• Korean Journal of Materials Research
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• v.28 no.12
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• pp.709-713
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• 2018

To improve the etch rate of $Si_3N_4$ thin film, $H_2SiF_6$ is added to increase etching rate by more than two times. $SiO_3H_2$ is gradually added to obtain a selectivity of 170: 1 at 600 ppm. Moreover, when $SiO_3H_2$ is added, the etching rate of the $SiO_2$ thin film increases in proportion to the radius of the wafer. In $Si_3N_4$ thin film, there is no difference in the etching rate according to the position. However, in the $SiO_2$ thin film, the etching rate increases in proportion to the radius. At the center of the wafer, the re-growth phenomenon is confirmed at a specific concentration or above. The difference in etch rates of $SiO_2$ thin films and the reason for regrowth at these positions are interpreted as the result of the flow rate of the chemical solution replaced with fresh solution.

• Korean Journal of Metals and Materials
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• v.50 no.9
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• pp.653-657
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• 2012

In this study, a molybdenum disilicide ($MoSi_2$) coating process was investigated by hydrogen reduction and Si-pack cementation. At first, the metallic Mo coating was carried out by hydrogen reduction of $MoO_3$ powder at $750^{\circ}C$ for various holding times (1, 2, 3 h) in hydrogen atmosphere. A $4.3{\mu}m$ thick metallic molybdenum thin film was formed at 3 h. $MoSi_2$ was obtained by Si-pack cementation on molybdenum thin film through hydrogen reduction processing. It was carried out using $Si:Al_2O_3:NH_4Cl=5:92:3$ (wt%) packs at $900^{\circ}C$ for various holding times (30, 60, 90 min) in Ar atmosphere. When the holding time was 90 min, a $MoSi_2$ layer was coated successfully and a $15.4{\mu}m$ thickness was observed.

• Journal of Welding and Joining
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• v.14 no.6
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• pp.93-100
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• 1996

Effect of a flux composition on weld metal toughness in submerged arc welding with 60kgf/$\textrm{mm}^2$ grade C-Mo type wires was investigated and interpreted in terms of weld metal microstructure and hardenability. Flux workability was also studied by characterizing a weld bead profile. Compared to other weld metals, .weld metal used alumina basic flux with nickel showed lowest oxygen content, highest hardenability and the most acicular ferrite. The highest impact toughness of that weld metal, however, was attributed to the tough matrix due to the nickel rather than to the larger amount of acicular ferrite. Manganese silicate flux had better workability than alumina basic flux, showing broader welding conditions resulting in a depth-to-width ratio of 0.5. The composition of oxides in the weld metal was dependent on the flux composition, showing MnO-SiO$_2$-TiO in manganese silicate flux and MnO-SiO$_2$-Al$_2$O$_3$-TiO in alumina basic flux. MnO-SiO$_2$composition in both oxides was similar to a tephroite.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07b
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• pp.799-802
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• 2003

[ $LaNiO_3$ ](LNO) thin films were deposited on various substrates as Si and $Al_2O_3$ by sol-gel process using lanthanum nitrate and nickel acetate. The structure and orientation of the films were characterized by X-ray diffraction. The orientation factors of films on Si(100), Si(111), $SiO_2/Si(100)$ and $Al_2O_3$were 97%, 63%, 73%, and 24% respective. The conductivity was $7.6{\times}10^{-3}{\Omega}{\cdot}cm$ with 10 times coating at Si(100) substrate.

• Journal of Plant Biology
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• v.30 no.3
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• pp.181-187
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• 1987

Copper inhibited PSII-mediated O2 evolution (H2OlongrightarrowDCIP, H2OlongrightarrowSiMo) but not PSImediated O2 uptake(DCIP. Asc.longrightarrowMV) in isolated Chinese cabbage chloroplasts. Copper toxicity on PSII-mediated O2 evolution was higher at alkaline condition than at acidic condition and was inhanced by light illumination after copper treatment. The increased toxicity by light illumination was not recovered by subsequent dark treatment. The inhibitory effect of copper on H2OlongrightarrowDCIP reaction was higher than that on H2OlongrightarrowSiMo reaction. This result suggests that there may be another inhibitory site of copper on PSII other than water oxidizing side of PSII.

• Journal of IKEEE
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• v.21 no.3
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• pp.252-255
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• 2017

$Mo_xW_{1-x}Si_2$ heaters were fabricated by self-propagating high-temperature synthesis (SHS) process and post sintering process. To validate the reliability of the $Mo_xW_{1-x}Si_2$ heaters, the accelerated life test (ALT) was conducted, and then lifetime to $Mo_xW_{1-x}Si_2$ heaters was estimated by using Minitab programs. Also, the failure analysis of $Mo_xW_{1-x}Si_2$ heaters after ALT was performed through electrical and structural properties. As the results, it was confirmed that the dominant failure mode of $Mo_xW_{1-x}Si_2$ heaters is the crack formation in heaters and the delamination of protective $SiO_2$ layers.

• Journal of Ocean Engineering and Technology
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• v.16 no.6
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• pp.60-64
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• 2002

This paper describes the machining characteristics of the MoSi$_2$--based composites through the process of electric discharge drilling with various tubular electrodes. In addition to hardness characteristics, microstructures of Nb/MoSi$_2$laminate composites were evaluated from the variation of fabricating conditions, such as preparation temperature, applied pressure, and pressure holding time. MoSi$_2$-based composites have been developed in new materials for jet engines of supersonic-speed airplanes and gas turbines for high-temperature generators. These high performance engines may require new hard materials with high strength and high temperature-resistance. Also, with the exception of grinding, traditional machining methods are not applicable to these new materials. Electric discharge machining (EDM) is a thermal process that utilizes a spark discharge to melt a conductive material. The tool electrode is almost -unloaded, because there is n direct contact between the tool electrode and the work piece. By combining a non-conducting ceramic with more conducting ceramic, it was possible to raise the electrical conductivity. From experimental results, it was found that the lamination from Nb sheet and MoSi$_2$ powder was an excellent strategy to improve hardness characteristics of monolithic MoSi$_2$. However, interfacial reaction products, like (Nb, Mo)SiO$_2$and Nb$_2$Si$_3$formed at the interface of Nb/MoSi$_2$, and increased with fabricating temperature. MoSi$_2$composites, with which a hole drilling was not possible through the conventional machining process, enhanced the capacity of ED-drilling by adding MbSi$_2$, relative to that of SiC or ZrO$_2$reinforcements.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.8 no.4
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• pp.532-538
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• 1998

Emerald ($3BeO{\cdot}Al_2O_3{\cdot}6SiO_2:Cr^{3+}$) single crystal was grown by temperature gradient reflux method with using Korean natural beryl. The flux of lithium-molibudenium-vanadium oxide system was made by means of mixing the 2 sort of flux which were differently melted $Mo_3-Li_2O$ and $V_2O_5-Li_2O$ each other. The optimum composition of flux was 3 mole ratio of molibudenium. vanadium oxides to lithium oxide ($(MoO_3+V_2O_5)/Li_2O$), flux additives were substituted more less then 0.2 mole% of $K_2O$ or $Na_2O$ to the $Li_2O$ amount. The melting concentration of mixing beryl material was 3~10% content to the flux, that of $Cr_2O_3$ color dopant was 1% to the beryl amount. In the crystal growing apparatus with temperature gradient in the 3 zone furnace which was separated into the block of melt, growth and return, the solution have got to circulate continuously between $1100^{\circ}C$ and $1000^{\circ}C$ in steady state. When thermal fluctuation was treated to during 2 hrs once on a day at 950~$1000^{\circ}C$ in growth zone, the supersaturation solution was maintained, controled and emerald single crystal can be grown large crystal which was prevented from the nucleation of microcrystallite. The preferencial growth direction of hexagonal columnar emerald single crystal was the c(0001) plane of botton side and vertical to the m(1010) plane of post side.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.30 no.5
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• pp.200-207
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• 2020

MoSi₂, (Mo_1/2W_1/2)Si₂, and WSi₂ powders were synthesized by self-propagating high-temperature synthesis (SHS) method. The synthesized powders were heat-treated at 500, 1,000, 1,200, 1,300, 1,400, 1,500 and 1,600℃ in ambient atmosphere. Oxidation of Mo-W silicide powder was found at low temperature of 500℃. XRD structure analysis and DTA/TG data showed that MoO₃ was formed with 500℃ heat treatment for 1 hour, and that it was α-cristobalite phase that was formed with 1200℃ heat treatment, not α-quartz phase which is commonly found and stable at room temperature. Existence of W accelerated decomposition at both low and high temperature. Fully sintered MoSi₂ and (Mo_1/2W_1/2)Si₂ specimen did not show decomposition or weight loss by oxidation, with 1 hour heat treatment at either low or high temperature. Notably, it was difficult to sinter WSi₂ because of oxidation reaction at low temperature.

• Korean Journal of Materials Research
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• v.5 no.8
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• pp.921-928
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• 1995

MoSi$_2$heating elements were fabricated using MoSi$_2$, powder prepared by SHS. Their apparent density, electrical resistivity, bending strength and victors hardness were measured as a function of sintering temperature, time and the amount of ceramic additives. The additives were A1$_2$O$_3$, SiO$_2$and bentonite which were added as a plastisizer. The electrical resistivity of MoSi$_2$decreased with the increase in the apparent density as expected. It decreased when the additives were added and the increase was the largest for the case of SiO$_2$. The bending strength and hardness decreased when the grain size becomes larger which is opposite to the expectation from the Hall-Petch type relation. Instead, they showed inverse proportionality with the volume fraction of pores probably in an exponential manner. The strength and hardness also decreased with the additives.