheres; and aqueous solutions, rather than organic-based solvents, could be used as the liquid media in the colloidal processing of AlN ceramics. Water-resistant AlN powders are commercially available; these materials are coated with hydrophobic substances, such as carboxylic acids. The problem is that the hydrophobic character of the as-treated powders makes it difficult to disper
Data Loading...
