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Hydrothermal Process (hydrothermal + process)
Selected AbstractsMagnetic-Field-Induced Phase-Selective Synthesis of Ferrosulfide Microrods by a Hydrothermal Process: Microstructure Control and Magnetic Properties,ADVANCED FUNCTIONAL MATERIALS, Issue 8 2006Z. He Abstract Microrods of the ferrosulfide minerals greigite (Fe3S4) and marcasite (FeS2) are selectively synthesized by an in,situ magnetic-field-assisted hydrothermal route. Each complex microrod is composed of fine building blocks with different shapes. The unique magnetic properties of the microrods and electrical performance of a single microrod are studied. The results demonstrate that the magnetic properties of the ferrosulfide minerals are strongly related to their corresponding microstructures. The value of the low-temperature transition increases as the greigite component in the product decreases. The combination of small-molecule sulfur precursors and an applied magnetic field makes possible the selective synthesis of ferrosulfide minerals with different phases and distinct microstructures, underlining the fact that the magnetic field can be a useful tool as well as an independent parameter for the phase-selective synthesis and self-assembly of inorganic building blocks in solution chemistry. [source] ,-Fe2O3 Nanorings Prepared by a Microwave-Assisted Hydrothermal Process and Their Sensing Properties,ADVANCED MATERIALS, Issue 17 2007X. Hu Free-standing , -Fe2O3nanorings are synthesized in solution through a rapid microwave-assisted hydrothermal process. The ringlike structure is a new member in the family of iron oxide nanostructures. The sensors made of the ,-Fe2O3 nanorings exhibit high sensitivity not only for bio-sensing of hydrogen peroxide in a physiological solution but also for gas-sensing of alcohol vapor at room temperature. [source] Surfactant-Assisted Growth of Novel PbS Dendritic Nanostructures via Facile Hydrothermal Process,ADVANCED MATERIALS, Issue 20 2003D. Kuang 3D PbS dendritic nanostructures (see Figure) have been fabricated by a facile hydrothermal method in the presence of N -cetyl- N,N,N -trimethyl-ammonium bromide (CTAB). Both CTAB and thiourea play important roles in the formation of well-defined PbS dendrites. X-ray diffraction, electron diffraction, and high-resolution transmission electron microscopy results show that the PbS nanostructure is a 3D dendrite of a single crystal. [source] Synthesis and Mechanism of Ferroelectric Potassium Tantalate Niobate Nanoparticles by the Solvothermal and Hydrothermal ProcessesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2007Nian Wei High-purity KTa0.3Nb0.7O3 nanoparticles have been successfully synthesized by hydrothermal and solvothermal methods. The KOH concentration and the solvent composition have significant effects on the final products. The synthesis mechanism was discussed. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy investigations show that the typical samples solvothermally synthesized are nanosized, well crystallized, and single crystalline. The KTa0.3Nb0.7O3 shows a pseudo-cubic to tetragonal transition with increasing crystallite size. It is believed that supercritical isopropanol plays an important role in synthesizing KTa0.3Nb0.7O3 nanoparticles under milder conditions than the hydrothermal route. The present solvothermal method provides a new potential route for synthesizing ferroelectric potassium tantalate niobate material. [source] Design and Synthesis of Hierarchical Nanowire Composites for Electrochemical Energy StorageADVANCED FUNCTIONAL MATERIALS, Issue 21 2009Zheng Chen Abstract Nanocomposites of interpenetrating carbon nanotubes and vanadium pentoxide (V2O5) nanowires networks are synthesized via a simple in situ hydrothermal process. These fibrous nanocomposites are hierarchically porous with high surface area and good electric conductivity, which makes them excellent material candidates for supercapacitors with high energy density and power density. Nanocomposites with a capacitance up to 440 and 200,F g,1 are achieved at current densities of 0.25 and 10 A g,1, respectively. Asymmetric devices based on these nanocomposites and aqueous electrolyte exhibit an excellent charge/discharge capability, and high energy densities of 16,W h kg,1 at a power density of 75,W kg,1 and 5.5,W h kg,1 at a high power density of 3,750,W kg,1. This performance is a significant improvement over current electrochemical capacitors and is highly competetive with Ni,MH batteries. This work provides a new platform for high-density electrical-energy storage for electric vehicles and other applications. [source] Principal features of impact-generated hydrothermal circulation systems: mineralogical and geochemical evidenceGEOFLUIDS (ELECTRONIC), Issue 3 2005MIKHAIL V. NAUMOVArticle first published online: 14 JUL 200 Abstract Any hypervelocity impact generates a hydrothermal circulation system in resulting craters. Common characteristics of hydrothermal fluids mobilized within impact structures are considered, based on mineralogical and geochemical investigations, to date. There is similarity between the hydrothermal mineral associations in the majority of terrestrial craters; an assemblage of clay minerals,zeolites,calcite,pyrite is predominant. Combining mineralogical, geochemical, fluid inclusion, and stable isotope data, the distinctive characteristics of impact-generated hydrothermal fluids can be distinguished as follows: (i) superficial, meteoric and ground water and, possibly, products of dehydration and degassing of minerals under shock are the sources of hot water solutions; (ii) shocked target rocks are sources of the mineral components of the solutions; (iii) flow of fluids occurs mainly in the liquid state; (iv) high rates of flow are likely (10,4 to 10,3 m s,1); (v) fluids are predominantly aqueous and of low salinity; (vi) fluids are weakly alkaline to near-neutral (pH 6,8) and are supersaturated in silica during the entire hydrothermal process because of the strong predominance of shock-disordered aluminosilicates and fusion glasses in the host rocks; and (vii) variations in the properties of the circulating solutions, as well as the spatial distribution of secondary mineral assemblages are controlled by tempera ure gradients within the circulation cell and by a progressive cooling of the impact crater. Products of impact-generated hydrothermal processes are similar to the hydrothermal mineralization in volcanic areas, as well as in modern geothermal systems, but impacts are always characterized by a retrograde sequence of alteration minerals. [source] Effects of Structural Variation on the Photocatalytic Performance of Hydrothermally Synthesized BiVO4,ADVANCED FUNCTIONAL MATERIALS, Issue 16 2006J. Yu Abstract Highly crystalline monoclinic scheelite BiVO4 powders are synthesized from aqueous Bi(NO3)3 and NH4VO3 solutions over a wide range of pH by a hydrothermal process. BiVO4 powders with various morphologies, surface textures, and grain shapes are selectively synthesized by adjusting the pH. The dependence of the Raman peak position and intensity on the synthesis conditions indicates that the symmetry distortions in the local structure of the synthesized BiVO4 are affected by the preparation conditions. These variations in the local structure result in the modification of the electronic structure of BiVO4, which results in a blue-shift in the UV-vis absorption spectrum of hydrothermally synthesized BiVO4 in comparison with a well-crystallized sample prepared by homogeneous coprecipitation. The photocatalytic activities for O2 evolution from an aqueous AgNO3 solution under visible-light irradiation are strongly dependent on the pH used in the synthesis. The differences in the photocatalytic activities between BiVO4 samples prepared under various conditions is attributed to the degree of structural distortion, leading to differences in the mobility of photogenerated holes formed in the valence band, which consists of Bi,6s and O,2p orbitals. [source] ,-Fe2O3 Nanorings Prepared by a Microwave-Assisted Hydrothermal Process and Their Sensing Properties,ADVANCED MATERIALS, Issue 17 2007X. Hu Free-standing , -Fe2O3nanorings are synthesized in solution through a rapid microwave-assisted hydrothermal process. The ringlike structure is a new member in the family of iron oxide nanostructures. The sensors made of the ,-Fe2O3 nanorings exhibit high sensitivity not only for bio-sensing of hydrogen peroxide in a physiological solution but also for gas-sensing of alcohol vapor at room temperature. [source] Hydrothermal Synthesis YbMnO3 and LuMnO3 PlateletsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2008Gangqiang Zhu Single-crystalline YbMnO3 and LuMnO3 platelets have been successfully synthesized via a simple hydrothermal process at 250°C for 24 h. X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, and selected area electron diffraction patterns were used to characterize the as-synthesized samples. The result reveals that both of the as-synthesized YbMnO3 and LuMnO3 are of hexagonal phase. The effect of treatment time on the phase of the final products has been studied, and a possible formation mechanism of YbMnO3 and LuMnO3 is proposed. [source] Hydrothermal Synthesis of Ba-Hexaferrite NanoparticlesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2007Miha Drofenik Barium hexaferrite BaFe12O19 nanoparticles with a single-domain size were synthesized using a controlled hydrothermal process involving the LaMer,Dinger principle and the Ostwald ripening mechanism. Nanocrystalline particles of BaFe12O19 were obtained when the molar ratio of the precursor composition Ba(OH)2·8H2O/,-Fe2O3 was 0.3 and the concentration of the suspension was about 1 wt%. The as-synthesized crystalline BaFe12O19 platelets approximately 50 nm in length and 5 nm in thickness exhibited a saturation magnetization of 40 Am2/kg. [source] Hydrothermal Synthesis and Characterization of CdWO4 NanorodsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2006Yonggang Wang Cadmium tungstate (CdWO4) nanorods were successfully synthesized by a hydrothermal process at as low a temperature as 70°C. The products were characterized by X-ray powder diffraction, transmission electron microscopy, and photoluminescent spectra techniques. The results showed that the morphology of nanocrystallites significantly varied with the reaction temperature, and CdWO4 nanorods exhibited a better luminescent property than nanofibers. [source] Effect of synthesis process on the Young's modulus of titanate nanowirePHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 2 2010Ming Chang Abstract Nanocrystalline materials have attracted a great deal of attention because of their intriguing size-/shape-dependent properties. Titanate nanowires have been synthesized from titania (TiO2) nanoparticles using conventional hydrothermal process. Young's moduli of as-prepared titanate nanowires have been determined in situ from the buckling instability of the nanowires due to application of axial compressive load using a nanomanipulator inside a scanning electron microscope. Based on Euler's buckling model, the Young's moduli of the nanowires are determined to be 32,±,11,GPa. The obtained Young's moduli have been compared to that of the titanate nanowires prepared with microwave hydrothermal process to study the effect of synthesis process on the mechanical behavior of nanomaterials. The prolonged holding time of a conventional hydrothermal process helps in the significant enhancement of the Young's modulus of nanowire in comparison to that prepared with microwave hydrothermal process. [source] Geochemistry of Platinum Group and Rare Earth Elements of the Polymetallic Layer in the Lower Cambrian, Weng'an, Guizhou ProvinceACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 3 2009Yong FU Abstract: The black shales of the Lower Cambrian Niutitang Formation in Weng'an, on the Yangtze platform of south China, contain voluminous polymetallic sulfide deposits. A comprehensive geochemical investigation of trace, rare earth, and platinum group elements (PGE) has been undertaken in order to discuss its ore genesis and correlation with the tectono-depositional setting. The ore-bearing layers enrich molybdenum (Mo), nickel (Ni), vanadium (V), lead (Pb), strontium (Sr), barium (Ba), uranium (U), arsenic (As), and rare earth elements (REE) in abundance. High uranium/thorium (U/Th) ratios (U/Th>1) indicated that mineralization was mainly influenced by the hydrothermal process. The ,U value was above 1.9, showing a reducing sedimentary condition. The REE patterns showed high enrichment in light rare earth elements (LREE) (heavy rare earth elements (HREE) (LREE/HREE=5,17), slightly negative europium (Eu) and cerium (Ce) anomalies (,Eu=0.81,0.93), and positive Ce anomalies (,Ce=0.76,1.12). PGE abundance was characterized by the PGE-type distribution patterns, enriching platinum (Pt), palladium (Pd), ruthenium (Ru) and osmium (Os). The Pt/Pd ratio was 0.8, which is close to the ratios of seawater and ultramafic rocks. All of these geochemical features suggest that the mineralization was triggered by hydrothermal activity in an extensional setting in the context of break-up of the Rodinian supercontinent. [source] 3D Architectures of Iron Molybdate: Phase Selective Synthesis, Growth Mechanism, and Magnetic PropertiesCHEMISTRY - A EUROPEAN JOURNAL, Issue 3 2007Yi Ding Abstract Monoclinic and orthorhombic Fe2(MoO4)3 microsized particles with complex 3D architectures have been selectively prepared by a template-free hydrothermal process. The pH value, reaction time, temperature, and molybdenian source have crucial influence on the phase formation, shape evolution, and microstructures. Monoclinic Fe2(MoO4)3 particles obtained at pH,1 and pH,1.65 display ferromagnetic ordering at 10.4,K and 10.5,K, respectively, and the ferromagnetic component is determined to be 0.0458,,B and 0.0349,,B per Fe-ion at 10,K, respectively. For orthorhombic ,-Fe2(MoO4)3, antiferromagnetic ordering was observed about 12,K. At higher temperatures, ,-Fe2(MoO4)3 began to follow the Curie,Weiss law with ,=,70,K. Such 3D architectures of monoclinic and orthorhombic ,-Fe2(MoO4)3 microparticles with unique shapes and structural characteristics may find applications as catalysts and as well as in other fields. [source] Principal features of impact-generated hydrothermal circulation systems: mineralogical and geochemical evidenceGEOFLUIDS (ELECTRONIC), Issue 3 2005MIKHAIL V. NAUMOVArticle first published online: 14 JUL 200 Abstract Any hypervelocity impact generates a hydrothermal circulation system in resulting craters. Common characteristics of hydrothermal fluids mobilized within impact structures are considered, based on mineralogical and geochemical investigations, to date. There is similarity between the hydrothermal mineral associations in the majority of terrestrial craters; an assemblage of clay minerals,zeolites,calcite,pyrite is predominant. Combining mineralogical, geochemical, fluid inclusion, and stable isotope data, the distinctive characteristics of impact-generated hydrothermal fluids can be distinguished as follows: (i) superficial, meteoric and ground water and, possibly, products of dehydration and degassing of minerals under shock are the sources of hot water solutions; (ii) shocked target rocks are sources of the mineral components of the solutions; (iii) flow of fluids occurs mainly in the liquid state; (iv) high rates of flow are likely (10,4 to 10,3 m s,1); (v) fluids are predominantly aqueous and of low salinity; (vi) fluids are weakly alkaline to near-neutral (pH 6,8) and are supersaturated in silica during the entire hydrothermal process because of the strong predominance of shock-disordered aluminosilicates and fusion glasses in the host rocks; and (vii) variations in the properties of the circulating solutions, as well as the spatial distribution of secondary mineral assemblages are controlled by tempera ure gradients within the circulation cell and by a progressive cooling of the impact crater. Products of impact-generated hydrothermal processes are similar to the hydrothermal mineralization in volcanic areas, as well as in modern geothermal systems, but impacts are always characterized by a retrograde sequence of alteration minerals. [source] Oscillatory zoning in garnet from the Willsboro Wollastonite Skarn, Adirondack Mts, New York: a record of shallow hydrothermal processes preserved in a granulite facies terraneJOURNAL OF METAMORPHIC GEOLOGY, Issue 8 2003C. C. Clechenko Abstract Oscillatory zoning in low ,18O skarn garnet from the Willsboro wollastonite deposit, NE Adirondack Mts, NY, USA, preserves a record of the temporal evolution of mixing hydrothermal fluids from different sources. Garnet with oscillatory zoning are large (1,3 cm diameter) euhedral crystals that grew in formerly fluid filled cavities. They contain millimetre-scale oscillatory zoning of varying grossular,andradite composition (XAdr = 0.13,0.36). The ,18O values of the garnet zones vary from 0.80 to 6.26, VSMOW and correlate with XAdr. The shape, pattern and number of garnet zones varies from crystal to crystal, as does the magnitude of the correlated chemistry changes, suggesting fluid system variability, temporal and/or spatial, over the time of garnet growth. The zones of correlated Fe content and ,18O indicate that a high Fe3+/Al, high ,18O fluid mixed with a lower Fe3+/Al and ,18O fluid. The high ,18O, Fe enriched fluids were likely magmatic fluids expelled from crystallizing anorthosite. The low ,18O fluids were meteoric in origin. These are the first skarn garnet with oscillatory zoning reported from granulite facies rocks. Geochronologic, stable isotope, petrologic and field evidence indicates that the Adirondacks are a polymetamorphic terrane, where localized contact metamorphism around shallowly intruded anorthosite was followed by a regional granulite facies overprint. The growth of these garnet in equilibrium with meteoric and magmatic fluids indicates an origin in the shallow contact aureole of the anorthosite prior to regional metamorphism. The zoning was preserved due to the slow diffusion of oxygen and cations in the large garnet and protection from deformation and recrystallization in zones of low strain in thick, rigid, garnetite layers. The garnet provide new information about the hydrothermal system adjacent to the shallowly intruded massif anorthosite that predates regional metamorphism in this geologically complex, polymetamorphic terrane. [source] | |||||||||||||