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Nanocrystalline Materials (nanocrystalline + material)
Selected AbstractsEffect 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] Mechanical activation of precursors for nanocrystalline materialsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 1 2003H. Heegn Abstract Nanostructured materials win big scientific interest and increasingly economic meaning through their specific exceptional properties. Precursors that were compacted by pressing and sintering are normally used preparation of materials. In present work, the influence of mechanical activation by grinding on the structure as well as on compacting and sintering behavior of oxides from magnesium, aluminium and silicon has been investigated. Starting materials for each metal oxide differ in microstructure, dispersity, and porosity. The influence of mechanical activation on the destruction of crystalline structure to nanocrystalline, as well as to the amorphous stage and the compaction of powders with nano-particles, as well as structures with nanoscale pores have been compared. The possibilities of the consolidation of nanostructured materials were investigated. The mechanical activation took place in a disc vibration mill. The mechanical activated materials as well as their pressing and their sintering products were characterized by density, particle-sizedistribution, specific surface, pore-structure, microstructure, and crystallite size by X-ray powder diffraction (XRD). The mechanical activation of the model-substances led, in most cases, to an improvement of the compaction properties; thus, this improvement can be achieved with subsequent sintering densities up to 98% of the theoretical density. From these experiments, generalizations transferable to other materials can be made. [source] Frameworks by Solvent-Free Synthesis of Rare Earth Chlorides with Molten 1,3-Benzodinitrile and Tailoring of the Particle Size: ,3[LnCl3{1,3-C6H4(CN)2}], Ln = Y, Dy, Ho, Er, YbEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 3 2010Christoph J. Höller Abstract The solvent-free melt reactions of anhydrous rare earth trichlorides with molten 1,3-benzodinitrile [1,3-C6H4(CN)2, C8H4N2] result in isophthalonitrile frameworks of the rare earth elements. The particle size of the products can bevaried from the millimeter to the nanometer scale (down to 50,400 nm) depending on the synthesis conditions. Thus, these network structures are among the very few coordination polymers that can be synthesized as nanoparticles. A constitution of 1:1 concerning LnCl3/1,3-C6H4(CN)2 is found for Y (1), Dy (2), Ho (3), Er (4), and Yb (5) in isotypic,3[LnCl3{1,3-C6H4(CN)2}]. The ligand 1,3-C6H4(CN)2 functions both as chemical scissors and replaces chloride linkages by degrading the rare earth chloride structures, and subsequently forms new 3D-framework structures. They consist of strands of chlorido-coordinated lanthanide atoms, which are linked in two dimensions by 1,3-C6H4(CN)2 molecules. Compounds 1,5 were obtained as single crystals from the melt reaction, and their crystal structures were determined by single-crystal X-ray analysis. They can also be obtained as nanocrystalline materials from a ball mill treatment, identified by electron microscopy (REM) and EDX analysis. [source] Bulk Nanostructured Materials: Non-Mechanical Synthesis,ADVANCED ENGINEERING MATERIALS, Issue 8 2010Yulia Ivanisenko An overview of the synthesis and processing techniques for bulk nanostructured materials that are based on "bottom-up" approaches is presented. Typically, these processes use nanoparticles, which can be produced by a variety of methods in the gas, liquid or solid state, as the basic building blocks. Their assembly into bulk nanostructured materials requires at least one more processing step, such as compaction or the formation of thick films. For certain nanostructures, film deposition techniques can also be employed. A wide range of nanostructures , from thick films with theoretical density to bulk nanocrystalline materials with nanoporosity , exhibiting novel structural and functional properties useful in many fields of applications are presented. Additionally, the properties of these bulk nanostructured materials can be categorized as either tailored, i.e., microstructure-dependent and inherently irreversible, or tunable, i.e., reversible by the application of an external field. Examples of both categories of properties are presented and the special role of the synthesis and processing routes to achieve the necessary nanostructures is emphasized. [source] Diffusion in Nanocrystalline Metals and Alloys,A Status Report,ADVANCED ENGINEERING MATERIALS, Issue 5 2003R. Würschum Abstract Diffusion is a key property determining the suitability of nanocrystalline materials for use in numerous applications, and it is crucial to the assessment of the extent to which the interfaces in nanocrystalline samples differ from conventional grain boundaries. The present article offers an overview of diffusion in nanocrystalline metals and alloys. Emphasis is placed on the interfacial characteristics that affect diffusion in nanocrystalline materials, such as structural relaxation, grain growth, porosity, and the specific type of interface. In addition, the influence of intergranular amorphous phases and intergranular melting on diffusion is addressed, and the atomistic simulation of GB structures and diffusion is briefly summarized. On the basis of the available diffusion data, the diffusion-mediated processes of deformation and induced magnetic anisotropy are discussed. [source] Microstrain and grain-size analysis from diffraction peak width and graphical derivation of high-pressure thermomechanicsJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 6 2008Yusheng Zhao An analytical method is presented for deriving the thermomechanical properties of polycrystalline materials under high-pressure (P) and high-temperature (T) conditions. This method deals with non-uniform stress among heterogeneous crystal grains and surface strain in nanocrystalline materials by examining peak-width variation under different P,T conditions. Because the method deals directly with lattice d spacing and local deformation caused by stress, it can be applied to process any diffraction profile, independent of detection mode. In addition, a correction routine is developed using diffraction elastic ratios to deal with severe surface strain and/or strain anisotropy effects related to nano-scale grain sizes, so that significant data scatter can be reduced in a physically meaningful way. Graphical illustration of the resultant microstrain analysis can identify micro/local yields at the grain-to-grain interactions resulting from high stress concentration, and macro/bulk yield of the plastic deformation over the entire sample. This simple and straightforward approach is capable of revealing the corresponding micro and/or macro yield stresses, grain crushing or growth, work hardening or softening, and thermal relaxation under high- P,T conditions, as well as the intrinsic residual strain and/or surface strain in the polycrystalline bulk. In addition, this approach allows the instrumental contribution to be illustrated and subtracted in a straightforward manner, thus avoiding the potential complexities and errors resulting from instrument correction. Applications of the method are demonstrated by studies of ,-SiC (6H, moissanite) and of micro- and nanocrystalline nickel by synchrotron X-ray and time-of-flight neutron diffraction. [source] Mechanical Properties of Monoclinic ZirconiaJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2004Jens Eichler Fracture toughness and fracture strength data are presented for the first time for monoclinic zirconia. An undoped nanocrystalline zirconia powder was sintered at 1100°C and yielded a theoretical density of more than 90% with a grain size of about 150 nm. The surface crack in flexure (SCF) technique was deemed most suitable for nanocrystalline materials. Measurements of Young's modulus and the determination of the fracture origin are also provided. [source] Electrical Conductivity and Lattice Defects in Nanocrystalline Cerium Oxide Thin FilmsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2001Toshio Suzuki The results of the electrical conductivity and Raman scattering measurements of CeO2 thin films obtained by a polymeric precursor spin-coating technique are presented. The electrical conductivity has been studied as a function of temperature and oxygen activity and correlated with the grain size. When compared with microcrystalline samples, nanocrystalline materials show enhanced electronic conductivity. The transition from extrinsic to intrinsic type of conductivity has been observed as the grain size decreases to <100 nm, which appears to be related to a decrease in the enthalpy of oxygen vacancy formation in CeO2. Raman spectroscopy has been used to analyze the crystalline quality as a function of grain size. A direct comparison has been made between the defect concentration calculated from coherence length and nonstoichiometry determined from electrical measurements. [source] Structure of nanocrystalline anatase solved and refined from electron powder dataACTA CRYSTALLOGRAPHICA SECTION A, Issue 4 2002T. E. Weirich Energy-filtered Debye,Scherrer electron powder data have been successfully employed to determine the structure of nanocrystalline anatase (TiO2). The performed structure analysis includes determining the unit cell, space group, solving the structure via direct methods from extracted intensities and refining the structure using the Rietveld technique. The refined structural parameters for space group I41amd are a = 3.872,(2), c = 9.616,(5),Å with titanium at 0.5,0.75,0.375 and oxygen at 0.5,0.75,0.1618,(6). The obtained structure indicates low internal stress as judged from the almost regular geometry of the TiO6 building blocks. Striking resemblance with the anatase structure determined previously by Burdett, Hughbanks, Miller, Richardson & Smith [J. Am. Chem. Soc. (1987). 109, 3639,3646] from neutron diffraction on coarse-grained material gives strong support for the correctness of the structure determined here. The result of the present study shows that the methods originally developed for determining structures from X-ray powder data work equally well with data from electron powder diffraction. This may open the window for structural investigations on the vast number of nanocrystalline materials and thin films whose structures are difficult to determine by X-ray diffraction since they are frequently only available in small quantities. [source] | ||||||||||||||||