• Journal of the Korean Crystal Growth and Crystal Technology
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• v.7 no.3
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• pp.377-383
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• 1997

Yttria-stabilized TZP alloyed with pentavalent oxides $(Ta_2O_5,\;Nb_2O_5)$ were fabricated by the conventional sintering method at $1500^{\circ}C$ in air to construct the simplified ternary phase diagram. The phase stability of tetragonal -$ZrO_2$ from the quasi-binary system $ZrO_2-YTa(Nb)O_4$, which do not transform to monoclinic-$ZrO_2$ even for a wide range of grain size and annealing temperature, was investigated to determine composition region of the non-transformable $t-ZrO_2$ solid solution$(NT_{ss})$. Phase stability of $NT_{ss}$ was probably due to the enhanced stability of $_YTa(Nb)O4$ having the tetragonal fergusonite structure. It was experimentally found that mixtures having $NT_{ss}$ alloyed with $T_{ss}$ by weight%% showed both excellent phase stability of $t-ZrO_2$ and fracture toughness even though the calculated composition of the mixture /was located outside $NT_{ss}$ composition region.

• Korean Journal of Materials Research
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• v.4 no.4
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• pp.472-476
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• 1994

Phase transformation of PbO-precursor prepared from $Pb(NO_{3})_{2}$ by precipitation technique was observed by TG-DTA, XRD, FT-IR, and Raman spectral analysis. PbO-precursor was derived from an aqueous solution of $Pb(NO_{3})_{2}$ at $45^{\circ}C$ and pH of 9.0. The precipitate showed it to be the mixture of hydrous lead oxynitrate and lead hydroxynitrate. With increasing heat-treatment temperature ranging up to $560^{\circ}C$, the precursor changed to $3Pb(NO_{3})_{2}$ . 7Pb0, $Pb(NO_{3})_{2}$. 5Pb0 and PbO(litharge), in turn. Finally, it transformed to massicot form of PbO above $560^{\circ}C$.

• Proceedings of the Materials Research Society of Korea Conference
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• 1993.05a
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• pp.64-65
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• 1993

MPB 조성영역인 Zr/Ti=52/48의 composite ceramic target을 사용하여 RF magnetron sputtering 방법으로 기판온도 약 30$0^{\circ}C$에서 RZT 박막을 Pt/Ti/Si 기판위에 증착시켰다. 안정상인 perovskite 구조를 형성시키기 위하여 PbO분위기에서 furnace annealing 과 Repid thermal annealing을 실시하여 열처리 방법에 따른 상형성 및 계면반응과 그에 따른 전기적 특성을 고찰 하였다. Pt 의 두께가 250$\AA$인 경우 furnace annealing 시 $650^{\circ}C$에서 perouskite 상이 형성되었으나 Pt층이 산소의 확산을 방지하지 못하여 상부의 Ti 층이 TiOx로 변태하였으며 하부의 Ti는 Si 과 반응하여 Ti-silicide 롤 변태하였다. 또한 75$0^{\circ}C$,60sec 인 경우 Pt 층의 응집화가 관찰되어 하부전극으로서 적용이 적절하지 못하다. 급속열처리를 실시한 경우에도 마찬가지로 Ti 층이 TiOx 와 silicide 층으로 변태되었다. Pt의 두께가 1000$\AA$인 경우에도 250$\AA$와는 달리 RTA 시 (III)방향으로 Furace annealing 시(001)방향으로 우선 성장하였다. 이는 Ti(001), P(111),PZT(111)면의 lattic mismatch 가 매우 작은데다 RTA 시 계면반응이 거의발생하지 않아 PZT 박막이 (111) 방향으로 우선 성장한 것으로 보인다. Furnace annealing 경우는 심한 계면반응이 발생하여 Pt층에 어느 정도 영향을 주었기 때문에 우선성장 방향이 바뀌었다구 생각한다.

• Applied Microscopy
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• v.31 no.3
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• pp.245-256
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• 2001

The morphological characteristics of spermatogenic cells during the spermiogenesis of Paradoxornis webbiana were studied by transmission electron microscope. Spermiogenesis of P. webbiana was divided into ten phase. The chromatin granules became fibrous granules at the Golgi phase, gradually condensed at the cap phases, condensed as a stick at the acrosomal phase, and finally, a perfect nucleus was formed at the maturation phase. The formation of sperm tail began at the early Golgi phase, and completed at the late maturation phase. In particular, the dense materials existed in the sperm neck, which is wedged between the tip of segmented columns and the first mitochondria of the middle piece. The axone in the neck were surrounded by the dense materials. The axonema in spermatozoon contains a 9+2 arrangement of microtubules: 9 doublets, and 2 central single microtubules. Mitochondrial bundles of middle piece were composed of a pair of arms, which surrounded the axone of the middle piece by the $15^{\circ}$ angled-helical structure. The outer membrane of mitochondria were surrounded by microtubules in plasma membrane of the sperm. The undulating membrane had a helical structure, and the sperm plasma membrane was surrounded by undulating membrane.

• Korean Journal of Materials Research
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• v.5 no.7
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• pp.858-868
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• 1995

Texture development and martensitic phase transformation, on rolling, are compared in two Hadfield's steels, one having low carbon content(0.65wt% C), the other high carbon content(1.35wt%). In spite of small difference in stacking fault energy(about 2 mJm$^{-2}$ ) between two Hadfield's steels, the differences in texture development are observed. In low carbon steel, the textures developed are similar to those of low stacking fault energy metals in low strain range. However, the abnormal textures such as {111} , {110} <001> are strongly developed at high strain, which are due to the disturbance of u martensite in the development of textures formed at the packets of shear bands or at the grain boundaries. In contrast to low carbon Hadfield's steel( LCHS), the texture development of high carbon Hadfield's steel(HCHS) is simitar to those of low stacking fault energy metals in the whole strain range. This may be due to the fact that the amount of deformation induced martensite was small, as observed by A.C. magnetic susceptibility and iron particle tests.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.03a
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• pp.201-201
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• 2003

• Journal of the Speleological Society of Korea
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• v.37 no.38
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• pp.46-78
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• 1994

동굴의 안전진단은 일반적인 민사사항에 대비하는 안전진단 만은 아니다. 즉, 동굴의 생태환경의 보전을 위한 보전책도 강구하며 특히 동굴생물의 생태유지 등의 실태를 조사하는데 그 목적이 있다고 하겠다. 사실상 동굴은 소중한 천연적인 자연자원이다. 최근에 이르러 세계의 모든 나라에서는 이와같은 지하세계의 탑승을 위한 관광개발이 활발하게 이루어지고 있다. 예를 들면 일본에서는 전국에 총93개소의 동굴들이 공개된 관광동굴로 개발되어 있다.(중략)

• 기계와재료
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• v.22 no.2
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• pp.48-58
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• 2010

전산 모사 기술은 재료의 물리 화학적 현상을 규명하고 재료의 물성을 예측하는 측면에서 새로운 재료를 개발하기 위한 효율적인 방법론으로 자리를 잡아가고 있다. 철강 재료는 다양한 합금 원소를 포함하고 있고 복잡한 상변태 및 자성 거동을 나타내 전산 모사 기술의 가장 적용하기 어려운 재료로 인식되어 왔으나, 최근 컴퓨터 기술의 발전과 새로운 전산 모사 방법론의 개발에 힘입어 전산 모사 기법의 적용 사례가 늘고 있다. 이 글에서는 철강 재료에 대한 전산 모사의 연구 동향을 기술하고 여러 적용 사례에 대하여 소개하고자 한다.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.33 no.3
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• pp.171-175
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• 2000

The ultrastructures of germinal cells of male marsh clam, Corbicujar lena were studied. The mature sperm was primitive type, consisting of head, middle piece and tail. The mature sperm was whip-shaped and its head was divided into two parts; the acrosomal part shaped long hollow cone about $3{\mu}m$ in length and the sperm nuclear part shaped a long stick about $9\;{\mu}m$ in length. The posterior part of the sperm nuclear projected to centriole, The middle piece of the sperm-nuclear had four mitochondria and two centrioles. The sperm tail part had the 9+2 microtubular arrangement known as a typical pattern, During spermiogenesis, chromatin within sperm nuclear became fiberic materials by condensation.

• Journal of the Korean Magnetics Society
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• v.4 no.4
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• pp.347-354
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• 1994

The structural change and magnetic properties of mechanically milled Fe-N and Mn-Al alloy powders have been investigated by XRD, TEM, VSM, $M\"{o}ssbauer$ spectroscopy and inelastic neutron scattering measurements. During milling of ${\gamma}'-Fe_{4}N$ powders, and fcc ${\gamma}'-Fe_{4}N$ phase is transformed to a bct ${\alpha}'-Fe(N)$ phase by stress-induced martensitic transformation, being accompanied by an initial increase in saturation magnetization. During annealing the bct ${\alpha}'-Fe(N)$ nanocrystalline phase which is obtained by mechanical grinding for a long time, an ${\alpha}'-Fe_{16}N_{2}$ phase partially appears as an intermediate phase at 673~773 K, causing an increase in saturation magnetization. During milling of Mn-45, 70 and 85 at.% Al mixed powders, Al atoms are partially solubilized into an ${\alpha}-Mn$ phase. The Al supersaturated ${\alpha}-Mn-type$ phases change from paramagnetic to ferromagnetic : the saturation magnetization is 11 emu/g for the as-milled Mn-70 at.% Al powders. Moreover, by removing almost all Al atoms from the as-milled Mn-85 at.% Al powders using chemical leaching, the saturation magnetization increases up to 36 emu/g. The above bct ${\alpha}'-Fe(N)$ and ferromagnetic ${\alpha}-Mn$ type alloys are the magnetic materials found for the first time, by using the present mechanochemical process.