• Corrosion Science and Technology
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• 제9권5호
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• pp.175-186
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• 2010

The auto industry is demanding more ductile high-strength steel grades to build lighter and stronger car bodies. The hot-dip galvanizing problems of these new steel grades are creating a demand for an improved method to control zinc wettability. The simplest way to improve zinc wettability on industrial hot-dip galvanizing lines is to increase the strip immersion temperature at zinc bath entry for enhancing the aluminothermic reaction. However, this practice increases the reactivity due to overheating the zinc in the snout which induces the formation of brittle Fe-Zn compounds at the strip/coating interface with the formation of higher amounts of dross in the zinc bath and snout contamination. Thus, this simple practice can only be utilized for short production periods of one to two hours without deteriorating coating quality. This problem has been solved by employing a technique that allows the use of a higher and attuned strip immersion temperature at zinc bath entry while still maintaining a constantly low zinc bath temperature. This has been proven to provide the solution for both the improved wettability and a significant reduction in the amounts of dross in the zinc bath.

• 한국주조공학회지
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• 제35권6호
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• pp.178-184
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• 2015

Due to excellent abrasion resistance the high-chrome white irons are widely used in mining and mineral industries. Minor variation of carbon content in 28% chrome white iron resulted in difference in primarily solidified microstructure. Sub-eutectic (hypoeutectic) composition led to formation of primarily solidified dendrites. Formation of primarily solidified dendrites which were supersaturated with carbon and chrome also caused precipitation of fine secondary carbides that are different from relatively large plate type $M_7C_3$ carbides in the eutectic structure. Small portion of primarily solidified dendrite expected to contribute significantly to the improvement of abrasion resistance of the white iron because the dendrites provided mechanical support to carbides. The relative fraction of primary dendrite increased with reduction of carbon content from the eutectic composition. The increased fraction of primary dendrite increased hardness value of the white irons.

• Journal of Periodontal and Implant Science
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• 제36권1호
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• pp.223-237
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• 2006

The purpose of the present study was to evaluate the effect of bone graft materials including deproteinized bovine bone(DBB), demineralized freeze-dried bone(DFDB), freeze-dried bone(FDB) on bone formation in guided bone regeneration using perforated titanium membrane(TM). 16 adult male rabbits(mean BW 2kg) were used in this study and 4 rabbits allotted to each test group. Intramarrow penetration(diameter 6.5mm) was done with round carbide bur on calvaria to promote blood supply and clot formation in the wound area. The test groups were devided into 4 groups as follows: TM only(test 1), TM +DBB(test 2), TM +DFDB(test 3), TM +FDB(test 4). Perforated titanium membrane was contoured in rectangular parallelepiped shape(0.5mm pore diameter, 10mm in one side, 2mm in inner height), filled the each graft material and placed on the decorticated carvaria. Perforated titanium membrane was fixed with resorbable suture materials. The animals were sacrificed at 2, 8 weeks after the surgery. Non-decalcified preparations were routinely processed for histologic analysis. The results of this study were as follows: 1. Perforated titanium membrane was biocompatible. 2. Perforated titanium membrane had capability of maintaining the space during the healing period but invasion of soft tissue through the perforations of titanium membrane decreased the space available for bone formation. 3. In test 1 group without bone graft material, the amount of bone formation and bone maturation was better than other test groups. 4. Among the graft materials, the effect of freeze-dried bone on bone formation was best. 5. In the test groups using deproteinized bovine bone, demineralized freeze-dried bone, bone formation was a little. The spacemaking capability of the membrane may be crucial for bone formation. The combined treatment with the perforated titanium membrane and deproteinized bovine bone or demineralized freeze-dried bone failed to demonstrate any added effect in the bone formation. Minimization of size and numbers of perforations of titanium membrane or use of occlusive titanium membrane might be effective to acquire predictable results in the vertical bone formation.

• 한국정밀공학회지
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• 제26권2호
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• pp.16-20
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• 2009

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2002년도 춘계학술대회 논문집
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• pp.1043-1046
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• 2002

In this paper, drill tests were carried out by modifying drill geometry for burr minimization. Final objective of this study is to develop compatible drill shape for minimization of burr formation. These experimented results with modified drill are measured with laser sensor after performing drilling with variable material. Simultaneously, the cutting force and the torque of various drill geometry have been observed with same cutting condition to judge drill stability. As a result, burr was minimized in step drill with 75$^{\circ}$ step angle at every material.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 춘계학술대회 논문집
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• pp.1281-1284
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• 2005

In the micro electrochemical machining (ECM), unfavorable oxide/passive layer formation and overall corrosion of electrodes must be prevented. Generally, the stainless steel electrode corrodes, passivates or dissolves in the electrochemical cell according to the electrode potential. Therefore, the electrode must maintain stable potential. The stable electrode potentials of tool and workpiece were determined with the potentiodynamic polarization test and verified experimentally from the point of machining stability and machined surface quality.

• 한국전기전자재료학회논문지
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• 제23권11호
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• pp.837-842
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• 2010

This paper describes the crystallinity, growth rate, and surface morphology of single crystalline 3C-SiC (cubic silicon carbide) thin films grown with several carbonization conditions such as temperature, $C_3H_8$ flow rate, time. In case of carbonization, an increase in the carbonization temperature caused a increase in the size and numbers of unsealed void (big black spot) which decrease the crystallinity. In addition, optimal $C_3H_8$ flow rate made carbonization layer form well and prevented the formation of voids. Also, after a period of time, the growth of carbonization layer did not increase no more. The single crystalline 3C-SiC thin films on optimal carbonized Si substrate showed an improvement on the crystallinity, the growth rate, the roughness, and the carrier concentration.

• 한국분말재료학회지
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• 제6권4호
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• pp.320-324
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• 1999

The formation, microstructure and properties of novel ceramic composite materials manufactured by active-filler-controlled polymer pyrolysis were investigated. In the presence of active filler particles such as transition metals, bulk components of various geometry could be fabricated from siliconorganic polymer. Molybdenum- and tungsten-filled polymer suspensions were prepared and their conversion to ceramic composites by annealing in $CH_4$ atmosphere were studied. Dimensional change. porosity and phase distribution (filler network) were analyzed and correlated to the resulting hardness values. Molybdenum and tungsten as active filler were carburized completely to $Mo_2C$, $W_2C$ and WC in $CH_4$ atmosphere. Consequently, microcrystalline composites with the filler reaction products embedded in a silicon oxycarbide glass matrix were formed. Hardness was increased with increasing carburization and reached 8.6-9.5 GPa in the specimen pyrolyzed in $CH_4$ atmosphere.

• 한국분말재료학회지
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• 제2권2호
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• pp.149-157
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• 1995

In this study, an attempt was made to fabricate TiAl as well as its in situ composite via combustion synthesis. The processing variable of the combustion synthesis which include aluminum content and the heating rate were found to affect the combustion temperature. The combustion temperature measured, however, was lower than the melting temperature of TiAl and the reaction product were found to include incomplet reaction products. Carbon was added in order to increase the combustion temperature as well as to form in situ reinforcements. The reaction products showed homogeneous microstructures with carbide phases formed within indicating that the addition of carbon increased the combustion temperature above the melting temperature of TiAl.

• 한국세라믹학회지
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• 제31권12호
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• pp.1588-1598
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• 1994

The SiC/MoSi2 composite materials were fabricated by infiltrating the mixture of molybdenum disilicide and metal silicon(MoSi2+Si=100) to a porous compact of silicon carbide and graphite under the vacuum atmosphere of 10-1 torr. The specimen were oxidized in dry air under 1 atm at 130$0^{\circ}C$~150$0^{\circ}C$ for 240 hours. The oxidation behavior was evaluated by the weight gain and loss per unit area of the oxidized samples. Also, SEM and XRD analysis of the oxidized surface of the samples were carried out. With increasing the MoSi2 content and oxidation temperature, the passive oxidation was found. The trend of weight gain of all samples was followed the parabolic rate law with the formation of a protective layer of cristobalite on the surface.