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Preparation and Characterization of High Purity Silica Obtained from Rice Husks

100%
Şımşek Y.
Acta Physica Polonica A
|
2017
|
vol. 132
|
issue 3
1002-1005
EN
Although SiO₂ is produced mostly from mineral sources like quartz, it has recently been obtained from lignocellulosic natural resources, such as rice husk (hull). Several methods for extracting silica (SiO₂) from rice husks are available in the literature. These methods are based essentially on heat treatment and/or extraction. This study represents a thorough account of heat treatment and acid-base extraction, to obtain silica from rice husks with a high purity and to eliminate other inorganic impurities. Rice husks, considered to be a potential silica source, were pretreated with various acids, base and water and then thermally degraded in a fixed bed reactor under an inert gas atmosphere (N₂). The materials produced in these conditions were characterized by Brauner-Emmett-Teller analysis, for surface area and pore volume, by Fourier transform infrared spectroscopy, powder X-ray diffraction, X-ray fluorescence, and scanning electron microscopy.
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Combustion synthesis and luminescent properties of a blue-green emitting phosphor: (Ba1.95, Eu0.05)ZnSi2O7:B3+

84%
Yao S.-s., Li Y.-y., Xue L.-h., You Y., Yan Y.-w.
Open Physics
|
2009
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vol. 7
|
issue 4
800-805
EN
A blue-green emitting phosphor (Ba1.95, Eu0.05)ZnSi2O7: Bx3+ was prepared by combustion synthesis and an efficient blue-green emission under near-ultraviolet was observed. The luminescence, crystallinity and particle sizes were investigated by using luminescence spectrometry, X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The emission spectrum shows a single band centered at 503 nm, which corresponds to the 4f 65d 1 →4f 7 transition of Eu2+. The excitation spectrum is a broad band extending from 260 to 465 nm, which matches the emission of ultraviolet light-emitting diodes. The optical absorption spectra of the (Ba1.95, Eu0.05)ZnSi2O7: B0.063+ exhibited band-gap energies of 3.9 eV. The results showed that boric acid was effective in improving the luminescence intensity of (Ba1.95, Eu0.05)ZnSi2O7, and the optimum molar ratio of boric acid to zinc nitrate was about 0.06. The phosphor (Ba1.95, Eu0.05)ZnSi2O7: B0.063+ synthesized by combustion method showed 1.5 times improved emission intensity compared with that of the Ba1.95ZnSi2O7: Eu0.052+ phosphor under λex = 353 nm.
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