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71.
Stress characterization of surface damages on soda-lime glass using a nanocontact deformation method
Yun-Hee Lee Ju-Young Kim Unbong Baek Seung-Hoon Nahm 《Journal of Materials Science》2007,42(19):8203-8208
A nanocontact deformation method was used to measure the local and graded residual stresses around contact damages. By analyzing
influences of the residual stress on nanocontact deformation itself instead of measuring the secondary crack emanated from
it, 0.65 μm spatial resolution, which was superior to the highest level 1.8 μm attained by previous indentation fracture mechanics
tests with an acute cube-corner indenter, was obtained with a general Berkovich indenter. However, a stress model combined
with the nanocontact deformation provided only average stress variation around the contact damages. Thus, a resolution of
two principal components from the residual stress in a biaxial state has been attempted in this study. By introducing radial
microcracks around artificial microVickers damages, a crack-normal circumferential stress component disappeared and a series
of nanoindentations close to the microcrack line yielded a variation of the radial stress component. By comparing this result
with the average stress variation mentioned above, the crack-opening circumferential stress was measured and showed a good
consistency with the previous study in soda-lime glass. In addition, distinctive features of present method were compared
with previous indentation fracture mechanics method. 相似文献
72.
Choon-W. Nahm 《Bulletin of Materials Science》2010,33(3):239-245
The electrical properties, dielectric characteristics, and its stability against d.c. accelerated aging stress of (Pr, Co,
Cr, Y)-added zinc oxide-based varistors were investigated for different aluminum concentrations under a sintering temperature
of 1280°C. As the aluminum concentration increased, the average grain size (d) increased in the range of 4.3–5.5 μm and the sintered density increased in the range of 5.63–5.67 g/cm3. As the aluminum concentration increased, the breakdown field decreased in the range of 6327-710 V/cm and the maximum nonlinear
coefficient (46.9) was obtained for 0.005 mol% in aluminum concentration, further additions impaired the nonlinear properties.
As the aluminum concentration increased, the apparent dielectric constant increased in the range of 500.5–1327.4 and dissipation
factor increased in the range of 0.00493–0.0724. The varistor added with 0.001 mol% Al exhibited the highest stability for
E-J characteristics in which %ΔE
1 mA is +1.4% and %Δα is −5.7%, under stress state of 0.95 E
1 mA/150°C/24 h. 相似文献
73.
Hyung Jin Kim Jin Kug Son Young Ho Seo Byeong Hee Kim Won Hee Lee Ki Tae Park Kieth Bong Nahm Eui Yul Choi 《Microsystem Technologies》2014,20(3):499-504
This paper presents a new air-bubble free microfluidic blood cuvette for the measurement of hemoglobin concentration. The microfluidic blood cuvette was filled with blood samples by capillary force, and hemoglobin levels in the blood were determined by measuring absorbance at the wavelength of 530 nm. Two different microfluidic blood cuvettes with dual and single sidewall microchannels were investigated. The microfluidic blood cuvette was fabricated using a polymethyl methacrylate substrate and a dry film photoresist. During the blood-filling process, air was trapped in the dual-sided wall-type cuvettes, while no air trapping occurred in the single sidewall-type cuvettes. The sensitivity of the hemoglobin measurements was more linear in a 105 μm deep microchannel than in a 35 μm deep microchannel. 相似文献
74.
75.
Mir Im Sang-Hyo Kweon Jin-Seong Kim Sahn Nahm Ji-Won Choi Seong-Ju Hwang 《Ceramics International》2014
KTiNbO5 (KTN) and K3Ti5NbO14 (3K5TN) ceramics sintered at 1150 °C and 1125 °C, respectively, exhibited a dense, homogeneous microstructure with a high relative density (≥96% of the theoretical density). Abnormal grain growth occurred in both specimens during sintering, and large (002) and (001) grains developed in KTN and 3K5TN ceramics, respectively. A dielectric constant (εr) of 13 and a dielectric loss of 2.9% at 10 MHz were obtained from KTN ceramics sintered at 1150 °C. The 3K5TN ceramics sintered at 1125 °C showed an εr of 15 and a dielectric loss of 12% at 10 MHz. The resistivity of KTN and 3K5TN ceramics was low and their εr and dielectric loss values displayed low-frequency dispersion (LFD); the presence of K+ ions between the layers could be responsible for their low resistivity and LFD. 相似文献
76.
77.
Hwi-Yeol Park In-Tae Seo Jae-Hong Choi Sahn Nahm Hyeung-Gyu Lee 《Journal of the American Ceramic Society》2010,93(1):36-39
(Na0.5 K0.5 )NbO3 (NKN) ceramic with 1.5 mol% CuO added (NKNC) was well sintered even at a low temperature of 900°C with the addition of ZnO. Most of the ZnO reacted with the CuO and formed the liquid phase that assisted the densification of the specimens at 900°C. A few Zn2+ ions entered the matrix of the specimens and increased the coercive field ( E c ) and Q m values of the specimens. High-piezoelectric properties of k p =0.37, Q m =755, and ɛ3 T /ɛ0 =327 were obtained from the NKNC ceramics containing 1.0 mol% ZnO sintered at 900°C for 2 h. 相似文献
78.
Sang Myoung Lee Myong Jae Yoo Seong Dae Park Jong Chul Park Sahn Nahm 《International Journal of Applied Ceramic Technology》2010,7(Z1):E9-E15
Conventional free sintering of low-temperature co-firing ceramic (LTCC) technology has several merits such as sintering temperature below 1000°C that enables co-firing with electrode materials of silver or copper metal and multilayer structure formation. But due to the free sintering process, large shrinkage occurs. To fabricate electronic devices and components with near zero shrinkage within x, y directions constrained sintering (CS) technology is required. In this study a constrained sintering paste (CSP) utilizing alumina powder, which has a higher sintering temperature than LTCC powders, was fabricated for CS technology. The effect of CSP formulated using alumina powder on shrinkage was studied according to variation in paste composition. As a result ceramic package structure with a cavity was fabricated with shrinkage control of 0.028%, which is far smaller than the current CS technology shrinkage of approximately 0.1%. 相似文献
79.
80.
Dae-Ryong Jung Jongmin Kim Changwoo Nahm Seunghoon Nam Jae Ik Kim Byungwoo Park 《Materials Research Bulletin》2012,47(2):453-457
To examine the effect of metal nanostructures on the photoluminescence of CdS nanoparticles, Au/SiO2 nanocomposites were prepared with back-reflection geometry. The contribution from the prolonged optical-path lengths was excluded, and the luminescence enhancement was attributed only to surface-plasmon resonance. The optimum nanostructures for the PL enhancement were examined, and correlated with the wavelength of the surface-plasmon peak of the Au/SiO2 nanocomposites and the PL emission peak of CdS nanoparticles. 相似文献