JOURNAL OF PHYCOLOGY, Issue 5 2002
Shi-Yan Li
Although red algae are known to be obligatory photoautotrophs, the red microalga Porphyridium sp. was shown to assimilate and metabolize floridoside. A pulse-chase experiment with [14C]floridoside showed that at the end of a 240-min pulse, 70% of total 14C-uptake by the cells remained in the floridoside fraction. To evaluate the assimilation of floridoside by Porphyridium sp. cells, we exposed Porphyridium sp. not only to [14C]floridoside but also to its constituents, [14C]glycerol and [14C]galactose, as compared with [14C]bicarbonate. The extent of incorporation of [14C] galactose by the Porphyridium sp. cells was insignificant (50,80 dpm·mL,1), whereas uptake of 14C from [14C]glycerol into the algal cells was evident (2.4 × 103 dpm·mL,1) after 60 min of the pulse. The pattern of 14C distribution among the major constituent sugars, xylose, glucose and galactose, of the labeled soluble polysaccharide was dependent on the 14C source. The relative content of [14C]galactose in the soluble polysaccharide was highest (28.8%) for [14C]floridoside-labeled culture and lowest (19.8%) for the [14C]glycerol-labeled culture. Upon incubation of [14C]floridoside with a crude extract of a cell-free system prepared from nonlabeled cells of Porphyridium sp., the label was indeed found to be incorporated into the sulfated polysaccharide. Our results suggested that the carbon metabolic pathway in Porphyridium sp. passes through the low molecular weight photoassimilatory product,floridoside,toward sulfated cell-wall polysaccharide production. [source]

TRANSACTION COST ECONOMICS: THE PRECURSORS

ECONOMIC AFFAIRS, Issue 3 2008
Oliver E. Williamson
Theories commonly progress through four stages, from informal to pre-formal to semi-formal and fully formal. This paper reports on the earliest stage of transaction cost economics that extended from the 1920s to the 1970s. That the gestation stage lasted so long is partly because transaction cost economics departed significantly from the then-prevailing economic orthodoxy. Also, and related, it is an interdisciplinary undertaking. As reported herein, transaction cost economics selectively combines economics, organisation theory and law and is the product of the contributions of some of the finest minds in those three fields. [source]

PERINATAL AND CHILDHOOD PRECURSORS OF ADULT CARDIOVASCULAR DISEASE

CLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 2007
Lawrence Beilin
SUMMARY 1Longitudinal studies from the US, Australia and Europe have demonstrated tracking of childhood risk factors for cardiovascular disease from adolescence into adult life. These factors include obesity, blood cholesterol levels, blood pressure and measures of insulin resistance. Worldwide increases in childhood obesity and overweight are already resulting in increases in adolescent diabetes and are likely to translate into earlier onset hypertension and cardiovascular disease in adults. 2Low birth weight has also been associated with increased risk of adult cardiovascular disease, diabetes and high blood pressure, but there is considerable debate as to the relative importance of pre- and postnatal influences. 3These issues are discussed in the context of results of a longitudinal cohort study of cardiovascular and metabolic risk factors in Western Australia, the ,Raine' childhood cohort, which showed that in a well-nourished Australian population at age 8 there was a U-shaped relationship between birth weight and a cluster of factors predisposing to adult cardiovascular disease, with postnatal weight gain being the dominant factor. 4Future public health programmes should focus on both pre- and early postnatal factors predisposing to obesity, hypertension and diabetes. [source]

A Single-Source Co/Li/O Organometallic Precursor for Nanocrystalline LiCoO2 , Synthesis, Formation Pathway, and Electrochemical Performance,

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 29 2010
Jayaprakash Khanderi
Abstract A single-source precursor route to phase-pure LiCoO2 by employing the organometallic precursor [(COD)2CoLi(thf)2] (1) to introduce a Co/Li/O 1:1:2 stoichiometry is described for the first time. Compound 1 undergoes decomposition in the presence of oxygen, forming nanoscaled, electrochemically active LiCoO2 starting at a temperature as low as 200 °C. Its temperature-dependent formation pathway was studied by various spectroscopic and microscopic techniques. The transition temperature for the evolution of layered LiCoO2 is above 400 °C. Electrochemical studies indicate that the low-temperature modification of LiCoO2 can be obtained at 500 °C, showing moderate electrochemical battery performance. [source]

Formation of Metastable Na2CrO4 -Type LiNiPO4 from a Phosphate,Formate Precursor

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 1 2010
Violeta Koleva
Abstract High-pressure modification of LiNiPO4 with a Na2CrO4 -type structure was obtained at ambient pressure and low temperature from a mixed LiNi,phosphate,formate precursor, LiNiPO4Hx(HCOO)x·yH2O (where x , 1.2 and y , 2.5). The structural and thermal characterization of the precursor and the LiNiPO4 compositions were carried out by powder XRD analysis, IR spectroscopy, and DSC analysis. Thermal treatment of LiNiPO4Hx(HCOO)x·yH2O precursors between 450 and 650 °C yields a mixture of the two structural modifications of LiNiPO4: the Na2CrO4 type and the olivine type. It was established that the obtained Na2CrO4 -type LiNiPO4 is a metastable phase, which completely transforms at 700 °C into the olivine-type phase. The enthalpy of the phase transition is ,H = ,43.40 kJ,mol,1. The mechanism of formation of the two forms of LiNiPO4 from the LiNi,phosphate,formate precursor is discussed. [source]

Insertion Reactions of an Aminogermylene and Formation of a Single-Source Precursor for GeTe Thin Films

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 14 2009
Tianniu Chen
Abstract Insertion reactions between a liquid germylene 1, and either a carbodiimide or dialkyl telluride lead to the formation of the group-14-metal(II) guanidinate complex 2 or the stable group-14-metal terminal alkyl tellurolate compound 3, respectively. The complexes 2 and 3 were structurally elucidated by multinuclear NMR and single-crystal X-ray crystallography. The use of 3 as a single-source precursor (SSP) for the MOCVD of GeTe films was demonstrated. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]

Microwave-Assisted Hydrothermal Synthesis of Structurally and Morphologically Controlled Sodium Niobates by Using Niobic Acid as a Precursor

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 8 2008
Amauri J. Paula
Abstract There are many advantages to using a microwave as a source of heat in hydrothermal reactions. Because it is a quick and homogeneous way to crystallize ceramic powders, it was used in this work for the production of antiferroelectric sodium niobate (NaNbO3) in a cubic-like form and its intermediary phase, disodium diniobate hydrate (Na2Nb2O6.H2O), with a fiber morphology. The syntheses were carried out by treating niobic acid (Nb2O5·nH2O) with NaOH. By changing the reaction time and the concentration of the reactants, particles with different structures and different morphologies could be obtained. The structural evolution of the products of this reaction was elucidated on the basis of the arrangement of the NbO6 octahedral units. Conclusive results were obtained with morphological and structural characterizations through XRD, TEM, MEV, and NMR and Raman spectroscopy. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

Aiding Factors in the Formation of Azaplatinacyclobutane Rings , X-ray and Crystal Structure of [Pt{CH(Ph)CH2NEt2 -,C,,N}(N,N,N,,N, -tetramethylethylenediamine)]+ and of Its Open-Chain Precursor

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 15 2007
Giuseppe Lorusso
Abstract The addition products 2 of a secondary amine to a coordinated olefin, in the cationic complexes [PtCl(,2 -CH2=CHR)(tmeda)]+ (tmeda = N,N,N,,N, -tetramethylethylenediamine; R = Me, 1a; Ph, 1b, H, 1c), undergo in basic medium an intramolecular nucleophilic substitution with elimination of the chlorido ligand and formation of an azaplatinacyclobutane ring 3. The ring-closing process occurs notwithstanding the absence of a labilizing ligand trans to the leaving chlorido ligand and of bulky substituents on the amino,ethanide chain. If the addition product 2 is a mixture of Markovnikov and anti-Markovnikov isomers, the ring-closing reaction is faster for the anti-Markovnikov form, and this leads to an increase of the relative amount of the anti-Markovnikov isomer in the cyclized species 3. The difference in the rate of formation of the azaplatinacyclobutane ring between the two isomers has been interpreted on the basis of a more favorable stereochemistry in the case of the anti-Markovnikov form. The X-ray crystal structures of [Pt{CH(Ph)CH2NEt2 -,C,,N}(tmeda)]+ (3bn) and of its open-chain precursor, [PtCl{CH(Ph)CH2NHEt2}(tmeda)]+ (2bn) fully support this hypothesis.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]

Niobium Oxide Mesophases Obtained by Self-Assembly of an Aqueous Soluble Niobium Complex Precursor and Organic Templates

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 4 2007
Marcos A. Bizeto
Abstract In this paper the use of triammonium trioxalato(oxido)niobate {(NH4)3[NbO(C2O4)3]} as an inorganic precursor to assemble organized hybrid niobium oxide mesophases using n -octylamine (OCT) and cetyltrimethylammonium (CTA) bromide as structure-directing agents is described for the first time. The niobium complex is water-soluble and its hydrolysis at controlled pH and in the presence of organic templates leads to the formation of hybrid mesophases. A lamellar mesophase is produced by a neutral route based on the interaction of hydrolyzed units with the octylamine micelles. On the other hand, a hexagonal (p6m) mesophase is obtained when hydrolyzed species interact with CTA micelles through a charge-matching route (ionic route). This is the first time that such an ionic route has been described for the production of organized niobium oxide hybrids.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]

Synthesis of (R)-(,)-2-Fluoronorapomorphine , A Precursor for the Synthesis of (R)-(,)-2-Fluoro- N -[11C]propylnorapomorphine for Evaluation as a Dopamine D2 Agonist Ligand for PET Investigations

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 20 2005
Kåre Søndergaard
Abstract 2-Fluoronorapomorphine, the PET labelling precursor to 2-fluoro- N -[11C]propylnorapomorphine, was prepared in 13 steps from codeine in a total yield of 10,%. Codeine was converted in four steps into N -benzylnorcodeine which was oxidised by using the Swern protocol. Subsequent acid-catalysed rearrangement afforded N -benzylnormorphothebaine which was selectively triflylated at the 2-position and pivaloylated at the 11-position. The triflate underwent palladium-catalysed amination with benzophenone imine. Amination conditions required sequential base addition to give substantial conversion of the triflate to the corresponding N -substituted benzophenone imine. After acidic hydrolysis the resulting aniline was transformed into the 2-fluoro compound via the Balz,Schiemann reaction. Hydrogenolysis of the N -benzyl group followed by deprotection of the catechol moiety using BBr3 provided 2-fluoronorapomorphine. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

Tuning and Transcription of the Supramolecular Organization of a Fluorescent Silsesquioxane Precursor into Silica-Based Materials through Direct Photochemical Hydrolysis,Polycondensation and Micropatterning

ADVANCED FUNCTIONAL MATERIALS, Issue 3 2009
Xavier Sallenave
Abstract A new fluorescent silsequioxane precursor with tuned optical properties and controlled aggregation properties is designed. The two cyclohexyl moieties introduced in the molecular structure allow the formation of very good quality films. The J-aggregated structure is transcribed into the solid by photoacid-catalyzed hydrolysis,polycondensation. Aggregation of the chromophores is reduced and highly fluorescent materials are obtained. The photoacid generator lies on the surface of the homogeneous layer of the sol,gel precursor. This phase separation presents several advantages, including UV protection of the chromophore and easy removal of the PAG. The first example of chemical amplification in the photolithography of the conjugated silsesquioxane precursor is demonstrated. As hydrolysis,polycondensation could be achieved in a controlled way by UV exposure, chemically amplified photolithography is achieved by irradiating a composite film (,110,nm thick) on silicon wafer by using a copper TEM grid as shadow mask. The pattern is produced uniformly on a miscroscopic scale of 3,mm, the photopatterned pixels remaining highly fluorescent. The sizes of the photolithographed pixels correspond to the sizes of the rectangular holes of the 300,×,75 mesh grid (hole: 63,<$>,<$>m,×,204,<$>,<$>m). [source]

Synthesis of Indium and Indium Oxide Nanoparticles from Indium Cyclopentadienyl Precursor and Their Application for Gas Sensing,

ADVANCED FUNCTIONAL MATERIALS, Issue 7 2003
K. Soulantica
Abstract Decomposition of the organometallic precursor [In(,5 -C5H5)] in toluene in the presence of methanol (8 vol.-%) at room temperature leads to the immediate formation of aggregates of indium nanoparticles of 15,±,2 nm mean diameter. The aggregates are roughly spherical with a mean size of 400,±,40 nm. The particles were characterized by means of transmission electron and high-resolution transmission electron microscopies (TEM and HRTEM), and X-ray diffraction (XRD) studies indicate that the powder consists of the tetragonal phase of indium. The thermal oxidation in air of these nanoparticles yields well-crystallized nanoparticles of In2O3 with unchanged morphology (aggregates of nanoparticles of 16.6,±,2 nm mean diameter with aggregate mean size of 400,±,40 nm) and without any sign of coalescence. XRD pattern shows that the powder consists of the cubic phase of In2O3. The electrical conductivity measurements demonstrate that this material is highly sensitive to an oxidizing gas such as nitrogen dioxide and barely sensitive to a reducing gas such as carbon monoxide. Its association with SnO2 -based sensors allows the selective detection of carbon monoxide (30 ppm) and sub-ppm amounts of nitrogen dioxide (400 ppb) in a mixture at 21,°C and at a relative humidity of 60,%. [source]

A Versatile "Click" Chemistry Precursor of Functional Polystyrene Nanoparticles

ADVANCED MATERIALS, Issue 28 2010
Lorea Oria
The synthesis of a versatile "click" chemistry precursor of functional polystyrene nanoparticles is reported. The resulting nanoparticles thereof offer inherent characteristics of ultrasmall polymeric nanoparticles (size ,4 nm) plus interesting functionalization possibilities, opening the door to new hybrid, soft nano-objects, bridging the gap between synthetic and natural polymers. [source]

Seed-Mediated Synthesis of Truncated Gold Decahedrons with a AuCl/Oleylamine Complex as Precursor

ADVANCED MATERIALS, Issue 17 2010
Yanyun Ma
A seed-mediated growth method is described for the synthesis of a novel type of Au nanoparticles,truncated decahedrons with a pentagonal, platelike structure (see figure). The precursor is based on the AuCl/oleylamine complex. TEM analyses reveal that the truncated Au nanoparticle has two types of truncation: one is parallel to the five-fold axis and the other is perpendicular to the five-fold axis. [source]

Facile Synthesis of Fe2O3 Nanocrystals without Fe(CO)5 Precursor and One-Pot Synthesis of Highly Fluorescent Fe2O3,CdSe Nanocomposites

ADVANCED MATERIALS, Issue 8 2009
Chung Yen Ang
,-Fe2O3 nanocrystals are synthesized in high yield (2,g) without a hazardous precursor and with a less-expensive oxidant in a one-pot synthesis (see figure). Bifunctional magnetic quantum-dot (, -Fe2O3,CdSe) nanocomposites are also synthesized in high yield, with a photoluminescence quantum yield of up to 42%. [source]

Preparation of Nano Carbonate-Substituted Hydroxyapatite from an Amorphous Precursor

INTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 5 2008
Yanbao Li
Carbonated amorphous calcium phosphate (CACP) precursors were precipitated by the wet chemical method at 5°C in the presence of poly(ethylene glycol) and carbonates. The nano carbonate-substituted hydroxyapatite (HAp) was obtained after heat treat CACP precursors at a low temperature (800°C) for 3 h. The calcium phosphates were investigated by X-ray diffraction, Fourier transform infrared spectroscopy, inductively coupled plasma, thermal gravimetric and differential thermal analysis, transmission electron microscopy, and scanning electron microscopy. The results show that calcium phosphate particles with a Ca/P molar ratio of 1.73 are AB-type carbonate-substituted HAp with about 50 nm in diameter. [source]

Hollow Zinc Oxide Mesocrystals from an Ionic Liquid Precursor (ILP),

ADVANCED MATERIALS, Issue 7 2008
Zhonghao Li
The highly hydrated ionic liquid tetrabutylammonium hydroxide (TBAH) is an efficient ionic liquid precursor (ILP) for the fabrication of zinc oxide mesocrystals. Upon reaction of TBAH with zinc acetate, individual nanometer-sized ZnO building blocks assemble into highly correlated ZnO mesocrystals. The mesocrystals are up to ca. 10 µm in length and the larger crystals have a channel running along the long crystal axis. [source]

Synthesis of Inorganic,Organic Diblock Copolymers as a Precursor of Ordered Mesoporous SiCN Ceramic,

ADVANCED MATERIALS, Issue 17 2007
D. Nghiem
A novel poly(vinyl)silazane- block -polystyrene diblock copolymer is successfully synthesized by living free-radical polymerization via a reversible addition fragmentation chain transfer (RAFT) route (see figure). The obtained diblock copolymer, having an inorganic volume fraction of 0.69, leads to phase-separation at the nanoscale to form an ordered nanostructure, which is converted to well-ordered mesoporous SiCN ceramic after heating at 800,°C and maintained up to 1400,°C. [source]

Preparation of Boron-Carbide/Carbon Nanofibers from a Poly(norbornenyldecaborane) Single-Source Precursor via Electrostatic Spinning,

ADVANCED MATERIALS, Issue 7 2005
T. Welna
Pyrolysis of poly(norbornenyldecaborane) that has been electrostatically spun provides a route to non-woven mats of boron-carbide/carbon ceramic nanofibers with narrow distributions and controllable dimensions (see Figure). This approach allows the fabrication of composite ceramic fibers with varying composition, which could be tailored to suit specific applications. [source]

A Lutidine-Bridged Bis-Perimidinium Salt: Synthesis and Application as a Precursor in Palladium-Catalyzed Cross-Coupling Reactions

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 7-8 2009
Tao Tu
Abstract A novel lutidine-bridged bis-perimidinium dibromide 3 was synthesized in quantitative yield from cheap commercial starting materials. The bisylidene prepared therefrom in situ upon deprotonation is a potent precatalyst in palladium-catalyzed Heck and Suzuki cross-coupling reactions under aerobic conditions, and is efficient even with a ppm scale catalyst loading. Its stronger ,-donor character is held to be responsible for its superior catalytic performance compared with imidazole- and benzimidazole-based analogues bearing the same skeleton precursors. [source]

[1.1]Ferrocenophane-1,12-dione as a Precursor of 1,12-Di(cyclopenta-2,4-dienylidene)-[1.1]ferrocenophane, a Doubly Bridged Difulvene

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 7-8 2009
José Ramon Garabatos-Perera
Abstract An improved synthesis of [1.1]ferrocenophane-1,12-dione (2) by oxidation of [1.1]ferrocenophane with 2,3-dichloro-5,6-dicyano- p -benzoquinone (DDQ) is presented. The syn conformer of dione 2 is structurally characterized. The compound undergoes various addition reactions at the bridging carbonyl groups. Attempts to add 1,1,-dilithioferrocene result, however, in the diadduct 9, not in the symmetric trinuclear diol 8. Reaction of 2 with sodium cyclopentadienide in the presence of aluminium trichloride (AlCl3) gives the respective difulvene 11 in excellent yield. The dynamic behavior of 11 is investigated by variable temperature 1H,NMR measurements (VT-NMR). The cyclovoltammogram of 11 indicates two reversible oxidation steps. Reduction of difulvene 11 with lithium aluminium hydride (LiAlH4) results in the formation of [1.1]ferrocenophane 12 with cyclopentadienyl anion substituents at either one of the two bridges. While attempts to generate a third ferrocene moiety by reaction with iron(II) choride (FeCl2) have failed so far, the formation of 12 is established by protonolysis and methylation reactions. [source]

A Bimetallic Ruthenium Complex as a Catalyst Precursor for the Atom Transfer Radical Polymerization of Methacrylates at Ambient Temperature

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 4-5 2006
Michel Haas
Abstract The bimetallic ruthenium complex [(1,3,5- i -Pr3C6H3)Ru(,-Cl)3RuCl(C2H4)(PCy3)] has been synthesized by reaction of [(1,3,5- i -Pr3C6H3)RuCl2)]2 with one equivalent of PCy3 in the presence of ethylene. It can be used as a catalyst precursor for the controlled atom transfer radical polymerization of methacrylates at 35,°C. The resulting polymers show low polydispersities. [source]

Myxofibrosarcoma Initially Presenting as a Pleomorphic Hyalinizing Angiectatic Tumor (PHAT): is PHAT a Precursor or Unique Type of Myxofibrosarcoma?

JOURNAL OF CUTANEOUS PATHOLOGY, Issue 1 2005
David S Cassarino
Myxofibrosarcoma (MFS) is a common soft tissue sarcoma of adults. We present an unusual case which initially showed features of a pleomorphic hyalinizing angiectatic tumor (PHAT). The lesion was characterized by abundant plump, eosinophilic cells exhibiting striking nuclear atypia, set in a dense, hyalinized stroma with a prominent, angiectatic vasculature. Rare mitotic figures were identified. These findings were felt to be most consistent with the diagnosis of PHAT. Four months after removal, local recurrence was noted, which demonstrated findings of a high grade MFS, including a cellular proliferation of pleomorphic spindle cells set in a prominent myxoid stroma. Multiple mitoses, including atypical ones, were present. In light of these findings, the original specimen was reexamined and the diagnosis was revised to high- grade MFS. MFS, especially low-grade lesions, may be confused with several benign lesions. Previous cases mimicking PHAT have not been reported. We describe a unique case of high-grade MFS which initially showed characteristic features of a PHAT, raising the possibility that MFS may occasionally arise in, or have areas that masquerade as, PHAT. It is possible that PHAT, currently considered a benign neoplasm, may actually represent a peculiar form of MFS of low malignant potential. [source]

Methyl 3-[3,,4,-(methylenedioxy)phenyl]-2-methyl glycidate: An Ecstasy Precursor Seized in Sydney, Australia

JOURNAL OF FORENSIC SCIENCES, Issue 4 2007
Michael Collins Ph.D.
Abstract:, Five 44 gallon drums labeled as glycidyl methacrylate were seized by the Australian Customs Service and the Australian Federal Police at Port Botany, Sydney, Australia, in December 2004. Each drum contained a white, semisolid substance that was initially suspected to be 3,4-methylenedioxymethylamphetamine (MDMA). Gas chromatography,mass spectroscopy (GC/MS) analysis demonstrated that the material was neither glycidyl methacrylate nor MDMA. Because intelligence sources employed by federal agents indicated that this material was in some way connected to MDMA production, suspicion fell on the various MDMA precursor chemicals. Using a number of techniques including proton nuclear magnetic resonance spectroscopy (1H NMR), carbon nuclear magnetic resonance spectroscopy (13C NMR), GC/MS, infrared spectroscopy, and total synthesis, the unknown substance was eventually identified as methyl 3-[3,,4,(methylenedioxy)phenyl]-2-methyl glycidate. The substance was also subjected to a published hydrolysis and decarboxylation procedure and gave a high yield of the MDMA precursor chemical, 3,4-methylenedioxyphenyl-2-propanone, thereby establishing this material as a "precursor to a precursor." [source]

Poly(vinyltriethoxysilane) modified MWCNT/polyimide nanocomposites,Preparation, morphological, mechanical, and electrical properties

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 3 2008
Siu-Ming Yuen
Abstract Multi-walled carbon nanotube (MWCNT) modified by vinyltriethoxysilane (VTES) via free radical reaction has been prepared (poly (vinyltriethoxysilane) modified MWCNTs, PVTES-MWCNT). Precursor of polyimide, polyamic acid has been synthesized by reacting 4,4,-oxydianiline with 3,3,,4,4,-benzophenone tetracarboxylic dianhydride. PVTES-MWCNT were then mixed with polyamic acid and heated to 300 °C to form CNT/polyimide composite. During the imidization processes, the silanes on CNT surface reacted with each other and may be connected together by covalent bond (SiOSi). The PVTES-MWCNT was analyzed by Fourier transform infrared and X-ray photoelectron spectroscopy. The PVTES-MWCNT/polyimide composites were analyzed by CP/MAS solid state 29Si nuclear magnetic resonance (NMR) spectroscopy. Morphological properties of the PVTES-MWCNT/polyimide composites were investigated by scanning electron microscope and transmission electron microscope. Electrical conductivity increased dramatically comparing to the unmodified MWCNT/polyimide composites. Mechanical properties of nanocomposite were enhanced significantly by PVTES-MWCNT. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 803,816, 2008 [source]

Nanosized PbZrO3 Powder from Oxalate Precursor: Microwave-Aided Synthesis and Thermal Characterization

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2009
Yuvraj S. Malghe
Nanosized lead zirconate (PbZrO3) powder was synthesized from its oxalate precursor, namely lead zirconyl oxalate (LZO). LZO heated in a microwave heating system for 1 h yielded the PbZrO3 at 600°C. The same precursor (LZO), when heated in a resistance-heated furnace at 850°C for 3 h, does not give a pure product. Thermogravimetry, differential thermal analysis, and X-ray diffraction techniques were used to characterize the precursor and optimize the conditions for microwave processing. The particle size of PbZrO3 powder prepared at 600°C using microwave heating was measured using transmission electron microscopy (TEM). The TEM images show that the particles of PbZrO3 are spherical in shape and that the particle size varies between 20 and 22 nm. [source]

From Chelating Precursor to Perovskite Oxides and Hollow Fiber Membranes

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2007
S. Liu
Perovskite Ba0.5Sr0.5Co0.8Fe0.2O3-, (BSCF) is a promising mixed-conducting ceramic membrane material in addition to being a good electrode catalyst for solid oxide fuel cells. In this study, BSCF powder was synthesized via a chelated water-soluble complex method at relatively low temperatures. The combined ethylenediaminetetraacetic acid and citric acid was used for the synthesis of a complex-based precursor, followed by thermal decomposition of the precursor at high temperatures. Thermal behavior, crystal phases, and structures of the prepared powders were characterized by thermogravimetric analysis/differential scanning calorimetry, XRD, and scanning electron microscopic (SEM) techniques, respectively. Pure and single-phase perovskite could be obtained after sintering at a temperature higher than 800°C for 5 h. The soft precursor powder synthesized at lower temperatures, i.e., 600°C, is water insoluble and more appropriate for use as a membrane material to prepare gas-tight tubular or hollow fiber ceramic membranes. By contrast, the hollow fibers prepared via the traditional techniques where the perovskite powder is used as the starting membrane materials display gas leakage. The fibers were characterized by SEM, XRD, and tested for air separation at ambient pressure and temperatures between 700° and 950°C. The oxygen flux measured in this work reached 3.90 mL·(min·cm2),1 and compares favorably with any experimental values reported in the open literature. [source]

Formation of Silicon-Doped Boron Nitride Bamboo Structures Via Pyrolysis of a Polymeric Precursor

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2006
Yi Fan
In this paper, we report the growth of bamboo-like silicon-doped boron nitride nanotubes via catalyst-assisted pyrolysis of a boron-containing polymeric precursor. The morphologies and structures of the nanotubes were characterized using electron microscopy and Raman spectroscopy. Two types of nanotubes are observed, one from a base-growth mode and the other from a tip-growth mode. The type II nanotubes contain encapsulated catalytic nanoparticles at the tip of every compartment. This unique structure is a promising candidate for applications in many nanodevices. [source]

Preparation of Ba6,3xNd8+2xTi18O54 via Ethylenediaminetetraacetic Acid Precursor

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2000
Yebin Xu
Ba6,3xNd8+2xTi18O54 ceramic powders were synthesized by the modified Pechini method using ethylenediaminetetraacetic acid (EDTA) as a chelating agent. A purplish red, molecular-level, homogeneously mixed gel was prepared, and transferred into a porous resin intermediate through charring. Single-phase and well-crystallized Ba6,3xNd8+2xTi18O54 powders were obtained from pulverized resin at a temperature of 900°C for 3 h, without formation of any intermediate phases. Meanwhile, the molar ratio of EDTA to total metal cation concentration had a significant influence on the crystallization behavior of Ba6,3xNd8+2xTi18O54. The Ba6,3xNd8+2xTi18O54 (x= 2/3) ceramics prepared via EDTA precursor have excellent microwave dielectric characteristics: ,= 87, Qf= 8710 GHz. [source]

Low-Temperature Synthesis of Bismuth Titanate Niobate (Bi7Ti4NbO21) Nanoparticles from a Metal-organic Polymeric Precursor

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2000
Pedro Durán
This paper describes the preparation of homogeneous Bi7Ti4NbO21 single-phase ceramic powders of ,55 nm crystallite size, at temperatures as low as 400°,500°C using a metal citrate complex method based on the Pechini-type reaction route. The thermal decomposition/oxidation of the polymerized resin, as investigated by TG/DTA, XRD, and SEM, led to the formation of a well-defined orthorhombic Bi7Ti4NbO21 compound with lattice parameters a= 0.544, b= 0.540, and c= 2.905 ± 0.0005 nm. Reaction takes place through an intermediate binary phase with a stoichiometry close to Bi20TiO32 which forms between 300° and 375°C. The metal-organic precursor synthesis method, where Bi, Ti, and Nb ions are first chelated to form metal complexes and then polymerized to give a gel, allows control of the Bi/Ti/Nb stoichiometric ratio leading to the rapid formation of nanosized bismuth titanate niobate (Bi7Ti4NbO21) ceramic powders, at temperatures much lower than usually needed by conventional processing of mixed-oxide powders. [source]