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Now showing items 129 - 144 of 10560

  • Microstructure and interfacial reactions between B(6)O and (Ni, Co) couples

    Johnson, O. T.   Sigalas, I.   Herrmann, M.  

    The search for suitable additives for boron suboxide (B(6)O) materials which could improve densification, reduce sintering temperature and tailor the microstructure has been of great importance. In an earlier study it was shown that transition metal borides qualify as sintering aids for B(6)O, but partial segregations of the boride secondary phases were found. In this work, efforts have been made to understand the chemical interaction between the B(6)O and boride phase. A reaction couple of sintered B(6)O, nickel and green compact B(6)O were assembled and heat-treated at 1850 degrees C for 20 min. XRD and SEM examinations of the reaction zone show the formation of nickel boride, diffusing into the B(6)O matrix and a substantial grain growth of B(6)O at the interface. (C) 2010 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
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  • A High-Q Microwave Dielectric Material Based on Mg(3)B(2)O(6)

    Dosler, Urban   Krzmanc, Marjeta Macek   Jancar, Bostjan   Suvorov, Danilo  

    The microwave dielectric properties and microstructure of Mg(3)B(2)O(6) ceramics with the addition of 0-5 wt% Mg(2)B(2)O(5) were investigated. Scanning electron microscopy of the Mg(3)B(2)O(6) ceramics sintered at 1310 degrees C revealed the presence of anisotropic, exaggeratedly grown grains with a crystallographic fault that extends along the direction of the anisotropy. The most pronounced, exaggerated grain growth was observed for Mg(3)B(2)O(6) with 5 wt% of Mg(2)B(2)O(5). The anisotropic grains were examined by electron backscatter diffraction. The analysis of the Kikuchi pattern showed that the crystallographic fault is a (011) twinning plane. The duration of annealing was found to have no significant effect on the dielectric permittivity, while the Q x f values increased two times with a prolongation of the annealing from 20 to 160 h. The highest Q x f value of 240 000 GHz was measured for Mg(3)B(2)O(6) ceramics with 5 wt% of Mg(2)B(2)O(5). These ceramics consisted of 10 times larger grains than the Mg(3)B(2)O(6) ceramics without the added Mg(2)B(2)O(5), which also showed high Q x f values of 200 000 GHz. The decrease of the amorphous phase during the annealing could be one of the reasons for this improvement of the Q x f values.
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  • Total Synthesis of Thelephantin O, Vialinin A/Terrestrin A, and Terrestrins B–D

    Fujiwara, Kenshu   Sato, Takuto   Sano, Yusuke   Norikura, Toshio   Katoono, Ryo   Suzuki, Takanori   Matsue, Hajime  

    The first total synthesis of natural, unsymmetrical 2',3'-diacyloxy-p-terphenyls, thelephantin O (1) and terrestrins C and D (2 and 3, respectively), was achieved via a practical route which was also applicable to the synthesis of the symmetrical diesters vialinin A/terrestrin A. (4) and terrestrin B (5). Compounds 1-5 exhibited cytotoxicity against cancer cells (HepG2 and Caco2) with IC50 values of 13.6-26.7 mu mol/L.
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  • Structural and Physical Properties of Fe(2)O(3)-B(2)O(3)-V(2)O(5) Glasses

    Kundu, Virender   Dhiman, R. L.   Maan, A. S.   Goyal, D. R.  

    The structural and physical properties of xFe(2)O(3)-(40- x) B(2)O(3)-60V(2)O(5) (0 <= x <= 20) glass system have been investigated. The samples were prepared by normal melt-quench technique. The structural changes were inferred by means of FTIR by monitoring the infrared (IR) spectra in the spectral range 600-4000 cm (1). The absence of boroxol ring (806 cm (1)) in the present glass system suggested that these glasses consist of randomly connected BO(3) and BO(4) units. The conversion of BO(3) to BO(4) and VO(5) to VO(4) tetrahedra along with the formation of non-bridging oxygen's (NBOs) attached to boron and vanadium takes place in the glasses under investigation. The density and molar volume of the present glass system were found to depend on Fe(2)O(3) content. DC conductivity of the glass system has been determined in the temperature range 310-500 K. It was found that the general behavior of electrical conductivity was similar for all glass compositions and found to increase with increasing iron content. The parameters such as activation energy, average separation between transition metal ions (TMIs), polaron radius, and so forth have been calculated in adiabatic region and are found consistent with Mott's model of phonon-assisted polaronic hopping. Copyright (C) 2008 Virender Kundu et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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  • Structural and electrical characterization of glasses in the Li 2 O–CaO–B 2 O 3 system

    Pimentel N.B.   Mastelaro V.R.   M'Peko J.-C.   Martin S.W.   Rojas S.S.   De Souza J.E.  

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  • O Prêmio Nobel de Física de 2010
    DOI:10.5007/2175-7941.2011v28n1p205

    Bassalo José Maria Filardo  

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  • O Prêmio Nobel de Física de 2010
    DOI:10.5007/2175-7941.2011v28n1p205

    Bassalo, José Maria Filardo  

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  • B–O–Th isotope systematics in Icelandic tephra

    Estelle F. Rose-Koga   Olgeir Sigmarsson  

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  • Acousto-optic interaction in alpha-BaB(2)O(4)and Li(2)B(4)O(7) crystals.

    Martynyuk-Lototska, Irina   Mys, Oksana   Dudok, Taras   Adamiv, Volodymyr   Smirnov, Yevgen   Vlokh, Rostyslav  

    Experimental studies and analysis of acousto-optic diffraction in alpha-BaB(2)O(4) and Li(2)B(4)O(7) crystals are given. Ultrasonic wave velocity, elastic compliance and stiffness coefficients, and piezo-optic and photoelastic coefficients of alpha-BaB(2)O(4) and Li(2)B(4)O(7) crystals are determined. The acousto-optic figure of merit has been estimated for different possible geometries of acousto-optic interaction. It is shown that the acousto-optic figures of merit for alpha-BaB(2)O(4) crystals reach the value M(2)=(270 +/- 70) x 10(-15) s(3)/kg for the case of interaction with the slowest ultrasonic wave. The directions of propagation and polarization of those acoustic waves are obtained on the basis of construction of acoustic slowness surfaces. The acousto-optic diffraction is experimentally studied for alpha-BaB(2)O(4) and Li(2)B(4)O(7) crystals.
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  • Eu(3+) emission in SrAl(2)B(2)O(7) based phosphors

    Yang, Yuming   Ren, Zhouyun   Tao, Yanchun   Cui, Yuming   Yang, Hua  

    Eu(3+) doped SrAl(2)B(2)O(7) phosphors were fabricated by the wet method. The structures of the phosphors were characterized by XRD. The doping content of Eu(3+) ions in SrAl(2)B(2)O(7):Eu(3+) phosphors are 1%, 4%, 6%, 8%, 10% (molar fraction), respectively. Luminescence properties were analyzed by measuring the excitation and photoluminescence spectra. The luminescent properties of SrAl(2)B(2)O(7):Eu(3+) phosphors are discussed. It is shown that from 4% to 6% of doping content of Eu(3+) ions under 392 nm excitation in SrAl(2)B(2)O(7):Eu(3+) phosphors is optimum. (C) 2008 Elsevier B.V. All rights reserved.
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  • Effect of B(2)O(3) on Melting Temperature of CaO-Based Ladle Refining Slag

    Wang Hong-ming   Li Gui-rong   Li Bo   Zhang Xue-jun   Yan Yong-qi  

    B(2)O(3) is selected as fluxing agent of CaO-based ladle refining slag to decrease the melting temperature as well as to improve the speed of slag forming and the refining efficiency. The effects of B(2)O(3) on the melting temperature of two series of refining slags including the low basicity slags (the mass ratio of CaO/SiO(2) is 3-4) and the high basicity slags (the mass ratio of CaO/SiO(2) is 5-8.75) were investigated. The slag melting temperature was measured using The hemisphere method. The results indicate that the fluxing action of B(2)O(3) is better than that of CaF(2) and Al(2)O(3). For the CaO-based refining slag with low basicity, the melting temperature is decreased effectively when B(2)O(3) is used to substitute for equal mass of CaF(2), Al(2)O(3) and SiO(2), respectively. For the CaO-based refining slag with high basicity, when CaF(2) is substituted by B(2)O(3), the melting temperature can be decreased remarkably. Especially, when the mass ratios of CaO/Al(2)O(3) and CaO/SiO(2) are in the range of 1.1-4.0 and 5.25-8.0, respectively, the slag melting temperature is lower than 1 300 degrees C. Therefore, the B(2)O(3)-containing refining slags with high ratios of CaO/Al(2)O(3) and CaO/SiO(2) have ultra low melting temperature.
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  • Liquid phase assisted densification of superhard B6O materials

    Mathias Herrmann   Jan Raethel   Axel Bales   Kerstin Sempf   Iakovos Sigalas   y Hoehn  

    B6O-based materials are known as some of the hardest materials after diamond and cubic boron nitride with a hardness of 45 GPa measured on single crystals. Several attempts were made to produce B6O materials by hot pressing, but without success. Based on thermodynamic considerations the possibility of the use of sintering additives was discussed and the developed concepts were validated by densification of the materials using FAST (field assisted sintering technique)/SPS methods and analysing the microstructure and properties of the resulting materials. Two groups of materials were found to be suitable for the densification: transition metals which form borides with B6O, the elements of the first to fourth main groups of the periodic table and the rare earths (Sc, Y, and lanthanides) which are in equilibrium in the oxide form with B6O and form a liquid phase during densification at 1700–1900 °C. Superhard dense B6O materials were produced and their properties investigated.
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  • La(2)O(3)-Al(2)O(3)-B(2)O(3)-SiO(2) glasses for solid oxide fuel cell applications

    Wang, Sea-Fue   Lu, Chien-Ming   Wu, Yu-Chuan   Yang, Yung-Chin   Chiu, Te-Wei  

    La(2)O(3)-Al(2)O(3)-B(2)O(3)-SiO(2) glasses free of alkaline earth metals were prepared in this study for SOFC applications to relieve the poison caused by BaCrO(4) or SrCrO(4) formation. The apparent densities, coefficients of thermal expansion (CTE), and softening points of the La(2)O(3-)-Al(2)O(3)-SiO(2)-B(2)O(3) glasses prepared in this study ranged respectively from 3.24 to 4.54 g/cm(3), 4.1 to 8.1 ppm/degrees C, and 912 to 937 degrees C, depending on the glass composition. The CTE value dropped with the rise in SiO(2) content and escalated with increase in La(2)O(3) content. Crystallization of La(9.51)(SiO(1.0404))(6)O(2) and La(4.67)(SiO(4))(3)O was observed in part of the glasses after soaking at 800 degrees C. Two CTE modifiers, MgO and SDC, effectively increased the CTE of La(2)O(3-)-Al(2)O(3)-SiO(2)-B(2)O(3) glasses. The composites of selected La(2)O(3)-Al(2)O(3)-B(2)O(3)-SiO(2) glasses and SDC additive on the YSZ substrate were evaluated for use as sealing materials of solid oxide fuel cells (SOFCs). Results indicated that the leakage rates for the composites of A07 glass and 60-70 vol% SDC on the YSZ plate read less than 0.02 (sccm/cm)(kg/cm(2)) per min at 800 degrees C. This property seems highly promising for ensuring long-term stability of the sealing materials for SOFC applications. Copyright (C) 2010, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
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  • Luminescent properties of SrAl(2)B(2)O(7): Ce(3+), Tb(3+)

    Yang, Yuming   Bao, Amurisana   Lai, Hua   Tao, Yanchun   Yang, Hua  

    By using metal nitrates as starting materials, SrAl(2)B(2)O(7): Tb(3+) and SrAl(2)B(2)O(7): Ce(3+), Tb(3+) powder phosphors were prepared by sol-gel method. X-ray diffraction (XRD), photoluminescence excitation and emission, as well as kinetic decays were employed to characterize the resulting samples. The results show that energy transfers from Ce(3+) to Tb(3+) ions. The emission intensity of Tb(3+) ions in SrAl(2)B(2)O(7) could be greatly intensified when Ce(3+) ions are doped into SrA(2)B(2)O(7): Tb(3+). The decay times of SrAl(2)B(2)O(7): Tb(3+) were prolonged when Ce(3+) ions were doped. The doping of Ce(3+) ions not only improved the luminescent intensity, but also made the materials gets stable luminescent properties. Crown Copyright (C) 2009 Published by Elsevier Ltd. All rights reserved.
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  • Crystal growth and characterization of K(2)B(4)O(11)H(8)

    Luo, Xingcheng   Pan, Shilie   Fan, Xiaoyun   Wang, Jide   Liu, Gang  

    Single crystals of K(2)B(4)O(11)H(8), a non-centrosymmetric borate material, have been prepared by slow evaporation of water Solution at room temperature. The crystals were colorless and transparent with smooth faces. The single-crystal X-ray diffraction analysis showed that K(2)B(4)O(11)H(8) crystallized in the orthorhombic space group P2(1)2(1)2(1) with a=6.8556(6)angstrom, b=11.7787(12)angstrom, c=12.8949(14)angstrom, Z=4, R(1)=0.0188, and wR(2)=0.0464. The powder X-ray diffractometry (PXRD), infrared spectrum, transmittance spectrum, TG-DTA curves and second harmonic generation properties of title compound have been determined. (C) 2009 Elsevier B.V. All rights reserved.
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  • Pb(2)B(5)O(9)I: An Iodide Borate with Strong Second Harmonic Generation

    Huang, Yi-Zhi   Wu, Li-Ming   Wu, Xin-Tao   Li, Long-Hua   Chen, Ling   Zhang, Yong-Fan  

    The combination of lone-pair effects on Pb(2+) cations and the smaller electronegativity of I(-) anions into the pentaborate framework generates a phase-matchable material, Pb(2)B(5)O(9)I, with the largest powder SHG response among borates, about 13.5 times that of KDP (KH(2)PO(4)), and transparency over the near-UV to middle-IR region. DFT calculations on electronic structure and cutoff-energy-dependent SHG coefficients confirm these origins.
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