• Proceedings of the Korea Concrete Institute Conference
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• 2006.05a
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• pp.606-609
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• 2006

In this study, it was selected that in order to make an investigation into the status of the unit water content control of the ready-mixed concrete plants in the country, Capacitance Measurement Method out of various methods which are able to gauge the amount of unit water content in fresh concrete. Then, it were estimated that the quantity of unit water in fresh concrete and the technical standard of every mixture design of the six ready-mixed concrete plants chosen at random in the country. Finally, based on this study, it was proposed as fundamental data to utilize measurement techniques of the quantity of unit water for the quality control of the ready-mixed concrete in construction field.

• Geomechanics and Engineering
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• v.6 no.4
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• pp.403-418
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• 2014

There are around 6700 millions tons of perlite reserves in the world. Although perlite possesses pozzolanic properties, it has not been so far used in soil stabilization. In this study, stabilization with perlite and lime of an expansive clayey soil containing smectite group clay minerals such as montmorillonite and nontronite was investigated experimentally. For this purpose, test mixtures were prepared with 8% of lime (optimum lime ratio of the soil) and without lime by adding 0%, 10%, 20%, 30%, 40% and 50% of perlite. Geotechnical properties such as compaction, Atterberg limits, swelling, unconfined compressive strength of the mixtures and changes of these properties depending on perlite ratio and time were determined. The test results show that stabilization of the soil with combination of perlite and lime improves the geotechnical properties better than those of perlite or lime alone. This experimental study unveils that the mixture containing 30% perlite and 8% lime is the optimum solution in stabilization of the soil with respect to strength.

• Journal of the Korean Chemical Society
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• v.12 no.4
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• pp.155-159
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• 1968

On the extraction of humic acid from peat, the optimum conditions were studied and the effects of them on the characteristics of humic acid were also examined by means of infrared spectroscopy. 1. Pretreatment of peat with diluted 6-8% HCl solution for 5 hrs. prior to extraction with alcohol-benzol azeotropic mixture have resulted the better yield of humic acid. The water soluble Na-humates were obtained by the subsequent extraction with one hundred times quantity of caustic soda solutieon for 1hr. at 90 $^{\circ}C$. Thus the pure humic acids have been yielded approximately 40% (by wt.) from the raw peat. 2. In characteristics of humic acid, the chemical structure, mainly the contents of such functional groups as -COOH, -OH (phenol type), $-CH_2CO-$, $-CH_2{\cdot}O{\cdot}CH_2-$ and aromatic rings were varied according to the concentration of alkaline solution, temperature and time when the humic acids were extracted with alkali.

• Steel and Composite Structures
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• v.28 no.3
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• pp.381-388
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• 2018

In this paper, forced vibration of micro cylindrical shell reinforced by functionally graded carbon nanotubes (FG-CNTs) is presented. The structure is subjected to transverse harmonic load and modeled by beam model. The size effects are considered based on strain gradient theory containing three small scale parameters. The mixture rule is used for obtaining the effective material properties of the structure. Based on sinusoidal shear deformation theory of beam, energy method and Hamilton's principle, the motion equations are derived. Applying differential quadrature method (DQM) and Newmark method, the frequency curves of the structure are plotted. The effect of different parameters including, CNTs volume percent and distribution type, boundary conditions, size effect and length to thickness ratio on the frequency curves of the structure is studied. Numerical results indicate that the dynamic deflection of the FGX-CNT-reinforced cylindrical is lower with respect to other type of CNT distribution.

• Journal of the Korean Society of Industry Convergence
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• v.12 no.3
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• pp.137-142
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• 2009

Burning velocity of methane-air mixtures with water vapor have been measured to study the process of flame propagation using schlieren photographs and computation. The computations were carried out for the burning velocity using premix code of Chemkin program to compare the experimental results. The quantity of water vapor contained were changed 5% and 10% of total mixtures, and equivalence ratio of mixtures between 0.8 and 1.2 were tested under the ambient temperature 323K and 373K. The results showed little difference between these two methods, the burning velocity was decreased by increasing the water vapor contents due to the interruption of flame development. And, the effect of ambient temperature was less significant by increasing the water contents on the burning velocity.

• Proceedings of the KIEE Conference
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• 1997.07e
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• pp.1819-1823
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• 1997

When flammable gases are mixed with air or oxygen in the explosion concentration range and are ignited by sufficiently large electrostatic discharge energy, they may explode causing severe disaster in workplaces. The minimum ignition energy (MIE) of single gas-air mixtures has been already investigated by many researchers, but the MIE of mixtures of more than three substances is not examined yet. The purpose of this study is to investigate the MIE of several three-component gas mixtures experimentally. The result of our experiment shows that the MIE of some gas mixtures is quite different from that we expected based on the characteristics of individual gas-air mixture.

• Steel and Composite Structures
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• v.23 no.6
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• pp.623-631
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• 2017

Present paper deals with the temperature-dependent buckling analysis of sandwich nanocomposite plates resting on elastic medium subjected to magnetic field. The lamina layers are reinforced with carbon nanotubes (CNTs) as uniform and functionally graded (FG). The elastic medium is considered as orthotropic Pasternak foundation with considering the effects of thermal loading on the spring and shear constants of medium. Mixture rule is utilized for obtaining the effective material properties of each layer. Adopting the Reddy shear deformation plate theory, the governing equations are derived based on energy method and Hamilton's principle. The buckling load of the structure is calculated with the Navier's method for the simply supported sandwich nanocomposite plates. Parametric study is conducted on the combined effects of the volume percent and distribution types of the CNTs, temperature change, elastic medium, magnetic field and geometrical parameters of the plates on the buckling load of the sandwich structure. The results show that FGX distribution of the CNTs leads to higher stiffness and consequently higher buckling load. In addition, considering the magnetic field increases the buckling load of the sandwich nanocomposite plate.

• Smart Structures and Systems
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• v.20 no.5
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• pp.583-593
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• 2017

This research deals with the nonlocal temperature-dependent dynamic buckling analysis of embedded sandwich micro plates reinforced by functionally graded carbon nanotubes (FG-CNTs). The material properties of structure are assumed viscoelastic based on Kelvin-Voigt model. The effective material properties of structure are considered based on mixture rule. The elastic medium is simulated by orthotropic visco-Pasternak medium. The motion equations are derived applying Sinusoidal shear deformation theory (SSDT) in which the size effects are considered using Eringen's nonlocal theory. The differential quadrature (DQ) method in conjunction with the Bolotin's methods is applied for calculating resonance frequency and dynamic instability region (DIR) of structure. The effects of different parameters such as volume percent of CNTs, distribution type of CNTs, temperature, nonlocal parameter and structural damping on the dynamic instability of visco-system are shown. The results are compared with other published works in the literature. Results indicate that the CNTs have an important role in dynamic stability of structure and FGX distribution type is the better choice.

• Journal of the Speleological Society of Korea
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• no.78
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• pp.1-8
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• 2007

The combination of mechano-chemical activation (MCA)and Self-propagating High-temperature Synthesis (SHS) has widened the technical possibilities for both methods. For YBCO systems the investigation showed that a short-term MCA of initial powders before SHS leads to single-phase and ultra-fine products. A new technique for preparation ultra-fine high-temperature superconductors (HTS) of YBCO composition with a grain size d <1m is developed using combination of MCA and SHS. The specific feature of the technique is formation of the $YBa_2Cu_3O_7-$ crystalline lattice directly from an X-ray amorphous state arising as a result of mechanical activation of the original oxide mixture. The technique allows the stage of formation of any intermediate reaction products to be ruled out. X-ray and magnetic studies of ultra-fine high temperature superconductors are carried out. Dimension effects associated with the microstructure peculiarities are revealed. A considerable enhancement of inter-grain critical currents is found to take place in the ultra-fine samples.

• Journal of the Korean Chemical Society
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• v.60 no.4
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• pp.251-256
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• 2016

This paper describes the synthesis of alkali metal salts of urea (ureates) and their application to the direct preparation of 4-nitrosoaniline from nitrobenzene via nucleophilic aromatic substitution of hydrogen. Sodium and potassium ureates were readily prepared from the reaction of urea with sodium hydride, metal methoxides, and metal hydroxides. The effect of ureates as nucleophiles on the conversion of nitrobenzene to 4-nitrosoaniline was investigated and compared with that of a urea-metal hydroxide mixture. It was found that the ureates were superior for producing 4-nitrosoaniline owing to their higher thermal stability of the ureate. The ureate obtained from the treatment of urea with sodium hydride gave the highest yield for the preparation of 4-nitrosoaniline. The ureates generated from the reaction of urea with metal hydroxide also gave high yields of 4-nitrosoaniline. Catalytic hydrogenation of 4-nitrosoaniline afforded polymer-grade 1,4-benzenediamine in quantitative yield.