1,721,123 research outputs found
A method of measurement for determination of relative density in the axisymmetric forming of sintered porous material
No full textA new method for the determination of relative density is proposed in this work. Density is one of the most important variables in the forming of sintered porous materials. In the proposed method, the distribution of relative density is obtained experimentally from the grid patterns of the deformed specimen. The nodal coordinates and the tangential slopes of the end-points of each segment of a grid element are measured by use of an optical projector. The measured data are curve-fitted using an appropriate interpolating equation, the relative density then being obtained by means of numerical integration on the basis of mass conservation. The validity of the proposed method is checked for the axisymmetric forward extrusion process through a curved die. The indirectly measured values of relative density distribution are compared with those obtained by the rigid-plastic finite-element method, the comparison showing that there is a good agreement between the two results considering the numerical errors involved in the two methods. It is thus shown that the proposed method can be utilized further in other forming processes for sintered materials. © 1992
Macrocrystalline colloidal assemblies in an electric field
No full textMacrocrystalline colloidal assemblies with tunable non-spherical shape are fabricated through colloidal crystallization under an AC electric field. Also, by field-induced drop breakup, uniform micrometer-sized macrocrystalline particles can be synthesized (see Figure). Interestingly, the electrical field promotes infiltration of the suspending oil, which can be used for fabricating photonic crystals with high refractive index mismatch
Ordered macroporous particles by colloidal templating
No full textOrdered macroporous particles of silica and titania were fabricated by colloidal templating. The colloidal templates were assembled through colloidal crystallization of suspended polystyrene latex sphere particles in aqueous droplets straddling an air-oil interface. The procedures involve first preparing spherical colloidal crystalline particles of polystyrene latex spheres and then infusing them with metal precursor solutions that form silica or titania in the interstices. Finally, calcination decomposes the polystyrene latex spheres, leaving macropores at their sites. The shape of the template was controlled by the presence of additive surfactant or by the action of an applied electric field. Specifically, spherical, concaved disklike, and ellipsoidal colloidal crystals were prepared successfully and used as templates for the fabrication of ordered macroporous particles. The SEM images of the prepared macroporous particles showed that the pores were interconnected and ordered into a hexagonal arrangement.We would like to thank Kyeong
Youl Jung for assistance with PXRD measurement, and
Dr. Jeong-Jin Hong for many useful discussions. This
work was supported by the Brain Korea 21 program.
Jong Man Jung (Korea Basic Science Institute) is also
acknowledged for his helpful guidance with the characterization
of scanning electron microscopy data
Fabrication of hollow colloidal crystal. cylinders and their inverted polymeric replicas
No full textWe fabricated colloidal crystals on a fiber by a dip-coating method. The self-assembly of monodisperse colloidal particles was affected by the curvature of the fiber (the reciprocal of the fiber radius). As the fiber became smaller in diameter, fewer layers of the colloidal spheres were coated for a given lift-up speed. The hollow colloidal crystal cylinders were used as a template for creating macroporous structure having three-dimensionally interconnected air cavities. Specifically, the polymer precursor was infiltrated into the colloidal crystal template and the macroporous polymer structures were obtained after the selective etching of colloidal particles. (c) 2005 Elsevier Inc. All rights reserved.KRF-2002-042-C0024 of the Korea Research Foundatio
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