• Journal of Applied Reliability
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• v.12 no.3
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• pp.177-186
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• 2012

This paper presents a comparison of the failure mechanism for high power converted white LEDs(3W) with the commercially available YAG:Ce and silicate phosphor. We carry out the normal aging life test for 10,000 hours, the high temperature aging test for 8,000 hours, the high temperature and humidity aging test for 8,000 hours and the current aging testing for 5,000 hours. The optical and electrical parameters of LEDs were monitored, such as lumen, correlated color temperature (CCT), chromaticity coordinates(x, y), thermal resistance, I -V curve and spectrum intensity. The stress induced a luminous flux decay on LED in all experiments and causes a failure. So we try to find out what's a main failure mechanism for a high power LED.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2415-2418
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• 2008

Polydiacetylenes (PDAs) are very attractive chemical substances which have distinctive features of color change and fluorescence emission by thermal or chemical stress. Especially, when PDAs contact with solutions of a particular pH, such as a strong alkaline sodium hydroxide (NaOH) solution or a strong acidic hydrogen chloride (HCl) solution, PDAs change their color from non-fluorescent blue to fluorescent red. In this study, we propose a novel method to detect alkaline pH using PDAs and NaOH solutions by hydrodynamic focusing on a microfluidic chip. Preliminary results indicate that the fluorescent intensity of PDAs increases in respond to the NaOH solution concentrations. Also, the fluorescence is quenched back when the PDAs are in contact with a HCl solution. These results are useful in a microfluidic PDA sensor chip design for pH detection.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2696-2699
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• 2008

Microfluidic chips have been frequently utilized to perform biochemical analysis, like cell culture, because they reduce the consumptions of analytes and reagents and automate multi-step analysis processes. It is often critical to monitor temperature in a microchannel for the analyses in order to control a reaction condition of bio or chemical molecules. We propose a novel method to monitor temperature of a microchannel flow by using polydiacetylene (PDA), a conjugated polymer, that has a unique property to transform its color from visible blue to fluorescent red by thermal stress. We inject PDA sensor droplets generated by hydrodynamic instability into a microchannel with a microheater incorporated on the channel bottom. Also, we change the channel temperature by providing the different electric power to the microheater. The results show that the florescence intensity of PDA sensor droplets linearly increases in response to the flow temperature increase within a certain range.

• Composites Research
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• v.17 no.1
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• pp.10-17
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• 2004

In this work, the blend system prepared from epoky(DGEBA)/polymethylmethacrylate(PMMA) was investigated in thermal and mechanical interfacial property measurements. The thermal properties were carried out by DSC, DMA, and TGA measurements. Also, the surface free energy and fracture toughness were determined by contact angle and critical stress intensity factor($K_{IC}$), respectively. And the fracture surface was observed by SEM after $K_{IC}$ tests. As experimental results, the curing temperature and glass transition temperature were slightly increased in addition of PMMA. Surface free energy of the blends showed an improved value at low contents of PMMA which could be attributed to the both increasings of London dispersive and polar components. From measurement of $K_{IC}$ of the blends, the highest value was found at 5 phr. This was due to the increasing of compatibility or physical interaction in macromolecular chains between DGEBA and PMMA of the blends.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.7
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• pp.543-551
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• 2012

In this study, transparent conducting Al-doped Zinc Oxide (AZO) films with a thickness of 150 nm were prepared on corning glass substrate by the RF magnetron sputtering with using a Al-doped zinc oxide (AZO), ($Al_2O_3$: 2 wt%) target at room temperature. This study investigated the effect of rapid thermal annealing temperature and oxygen ambient on structural, electrical and optical properties of Al-doped zinc oxide (AZO) thin films. The films were annealed at temperatures ranging from 400 to $700^{\circ}C$ by using Rapid thermal equipment in oxygen ambient. The effect of RTA treatment on the structural properties were studied by x-ray diffraction and atomic force microscopy. It is observed that the Al-doped zinc oxide (AZO) thin film annealed at $500^{\circ}C$ at 5 minute oxygen ambient gas reveals the strongest XRD emission intensity and narrowest full width at half maximum among the temperature studied. The enhanced UV emission from the film annealed at $500^{\circ}C$ at 5 minute oxygen ambient gas is attributed to the improved crystalline quality of Al-doped zinc oxide (AZO) thin film due to the effective relaxation of residual compressive stress and achieving maximum grain size.

• Polymer(Korea)
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• v.27 no.1
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• pp.33-39
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• 2003

In this study, the bisphenol-based DGEBA/GEBS blend systems were studied in cure kinetics, thermal stabilities, and fracture toughness of the casting specimen. The content of DGEBA/DCEBS was varied in 100 : 0, 90 : 10, 80 : 20, 70 : 30, and 60 : 40 wt%. The cure activation energies ($E_a$) of the blend systems were determined by Ozawa's equation. The thermal stabilities, including initial decomposed temperature (IDT), temperatures of maximum rate of degradation ($T_{max}$), and integral procedural decomposition temperature (IPDT) of the cured specimen were investigated by thermogravimetric analysis (TGA). For the mechanical interfacial properties of the specimens, the critical stress intensity factor ($K_{IC}$) test was performed and their fractured surfaces were examined by using a scanning electron microscope (SEM). As a result, $E_a$, IPDT, and $K_{IC}$ show maximum values in the 20 wt% DGEBS content compared with the neat DGEBA resins. This was probably due to the fact that the elevated networks were farmed by the introduction of sulfonyl groups of the DCEBS resin.

• Journal of Animal Environmental Science
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• v.11 no.3
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• pp.177-188
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• 2005

In this study, the thermal environmental factors in a layer f(arm such as dry bulb temperature, relative humidity, black globe temperature and illumination intensity were measured and analyzed to serve as basis for effective design and plan of poultry houses. The correlation analysis between the different factors was also done. Heat Index as measure of the thermal stress was also calculated and analyzed. A $1,000m^2$ laying house, 4 meters high with 52,000 layers in six-stage type cages was used in the measurement of the different environmental parameters. The results were as follows; 1. The temperature of the inside air and materials was directly related to the increase in aerial temperature based on the dry-bulb, black globe temperature reading. The correlation factor of the outside to inside air based on dry bulb setting was very significant at 0.927 The dry bulb temperature for inside temperature ranged from $19.9\~28.8^{\circ}C\;with\;SD+2.2^{\circ}C$ while that of the outside air was $16.2\~33.1^{\circ}C,\;SD+3.5^{\circ}C$. In addition, the temperature of the inside air was very stable. 2. The black globe temperature of the inside air ranged from $20.1\~28.8^{\circ}C,\;SD+2.3^{\circ}C$ while that of the outside air was $16.2\~47.5^{\circ}C,\;SD+6.0^{\circ}C$. 3. The relative humidity of the outside and inside air was $72.4\~100\;and\;50.2\~85.6\%$ with an average of $89.2\;and\;71.7\%$, respectively. 4. The illumination intensity in the laying house was less than 7 lux, with an average of $1.2\~2.5lux$ relative to height indicating that the laying house was well isolated from outside radiation. 5. The heat index of the inside air of the laying house had a high variation from $20.5^{\circ}C,\;SD+2.5^{\circ}C$ while that of the outside air was $13.1\~45.5^{\circ}C$, with an average of $21.6^{\circ}C,\;SD+6.3^{\circ}C$.

• Polymer(Korea)
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• v.26 no.5
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• pp.599-606
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• 2002

In this study, 4,4'-tetraglycidyl diaminodiphenyl methane (TGDDM)/polyamideimide (PAI) blends were cured using diaminodiphenyl sulfone (DDS). And the effect of addition of different PAI contents to neat TGDDM was investigated in the thermal, mechanical, and morphological properties of the blends. The cure behavior and thermal stability of the cured specimens were monitored by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), respectively. Also, the critical stress intensity factor (K$\_$IC/) was measured in UTM, and the phase separation behavior and final morphology of TGDDM/PAI blends were examined in scanning electron microscopy(SEM). As a result, the cure temperature and cure activation energy (E$\_$a/) were decreased with increasing the PAI content. The decreasing of cure temperature and cure activation energy were probably due to the presence of secondary amine group of PAI backbone used as co-initiator. But, the decomposition activation energy (E$\_$t/) and K$\_$IC/ value were increased up to 5. 10 phr of PAI content, respectively and they were decreased above the PAI contents. These results were explained on the basis of chain scission reaction by etherification. And morphology of blends observed from SEM was confirmed in co-continuous structures.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.233-233
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• 2010

CdS thin films were deposited on glass substrates by R.F. magnetron sputtering method and some of the samples were treated by rapid thermal annealing (RTA) process. Effects of thermal annealing on structural and optical properties were investigated at different temperatures ranging from 100 to $600^{\circ}C$. The crystallographic structure of the films and the size of the crystallites in the films were studied by X-ray diffraction. The crystallite sizes were found to increase, and the X-ray diffraction patterns were seen to sharpen by annealing. Optical properties of the films were calculated using the envelope method and the photoluminescence measurements. The optical properties of the films were seen to be dependent on the film thicknesses. The energy gap of the films was found to decrease by annealing. The band edge sharpness of the optical absorption was seen to oscillate by thermal annealing. Annealing over $400^{\circ}C$ was seen to degrade the optical properties of the film. The best annealing temperature for the films was found to be $400^{\circ}C$ from the optical properties. It is observed that the CdS film annealed at $400^{\circ}C$ reveals the strongest UV emission intensity and narrowest full width at half maximum among the temperature ranges studied. The enhanced UV emission from the film annealed at $400^{\circ}C$ is attributed to the improved crystalline quality of CdS thin film due to the effective relaxation of residual compressive stress and achieving maximum grain size. The results show that heat treatments under optimal annealing condition can provide significant improvements in the properties of CdS thin films.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.94.2-94.2
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• 2010

Indium tin oxide (ITO) Thin films were grown on Non-alkarai glass Substrates by PVD method and Subsequently Subjected to ($100^{\circ}C-350^{\circ}C$) Thermal Annealing (TA) In Nitr Oxygen ambinent. Most of all, The effect of TA treatment on the structural properties were studied by using X-Ray diffraction and atomic force microscopy, while optical properties were studied by UV-Transmittance measurements. After TA treatment, the XRD spectra have shown an effective relaxation of the residual compressive stress, As a result, XRD peaks increase of the intensity and narrowing of full width at half-maximun (FWHM). In addtion The microstructure, The surface morphology, the optical transmittance changed and improved, and we investigated The effects of temperature, Time and atmosphere during the TA on the structural and electrical properties of the ITO/glass on TA at $300^{\circ}C$. As a results, the films are highly transparent (80%～89%) in visible region. AFM analysis shows that the films are very smooth with root mean square surface roughness 0.58nm -2.75nm thickness film. It is observed that resistivity of the films drcreases T0 $1.05{\times}10^{-4}{\Omega}cmt$ $6.06{\times}10^{-4}{\Omega}cm$, while mobility increases from $152cm^2/vs$ to $275cm^2/vs$.