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Precursor Material (precursor + material)

Distribution by Scientific Domains

Polymers and Materials Science	58%
Chemistry	25%

Selected Abstracts

The relationship between disinfection by-product formation and structural characteristics of humic substances in chloramination

ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 12 2003
Wells W. Wu
Abstract The influence of structural characteristics of humic substances on disinfection by-product (DBP) formation was investigated for seven humic substances isolated from aquatic and terrestrial sources. The structural characterizations included 13C nuclear magnetic resonance (13C NMR) spectroscopy and ultraviolet (UV) spectroscopy. The aqueous humic substances were chloraminated at pH 7.0 and 8.5, with and without the presence of the bromide ion, and analyzed for total organic halogen (TOX), trihalomethanes (THMs), and haloacetic acids (HAAs). Aromatic contents determined by 13C NMR and differential UV absorbance at 254 nm statistically correlated with TOX formation for the humic substances investigated at p < 0.08. In contrast, a lack of correlation was observed for THM and HAA formation and these parameters. This paper also compiles relevant literature and discusses the contrasting reaction response of DBP precursor material to chlorination and chloramination. [source]

Three-Dimensional Printing of Complex-Shaped Alumina/Glass Composites,

ADVANCED ENGINEERING MATERIALS, Issue 12 2009
Wei Zhang
Abstract Alumina/glass composites were fabricated by three-dimensional printing (3DPÔ) and pressureless infiltration of lanthanum-alumino-silicate glass into sintered porous alumina preforms. The preforms were printed using an alumina/dextrin powder blend as a precursor material. They were sintered at 1600,°C for 2,h prior to glass infiltration at 1100,°C for 2,h. The influence of layer thickness and sample orientation within the building chamber of the 3D-printer on microstructure, porosity, and mechanical properties of the preforms and final composites was investigated. The increase of the layer thickness from 90 to 150,µm resulted in an increase of the total porosity from ,19 to ,39,vol% and thus, in a decrease of the mechanical properties of the sintered preforms. Bending strength and elastic modulus of sintered preforms were found to attain significantly higher values for samples orientated along the Y -axis of the 3D-printer compared to those orientated along the X - or the Z -axis, respectively. Fabricated Al2O3/glass composites exhibit improved fracture toughness, bending strength, Young's modulus, and Vickers hardness up to 3.6,MPa m1/2, 175,MPa, 228,GPa, and 12,GPa, respectively. Prototypes were fabricated on the basis of computer tomography data and computer aided design data to show geometric capability of the process. [source]

Net Shape Reaction Bonded Ceramic Micro Parts by Mechanical Microstructuring

ADVANCED ENGINEERING MATERIALS, Issue 10 2006
H.-J. Ritzhaupt-Kleissl
Net shape ceramic micro components can be realized by mechanical microstructuring green blanks consisting of precursor materials followed by reaction bonding. The precursor material is composed of mainly zirconium silicide as reactive precursor material, organosilicon polymer (PMSS) as low loss binder and zirconium oxide as an inert phase. Shaping in the green state can easily be performed by micro milling, even if different cutting strategies are applied. Subsequently the components are thermally processed for ceramization and for sintering them to full density. Dependent on the material composition and on the green density the dimensions of the sintered components are retained unchanged compared to the dimensions of the green parts. [source]

Nanofibers from Laser Spinning: Laser Spinning of Bioactive Glass Nanofibers (Adv. Funct.

ADVANCED FUNCTIONAL MATERIALS, Issue 19 2009
Mater.
This cover image is a graphical representation of the laser spinning process described by Félix Quintero et al. on page 3084. Laser spinning involves the use of a high power laser to melt a very small volume from a plate of the precursor material. A high speed supersonic gas jet causes the rapid elongation and cooling of the melt, yielding a glass nanofiber. The authors also describe the use of this technique in producing Bioglass nanofibers. [source]

Laser Spinning of Bioactive Glass Nanofibers

ADVANCED FUNCTIONAL MATERIALS, Issue 19 2009
Félix Quintero
Abstract The production of nanofibers of bioactive glass by laser spinning is reported. The technique yields a great quantity of free-standing fibers in the form of a mesh of disordered intertwined fibers. The method does not rely on chemical processing and does not need any chemical additive. It involves melting of a precursor material with tailored composition, which makes it possible to produce nanofibers from materials with which conventional melt drawing techniques cannot be used. Herein, the production of 45S5 Bioglass nanofibers is reported for the first time. The process is very fast (nanofibers of several centimeters are grown in a fraction of a second), without the necessity of post heat treatments, and no devitrification is observed as a result of the laser-spinning process. The morphology, composition, and structure of the nanofibers are characterized and an assessment of their bioactivity is carried out by immersion in simulated body fluid. This technique provides a method for the rapid production of dense glass nanofibers that can be employed as bioactive nanocomposite reinforcement, as a synthetic bone graft to replace missing bone, or to produce 3D structures for use as scaffolds for bone-tissue engineering. [source]

Phase Morphology in Electrospun Zirconia Microfibers

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2008
Erin Davies
Electrospinning of sol,gels has been used to produce zirconium-doped polymer microfibers from zirconyl chloride and poly(vinylpyrollidone) precursors. Calcination of these structures between temperatures of 370° and 930°C resulted in the formation of zirconia nanograined microfibers whose diameters ranged from 1200 to 800 nm at the higher temperatures and whose average grain size ranged from 9 to 33 nm. X-ray diffraction analysis revealed varying amounts of monoclinic and tetragonal zirconia present in the fibers and established how this varied with calcination temperature and time. The tetragonal phase was shown to be unstable and disappeared on heating the material beyond around 750°C. The amount of zirconia yielded from the precursor material was measured and was found to be consistently greater than the theoretical yield. Average grain size within the microfibers increased with increasing calcination temperature and is effectively doubled when a 10 kPa pressure was applied. The effect of pressure also results in the creation of new crystal structures within the nanofibers and, as with traditional zirconia processing, the addition of impurity ions was found to stabilize the tetragonal phase. [source]

Synthesis of Nanocrystalline ,-Alumina Powder Using Triethanolamine

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2001
Ranjan K. Pati
Nanocrystalline ,-Al2O3 powders have been prepared by pyrolysis of a complex compound of aluminum with triethanolamine (TEA). The soluble metal-ion,TEA complex forms the precursor material on complete dehydration of the complex of aluminum-TEA. The single-phase ,-Al2O3 powder has resulted after heat treatment at 1025°C. The precursors and the heat-treated final powders have been characterized by X-ray diffractometry, thermogravimetric and differential thermal analysis, and transmission electron microscopy (TEM). The average particle sizes as measured from X-ray line broadening and TEM are ,25 nm. The powder has crystallite sizes of the same order indicates the poor agglomeration of crystallites. [source]

State of the art of carbon molecular sieves supported on tubular ceramics for gas separation applications

ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2010
Kelly Briceño
Abstract During recent years, research into alternative power generation and less polluting vehicles has been directed towards the fabrication of compact and efficient devices using hydrogen fuel cells. As a compact viable proposal, membrane reactors (MR) have been studied as means of providing a fuel cell with an on-board supply device for pure hydrogen streams obtained by reforming hydrocarbons. However, the development of MRs is strongly dependant on the membrane having high permeation flux and high selectivity ratios towards H2 in a mixture of gases. To meet this need, carbon membranes are proposed materials, which have pores that are the same size as the kinetic diameters of syngases. These would provide an alternative to polymers, metals and ceramics in MR applications. Moreover, a tubular shape is a highly recommended configuration for achieving a compact and large reaction surface area. However, it is not easy to obtain a supported and amorphous carbon layer from polymer pyrolysis because the fabrication methods, the type of precursor material, characteristics of the support and pyrolysis conditions are all closely connected. The combination of all these factors and the stability problems of carbon membranes have limited the use of carbon molecular sieves (CMS) in large-scale applications. This review attempts to provide an overview of the use of carbon membranes in MRs for gas separation. It also reviews the advances in the materials, fabrication methods and characterisation techniques of specific supported carbon molecular sieve membranes that have been supported on tubular carriers so they can take advantage of the high permeation and selectivity values previously reported for unsupported CMS. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source]

Biomimetic Synthesis of Metal Ion-Doped Hierarchical Crystals Using a Gel Matrix: Formation of Cobalt-Doped LiMn2O4 with Improved Electrochemical Properties through a Cobalt-Doped MnCO3 Precursor

CHEMISTRY - AN ASIAN JOURNAL, Issue 4 2010
Takao Kokubu
Abstract We have synthesized spinel type cobalt-doped LiMn2O4 (LiMn2,yCoyO4, 0,y,0.367), a cathode material for a lithium-ion battery, with hierarchical sponge structures via the cobalt-doped MnCO3 (Mn1- xCoxCO3, 0,x,0.204) formed in an agar gel matrix. Biomimetic crystal growth in the gel matrix facilitates the generation of both an homogeneous solid solution and the hierarchical structures under ambient condition. The controlled composition and the hierarchical structure of the cobalt-doped MnCO3 precursor played an important role in the formation of the cobalt-doped LiMn2O4. The charge,discharge reversible stability of the resultant LiMn1.947Co0.053O4 was improved to ca. 12,% loss of the discharge capacity after 100,cycles, while pure LiMn2O4 showed 24,% loss of the discharge capacity after 100,cycles. The parallel control of the hierarchical structure and the composition in the precursor material through a biomimetic approach, promises the development of functional materials under mild conditions. [source]

Facile Synthesis of Bastnaesite -Type LaF[CO3] and Its Thermal Decomposition to LaOF for Bulk and Eu3+ -Doped Samples

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 3 2009
Oliver Janka
Abstract Rare-earth metal(III) oxide fluorides with the composition MOF (M = La,Lu) seem to offer promising host lattices for luminescence applications by doping these materials with trivalent lanthanoid cations. Unfortunately, there was no simple and practicable way to synthesize the compounds in phase-pure quality with classical solid-state chemistry reactions. However, by using the rare-earth metal(III) fluoride oxocarbonates, MF[CO3], as solution-born precursor materials that crystallize with a bastnaesite -type structure, easy access is now possible by mild thermal decomposition. Synthetic details, investigations on the phase purity and the presence of the oxocarbonate anion [CO3]2, proved by IR measurements as well as from X-ray powder diffraction data are given in this paper for the example of bulk LaF[CO3] and Eu3+ -doped samples. The latter (LaF[CO3]:Eu3+) shows a bright orange-red luminescence that is stronger than that of the product of its thermal decomposition: trimorphic LaOF:Eu3+.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]

Net Shape Reaction Bonded Ceramic Micro Parts by Mechanical Microstructuring

Structural Evolvement of Heating Treatment of Mg/Al-LDH and Preparation of Mineral Mesoporous Materials

ACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 2 2006
CHEN Tianhu
Abstract, Although hydrotalcite, or layered double hydroxides (LDHs), is not a common mineral, it is an important material that can be easily synthesized in laboratory. In this study, structural evolvement and BET surface area changes of heat treated Mg/Al-LDH is evaluated by XRD, TEM and N2 -BET analyses. The results indicate that the magnesium-aluminum LDH with carbonate as interlayer anion, periclase-like oxides was formed at temperatures of 400,800°C. Meanwhile, 2,3 nanometer mesoporous were formed during decomposition of LDH. However, the heat treated samples still preserve the morphology of the original LDH plates. Periclase-like formed from LDH heat treatment may re-hydrolyze and recover the structure of LDH. However, crystallinity of the recovered LDH is lower than that of the original LDH. This heat treatment will result in formation of (Mg, Al)-oxide nano-crystals and nanopores among the nano-crystals. When heating temperature exceeds 1000, the periclase-like (Mg, Al)-oxide is transformed into a composite with periclase (MgO) and spinel phases. The periclase can be re-hydrolyzed and dissolved in HCI solution. After acid treatment, the sample with a high surface area is composed of spinel nano-crystals and nanopores among them. Our results will provide a new and economic way to synthesize mesoporous materials through pathways of phase transformation of precursor materials with different composition. [source]