• 한국건축시공학회지
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• 제18권3호
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• pp.305-312
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• 2018

This study is about the development of a non-sintered binder (NSB) which does not require a sintering process by using the industrial by-products Phosphogypsum (PG), Waste Lime (WL) and Granulated Blast Furnace Slag (GBFS). In this report, through SEM analysis of the NSB paste hardening body, micropore analysis of paste using the mercury press-in method and microstructure observation were executed to consider the influence of the formation of the pore structure and the distribution of pore volume on strength, and the following conclusions were reached. 1) Pore structure of NSB paste of early age is influenced by hydrate generation amount by GBFS and activator. 2) Through observing the internal microstructure of NSB binder paste, it was found that the strength expression at early age due to hydration reaction was achieved with a large amount of ettringite serving as the frame with C-S-H gel generated at the same time. It was confirmed that C-S-H gel wrapped around ettringite, and as time passed, the amount generated continually increased, and C-S-H gel tightly filled the pores of hardened paste, forming a dense network-type web structure. 3) For NSB-type cement, the degree of formation of gel pores below $10{\mu}m$ had a greater influence on strength improvement than simple pore reduction by charging capillary pores, and the pore size that had the greatest effect on strength was micropores with diameter below $10{\mu}m$.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2004년도 하계학술대회 논문집 Vol.5 No.1
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• pp.551-554
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• 2004

Bi-2223 HTS tapes are used widely for application of superconducting power systems. However there are need the properties of high strength and low AC loss. Two kinds of Bi-2223 HTS tapes with different Ag sheath were used to know the effect of sheath alloying for the strength and the resistivity. The workability and reaction degree of superconducting phase at Bi-2223 HTS tapes were investigated. We designed conventional type-Ag/alloy and double sheathed mono filament type-Ag/alloy/alloy in order to increase the strength and resistivity of matrix in Bi-2223 HTS tapes. The effect of axial strain and thermal cycling on the critical current was investigated for the Bi-2223 HTS tapes. Because the workability of double sheath Bi-2223 HTS tape was lower than one sheath Bi-2223 HTS tape, it was need additional softening treatment. Bi-2223 formation reaction was decreased by Ag alloy matrix during sintering process. Two kinds of Bi-2223/Ag tapes with different Ag sheath were used to know the effect of sheath alloying for the tensile strain. Critical current is drastically decreased for Ag/alloy and Ag/alloy/alloy sheathed tapes at tensile strain above 0.24 % and 0.34 %, respectively. This result showed that mechanical strength was increased over than 40 % by introduce double sheath at mono filament stage.

• 한국재료학회지
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• 제17권10호
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• pp.560-566
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• 2007

AlN plates were fabricated by hot pressing at $1700-1900^{\circ}C$ using yttria and alumina (3 and $10\;{\mu}m$ particle size) powders as additives and characterized: density, thermal conductivity, transverse rupture strength, and grain size measurement by SEM and EDS. Density values of $3.31-3.34\;g/cm^3$ are largely attributed to hot pressing of powder mixtures in carbon mold under $N_2$ atmosphere which caused effective degree of oxygen removal from yttrium-aluminate phase expected to form at $1100^{\circ}C$. The grain size of hot pressed AlN was almost homogeneous, with size approximately from 3.2 to $4.0\;{\mu}m$ after hot pressing. $Al_2O_3$ powder of $3\;{\mu}m$ particle size resulted in better transverse rupture strength and finer grain size compared to $10\;{\mu}m$ $Al_2O_3$ powder. The thermal conductivity of AlN ranged between $83-92.7\;W/m{\cdot}K$ and decreased with $Al_2O_3$ addition. Fine grain size is preferred for better mechanical properties and thermal conductivity.

• 대한치과보철학회지
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• 제22권1호
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• pp.51-68
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• 1984

The purpose of this study is primarily to test the use value of tooth ash as an alternative material of the synthetic hydroxyapatite. For this purpose the author performed the experimental study to investigate the phsyical properties of sintered tooth ash and its histocompatibility in vitro. The tooth ash was made by incinerating procedure at $650^{\circ}C,\;750^{\circ}C,\;850^{\circ}C,\;950^{\circ}C\;and\;1050^{\circ}C$ respectively. The composition of tooth ash was analyzed and X-ray diffraction was done. The experimental specimens were molded to the cylinderical form 1 cm high, 1 cm in diameter under the pressure of $1000kg/cm^2$, which were divided into two groups; the one is sintered tooth ash at $1100^{\circ}C$ and the other is fired mixture of tooth ash and dental porcelain mixed to the weight ratio of 4:6, 5:5, 6:4 and 7:3. The physical propoerties of the sintered specimens were examined and their microstructure was observed under the Scanning Electron Microscope. The results obtained were as followings: 1. The difference of the tooth ash composition depending on incinerating temperature was of no significance, but the $CO_2$ disappeared from $950^{\circ}C$. 2. X-ray diffraction showed the tooth ash was mainly composed of hydroxyapatite and a small amount of - white lockite. But phase transformation was not disclosed. 3. The microstructure of the sintered specimens of the ashed tooth powder was of no difference in the structure and grain size accompanying the ashed temperature, but sintering ability seemed to be the best in the specimen incinerated at $950^{\circ}C$. 4. There was good wettability in the mixed sintered specimens of the ashed tooth powder and the porcelain powder. 5. The compressive strength of the sintered specimens of the tooth ash incinerated at $950^{\circ}C$ was the highest with $589.75kg/cm^2$ and the porosity and the absorption were the lowest as well. 6. The mixed sintered specimens of the tooth ash and porcelain powder was good in the physical properties in the case of mixed weight ratio of 6:4. 7. The animal fibroblast cultures with porcelain showed increase in the cell number, whereas the tooth ash showed a small degree of growth inhibition. But the difference of cell multiplication efficiency between control cultures and test cultures with tooth ash was not observed.

• 한국자기학회지
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• 제21권2호
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• pp.77-82
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• 2011

우리 삶의 질을 좌우하는 전자기 기기의 고기능화, 자동화, 소형화 추이에 따라 사용량이 급격히 증가하고 있는 연자성 소재로서 가장 널리 사용되고 있는 전기강판과 에너지 고효율화라는 시대의 요구에 따라 새롭게 부상되고 있는 연자성 복합 분말 소재에 대해 각 연자성 소재 분야에서 철손 제어 인자 및 이들 인자들의 제어 방안에 대해 문헌을 고찰했다. 전기강판에서는 히스테리시스 손실을 낮추기 위해 정련공정을 통해 자구이동을 방해하는 결함을 제거하고 결정립의 크기를 최적화하고 있으며, 와전류 손실의 감소를 위해 합금첨가원소를 통해 비저항을 높이고 판재의 두께를 박판화하고 있다. 이와 동시에 코팅을 통해 자구의 이동이 용이하도록 응력의 방향 및 크기를 제어하며, 압연기술과 열처리 기술을 통해 집합조직을 최적화하여 고투자율 및 저철손을 동시에 충족시켜 나가고 있다. 연자성 복합 분말 소재의 경우, 분말 표면의 복합화를 통해 철계 조성, 코팅, 윤활재 및 바인더, 성형 및 열처리 조건 등에 복합적으로 의존하는 연자성 코어의 최종 자기특성을 제어하고 있다. 온간 및 다단 성형과 같은 새로운 성형공정, 2단 소둔/자성 열처리와 같은 소둔 조건, 나노결정질, 비정질 및 벌크 비정질 등과 같은 새로운 조성, 적절한 코팅층의 변수들을 최적화할 경우, 연자성 복합 소재의 자성특성은 향상될 것으로 기대된다.

• 한국가스학회지
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• 제22권1호
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• pp.26-36
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• 2018

기존 건식 개질 반응에 사용되는 니켈 기반 촉매 공정은 활성화 온도가 높고, 촉매 표면의 활성점에 탄소 침착 및 금속 소결 현상 등의 문제점이 있다. 이에 본 연구에서는 촉매공정에 DBD 플라즈마 공정이 결합된 촉매+플라즈마 공정을 이용하여 뷰테인 건식 개질 반응 특성을 조사하고 기존 촉매 공정과 비교 분석하였다. 촉매의 특성을 파악하기 위해 비표면적 분석기, XRD, SEM 및 TEM 등을 사용하여 물리 화학적 특성을 조사 하였다. $580^{\circ}C$에서 $10%Ni/{\gamma}-Al_2O_3$촉매를 사용한 경우 촉매+플라즈마 공정의 경우 촉매 단독 공정에 비해 이산화탄소와 뷰테인 전환율이 각각 27%, 39%향상되었다. 촉매+플라즈마 공정의 경우 플라즈마에 의해 생성된 다양한 활성종의 영향으로 이산화탄소와 뷰테인 전환율 및 생성되는 수소 농도가 증가하였으며, 뷰테인 건식 개질 반응 과정에서 플라즈마에 의해 니켈 촉매의 크기가 감소하고 분산도가 증가하여 반응 효율이 향상되는 것으로 판단되었다.

• 천문학회보
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• 제46권2호
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• pp.57.4-58
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• 2021

Asteroids have undergone various processes such as impacts, space weathering, and thermal evolution. Because they expose their surfaces to space without atmosphere, these evolutional processes have been recorded directly on their surfaces. The remote-sensing observations have been conducted to reveal these evolutional histories of the target asteroids. For example, crater and boulder distributions are unambiguous evidence for past nondestructive impacts with other celestial bodies. Multiband and spectroscopic observations have revealed space-weathering history (as well as compositions). Whereas most physical quantities have been examined intensively using spacecraft and telescopes, only a little has been studied on "the grain size". It is one of the fundamental physical quantities for diagnosing the collisional and thermal history of asteroids. Our group has conducted polarimetric research of asteroids (as well as Moon [1]) to determine the particle size and further investigate the evolutional histories of target asteroids [2],[3]. For example, the existence of regolith on an S-type asteroid, Toutatis, was suggested almost twenty years before space exploration [4]. Moreover, we reported that near-Sun asteroids indicate a signature of submillimeter grains, which could be created by a thermal sintering process by solar radiation [5]. However, it is important to note that in-situ polarimetry has not been reported on the asteroid surface, although the Korean Lunar Exploration Program aims to do polarimetry on the lunar surface [6]. Therefore, it is expected that the polarizer mounted on the Korean Apophis spacecraft can make the first estimate of the grain size and its regional variation over the Apophis surface. In this presentation, we outline research of S-type asteroid surfaces through remote-sensing observations and consider the role of polarimetry. Based on this review, we consider the purpose, potentiality, and strategy of the polarimetry using the onboard device for the Apophis spacecraft. We will report a possible polarization phase curve of Apophis estimated from ordinary chondrites and past observational data of S-type asteroids, taking account of the space weathering effect. Based on this estimation, we will consider the strategy of how to determine the particle size (and space weathering degree) of the Apophis surface. We will also mention the detectability of dust hovering on the surface.