• Title/Summary/Keyword: Grain sizes

Search Result 446, Processing Time 0.019 seconds

Effect of the Sintering Temperature on Electrical Properties of Porous Barium-strontium Titanate Ceramics

  • Kim, Jun-Gyu;Sim, Jae-Hwang;Cho, Won-Seung
    • Journal of the Korean Ceramic Society
    • /
    • v.40 no.1
    • /
    • pp.5-10
    • /
    • 2003
  • Porous barium-strontium titanate ceramics were fabricated by adding corn- or potato-starch (are referred to as starch). The effect of sintering temperature on the microstructure and electrical properties of the porous ceramics was investigated. The room-temperature electrical resistivity of the barium-strontium titanate ceramics decreased with sintering temperature. The porosity and pore size were decreased and the grain size was increased with increasing the sintering temperature. The porosity and grain size of the barium-strontium titanate ceramics with corn-starch sintered at 1300 and 1450$^{\circ}C$ were 28.5, 22.6% and 3.2, 6.2 $\mu\textrm{m}$, respectively. The average pore sizes of the barium-strontium titanate ceramics with corn-starch sintered at 1300, 1400 and 1450$^{\circ}C$ were 0.5, 0.3 and 0.2 $\mu\textrm{m}$, respectively. The decrease in the room-temperature resistivity with increasing sintering temperature is attributed mainly due to the increase of grain size and the decrease of the electrical barrier height of grain boundaries as well as the partial decrease of porosity.

Wear Properties of Silicon Nitride Nano-Ceramics (나노 질화규소 세라믹스의 내마모 특성)

  • Kim, Jae-Hee;Kumar B, Venkata Manoj;Kim, Won-Sik;Hong, Seong-Hyeon
    • Journal of the Korean Ceramic Society
    • /
    • v.46 no.5
    • /
    • pp.505-509
    • /
    • 2009
  • In this study, bulk nano-crystalline $Si_3N_4$ ceramics were fabricated by spark plasma sintering (SPS) and their mechanical properties, in particular wear, were investigated. A wide range of grain sizes, from 80 nm and 250 nm were obtained by varying sintering conditions ($1550^{\circ}C$-5 min to $1650^{\circ}C$-20 min). The elastic modulus of obtained ceramics was ${\sim}250$ GPa and hardness was in the range of $13{\sim}14$ GPa. The indentation fracture toughness increased from $2.58MPa{\cdot}m^{1/2}$ to $3.24MPa{\cdot}m^{1/2}$ with increasing sintering temperature possibly due to the elongated grains. Sliding wear tests revealed at least an order magnitude improvement in wear resistance with grain refinement. Microstructure analysis indicated that nano-$Si_3N_4$ specimens worn mainly through delamination and microcracking, while that of coarser specimens revealed severe wear with grain debonding and fracture.

Computer aided simulation of spark plasma sintering process (Part 2 : analysis) (스파크 플라스마 소결공정의 전산모사(2부 : 해석))

  • Keum Y.T.;Jung S.C.;Jean J.H.
    • Journal of the Korean Crystal Growth and Crystal Technology
    • /
    • v.16 no.1
    • /
    • pp.43-48
    • /
    • 2006
  • In this Part 2, the grain growth processes of $Al_2O_3$ ceramics is numerically simulated using Monte Carlo method (MCM) and finite element method (FEM) and the pore sizes are analyzed. As the green ceramics whose thermal conductivities in high temperatures are generally low are sintered by the plasma heat and are rapidly cooled, the grain growth of the sintered body in the center is different from that in the outer. Also, even in the same sintering temperature, the pore size differs according to the pressing pressure. In order to prove the difference, the temperature distribution of the sintered body was analyzed using the finite element method and then the grain growth process associated with pressing pressures and relative densities was simulated using Monte Carlo method.

Effects of Grain Size on the Fatigue Properties in Cold-Expanded Austenitic HNSs

  • Shin, Jong-Ho;Kim, Young-Deak;Lee, Jong-Wook
    • Metals and materials international
    • /
    • v.24 no.6
    • /
    • pp.1412-1421
    • /
    • 2018
  • Cold-expanded austenitic high nitrogen steel (HNS) was subjected to investigate the effects of grain size on the stress-controlled high cycle fatigue (HCF) as well as the strain-controlled low cycle fatigue (LCF) properties. The austenitic HNSs with two different grain sizes (160 and $292{\mu}m$) were fabricated by the different hot forging strain. The fine-grained (FG) specimen exhibited longer LCF life and higher HCF limit than those of the coarse-grained (CG) specimen. Fatigue crack growth testing showed that crack propagation rate in the FG specimen was the same as that in the CG specimen, implying that crack propagation rate did not affect the discrepancy of LCF life and HCF limit between two cold-expanded HNSs. Therefore, it was estimated that superior LCF and HCF properties in the FG specimen resulted from the retardation of the fatigue crack initiation as compared with the CG specimen. Transmission electron microscopy showed that the effective grain size including twin boundaries are much finer in the FG specimen than that in the CG specimen, which can give favorable contributions to strengthening.

Monsoonal sediment transport along the subaqueous Mekong Delta: An analysis of surface sediment grain-size changes

  • Thanh C., Nguyen;An T., Dang;Khuong N.T., Tran
    • Ocean Systems Engineering
    • /
    • v.12 no.4
    • /
    • pp.403-411
    • /
    • 2022
  • Annually, about 48-60% of sediment discharge of the Mekong River is delivered near the mouths of the Mekong River branches which is mostly coinciding with the southwest (SW) monsoon. This sediment budget in turn will be southwestwardly transported along the coast of the Mekong Delta (MD) during the northeast (NE) monsoon. Analysis of monsoonal changes in grain-size distribution (GSD) of surface sediment contributes to a better understanding of erosion and deposition processes along the MD. This study aims to figure out changes in GSD and sediment textures along the MD between SW and NE monsoons based on 183 surficial sediment samples collected along the MD during two field surveys carried-out in October 2016 and February-March 2017. Compared to the GSD during the SW and NE monsoon, the GSD along the MD changed significantly, especially in the estuary areas and along the coast of Bac Lieu and Ganh Hao. Whereas, in the west coast of the MD, GSD seem no changes between the two seasons. These changes in seabed sediment suggest that sediment with grain-sizes ranging from silt to fine sand can be transported during only a NE season.

Structural and Optical Properties of ZnO Thin Films Grown on SiO2/Si(100) Substrates by RF Magnetron Sputtering (RF 마그네트론 스퍼터링 방법으로 SiO2/Si(100) 기판위에 성장시킨 ZnO 박막의 구조 및 광특성)

  • Han Seok Kyu;Hong Soon-Ku;Kim Hyo-Jin;Lee Jae-Wook;Lee Jeong-Yong
    • Korean Journal of Materials Research
    • /
    • v.16 no.6
    • /
    • pp.360-366
    • /
    • 2006
  • A series of ZnO thin films were grown by radio-frequency (RF) magnetron sputtering with various RF powers on $SiO_2/Si$(100) substrates at $500^{\circ}C$. Thicknesses of the investigated ZnO films were fixed to about 250nm by changing the growth time based on the changes of growth rates with RF powers. All the ZnO thin films were grown with <0001> preferred orientation. Average grain sizes of about 250nm-thick ZnO films evaluated by FE-SEM, AFM, and TEM were increased by decreasing the RF power. Structural properties addressed by FWHM values of XRD (0002) omega rocking curves and their intensities were better for the smaller grain sized ZnO films grown with high RF powers, which implies small values of tilt for smaller grain sized ZnO films. However, optical properties addressed by intensities of band edge emissions from room temperature and low temperature photoluminescence were better for the larger grain sized ZnO films with low RF power, which implies grain boundaries acted as nonradiation recombination centers.

A Study on the Determination of Grain Size of Heat-treated Stainless Steel Using Digital Ultrasonic Signal Processing Techniques. (디지털 초음파 신호처리 기법을 이용한 열처리된 스테인레스 스틸의 그레인 크기 결정에 관한 연구)

  • 임내묵;이영석;김성환
    • The Journal of the Acoustical Society of Korea
    • /
    • v.18 no.8
    • /
    • pp.84-93
    • /
    • 1999
  • Determination of grain size of heat-treated stainless steel based fm digital ultrasonic signal processing technique is presented. This techniques consist in evidence accumulation with multiple feature parameters, difference absolute mean value(DAMV), variance(VAR), mean frequency (MEANF), auto regressive model coefficient(ARC) and linear cepstrum coefficient(LCC). Feature parameters were extracted from ultrasonic echo signal of heat-treated metals. It was found that a few parameters might not be sufficient to exactly evaluate the grain size of heat-treated metals. The determination of grain size of heat-treated metals was carried out through the evidence accumulation procedure using the distances measured with reference parameters. A fuzzy mapping function is designed to transform the distances for the application of the evidence accumulation method. In the work presented, heat-treated stainless steel samples with various grain sizes are examined. The processed experimental results supports the feasibility of the grain size determination technique presented.

  • PDF

The Effects of Seed Size on the Early Seedling Growth and Yield of Three Soybean(Glycine max. L.) Cultivars (대두종자(大豆種子)의 대소(大小)가 초기생육(初期生育) 및 수량(收量)에 미치는 영향(影響))

  • Park, Ki Sun;Choi, Chang Yeol;Kang, Jea Chul
    • Korean Journal of Agricultural Science
    • /
    • v.16 no.2
    • /
    • pp.138-151
    • /
    • 1989
  • In order to find the effects of seed size on the early seedling growth and yield of soybean, three soybean cultivars in Korea were investigated. Seed size was classified into large and small according to the weight and planted in pots(1/5000a) and in the field. Three soybean cultivars respresenting large, medium and small grains were Hwangkeum-kong, Kwangkyo and Bangsa-kong respectively. These cultivars were planted on June 20, 1987. 1. The plant height, stem diameter, root length and leaf area index(LAI) of the seed with large size seemed larger than the seed with small size regardless of cultivars. 2. The fresh and dry weight were different depending upon the grain sizes. The large grain had heavier fresh and dry weight than the small grains. 3. The protein consumption rate of the cotyledon of Bangsa-kong with small grain size was faster than the Hwangkeum-kong with large grain size. 4. The stem length, stem diameter and number of main stem node of the seed with large size seemed larger than the seed with small size. Large grains of Hwangkeum-kong were the highest in the number of branch node and number of node. 5. The number of pods and grains per plant of Bangsa-kong with small grain size was larger than the Kwangkyo with large grain size. 6. The yield per 10a for Hwangkeum-kong, Hwangkyo and Bangsa-kong were 226.3kg, 193.0kg and 192.8kg, respectively and they were all statistically different. The yield increases of large grains over small grains in the Hwangkeum-kong, Kwangkyo, and Bangsa-kong were 7.4%, 8.0% and 9.2%, respectively.

  • PDF

Microstructural Changes of OFC according to the Processing Number of Multi-Axial Diagonal Forging (MADF) (다축대각단조(MADF) 가공횟수에 따른 OFC의 미세조직 변화)

  • Kim, S.T.;Kwon, S.C.;Kim, D.V.;Lee, S.;Choi, S.H.;Jeong, H.T.
    • Transactions of Materials Processing
    • /
    • v.27 no.6
    • /
    • pp.347-355
    • /
    • 2018
  • This study investigated the effects of the processing number of multi-axial diagonal forging (MADF) on the microstructural changes of OFC fabricated by MADF processes. The as-extruded OFC was cut to $25mm^3$ cube for the MADF processes. The MADF process consists of plane forging with a thickness reduction of 30% and diagonal forging with a diagonal forging angle of $135^{\circ}$. In order to analyze the microstructural evolutions according to the number of repetitions, 1, 2, 3 and 4 cycles of the MADF process were performed. OFC specimens were successfully deformed without surface cracking for up to 4 cycles of MADF. The grain size, average misorientation and average grain orientation spread (GOS) of MADF processed materials were analyzed using EBSD technique and their Vicker's hardness were also measured. The results showed that MADF process effectively refined the microstructure of OFC with initial average grain size of $84.2{\mu}m$. The average grain sizes of specimens MADF processed for 1, 2, 3, 4 cycles were refined to be $8.5{\mu}m$, $2.2{\mu}m$, $1.5{\mu}m$, $1.1{\mu}m$, respectively. The grain refinement seemed to be saturated when OFC was MADF processed over 2 cycles. In the case of specimens subjected to two or more cycles of MADF, the degree of decrease in average grain size was drastically reduced as the number of cycles increased due to softening phenomena such as dynamic recovery or dynamic recrystallization during processing. The degree of increase in average Vicker's hardness was also dramatically reduced as the number of cycles increased due to the same reason.

Microstructural Changes of AA1100 According to the Processing Number of Multi-Axial Diagonal Forging (MADF) (다축대각단조(MADF) 가공횟수에 따른 AA1100의 미세조직 변화)

  • Kwon, S.C.;Kim, S.T.;Kim, D.V.;Kim, M.S.;Lee, S.;Choi, S.H.;Jeong, H.T.
    • Transactions of Materials Processing
    • /
    • v.28 no.2
    • /
    • pp.63-70
    • /
    • 2019
  • This study investigates the effects of multi-axial diagonal forging (MADF) processing number on the microstructures of AA1100 fabricated using MADF processes. The cast AA1100 was annealed at $400^{\circ}C$ for 3hrs in $N_2$ atmosphere and cut into $25mm^3$ cubes for the MADF processes. The MADF process consist of plane forging with a thickness reduction of 30% and a diagonal forging with a diagonal forging angle of 135 degrees. In order to analyze the microstructural variations based on the number of repetitions, 1, 2, 3 and 4 cycles of the MADF process were performed. AA1100 specimens were successfully deformed without cracking of the surface for up to 4 cycles of MADF. The grain size, average misorientation and average grain orientation spread (GOS) of MADF processed materials were analyzed using EBSD technique. The results showed that MADF process effectively refined the microstructure of AA1100 with an initial average grain size of $337.4{\mu}m$. The average grain sizes of specimens which were MADF processed for 2, 3, 4 cycles were refined to be $1.9{\mu}m$, $1.6{\mu}m$, $1.4{\mu}m$, respectively. The grain refinement appeared saturated when AA1100 got MADF processed over 2 cycles. When the specimen was subjected to two or more cycles of MADF, the degree of decrease in the average grain size drastically decreased with an increase in the number of cycle due to the softening phenomena such as dynamic recovery or dynamic recrystallization during processing.