resumo
Dense beta-Si(4)Al(2)O(2)N(6) and beta-Si(4)Al(2)O(2)N(6)-0.5SiO(2) ceramics were obtained from alpha-Si(3)N(4), alpha-Al(2)O(3), AlN, and Y(2)O(3) upon sintering green bodies consolidated by aqueous gel casting. For comparison purposes, a beta-Si(4)Al(2)O(2)N(6) was also prepared by the conventional dry-powder processing route. In the case of gel-cast beta-Si(4)Al(2)O(2)N(6), the as-purchased AlN powder was treated with H(3)PO(4) and Al(H(2)PO(4))(3) prior to use along with alpha-Si(3)N(4), alpha-Al(2)O(3), and Y(2)O(3). The gel-cast beta-Si(4)Al(2)O(2)N(6) exhibited superior hardness (1423 +/- 6 Hv), fracture toughness (3.95 +/- 0.3 MPa.m(1/2)), and coefficient of thermal expansion (CTE) (3.798 x 10(-6)/degrees C between 30 and 1000 degrees C) in comparison to the ceramic consolidated by conventional dry pressing, which exhibited only 1317 5 Hv, 3.30 +/- 0.2 MPa-m(1/2), and 3.532 x 10(-6)/degrees C between 30 and 700 degrees C. The in situ-generated similar to 9 wt% SiO(2) has considerably reduced the dielectric constant and CTE of beta-Si(4)Al(2)O(2)N(6) from 7.30 to 6.32 and from 3.798 x 10(-6)/degrees C to 3.519 x 10(-6)/degrees C respectively. The loss tangent property of the investigated materials was little influenced by the variation of chemical composition and processing route.
palavras-chave
HYDROLYSIS-ASSISTED SOLIDIFICATION; BETA-SIALON CERAMICS; ALN POWDER; SUSPENSIONS; Y2O3
categoria
Materials Science
autores
Ganesh, I; Thiyagarajan, N; Jana, DC; Sundararajan, G; Olhero, SM; Ferreira, JMF
nossos autores
José Maria da Fonte Ferreira
Professor(a) Jubilado(a)
Susana Maria Henriques Olhero
Professor Auxiliaragradecimentos
I.G. thanks SERC-DST (Government of India) for the awarded BOYSCAST fellowship (SR/BY/E-04/06). S.M.O. thanks the Foundation for Science and Technology of Portugal for financial support under grant SFRH/BPD/27013/2006. Financial support of CICECO is also acknowledged.