Definitive replacement of organic solvents by water in the colloidal processing of aluminium nitride


Innovative methods for protecting AlN powders against hydrolysis and for preparing stable and high concentrated ( greater than or equal to 50-vol.% solids) aqueous suspensions for colloidal processing (slip casting, tape casting, pressure casting, etc.) and for granulation of powders for dry pressing technologies were presented. The results achieved enabling to replace the organic-based solvents used in colloidal processing of AlN, which are much more volatile and require the control of emissions to the atmosphere, by the incombustible and non-toxicity water. Innovative features characterizing the actual method were described, which include: (i) the use of hydrophilic substances to protect the AlN surface particles against hydrolysis; (ii) the one step passivation of the hydrolysis reactions and the preparation of stable and high concentrated ( greater than or equal to 76-wt.%) aqueous suspensions compared with the best results already reported ( approximate to 60-wt.%). Different consolidation methods from these suspensions could be used, namely slip casting and tape casting. Granulated powders could be produced by freeze granulation to obtain high green packing density samples by dry pressing. All the greens consolidated by the different shaping techniques could be pressureless sintered at 1750degreesC to achieve full dense AlN-based ceramics. The aqueous processing did not negatively affect the thermal properties of sintered bodies when compared with those processed from organic media.




Materials Science


Ferreira, JMF; Olhero, SMH; Oliveira, MILL

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