• 한국세라믹학회지
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• 제11권3호
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• pp.27-32
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• 1974

The effect of impurities of andalusite on the morphology of the crystallization of mullite was investigated. The raw, concentrated and purified andalusite were fired at 145$0^{\circ}C$. and 150$0^{\circ}C$. Each of three grades of andalusite was examined in a scanning electron microscope, X-ray diffractometer and etc. The raw andalusite showed deeply etched textures and prismatic crystals which are estimated to be an average of 2.5u in width and 15u in length. Concentrated andalusite showed poorly formed and elongated prismatic crystals. Purified andalusite showed condensed needle-like crystals which are estimated to be an average of 0.4$\mu$ in width and 2.0$\mu$ in length, but at the boundary of the original andalusite grain, prismatic crystals were seen. It is supposed that the purified andalusite is able to utilize as a raw material for high alumina refractories with refractoriness S.K. 38.

• 한국진공학회지
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• 제8권3A호
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• pp.224-230
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• 1999

$SrBi_{2x}Ta_2O_9$ (SBT) thin films were prepared on platinized silicon substrates by MOD process, and their ferroelectric and leakage current characteristics were investigated. The grain size of the MOD derived SBT films increased with increasing the BI/Ta mole ration. Although the SBT films with x of 0.8~1.2 were composed of the equiaxed grains, the elongated grains were also observed for the SBT films with x of 1.4 and 1.6. The SBT film with x of 1.2 exhibited the optimum ferroelectric properties of 2PR : 9.79 $\muC/\textrm{cm}^2$ and Ec : 24.2kV/cm at applied voltage of 5V. The leakage current density of the SBT films increased with increasing the BI/Ta mole ratio. With post annealing process, 2Pr and $E_c$of the SBT film with x of 1.2 increases 11.3 $\muC/\textrm{cm}^2$ and 39.6kV/cm, respectively. decrement of the leakage current density by post annealing process increased remarkably with increasing the Bi/ta mole ratio, and the SBT film with x=1.6 exhibited the lowest leakage current density after post annealing process.

• 한국재료학회지
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• 제24권5호
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• pp.229-235
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• 2014

In this paper, the effects of precipitates and Mn-solute atoms on the recrystallization behavior of an Al-Mn alloy was studied using micro-Vickers hardness, electrical conductivity measurements and optical microscopy. Various thermo-mechanical processes were designed to investigate the different morphologies, and the solute concentration, of Mn in the matrix. The results indicate that the recrystallization temperature, $T_R$ and time, $t_R$, are influenced by the amount of M-solute atoms in the matrix, and that the recrystallization microstructure is influenced by the amount of precipitates. Recrystallization in the Slow-Cooling specimen was rapid due to its low concentration of Mn-solute atoms, and the crystal-grain size was the smallest due to finely distributed precipitates. However, in the case of the No-Holding specimen, elongated grains were observed at the low annealing temperature and the largest recrystallized grains were observed at the high annealing temperatures (compared with Slow-Cooling and Base specimens) due to the high Mn-solute atoms in the matrix.

• 한국재료학회지
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• 제32권2호
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• pp.72-79
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• 2022

A cold roll-bonding process using AA1050, AA5052 and AA6061 alloy sheets is performed without lubrication. The roll-bonded specimen is a multi-layer complex aluminum alloy sheet in which the AA1050, AA5052 and AA6061 sheets are alternately stacked. The microstructural evolution with the increase of annealing temperature for the roll-bonded aluminum sheet is investigated in detail. The roll-bonded aluminum sheet shows a typical deformation structure in which the grains are elongated in the rolling direction over all regions. However, microstructural evolution of the annealed specimen is different depending on the type of material, resulting in a heterogeneous microstructure in the thickness direction of the layered aluminum sheet. Complete recrystallization occurs at 250 ℃ in the AA5052 region, which is lower by 100K than that of the AA1050 region. Variation of the misorientation angle distribution and texture development with increase of annealing temperature also differ depending on the type of material. Differences of microstructural evolution between aluminum alloys with increase of annealing temperature can be mainly explained in terms of amounts of impurities and initial grain size.

• 한국재료학회지
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• 제30권10호
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• pp.542-549
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• 2020

Effects of Sc addition on microstructure, electrical conductivity, thermal conductivity and mechanical properties of the as-cast and as-extruded Al-2Zn-1Cu-0.3Mg-xSc (x = 0, 0.25, 0.5 wt%) alloys are investigated. The average grain size of the as-cast Al-2Zn-1Cu-0.3Mg alloy is 2,334 ㎛; however, this value drops to 914 and 529 ㎛ with addition of Sc element at 0.25 wt% and 0.5 wt%, respectively. This grain refinement is due to primary Al₃Sc phase forming during solidification. The as-extruded Al-2Zn-1Cu-0.3Mg alloy has a recrystallization structure consisting of almost equiaxed grains. However, the as-extruded Sc-containing alloys consist of grains that are extremely elongated in the extrusion direction. In addition, it is found that the proportion of low-angle grain boundaries below 15 degree is dominant. This is because the addition of Sc results in the formation of coherent and nano-scale Al₃Sc phases during hot extrusion, inhibiting the process of recrystallization and improving the strength by pinning of dislocations and the formation of subgrain boundaries. The maximum values of the yield and tensile strength are 126 MPa and 215 MPa for the as-extruded Al-2Zn-1Cu-0.3Mg-0.25Sc alloy, respectively. The increase in strength is probably due to the existence of nano-scale Al₃Sc precipitates and dense Al₂Cu phases. Thermal conductivity of the as-cast Al-2Zn-1Cu-0.3Mg-xSc alloy is reduced to 204, 187 and 183 W/MK by additions of elemental Sc of 0, 0.25 and 0.5 wt%, respectively. On the other hand, the thermal conductivity of the as-extruded Al-2Zn-1Cu-0.3Mg-xSc alloy is about 200 W/Mk regardless of the content of Sc. This is because of the formation of coherent Al₃Sc phase, which decreases Sc content and causes extremely high electrical resistivity.

• 한국작물학회지
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• 제42권2호
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• pp.166-172
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• 1997

본 시험은 관개방법에 따른 벼의 생육조절 효과를 구명코자 직파재배답에 관행관개, 심수관개 및 절수관개 등의 3가지 처리로 검토하였던 바 몇가지 결과를 요약하면 다음과 같다. 1. 관개방법간 $m^2$당 최고분벽수는 관행관개 551개, 절수관개 466개, 심수관개 455개로 심수관개에서 가장 적었으나 유효경 비율이 88%로 매우 높게 나타나 최고분얼기때 무효분벽이 상당히 억제되었다. 2. 출수기는 심수관개가 절수관개보다 약 4일 정도 지연되었고, 출수후 함량은 심수관개에서 높게 유지되어 출수지연과 더불어 생육지속효과가 현저하였다. 3. 관계방법에 따른 벼의 형태적 특성 변화를 보면 지엽, 제 2, 3 엽장 및 엽폭 등은 심수 관개에 의하여 증대되는 경향이었고, 심수관개처리에서 간장이 약간 길어지는 경향이었다. 4. 심수관개는 특히 잎집이 발달하여 잎집을 포함한 줄기의 단직경 및 장직경이 커져 경이 굵었으며, 간기중이 무거워 상대적으로 도복에 대한 저항성이 증대되었다. 5. $m^2$당 수수, 등숙비율, 천입동등이 심수관개에서 증가하여 수량은 관행관개보다 약 11% 증수되었다.

• 한국세라믹학회지
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• 제42권8호
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• pp.567-574
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• 2005

Densification of SiC powder with additives of total amount of2, 4, 8 $wt\%$ Al-B-C was carried out by Spark Plasma Sintering (SPS). The unique features of the process are the possibilities of a very fast heating rate and a short holding time to obtain fully dense materials. The heating rate and applied pressure were kept at $100^{\circ}C/min$ and 40 MPa, while the sintering temperature and holding time varied from 1700 - $1800^{\circ}C$ for 10 - 40 min, respectively. The SPS-sintered specimens with different amount of Al-B-C at $1800^{\circ}C$ reached near-theoretical density. The $3C{\rightarrow}6H,\;15R{\rightarrow}4H$ phase transformation of SiC was enhanced by increasing the additive amount. The microstructure of SiC sintered up to $1750^{\circ}C$ consisted of fine equiaxed grains. In contrast, the growth of large elongated grains in small matrix grains was shown in sintered bodies at $1800^{\circ}C$, and the plate-like grains interlocking microstructure had been developed by increasing the holding time at $1800^{\circ}C$. The grain growth rate decreases with increasing amount of Al-B-C in SiC starting powder, however, the both of volume fraction and aspect ratio of large grains in sintered body increased.

• 한국작물학회지
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• 제34권3호
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• pp.296-302
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• 1989

수도의 직파재배에 있어서 가장 취약점인 출아.입묘율을 향상시키는데 많은 영향을 미치는 중배축 신장에 대하여 검토하였던 바 그 결과를 요약하면 다음과 같다. 1. 품종의 기원별 중배축장은 다수형 품종이 9.6mm로 재래종과 일본형 각각 4.4, 3.2mm 보다도 훨씬 컸다. 2. 생태형별 중배축 신장은 tjereh, aman, aus, boro 및 bulu 순으로 tjereh가 29.3mm로 buld의 5.4mm에 비해 약 5배나 컸다. 3. 품종간 중배축장은 재래종에서 백경조, 다다조 및 해조가, 일본형은 상풍벼, 팔달 및 간량도가, 다수형 품종에서는 원풍벼, 가야벼, 밀양30호 및 수정벼가 컸다. 4. 종자 숙도별 중배축장은 개화 1주후 채종 종자가 39.3mm로 가장 컸고, 성숙일수가 길어짐에 따라 중배축장은 점차 작아졌다. 5. 종자 저장기간이 길어질수록 종자숙도와 관계없이 중배축장은 점차 감소하는 경향이었고, 저장온도 5$^{\circ}C$구가 15$^{\circ}C$, $25^{\circ}C$에 비하여 중배축장의 감소정도가 작았다.

• 자원환경지질
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• 제12권3호
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• pp.115-126
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• 1979

The Jecheon granite mass has turtle-shape exposure of about $190km^2$ at vicinity of Jecheon-eup, and is elongated in the direction of NEE-SWW. It discordantly intrudes the Bakdalryong metamorphic rocks and the great limestone series(Samtaesan and Hungwolri formation) which belong to the pre-Cambrian and Ordovician, respectively. The mass is composed of five facies of different grain size; texture and charecteristic minerals. The five facies are (1) coarse grained biotite granodiorite, (2) fine grained hornblende biotite granodiorite, (3) coarse grained pink feldspar granodiorite (4) leucogranite, and (5) porphyritic biotite granite. The mutual relationship between each facies is intrusion in (1)-(2) and (2)-(3), but unknown in (3)-(4) and (4)-(5). 22 modal analyses and and 10 chemical analyses on more than a hundred of representative samples taken from the mass are listed as tables. Triangular plot of modal and normative Q-Kf-Pl of this mass show a continuous differentiation products from certain common magma by change of chemical composition and anorthite contents in plagioclase. The metamorphic facies of contact aureole in surrounding rocks adjacent to the granite body are corresponded to hornblende hornfels facies with mineral assemblages of wollastonite-diopside-calcite in calcareous rocks, and of quartz-biotite-muscovite-cordierite in argillaceous rocks. Variation of silica versus oxides of major elements shows that the mass is similar to the trend of Daly's average basalt-andesite-dacite-rhyolite which shows the trend of the fractional crystallization of magma, and is equivalent to the calc-alkali rock series by Peacock. AMF diagram shows that Jecheon granite mass is equivalent to normal diffentiation products such as skaergaard intrusion. The above evidences suggest that the Jecohon granite mass is normal differentiation products formed by fractional crystallization under relatively slow cooling condition.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제49권2호
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• pp.92-97
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• 2000

The mechanical and electrical properties of the hot-pressed and annealed $\beta$-SiC+39vol. %ZrB2 electroconductive ceramic composites were investigated by adding 1, 2, 3wt% Al2O3+Y2O3(6:4wt%) of the liquid forming additives. In this microstructures, no reactions were observed between $\beta-SiC$ and ZrB2. The relative density is over 90.8% of the theoretical density and the porosity decreased with increasing Al2O3+Y2O3 contents. Phase analysis of the composites by XRD revealed $\alpha-SiC(6H, 4H)$, ZrB2 and $\beta-SiC$(15R). Flexural srength showed the highest of 315.5MPa for composites added with 3wt% Al2O3+Y2O3 additives as room temperature. Owing to crack deflection and crack bridging of fracture toughness mechanism, the fracture toughness showed 5.5MPa.m1/2 and 5.3MPa.m1/2 for composites added with 2wt% and 3wt% Al2O3+Y2O3 additives respectively at room temperature. The area fraction of the elongated SiC grain in the etched surface of sample showed 65% and 65.1% for composite added with 2wt% and 3wt% Al2O3+Y2O3 additives respectively. The electrical resistivity at room temperature. The electrical resistivity of the composites wall all positive temperature coefficient(PTCR) against temperature up to $700^{\circ}C$.