• Journal of the Korean Ceramic Society
• /
• v.50 no.2
• /
• pp.93-102
• /
• 2013

Macro porous ceramics possessing controlled microstructures and chemical compositions have increasingly proven useful in the industrial sphere. Their sintered structures have found application in both established and emerging, areas such as thermal insulation in buildings, filtration of liquids and molten materials, refractory insulation, bone scaffolds and tissue engineering. Stable ceramic foams can be formed by wet chemical methods using inorganic particles(e.g., $Al_2O_3$ or $SiO_2$). The wet foams are dried and sintered with improved porosity and mechanical properties. This review examines the different techniques used to prepare porous ceramics from ceramic foams, focusing on the explanation of this versatile method of direct foaming from the past to the present. Comparisons of the processes and the processing parameters are explained with the produced microstructures.

• Journal of Powder Materials
• /
• v.18 no.6
• /
• pp.488-495
• /
• 2011

This study was performed to fabricate the porous titanium foam by space holder method using NaCl powder, and to evaluate the effect of NaCl volume fractions (33.3~66.6 vol.%) on the porosities, compressive strength, Young's modulus and permeability. For controlling pore size, CP titanium and NaCl particles were sieved to different size range of 70~150 ${\mu}m$ and 300~425 ${\mu}m$ respectively. NaCl of green Ti compact was removed in water followed by sintered at $1200^{\circ}C$ for 2 hours. Total porosities of titanium foam were in the range of 38-70%. Pore shape was a regular hexahedron similar that of NaCl shape. Porous Ti body showed that Young's modulus and compressive strength were in the range of 0.6-6 GPa and 8-127 MPa respectively. It showed that pore size and mechanical properties of Ti foams was controllable by NaCl size and volume fractions.

• Journal of the Korean Ceramic Society
• /
• v.45 no.2
• /
• pp.132-137
• /
• 2008

The main purpose of this study is enhancing the filtering efficiency, performance and durability of filter by growing SiC whiskers on cordierite honeycomb substrate. The experiment was performed by Chemical Vapor Infiltration (CVI) in order to control pore morphology of substrate. Increasing the mechanical strength of porous substrate is one of important issues. The formation of "networking structure" in the pore of porous substrate increased mechanical strength. The high pressure gas injection to the specimen showed that a little of whiskers were separated from substrate but additional film coating enhanced the stability of whisker at high pressure gas injection. Particle trap test was performed. More nano-particle was trapped by whisker growth at the pore of substrate. Therefore it is expected that the porous cordierite which deposited the SiC whisker will be the promising material for the application as filter trapping the nano-particles.

• Journal of Powder Materials
• /
• v.9 no.1
• /
• pp.50-60
• /
• 2002

SPS(Spark Plasma Sintering ) is known to be an excellent sintering method for porous materials. In the present work an attempt has been made of fabricating porous 316L Stainless steel with good mechanical properties by using controlled SPS process Porosity was 21%~53% at sintering temperature of $600^{\circ}C$~100$0^{\circ}C$ The limit of porosity with available mechanical strength was 30% at given experimental conditions. Porosity can be controlled by manipulating the intial height of the compact by means of the supporter and punch length. The applied pressure can be exerted entirely upon the supporter, giving no influence on the specimen. The specimen is then able to be sintered pressurelessly. In this case porosity could be controlled from 38 to 45% with good mechanical strength at sintering temperature of 90$0^{\circ}C$. As the holding time increased, neck between the particles grew progressively, but shrinkage of the specimen did not occur, implying that the porosity remained constant during the whole sintering process.

• Journal of Electrochemical Science and Technology
• /
• v.7 no.2
• /
• pp.161-169
• /
• 2016

Porous tungsten oxide thin films were prepared by electrodeposition and tested as anodes of lithium secondary batteries. The synthesized films were composed of nanoparticles of 60-140 nm size, with porosities of 30-40 %. Increasing the temperature turned out to be a more effective approach to introduce porosity in the structure than increasing the electrolyte viscosity. The assessment of the synthesized films as anodes of lithium secondary batteries revealed a much higher initial discharge capacity for the porous than the dense samples. The discharge capacity retention significantly increased with increasing porosity and was further enhanced by heat treatment. In particular, a thin film composed of particles of about 140 nm in size and with a porosity of 40 % exhibited an initial discharge capacity higher than 600 mAh/g and a remaining capacity above 300 mAh/g after 30 cycles. Following heat treatment, the remaining capacity of this sample after 30 cycles increased to about 500 mA h/g.

• Journal of the Korean Ceramic Society
• /
• v.44 no.6 s.301
• /
• pp.338-342
• /
• 2007

Porous silicon nitride ceramics were prepared by SHS (Self-Propagating High Temperature Synthesis) from silicon powder, silicon nitride powder and pore-forming precursor. The microstructure, porosity and the flexural strength of the porous silicon nitride ceramics were varied according to the Si/Si3N4 ratio, size and amount of the pore-forming precursors. Some sample exhibited as high flexural strength as $162{\pm}24\;MPa$. The high strength is considered to result from the fine pore size and the strong bonding amoung the silicon nitride particles.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2015.08a
• /
• pp.59.1-59.1
• /
• 2015

In the Linford group at Brigham Young University we have recently developed three new sets of materials for three different areas of separations science: thin layer chromatography (TLC), high performance liquid chromatography (HPLC), and solid phase microextraction (SPME). First, via microfabrication we have grown patterned carbon nanotube (CNT) forests on planar substrates that we have infiltrated with inorganic materials such as silicon nitride. The coatings on the CNTs are conformal and typically deposited in a process like low pressure chemical vapor deposition. The resulting materials have high surface areas, are porous, and function as effective separation devices, where separations on our new TLC plates are typically significantly faster than on conventional devices. Second, we used the layer-by-layer (electrostatically driven) deposition of poly (allylamine) and nanodiamond onto carbonized poly (divinylbenzene) microspheres to create superficially porous particles for HPLC. Many interesting classes of molecules have been separated with these particles, including various cannabinoids, pesticides, tricyclic antidepressants, etc. Third, we have developed new materials for SPME by sputtering silicon onto cylindrical fiber substrates in a way that creates shadowing of the incoming flux so that materials with high porosity are obtained. These materials are currently outperforming their commercial counterparts. Throughout this work, the new materials we have made have been characterized by X-ray photoelectron spectroscopy, time-of-flight secondary ion mass spectrometry, scanning electron microscopy, transmission electron microscopy, etc.

• The Korean Journal of Ceramics
• /
• v.3 no.4
• /
• pp.229-234
• /
• 1997

Silicon carbide-carbon fiber composites have been prepared by partially Infiltrating porous carbon fiber composites with liquid silicon at a reaction temperature of $1670^{\circ}C$. Reaction between molten silicon and the fiber preform yielded silicon carbide-carbon fiber composites composed of aggregates of loosely bonded SiC crystallites of about 10$\mu\textrm{m}$ in size and preserved the appearance of a fiber. In addition, the SiC/C fiber composites had carbon fibers coated with a dense layer consisted of SiC particles of sizes smaller than 1$\mu\textrm{m}$. The physical and mechanical properties of SiC/C fiber composites were discussed in terms of infiltrated pore volume fraction of carbon preform occupied by liquid silicon at the beginning of reaction. Lower bending strength of the SiC/C fiber composites which had a heterogeneous structure in nature, was attributed to the disruption of geometric configuration of the original carbon fiber preform and the formation of the fibrous aggregates of the loosely bonded coarse SiC particles produced by solution-precipitation mechanism.

• Journal of Powder Materials
• /
• v.25 no.4
• /
• pp.336-339
• /
• 2018

A unique porous material with controlled pore characteristics can be fabricated by the freeze-drying process, which uses the slurry of organic material as the sublimable vehicle mixed with powders. The essential feature in this process is that during the solidification of the slurry, the dendrites of the organic material should repel the dispersed particles into the interdendritic region. In the present work, a model experiment is attempted using some transparent organic materials mixed with glass powders, which enable in-situ observation. The organic materials used are camphor-naphthalene mixture (hypo- and hypereutectic composition), salol, camphene, and pivalic acid. Among these materials, the constituent phases in camphor-naphthalene system, i.e. naphthalene plate, camphor dendrite, and camphor-naphthalene eutectic exclusively repel the glass powders. This result suggests that the control of organic material composition in the binary system is useful for producing a porous body with the required pore structure.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.12 no.5
• /
• pp.1130-1137
• /
• 1988

Heat transfer characteristics of evaporative transpiration cooling was investigated experimentally in the range of coolant mass flux, 0.002kg/m$^{2}$.sec~0.015m$^{2}$.sec. Glass beads, sand and copper particles were used as porous media and distilled water was used as a conant. The existence of evaporation zone was confirmed on this experimental conditions and its length increases with increasing article size and with decreasing mass flux. In order to get the low surface temperature, porous materials with high thermal conductivity is preferred when the panicle sizes are same, and small particles with low porosity is effective in case of the same material. Due to the relatively small coolant mass flux, evaporative transpiration cooling system could be stable by the capillary effect.