• Proceedings of the KIEE Conference
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• 1999.11d
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• pp.1011-1014
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• 1999

An on-board monitoring system for an automobile emission gas has a test chamber remote from the automobile's engine exhaust gas stream: apparatus for supplying the chamber with sampled exhaust gases. A single hydrocarbon sensor exposed to the exhaust gas in the chamber to render a signal responsive to the hydrocarbon. The conductive ions in emission gas was checked by the HC sensor in test chamber. A preferred application includes hydrocarbons in an automotive exhaust gas stream by exposing a transition porous alumina($Al_{2}O_{3}$) ceramic based sensor to the same exhaust gas stream. By combining the electrical signal, a measure of hydrocarbons can be provided.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.10a
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• pp.231-234
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• 2002

Ultrasonic machining technology has been developed over recent years for the manufacture of cost-effective and quality-assured precision parts for several industrial application such as optics, semiconductors, aerospace, and automobile. Ultrasonic machining process is an efficient and economical means of precision machining of ceramic materials. The process is non-thermal, non-chemical and non-electric and hardly creates changes to the mechanical properties of the brittle materials machined. This paper describes the characteristics of the micro-hole of $\textrm{Al}_2\textrm{O}_3$ by ultrasonic machining with tungsten carbide tool. The effects of various parameters of ultrasonic machining, including abrasives, machining force and pressure, on the material removal rate, hole quality, and tool wear presented and discussed. The ultrasonic Machining of micro-holes in ceramics has been under taken and the machining mechanism in the ultrasonic machining of ceramics based on the fracture-mechanics concept has been analyzed.

• Proceedings of the KIEE Conference
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• 2003.07c
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• pp.1529-1531
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• 2003

Thick film mechanical sensors can be categorized into four main areas piezoresistive, piezoelectric, piezocapastive and mechanic tube. In this areas, the thick film strain gage is the earliest example of a primary sensing element based on the substrates. The latest thick film sensor is used various pastes that have been specifically developed for pressure sensor application. The screen printing technique has been used to fabricate the pressure sensors on alumina substrate($Al_2O_3$). Thick film capacitive of strain sensing characteristics are reported and dielectric paste based on (Ti+Ba) materials. The electric property of dielectric paste has been studied and exhibit good properly with good gage factor comparable to piezoresistive strain gage. New piezocapacitive strain sensor was designed and tested. The output of capacitive value was good characteristics.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.207-208
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• 2006

In this experimental work, the development of a multicomponent binder system based on high density polyethylene (HDPE) and paraffin wax for Powder Injection Molding of Alumina $(Al_2O_3)$ parts was carried out. The optimum composition of the injection mixture was established through mixing torque measurements and a rheological study. The maximum powder loading was 58 vol%. The miscibility of organic components and the optimum injection temperature was evaluated by thermal characterization of binder and feedstock. The thermal debinding cycle was developed on the basis of thermogravimetrical analysis of the binder. After sintering the densities achieved were closed to 98% of the theoretical one.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.495-496
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• 2006

The kneading process and formulations of feedstock obviously affect the quality of MIM products. In the present work, the rheological behaviour of the composite MIM feedstock, metal matrix (Cu) with few additions of ceramic powders $(Al_2O_3)$, was measured by a self-designed/manufactured simple capillary rheometer. Experimental results show that the distribution between powders and binder is more uniformly when blending time increased. Though high powder loading will increase the feedstock viscosity, the fluidity reveals relatively stable through the load curves of extrusion. Besides, the temperature-dependence of viscosity of the feedstock approximately follows an Arrehnius equation. Basing on Taguchi's method, the kneading optimization conditions and the rheological model of the feedstock were established, respectively.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1349-1352
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• 2005

This paper is to investigate a defect for thermal barrier coating layers by acoustic emission method in 4-point bending test. The two-layer thermal barrier coating is composed of $150\mu{m}\;CoNiCrAlY\;bond\;coating\;by\;vacuum\;plasma\;spray(VPS)\;process\;and\;250\mu{m}\;ZrO_2-8wt%Y_2O_3$ ceramic coating layer by air plasma spray(APS) process on Inconel-718. The specimen prepared by cyclic thermal test(500, 1000, 2000cycle) at $1050^{\circ}C$ The AE monitoring system is composed of PICO type sensor, a wide band pre-amplifier(40dB), PC and AE DSP(16/32 PAC) board. The AE event, amplitude, Cumulative energy and count of coating specimens is evaluated according to cyclic thermal test.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.07a
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• pp.44-45
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• 2005

Both $Al_2O_3$ and $SiO_2$ nanopowders were ball-milled to break large agglomerates$(500nm\sim10{\mu}m$). To improve the dispersion of ball-milled nanoparticles in transformer oil, surface modification was performed with oleic acid(OA). The modified nanoparticles were examined by the particle size analyzer, electron microscope, Infrared spectroscopy and stability analyser. Particle Size distributions were measured for ball-milled particles, and the results were compared with the size distribution of primary particles. FTIR results indicated that hydrophobicity of modified nanoparticles was due to the chemical reaction between hydroxyl groups of particle surface and oleic acid. The dispersion stability of surface-modified nanoparticles was quite good in transformer oil.

• Corrosion Science and Technology
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• v.17 no.3
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• pp.101-108
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• 2018

AA7010 is an Al-Zn-Mg-Cu alloy containing Zr, developed as an alternate to traditional AA7075 alloy owing to their high strength combined with better fracture toughness. It is necessary to improve the corrosion resistance and surface properties of the alloy by incorporating plasma electrolytic oxidation (PEO) method. AA7010-T7452 aluminum alloy has been processed through the forging route with multi-stage working operations, and was coated with $10{\mu}m$ thick $Al_2O_3$ ceramic aluminina coating using the plasma electrolytic oxidation (PEO) method. The corrosion, stress corrosion cracking (SCC) and nano-mechanical behaviours were examined by means of potentiodynamic polarization, slow strain rate test (SSRT) and nano-indentation tests. The results indicated that the additional thermomechanical treatment during the forging process caused a fully recrystallized microstructure, which lead to the poor environmental cracking resistance of the alloy in 3.5% NaCl solution, despite the overaging treatment. Although the fabricated PEO coating improved general corrosion resistance, the brittle nature of the coating did not provide any improvement in SCC resistance of the alloy. However, the hardness and elastic modulus of the coating were significantly higher than the base alloy.

• Journal of the Korean institute of surface engineering
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• v.52 no.2
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• pp.58-61
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• 2019

The aim of this study is to quantitatively demonstrate the possibility of heat transfer by thermal radiation by comparing heat transfer by conventional heat transfer and radiation by radiation. 1) The heat transfer was measured by using filler of TIM material with low thermal conductivity (CuS). As a result, heat transfer was easier than ceramic with high thermal conductivity ($Al_2O_3$ and $Si_3N_4$). 2) The reason for this is thought to be that the infrared wave due to radiation of the air diaphragm has moved easily. 3) From the above results, the heat dissipation of the TIM material indicates the possibility of heat transfer by thermal radiation.

• Journal of the Korean Ceramic Society
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• v.53 no.2
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• pp.206-214
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• 2016

This study aims to produce dolomitic hydraulic lime (D-NHL) using domestic low grade dolomitic limestone and to determine the effect of adding blast furnace slag (BFS) and gypsum as part of an investigation of the hydration properties of D-NHL to increase the mechanical properties. The main mineral phases of D-NHL as a hydraulic lime binder were $Ca(OH)_2$, $Mg(OH)_2$, $C_2S$, $C_3S$, and MgO residues. $Ca(OH)_2$ transformed into $CaCO_3$ in D-NHL paste over the period of 28 days, but the carbonation of $Mg(OH)_2$ and the hydration of $C_2S$ did not occur until hydration, after 28 days. Through an investigation of the hydration properties of D-NHL pastes mixed with BFS and gypsum, Al-based compounds such as calcium aluminate hydrates ($C_4AH_{13}$) and ettringite were observed at early hydration time. The compressive strength was improved due to the increased quantities of these hydration products. These results show that good performance results from the application of dolomitic hydraulic lime and that a high value product can be made from domestic waste materials.