Controlling hydrolysis and dispersion of AlN powders in aqueous media

AlN ceramics processed by aqueous slip casting

“…Based on the electrophoretic measurements and on some results already reported, 21,22 aqueous suspensions with 50 vol% powder mixtures containing different weight proportions of AlN/CaF 2 /YF 3 were prepared using the optimized dispersion conditions (1 wt% Duramax 3005). Table I summarizes the different compositions tested and the respective sample codes.…”

“…However, organic solvents are expensive, unsafe, and volatile, requiring the control of emissions into the atmosphere. These drawbacks pose new challenges to the scientific community, and much research has been undertaken in recent years aimed at replacing the traditional organic solvents with water [21][22][23][24][25][26][27] and sintering AlN powders at temperatures lower than those typically used. [28][29][30][31][32] The achievement of these goals would have positive impacts at different levels (scientific, technologic, environment, economic, health, and other societal aspects).…”

Last Advances in Aqueous Processing of Aluminium Nitride (AlN) - A Review

“…This protection process involves the use of aluminium phosphate groups to coat the surface of the AlN particles. The protection efficiency of phosphoric acid, acetic acid and a thermochemical treatment with aluminium dihydrogenophosphate solutions in shielding AlN particles from hydrolysis could be described by the evolution of the pH of the AlN aqueous suspensions, as well as, by the crystallinity of AlN particles after hydrolysis, as presented in Figure 1 ( Oliveira et al, 2003;Olhero et al, 2004).…”

“…al. 2000;Oliveira et al, 2003;Reetz et al, 1992;Shan et al, 1999). According to this, recently Kocjan (Kocjan et al, 2011) presented a detailed study about the reactivity of AlN powder in diluted aqueous suspensions in the temperature range 22-90•C in order to better understand and control the process of hydrolysis.…”

“…Another disadvantage of this process is that it involves the use of organic solvents that are flammable and dangerous to health, therefore, just transferring the use of this kind of solvents to an earlier step of the processing. Therefore, it is not surprising that more attractive approaches have been attempted to protect AlN surface powders by chemisorbing hydrophilic anions from acidic species such as phosphoric, H 3 PO 4 , or silicic acids from aqueous media (Kosmac et al, 1999;Oliveira et al, 2003;Uenishi et al, 1990). The efficiency of H 3 PO 4 in protecting aluminium from corrosion through anodization was already known to result on impermeable and low soluble phosphate complexes, preventing the reaction.…”