Phase Transformation and Microstructure of Zn 2 Ti 3 O 8 Nanocrystallite Powders Prepared Using the Hydrothermal Process
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ZINC titanates, particularly Zn2TiO4, as attractive sorbents for removing sulfur from hot coal gasification product have been reported by Swicher et al.[1,2] Due to recent progress in microwave applications for mobile telephones and satellite communications, the development of microwave dielectrics with low dielectric loss, high dielectric constant, and low-temperature coefficient of resonant frequency has been intensified so that they can be used as dielectric resonators and filters.[3,4] Kim et al.[5,6] demonstrated that zinc titanates can be used as dielectric materials for microwave devices. CHENG-LI WANG, Graduate Student, is with the Department of Materials Science and Engineering, National Cheng Kung University, 1 Ta-Hsueh Road, Tainan 70101, Taiwan, R.O.C. WENG-SING HWANG, Professor, is with the Department of Materials Science and Engineering, National Cheng Kung University, and also with the Institute of Nanotechnology and Microsystems Engineering, National Cheng Kung University. HORNG-HUEY KO and MOO-CHIN WANG, Professors, are with the Department of Fragrance and Cosmetic Science, Kaohsiung Medical University, 100 Shih-Chuan 1st Road, Kaohsiung 80782, Taiwan, R.O.C. Contact e-mail: [email protected], [email protected] CHI-SHIUNG HSI, Professor, is with the Department of Materials Science and Engineering, National United University, 1 Lein-Da, Kung-Ching Li, Miao-Li 36003, Taiwan, R.O.C. KUO-MING CHANG, Professor, is with the Department of Mechanical Engineering, National Kaohsiung University of Applied Sciences, 415 Chien-Kung Road, Kaohsiung 80782, Taiwan, R.O.C. Manuscript submitted June 3, 2012. Article published online October 16, 2013 250—VOLUME 45A, JANUARY 2014
In the first comprehensive investigation of the ZnO-TiO2 phase diagram, Dulin and Rase[7] pointed out the stable composition and temperature ranges of zinc metatitanate (ZnTiO3) and zinc orthotitanate (ZnTiO4). In the ZnO-TiO2 system, only Zn2Ti3O8, ZnTiO3, and ZnTiO4 were confirmed to exist.[7–10] The existence of metastable Zn2Ti3O8 was first reported by Bartram and Slepetys.[8] Zn2Ti3O8 has a simple cubic structure with a lattice constant of ao = 0.8390 ± 0.0005 nm, and was found to be a form of ZnTiO3 that exists at temperatures below 1093 K (820 C).[10] ZnTiO3 has a rhombohedral structure with lattice constants of ao = 0.5077 ± 0.0002 nm and co = 1.392 ± 0.001 nm.[8] When heated to a temperature higher than 1218 K (945 C), ZnTiO3 decomposed to a face-centered cubic structure of Zn2TiO4 with a lattice constant of ao = 0.8456 ± 0.0002 nm and rutile TiO2.[11] The compound of Zn2Ti3O8 is formed based on the Zn2TiO4 phase only.[12] Both chemical and microstructure are important factors in the application of zinc titanate powders. Therefore, two methods have been adopted for the preparation of ZnTiO3 powders including the conventional solid-state reaction[8] and the sol–gel method.[9,13–16] In addition, Zn2TiO4 powders have been obtained using the solid-state reaction[12] and the ball-milled method.[17] The solid-state reaction method has some
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