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Magnesium Compound (magnesium + compound)
Selected AbstractsProcessing and Thermal Conductivity of Sintered Reaction-Bonded Silicon Nitride: (II) Effects of Magnesium Compound and Yttria AdditivesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2007Xinwen Zhu The effects of the magnesium compound and yttria additives on the processing, microstructure, and thermal conductivity of sintered reaction-bonded silicon (Si) nitride (SRBSN) were investigated using two additive compositions of Y2O3,MgO and Y2O3,MgSiN2, and a high-purity coarse Si powder as the starting powder. The replacement of MgO by MgSiN2 leads to the different characteristics in RBSN after complete nitridation at 1400°C for 8 h, such as a higher ,-Si3N4 content but finer ,-Si3N4 grains with a rod-like shape, different crystalline secondary phases, lower nitrided density, and coarser porous structure. The densification, ,,, phase transformation, crystalline secondary phase, and microstructure during the post-sintering were investigated in detail. For both cases, the similar microstructure observed suggests that the ,-Si3N4 nuclei in RBSN may play a dominant role in the microstructural evolution of SRBSN rather than the intergranular glassy chemistry during post-sintering. It is found that the SRBSN materials exhibit an increase in the thermal conductivity from ,110 to ,133 (Wm·K),1 for both cases with the increased time from 6 to 24 h at 1900°C, but there is almost no difference in the thermal conductivity between them, which can be explained by the similar microstructure. The present investigation reveals that as second additives, the MgO is as effective as the MgSiN2 for enhancing the thermal conductivity of SRBSN. [source] Preferred Functionalization of Metallic and Small-Diameter Single-Walled Carbon Nanotubes by Nucleophilic Addition of Organolithium and -Magnesium Compounds Followed by ReoxidationCHEMISTRY - A EUROPEAN JOURNAL, Issue 5 2008David Wunderlich Dipl.-Chem Abstract Covalent sidewall addition to single-walled nanotubes (SWNTs) of a series of organolithium and organomagnesium compounds (nBuLi, tBuLi, EtLi, nHexLi, nBuMgCl, tBuMgCl) followed by reoxidation is reported. The functionalized Rn -SWNTs were characterized by Raman and NIR emission spectroscopy. The reaction of SWNTs with organolithium and magnesium compounds exhibits pronounced selectivity: in general, metallic tubes are more reactive than semiconducting ones. The reactivity of SWNTs toward the addition of organometallic compounds is inversely proportional to the diameter of the tubes. This was determined simultaneously and independently for both metallic and semiconducting SWNTs. The reactivity also depends on the steric demands of the addend. Binding of the bulky t- butyl addend is less favorable than addition of primary alkyl groups. Significantly, although tBuLi is less reactive than, for example, nBuLi, it is less selective toward the preferred reaction with metallic tubes. This unexpected behavior is explained by fast electron transfer to the metallic SWNTs having low-lying electronic states close to the Fermi level, a competitive initial process. The NIR emission of weakly functionalized semiconducting SWNTs, also reported for the first time, implies interesting applications of functionalized tubes as novel fluorescent reporter molecules. [source] Sildenafil citrate (Viagra) complexes with bivalent ionsJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 1 2006Petr Melnikov Abstract The interaction of Ca2+ -ions with sildenafil citrate (Viagra) leads to the precipitation of a new polymorph variety of sildenafil base. Under the same conditions, Mg2+, Zn2+, and Cd2+ ions form structurally related crystalline complexes of the composition Me2+C28H34N6O11S. Lattice parameters have been determined showing that magnesium compound belongs to an orthorhombic system, while the zinc and cadmium compounds are its monoclinic distortions. All three compounds are thermally stable, undergoing decomposition above 175°C with the consequent formation of carbonates Me2+CO3 and oxides. © 2005 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 95:225,227, 2006 [source] Processing and Thermal Conductivity of Sintered Reaction-Bonded Silicon Nitride: (II) Effects of Magnesium Compound and Yttria AdditivesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2007Xinwen Zhu The effects of the magnesium compound and yttria additives on the processing, microstructure, and thermal conductivity of sintered reaction-bonded silicon (Si) nitride (SRBSN) were investigated using two additive compositions of Y2O3,MgO and Y2O3,MgSiN2, and a high-purity coarse Si powder as the starting powder. The replacement of MgO by MgSiN2 leads to the different characteristics in RBSN after complete nitridation at 1400°C for 8 h, such as a higher ,-Si3N4 content but finer ,-Si3N4 grains with a rod-like shape, different crystalline secondary phases, lower nitrided density, and coarser porous structure. The densification, ,,, phase transformation, crystalline secondary phase, and microstructure during the post-sintering were investigated in detail. For both cases, the similar microstructure observed suggests that the ,-Si3N4 nuclei in RBSN may play a dominant role in the microstructural evolution of SRBSN rather than the intergranular glassy chemistry during post-sintering. It is found that the SRBSN materials exhibit an increase in the thermal conductivity from ,110 to ,133 (Wm·K),1 for both cases with the increased time from 6 to 24 h at 1900°C, but there is almost no difference in the thermal conductivity between them, which can be explained by the similar microstructure. The present investigation reveals that as second additives, the MgO is as effective as the MgSiN2 for enhancing the thermal conductivity of SRBSN. [source] An efficient MnCl2 -catalyzed tandem acylation-cross-coupling reaction of o -halobenzoyl chloride with diorganyl magnesium compoundsAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 1 2010Fengmin Zhang Abstract An efficient tandem cross-coupling reaction of o -chlorobenzoyl chloride with dialkyl and diaryl magnesium compounds in the presence of manganese (II) chloride was developed, which proceeds in good yield under mild conditions. Copyright © 2009 John Wiley & Sons, Ltd. [source] | ||||||||||