• Journal of the Microelectronics and Packaging Society
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• v.24 no.3
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• pp.57-62
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• 2017

In the process for preparing Ag-coated Cu flakes by electroless silver plating using hydroquinone reducing agent, Ag coating qualities were compared by changing various process parameters such as type of pretreatment solution, plating temperature, pH of plating solution, type and injection rate of plating solution, and pulp density. Effective pretreatment solution for removing the oxide layer on a Cu flake was preferentially suggested. The conditions of low plating temperature, pH value of 4.34, slow injection rate of Ag plating solution, elimination of deionized water in the Ag plating solution, and high pulp density significantly suppressed the formation of separated tiny Ag particles, and thus the surface coverage of Ag coating on Cu flakes was enhanced.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.150-150
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• 2016

Mankind is enjoying a great convenience of their life by the rapid growth of secondary industry since the Industrial Revolution and it is possible due to the invention of huge power such as engine. The automobile which plays the important role of industrial development and human movement is powered by the Engine Module, and especially Diesel engine is widely used because of mechanical durability and energy efficiency. The main work mechanism of the Diesel engine is composed of inhalation of the organic material (coal, oil, etc.), combustion, explosion and exhaust Cycle process then the carbon compound emissions during the last exhaust process are essential which is known as the major causes of air pollution issues in recent years. In particular, COx, called carbon oxide compound which is composed of a very small size of the particles from several ten to hundred nano meter and they exist as a suspension in the atmosphere. These Diesel particles can be accumulated at the respiratory organs and cause many serious diseases. In order to compensate for the weak point of such a Diesel Engine, the DPF(Diesel Particulate Filter) post-cleaning equipment has been used and it mainly consists of ceramic materials(SiC, Cordierite etc) because of the necessity for the engine system durability on the exposure of high temperature, high pressure and chemical harsh environmental. Ceramic Material filter, but it remains a lot of problems yet, such as limitations of collecting very small particles below micro size, high cost due to difficulties of manufacturing process and low fuel consumption efficiency due to back pressure increase by the small pore structure. This study is to test the possibility of new structure by direct infiltration of SiC Whisker on Carbon felt as the next generation filter and this new filter is expected to improve the above various problems of the Ceramic DPF currently in use and reduction of the cost simultaneously. In this experiment, non-catalytic VS CVD (Vapor-Solid Chemical Vaporized Deposition) system was adopted to keep high mechanical properties of SiC and MTS (Methyl-Trichloro-Silane) gas used as source and H2 gas used as dilute gas. From this, the suitable whisker growth for high performance filter was observed depending on each deposition conditions change (input gas ratio, temperature, mass flow rate etc.).

• Transactions of the Korean hydrogen and new energy society
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• v.17 no.1
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• pp.62-68
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• 2006

High temperature electrolysis is a promising technology to produce massively hydrogen using renewable and nuclear energy. Solid oxide fuel cell materials are candidates as the components of steam electrolysers. However, the polarization characteristics of the typical electrode materials during the electrolysis have not been intensively investigated. In this study, NiO electrode was deposited on YSZ electrolyte by spin coat process and firing at $1300^{\circ}C$. Pt electrode was applied on the other side of the electrolyte to compare the polarization characteristics with those by NiO during electrolysis. The $H_2$ evolution rate was also monitored by measuring the electromotive force of Lambda probe and calculated by thermodynamic consideration. At low current density, Pt showed lower cathodic polarization and thus higher current efficiency than Ni, but the oxidation of Ni into NiO caused the increase of anodic resistance with increasing current density. High overpotential induced high power consumption to produce hydrogen by electrolysis.

• Composites Research
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• v.27 no.4
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• pp.123-129
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• 2014

Ceramic matrix composites (CMCs) consist of such reinforcements as carbides, nitrides, borides and oxides, which have high melting points, low density, high modulus and high strength, for the purpose of increasing toughness. These materials are used for heat shielding systems for aerospace vehicles, high-temperature gas turbine combustion chambers, turbine blades, stator vane parts, etc. Oxide CMCs are used for the components of burner and flame holder and the high-temperature gas duct. CMCs are also applied to brake disks, which are subjected to severe thermal shock, and slide bearing parts under heavy loads. The research and development of the CMC are progressed for the strategic purpose in defense and energy industry; for instance, for aerospace applications in the U.S., and for hyper-speed aircraft, gas turbines, and atomic fissions in U.S., Japan, and Europe.

• Journal of Astronomy and Space Sciences
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• v.31 no.4
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• pp.325-333
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• 2014

We are motivated by both the accumulating evidence for the connection of solar variability to the chemistry of nitrogen oxide in the atmosphere and recent finding that the Galactic cosmic-ray (GCR) influx is associated with the solar north-south asymmetry. We have analyzed the measured pH in precipitation over the 109 stations distributed in the United States. We have found that data of pH in precipitation as a whole appear to be marginally anti-correlated with the solar asymmetry. That is, rain seems to become less acidic when the southern hemisphere of the Sun is more active. The acidity of rain is also found to be correlated with the atmospheric temperature, while not to be correlated with solar activity itself. We have carried on the analysis with two subsamples in which stations located in the east and in the west. We find that the pH data derived from the eastern stations which are possibly polluted by sulfur oxides and nitrogen oxides are not correlated with the solar asymmetry, but with the temperature. On the contrary, the pH data obtained from the western stations are found to be marginally anti-correlated with the solar asymmetry. In addition, the pH data obtained from the western stations are found to be correlated with the solar UV radiation. We conclude by briefly pointing out that a role of the solar asymmetry in the process of acidification of rain is to be further examined particularly when the level of pollution by sulfur oxides and nitrogen oxides is low.

• Journal of the Korean Ceramic Society
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• v.41 no.2
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• pp.151-157
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• 2004

Because of the excellent thermal and chemical properties of mullite and cordierite as the stable oxide ceramic materials, they were widely used from engineering materials to electronic materials. Notwithstanding of their high demands, mullite was synthesised because it is not existed in nature. It is also difficult to produce cordierite of fine powder with high purity due to the narrow range of synthetic temperature. Mullite was synthesised by solid state reaction. However, synthesized mullite has been inhomogeneous. Because of the facts, various synthetic methods have been studied so far including sol-gel method. The purpose of this study is to synthesis mullite and cordierite of fine powder with high purity at the lower temperature by solution-polymerization route using PVA as a polymer carrier, which is an economical method by using low cost materials. As a result, mullite and cordierite were produced with mono crystal phase at 1200$^{\circ}C$ and 1250$^{\circ}C$, respectively, and their surface area over 20 ㎡/g.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.11 no.2
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• pp.111-120
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• 1998

In this paper, the $(SrPb)(CaMg)TiO_3$ ceramics with paraelectric properties were fabricated by the mixed oxide method. It was investigated that which the variation of contents of $Bi_2O_3{\cdot}3TiO_2$ effects on structural, dielectrical and electrical properties of specimens. As a result, the grain size were grown with increasing the contents of $Bi_2O_3{\cdot}3TiO_2$. The relative dielectric constants were increased up to 4[mol%] of $Bi_2O_3{\cdot}3TiO_2$, and decreased more or less at a low temperature in the specimens which had more than. But the temperature coefficient. of capacitance were showed ${\pm}25$[%]. The dielectric loss were less than 0.05 in all specimens which had more than 4[mol%] of $Bi_2O_3{\cdot}3TiO_2$. In order to investigate the behavior of charged particles, the characteristics of electrical conduction were measured. As a result, the conduction current was divided into the three steps as a function of DC electric field. The first step was Ohmic region due to ionic conduction, below 15[kV/cm]. The second step was showed a saturation which seems to be related to a depolarizing field occuring in field-enforced ferroelectric phase, between 15[kV/cm] and 40[kV/cm]. The third step was attributed to Child's law related to space charge which injected from electrode, above 40[kV/cm].

• Proceedings of the Materials Research Society of Korea Conference
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• 2010.05a
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• pp.19.2-19.2
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• 2010

Printed electronics using printing process has broadened in all respects such as electrics (lighting, batteries, solar cells etc) as well as electronics (OLED, LCD, E-paper, transistor etc). Copper is considered to be a promising alternative to silver for printed electronics, due to very high conductivity at a low price. However, Copper is easily oxidized, and its oxide is non-conductive. This is the highest hurdle for making copper inks, since the heat and humidity that occurs during ink making and printing simply accelerates the oxidation process. A variety of chemical treatments including organic capping agents and metallic coating have been used to slow this oxidation. We have established synthetic conditions of copper nanoparticles (CuNPs) which are resistant to oxidation and average diameter of 20 to 50nm. Specific resistivity should be less than $4\;{\mu}{\Omega}{\cdot}cm$ when sintered at lower temperature than $250^{\circ}C$ to be able to apply to conductive patterns of FPCBs using ink-jet printing. Through this study, the parameters to control average diameter of CuNPs were found to be the introduction of additive agent, the feeding rate of reducing agent, and reaction temperature. The CuNPs with various average diameters (58, 40, 26, 20nm) could be synthesized by controlling these parameters. The dispersed solution of CuNPs with an average size of 20 nm was made with nonpolar solvent containing 3 wt% of binder, and then coated onto glass substrate. After sintering the coated substrates at $250^{\circ}C$ for 30 minutes in nitrogen atmosphere, metallic copper film resulted in a specific resistivity of $4.2\;{\mu}{\Omega}{\cdot}cm$.

• Journal of the Korean institute of surface engineering
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• v.29 no.6
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• pp.766-772
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• 1996

Undoped $SnO_x$ thin films were deposited on Si(100) substrate by using reactive ioassisted deposition technique (R-IAD). In order to investigate the effect of initial oxygen content and heat treatment on the oxidation state and crystalline structure of tin oxide films, $SnO_x$ thin films were post-annealed at 400~$600^{\circ}C$ for 1 hr. in a vacuum ~$5 \times 10^{-3}$ -3/ Torr or were directly deposited on the substrate of $400^{\circ}C$ and the relative arrival ration ($Gamma$) of oxygen ion to Sn metal varied from 0.025 to 0.1, i.e., average impinging energy ($E_a$) form 25 to 100 eV/atom. As $E_a$ increased, the composition ratio of $N_ON{sn}$ changed from 1.25 to 1.93 in post-annealing, treatment and 1.21 to 1.87 in in-situ substrate heating. In case of post-annealing, the oxidation from SnO to $SnO_2$ was closely related to initial oxygen contents and post-annealing temperature, and the perfect oxidation of $SnO_2$ in the film was obtained at higher than $E_a$=75 eV/atom and $600^{\circ}C$. The temperature for perfect oxidation of $SnO_2$ was reduced as low as $400^{\circ}C$ through in-situ substrate heating. The variation of the chemical state of $SnO_x$ thin films with changing $E_a$'s and heating method were also observed by Auger electron spectroscopy.

• Fire Science and Engineering
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• v.21 no.1 s.65
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• pp.90-97
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• 2007

Combustion characteristics and toxicity of combustion gas of wallpaper samples were analyzed to evaluate the fire risk of wallpaper furnished in living space. In this study ash residue ratio was measured with high temperature electric furnace, and thermal analysis was carried out with TGA. Combustion time and smoke concentration were measured with cone heater and combustion gas analyzer. Smoke density of samples was measured using smoke chamber of ASTM E 662. The experimental results were showed as followings. Pyrolysis of silk wallpaper started at lower temperature compared to the other samples. It means that the silk wallpaper can be ignited at low heat flux and will have more fire risk than the others. Ignition time by radiation heat flux of silk wallpaper is shorter compared to the other samples, so evacuation time must be reduced. In the case of vinyl coated silk wall paper, carbon mono oxide concentration is the highest and the toxicity and damage effect to consciousness was stronger compared to the other samples. Smoke density of silk wall paper and fire retardant mixed coated silk wall paper were very high due to vinyl coating.