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Nanocrystalline
Terms modified by Nanocrystalline Selected AbstractsNanocrystalline transparent SnO2 -ZnO films fabricated at lower substrate temperature using a low-cost and simplified spray techniqueCRYSTAL RESEARCH AND TECHNOLOGY, Issue 3 2010K. Ravichandran Abstract Nanocrystalline and transparent conducting SnO2 - ZnO films were fabricated by employing an inexpensive, simplified spray technique using a perfume atomizer at relatively low substrate temperature (360±5 °C) compared with conventional spray method. The structural studies reveal that the SnO2 -ZnO films are polycrystalline in nature with preferential orientation along the (101) plane. The dislocation density is very low (1.48×1015lines/m2), indicating the good crystallinity of the films. The crystallite size of the films was found to be in the range of 26,34 nm. The optical transmittance in the visible range and the optical band gap are 85% and 3.6 eV respectively. The sheet resistance increases from 8.74 k,/, to 32.4 k,/, as the zinc concentration increases from 0 to 40 at.%. The films were found to have desirable figure of merit (1.63×10,2 (,/,),1), low temperature coefficient of resistance (,1.191/K) and good thermal stability. This simplified spray technique may be considered as a promising alternative to conventional spray for the massive production of economic SnO2 - ZnO films for solar cells, sensors and opto-electronic applications. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Continuum Mechanical Approach to Sintering of Nanocrystalline Zirconia,ADVANCED ENGINEERING MATERIALS, Issue 10 2005R. Zuo Nanocrystalline 3,mol,% yttria-stabilized zirconia was sinter-forged isothermally under varying external uniaxial stresses. The applied uniaxial stresses were relatively low, compared to the intrinsic sintering stress of the material studied. Uniaxial sintering stresses and uniaxial viscosities were experimentally determined as function of density by means of a continuum mechanical approach which involves measuring the sintering rate of a free-sintered specimen, and a specimen sintered under the application of an external uniaxial stress. The uniaxial viscosity increased strongly with density only in the final stage sintering regime. The magnitude of the uniaxial sintering stress exhibited a decrease with density. [source] Nanocrystalline Electroplated Cu,Ni: Metallic Thin Films with Enhanced Mechanical Properties and Tunable Magnetic BehaviorADVANCED FUNCTIONAL MATERIALS, Issue 6 2010Eva Pellicer Abstract Nanocrystalline 3,µm thick Cu1,xNix (0.45,,,x,,,0.87) films are electrodeposited galvanostatically onto Cu/Ti/Si (100) substrates, from a citrate- and sulphate-based bath containing sodium lauryl sulphate and saccharine as additives. The films exhibit large values of reduced Young's modulus (173,<,Er,<,192,GPa) and hardness (6.4,<,H,<,8.2,GPa), both of which can be tailored by varying the alloy composition. The outstanding mechanical properties of these metallic films can be ascribed to their nanocrystalline nature,as evidenced by X-ray diffraction, transmission electron microscopy, and atomic force microscopy,along with the occurrence of stacking faults and the concomitant formation of intragranular nanotwins during film growth. Due to their nanocrystalline character, these films also show very low surface roughness (root mean square deviation of around 2,nm). Furthermore, tunable magnetic properties, including a transition from paramagnetic to ferromagnetic behavior, are observed when the Ni percentage is increased. This combination of properties, together with the simplicity of the fabrication method, makes this system attractive for widespread technological applications, including hard metallic coatings or magnetic micro/nano-electromechanical devices. [source] Influence of Wet Mechanical Mixing on Microstructure and Vickers Hardness of Nanocrystalline Ceramic,Metal CompositesINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 5 2008Tatsuo Kumagai Nanocrystalline (nc) ceramic,metal composite bulk samples have been fabricated by consolidation of mixture of attrition-milled (AM) amorphous base ceramic ((ZrO2,3 mol% Y2O3),20 mol% Al2O3) and AM amorphous base metallic (Ti,48 mol% Al) powders using a pulse-current pressure sintering system. Microstructural observations revealed that the ceramic and metallic colonies appear blocky in morphology in the composite bulk samples, and both the ceramic and the metallic colonies consist of a large number of equiaxed fine grains with the sizes of 78,82 and 81,86 nm, respectively. Mechanical mixing treatments by wet ball milling in ethanol before consolidation process are effective for refinement of the ceramic and metallic colonies. In all the obtained composite bulk samples, the ceramic colonies consist of the dominant phase of tetragonal (t) ZrO2 solid solution (ss) together with the minor phases of monoclinic (m) ZrO2ss and ,-Al2O3. On the other hand, the dominant phase in the metallic colonies changes from Ti3Al (,2) to Tiss (,) with an increase in the t -ZrO2ss volume fraction by abrasion of 3 mol% yttria-stabilized tetragonal polycrystalline zirconia balls during wet mechanical mixing treatments. Such a phase transformation from ,2 to , is considered to be due to the decrease in the aluminum content in the metallic colonies by combination of aluminum with oxygen (i.e., the formation of ,-Al2O3), which is probably taken from ethanol (C2H5OH) into the powders during wet mechanical mixing treatments. The obtained nc composite bulk samples show good Vickers hardness values, which are considerably higher than those estimated from the rule of mixture. [source] Optical and Electrical Properties of Amorphous and Nanocrystalline (La0.8Sr0.2)0.9MnO3 Thin Films Prepared from Low-Temperature Processing TechniqueJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2006Toshio Suzuki The results of a study on the optical and electrical properties of (La0.8Sr0.2)0.9MnO3 (LSM) thin films obtained by a polymeric precursor spin coating technique were presented. This method allowed preparation of optical quality thin films at annealing temperatures around 800°C. Amorphous and crystalline LSM thin films were studied by optical and electrical conductivity measurements. The energy-dependent absorption coefficients for the crystalline specimen were calculated from optical spectra and extra absorption was observed in the range of 1.8,2.5 eV with the exchange-gap excitation behavior in the 3,5 eV range. In comparison to the amorphous specimens, the electrical conductivity of the nanocrystalline specimen increased two to three orders of magnitude with decreasing activation energy. The charge carrier absorption model suggested an increase of the carrier concentration in the nanocrystalline specimen which may be a reason for the change in the electrical conductivity. [source] Structural and Dielectric Characterization of Nanocrystalline (Ba, Pb)ZrO3 Developed by Reverse Micellar SynthesisJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2006Tokeer Ahmad Nanocrystalline zirconates of barium and lead have been synthesized using a modified reverse micellar route (avoiding alkoxides). The entire solid solution of Ba1,xPbxZrO3 (0,x,1) has been synthesized for the first time. Powder X-ray diffraction studies show the monophasic nature of the powders after heating at 800°C except minor impurities of ZrO2 (2%,3%) at a higher lead content (x=0.50 and 0.75). The oxides crystallize in the cubic structure till x=0.25; for higher values, they crystallize in the orthorhombic structure. The particle size obtained from X-ray line-broadening studies and transmission electron microscopic studies is found to be in the range of 20,60 nm for all the oxides obtained after heating at 800oC. The grain size of the solid solution of Ba1,xPbxZrO3 (0,x,1) was found to increase with the lead content. The dielectric constant of the solids corresponding to Ba1,xPbxZrO3 (0,x,1) was found to be a maximum at x=0.50. Note that the cubic to orthorhombic transition is also observed between x=0.25 and 0.5. Dielectric properties with respect to variation in frequency and temperature are reported for these nanocrystalline oxides for the first time. [source] Analysis of Nanocrystalline and Microcrystalline ZnO Sintering Using Master Sintering CurvesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2006Kevin G. Ewsuk Master sintering curves were constructed for dry-pressed compacts composed of either a nanocrystalline or a microcrystalline ZnO powder using constant heating rate dilatometry data and an experimentally determined apparent activation energy for densification of 268±25 and 296±21 kJ/mol, respectively. The calculated activation energies for densification are consistent with one another, and with values reported in the literature for ZnO densification by grain boundary diffusion. Grain boundary diffusion appears to be the single dominant mechanism controlling intermediate-stage densification in both the nanocrystalline and the microcrystalline ZnO during sintering from 65% to 90% of the theoretical density (TD). Based on both the consistency of the calculated activation energy as a function of density and the narrow dispersion of the sintering data about the master sintering curve (MSC) for the nanocrystalline ZnO, there is no evidence of either significantly enhanced surface diffusion or grain growth during sintering relative to the microcrystalline ZnO. The MSC constructed for the nanocrystalline ZnO was used to design time,temperature profiles to successfully achieve four different target sintered densities on the MSC, demonstrating the applicability of the MSC theory to nanocrystalline ceramic sintering. The most significant difference in sintering behavior between the two ZnO powders is the enhanced densification in the nanocrystalline ZnO powder at shorter times and lower temperatures. This difference is attributed to a scaling (i.e., particle size) effect. [source] Synthesis of Nanocrystalline ,-Alumina Powder Using TriethanolamineJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2001Ranjan 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] Nanocrystalline boron-doped diamond films, a mixture of BCS-like and non-BCS-like superconducting grainsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 9 2010F. Dahlem Abstract Scanning tunneling topography and spectroscopy are performed below 100,mK on granular nanocrystalline boron-doped diamond (BDD) films. We found the superconductivity behavior to follow mainly the granular features of the BDD films. The temperature dependence of the local differential conductance spectra shows our nanocrystalline BDD films as made of grains with a supercondutivity either BCS-like or non-BCS-like. Such a distribution is not discernible in transport measurements, which present a sharp macroscopic superconducting transition at a temperature of a few Kelvins. Our local scanning tunneling microscopies also confirm the good coupling between these grains: only a few opaque interfaces are detected. Such a transparency of intergrain interfaces is responsible for a proximity effect in weakly superconductive grains and an inverse proximity effect in strongly superconducting grains. [source] Growth and properties of nanocrystalline diamond filmsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 13 2006Oliver A. Williams Abstract The aim of this paper is to summarise recent progress in the growth of small grain-sized Chemical Vapor Deposition (CVD) diamond often called nanocrystalline diamond, i.e., diamond with grains typically smaller than 500 nm. Nanocrystalline (NCD) and Ultrananocrystalline diamond (UNCD) films are new materials offering interesting applications to nanobioelectronics and electrochemistry. However NCD and UNCD thin films comprise of entirely different structures which is highlighted here in this paper. We discuss in detail the main differences in Raman spectra, optical properties and electrical transport properties. Finally we present a simple model of the conductivity mechanism in nitrogenated UNCD (N-UNCD) and boron doped NCD (B-NCD) films, and show the possibility of achieving the superconductive transition in B-NCD films. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] ChemInform Abstract: Li+ Diffusion and Its Structural Basis in the Nanocrystalline and Amorphous Forms of Two-Dimensionally Ion-Conducting LixTiS2.CHEMINFORM, Issue 40 2001Rudolf Winter Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Sol,Gel Fabrication and Electrical Property of Nanocrystalline (Ln2O3)0.08(ZrO2)0.92 (Ln: Sc, Y) Thin Films.CHEMINFORM, Issue 24 2001Y. W. Zhang Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Thermochemical Study on the Chiral Sodium Zincophosphate NanocrystallineCHINESE JOURNAL OF CHEMISTRY, Issue 4 2006Jian Wu Abstract Chiral sodium zincophosphate nanocrystalline has been prepared and characterized. The standard molar enthalpy of the following reaction 12Na3PO4·12H2O(s)+12ZnSO4·7H2O(s)=Na12(Zn12P12O48)·12H2O(s)+12Na2SO4(s)+216H2O(l) was determined by solution reaction calorimetric at 298.15 K, and calculated to be 33.666±0.195 kJ/mol. From the results and other auxiliary quantities, the standard enthalpy of formation for sodium zincophosphate nanocrystalline was derived to be , fH,m [Na12(Zn12P12O48)·12H2O(s), 298.15 K]=,24268.494±0.815 kJ/mol. [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] Immobilization and Electrochemistry of Negatively Charged Proteins on Modified Nanocrystalline Metal Oxide ElectrodesELECTROANALYSIS, Issue 12 2005Emmanuel Topoglidis Abstract The immobilization of two acidic, low isoelectric point proteins, green fluorescence protein and ferredoxin (FRD) is investigated on nanocrystalline, mesoporous TiO2 and SnO2 electrodes. Modification of these electrodes with a cationic polypeptide (poly- L -lysine) or an aminosilane prior to protein immobilization is found to enhance protein binding at least ten fold, attributed to more favorable protein/electrode electrostatic interactions. Cyclic voltammetry studies of FRD-modified SnO2 electrodes indicate reversible protein electrochemistry with a midpoint potential of ,0.59,V (vs. Ag/AgCl) and an interfacial electron transfer rate constant of 0.45,s,1. [source] Suppression of Ni4Ti3 Precipitation by Grain Size Refinement in Ni-Rich NiTi Shape Memory Alloys,ADVANCED ENGINEERING MATERIALS, Issue 8 2010Egor A. Prokofiev Severe plastic deformation (SPD) processes, such as equal channel angular pressing (ECAP) and high pressure torsion (HPT), are successfully employed to produce ultra fine grain (UFG) and nanocrystalline (NC) microstructures in a Ti,50.7,at% Ni shape memory alloy. The effect of grain size on subsequent Ni-rich particle precipitation during annealing is investigated by transmission electron microscopy (TEM), selected area electron diffraction (SAD, SAED), and X-ray diffraction (XRD). It is observed that Ni4Ti3 precipitation is suppressed in grains of cross-sectional equivalent diameter below approximately 150,nm, and that particle coarsening is inhibited by very fine grain sizes. The results suggest that fine grain sizes impede precipitation processes by disrupting the formation of self-accommodating particle arrays and that the arrays locally compensate for coherency strains during nucleation and growth. [source] Effect of Decrease of Hydride-Induced Embrittlement in Nanocrystalline Titanium,ADVANCED ENGINEERING MATERIALS, Issue 8 2010M.A. Murzinova Abstract The room-temperature impact toughness, strength and ductility of nanocrystalline (NC) and microcrystalline (MC) titanium with hydrogen content ranging from 0.1 to 16,at.-% (0.002 to 0.450,wt.-%) are studied. NC titanium has higher strength and lower sensitivity to hydride-induced brittle fracture than the MC material. In contrast to MC titanium, the elongation and impact toughness in the NC material does not decrease dramatically with increasing hydrogen content. Moreover, the fracture toughness in hydrogenated NC condition is found to be higher than that in MC titanium. This unusual result may be associated with the precipitation of equiaxial nanoscale hydrides in the interior of ,-grains in the NC material, while platelet hydrides are formed in MC titanium. One can expect that the risk of hydride-induced embrittlement is lower in NC than in MC titanium, making the NC material attractive for potential application under conditions that may cause hydrogen saturation above the permissible level for MC titanium. [source] Layer-By-Layer Dendritic Growth of Hyperbranched Thin Films for Surface Sol,Gel Syntheses of Conformal, Functional, Nanocrystalline Oxide Coatings on Complex 3D (Bio)silica TemplatesADVANCED FUNCTIONAL MATERIALS, Issue 17 2009Guojie Wang Abstract Here, a straightforward and general method for the rapid dendritic amplification of accessible surface functional groups on hydroxylated surfaces is described, with focus on its application to 3D biomineral surfaces. Reaction of hydroxyl-bearing silica surfaces with an aminosilane, followed by alternating exposure to a dipentaerythritol-derived polyacrylate solution and a polyamine solution, allows the rapid, layer-by-layer (LBL) build-up of hyperbranched polyamine/polyacrylate thin films. Characterization of such LBL-grown thin films by AFM, ellipsometry, XPS, and contact angle analyses reveals a stepwise and spatially homogeneous increase in film thickness with the number of applied layers. UV,Vis absorption analyses after fluorescein isothiocyanate labeling indicate that significant amine amplification is achieved after the deposition of only 2 layers with saturation achieved after 3,5 layers. Use of this thin-film surface amplification technique for hydroxyl-enrichment of biosilica templates facilitates the conformal surface sol,gel deposition of iron oxide that, upon controlled thermal treatment, is converted into a nanocrystalline (,9.5,nm) magnetite (Fe3O4) coating. The specific adsorption of arsenic onto such magnetite-coated frustules from flowing, arsenic-bearing aqueous solutions is significantly higher than for commercial magnetite nanoparticles (,50,nm in diameter). [source] Luminescence of Nanocrystalline Erbium-Doped YttriaADVANCED FUNCTIONAL MATERIALS, Issue 5 2009Yuanbing Mao Abstract In this paper, the luminescence, including photoluminescence, upconversion and cathodoluminescence, from single-crystalline erbium-doped yttria nanoparticles with an average diameter of 80,nm, synthesized by a molten salt method, is reported. Outstanding luminescent properties, including sharp and well-resolved photoluminescent lines in the infrared region, outstanding green and red upconversion emissions, and excellent cathodoluminescence, are observed from the nanocrystalline erbium-doped yttria. Moreover, annealing by the high power laser results in a relatively large increase in photoluminescent emission intensity without causing spectral line shift. These desirable properties make these nanocrystals promising for applications in display, bioanalysis and telecommunications. [source] New Ruthenium Complexes Containing Oligoalkylthiophene-Substituted 1,10-Phenanthroline for Nanocrystalline Dye-Sensitized Solar Cells,ADVANCED FUNCTIONAL MATERIALS, Issue 1 2007C.-Y. Chen Abstract Two new ruthenium complexes [Ru(dcbpy)(L)(NCS)2], where dcbpy is 4,4,-dicarboxylic acid-2,2,-bipyridine and L is 3,8-bis(4-octylthiophen-2-yl)-1,10-phenanthroline (CYC-P1) or 3,8-bis(4-octyl-5-(4-octylthiophen-2-yl)thiophen-2-yl)-1,10-phenanthroline (CYC-P2), are synthesized, characterized by physicochemical and semiempirical computational methods, and used as photosensitizers in nanocrystalline dye-sensitized solar cells. It was found that the difference in light-harvesting ability between CYC-P1 and CYC-P2 is associated mainly with the location of the frontier orbitals, in particular the highest occupied molecular orbital (HOMO). Increasing the conjugation length of the ancillary ligand decreases the energy of the metal-to-ligand charge transfer (MLCT) transition, but at the same time reduces the molar absorption coefficient, owing to the HOMO located partially on the ancillary ligand of the ruthenium complex. The incident photon-to-current conversion efficiency curves of the devices are consistent with the MLCT band of the complexes. Therefore, the overall efficiencies of CYC-P1 and CYC-P2 sensitized cells are 6.01 and 3.42,%, respectively, compared to a cis- di(thiocyanato)-bis(2,2,-bipyridyl)-4,4,-dicarboxylate ruthenium(II)-sensitized device, which is 7.70,% using the same device-fabrication process and measuring parameters. [source] High Plasticity and Substantial Deformation in Nanocrystalline NiFe Alloys Under Dynamic LoadingADVANCED MATERIALS, Issue 48 2009Sheng Cheng A nanocrystalline (NC) NiFe alloy is presented, in which both highly improved plasticity and strength are achieved by the dynamic-loading-induced deformation mechanisms of de-twinning (that is, reduction of twin density) and significant grain coarsening (see figure). This work highlights potential ingenious avenues to exploit the superior behavior of NC materials under extreme conditions. [source] Cover Picture: Ductile-to-Brittle Transition in Nanocrystalline Metals (Adv. Mater.ADVANCED MATERIALS, Issue 16 200516/2005) Abstract Uniaxial tensile studies concerning electrodeposited nanocrystalline face-centered cubic Ni and Ni,Fe alloys are reported on p.,1969 by Ebrahimi and Li. The nanograined metals display a transition in the deformation mechanism at a critical grain size. The cover shows that their fracture surfaces exhibited a ductile-to-brittle transition from the "cup,cup" (intragranular, ductile failure, dislocation controlled) (top panels) to "cup,cone" (intergranular, brittle fracture, probably due to breaking of atomic bonds) (bottom panels) characteristics at room temperature across this critical grain size value. [source] Wear mechanisms in metal-on-metal bearings: The importance of tribochemical reaction layersJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 4 2010Markus A. Wimmer Abstract Metal-on-metal (MoM) bearings are at the forefront in hip resurfacing arthroplasty. Because of their good wear characteristics and design flexibility, MoM bearings are gaining wider acceptance with market share reaching nearly 10% worldwide. However, concerns remain regarding potential detrimental effects of metal particulates and ion release. Growing evidence is emerging that the local cell response is related to the amount of debris generated by these bearing couples. Thus, an urgent clinical need exists to delineate the mechanisms of debris generation to further reduce wear and its adverse effects. In this study, we investigated the microstructural and chemical composition of the tribochemical reaction layers forming at the contacting surfaces of metallic bearings during sliding motion. Using X-ray photoelectron spectroscopy and transmission electron microscopy with coupled energy dispersive X-ray and electron energy loss spectroscopy, we found that the tribolayers are nanocrystalline in structure, and that they incorporate organic material stemming from the synovial fluid. This process, which has been termed "mechanical mixing," changes the bearing surface of the uppermost 50 to 200 nm from pure metallic to an organic composite material. It hinders direct metal contact (thus preventing adhesion) and limits wear. This novel finding of a mechanically mixed zone of nanocrystalline metal and organic constituents provides the basis for understanding particle release and may help in identifying new strategies to reduce MoM wear. © 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:436,443, 2010 [source] Flexible nanocrystalline-titania/polyimide hybrids with high refractive index and excellent thermal dimensional stabilityJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 6 2010Guey-Sheng Liou Abstract In this study, a novel synthetic route was developed to prepare polyimide,nanocrystalline,titania hybrid optical films with a relatively high titania content (up to 50 wt %) and thickness (20,30 ,m) from soluble polyimides containing hydroxyl groups. Two series of newly soluble polyimides were synthesized from the hydroxy-substituted diamines with various commercial tetracarboxylic dianhydrides. The hydroxyl groups on the backbone of the polyimides could provide the organic,inorganic bonding and resulted in homogeneous hybrid solutions by controlling the mole ratio of titanium butoxide/hydroxyl group. AFM, SEM, TEM, and XRD results indicated the formation of well-dispersed nanocrystalline-titania. The flexible hybrid films could be successfully obtained and revealed relatively good surface planarity, thermal dimensional stability, tunable refractive index, and high optical transparency. A three-layer antireflection coating based on the hybrid films was prepared and showed a reflectance of less than 0.5% in the visible range indicated its potential optical applications. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1433,1440, 2010 [source] Spray Pyrolysis of Fe3O4,BaTiO3 Composite ParticlesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2009Tomoyuki Adachi Fe3O4,BaTiO3 composite particles were successfully prepared by ultrasonic spray pyrolysis. A mixture of iron(III) nitrate, barium acetate and titanium tetrachloride aqueous solution were atomized into the mist, and the mist was dried and pyrolyzed in N2 (90%) and H2 (10%) atmosphere. Fe3O4,BaTiO3 composite particle was obtained between 900° and 950°C while the coexistence of FeO was detected at 1000°C. Transmission electron microscope observation revealed that the composite particle is consisted of nanocrystalline having primary particle size of 35 nm. Lattice parameter of the Fe3O4,BaTiO3 nanocomposite particle was 0.8404 nm that is larger than that of pure Fe3O4. Coercivity of the nanocomposite particle (390 Oe) was much larger than that of pure Fe3O4 (140 Oe). These results suggest that slight diffusion of Ba into Fe3O4 occurred. [source] Analysis of Nanocrystalline and Microcrystalline ZnO Sintering Using Master Sintering CurvesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2006Kevin G. Ewsuk Master sintering curves were constructed for dry-pressed compacts composed of either a nanocrystalline or a microcrystalline ZnO powder using constant heating rate dilatometry data and an experimentally determined apparent activation energy for densification of 268±25 and 296±21 kJ/mol, respectively. The calculated activation energies for densification are consistent with one another, and with values reported in the literature for ZnO densification by grain boundary diffusion. Grain boundary diffusion appears to be the single dominant mechanism controlling intermediate-stage densification in both the nanocrystalline and the microcrystalline ZnO during sintering from 65% to 90% of the theoretical density (TD). Based on both the consistency of the calculated activation energy as a function of density and the narrow dispersion of the sintering data about the master sintering curve (MSC) for the nanocrystalline ZnO, there is no evidence of either significantly enhanced surface diffusion or grain growth during sintering relative to the microcrystalline ZnO. The MSC constructed for the nanocrystalline ZnO was used to design time,temperature profiles to successfully achieve four different target sintered densities on the MSC, demonstrating the applicability of the MSC theory to nanocrystalline ceramic sintering. The most significant difference in sintering behavior between the two ZnO powders is the enhanced densification in the nanocrystalline ZnO powder at shorter times and lower temperatures. This difference is attributed to a scaling (i.e., particle size) effect. [source] Nanostructure and Micromechanical Properties of Silica/Silicon Oxycarbide Porous CompositesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2004Araceli Flores The microhardness,nanostructure correlation of a series of silica/silicon oxycarbide porous composites has been investigated, as a function of pyrolysis temperature, Tp. The pyrolyzed products have been studied by means of scanning electron microscopy, mercury porosimetry, chemical analysis, solid-state 29Si-NMR, X-ray diffraction, Raman spectroscopy, and microindentation hardness. Two distinct regimes are found for the microhardness behavior with Tp. In the low-temperature regime (1000°C ,Tp < 1300°C), the material response to indentation seems to be dominated by the large amount of pores present in the samples. In this Tp range, low microhardness values, H, are found (<110 MPa). Above Tp= 1300°C, a conspicuous H increase is observed. In this high-temperature regime (Tp= 1300,1500°C), microhardness values are shown to notably increase with increasing pyrolysis temperature. The H behavior at Tp= 1300,1500°C is discussed in terms of (i) the volume fraction of pores and the average pore size, (ii) the bond density of the oxycarbide network, and (iii) the occurrence of a nanocrystalline SiC phase. [source] A Novel Processing Route to Develop a Dense Nanocrystalline Alumina Matrix (<100 nm) Nanocomposite MaterialJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2003Guo-Dong Zhan A dense 3-mol%-yttria-stabilized tetragonal zirconia polycrystalline (3Y-TZP) toughening alumina matrix nanocomposite with a nanocrystalline (<100 nm) matrix grain size has been successfully developed by a novel processing method. A combination of very rapid sintering at a heating rate of 500°C/min and at a sintering temperature as low as 1100°C for 3 min by the spark-plasma-sintering technique and mechanical milling of the starting ,-Al2O3 nanopowder via a high-energy ball-milling process can result in a fully dense nanocrystalline alumina matrix ceramic nanocomposite. The grain sizes for the matrix and the toughening phase were 96 and 265 nm, respectively. A great increase in toughness almost 3 times that for pure nanocrystalline alumina has been achieved in the dense nanocomposite. Ferroelastic domain switching without undergoing phase transformation in nanocrystalline t -ZrO2 is likely as a mechanism for enhanced toughness. [source] Microstructure Development in Unsupported Thin FilmsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2002Brian P. Gorman To better understand the role of the substrate in the microstructural evolution of thin films, unsupported nanocrystalline yttrium-stabilized zirconia (ZrO2:16%Y or YSZ) films were examined as a function of temperature and annealing time. Grain growth, texturing, and pinhole formation were measured using transmission electron microscopy (TEM) and electron diffraction. Films were produced and subsequently annealed on metallic grids using a previously developed technique that results in near full density films at low annealing temperatures. Microstructural evolution in these films was unique compared with constrained films. Grains were found to spheroidize much more readily, ultimately resulting in the formation of porosity and pinholes. Grain growth was found to stagnate at a size particular to each annealing temperature, presumably due to the effects of Zener pinning. It is proposed that the lack of substrate strain and confinement effects allows for the dominance of surface energetics with respect to microstructural evolution. [source] Preparation and Electric Properties of Dense Nanocrystalline Zinc Oxide CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2002Lian Gao This communication reports on the preparation and electric properties of dense nanocrystalline ZnO ceramics. By spark plasma sintering, nanocrystalline (,100 nm) ZnO ceramics with a high density of 98.5% were obtained at a very low temperature of 550°C. Electric property measurement revealed a novel conduction nonlinearity in the sample sintered at 500°C. This phenomenon is due to the nanometerization of ZnO crystal and the grain boundary layer with an amorphous interfacial layer. [source] | ||||||||||||||||||||||||||||||||||