• 대한환경공학회지
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• 제36권2호
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• pp.109-112
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• 2014

세노스피어(Cenosphere)와 볼 클레이(Ball Clay)를 이용하여 소성온도 $1,250^{\circ}C$, 소성시간 30분의 조건하에서 미세 기공을 가지며 비중이 작은 세라믹 다공체를 제조하였다. 제조된 세라믹 다공체의 평균 기공크기는 $2.5{\times}10^{-5}$ m 전후였으며, 기공이 잘 발달되었다. 세라믹 다공체의 기공율은 세노스피어 100중량비 대비 볼 클레이를 5중량비로 투입했을 때 기공율이 67.1%였다. 그러나 볼 클레이의 중량비가 20, 40, 100 증가함에 따라 기공율은 각각 58.4, 56.7, 47%로 감소하였다. 세노스피어 100중량비 대비 볼 클레이 투입량이 100중량비일 때, 세라믹 다공체의 겉보기 밀도는 $1.04g/cm^3$로 볼 클레이 5중량 값인 $0.51g/cm^3$ 대비 약 2배 증가하였으며, 반면에 흡수율은 100% 이상이 감소하였다. 세노스피어 100중량비 대비 볼 클레이 투입량이 100중량비일 때, 세라믹 다공체의 압축강도가 30 (MPa)였으며, 볼 클레이 5중량비 대비 약 76% 이상으로 향상되었다.

• 한국세라믹학회지
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• 제35권4호
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• pp.406-412
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• 1998

The reaction bonded alumina ceramics was prepared through the addition of each SiC and ZrO2 powder to the mixture of Al metal powder and Al2O3 The mono sized (3mm) and biodal sized (3mm+5mm) balls were used in attrition milling of Al and starting powders. The milling efficiency of both cases was compared by the analysis of particle size and X-ray diffraction. After the forming and sintering of each powder batchs the weight gains dimensional changes and densities were determined. The specimens were investigated by X-ray diffraction analysis and scanning electron microscope. Bimodal sized balls had better milling effect than single ball size in the milling of Al powder. However in the milling which ceramic powders mono sized the green body during the reaction sintering at 1$600^{\circ}C$ for 5 hour was about 10% The densities attained the values of 92-98% theoretical. The SiC added specimen that was milled with 3mm ball media had 96% theoretical density and dense microstructure.

• 한국전기전자재료학회논문지
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• 제28권12호
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• pp.852-856
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• 2015

In this study, we investigate the effect of high-energy ball milling on thermoelectric transport properties in double-filled $CoSb_3$ skutterudite ($In_{0.2}Yb_{0.1}Co_4Sb_{12}$). $In_{0.2}Yb_{0.1}Co_4Sb_{12}$ powders are milled using high-energy ball milling for different periods of time (0, 5, 10, and 20 min), and the milled powders are consolidated into bulk samples by spark plasma sintering. Microstructure analysis shows that the high-energy ball milled bulk samples are composed of nano- and micro-grains. Because the filling fractions are reduced in the bulk samples due to the kinetic energy of the high-energy ball milling, the carrier concentration of the bulk samples decreases with the ball milling time. Furthermore, the mobility of the bulk samples also decreases with the ball milling time due to enhanced grain boundary scattering of electrons. Reduction of electrical conductivity by ball milling has a decisive effect on thermoelectric transport in the bulk samples, power factor decreases with the ball milling time.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2005년도 추계학술발표회 및 workshop
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• pp.179-180
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• 2005

Non linear finite element analyses were performed in various configurations of stem-ball head. High stresses were found for the cases when the stem tended to penetrate less into the ball head. An upgraded design of the cone may improve the loading of the ball head to resist trauma-like loading more effectively than manipulating the ball diameter. When the surgeon needs to use small ball heads (i.e. 22 mm), the use of zirconia seems to be appropriate also. After simulating a trauma like loading of the materials, it was found that the deepness of the cone to locate the stem is of major importance for the performance of the device. Further work, considering more sizes for the cone design should be performed in order to determine an optimal depth for the cone in relation to the diameter of the ball head. Also the simulation of contacts pairs including polyethylene and CoCr is important for further research.

• 한국세라믹학회지
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• 제36권7호
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• pp.711-717
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• 1999

Biaxial fracture behavior of alumina specimens with the diameter of 20mm and four kinds of thickness of 1.9, 2.3, 2.6 and 2.8mm was studied by the ball-on-3-ball test and the fracture results were analyzed by he analysis of variance (ANOCA), The strength measured with the down speed prescribed in ASTM showed that the measured strength was not dependent on the thickness of the specimens. Equivalent radius and crack-braching number were observed to increase lineraly with the thickness of the specimens. The jog direction was observed to study the effect of grinding direction on surface flaws. It is though that the surface finishing with #600 grit diamond wheel did not affect the surface flaws of the specimens.

• 한국세라믹학회지
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• 제37권7호
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• pp.713-720
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• 2000

The biaxial fracture behavior of alumina ceramics was studied using ball-on-3-ball test. The polished surfaces of alumina specimens were indented at 0mm, 1mm, 2mm, 3mm apart from the center of the specimen along path A, passing between the two supporting balls from the center of the specimen, and along path B, passing above the three supporting balls from the center of the specimen. The fracture strength of the indented specimens was measured using the ball-on-3-ball test, a kind of biaxial strength test. The fracture strength increased with increasing the distance from the center to indented position. The fracture strength of the specimen indented along path B was higher than that of the specimens indented along path A. It was presented that the fracture caused by tangential stress rather than radial stress when the indented positions are 1mm and 2mm from the center of the specimen. This phenomenon was in good agreement with FEM analysis.

• 한국세라믹학회지
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• 제24권1호
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• pp.47-55
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• 1987

The purpose of this work is to establish the basic calibration data for the efficiency of grinding by investigating the Bond's Work Index employing Korean Kaolin as a reference mateial with the laboratory-scale ball mill. A small ordinary ball mill has a dimension of 133 inside diameter and 144mm long. The analysis of the experimental results in this work sets up a equivalent calibration method with the laboratory-scale ball mill to those with special mill. The theoretical expression, derived from the rate equation proposed by Miwa, is obtained to anticipitate the stable revolution number for the next grinding cycle. The proposed equation is more systematic and acurate than lshihara's empirical equation is more systematic and acurate than lshihara's empirical equation for the measurement of gindability of a ball mill.

• 한국세라믹학회지
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• 제35권2호
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• pp.115-122
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• 1998

The effect of sintering conditions on the sinterability for silicon nitride has been studied by many in-vestigators. However the effect of sintering conditions on the machinability which is the major barrier to the field applications of the ceramic components has not been fully studied. In this study the sintering con-ditions such as temperature gas pressure and time in silicon nitride were varied. The physical and mechan-ical properties of the gas pressure sintered (GPS) silicon nitride were measured. The optimum mi-crostructure of silicon nitride with the excellent machinability was investigated by MFG(magnetic-fluid grinding) technique. An attempt was made to figure out how the mechanical properties influence upon the machinability of silicon nitride ball.

• 한국분말재료학회지
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• 제15권4호
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• pp.302-307
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• 2008

$Gd_2O_3$-doped $CeO_2$(GDC) solid solutions have been considered as a promising materials for electrolytes in intermediate-temperature solid oxide fuel cells. In this study, the nano-sized GDC powder with average panicle size of 69nm was prepared by a high energy ball milling process and its sintering behavior was investigated. Heat-treatment at $1200^{\circ}C$ of nano-sized GDC powder mixture led to GDC solid-solution. The enhanced densification over 96% of relative density was obtained after sintering at $1300^{\circ}C$ for 2h. It was found that the sinterability of GDC powder could be significantly improved by the introduction of a high energy ball milling process.

• 한국세라믹학회지
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• 제45권9호
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• pp.507-511
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• 2008

A "C-sphere" specimen geometry was used to determine the failure strength distributions of a commercially-available bearing-grade silicon nitride ($Si_3N_4$) with ball diameters of 12.7 and 25.4 mm. Strengths for both diameters were determined using the combination of failure load, C-sphere geometry, and finite element analysis and fitted using two-parameter Weibull distributions. Effective areas of both diameters were estimated as a function of Weibull modulus and used to explore whether the strength distributions predictably scaled between each size. They did not. That statistical observation suggested that the same flaw type did not limit the strength of both ball diameters indicating a lack of material homogeneity between the two sizes. Optical fractography confirmed that. It showed there were two distinct strength-limiting flaw types common to both ball diameters, that one flaw type was always associated with lower strength specimens, and that a significantly higher fraction of the 25.4-mm-diameter C-sphere specimens failed from it. Predictable strength-size-scaling would therefore not result as a consequence of this because these flaw types were not homogenously distributed and sampled in both C-sphere geometries.