Use of Centrifuge Force to Fabricate Reticulated Porous Ceramics Results in Uniform Structure
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of applications in the fabrication of microfluidic devices, and optical and sensing elements. SOMA CHATTOPADHYAY
Use of Centrifuge Force to Fabricate Reticulated Porous Ceramics Results in Uniform Structure
Figure 1. Fabrication of suspended nanostructures by direct drawing of polymer fibers. A drop of polymer is applied at the edge of a sheet and quickly drawn across a tip array creating multiple suspended parallel fibers.
polymer fibers with desired materials using various deposition techniques followed by selective removal of the polymer core. The researchers demonstrated capillaries in chrome, parylene, gold, and glass.
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The speed and ease of fabrication by this direct-drawing method compared to conventional multi-step lithography, together with choice of polymer with desirable properties, opens the possibility
Reticulated porous ceramics (RPCs) are synthesized materials composed of an arrangement of superimposed ceramic lattices. These materials exhibit porosity higher than 70%. Control of the pore structure is key for application of RPCs. A common method for manufacturing RPCs consists in immersing a polyurethane sponge in prepared ceramic slurry, removing the excess slurry by roll pressing and then sintering. However, the rollpress method does not effectively remove the excess slurry accumulated in the joints of the lattice. An alternative process to remove the excess slurry from the preform by utilizing centrifugal force has been presented by X. Pu, X. Liu, F. Qiu,
MRS BULLETIN/NOVEMBER 2004
RESEARCH/RESEARCHERS
and L. Huang from the Shanghai Institute of Ceramics of the Chinese Academy of Sciences. Their technique ensures a uniform structure on the ceramic reticule. As reported in the July issue of the Journal of the American Ceramic Society (p. 1392), the researchers prepared a slurry from silicon nitride powders mixed with 7 wt% alumina added as a sintering additive, 23 wt% silica sol as a binder, 1.5 wt% carboxymethylcellulose as a thickening agent, and 0.2 wt% of Nopco 267-A as an antifoaming agent. The slurry was ball milled using silicon nitride balls. A polyurethane sponge was submerged in slurry and compressed there to achieve the most adsorption possible, then centrifuged at high speed. In this manner, the lattice was uniformly covered with a thin film. The preform thus obtained was dried and recoated in slurry, this time using vacuum to ensure coverage. This process was repeated using slurries of different viscosities. The measured weight gain of the sample after the first coating in slurry slightly increased with increasing slurry viscosity, and became constant for high-viscosity slurries. However, for the second coating, the measured weight gain was double that of the first coating for low-viscosity slurries, and increased dramatically with slurry viscosity. This is an effect of the enhanced adsorption created by the first thin film deposited on the lattice, said the researchers. Measurements of the diameters in the lattice struts were fairly uniform and almost identical to the joi
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