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Zhang L.,Northwestern Polytechnical University | Lin Z.,Xiamen University | Jiang Y.,Xiamen University | He J.,Xiamen University | And 3 more authors.
Ceramics International | Year: 2014

β-SiAlON powder was prepared from silica-alumina gel and by heat-treatment in ammonia. Element analysis, X-ray diffraction, magic-angle spinning nuclear magnetic resonance, scanning electron microscopy and transmission electron microscopy were used to characterize the powder. It was found that nitridation reactions took place at 1100 C and β-SiAlON began to crystallize at 1300 C with mullite, O-SiAlON and χ-SiAlON as the intermediate phases. Nano-sized single phase β-SiAlON powder was obtained after heating at 1350 C for 3 h. © 2013 Elsevier Ltd and Techna Group S.r.l.


Zhang L.,Northwestern Polytechnical University | Lin Z.,Xiamen University | Lin Z.,Key Laboratory of High Performance Ceramic Fibers | Jiang Y.,Xiamen University | And 5 more authors.
Journal of the American Ceramic Society | Year: 2013

Nitrogen-doped mullite fibers were first synthesized through the nitridation of Al2O3-SiO2 gel fibers in NH 3. The results showed that nitrogen take-up began at 800°C, reached the maximum at 900°C, and then decreased with increasing temperature. The ceramic fibers nitridated at 900°C were essentially amorphous, but contained a small amount of nano-sized Al-Si spinel crystals. Mullite was formed after nitridation at 1200°C, accompanied by crystallization of χ-SiAlON and δ-Al2O3. The incorporation of nitrogen resulted in the formation of a variety of nitrogen-containing crystalline phases. The grain size of the mullite fibers can be adjusted by changing of the nitrogen content. © 2013 The American Ceramic Society.


Zhang L.,Northwestern Polytechnical University | Lin Z.,Xiamen University | Jiang Y.,Xiamen University | He J.,Xiamen University | And 3 more authors.
Journal of the American Ceramic Society | Year: 2014

A simple method for synthesis of β-SiAlON powder by nitridation of alumina-silica gel in ammonia was provided. Precursor was obtained from a mixture of nanosized alumina and colloidal silica. Nitridation reactions took place at 1100°C and conversion to β-SiAlON was achieved at 1300°C for 2-3 h. The synthesized β-SiAlON powder was nanocrystalline in size (<100 nm). © 2013 The American Ceramic Society.


Su Z.,Xiamen University | Su Z.,Key Laboratory of High Performance Ceramic Fibers | Zhang L.,Northwestern Polytechnical University | Li Y.,Xiamen University | And 5 more authors.
Journal of the American Ceramic Society | Year: 2015

Polycarbosilane (PCS) fiber was irradiated by electron beam at low dose in a flowing N2/O2 mixture with O2 concentration of 1%. After the pyrolysis of the irradiated precursor fibers, SiC fibers with high strength of 2.4 GPa were obtained. Microstructural evolutions of the resultant fibers were explored. It was found that during the irradiation, free radicals were formed in the PCS and were oxidized by oxygen as Si-OH groups. The Si-OH groups then transformed into Si-O-Si linkage and resulted in further cross-linking of the PCS during pyrolysis. A remarkable structure gradient along the fiber diameter was formed under the coupled effects of irradiation and oxidation. The content of oxygen decreased from the fiber surface to the core, whereas the crystallinity of β-SiC increased in the same direction. The electrical resistivity of the as-prepared ceramic fiber was 80.7 Ω cm, showing good potential for being as electromagnetic wave absorber. © 2015 The American Ceramic Society.


Xu J.,Xiamen University | Hassan D.A.,Xiamen University | Hassan D.A.,University of Basrah | Zeng R.,Xiamen University | And 3 more authors.
Materials Research Bulletin | Year: 2015

Abstract A high performance strontium silicate phosphor has been successfully synthesized though a facile vapor-phase deposition method. The product consists of single crystal whiskers which are smooth and uniform, and with a sectional equivalent diameter of around 5 μm; the aspect ratio is over 50 and no agglomeration can be observed. X-ray diffraction result confirmed that the crystal structure of the whisker was α'-Sr2SiO4. The exact chemical composition was Sr1.98Eu0.02SiO4 which was analyzed by energy dispersive spectrometer and inductively coupled plasma-mass spectrometer. The whisker shows broad green emission with peak at 523 nm ranging from 470 to 600 nm (excited at 370 nm). Compared with traditional Sr2SiO4:Eu phosphor, durability (at 85% humidity and 85 °C) and thermal stability of the whisker are obviously improved. Moreover, growth mechanism of the Sr1.98Eu0.02SiO4 whiskers is Vapor-Liquid-Solid. On a macro-scale, the product is still powder which makes it suitable for the current packaging process of WLEDs. © 2015 Elsevier Ltd.

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