• 열처리공학회지
• /
• 제16권4호
• /
• pp.197-204
• /
• 2003

Honeycomb structure has been fabricated by brazing method using 0.1 wt%C and 1.0wt%C carbon steel core and STS304 stainless steel face sheet. Core shear strength ratio in W and L directions was 1:1.03 in 7 mm cell size, whereas 1:1.45 in 4 mm cell size. Flexural strength on face sheet was 166.4 MPa (0.1 wt%C, W direction), 171.1 MPa (0.1 wt%C, L direction), and 120.2 MPa (1.0 wt%C, W direction) in 7 mm cell size. And in 4mm cell size specimen, it was 169.2 MPa (0.1 wt%C, W direction), 224.2 MPa (0.1 wt%C, L direction). This means that flexural strength of 0.1 wt%C core material was higher than that of 1.0wt%C core material, which was contrary to expectation. SEM and EDS analysis represented that grain boundary diffusion had occurred in0.1 wt%C core, but no grain boundary diffusion in 1.0 wt%C core. And corrugated surface of 0.1 wt%C core was flat, whereas that of 1.0 wt%C core was not flat. As a result, contact area between two 1.0 wt%C cores was much less than that of 0.1 wt% cores, It is thought to be main reason for lower flexural strength of 1.0 wt%C core.

• Progress in Superconductivity
• /
• 제4권1호
• /
• pp.10-13
• /
• 2002

We report the effect of Ca doping in $YBa_2Cu_3O_{7-\delta}$ (YBCO) thin films grown on the Rolling- Assisted, Biaxially Textured Substrates (RABiTS) with the architecture of $CeO_2/YSZ/CeO_2/Ni$. Critical currents of bilayer and trilayer structures of $YBCO/Y_{0.7}Ca_{0.3}Ba_2Cu_3O_{7-\delta}$/(YCaBCO) as well as undoped YBCO for comparison have been measured in a wide range of temperatures and fields. For $6-8^{\circ}$ grain boundaries, 30% Ca-doping in bilayer structure enhances $J_c$ as high as 35%. The enhancement is larger at low temperatures and at magnetic fields. On the other hand, 30% Ca-doping in trilayer structure reduces $J_c$ as high as 60%. Combined with slightly lower $T_c$, this indicates that Ca is overdoped in this structure and degrades GBs.

• 열처리공학회지
• /
• 제35권2호
• /
• pp.74-81
• /
• 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.

• Korean Chemical Engineering Research
• /
• 제43권2호
• /
• pp.278-285
• /
• 2005

연속식 유동층 반응기에서 흡착제인 천연망간광석을 이용한 탈황반응과, grain model과 two-phase 이론에 근거한 탈황 모사를 연구하였다. 입자 내의 기공 구조변화를 고려한 grain model을 통하여 탈황 반응시간, 천연망간광석의 입자 크기, 기공 내에서 $SO_2$의 확산속도에 대한 영향을 고찰한 결과, 입자의 기공 내에서 $SO_2$ 가스 확산이 탈황 반응의 가장 중요한 요소로 나타났다. 또한, 연속식 유동층 반응기에서 흡착제인 천연망간광석을 이용한 탈황반응 실험결과는 grain model과 two-phase 이론과 잘 일치하였으며, 탈황 결과를 잘 예측할 수 있었다.

• 한국결정성장학회지
• /
• 제33권6호
• /
• pp.261-267
• /
• 2023

마이크로파 유전체 적용을 위해 (Ca, Sr)(Zr, Ti)O₃ (CSZT) 계에서 MgO 첨가에 따른 결정 구조, 미세 구조, 및 유전 특성을 연구하였다. 고상 반응법을 통해 합성된 CSZT 분말은 orthorhombic 단일상을 형성하였다. CSZT의 시편을 각각 1200℃, 1300℃ 및 1400℃에서 소결하였고, 소결 후 모든 시편은 orthorhombic 단일상을 확인하였다. 또한 모든 소결 시편은 온도가 증가함에 따라 입자 크기가 증가하였다. 1 mol% MgO를 첨가한 시편의 경우도 소결 이후에 orthorhombic 구조를 갖는 것을 확인하였다. EDS 분석을 통해 1400℃에서 소결 중에 이차상이 형성된 것을 확인하였다. MgO 첨가된 CSZT의 입자크기분포와 치밀화는 첨가하지 않은 경우와 거의 유사했으나, 입자크기분포가 좁아지며 균일해지는 것을 확인하였다. MgO 첨가된 CSZT는 1 k Hz에서 ε_r = 34.14, tanδ = 0.00047, τ_ε = -3.58 ppm/℃로 우수한 저손실 유전 특성을 가졌다.

• 동아시아식생활학회지
• /
• 제16권3호
• /
• pp.323-331
• /
• 2006

The manufacture and consumption of traditional Korean rice cake is being revived due to the introduction of various desserts and confectionaries in the food industry. In order to develop this traditional food of Korea and allow various types of rice cakes to enter the market, it is essential to standardize the cooking methodology. In particular, there has been little research on Dutubpyun, a traditional food famous for its good taste. In addition, the original cooking methodology varies between cookbooks. Therefore, in order to standardize the cooking methodology for Dutubpyun referring to various cookbooks, different types Dutubpyun were made by varying the grain fineness of the glutinous rice powder to 16, 20, 30 and 40 meshes, adding up water to 10%, up sugar to 10% and up soy sauce to 5%. Subsequently, a sensory evaluation, and a test on the moisture, degree of gelatinization and hardness during storage were measured to determine the optimal grain fineness of the powder. For the sensory evaluation, where the grain sizes of the glutinous rice powder were different, the 30 and 40 mesh samples received high scores for grain fineness, moisture and chewiness. The 40 mesh samples received high scores for softness, while the overall quality was the highest in the 30 mesh samples. The moisture content during storage was $38.0{\sim}40.6%$ for the samples on the day of cooking, while it was reduced to $33.3{\sim}35%$ after 3 days of storage. Regarding the degree of gelatinization during storage, the maltose content was $2.4{\sim}2.7 mg$ for the samples on the day of cooking. After 3 days, the maltose content was $2.3{\sim}2.8 mg$ but the maltose content was higher in the 40 mesh samples than in the other samples. Regarding the change in hardness during storage, the hardness marked high in the 20 mesh samples on the day of cooking (p<0.05), while it was high in the 16 mesh samples after 3 days of storage (p<0.001). The hardness tended to increase with increasing storage time. Regarding the surface structure of the glutinous rice powder and Dutubpyun, a difference in grain fineness was clearly seen in the 15x-magnifications photograph of the rice powder structure taken by SEM. At 60x and 180x magnifications of surface of Dutubpyun, the 16 mesh samples had a uniform air gap, and a lumpy configuration. Smaller air gaps were dispersed homogeneously and similar to a net in the 20 and 30 mesh samples. The 40 mesh samples showed to a net-likes structure with cracks. Overall, for the best conditions for cooking Dutubpyun, the grain fineness of the glutinous rice power needs to be 30 mesh.

• 한국산업융합학회 논문집
• /
• 제6권4호
• /
• pp.299-305
• /
• 2003

This research is for the relationship with heat treatment cooling temprature and the characteristic of Mechanical properties of Boron-Addition-Steel, the main material and SM25C steel, the sub material, structure viewing fractography, hardness test, tensite test and are carried out after the manufacturing small-specimen treated with heat of $750^{\circ}C$, $850^{\circ}C$, $1050^{\circ}C$. The influence to the Mechanical properties accompanied by AISI51B20, Boron-Addition-steel shows the following result. 1. The influenc of heat treatment by the content of cabon-steel is dominant. Addition of boron result is Strengthening structure effectively by segregation and improving over all mechanical characters such as good. it results from the increase of temacity by the stability of inter granular with improvement of harden-ability. 2. Boron-Addition-Steel exist in the from of martensite structure accompanied by the ferrite precipitition centering around grain boundary, and is improved to Hv 200. 3. The height of harden-ability and fatigue stress the influence of heat results from crystal structure of martensite by difference of strength level in the structure of ferrite and doesn't have am effect on sensibility of temperature, and turns out to defend on production and growth of Matrix-structure-factor.

• 한국주조공학회지
• /
• 제22권5호
• /
• pp.231-237
• /
• 2002

The structure and properties of HSLA steel obtained by Osprey forming process were investigated. The porosities were generated at the bottom of specimen due to the quenching effect of cold substrate during forming. The steel had a bainitic structure. The grain size were different among positions due to the cooling rates. The elements such as Mn, S, Si, Cr, Mo and etc. were contained in inclusions. They were formed at grain boundries. The size of them was $1{\sim}2{\mu}m$ and has nothing to do with the chemical composition. MnS and NbC were precipitated during rolling and aging.

• 한국분말재료학회지
• /
• 제16권6호
• /
• pp.403-409
• /
• 2009

Plasma spray forming is recently explored as a near-net-shape fabrication route for ultra-high temperature metals and ceramics. In this study, monolithic tungsten has been produced using an atmospheric plasma spray forming and subsequent high temperature sintering. The spray-formed tungsten preform from different processing parameters has been evaluated in terms of metallurgical aspects, such as density, oxygen content and hardness. A well-defined lamellae structure was formed in the as-sprayed deposit by spreading of completely molten droplets, with incorporating small amounts of unmelted/partially-melted particles. Plasma sprayed tungsten deposit had 84-87% theoretical density and 0.2-0.3 wt.% oxygen content. Subsequent sintering at 2500$^{\circ}C$ promoted the formation of equiaxed grain structure and the production of dense preform up to 98% theoretical density.

• 한국지반공학회:학술대회논문집
• /
• 한국지반공학회 2008년도 추계 학술발표회
• /
• pp.831-835
• /
• 2008

Recently, the use of C.S.G is gradually increasing as the construction material for dam, road, revetment and so on. The strength characteristics of C.S.G is affected by various influence factors such as specimen size, maximum grain size and water contents. Therefore, When designing and constructing the C.S.G structure, it is very important for us to understand the nature of used materials well and to test it's quality. Commonly, C.S.G strength test is used the cylinders specimen size of $15{\times}30$ at KS F2405. But, the specimen size extracted from the field structure is not regular. This paper aims at offering the experimental data about the compressive strength and elasticity modulus by change of the specimen size for the effective quality control of the C.S.G structure.