• International Journal of Advanced Culture Technology
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• v.3 no.2
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• pp.100-109
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• 2015

Environmental problems from petroleum-based plastic wastes have been rapidly increasing in recent years. The alternative solution is focus on the development of environmental friendly plastic derived from renewable resource. Poly(lactic acid) (PLA) is a biodegradable polymer synthesized from biomass having potential to replace the petroleum-based non-degradable polymers utilizations. PLA can be synthesized by two methods: (1) ring-opening of lactide intermediate and (2) direct polycondensation of lactic acid processes. The latter process has advantages on high yields and high purity of polymer products, materials handling and ease of process treatments. The polymerization process of PLA synthesis has been widely studied in a laboratory scale. However, the mass scale production using direct polycondensation of lactic acid has not been reported. We have investigated the kinetics and scale-up process of direct polycondensation method to produce PLA in a pilot scale. The order of reaction is 2 and activation energy of lactic acid to lactic acid oligomers is 61.58 kJ/mol. The pre-polymer was further polymerized in a solid state polymerization (SSP) process. The synthesized PLA from both the laboratory and pilot scales show the comparable properties such as melting temperature and molecular weight. The appearance of synthesized PLA is yellow-white solid powder.

• Journal of Periodontal and Implant Science
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• v.38 no.1
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• pp.67-74
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• 2008

Purpose: The aim of this study was to evaluate the effect of Er:YAG laser on microstructure and roughness of $TiO_2$ blasting implant surface. Materials and Methods: Ten $TiO_2$ blasting implant were used in this experiment. One implant was control group, and nine $TiO_2$ blasting implant surfaces were irradiated with Er:YAG laser under 100 mJ/pulse, 140 mJ/pulse, and 180 mJ/pulse condition for 1 min, 1.5 min, and 2 min respectively. Optical interferometer and scanning electron microscopy was utilized to measure roughness and microstructure of specimens. Results: The surface roughness was decreased after Er:YAG laser irradiation in all groups, but there was no significant difference. 100 mJ/pulse and 140 mJ/pulse group did not alter the $TiO_2$ blasting implant surface in SEM study while 180 mJ/pulse group altered the $TiO_2$ blasting implant surface. Implant surfaces showed melting, microfracture and smooth surface in 180 mJ/pulse group. Conclusion: Detoxification of implant surface using Er:YAG laser must be irradiated with proper energy output and irradiation time to prevent implant surface alteration.

• Journal of the Korean Society of Propulsion Engineers
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• v.21 no.6
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• pp.32-38
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• 2017

Plasticizers play roles in increasing plasticity or fluidity during mixing. Representative plasticizers are DOS, DOA, IDP and BTTN. In particular, BTTN is an energy plasticizer that helps propellant performance and is widely used. However these compounds are sensitive relatively. So, in order to develop insensitive energetic plasticizer, synthesis of one of the derivatives of triazole, 4,5-bis (azido methyl)-(1-butyl)-1,2,3-triazole (1-DABTR), was studied. Also, the compound was characterized by NMR, IR spectroscopy, and physicochemical properties such as glass transition temperature, melting point, decomposition temperature, density, viscosity and impact sensitivity were measured. In addition, the heats of formation (${\Delta}H_f$) of 1-DABTR was also calculated using Gaussian 09.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.11
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• pp.1133-1137
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• 2011

A novel technique for the fabrication of a glass micropipette-based thermal sensor was developed utilizing inexpensive thermocouple materials. Thermal fluctuation with a resolution of ${\pm}0.002$ K was measured using the fabricated thermal probe. The sensors comprise unleaded low-melting point solder alloy (Sn) as a core metal inside a borosilicate glass pipette coated with a thin film of Ni, creating a thermocouple junction at the tip. The sensor was calibrated using a thermally insulated calibration chamber, the temperature of which can be controlled with a precision of ${\pm}0.1$ K and the thermoelectric power (Seebeck coefficient) of the sensor was recorded from 8.46 to $8.86{\mu}V$/K. The sensor we have produced is both cost-effective and reliable for thermal conductivity measurements of micro-electromechanical systems (MEMS) and biological temperature sensing at the micron level.

• Korean Journal of Materials Research
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• v.24 no.1
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• pp.48-52
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• 2014

The Mg-enriched magnesium aluminum silicate (MAS) glass is known for its higher mechanical strength and chemical resistance. Among such glasses, cordierite ($Mg_2Al_4Si_5O_{18}$) is well known to have a low thermal expansion and low melting point. Polycrystalline engineering ceramics such as alumina can be strengthened by a surface modification with low thermal expansion materials. The present study involves the synthesis of cordierite by a sol-gel process and investigates the effect of glass penetration on the surface of alumina. The cordierite powders were prepared from $Al(OC_3H_7)_3$, $Mg(OC_2H_5)_2$ and tetraethyl orthosilicate by hydrolysis and condensation reaction. The cordierite powders were characterized by X-ray diffraction (XRD, Rigaku), scanning electron microscope (SEM, JEOL: JSM-5610), energy dispersive spectroscopy (EDS, JEOL: JSM-5610), and universal testing machine (UTM, INSTRON). The X-ray diffraction patterns showed that the synthesized particles were ${\mu}$-cordierite calcined at $1100^{\circ}C$ for 1 h. The shape of synthesized cordierite was changed from ${\mu}$-cordierite to ${\alpha}$-cordierite with increasing calcination temperature. Synthesized cordierite was used for surface modification of alumina. Cordierite powders penetrated deeply into the alumina sample along grain boundaries with increasing temperature. The results of surface modification tests showed that the strength of the prepared alumina sample increased after surface modification. The strength of a surface modified with synthesized cordierite increased the most, to about 134.6MPa.

• Journal of the Korea Institute of Military Science and Technology
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• v.15 no.2
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• pp.201-207
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• 2012

Pulsed lasers at the 613 nm and 1064 nm wavelengths on nanoseconds have been utilized to characterize the damage on Si photodiode exposed to intense illumination. Morphological damages and structural changes at sites on the photodiode irradiated during microseconds of laser pulses were analyzed by FE-SEM images and XRD patterns, respectively. The removal of oxide coating, ripple, melting marks, ridges, and crater on photodiodes were definitely observed in order of increasing the pulse intensities generated above the damage threshold. Then, the degradation in photosensitivity of the Si photodiode irradiated by high power density pulses was measured as a function of laser irradiation time at the various wavelengths. The free charge carrier and thermal diffusion mechanisms could have been invoked to characterize the damage. The relative photosensitivity data calculated using the thermal diffusion model proposed in this paper have been compared with the experimental data irradiated above the damage threshold.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.51 no.6
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• pp.229-235
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• 2002

This paper presents the fabrication of polycrystalline thin film transistor(TFT) using sequential lateral solidification(SLS) of amorphous silicon. The fabricated SLS TFT showed high Performance suitable for active matrix liquid crystal display(AMLCD). The SLS process involves (1) a complete melting of selected area via irradiation through a patterned mask, and (2) a precisely controlled pulse translation of the sample with respect to the mask over a distance shorter than the super lateral growth(SLG) distance so that lateral growth extended over a number of iterative steps. The SLS experiment was performed with 550$\AA$ a-Si using 308nm XeCl laser having $2\mu\textrm{m}$ width. Irradiated laser energy density is 310mJ/$\textrm{cm}^2$ and pulse duration time was 25ns. The translation distance was 0.6$\mu$m/pulse, 0.8$\mu$m/pulse respectively. As a result, a directly solidified grain was obtained. Thin film transistors (TFTs) were fabricated on the poly-Si film made by SLS process. The characteristics of fabricated SLS p -type poly-Si TFT device with 2$\mu\textrm{m}$ channel width and 2$\mu\textrm{m}$ channel length showed the mobility of 115.5$\textrm{cm}^2$/V.s, the threshold voltage of -1.78V, subthreshold slope of 0.29V/dec, $I_{off}$ current of 7$\times$10$^{-l4}$A at $V_{DS}$ =-0.1V and $I_{on}$ / $I_{off}$ ratio of 2.4$\times$10$^{7}$ at $V_{DS}$ =-0.1V. As a result, SLS TFT showed superior characteristics to conventional poly-Si TFTs with identical geometry.y.y.y.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2001.11a
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• pp.67-67
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• 2001

The structure zone model has been used to provide an overview of the relationship between the microstructure of the films deposited by PVD and the most prominent deposition condition.s. B.AMovchan and AV.Demchishin have proposed it firstls such model. They concluded that the general features of the resulting structures could be correlated into three zones depending on $T/T_m$. Here T m is the melting point of the coating material and T is the substrate temperature in kelvines. Zone 1 ($T/Tm_) is dominated by tapered macrograins with domed tops, zone 2 ($O.3) by columnar grains with denser boundaries and zone 3 ($T/T_m>O.5$) by equiaxed grains formed by recrystallization. J.AThomton has extended this model to include the effect of the sputtering gas pressure and found a fourth zone termed zone T(transition zone) consisting of a dense array of poorly defined fibrous grains. R.Messier found that the zone I-T boundary (fourth zone of Thorton) varies in a fashion similar to the film bias potential as a function of gas pressure. However, there has not nearly enough model for explaining the change in morphology with crystal orientation of the films. The structure zone model only provide an information about the morphology of the deposited film. In general, the nucleation and growth mechanism for granular and fine structure of the deposited films are very complex in an PVD technique because the morphology and orientation depend not only on the substrate temperature but also on the energy of deposition of the atoms or ions, the kinetic mechanism between metal atoms and argon or nitrogen gas, and even on the presence of impurities. In order to clarify these relationship, AI and Mg thin films were prepared on SPCC steel substrates by PVD techniques. The influence of gas pressures and bias voltages on their crystal orientation and morphology of the prepared films were investigated by SEM and XRD, respectively. And the effect of crystal orientation and morphology of the prepared films on corrosion resistance was estimated by measuring polarization curves in 3% NaCI solution.

• Journal of the Korean Society of Safety
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• v.26 no.4
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• pp.41-46
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• 2011

The purpose of this paper is to analyze the causes of accidents related to the 3 phase 170 kV gas insulated switchgear of a power system collected from accident sites to secure data for the prevention of similar accidents and provide important points of view regarding diagnosis for the prevention of accidents involving gas insulated switchgears. The analysis results of the causes of accidents involving gas insulated switchgears showed deformation of the manipulation lever installed at the S-phase, disconnection of the insulation rod connection, melting of the upper conductor, a damaged tulip, damage to the lower spacer and the spacer at the breaker, etc. It is believed from this result that the potential for accidents has expanded due to accumulated energy as a result of repeated deterioration. The carbonization depth of a GIS was formed near the screw (T2, T3) used to secure the lower pole of the S-phase tulip. It is not known what has caused the screws to be extruded and melted. However, it is thought that an unbalanced electromagnetic force, micro-discharge, surface discharge, etc., have occurred at that point. In addition, even though 16 years have passed since its installation, there was no installation defect, act of arson, accidental fire, etc. General periodical inspection and diagnosis failed to find the factors causing the accidents. As a system contained in a closed metal container, it has a high risk factor. Therefore, it is necessary to design, install and operate a GIS in accordance with the standard operational procedure (SOP). In addition, it is necessary to apply conversion technology for periodical SF6 gas analysis and precision safety diagnosis. It is expected that tracking and managing these changes in characteristics by recording the results on the history card will provide a significant accident prevention effect.

• Polymer(Korea)
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• v.29 no.1
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• pp.41-47
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• 2005

The transesterification of dimethyl terephthalate (DMT) with 1,3-propanediol (PDO) was investigated in the presence of catalyst, titanium (IV) butoxide (TBO), at 175~190 $^{\circ}C$ . The degree of transesterification reaction was measured by the output of methanol which was distilled from the reactor. The amount of methanol increased as the reaction temperature, molar ratio and catalyst concentration increased. The observed overall rate of the transesterification was third order; first order with respect to DMT, PDO, and the concentration of catalyst, respectively. Using calculated rate constants, the activation energy for transesterification was 26.93 kcal/mole. The melting temperature of bis(2-hydroxytrimethyl) terephthalate (BHTMT) was 85.2$^{\circ}C$ and heat of fusion 141.3 J/g.