• Korean Journal of Materials Research
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• v.12 no.12
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• pp.941-946
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• 2002

Both Cu and Cu-oxide nanopowders have great potential as conductive paste, solid lubricant, effective catalysts and super conducting materials because of their unique properties compared with those of commercial micro-sized ones. In this study, Cu and Cu-oxide nanopowders were prepared by Pulsed Wire Evaporation (PWE) method which has been very useful for producing nanometer-sized metal, alloy and ceramic powders. In this process, the metal wire is explosively converted into ultrafine particles under high electric pulse current (between $10^4$ and $10^{ 6}$ $A/mm^2$) within a micro second time. To prevent full oxidations of Cu powder, the surface of powder has been slightly passivated with thin CuO layer. X-ray diffraction analysis has shown that pure Cu nanopowders were obtained at $N_2$ atmosphere. As the oxygen partial pressure increased in $N_2$ atmosphere, the gradual phase transformation occurred from Cu to $Cu_2$O and finally CuO nanopowders. The spherical Cu nanopowders had a uniform size distribution of about 100nm in diameter. The Cu-oxide nanopowders were less than 70nm with sphere-like shape and their mean particle size was 54nm. Smaller size of Cu-oxide nanopowders compared with that of the Cu nanopowders results from the secondary explosion of Cu nanopowders at oxygen atmosphere. Thin passivated oxygen layer on the Cu surface has been proved by XPS and HRPD.

• Journal of Powder Materials
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• v.26 no.5
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• pp.395-404
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• 2019

Aluminum nitride (AlN) has excellent electrical insulation property, high thermal conductivity, and a low thermal expansion coefficient; therefore, it is widely used as a heat sink, heat-conductive filler, and heat dissipation substrate. However, it is well known that the AlN-based materials have disadvantages such as low sinterability and poor mechanical properties. In this study, the effects of addition of various amounts (1-6 wt.%) of sintering additives $Y_2O_3$ and $Sm_2O_3$ on the thermal and mechanical properties of AlN samples pressureless sintered at $1850^{\circ}C$ in an $N_2$ atmosphere for a holding time of 2 h are examined. All AlN samples exhibit relative densities of more than 97%. It showed that the higher thermal conductivity as the $Y_2O_3$ content increased than the $Sm_2O_3$ additive, whereas all AlN samples exhibited higher mechanical properties as $Sm_2O_3$ content increased. The formation of secondary phases by reaction of $Y_2O_3$, $Sm_2O_3$ with oxygen from AlN lattice influenced the thermal and mechanical properties of AlN samples due to the reaction of the oxygen contents in AlN lattice.

• Korean Chemical Engineering Research
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• v.54 no.3
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• pp.410-418
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• 2016

In this study, we prepared electrically conducting composites using epoxy resin of diglycidyl ether of bisphenol A (DGEBA) as a matrix, triethylenetetramine (TETA) as a hardener and nickel powder or multi-walled carbon nanotubes (MWCNTs) grafted with $-NH_2$ groups (MWCNT-$NH_2$) as electrically conducting fillers. Electrical conductivity of composite films were measured by coating on the slide glass with a doctor blade. We measured modification reactions of MWCNT and reaction of MWCNT-$NH_2$ with DGEBA epoxy resin by fourier transform infrared spectrometer (FTIR), thermogravimetric analyzer (TGA) and elemental analyzer (EA). Morphology of composites was investigated by scanning electron microscope (SEM) and sheet resistances of composites were measured by 4-point probe. We found $(9.87{\pm}1.09){\times}10^4{\Omega}/sq$ of sheet resistance for epoxy composite containing both 40 wt% nickel powder and 0.5 wt% of MWCNT-$NH_2$ as fillers, equivalent to epoxy composite containing 53.3 wt% nickel powder only as a filler.

• Transactions on Electrical and Electronic Materials
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• v.13 no.4
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• pp.212-214
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• 2012

Both the electrically positive and negative particles in a cell of quick response-liquid powder display (QR-LPD) are surrounded by conductive electrodes on the upper and lower substrate and the dielectric materials of the barrier ribs. Particles in a cell are attached to or detached from the other materials by image force, electric field, Coulomb's force, and Van der Waals' force. Through these forces, the moving particles form an image but induce clumping phenomena. Particles having a large kinetic energy by a large q/m value crash into the opposite electrode with high speed at a large driving voltage and quickly lose electrically charged material. As a result, these particles are clumped and degrade panel performance. The clumped particles in a cell are observed by microscopic photographs and ascertained by a response time. When the bias voltage is increased to 0.68-0.76 $V/{\mu}m$, particle clumping occurs abruptly and the response time increases sharply. This particle clumping is similarly observed after the number of driving times at the driving voltage (0.42-0.64 $V/{\mu}m$).

• Clean Technology
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• v.19 no.2
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• pp.90-94
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• 2013

We investigated one-dimensional thermal conduction for gypsum objects incorporating oyster shell powder. We presumed that according to the portion of oyster shell in the hybrid structure conductive characteristics of that would also change as some physicochemical properties such as volatile organic compound (VOC) adsorption were found to be changed considerably. Based on Fourier's 2nd law of heat conduction an analytical analysis in a flat slab (one axis perpendicular to an infinite plane) was performed. We found that composition of oyster shell and conduction-related coefficients and parameters could greatly influence on the thermal profile of that conduction, and some model experiments also served for it in the affirmative.

• Computers and Concrete
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• v.16 no.6
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• pp.865-880
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• 2015

Standard test method for bulk electrical conductivity (ASTM C1760) provides a rapid indication of the concrete's resistance to the penetration of chloride ions by diffusion. In this paper a new approach for assessing the bulk electrical conductivity of saturated specimens of hardened concrete is presented. The test involves saturating concrete specimens with a 5 M NaCl solution before measuring the conductivity of the samples. By saturating specimens with a highly conductive solution, they showed virtually the same pore solution conductivity. Different concrete samples yield different conductivity primarily due to differences in their pore structure. The feasibility of the method has been demonstrated by testing different concrete mixtures consisting ordinary and blended cement of silica fume (SF) and calcined perlite powder (CPP). Two standard test methods of RCPT (ASTM C1202) and Bulk Conductivity (ASTM C1760) were also applied to all of the samples. The results show that for concretes containing SF and CPP, the proposed method is less sensitive towards the variations in the pore solution conductivity in comparison with RCPT and Bulk Conductivity tests. It seems that this method is suitable for the assessment of the performance and durability of different concretes containing supplementary cementitious materials.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.23 no.6 s.165
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• pp.1048-1054
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• 1999

It is important to study the shielding effectiveness(SE) of reinforcing material of plastic composite materials against the electromagnetic(EM) waves. In this paper, SE of the shielding material of EM waves was investigated with actual experiments. The materials used in this study were made up of film, fiber and powder of conductive materials - Cu, Al, CF etc. Also, The resin film was used as matrix. The experiment was carried out by using a shielding evaluator(Shielding box) TR17302 with an ADVANTEST spectrum analyzer, model R3361C. It was found from the experimental results that copper, aluminum and carbon fiber were good candidates as a shielding material against the EM waves with increasing the SE as the composite was laminated. The characteristics of the SE against the EM waves depended on a mode of preparation of specimen. The effects of interval of wires on the SE were studied when the orientation and the space of Cu wires were changed. The SE strongly depended on the. orientation and the space of the Cu wire. SE decreased as the space of the Cu wires was increasing.

• Journal of the Korean Ceramic Society
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• v.35 no.4
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• pp.355-363
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• 1998

The oxygen flux of SDC ($Sm_2O_3\;doped\;CeO_2$) solid electrolyte membranes with electronic and oxygen ion-ic conductivities has been investigated as a basic research in order to develop the conversion process of na-tural gas to syngas using the ceramic membrane reactor. Tube type membranes(1 mm thickness) were fa-bricated by slip casting of SDC powders prepared by the oxalate coprecipitaion method. Dense oxygen per-meation membranes(0.1 mm thickness) could be synthesized via sintering at $1450^{\circ}C$ for 2h and their re-lative density was over 95% The oxygen flux through SDC membranes doped 20mol% $Sm_15$ was about $1.13{\times}10^{-5}\;mol/m_2{\cdot}sec$ at low temperature around $800^{\circ}C$. In addition the SDC membranes showed a good thermaal stability for a long period of service.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.12
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• pp.966-972
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• 2010

Single-phase $Sr_2FeMoO_6$ thin films were produced by RF magnetron sputtering for use as electrodes in integrated sensors and found to be good conductors at room temperature. The films were deposited from a powder-type sputtering target under various conditions, and were crystallized by annealing. Elimination of $O_2$ gas during deposition, by the use of a solely Ar sputtering gas under a working pressure as low as possible, and vacuum annealing were important to promote the $Sr_2FeMoO_6$ phase. However, oxygen exclusion from sputtering and annealing was not enough to yield single-phase $Sr_2FeMoO_6$: hydrogen annealing was also required. Film production was optimized by varying the deposition parameters and hydrogen annealing conditions. The film had good electrical conduction, with a low resistivity of $1.6{\times}10^{-2}\Omega{\cdot}cm$ at room temperature.

• Journal of Electrical Engineering and Technology
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• v.12 no.6
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• pp.2256-2261
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• 2017

Carbon nanotube (CNT) and alumina ($Al_2O_3$) are synthesized into hybrid composites, and an advanced electrical discharge machining (EDM) system is developed for the machining of hard and conductive materials. CNT nanoparticles are mixed with $Al_2O_3$ powder and the $Al_2O_3$/CNT slurry is sintered by spark plasma. The hardness and the electrical conductivity of the $Al_2O_3$/CNT hybrid composite were investigated. The electrical discharge is controlled by a capacitive ballast circuit. The capacitive ballast circuit is applied to the tungsten carbide and the $Al_2O_3$/CNT hybrid composite. The voltage-current waveforms and scanning electron microscope (SEM) images were measured to analyze the characteristics of the boring process. The developed EDM process can manufacture the ceramic based hybrid composites, thereby expecting the variety of applications.