• 한국재료학회지
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• 제5권6호
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• pp.644-649
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• 1995

$UO_2$-6wt%Gd$_2$O$_3$가연성 독물질 소결체에 미량첨가한 Al 화합물(Al(OH)$_3$, ADS(aluminium disterate), Al(OH)$_3$+ADS)이 소결성 및 미세조직에 미치는 영향을 고찰하고자 하였다. 이를 위하여 Al이 첨가된 $UO_2$-6wt%Gd$_2$O$_3$압분체를 1$700^{\circ}C$, 수소 분위기에서 4시간동안 소결한 후 특성시험을 수행하였다 Al을 첨가한 $UO_2$-6wt%Gd$_2$O$_3$의 소결밀도는 94% T.D.이상이였고, ADS를 이용한 Al 첨가가 개기공도 감소에 상대적으로 크게 기여하였다. 또한 Al을 첨가하면 10$\mu\textrm{m}$ 이상의 큰 기공과 1$\mu\textrm{m}$ 이하의 작은 기공은 많이 줄어들었고 첨가된 Al 화합물의 종류와는 무관하게 평균 기공크기는 2-3$\mu\textrm{m}$였다. 그리고 Al을 첨가하지 않은 소결체의 결정립은 이중 결정립 형태를 갖는 반면에 Al을 첨가하면 결정립은 균일하였다. 특히, ADS를 첨가한 소결체의 평균 결정립 크기는 4.6$\mu\textrm{m}$로 가장크게 증가하였다.

• 한국표면공학회지
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• 제50권5호
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• pp.411-420
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• 2017

In this paper, two methods of making the Pd-added $SnO_2$ ($Pd-SnO_2$) powder with pure tetragonal phase by the hydrazine method were suggested and compared in terms of crystal structure, surface morphology, and alcohol gas response. One of the addition methods is to use $PdCl_2$ as a Pd source, the other is to use Pd-based organic with oleylamine (OAM). When Pd concentration was increased from 0 to 5 wt%, the average grain size of $Pd-SnO_2$ made with Pd-OAM were decreased from 32 to 12 nm. In the case of using with $PdCl_2$, grain size of the $PdCl_2$ fell to less than 10 nm. However, agglomerated and extruded surface morphology was observed for the films with Pd addition over 4 wt%. The crack-free $Pd-SnO_2$ thick films were able to successfully fill the $30{\mu}m$ gap of patterned Pt electrodes by optimized ink dropping method. Also, the 2 wt% $Pd-SnO_2$ thick film made with PdCl2 showed gas responses ($R_{air}/R_{gas}$) of 3.7, 5.7 and 9.0 at alcohol concentrations of 10, 50 and 100 ppm, respectively. On the other hand, the prepared 3 wt% $Pd-SnO_2$ thick film with Pd-OAM exhibited very excellent responses of 3.4, 6.8 and 12.2 at the equivalent measurement conditions, respectively. The 3 wt% $Pd-SnO_2$ thick film with Pd-OAM has a specific surface area of $31.39m^2/g$.

• 한국결정성장학회지
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• 제19권1호
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• pp.33-38
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• 2009

AIN 소결에 있어서 ${Y_2}{O_3}$를 소결 조제로하여 $1,700{\sim}1,900^{\circ}C$의 온도에서 상압소결하엿을 때 ${Y_2}{O_3}$ 첨가와 소결 유지 시간이 소결 특성, 미세 구조 및 열전도도에 미치는 영향에 관하여 평가하였다. ${Y_2}{O_3}$의 첨가에 따라 AIN 시편은 치밀화가 증진되고 열전도도가 증가됨을 확인할 수 있었다. 이러한 결과는 AIN 분말 표면의 ${Al_2}{O_3}$와 ${Y_2}{O_3}$의 반응으로 형성된 이차상에 기인한 것으로, 첨가된 ${Y_2}{O_3}$는 ${Al_2}{O_3}$와의 반응으로 치밀화에 기여를 하여 고온에서 액상의 형성으로 급속히 치밀화를 증진시키며, AIN 결정격자 내부로 유입될 수 있는 산소의 양을 감소시킴으로써 AIN 시편의 열전도도를 증가시키는 것을 알 수 있었다. 또한 소결시간의 증가에 따라 열전도도는 급격히 증가하였는데 이는 결정립계의 이차상이 고온에서 휘발되어 그 양이 감소함에 기인하는 것으로 파악되었다. $1,900^{\circ}C$ 5시간 소결한 시편의 열전도도는 약 $141\;Wm^{-1}K^{-1}$ 값을 나타내었고 이는 1시간 소결한 시편과 비교하여 20% 이상 증가된 값이었다.

• 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.

• 한국식품조리과학회지
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• 제31권5호
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• pp.551-556
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• 2015

Iksan370 is a long-spike wheat developed by the Rural Development Administration yielding excellent features components such as cold resistance, disease resistance, and viviparous germination. The physicochemical and material properties of the raw wheat and milled flour of Iksan370 were analyzed to derive its appropriate uses. The raw wheat of Iksan370 showed high contents of ash and proteins at 1.71% and 13.7%, respectively. Its test weight of 763.0 g/L was similar to those of other varieties and its 1,000 kernel weight was high at 45.38 g. The milled flour of Iksan370 had an ash content of 0.45%, which corresponds with a class 1 flour, and its protein content is 12.18%, corresponding with strong flour. The damaged starch was 5.41%, which was lower than that of other varieties. The average grain size was $70.67{\mu}m$ and the grain distribution was at the level of a typical hard wheat. In the farinogram, the water absorption was 58.63%, which corresponded to the level of medium flour. The development time was 7.00 minutes, which was significantly lower than those of Jokyung and Keumkang. The degree of softening was 67.00 BU, similar to those of Yunbaek and Baekjoong. Among the physico-chemical characteristics, the high protein content and typical hard wheat grain distribution of Iksan370 were similar to those of strong wheat, usually used for bread making. However, in the farinogram, the dough development time was short and the degree of softening was high. As a result, Iksan370 was expected to have poor breadmaking properties and a small volume of the final bread product due to insufficient dough durability. On the other hand, Iksan370 showed the highest maximum gelatinization viscosity at 864.00 BU. Therefore, Iksan370 is expected to show glutinous texture when used for noodles and its flour appears to be appropriate for frying powders as well.

• 한국재료학회지
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• 제33권10호
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• pp.393-399
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• 2023

In this study, changes in the microstructure and mechanical properties of cast and extruded Al-2Li-1Ce alloy materials were investigated as the Mg content was varied. The density decreased to 2.485, 2.46 and 2.435 g/cm³ when the Mg content in the Al-2Li-1Ce alloy was increased to 2, 4 and 6 wt%, respectively. Intermetallic compounds of Al₁₁Ce₃ were observed in all alloys, while the β-phase of Al₃Mg₂ was observed in alloys containing 6 wt% of Mg. In the extruded material, with increasing Mg content the average grain size decreased to 84.8, 71.6 and 36.2 ㎛, and the fraction of high-angle grain boundaries (greater than 15°) increased to 82.8 %, 88.6 %, and 91.8 %, respectively. This occurred because the increased Mg content promotes dynamic recrystallization during hot extrusion. Tensile test results showed that as the Mg content increased, both the yield strength and tensile strength increased. The yield strength reached 86.1, 107.3, and 186.4 MPa, and the tensile strength reached 215.2, 285, and 360.5 MPa, respectively. However, it is worth noting that the ductility decreased to 27.78 %, 25.65 %, and 20.72 % as the Mg content increased. This reduction in ductility is attributed to the strengthening effect resulting from the increased amount of dissolved Mg, and grain refinement due to dynamic recrystallization.

• 한국초지조사료학회지
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• 제35권2호
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• pp.105-111
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• 2015

국립식량과학원에서 국내 환경에 적합한 조사료용 호밀 품종을 개발하기 위하여 1995년에 '조춘호밀' 등 10개 품종을 방임수분으로 혼합 교배하여 그 중에서 형질이 우수한 'SR95POP-S1-140-9-1-3-7-5-3' 계통을 선발하였다. 선발 계통에 대해 생산력을 검정한 결과 특성이 우수하여 '호밀 50호'로 계통명을 부여하고 5개 지역에서 3개년간 지역적응성을 검정하였으며, 조사료 수량뿐만 아니라 종실 수량이 높은 것으로 나타나 2013년 직무육성신품종 선정위원회에서 신품종으로 선정됨과 함께 '씨드그린'으로 명명되었다. '씨드그린'은 초형이 직립이고, 잎색은 농록색이며, 길이는 길고, 폭은 넓은 편이다. 줄기는 황백색으로 중간 정도의 굵기이며, 종실은 갈색이고, 중간 크기이다. '씨드그린'의 출수기는 4월 22일로 표준품종인 '곡우' 보다 3일, 성숙기는 6월 16일로 2일 빠르다. 초장은 141 cm로 '곡우' 보다 3 cm 길다. 한해는 평균 2로 표준품종인 '곡우'의 1과 대등한 수준이며, 도복은 '곡우' 보다 약간 강하였으며, 습해와 병해는 발생하지 않았다. '씨드그린'의 생초수량은 ha 당 39.8톤(곡우 40.8톤), 건물수량은 평균 8.3톤(곡우 8.4톤)으로 '곡우' 보다 약간 적었으나, 종실수량은 4톤으로 '곡우'보다 16% 증수하였다. '씨드그린'의 조단백질 함량은 10.5%로서 '곡우' 보다 0.8% 높았으며, ADF와 NDF 함량(%)은 각각 38.8%와 66.4%로 '곡우' 보다 낮았으나, TDN 함량(%)은 58.3%로 '곡우' 보다 1.3% 높았으며, TDN 수량 또한 4.81 톤/ha로 '곡우' 보다 약간 높았다.

• 한국농공학회지
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• 제19권1호
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• pp.4312-4322
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• 1977

In order to investigate the effect of the water content and the accelerated curing on the strength of the soil-cement mixtures, laboratory test of soil cement mixtures was performed at five levels of water content, four levels of accelerated curing temperatures, three levels of normal curing periods, and six levels of accelerated curing time. Also this study was carried out to investigate the effect of grain size distribution of 21 types of soils on the strength of soil-cement mixtures at four levels of cement content and three levels of curing time. The results are summarized as follows: 1. Optimum moisture content increased with increase of the cement content, but maximum dry density was changed ununiformly with cement content. Water content corresponding to the maximum strength was a little higher than the optimum moisture content along the increase of cement content. 2. In molding the specimens with the optimum moisture content, the maximum strength appeared at the wet side of the optimum moisture content. 3. According to increase of curing temperature as 30, 40, 50, and 60$^{\circ}C$, unconiiend compressive strength of soil-cement mixtures increased, the rate of increase at the early curing period was large, and approximately 120 hours was suifficient to harden soil-cement mixtures completely. 4. The strength of soil-cement mixtures at the curing temperature of 10$^{\circ}C$ decreased at the rate of 30 to 50 percent than at the curing temperature of 20$^{\circ}C$, and the strength of soil-cement mixtures at the curing temperature of 0$^{\circ}C$ increased a little with increase of curing time. 5. Although the strength of soil-cement mixtures seemed to be a little affected by the temperature difference between day time and night, it was recommended that reasonable working period was the duration from July to August of which average maximum temperature of Korea was approximately 30$^{\circ}C$. 6. Accelerated curing time corresponding to the normal curing time of 28-day was shorten with increase of curing temperature, also it was a little affected by the cement. Accelerated curing time that the strength of soil-cement mixtures for the cement of 9 percent and the curing temperature of 60was shorten with increase of curing temperature, also it was a little affected by the cement. Accelerated curing time that the strength of soil-cement mix- tures for the cement of 9 percent and the curing temperature of 60$^{\circ}C$ was 45 hours at the KY sample, 50 hours at the MH, 40 hours at the SS, and 34 hours at the JJ respectively. 7. Accelerated curing time was depended upon the grain size distribution of soil, it decreased with increase the percent passing of No. 200 sieve. 8. Relationship between the normal curing times and the accelerated curing times showed that there was a linear relationship between them, its slope decreased with increase of curing temperature. 9. The most reasonable soil of the soil-cement mixtures was the sandy loam which was a well graded soil. Assuming the base of road requiring 7-day strength of 21 kg/$\textrm{cm}^2$ being used, the soil-cement mixtures could be obtained with adding 6 percent of cement in such a sails S-7, S-8, S-9, S-10, S-11, S-12, S-13. 10. The regression equation between the 28-day and the 7-day strength was obtained as follow; q28=1.12q7,+6.5(r=0.96).

• 자원환경지질
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• 제54권5호
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• pp.595-603
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• 2021

하천 및 육상 골재 자원의 주 대상인 모래층의 분포는 제4기 퇴적 환경 중 충적 및 하천 퇴적환경에 주로 속한다. 충청남도 금산군 일대의 골재 자원 분포는 특징적으로 감입곡류 하천이 우세한 퇴적 환경 중심으로 발달하고 있는 반면, 붕적이나 선상지성 퇴적환경에서 형성된 퇴적층은 육상 및 하천 골재 분포 비율이 상대적으로 낮다. 봉황천 주변과 소하천들이 합류하는 부근 일대는 소규모이지만 하천의 범람원이 발달하며 골재 분포 지역에 해당된다. 금산군 제4기 퇴적층의 수직 분포는 약 5~12m 범위와 평균 8m의 제4기 퇴적층 두께를 갖는다. 골재 부존 구간은 평균 3.6m 두께이며 평균 입도는 점토-실트 약 21%, 모래 67%, 그리고 자갈 12%이다. 골재 부존 구간의 주요 특징은 조립질 모래가 우세하고 자갈은 아각형 또는 아원형, 분급은 일반적으로 불량하고 괴상의 형태를 띠며 암회색~황갈색 범위의 토색을 보인다. 금산군 내에서 골재 개발 가능성이 큰 분포 지역은 금강본류, 봉황천과 소하천 지류의 현 하상과 구하상을 따라 분포하는 충적 퇴적층 및 하천 퇴적층이다.

• 한국재료학회지
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• 제33권11호
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• pp.465-474
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• 2023

The effects of La³⁺ substitution for Sr²⁺-site on the crystal structure and the dielectric properties of (Ba_0.7Sr_0.3-3x/2La_x) (Ti_0.9Zr_0.1)O₃ (BSLTZ) (0.005 ≤ x ≤ 0.02) ceramics were investigated. The structural characteristics of the BSLTZ ceramics were quantitatively evaluated using the Rietveld refinement method from X-ray diffraction (XRD) data. For the specimens sintered at 1,550 ℃ for 6 h, a single phase with a perovskite structure and homogeneous microstructure were observed for the entire range of compositions. With increasing La³⁺ substitution (x), the unit cell volume decreased because the ionic size of La³⁺ (1.36 Å) ions is smaller than that of Sr²⁺ (1.44 Å) ions. With increasing La³⁺ substitution (x), the tetragonal phase fraction increased due to the A-site cation size mismatch effect. Dielectric constant (ε_r) increased with the La³⁺ substitution (x) due to the increase in tetragonality (c/a) and the average B-site bond valence of the ABO₃ perovskite. The BSLTZ ceramics showed a higher dielectric loss due to the smaller grain size than that of (Ba_0.7Sr_0.3)(Ti_0.9Zr_0.1)O₃ ceramics. BSLTZ (x = 0.02) ceramics met the X7R specification proposed by the Electronic Industries Association (EIA).