• 한국분말재료학회지
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• 제29권6호
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• pp.485-491
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• 2022

Lithium lanthanum titanium oxide (LLTO) is a promising ceramic electrolyte because of its high ionic conductivity at room temperature, low electrical conductivity, and outstanding physical properties. Several routes for the synthesis of bulk LLTO are known, in particular, solid-state synthesis and sol-gel method. However, the extremely low ionic conductivity of LLTO at grain boundaries is one of the major problems for practical applications. To diminish the grain boundary effect, the structure of LLTO is tuned to nanoscale morphology with structures of different dimensionalities (0D spheres, and 1D tubes and wires); this strategy has great potential to enhance the ion conduction by intensifying Li diffusion and minimizing the grain boundary resistance. Therefore, in this work, 0D spherical LLTO is synthesized using ultrasonic spray pyrolysis (USP). The USP method primarily yields spherical particles from the droplets generated by ultrasonic waves passed through several heating zones. LLTO is synthesized using USP, and the effects of each precursor and their mechanisms as well as synthesis parameters are analyzed and discussed to optimize the synthesis. The phase structure of the obtained materials is analyzed using X-ray diffraction, and their morphology and particle size are analyzed using field-emission scanning electron microscopy.

• Progress in Superconductivity
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• 제9권2호
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• pp.173-176
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• 2008

[ $MgB_2$ ] films grown by hybrid physical chemical vapor deposition under appropriate growth conditions commonly exhibit columnar grain structure. The grain boundaries between adjacent columnar grains have been reported to be good flux pinning centers. In this work, we measured the angular dependence of critical current density ($J_c$) and observed the enhanced flux pinning when an external magnetic field was aligned parallel to the columnar direction. This $J_c$ was almost comparable to the $J_c$ for intrinsic pinning case up to 1 T at low temperatures, indicating that grain boundary pinning is very effective. At high fields, however, $J_c$ decreased rapidly resulting from the fact that the density of flux pinning centers provided by grain boundaries was outnumbered by the flux density.

• 열처리공학회지
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• 제35권2호
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• pp.74-81
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• 2022

This study aims to mitigate the microstructural heterogeneity arising from the manufacture of magnesium alloy plates using the twin roll casting (TRC) process. Homogenization was introduced through hot rolling and heat treatment, followed by confirmation of observed changes in the microstructure. Following the TRC process, the hot rolled 2mm plate exhibited a dendritic cast structure tilted in the roll rotation direction, while central segregation were developed. This nonuniform structure and central segregation disappeared upon heat treatment, followed by recrystallization to form uniform and fine grains. Abnormal grain growth (AGG) was observed over the course of heat treatment; grains exhibiting AGG occupied up to 75% of the total area after having held the sample at 400℃ for 64 h. The formation of coarse grains was also observed during heat treatment at 340℃ over a relatively long duration, though the maximum grain size was significantly smaller than that corresponding to the heat treatment at 400℃. AGG in the 400℃ heat treatment occurred because of movement of the grain boundary, which had been fixed prior as a result of the grain boundary fixing effect of the precipitation phase. The re-dissolution of the Ca₂Mg₅Zn₅ precipitated phase over the long duration of the high-temperature annealing process caused the surrounding grains to disappear and regrow.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 추계학술대회 논문집 Vol.16
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• pp.615-618
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• 2003

To investigate the electrical fire identification due to conductor structure analysis of an electrical wire, we are studied by temperature heating test, over current test, short test and electric molten marks. And metal structure analysis of wire by short, we are found out increase in crystal grain with heating temperature. Structure of specimen at over current 300[%] occurred hardly structure formation and boundary of grain.

• 열처리공학회지
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• 제26권3호
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• pp.105-112
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• 2013

The microstructural changes of Fe-20Mn-12Cr-1Cu alloy have been studied during high temperature gas nitriding (HTGN) at the range of $1000^{\circ}C{\sim}1150^{\circ}C$ in an atmosphere of nitrogen gas. The mixed microstructure of austenite and ${\varepsilon}$-martensite of as-received alloy was changed to austenite single phase after HTGN treatment at the nitrogen-permeated surface layer, however the interior region that was not affected nitrogen permeation remained the structure of austenite and ${\varepsilon}$-martensite. With raising the HTGN treatment temperature, the concentration and permeation depth of nitrogen, which is known as the austenite stabilizing element, were increased. Accordingly, the depth of austenite single phase region was increased. The outmost surface of HTGN treated alloy at $1000^{\circ}C$ appeared Cr nitride. And this was in good agreement with the thermodynamically calculated phase diagram. The grain growth was delayed after HTGN treatment temperature ranges of $1000^{\circ}C{\sim}1100^{\circ}C$ due to the grain boundary precipitates. For the HTGN treatment temperature of $1150^{\circ}C$, the fine grain region was shown at the near surface due to the grain boundary precipitates, however, owing to the depletion of grain boundary precipitates, coarse grain was appeared at the depth far from the surface. This depletion may come from the strong affinity between nitrogen and substitutional element of Al and Ti leading the diffusion of these elements from interior to surface. Because of the nitrogen dissolution at the nitrogen-permeated surface layer by HTGN treatment, the surface hardness was increased above 150 Hv compared to the interior region that was consisted with the mixed microstructure of austenite and ${\varepsilon}$-martensite.

• Restorative Dentistry and Endodontics
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• 제4권1호
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• pp.7-9
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• 1978

Brass specimen, copper based alloy was prepared in cubic form about $1cm{\times}1cm{\times}1cm$ in volume. The specimens were mechanically compressed in one direction until the dimension distorted to 20%, 40%, 60% and 80% in length. The compressed specimens with 80% distorted in length were then heat treated in $200^{\circ}C$, $300^{\circ}C$, $400^{\circ}C$, $500^{\circ}C$ and $600^{\circ}C$ for 30 minutes. Microscopic examination was made on both compressed and heat treated specimens. The results obtained from the study were as follows: 1. Grain boundary and twin phenomenon was clearly seen in 0% and 20% compressed cases. Slip bands was appeared in 40% cases and distributed equally as well as twin. 2. The first evidence of slip bands was observed in 20% and the bands grew thicker and denser as the compression increased. 3. The density of the bands were reduced after annealing in $200^{\circ}C$ and completely disappeared at $300^{\circ}C$ cases. 4. Recrystallization was noticed unevenly in $300^{\circ}C$ cases and the evidence of twin was observed in these crystallized area. 5. In $400^{\circ}C$ cases the grain boundary was evenly found and the twin phenomenon was clearly observed. Grain boundary and twin was noticeably formed in size according to the annealing temperature increased.

• 한국전기전자재료학회논문지
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• 제13권10호
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• pp.834-839
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• 2000

The structural properties that SEM photograph of ZnO varistors surface studied by fractal mathematics program were investigated to verify the relations of electrical characteristics. The SEM photograph of ZnO varistors surface were changed by binary code and the grain shape of that were analyzed by fractal dimension. The void of ZnO varistors surface was found by fractal program. The relation between grain density and electrical properties depend on fractal dimension. The grain size in ZnO varistors surface was decreased by increasing of Sb$_2$O$_3$ addition. The spinel structure was formed by Sb$_2$O$_3$addition and it was depressed the ZnO grain formation. The grain size of ZnO by Sb$_2$O$_3$addition were from 5 to 10[${\mu}{\textrm}{m}$]. Among of ZnO varistors, fractal dimension of ZnO4 was very high as a 1.764. The density of grain boundary in ZnO2 and ZnO3 varistors surface was 15[%] by formed spinal structure. The breakdown electric field of ZnO2 that fractal dimension has 1.752 was very high to be 8.5[kV/cm]. When the fractal dimensin was high, the grain shape of ZnO varistors was complex and the serial layers of ZnO grain was increased.

• 분석과학
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• 제6권2호
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• pp.157-165
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• 1993

강 중 석출물을 추출분리한 후 이를 정량분석하는 것을 목적으로 개발된 정전위 전해법을 304 스테인레스 판재 및 선재 제조시에 발생한 결함 원인 분석에 활용하여 시료의 조직을 관찰하였으며, 결함 원인을 조사하였다. 스테인레스 선재 및 판재의 균열 전파 양상은 정전위 전해법을 이용하여 에칭한 후 주사전자현미경으로 관찰하였고, 입계를 따라서 존재하는 조대한 석출물은 EDS 및 EPMA를 이용하여 성분분석을 행하였다. 이들 조대한 석출물의 구조분석은 X-선 회절 패턴을 이용하여 행하였다. 판재 및 선재 두 경우 모두 균열은 입계를 따라서 전파하고 있었으며, 입계에는 $M_{23}(C,\;B)_6$ 이외에 조대한 $M_2C$ 석출물이 존재하는 것으로 확인되었다. 이들 석출물들의 분석에 정전위 전해에칭법을 이용함으로써 양호한 시료를 얻을 수 있었다.

• 센서학회지
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• 제9권1호
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• pp.76-82
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• 2000

본 연구에서는 내부전극 접합기술을 이용하여 적층구조의 PTC 서미스터를 제작하였다. 적층구조 PTC 서미스터는 저항, 소형, 대전류 등의 특징을 갖는다. PTC 특성을 조사하기 위하여 첨가제효과, 전압-전류특성, 온도특성, 복합임피던스 특성 등을 측정하였다. 적층구조 PTC서미스터는 저항의 온도특성과 전압-전류특성에서 높은 비선형성을 나타내었다. 적층수가 증가함에 따라 상온저항이 감소되는 특성이 결정립의 효과에 기인됨을 알았다. 전류의 스윗칭 변화는 적층구조가 갖는 열용량의 크기에 비례하였으며, 적층수가 증가할수록 스윗칭 시간이 증가하였다.

• Progress in Superconductivity
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• 제8권1호
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• pp.8-15
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• 2006

The size of the superconducting domains and the critical current density inside these domains have to be enhanced for most of cryomagnetic applications of melt-textured YBCO bulks. To enlarge the size of the domains we studied the multi-seeding technique based on a well-established procedure for preparing high quality YBCO monoliths using self-made SmBCO seeds. The distance between the seeds was optimised as a result of the investigation of the effects of various seed distances on the characteristics of the grain boundary Junctions. The influences of a-b plane intersections and c-axis misalignments were researched. Thereby, a small range of tolerance of the misorientations between the seed crystals was found. Field mapping was applied to control the materials quality and the superconductor's grain structure was investigated using polarisation microscopy. YBCO function elements with iou. seeds in a line and an arrangement of making type (100)/(100) and (110)/(110) boundary junctions, respectively, were processed. The trapped field profile in both sample types shows single domain behaviour. To demonstrate the potential of the multi-seeding method a ring-shaped sample was processed by placing sixteen seeds in a way to make both (100)/(100) and (110)/(110) grain junctions at the same time. The results up to now are very promising to prepare large single domain melt-textured YBCO semi-finished products in complex shapes.