abstract
Fully dense aluminium nitride (AlN) ceramics consolidated by aqueous slip casting were obtained after sintering at 1750 degrees C for 2 h. The obtained samples were characterized by Vickers hardness (1000 Hv), flexural strength (200 MPa) and thermal conductivity (115 W/mK). YF3 and CaF2 were used as sintering additives in total amounts ranging from 5 to 7 wt% in YF3/CaF2 weight ratios of 1.25, 1.5, and 2. The compatibility between the thermochemically treated AlN powder and the sintering additives in the aqueous suspensions was investigated by theological and zeta potential measurements. Highly concentrated (50 vol%) and well-dispersed suspensions could be prepared and used to consolidate homogeneous green bodies by slip casting. The phosphate species used to protect the surface AlN particles against hydrolysis could no longer be detected at temperatures higher than 1400 degrees C. X-ray diffraction results revealed that all the new crystalline phases formed upon sintering belong to the system Al-Y-O-Ca, but their specific compositions as well as the thermal properties of the sintered materials were shown to depend on the total amount and ratio of sintering aids.
keywords
ALUMINUM NITRIDE POWDER; THERMAL-CONDUCTIVITY; ALN CERAMICS; SINTERING AIDS; YF3; HYDROLYSIS; DISPERSION
subject category
Materials Science
authors
Olhero, SM; Miranzo, P; Ferreira, JMF
our authors
José Maria da Fonte Ferreira
Associate Professor with Aggregation