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Ceramic Yields (ceramic + yield)
Selected AbstractsA novel route to perovskite lead zirconate titanate from glycolate precursors via the sol,gel processAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 2 2008N. Tangboriboon Abstract A perovskite lead zirconate titanate was synthesized by the sol-gel process, using lead glycolate, sodium tris(glycozirconate) and titanium glycolate as the starting precursors. For the mole ratio Pb:Zr:Ti of 1:0.5:0.5 [Pb(Zr0.5Ti0.5)O3], TGA-DSC thermal analysis indicated that the percentage of ceramic yield was 55.8, close to the calculated chemical composition value of 49.5. The exothermic peak occurred at 268 °C below the theoretical Curie temperature of 400 °C. The pyrolysis of Pb(Zr0.5Ti0.5)O3 of the perovskite phase was investigated in terms of calcination temperature and time. The structure obtained was of the tetragonal form when calcined at temperatures below 400 °C; it transformed to the tetragonal and the cubic forms of the perovskite phase on calcination above the Curie temperature, as verified by X-ray data. The lead zirconate titanate synthesized and calcined at 400 °C for 1 h had the highest dielectric constant, the highest electrical conductivity and the dielectric loss tangent of 10 190, 0.803 × 10,3 (,.m),1 and 1.513 at 1000 Hz, respectively. The lead zirconate titanate powder synthesized has potential applications as an electronic material. Copyright © 2008 John Wiley & Sons, Ltd. [source] Hyperbranched polycarbosiloxane with dendritic boron cores: Synthesis, characterization, and structure regulationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 12 2006Jie Kong Abstract The synthesis, characterization, and structure regulation of hyperbranched polycarbosiloxane with dendritic boron cores were realized in this paper. First, dendritic boron core was synthesized via hydroboration with borane dimethylsulfide and bis(allyloxy)dimethylsilane. Then, the hyperbranched polycarbosiloxanes with dendritic boron cores were synthesized via hydrosilylation with AB2 type monomer of bis(allyloxy)methylsilane and dendritic boron cores. The molecular structures of the dendritic boron core and resulting hyperbranched polymers were characterized by using Fourier transform infrared spectroscopy, 1H nuclear magnetic resonance, and 13C nuclear magnetic resonance spectroscopies. Size exclusion chromatography/multiangle laser light scattering analysis reveals that the structures of hyperbranched polycarbosiloxane can be regulated effectively by incorporation of functional dendritic boron cores. Compared with hyperbranched polycarbosiloxane of the same molecular weight level, the hyperbranched polycarbosiloxane with dendritic boron cores presents narrower molecular weight distribution as well as much smaller hydrodynamic radius and intrinsic viscosity. Thermalgravimetric analyzer analysis indicates that both the decomposition temperature and ceramic yields are increased as the results of the incorporation of dendritic boron cores into hyperbranched polycarbosiloxane. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3930,3941, 2006 [source] Sol-Gel-Derived Silicon-Boron Oxycarbide Glasses Containing Mixed Silicon Oxycarbide (SiCxO4,x) and Boron Oxycarbide (BCyO3,y) UnitsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2001Christel Gervais The introduction of B atoms in SiOC glass networks has been achieved through the pyrolysis of sol-gel-derived polyborosiloxanes under an inert atmosphere. The starting gels were obtained from hydrolysis-condensation reactions of triethylborate (B(OEt)3) and an organically modified trialkoxysilane (EtSi(OEt)3). The resulting hybrid EtSiO1.5 -B2O3 gels showed a homogeneous dispersion of the B atoms in the siloxane network via ,Si,O,B, bonds. The presence of such borosiloxane bridges prevents the formation of cyclic or cage siloxane entities and leads to relatively high ceramic yields (,80%). The transformation of the polyborosiloxanes into amorphous SiBOC glasses was followed using Fourier transform infrared spectroscopy and multinuclear magic-angle spinning-nuclear magnetic resonance (MAS-NMR) (11B, 13C, and 29Si). An important change in the carbon, silicon, and boron environments occurs during pyrolysis. Interestingly, the 11B MAS-NMR spectra suggest a progressive replacement of the B,O bonds by B,C bonds, which leads to a distribution of trigonal BCxO3,x sites in the glass that was pyrolyzed at 1000°C, with a residual amount of B(OSi)3 sites. The resulting glasses can thus be described as silicon-boron oxycarbide networks that are based on SiCxO4,x and BCyO3,y mixed environments. [source] Synthesis and Characterization of Organic/Inorganic Polyrotaxanes from Polyhedral Oligomeric Silsesquioxane and Poly(ethylene oxide)/, -Cyclodextrin Polypseudorotaxanes via Click ChemistryMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 9 2009Ke Zeng Abstract Organic/inorganic polyrotaxanes were synthesized via Huisgen 1,3-dipolar cycloaddition between 3-azidapropylhepta(3,3,3-trifluoropropyl) POSS and dialkyne-terminated PEO/, -cyclodextrin polypseudorotaxanes. The organic/inorganic hybrid polyrotaxanes were characterized by means of 1H NMR spectroscopy and WAXRD. It was found that the nanosized POSS blocking agents significantly affected the crystal structures of polyrotaxanes. Thermal gravimetric analysis showed that the organic/inorganic hybrid polyrotaxanes exhibited enhanced thermal stability compared to their parent polypseudorotaxanes, in terms of rate of thermal degradation and the summation of char and ceramic yields. [source] Effect of an epoxy octasilsesquioxane on the thermodegradation of an epoxy/amine systemPOLYMER INTERNATIONAL, Issue 1 2010Belén Montero Abstract Polyhedral oligomeric silsesquioxanes (POSS®) can be added to thermoplastic and thermostable polymers to obtain hybrid materials with only a minor tendency to suffer ignition. The aim of the work reported was to analyse the influence of an octafunctional POSS® in the pyrolysis of an epoxy/amine system as well as during the combustion process. Thermal degradation of the modified materials, with respect to the unmodified ones, was analysed using thermogravimetric analysis. As the content of POSS® increased the stability improved and the char/ceramic yields were higher. The Kissinger,Akahira,Sunose method was applied to the modified blends and it showed a decrease in the activation energy with POSS® content. Empirical kinetic models, as well as generalized master plots, were applied to explain the degradation mechanism for ternary blends. The limiting oxygen index parameter was measured to analyse the fire retardancy effect of POSS®: it increased from 24.3 to 25.4% with the addition of 2.5 wt% of POSS®. The mechanism of thermal degradation of the hybrid materials based on an epoxy resin is affected by the presence of the octaepoxy POSS®. Only small amounts of POSS® are necessary to enhance the combustion resistance of the system. Copyright © 2009 Society of Chemical Industry [source] | ||||||||||