Search results for "Microstructure"
showing 10 items of 707 documents
Structural Study of Star Polyelectrolytes and Their Porous Multilayer Assembly in Solution
2015
Star polyelectrolytes with responsive properties to external stimuli, such as pH, temperature and ionic condition, were utilized to fabricate layer-by-layer (LbL) microcapsules . The microstructure of star polyelectrolytes was first studied in semi-dilute solution by in situ small-angle neutron scattering (SANS). These measurements show that with the addition of salts, arms of strong cationic star polyelectrolytes will contract and the spatial ordering of the stars would be interrupted. SANS measurements were also performed on the microcapsules in order to study their internal structure and responsive properties in solution. The results show that with the increase of shell thickness, microc…
Recent advances in the development of holey optical fibers based on sulfide glasses
2006
International audience; Microstructured optical fibers as new optical objects have been developed in the recent past years, firstly from silica glass and then from other oxide glasses such as tellurite or different heavy cations oxide glasses. However very few results have been reported concerning non-oxide glasses and more particularly chalcogenide glasses. In a photonic crystal fiber the arrangement of air holes along the transverse section of the fiber around a solid glassy core leads to unique optical properties, such as for example broadband single-mode guidance, adjustable dispersion, nonlinear properties. Since the effective modal area is adjustable thanks to geometrical parameters, …
Design of experiment approach applied to reducing and oxidizing tolerance of anode supported solid oxide fuel cell. Part I: Microstructure optimizati…
2011
The main drawback of Ni/YSZ anode supports for solid oxide fuel cell application is their low tolerance to reducing and oxidizing (RedOx) atmosphere changes, owing to the Ni/NiO volume variation. This work describes a structured approach based on design of experiments for optimizing the microstructure for RedOx stability enhancement. A full factorial hypercube design and the response surface methodology are applied with the variables and their variation range defined as: (1) NiO proportion (40-60 wt% of the ceramic powders), (2) pore-former proportion (0-30 wt% corresponding to 0-64 vol.%), (3) NiO particle size (0.5-8 mu m) and (4) 8YSZ particle size (0.6-9 mu m).
Metal/Semiconductor Barrier Properties of Non-Recessed Ti/Al/Ti and Ta/Al/Ta Ohmic Contacts on AlGaN/GaN Heterostructures
2019
This paper compares the metal/semiconductor barrier height properties of non-recessed Ti/Al/Ti and Ta/Al/Ta contacts on AlGaN/GaN heterostructures. Both contacts exhibited a rectifying behavior after deposition and after annealing at temperatures up to 550 °
Controlling melt convection—an innovation potential for concerted microstructure evolution of Nd-Fe-B alloys
2005
The solidification process and the resulting microstructure of Nd-Fe-B alloys in consideration of melt convection has been investigated experimentally with a specially designed forced crucible rotation technique. Samples were subjected to well-defined forced rotation and vibration, respectively, during induction heating and solidification. A concerted microstructure evolution is possible by enhancement or suppression of the melt convection. As a result, the microstructure pattern, mainly the volume fraction of the soft magnetic a-Fe phase, vary strongly with the strength of the internal flow motion. A distinct reduction of the a-Fe volume fraction in samples with strong melt rotation was ob…
FATIGUE CRACK PROPAGATION THROUGH AUSTEMPERED DUCTILE IRON MICROSTRUCTURE
2010
Austempered ductile iron (ADI) has a wide range of application, particularly for castings used in automotive and earth moving machinery industries. These components are usually subjected to variable dynamic loading that may promote initiation and propagation of fatigue cracks up to final fracture. Thus, it is important to determine the fatigue crack propagation behavior of ADI. Since fatigue crack growth rate (da/dN) vs. stress intensity factor K data describe fatigue crack propagation resistance and fatigue durability of structural materials, da/dN vs. Ka curves of ADI 1050 are reported here. The threshold amplitude of stress intensity factor Kath is also determined. Finally, the influence…
Heterogeneous and homogeneous crystal nucleation in a colloidal model system of charged spheres at low metastabilities
2011
We have studied the nucleation kinetics in the bulk as well as at the container walls of a charged sphere colloidal model system under salt-free conditions close to the fluid–crystal phase boundary. We determined time resolved nucleation rate densities for heterogeneous nucleation on the wall, the corresponding nucleation rate densities for homogeneous nucleation and compare the resulting nucleation barrier heights. The homogeneous barrier height decreases exponentially with increasing metastability, while the heterogeneous barrier displays a sharp transition from a constant value close to the phase boundary to zero at higher metastability. As a consequence the microstructure evolution is d…
Microstructural evolution of mullites produced from single-phase gels
2007
The crystalline microstructure of mullites obtained by heating monophasic gels has been investigated. Gels with alumina to silica molar ratio of 3:2 (as in secondary mullite) and 2:1 (as in primary mullite) were prepared by gelling mixtures of aluminium nitrate and tetraethylorthosilicate. Phase transformations were induced by heating the gel precursors, with different final treatment temperatures between 1173 and 1873 K. The mullites formed as a result of thermal treatment were studied by means of X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The crystalline structure (unit-cell parameters) and microstructure were determined from X-ray diffraction pa…