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Translucent Yttria‐ and Silica‐Doped Mullite Ceramics with Anisotropic Grains Produced by Spark Plasma Sintering
Author(s) -
Kocjan Andraž,
Češnovar Mark,
Vengust Damjan,
Kosmač Tomaž,
Dakskobler Aleš
Publication year - 2016
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/jace.14302
Subject(s) - materials science , mullite , spark plasma sintering , composite material , ceramic , cristobalite , sintering , fracture toughness , flexural strength , transparent ceramics , transmittance , vickers hardness test , microstructure , quartz , optoelectronics
Translucent, high‐performance, mullite ceramics with anisotropic grains were prepared by the spark plasma sintering ( SPS ) of a powder mixture consisting of commercial mullite powder, which already contained small amounts of alumina (θ and α) and silica (cristobalite) (≤3 wt% in total), to which 2 and 1 wt% of yttria and amorphous silica was admixed, respectively. The combination of low‐viscosity Y 2 O 3 –Al 2 O 3 –SiO 2 transient liquid formation and SPS sintering provided enhanced densification, also provoking anisotropic grain growth (which became exaggerated after 20 min of SPS dwell time), at a relatively low sintering temperature of 1370°C. In this way, it was possible to meet the conflicting demands for obtaining a dense mullite ceramic with anisotropic grains, ensuring good mechanical properties, while preserving a noticeable light transmittance. In terms of mechanical and optical properties, the best results were obtained when SPS dwell times of 5 and 10 min were employed. The as‐sintered samples possessed densities in the range 3.16–3.18 g/cm 3 , anisotropic grains with an aspect ratio ( AR ) of 7 and a grain thickness of approximately 0.45 μm, a flexural strength between 350 and 420 MPa, a Vickers indentation toughness and a hardness of approximately 2.45 MPa·m 1/2 and 15 GPa, respectively, and an optical transmittance of between 30% and almost 50% in the IR range.