• Korean Journal of Materials Research
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• v.18 no.5
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• pp.283-288
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• 2008

The effect of sintering aids and glass-frit on the densification and resistivity of silver paste was investigated in an effort to enhance the sintered density and electrical conductivity of the silver electrode. To prepare Pb-free silver paste for use at low sintering temperatures, two commercial silver powders ($0.8\;{\mu}m$ and $1.6\;{\mu}m$ in size) and 5wt.% lab-synthesized nanoparticles (30-50 nm in size) as a sintering aids were mixed with 3 wt.% or 6 wt.% of glass frit ($Bi_2O_3$-based) using a solvent and three roll mills. Thick films from the silver paste were prepared by means of screen printing on an alumina substrate followed by sintering at $450^{\circ}C$ to $550^{\circ}C$ for 15 min. Silver thick films from the paste with bimodal particles showed a high packing density, high densification during sintering and low resistivity compared to films created using monomodal particles. Silver nanoparticles as a sintering aid enhanced the densification of commercial silver powder at a low sintering temperature and induced low resistivity in the silver thick film. The glass frit also enhanced the densification of the films through liquid phase sintering; however, the optimum content of glass frit is necessary to ensure that a dense microstructure and low resistivity are obtained, as excessive glass-frit can provoke low conductivity due to the interconnection of the glass phase with the high resistivity between the silver particles.

• Journal of Korean Ophthalmic Optics Society
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• v.11 no.2
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• pp.85-89
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• 2006

To research of the improved mechanical properties of materials for spectacle lens cutting, SiC and TiC were used as the main powder. Also, $Al_2O_3$ and $Y_2O_3$ was included as a sintering additive. The weight ratio of the alumina($Al_2O_3$) to yttria($Y_2O_3$) was set to 1:1. The materials for spectacle lens cutting were fabricated by hot-pressing at $1810^{\circ}C$ for 1h and subsequently annealed at $1860^{\circ}C$ for 3, 6 and 12h to initiated grain growth. The longer annealing time is, the bigger the grain size is. The microstructures were observed by scanning electron microscopy (SEM). The SEM images were quantitatively analyzed by image analysis (Image-Pro Plus, Media Cybernetics, Maryland, U.S.A.). Crack deflection by elongated SiC grains was most frequently observed as the dominant toughening mechanism. Crack deflection was generally observed for elongated SiC grains with aspect ratio(AR) > 2.5 and grain thickness < $2.3{\mu}m$. Crack bridging was also observed as one of the operating toughness mechanism.

• Journal of the Korean institute of surface engineering
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• v.49 no.6
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• pp.530-538
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• 2016

There is a close relationship between the performance and the heat generation of the electronic device. Heat generation causes a significant degradation of the durability and/or efficiency of the device. It is necessary to have an effective method to release the generated heat. Based on demands of the printed circuit board (PCB) manufacturing, it is necessary to develop a robust and reliable plating technique for substrates with high thermal conductivity, such as alumina ($Al_2O_3$), aluminium nitride (AlN), and silicon nitride ($Si_3N_4$). In this study, the plating of metal layers on an insulating silicon nitride ($Si_3N_4$) ceramic substrate was developed. We formed a Pd-$TiO_2$ adhesion layer and used APTES(3-Aminopropyltriethoxysilane) to form OH groups on the surface and adhere the metal layer on the insulating $Si_3N_4$ substrate. We used an electroless Ni plating without sensitization/activation process, as Pd particles were nucleated on the $TiO_2$ layer. The electrical resistivity of Ni and Cu layers is $7.27{\times}10^{-5}$ and $1.32{\times}10^{-6}ohm-cm$ by 4 point prober, respectively. The adhesion strength is 2.506 N by scratch test.

• Journal of the Korean Ceramic Society
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• v.35 no.1
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• pp.5-10
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• 1998

Mullitization in a multicomponent oxide system(alumina-kaolin-quartz-feldspar-talc) was studied as a function of sintering temperature from 1200 to 1500$^{\circ}C$ based upon a quantitative X-ray diffraction analysis. In the present study mullite grew as wiskers and its formation reaction showed characteristic there stages as follows In the first stage(1255-1295$^{\circ}C$) an appreciable mullitization(nucleation) occurred while corun-dum dissolution into glass (increasing glass content ) limited the rate of the reaction. At 1295-1335$^{\circ}C$ (second state) the reaction was significantly enhanced with a considerable glass consumption and with no appreciable change in corundum content. Finally (above 1335$^{\circ}C$) the reaction rate was attenuated re-markably with an apparent decrease in glass consumption rate. The impingement of mullite whiskers by oth-er whiskers and crystals was speculated to cause mullite growth in thickness direction with a slow growth rate resulting in the diminished reaction rate in the final stage.

• Journal of the Korean Ceramic Society
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• v.28 no.1
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• pp.19-19
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• 1991

Fracture of Al2O3 tubes for different loading path under combined tension/torsion was investigated. Macroscopic directions of crack propagation agreed well with the maximum principal stress criterion, independent of the loading path. However, fracture strength from the proportional loading test(τ/σ= constant) showed either strengthening or weakening compared to that from uniaxial tension, depending on the ratio τ/σ. The Weibull theory was capable to predict the strengthening of fracture strength in pure torsion, but not the weakening in the proportional loading condition. The strengthening or weakening of fracture strength in the proportional loading condition was explained by the effect of shear stresses in the plane of randomly oriented microdefects. Finally, a new empirical fracture criterion was proposed. This criterion is based on a mixed mode fracture criterion and experimental data for fracture of Al2O3 tubes under combined tension/torsion. The proposed fracture criterion agreed well with experimental data for both macroscopic directions of crack propagation and fracture strengths.

• Korean Chemical Engineering Research
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• v.56 no.5
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• pp.752-760
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• 2018

The lowering of temperature for combustion of diesel particulate matters (or diesel soot) is one of the important tasks in automotive industry that is searching for a way to meet up "high-fuel efficiency, low-emission" standard. In this study, it was discussed how the use of ozone over platinum-based catalyst promotes a low-temperature soot oxidation occurred at $150^{\circ}C$. The use of platinum catalyst did not increase oxidation rate largely but was very effective in improving the selectivity of carbon dioxide. The pre-oxidation of NO into $NO_2$ using ozone was rather crucial in improving the oxidation rate of soot at $150^{\circ}C$.

• Transactions of the Korean hydrogen and new energy society
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• v.14 no.2
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• pp.155-170
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• 2003

$Cu-Ce/{\gamma}-Al_2O_3$ based catalysts were prepared and tested for selective oxidation of CO in a $H_2$-rich stream(1% CO, 1% $O_2$, 60% $H_2$, $N_2$ as balance). The effects of Cu loading and weight ratio(=Cu/(Cu+Ce)) upon both activity and selectivity were investigated upon the change in temperatures, It was also examined how the activity and selectivity of catalysts were varied with the presence of $CO_2$ and $H_2O$ in the reactant feed. Among the various Cu-Ce catalysts with different catalytic metal composition, Cu-Ce(4 : 16 wf%) /${\gamma}-Al_2O_3$ catalyst showed the highest activity(>$T_{99}$) and selectivities(50-80%) under wide range of temperatures($175-220^{\circ}C$). However, in the Cu-Ce(4 : 16 wt%)/ ${\gamma}-Al_2O_3$, the presence of $CO_2$ and $H_2O$ in the reactant feed decreased the activity and the maximum activity(>$T_{99}$) in terms of reaction temperature moved by about $25^{\circ}C$ toward higher temperature, the $T_{>99}$ window was seen between $210-230^{\circ}C$ (selectivity 50-75%). From $CO_2-/H_2O-TPD$, it can be concluded that the main cause for the decrease in catalytic activity may be attributed to the blockage of the active sites by competitive adsorption of water vapor and $CO_2$ with the reactant at low temperatures.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.05c
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• pp.45-48
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• 2003

The polishing mechanism of W-CMP process has been reported as the repeated process of passive layer formation by oxidizer and abrasion action by slurry abrasives. Thus, it is important to understand the effect of oxidizer on tungsten passivation layer in order to obtain higher removal rate (RR) and very low non-uniformity (NU%) during W-CMP process. In this paper, we investigated the effects of oxidizer on W-CMP process with three different kinds of oxidizers, such as $H_2O_2$, $Fe(NO_3)_3$, and $KIO_3$. In order to compare the removal rate and non-uniformity of three oxidizers, we used alumina-based slurry of pH 4. According to the CMP tests, three oxidizers showed different removal mechanism on tungsten surface. Also, the microstructures of surface layer by AFM image were greatly influenced by the slurry chemical, composition of oxidizers. The difference in removal rate and roughness of tungsten surface are believed to caused by modification in the mechanical behavior of $Al_2O_3$ abrasive particles in CMP slurry. Our stabilized slurries can be used a guideline and promising method for improved W-CMP process.

• Resources Recycling
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• v.26 no.1
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• pp.11-15
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• 2017

The amount of the wood chip ash is expected to increase continuously as demand of wood chip-based heat and electricity increase. Thus, there is increased interest in wood chip ash utilization. In this study, as a program of utilization in wood chip ash, the physical and chemical properties of wood chip ashes generated from a combined heat and power plant were investigated. The chemical analysis showed that the main contents of wood chip ash are composed of silica, alumina and alkali. A possibility of reuse as secondary cementitious materials was investigated by the analysis of strength activity index, and compared with coal ash. The highest value for Strength activity index of wood chip fly ash was 78% at 90 days curing time. This result revealed that wood chip fly ash has the potential to be utilized as the admixture for cementitious material.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.1275-1276
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• 2007

For fabrication of $BaTiO_3$ system Ferroelectric thick films, (Ba,Sr,Ca)$TiO_3$ (BSCT) powders, prepared by using the alkoxide-based sol-gel method, were doped $MnCO_3$ as acceptor and $Dy_{2}O_{3}$ as donor. $MnCO_3$ and $Dy_{2}O_{3}$-doped (Ba,Sr,Ca)$TiO_3$ thick films were fabricated by screen printing techniques on high purity alumina substrates. The structure and dielectric properties were investigated with variation of $Dy_{2}O_{3}$ amount. As a result of the differential thermal analysis(DTA), exothermic peak was observed at around $670^{\circ}C$ due to the formation of the polycrystalline perovskite phase. All the BSCT thick films, sintered at $1420^{\circ}C$ for 2h, showed the typical XRD patterns of perovskite polycrystalline structure and no pyrochlore phase was observed. The average grain size and thickness of specimens no doped with $Dy_{2}O_{3}$ was 1.32mm, 52mm, respectively. The relative dielectric constant decreased and dielectric loss increased with increasing amount of $Dy_{2}O_{3}$ dopant, the values of the BSCT thick films no doped with $Dy_{2}O_{3}$ were 4043 and 0.4% at 1 kHz, respectively. The relative dielectric constant gradually decreased in the measured frequency range from 0.1 to 100 kHz