• Korean Journal of Metals and Materials
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• v.46 no.4
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• pp.223-226
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• 2008

The comparison of sintering behavior and mechanical properties of ultra-fine WC-10wt.%Co and WC-10wt.%Fe hard materials produced by high-frequency induction heated sintering (HFIHS) was accomplished using ultra fine powder of WC and binders(Co, Fe). The advantage of this process allows very quick densification to near theoretical density and prohibition of grain growth in nano-structured materials. Highly dense WC-10Co and WC-10Fe with a relative density of up to 99% could be obtained with simultaneous application of 60 MPa pressure and induced current within 1 minute without significant change in grain size. The hardness and fracture toughness of the dense WC-10Co and WC-10Fe composites produced by HFIHS were investigated.

• Proceedings of the Membrane Society of Korea Conference
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• 2002.05a
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• pp.35-41
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• 2002

Dense oxygen ionic conducting materials can be used for oxygen separation membranes at high temperatures. However, they show relatively low permeation flux because of their large resistances. To reduce resistances and improve the oxygen permeation flux, thin dense yttria-stabilized-zirconia (YSZ)/Pd composite dual-phase membranes were fabricated by a new approach that combines the reservoir method and chemical vapor deposition (CVD). A thin porous YSZ layer was coated on a porous alumina support by dip-coating the YSZ suspension. A continuous Pd phase was formed inside pores of the YSZ layer by the reservoir method. The residual pores of the YSZ/Pd layer were plugged with yttria/zirconia by CVD to ensure the gas tightness of the membranes. The oxygen permeation fluxes through these composite membrane were 2.0$\times$10$^{-8}$ mol/cm$^2$.s and 4.8$\times$10$^{-8}$ mol/cm$^2$.s at 105$0^{\circ}C$ when air and oxygen were used as the permeate gases, respectively. These oxygen permeation values are about 1 order of magnitude higher than those of pure YSZ membranes prepared under similar conditions.

• Journal of Powder Materials
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• v.8 no.4
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• pp.231-238
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• 2001

We combined Field-Activated Combustion Synthesis(FACS) with mechanical pressure to produce dense WC-20 vol.%Co composite in one step. The hardness, the fracture toughness and the relative density of the dense WC-20 vol.%Co were investigated. Under the application of 60 MPa pressure and 3000A current on the reactants, the relative density of WC-20 vol.%Co composite was 99.4%. The fracture toughness and hardness were $9.4 MPa.m^{1/2}$ and $1672kg\textrm{mm}^2$ respectively. The fracture toughness and hardness of WC-20 vol.%Co composite produced by FAPACS were lower than that of nanostructured composite, but similar to commercial ones. Therefore we concluded that the FAPACS method which can produce WC-20 vol.%Co within several minutes in one step is superior to conventional ones.

• Journal of Surface Science and Engineering
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• v.49 no.5
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• pp.401-407
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• 2016

In this work, effect of zincate treatment of AZ91 Mg alloy on the following electrodeposition of copper was examined in a non-cyanide bath containing pyrophosphate ions in view of surface morphology and adhesion of the electrodeposited copper layer. Without zincate treatment, the electrodeposited copper layer showed very porous structure and poor adhesion. On the other hand, the copper layer electrodeposited on the zincate-treated surface showed dense structure and good adhesion. The dissolution rate of AZ91 Mg alloy after the zincate treatment appeared to decrease about 40 times in the copper pyrophosphate bath, as compared to that of the surface without zincate treatment. The porous morphology and poor adhesion of a copper layer on the AZ91 Mg alloy surface without zincate treatment were attributed to small number of nucleation sites of copper because of rapid dissolution of the magnesium substrate in the pyrophosphate bath. Based on the experimental results, it is concluded that the zincate treatment to form a conducting and protecting layer on the AZ91 Mg alloy surface is essential for successful electrodeposition of a copper layer on AZ91 Mg alloy with good adhesion and dense structure in the copper pyrophosphate bath.

• Korean Journal of Materials Research
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• v.25 no.1
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• pp.48-53
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• 2015

$TiH_2$ nanopowder was made by high energy ball milling. The milled $TiH_2$ and CNT powders were then simultaneously synthesized and consolidated using pulsed current activated sintering (PCAS) within one minute under an applied pressure of 80 MPa. The milling did not induce any reaction between the constituent powders. Meanwhile, PCAS of the $TiH_2$-CNT mixture produced a Ti-TiC composite according to the reaction ($0.92TiH_2+0.08CNT{\rightarrow}0.84Ti+0.08TiC+0.92H_2$, $0.84TiH_2+0.16CNT{\rightarrow}0.68Ti+0.16TiC+0.84H_2$). Highly dense nanocrystalline Ti-TiC composites with a relative density of up to 99.7% were obtained. The hardness and fracture toughness of the dense Ti-8 mole% TiC and Ti-16 mole% TiC produced by PCAS were also investigated. The hardness of the Ti-8 mole% TiC and Ti-16 mole% TiC composites was higher than that of Ti. The hardness value of the Ti-16 mole% TiC composite was higher than that of the Ti-8 mole% TiC composite without a decrease in fracture toughness.

• Applied Microscopy
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• v.14 no.2
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• pp.38-51
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• 1984

Fine structure of dormant and swollen conidiospore from Trichoderma koningii and the mechanism of protoplasting from the conidiospore were studied by scanning and transmission electron microscopy. The cell wall of dormant conidiospore was two-layered structure which consisted of electron dense outer layer and electron transparent inner layer. After 8.5 hrs incubation. the conidiospore was swollen and the outer layer of cell wall shown unequal thickness and partial breakage. Protoplast was released through the pore which has been formed by the breakage of outer layer and dissolution of newly synthesized cell wall for germ-tube formation. Swollen conidiospore and protoplast in releasing process contained various cell organelles and vacuoles with electron dense materials. The protoplast contained looser cytoplasm and had no cell wall materials outside of plasmamembrane.

• Journal of the Korean Ceramic Society
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• v.31 no.10
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• pp.1169-1175
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• 1994

Five Al2O3/SiC/metal composites with four different particle sizes of green SiC abrasive grains are grown by the directed oxidation of an commercially available Al-alloy. Oxidation was conducted in air at 100$0^{\circ}C$, 96 hours long. Slip casted SiC-fillers were placed on the alloy or SiC powder deposited up to the required layer thickness. Their microstructures are described and measurements of density, elastic constants, frexural strength, fracture toughness and work of fracture are reported. The results are compared with those of commercial dense sintered Al2O3. The properties of produced materials have a strong relationship to not only the properties of Al2O3, SiC, Al and Si but also to the phase share and phase distribution. The composite materials are dense (0.5% porosity), tough (KIC = 3.4~6.4 MPa{{{{ SQRT { m} }}), strong ({{{{ sigma }}B = 170~345 MPa) and reasonably shrinkage free producible. The reinforcements is attained mainly through the plastic deformation of ductile metal phase.

• Journal of the Korean Ceramic Society
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• v.20 no.1
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• pp.55-62
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• 1983

the preliminary work on the prepartion of fine hydroxyapatite powder and the synthesis of dense hydroxyapatite ceramic from the powder were investigated for the development of artificial bone and tooth materials for implants. The effects of the process variables such as compositions of the raw materials the initial pH of the solutions and sintering temperature on the physical properties were investigated in order to determine the optimum conditions for the fabrication of tooth implant material. As the initial pH of the solutions was increased in the range of 10-11.6 the initial particle size of precipitates was decreased thus the sinterability of precipitates was improved. It was found that the composition of calcium rich of 1.75 in Ca/P mole ratio exhibited better sinterability and mechanical strength of the apatite ceramics for example the highest value of Vicker's hardness obtained from the compositions of 1.75 in Ca/P mole ratio was 764±30 Kg/mm2 compared to the maximum value of 600 kg/mm2 obtained from the compositions of 1.67 in Ca/P mole ratio.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2003.04a
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• pp.43-44
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• 2003

• Journal of Powder Materials
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• v.14 no.4
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• pp.245-250
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• 2007

Dense nanostructured $2MoSi_{2}-SiC$ composites were synthesized by the pulsed current activated combustion synthesis (PCACS) method within 3 minutes in one step from mechanically activated powders of $Mo_{2}C$ and 5Si. Simultaneous combustion synthesis and densification were accomplished under the combined effects of a pulsed current and mechanical pressure. Highly dense $2MoSi_{2}-SiC$ with relative density of up to 96% was produced under simultaneous application of a 60 MPa pressure and the pulsed current. The average grain size of $MoSi_{2}$ and SiC were about 120 nm and 90 nm, respectively. The hardness and fracture toughness values obtained were 1350 $kg/mm^{2}$ and 4 $MPa{\cdot}m^{1/2}$, respectively.