• Current Photovoltaic Research
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• v.1 no.2
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• pp.82-89
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• 2013

$Cu_2ZnSnS_4$ thin film have been fabricated by rapid thermal annealing of dc-sputtered metal precursor with Cu/ZnSn/Cu stack in sulfur ambient. A CZTS film with a good uniformity was formed at $560^{\circ}C$ in 6 min. $Cu_2SnS_3$ and $Cu_3SnS_4$ secondary phases were present at $540^{\circ}C$ and a trace amount of $Cu_2SnS_3$ secondary phase was present at $560^{\circ}C$. Single-phase large-grained CZTS film with rough surface was formed at $560^{\circ}C$. Solar cell with best efficiency of 4.7% ($V_{oc}=632mV$, $j_{sc}=15.8mA/cm^2$, FF = 47.13%) for an area of $0.44cm^2$ was obtained for the CZTS absorber grown at $560^{\circ}C$ for 6 min. The existence of second phase at lower-temperature annealing and rough surface at higher-temperature annealing caused the degradation of cell performance. Also poor back contact by void formation deteriorated cell performance. The fill factor was below 0.5; it should be increased by minimizing voids at the CZTS/Mo interface. Our results suggest that CZTS absorbers can be grown by rapid thermal annealing of metallic precursors in sulfur ambient for short process times ranging in minutes.

• Journal of environmental and Sanitary engineering
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• v.21 no.4 s.62
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• pp.77-86
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• 2006

The water purification was very important in Korea which has not sufficient water resource and while adsorption method among the various methods to eliminate the water pollutants has been widely used by activated carbon. This study was conducted the basic experiment for hall distribution, pH, conductivity, electronic microscope, cation exchange and inorganic materials the adsorption capacity of Korean traditional charcoal which has similar characteristics to activated carbon of organic pollutants. As a result of observing Korean traditional charcoal with electronic microscope, it was found that it has porous structure, oak charcoal has circular structure, pine charcoal has square structure and bamboo charcoal has hexagonal structure, which has high void fraction per unit area because of its thin cell wall structure. As a result of experimenting hall distribution, hall distribution of bamboo high temperature charcoal is high as 0.269cc/g and has the greatest inorganic contents and cation exchange capacity(CEC) which are the important factor of chemical adsorption.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.71-77
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• 2008

Microstructural changes may arise due to the particle vanishing, fluid diffusion, heating, etc. This study focuses on the changes in small-strain shear stiffness in k0 loading produced by local straining in particular system made of sand-salt mixtures. Local strains were induced by dissolution of salt particles. Experiments were carried out in a conventional oedometer cell equipped with bender elements. Axial displacement and shear wave signals are recorded at each loading stage and during saturation process. Experimental data showed that microstructural changes due to particle vanishing were clearly captured by using shear wave measurement. Saturation of sand-salt mixture at a larger axial stress did not always create a more condense soil at the end of loading stage. Sand-salt mixture is useful for laboratory test on controlled artificial specimen.

• Geomechanics and Engineering
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• v.1 no.3
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• pp.241-257
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• 2009

The one-dimensional compressibility of sand is an important property for the estimation of settlement or deformation of sand deposits. The $K_0$ value of sand is also an important design parameter. Experimental results are presented in this paper to study the compressibility of sand in $K_0$ consolidation tests. The $K_0$ consolidation tests were carried out using a triaxial cell and a plane-strain apparatus. Specimens prepared using both the moist tamping and the water sedimentation methods were tested. The testing data demonstrate that the type of testing apparatus does not affect the $K_0$ measurement if proper boundary conditions are imposed in the tests. The data also show that the compressibility and the $K_0$ value of loose sand specimens prepared using the moist tamping method are very sensitive to the variation of void ratio. The $K_0$ values measured from these tests do not agree with the $K_0$ values calculated from Jaky's equation. The compressibility and $K_0$ values of sand obtained from tests on specimens prepared using different preparation methods are different which may reflect the influence of soil fabrics or structures on the one dimensional compression behavior of sand.

• Nuclear Engineering and Technology
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• v.41 no.10
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• pp.1347-1360
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• 2009

A multi-dimensional component for the thermal-hydraulic system analysis code, MARS, was developed for a more realistic three-dimensional analysis of nuclear systems. A three-dimensional and two-fluid model for a two-phase flow in Cartesian and cylindrical coordinates was employed. The governing equations and physical constitutive relationships were extended from those of a one-dimensional version. The numerical solution method adopted a semi-implicit and finite-difference method based on a staggered-grid mesh and a donor-cell scheme. The relevant length scale was very coarse compared to commercial computational fluid dynamics tools. Thus a simple Prandtl's mixing length turbulence model was applied to interpret the turbulent induced momentum and energy diffusivity. Non drag interfacial forces were not considered as in the general nuclear system codes. Several conceptual cases with analytic solutions were chosen and analyzed to assess the fundamental terms. RPI air-water and UPTF 7 tests were simulated and compared to the experimental data. The simulation results for the RPI air-water two-phase flow experiment showed good agreement with the measured void fraction. The simulation results for the UPTF downcomer test 7 were compared to the experiment data and the results from other multi-dimensional system codes for the ECC delivery flow.

• Smart Structures and Systems
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• v.7 no.4
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• pp.275-287
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• 2011

The behaviors of saturated soils such as compressibility and permeability are distinguished by preconsolidation stress. Preconsolidation stress becomes an important design parameter in geotechnical structures. The goal of this study is to introduce a new method for the evaluation of preconsolidation stress based on the shear wave velocity at small strain, using Busan, Incheon, and Gwangyang clays in Korea. Standard consolidation tests are conducted by using an oedometer cell equipped with bender elements. The preconsolidation stresses estimated by shear wave velocity are compared with those evaluated by the Casagrande, constrained modulus, work, and logarithmic methods. The preconsolidation stresses estimated by the shear wave velocity produce very similar values to those evaluated by the Onitsuka method (one of the logarithmic methods), which yields an almost real preconsolidation stress. This study shows that the shear wave velocity method provides a reliable method for evaluating preconsolidation stress and can be used as a complementary method.

• International Journal of Highway Engineering
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• v.16 no.4
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• pp.63-74
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• 2014

PURPOSES: This research is to evaluate the mechanical performance of different types of Hot Mix Asphalt (HMA) pavement cells prepared for MN/Road field testing section through an extensive experimental analysis of air voids and simple statistical evaluation tools (i.e. hypothesis test). METHODS: An extensive experimental work was performed to measure air voids in 82 asphalt mixture cores (238 samples in total) obtained from nine different types of road cell located in MN/Road testing field. In order to numerically and quantitatively address the differences in air voids among the different test Cells built in MN/Road, a simple statistical test method (i.e. t-test) with 5% significance was used. RESULTS: Similar trends in air voids content were found among the mixtures including conventional HMA, Reclaimed Asphalt Pavement (RAP) and Warm Mix Asphalt (WMA) combined with taconite aggregate this provides support to the use of RAP and WMA technology in the constructions of asphalt pavement. However, in case of acid modified HMA mixtures, significant differences in air void content were observed between on the wheel path and between wheel path location, which implies negative performances in rutting and thermal cracking resistances. Conclusions : It can be concluded that use of RAP and WMA technology in the construction of conventional asphalt pavement and the use of PPA (Poly Phosphoric Acid) in combinations with SBS (Styrene Butadiene Styrene) in asphalt binder production provide satisfactory performance and, therefore, are highly recommended.

• Korean Journal of Materials Research
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• v.23 no.3
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• pp.183-189
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• 2013

$Cu_2ZnSn(S,Se)_4$ material is receiving an increased amount of attention for solar cell applications as an absorber layer because it consists of inexpensive and abundant materials (Zn and Sn) instead of the expensive and rare materials (In and Ga) in $Cu(In,Ga)Se_2$ solar cells. We were able to achieve a cell conversion efficiency to 4.7% by the selenization of a stacked metal precursor with the Cu/(Zn + Sn)/Mo/glass structure. However, the selenization of the metal precursor results in large voids at the absorber/Mo interface because metals diffuse out through the top CZTSe layer. To avoid the voids at the absorber/Mo interface, binary selenide compounds of ZnSe and $SnSe_2$ were employed as a precursor instead of Zn and Sn metals. It was found that the precursor with Cu/$SnSe_2$/ZnSe stack provided a uniform film with larger grains compared to that with $Cu_2Se/SnSe_2$/ZnSe stack. Also, voids were not observed at the $Cu_2ZnSnSe_4$/Mo interface. A severe loss of Sn was observed after a high-temperature annealing process, suggesting that selenization in this case should be performed in a closed system with a uniform temperature in a $SnSe_2$ environment. However, in the experiments, Cu top-layer stack had more of an effect on reducing Sn loss compared to $Cu_2Se$ top-layer stack.

• Current Photovoltaic Research
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• v.7 no.1
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• pp.1-8
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• 2019

The $Cu(In,Ga)Se_2$ (CIGS) thin film obtained by two-step process (metal deposition and Se annealing) has a rough surface morphology and many voids at the CIGS/Mo interface. To solve the problem a precursor that contains Se was employer by depositing a (In,Se)/(Cu,Ga) stacked layer. We devised a two-step annealing (vacuum pre-annealing and Se annealing) for the precursor because direct annealing of the precursor in Se environment resulted in the small grains with unwanted demarcation between stacked layers. After vacuum pre-annealing up to $500^{\circ}C$ the CIGS film consisted of CIGS phase and secondary phases including $In_4Se_3$, InSe, and $Cu_9(In,Ga)_4$. The secondary phases were completely converted to CIGS phase by a subsequent Se annealing. A void-free CIGS/Mo interface was obtained by the two-step annealing process. Especially, the CIGS film prepared by vacuum annealing $450^{\circ}C$ and subsequent Se annealing $550^{\circ}C$ showed a densely-packed grains with smooth surface, well-aligned bamboo grains on the top of the film, little voids in the film, and also little voids at the CIGS/Mo interface. The smooth surface enhanced the cell performance due to the increase of shunt resistance.

• Journal of the Korean Geotechnical Society
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• v.23 no.6
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• pp.23-36
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• 2007

To overcome the limits of the static pile load test for large diameter drilled shafts, bi-directional low pressure pile load test (BDL PLT) has been used but this test method containes some problems that has not been solved basically. That is, BDL PLT has some problems: difficulty in jack (or cell) arrangement for large test capacity, void remain inside jack (or cell) due to the unrecovery of piston after test etc. In this study, bi-directional double-acting high pressure pile load test (BDH PLT W/DOJ) was developed and confirmed for a in-situ large diameter drilled shaft. At present, test specification of bi-directional pile load test (BDPLT) is being made, and severed main issues (such as, test kinds, test capacity, necessity of use of double-acting and attention of application to service pile) will be contained at the specification.