• Journal of Korea Foundry Society
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• v.32 no.2
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• pp.86-90
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• 2012

Aluminium-silicon based casting alloys have received an attention for high electrical and thermal conductivity applications, however relatively low conductivity of Al-Si alloys often limits the application. Efforts have been made to develop new high conductivity aluminium casting alloys containing no or less silicon. In this study Al-Zn-Fe based alloys were selected as the new alloys, and the effect of Mg additions on their properties and casting characteristics were investigated. As the magnesium content was increased, the tensile strength of Al-2Zn-0.2Fe based alloy was remarkably increased, while the electrical conductivity was deteriorated. It was observed that the fluidity of the alloys was generally inversely proportional to the Mg content but the hot cracking resistance was rather proportional to it. Cooling curve analyses were carried out to measure the actual solidification range and dendrite coherency temperature.

• Journal of Korea Foundry Society
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• v.32 no.6
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• pp.284-288
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• 2012

The effects of Si content on the variation of microstructure and processing window of austempered ductile cast iron were investigated. Four different Si contents between 2.42 and 3.37 wt.% were used. The influence of silicon on the microstructure and processing window of these materials were studied. Austenitizing was performed at $900^{\circ}C$ for 60min and austempering temperature were both $340^{\circ}C$ and $360^{\circ}C$ and austempering time were for 4min upto 119min and for 5min upto 160min respectively. After heat treatment, the evolution of stage I and stage II were performed by optical metallography, XRD, hardness test. The results showed that $t_2$ was delayed as Si contents was increased due to the fact that Si retarded the formation of cementite ($Fe_3C$). The high silicon content promoted the stability of the metastable two-phase combination of austenite and ausferrite.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.141-141
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• 2010

The effect of thermal anneal on the characteristics of structural properties and the enhancement of luminescence and photovoltaic (PV) characteristics of silicon-rich silicon-nitride films were investigated. By using an ultra high vacuum ion beam sputtering deposition, B-doped silicon-rich silicon-nitride (SRSN) thin films, with excess silicon content of 15 at. %, on P-doped (n-type) Si substrate was fabricated, sputtering a highly B doped Si wafer with a BN chip by N plasma. In order to examine the influence of thermal anneal, films were then annealed at different temperature up to $1100^{\circ}C$ under $N_2$ environment. Raman, X-ray diffraction, and X-ray photoemission spectroscopy did not show any reliable evidence of amorphous or crystalline Si clusters allowing us concluding that nearly no Si nano-cluster could be formed through the precipitation of excess Si from SRSN matrix during thermal anneal. Instead, results of Fourier transform infrared and X-ray photoemission spectroscopy clearly indicated that defective, amorphous Si-N matrix of films was changed to be well-ordered thanks to high temperature anneal. The measurement of spectral ellipsometry in UV-visible range was carried out and we found that the optical absorption edge of film was shifted to higher energy as the anneal temperature increased as the results of thermal anneal induced formation of $Si_3N_4$-like matrix. These are consistent with the observation that higher visible photoluminescence, which is likely due to the presence of Si-N bonds, from anneals at higher temperature. Based on these films, PV cells were fabricated by the formation of front/back metal electrodes. For all cells, typical I-V characteristic of p-n diode junction was observed. We also tried to measure PV properties using a solar-simulator and confirmed successful operation of PV devices. Carrier transport mechanism depending on anneal temperature and the implication of PV cells based on SRSN films were also discussed.

• Journal of Korea Foundry Society
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• v.3 no.3
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• pp.174-180
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• 1983

The matrix changes and graphite formation in high manganese cast iron (Fe-12Mn-3.5C) are studied with increasing nickel and silicon content. Also, the decomposition of carbides and graphite precipitation are studied by adequate heat treatment.The results obtained in this work are as follows. 1. In high manganese cast iron, fine flakes graphite appeared by adding 5 wt% nickel and A-type flakes graphite can be obtained by adding 7 wt% nickel. 2. Nodular graphite are obtained by graphite spheroidizing treatment with same melt. 3. In high manganese cast iron containing 7 wt% nickel, full austenitic matrix with nodular graphite can be achieved by water quenching after 10 hours' solution heat treatment at $1050^{\circ}C$ in case of containing 2.0 wt% silicon, and 6 hours' at the same temperature in case of containing 2.5 wt% silicon.

• Tribology and Lubricants
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• v.16 no.6
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• pp.477-483
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• 2000

Rolling contact fatigue (RCF) tests were performed for two kinds of commercial silicon nitride balls using 4-Ball rolling contact fatigue life tester under EHL condition (Λ=8.9) and boundary lubrication condition (Λ=0.2). All the test balls were finished up to the dimensional accuracy of Grade 5 defined in KS B 2001 (Steel Balls for Ball Bearings) with a size of 8.731 mm. RCF tests were then conducted under the initial theoretical maximum contact stress 6.63 GPa and the spindle speed 10,000 rpm. All the test balls were not failed until 3.75 $\times$ 107 contact cycles and wear tracks of test balls were not conspicuous under EHL condition (Λ= 8.9). In the operations of low lambda regime (Λ= 0.2), all the test balls were surface damaged and high rolling wear resistance was achievable in fully densified using MgO 1 wt% and HIPed balls. Rolling wear of silicon nitride balls under boundary lubrication condition depend mainly on grain size and intergranular phase content of silicon nitride balls.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.5 no.4
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• pp.332-342
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• 1995

The important factors of reaction conditions in sol-gel transition of silicon alkoxide solution have been reviewed and discussed on the basis of Raman study. Various factors such as type of catalyst, alkoxide, solvent, drying control chemical additive and water content affect the conversion mechanism in sol-gel process.

• Transactions of the Korean hydrogen and new energy society
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• v.5 no.1
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• pp.51-57
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• 1994

Compaction techniques of hydrogen storage alloy 'powders, to solve the problems due to disintegration during the cyclic hydriding and dehydriding, by using polytetrafluoroethylene (PTFE) and silicon sealant as a polymer binder were studied. Optimum conditions of compaction were as follows. Binder content, 10 % for PTFE and 5 % for silicon sealant ; particle size of alloy powders, $-25{\mu}m$ ; compacting pressure, $4ton/cm^2$. Compacts obtained were easily activated and had a good strength even after 30 cycles of hydriding and dehydriding. PTFE added compacts showed very good rate capability, however, in the silicon added compacts hydrogen absorption rate was somewhat slow because of higher elasticity and adhesiveness of the binder.

• Journal of the Korean Ceramic Society
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• v.31 no.5
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• pp.561-571
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• 1994

For the preparation of SiC composite, the properties of reaction sintering in the SiC-C-Si-Ti system with the titanium contents variation were investigated. Either the case of titanium additions or the case of direct infiltration of titanium in SiC+C preform, the newly formed fine-grained $\beta$-SiC, which was reacted from the molten silicon with graphite, was intergranulated between the original $\alpha$-SiC particles. Also titanium disilicide (TiSi2) was discontinuously formed isolated pocket in silicon matrix. The amount of titanium disilicide was gradually increased as titanium content increase. With the results of hardness and fracture toughness measurement, SiC-titanium disilicide (TiSi2) composite represented high properties compared with the system of the infiltrated pure silicon.

• Bulletin of the Korean Chemical Society
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• v.10 no.1
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• pp.30-32
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• 1989

Traces of nine elements, gold, arsenic, cobalt, chromium, copper, europium, hafnium, sodium and antimony in commercially available silicon crystals were determined by the instrumental neutron activation analysis using the single comparator method. The values of the concentrations of these elements in both single and polycrystals were found to decrease significantly to a low limiting level by simply washing and etching surface contaminants having been introduced during various steps of sample preparation and irradiation. However, the chromium levels in polycrystals were not easily decreased, these depending upon the cutting tools employed. The Sb-doped content in each semiconductor has been compared with the associated quantities such as the concentration and the conductivity range given by the sample donor. Uncertainty in the sodium analysis due to the fission neutron reaction by silicon itself was discussed.

• Textile Coloration and Finishing
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• v.33 no.4
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• pp.309-316
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• 2021

Due to the rigid nature of the silicon carbide fiber(SiC), fiber damage occurs from the friction during the carding process. This damage not only lowers the spun yarn yield, but also lowers the heat resistance of the spun yarn, so that ultra-high heat resistant yarn cannot be manufactured. Therefore, in the carding process where the most friction between fiber and machine(wire, etc.) occurs, some factors were modified and tested, and as a result of measuring the change in physical properties, fiber damage decreased due to the wire angle or wire density, resulting in improved yield. The test method used to measure the yield of SiC fiber was the carbonization method, and the content of SiC fibers was calculated using the remaining amount after carbonization. Carbonization test was performed at air condition, 700℃, and for 2 hours. Analysis by SEM-EDX showed that the carbide was consistent with the composition of the SiC fiber.