Synthesis of Al2O3/SiO2 nano‐nano composite ceramics under high pressure and its inverse Hall–Petch behavior. Issue 1 (6th October 2016)

• Record Type: Journal Article
• Authors: Gaida, Nico A.; Nishiyama, Norimasa; Masuno, Atsunobu; Holzheid, Astrid; Ohfuji, Hiroaki; Schürmann, Ulrich; Szillus, Christin; Kulik, Eleonora; Bednarcik, Jozef; Beermann, Oliver; Giehl, Christopher; Kienle, Lorenz
• Is Part Of: Journal of the American Ceramic Society. Volume 100:Issue 1(2017)
• Page Start: 323
• Page End: 332
• Publication Date: 2016-10-06
• Subjects: alumina -- hardness -- nanocomposites -- silica; Ceramics -- Periodicals; 620.1405
• DOI: 10.1111/jace.14551
• Languages: English
• ISSNs: 0002-7820

Abstract

Abstract: We report the synthesis of alumina/stishovite nano‐nano composite ceramics through a pressure‐induced dissociation in Al2 SiO5 at a pressure of 15.6 GPa and temperatures of 1300°C‐1900°C. Stishovite is a high‐pressure polymorph of silica and the hardest known oxide at ambient conditions. The grain size of the composites increases with synthesis temperature from ~15 to ~750 nm. The composite is harder than alumina and the hardness increases with reducing grain size down to ~80 nm following a Hall–Petch relation. The maximum hardness with grain size of 81 nm is 23 ± 1 GPa. A softening with reducing grain size was observed below this grain size down to ~15 nm, which is known as inverse Hall–Petch behavior. The grain size dependence of the hardness might be explained by a composite model with a softer grain‐boundary phase.