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Alumina Content (alumina + content)
Selected AbstractsGeochemical and mineralogical distinctions between Bonnin and Morris (Philadelphia, 1770,1772) porcelain and some contemporary British phosphatic waresGEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 7 2001J. Victor Owen The major element compositions of 15 ceramic sherds from the Bonnin and Morris factory site were determined by electron microprobe. Thirteen samples are phosphatic; the others consist of (a) "soapstone" (magnesian/plombian) and (b) true porcelain, and are interpreted as exotic artifacts, as is one compositionally distinct (relatively SiO2 -poor, P2O5+CaO-rich) phosphatic sample. Although long considered to be virtually indistinguishable from Bow porcelain (London: ca. 1747,1776), the phosphatic Philadelphia wares have a relatively low mean CaO/P2O5 ratio (3.3 versus 3.8; molecular proportions) and high alumina content (6.6 versus 5.4 wt % Al2O3). Furthermore, unlike Bow, the Bonnin and Morris samples contain calcic plagioclase (bytownite), and in some instances, an orthoclase-rich ternary feldspar. The preservation of calcic plagioclase indicates that Philadelphia porcelain was fired at (rather than above) the thermal minimum in the An-SiO2 -C3P system, although the presence of Na (and other fluxes) in these wares precludes the exact determination of the maximum firing temperature from this phase diagram. These wares are also distinctive insofar as the phosphate and melt phases can contain small amounts of lead; they have bulk lead contents of approximately 0.1,1.2 wt % PbO. This component has not been detected in the body of Bow or other contemporary British phosphatic porcelains. Their principal similarity lies in the fact that both wares contain sulfate. In addition, the glazes on Bonnin and Morris porcelain (e.g., PbO , 35,50 wt %; SnO2 , 1,2%) compositionally resemble those used at Bow. If feldspar is formed at all, then Al-poor phosphatic porcelain (or those with low CaO/P2O5 ratios) will have comparatively low modal calcic plagioclase contents, thereby allowing the rapid depletion of this mineral via resorption by the melt phase during vitrification. Such appears to have been the case for analyzed Bow porcelain, which is therefore interpreted to have been overfired (sensu lato) relative to its Philadelphia counterpart. Conceivably, calcic plagioclase could be preserved in low-Al wares that were fired only briefly at vitrification temperatures. Given the role of firing history in governing the mineralogy of porcelain, compositional criteria are more reliable for distinguishing these wares. © 2001 John Wiley & Sons, Inc. [source] Sintering Behavior of Nanocrystalline Zirconia Doped with Alumina Prepared by Chemical Vapor SynthesisJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2000Vladimir V. Srdi Powders of nanocrystalline zirconia doped with 3,30 mol% alumina have been synthesized using chemical vapor synthesis (CVS). Dense or mesoporous ceramics of small and narrowly distributed grain and pore sizes in the nanometer range are obtained via pressureless vacuum sintering. The microstructural development of the doped samples is strongly dependent on the alumina content. Sintering of zirconia samples with 3 and 5 mol% alumina at temperatures of 1000°C for 1 h results in fully dense, transparent ceramics with grain sizes of 40,45 nm and homogeneous microstructures. [source] Preparation and Characterization of Trialkoxysilane-Containing Acrylic Resin/Alumina Hybrid MaterialsMACROMOLECULAR MATERIALS & ENGINEERING, Issue 8 2006Mingqi Li Abstract Summary: In the present study (3-methacryloxypropyl)trimethoxysilane (MPMS) containing acrylic resin/alumina hybrid materials with various alumina contents were prepared. The effects of ethylacetoacetate (EAA) content, catalyst type, and water content during sol,gel process for alumina sols on the microstructure and properties of the hybrid materials were investigated by SAXS, AFM, DSC, TGA, and nano-indentation tester, respectively. It was found that the hybrid materials exhibited a homogeneity and the alumina phase of the hybrids had mass fractal dimension and open structure. The thermal and mechanical properties of the hybrid materials were obviously improved when alumina was incorporated. The EAA contents, catalyst type, and water content during sol,gel process for alumina sols had obvious effects on the microstructure and properties of the hybrid materials. Typical load,displacement curves of the pure acrylic resin and hybrid materials with increasing alumina content. [source] Deposition of Compositionally Graded Mullite/Alumina Coatings from Mixtures of SiCl4, AlCl3, CO2 and H2,CHEMICAL VAPOR DEPOSITION, Issue 2 2003S.F. Nitodas Abstract Using CVD, compositionally graded coatings of mullite (3,Al2O3·2,SiO2) and alumina (Al2O3) were deposited on Si-coated substrates from mixtures of silicon tetrachloride, aluminum trichloride, carbon dioxide, and hydrogen. The coatings were compositionally graded, with the Al/Si ratio increasing towards the outer layer of the coatings. The preparation of the coatings was carried out in a vertical, hot-wall CVD reactor. The results of previous experimental studies on the deposition of aluminosilicate species have been used to identify operating conditions where deposition of coatings with alumina content equal to, or greater than, that corresponding to stoichiometric mullite was possible. The scheme for the preparation of the graded mullite/alumina coatings was based on utilizing the positive effect of decreasing the residence time of the reactive mixture in the reactor, and of increasing the Al/Si ratio in the feed on the incorporation of Al2O3 in the deposit. [source] Direct Laser Sintering of Al2O3,SiO2 Dental Ceramic Components by Layer-Wise Slurry DepositionJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2006André Gahler This publication presents a solid freeform fabrication technique for ceramics in the alumina,silica system by layering binder-free, high-loaded ceramic slurries, followed by selective laser sintering. The low melting silica phase and the reaction sintering between silica and alumina favor the rapid prototyping of pure ceramic parts. On the basis of electroacoustic and viscosity measurements, stable slurries from Al2O3/SiO2 powder mixtures and water with a high fluidity have been prepared for the layer deposition with a doctor blade like in tape casting. Layers with a thickness of about 100 ,m were processed. It was found in laser parameter studies that ceramic parts can only be obtained using special alumina contents and laser parameters. But the biphasic approach may allow greater flexibility in the processing regime than is afforded by the use of just one material. The microstructure of these parts depends mainly on the temperature gradient induced by the laser absorption and thermal conduction. The wet shaping facilitates laser-sintered parts with a relatively high density, which could be increased by a thermal post-treatment. [source] Preparation and Characterization of Trialkoxysilane-Containing Acrylic Resin/Alumina Hybrid MaterialsMACROMOLECULAR MATERIALS & ENGINEERING, Issue 8 2006Mingqi Li Abstract Summary: In the present study (3-methacryloxypropyl)trimethoxysilane (MPMS) containing acrylic resin/alumina hybrid materials with various alumina contents were prepared. The effects of ethylacetoacetate (EAA) content, catalyst type, and water content during sol,gel process for alumina sols on the microstructure and properties of the hybrid materials were investigated by SAXS, AFM, DSC, TGA, and nano-indentation tester, respectively. It was found that the hybrid materials exhibited a homogeneity and the alumina phase of the hybrids had mass fractal dimension and open structure. The thermal and mechanical properties of the hybrid materials were obviously improved when alumina was incorporated. The EAA contents, catalyst type, and water content during sol,gel process for alumina sols had obvious effects on the microstructure and properties of the hybrid materials. Typical load,displacement curves of the pure acrylic resin and hybrid materials with increasing alumina content. [source] A mass spectrometric study of Al2O3 -SiO2 melts using a Knudsen cellRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 10 2001Johan Björkvall The thermodynamic activities of SiO2 in Al2O3 -SiO2 liquid slags were measured by the high-temperature Knudsen cell mass spectromeric method in the present work. The measurements were carried out in the temperature range 1863,2169,K. Tungsten crucibles were used to hold the slags. The system was calibrated using a CaF2 standard. The mass spectra obtained for pure SiO2 were in agreement with earlier data. The activities of silica, measured in the present work at 2150,K, show a slight negative deviation at very low alumina mole fractions which changed to a positive deviation at higher alumina contents. The activity values are in reasonable agreement with the assessment carried out by Hillert et al. The results were analysed on the basis of a slag model developed earlier at KTH, Stockholm. The present results are found to be compatible with the phase diagram proposed by Klug et al. Copyright © 2001 John Wiley & Sons, Ltd. [source] | ||||||||||