• 한국식품과학회지
• /
• 제47권5호
• /
• pp.593-598
• /
• 2015

This study determined the thermal resistance of Bacillus cereus, Escherichia coli O157:H7, and Listeria monocytogenes in multi-grain soymilk and proposes processing conditions that meet the national standard for retort food products in Korea. D and z values were calculated from thermal inactivation kinetic curves after heating at 55, 60, and $65^{\circ}C$. The D value for B. cereus at $55^{\circ}C$ was the highest (22.8 min), followed by that for E. coli O157:H7 (18.8 min) and L. monocytogenes (17.6 min). At $60-65^{\circ}C$, the order was L. monocytogenes ($D_{60-65^{\circ}C}=3.4-0.9min$), E. coli O157:H7 (3.0-0.3 min), and B. cereus (1.2-0.3 min). The z values for these species were 5.2, 5.5, and $7.7^{\circ}C$, respectively. The Korean national standard for retort food products was achieved by thermal processing at $124{\pm}2^{\circ}C$ for 0.3-2.2 min. This study provides useful data for ensuring both the microbiological safety and product quality of multi-grain soymilk products.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2001년도 하계학술대회 논문집
• /
• pp.489-494
• /
• 2001

In this thesis, the microstructure and electrical properties of ZnO varistors were investigated according to ZnO varistors with various formulation. A∼E's ZnO varistor ceramics were exhibited good density, 95% of theory density and low porosity, 5%, wholly. The average grain size of A-E's ZnO varistor ceramics exhibited 11.89$\mu\textrm{m}$, 13.57$\mu\textrm{m}$, 15.44$\mu\textrm{m}$, 11.92$\mu\textrm{m}$, 12.47$\mu\textrm{m}$, respectively. Grain size of C's ZnO varistor is larger and grain size of A and D's are smaller than other varistors. In the microstructure, A∼E's ZnO varistor ceramics sintered at l130$^{\circ}C$ was consisted of ZnO grain(ZnO), spinel phase(Zn$\sub$2.33/Sb$\sub$0.67/O$_4$), Bi-rich Phase(Bi$_2$O$_3$) and inergranular phase, wholly. Reference voltage of A∼E's ZnO varistor sintered at 1130$^{\circ}C$ decreased in order D, E > A > B > C's ZnO varistors. Nonlinear exponent of varistors exhibited high characteristics, above 30, wholly. Consequently, C's ZnO varistor exhibited good nonlinear exponent, 68. Lightning impulse residual voltage of A, B, C and E's ZnO varistors suited standard characteristics, below 12kV at current of 5kA.

• 한국분말재료학회지
• /
• 제18권6호
• /
• pp.562-567
• /
• 2011

This paper reports the effect of sintering processes and additives on the microstructures and mechanical properties of $ZrB_2$-SiC composite ceramics. We fabricated sintered bodies of $ZrB_2$-20 vol.% SiC with or without sintering additive, such as C or $B_4C$, densified by spark plasma sintering as well as hot pressing. While almost full densification was achieved regardless of sintering processes or sintering additives, significant grain growth was observed in the case of spark plasma sintering, especially with $B_4C$. With sintered bodies, mechanical properties, such as flexural strength and Vickers hardness, were also examined.

• 한국초전도ㆍ저온공학회논문지
• /
• 제24권4호
• /
• pp.55-58
• /
• 2022

Carbon-based doping to MgB₂ superconductor is the simplest approach to enhance the critical current densities under magnetic fields. Carbon quantum dots is synthesized in this work as a carbon provider to MgB₂ superconductors. Polyvinyl Pyrrolidone is pyrolyzed and dispersed in dimethylfomamide solvent as a dopant to the mixture of Mg and B powders. Doped MgB₂ bulk samples clearly show the decrease of a-axis lattice constant, grain refinements, and broadening of FWHM of diffraction peaks compared to un-doped MgB₂ possibly due to the carbon substitution and/or boron vacancy at the boron site in MgB₂ lattice. Also, high-field J_c for the doped MgB₂ is enhanced significantly with the crossover about 3 T at 5 & 20 K when increasing the doping of carbon quantum dots.

• 대한금속재료학회지
• /
• 제48권8호
• /
• pp.780-789
• /
• 2010

The aim of this study is to evaluate the microstructure and tensile property of in-situ (TiB+TiC) particulate reinforced titanium matrix composites (TMCs) synthesized by the investment casting process. Boron carbide ($1,500{\mu}m$ and $150{\mu}m$) was added to the titanium matrix during vacuum induction melting, which can provide the in-situ reaction of $5Ti+B_4C{\rightarrow}4TiB+TiC$. 0.94, 1.88 and 3.76 wt% of $B_4C$ were added to the melt. The phases identification of the in-situ synthesized TMCs was examined using scanning electron microscopy, an X-ray diffractometer, an electron probe micro-analyzer and transmission electron microscopy. Tensile properties of TMCs were investigated in accordance with the reinforcement size and volume fraction. The improvement of tensile property of titanium matrix composites was caused by load transfer from the titanium matrix to the reinforcement and by grain refinement of titanium matrix and reinforcements.

• 한국세라믹학회지
• /
• 제46권5호
• /
• 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.

• Journal of Welding and Joining
• /
• 제13권3호
• /
• pp.147-156
• /
• 1995

The change of microstructure in the bonded interlayer and tensile properties of joints were studied for liquid phase diffusion bonding using STS-310 and Incoloy-825 as base metal and base metal+B alloy as insert inetal. Main experimental results obtained in this study are as follows. 1) The optimum amount of B addition into the insert metal was found to be about 4mass%. 2) When isothermal solidification was completed, the microstructure in the bonded interlayer was the same with that of the base metal because of the grain boundary migration in the bonded interlayer. 3) All of the tensile specimen fractured at base metal and joints bonded at optimum condition exhibited tensile properties in excess of base metal requirements. 4) It was determined that fine car-borides and bordes such as M$_{23}$(C,B)$_{6}$, Cr$_{2}$B, and CrB in STS-310S and TiB in Incoloy-825 exist at the grain boundary around bonded interlayer. These precipitates almost disappeared after homogenizing treatment at 1373K for 86.4ks.s.

• 한국전기전자재료학회논문지
• /
• 제13권4호
• /
• pp.343-348
• /
• 2000

NCZF ferrites doped with B-Bi-Zn(35-25-40) glass ceramics were prepared to investigate the magnetic properties. The XRD peaks of all of samples were observed only spinel phase. As the additive increased at sintering temperature 750$^{\circ}C$ and 850$^{\circ}C$ for 3 hours, the density and shrinkage of the samples increased until 5.28 g/cm$^3$ and 20% respectively. And other samples showed constant trends having the density about 5.4g/cm$^3$. According to SEM images the growth of grain progressed rapidly at sintering temperature of 850$^{\circ}C$ for 3 hours. Increasing the additive initial permeability and complex permeability decreased. The high values of complex permeability as a function of frequency showed that NCZF doped with 3 wt%, 5wt%, samples at sintered temperature of 850$^{\circ}C$/3h and 900$^{\circ}C$/3h.

• 한국자기학회지
• /
• 제1권2호
• /
• pp.60-68
• /
• 1991

급속냉각기술로 제조된 $Nd_{14}Fe_{76}Co_{4}B_{6}$ 및 $Nd_{10.5}Fe_{79}Co_{2}Zr_{15}B_{7}$ 자성분말을 사용하여 성형체와 본드자석을 제조하였다. 자기특성, 최적충진률 등의 분말입도 및 형상비에 따른 거동은 합금조성에 따라 달리 나타난다. Co/Fe 비가 작은 저밀도의 $Nd_{10.5}Fe_{79}Co_{2}Zr_{1.5}B_{7}$ 합금이 같은 성형압력에서 성형체의 성형밀도 및 최적충진률이 높아 자기특성이 우수하였으나 반면에 분말입도에 따라 자기특성이 변화하였다. 성형밀도(p)와 성형압력(P) 사이 에는 ${\phi}(g/cm^{2})=5.2~5.6{\times}P^{0.045~0.065}(ton/cm^{2})$의 관계식이 성립된다. 높은 Nd/Fe 비를 갖는 급속냉각된 $Nd_{14}Fe_{76}Co_{4}B_{6}$ 합금의 초미세립(50~60 nm)으로써 높은 보자력($iH_{c}=14~15kOe$)을 보유하나, Nd/Fe비가 낮은 $Nd_{10.5}Fe_{79}Co_{2}Zr_{1.5}B_{7}$ 합금은 결정립이 조대하고(150~400 nm)Nd-rich한 입경계상의 발달이 부진하여 자벽고착기구가 주 보자력 기구 로 판명된 두 합금에서 고착지점으로서의 역할이 불충분하여 보자력이 낮은 것으로 판명되었다.

• 소성∙가공
• /
• 제21권5호
• /
• pp.324-329
• /
• 2012

Mg-(9-x)Sn-xAl-1Zn (x=1, 2, 3 and 4 wt.%) alloys were subjected to indirect extrusion, and the microstructure and mechanical properties of the as-extruded Mg-Sn-Al-Zn (TAZ) alloys were investigated. The TAZ 811 alloy exhibited a finer grain structure than the TAZ 541 alloy due to a larger number of Mg2Sn particles, which pinned the grain boundaries and prevented growth of recrystallized grains. The TAZ alloys showed an unusual yield asymmetry behavior. The tension-compression yield asymmetry increased with decreasing average grain size. The TAZ 811 alloy with a small grain size exhibited a larger yield asymmetry than that of the TAZ 541 alloy having a relatively large grain size, which is mainly attributed to the low Al content and large number of second phase particles in the TAZ 811 alloy.