• Korean Journal of Materials Research
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• v.30 no.2
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• pp.61-67
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• 2020

BiFeO₃ with perovskite structure is a well-known material that has both ferroelectric and antiferromagnetic properties called multiferroics. However, leaky electrical properties and difficulty of controlling stoichiometry due to Bi volatility and difficulty of obtaining high relative density due to high dependency on the ceramic process are issues for BiFeO₃ applications. In this work we investigated the sintering behavior of samples with different stoichiometries and sintering conditions. To understand the optimum sintering conditions, nonstoichiometric Bi_1±xFeO_3±δ ceramics and Ti-doped Bi_1.03Fe_1-4x/3Ti_xO₃ ceramics were synthesized by a conventional solid-state route. Dense single phase BiFeO₃ ceramics were successfully fabricated using a two-step sintering and quenching process. The effects of Bi volatility on microstructure were determined by Bi-excess and Ti doping. Bi-excess increased grain size, and Ti doping increased sintering temperature and decreased grain size. It should be noted that Ti-doping suppressed Bi volatility and stabilized the BiFeO₃ phase.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.43 no.3 s.345
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• pp.9-14
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• 2006

The dependence of NBTI lifetime on the BEOL processes such as sintering gas type and passivation layer has been characterized in depth. Then, optimized BEOL process scheme is proposed to improve NBTI lifetime. NBTI showed degradation due to the plasma enhanced nitride (PE-SiN) passivation film and $H_2$ sintering anneal. Then, new process scheme of $N_2$ annealing instead of $H_2$ annealing prior to PE-SiN deposition is proposed. The proposed BEOL process flow showed that NBTI lifetime can be improved a lot without degradation of device performance and NMOS hot carrier reliability.

• Proceedings of the Materials Research Society of Korea Conference
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• 2012.05a
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• pp.56.2-56.2
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• 2012

Clinically-favored materials for bone regeneration are mainly based on bioceramics due to their chemical similarity to the mineral phase of bone. A successful scaffold in bone regeneration should have a 3D interconnected pore structure with the proper biodegradability, biocompatibility, bioactivity, and mechanical property. The pore architecture and mechanical properties mainly dependent on the fabrication process. Bioceramics scaffolds are fabricated by polymer sponge method, freeze drying, and melt molding process in general. However, these typical processes have some shortcomings in both the structure and interconnectivity of pores and in controlling the mechanical stability. To overcome this limitation, the rapid prototyping (RP) technique have newly proposed. Researchers have suggested RP system in fabricating bioceramics scaffolds for bone tissue regeneration using selective laser sintering, powder printing with an organic binder to form green bodies prior to sintering. Meanwhile, sintering process in high temperature leads to bad cost performance, unexpected crystallization, unstable mechanical property, and low bio-functional performance. The development of RP process without high thermal treatment is especially important to enhance biofunctional performance of scaffold. The purpose of this study is development of new process to fabricate ceramic scaffold at room temperature. The structural properties of the scaffolds were analyzed by XRD, FE-SEM and TEM studies. The biological performance of the scaffolds was also evaluated by monitoring the cellular activity.

• Journal of the Microelectronics and Packaging Society
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• v.14 no.4
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• pp.43-48
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• 2007

This study is focused on the effect of the surface properties for the post electrode, which is used in pad formation consisted of SMT such as IC, passive component, combined with fired LTCC substrate, We carried out the surface microstructure of sintered electrode and the basic reliability evaluations with sample fired by microwave sintering to solve the problems occurred in post electrode by electric sintering. We evaluated surface densification status of post electrode according to various conditions of microwave sintering. In additions, it is obtained strong effect on blister improvement of post electrode because of over-sintering and the insufficient out gas in bum out process. As a result of adhesion strength, we confirmed $44.3N/mm^2$ in microwave sintering and $34.5N/mm^2$ in electric sintering, respectively. This result will be used for the basic reliability test. Finally, microwave sintering seems to be economic in process time with 30 min compared to electric sintering with 10 hr. In terms of Mass production and efficiency, microwave sintering are excepted to be higher than electric sintering.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 1999.04a
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• pp.5-5
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• 1999

The Principal deficiency of the existing notion about the sintering-mixtures consists in the fact that almost no attention is focused on the Phenomenon of alloy formation during sintering, its connection with dimensional changes of powder bodies, and no correct ideas on the driving force for the sintering process in the stage of establishing chemical equilibrium in a system are available as well. Another disadvantage of the classical sintering theory is an erroneous conception on the dissolution mechanism of solid in liquid. The two-particle model widely used in the literature to describe the sintering phenomenon in solid state disregards the nature of the neighbouring surrounding particles, the presence of pores between them, and the rise of so called arch effect. In this presentation, new basic scientific principles of the driving forces for the sintering process of a two-component powder body, of a diffusion mechanism of the interaction between solid and liquid phases, of stresses and deformation arising in the diffusion zone have been developed. The major driving force for sintering the mixture from components capable of forming solid solutions and intermetallic compounds is attributed to the alloy formation rather than the reduction of the free surface area until the chemical equilibrium is achieved in a system. The lecture considers a multiparticle model of the mixed powder-body and the nature of its volume changes during solid-state and liquid-phase sintering. It explains the discovered S-and V-type concentration dependencies of the change in the compact volume during solid-state sintering. It is supposed in the literature that the dissolution of solid in liquid is realised due to the removal of atoms from the surface of the solid phase into the melt and then their diffusicn transfer from the solid-liquid interface into the bulk of liquid. It has been shown in our experimental studies that the mechanism of the interaction between two components, one of them being liquid, consist in diffusion of the solvent atoms from the liquid into the solid phase until the concentration of solid solutions or an intermetallic compound in the surface layer enables them to pass into the liquid by means of melting. The lecture discusses peculimities of liquid phase formation in systems with intermediate compounds and the role of the liquid phase in bringing about the exothermic effect. At the frist stage of liquid phase sintering the diffusion of atoms from the melt into the solid causes the powder body to grow. At the second stage the diminution of particles in size as a result of their dissolution in the liquid draws their centres closer to each other and makes the compact to shrink Analytical equations were derived to describe quantitatively the porosity and volume changes of compacts as a result of alloy formation during liquid phase sinteIing. Selection criteria for an additive, its concentration and the temperature regime of sintering to control the density the structure of sintered alloys are given.

• 한국연소학회:학술대회논문집
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• 2004.11a
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• pp.33-40
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• 2004

Combustion of coke/anthracite in an iron ore sintering bed is characterized quantitatively by introducing newly defined parameters related to propagation and thickness of combustion zone and maximum temperature. The parameters are obtained by sintering pot experiment and I-D, unsteady numerical model which treats solid material as multiple solid phases. Experiments and calculations are performed for various major operating parameters: air inlet velocity, different type of fuels which have different reactivity and diameter of the solid fuel. Effects of the operating parameters on the productivity and quality of the sintering process are investigated and evaluated quantitatively and the results show that optimized air supply rate and diameter of anthracite for replacement of coke can be obtained. This approach can be applied to other kinds of combustors for characterization of the combustion in the solid fuel beds.

• 한국신재생에너지학회:학술대회논문집
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• 2011.05a
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• pp.114.1-114.1
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• 2011

Electrical sintering of the front electrode for crystalline silicon solar cells was performed applying a constant DC current to the printed lines. Conducting lines were printed on glass substrate by a drop-on-demand (DOD) inkjet printer and silver nanoparticle ink. Specific resistance and microstructure of sintered silver lines and were measured with varying DC current. To find the relation between temperature increase with changing applied current and specific resistance, temperature elevation was also calculated. Sintering process finished within a few milliseconds. Increasing applied DC current, specific resistance decreased and grain size increased after sintering. Achieved minimum specific resistance is approximately 1.7 times higher than specific resistance of the bulk silver.

• Journal of Powder Materials
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• v.15 no.4
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• pp.271-278
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• 2008

Sintering behavior of iron nanopowder agglomerate compact prepared by slurry compaction method was investigated. The Fe nanopowder agglomerates were prepared by hydrogen reduction of spray dried agglomerates of ball-milled $Fe_2O_3$ nanopowder at various reduction temperatures of $450^{\circ}C$, $500^{\circ}C$ and $550^{\circ}C$, respectively. It was found that the Fe nanopowder agglomerates produced at higher reduction temperature have a higher green density compact which consists of more densified nanopowder agglomerates with coarsed nanopowders. The sintering behavior of the Fe nanopowder agglomerates strongly depended on the powder packing density in the compact and microstructure of the agglomerated nanopowder. It was discussed in terms of two sintering factors affecting the entire densification process of the compact.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.04a
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• pp.181-185
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• 1996

Rapid prototyping is becoming an increasingly importnat techniuqe involved in the design cycles of modern industry. The majority of the rapid prototyping systems currently available use photo-reactive resins and waxes as the raw materials. The models produced by these systems often have relatively poor mechanical and physical properties and as such have a limited application to the production of advance prototypes but are excellently suited to the manufacture of engineering prototyes. This work identifies the need to produed near production grade advance prototypes from a variety of metals and a novel prototyping process based on the techniques of selective laser sintering and conventional machining is proposed. The integration of a carbon dioxide laser and a conventional machine tool to create the opto-mechanical by multi-layer sintering and some of the problems involved are also discussed.

• Journal of the Korean Ceramic Society
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• v.27 no.4
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• pp.473-480
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• 1990

Low-voltage ZnO-based varistors were made by seed grain method at various sintering conditions. Their microstructure and electrical properties were investigated and comlpared with those of the ZnO varistors made by a conventional method at the same sintering condition. During the sintering process, the added seed ZnO grain rapidly grew to be a gaint grain(above 500$\mu\textrm{m}$) provinding easy current path. Therefore the breakdown voltage was lowered as much as the order of 1/10-1/5 in comparison to that of the varistor made by a conventional method. But the grain size of the giant ZnO was little influenced by sintering condition, so the breakdown voltate was also little influenced. The weight loss was decreased by the addition of the seed grain, because the giant grain decreased the evaporation area. Therefore the nonobmic property of the specimen made by seed grain method was little influencedby sintering condition. In this research the low-voltage varistor made by seed grain method showed the least leakage current when sintered at 1150$^{\circ}C$ for zero hour.