• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.23 no.5
• /
• pp.255-264
• /
• 2013

Cobalt aluminate ($CoAl_2O_4$) is a highly stable pigment with excellent resistance to light, weather, etc., which has resulted in widespread use as a ceramic pigment. Due to the unique optical characteristics, $CoAl_2O_4$ is generally used as a coloring agent to decorate porcelain products, glass, paints and plastics. Here, $CoAl_2O_4$ pigments were synthesized by polymerized complex method and solid state reaction. Then $CoAl_2O_4$ pigment were grinded using the attrition milling with 1 mm size zirconia ball for 3 hours. The attrition milling process was performed at the constant speed of 800 rpm and ball to powder weight ratio (BPR) was 100 : 1. The characteristics of synthesized pigment were analyzed by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), particle size analyser (PSA) and CIE $L^*a^*b^*$. The XRD patterns of $CoAl_2O_4$ show single phase spinel structure. The particle size of $CoAl_2O_4$ measured by FE-SEM, TEM and PSA analysis was in the range of 100~200 nm. The blue color of obtained $CoAl_2O_4$ pigments could be confirmed through CIE $L^*a^*b^*$ measurement.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.23 no.1
• /
• pp.51-57
• /
• 2013

We have applied mechanical alloying (MA) to produce Heusler $Fe_2VAl$ thermoelectric alloy using a mixture of elemental $Fe_{50}V_{25}Al_{25}$ powders. An optimal milling and heat treatment conditions to obtain the single phase of Fe2VAl compound with fine microstructure were investigated by X-ray diffraction and differential scanning calorimetry (DSC) measurement. The $Fe_{50}V_{25}Al_{25}$ MA sample ball-milled for 60 hours exhibits a bcc ${\alpha}$-(Fe,V,Al) solid solution. Single phase of Heusler $Fe_2VAl$ compound can be obtained by MA of $Fe_{50}V_{25}Al_{25}$ mixture for 60 hours and subsequently heated up to $700^{\circ}C$. Sintering of the MA powders was performed in a spark plasma sintering (SPS) machine using graphite dies at $900{\sim}1000^{\circ}C$ under 60 MPa. The Vickers hardness of bulk sample sintered at $1000^{\circ}C$ was high value of Hv 870. All compact bodies have a high relative density above 90 % with metallic glare on the surface.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.17 no.3
• /
• pp.121-127
• /
• 2007

We have applied mechanical alloying (MA) to get $Mg_2Si$ thermoelectric material with nano-sized grains. An optimal milling and heat treatment conditions to obtain the single phase of $Mg_2Si$ compound with fine microstructure were investigated by X-ray diffraction and differential scanning calorimetry (DSC) measurement. The $Mg_{66.7}Si_{33.3}$ MA samples ball-milled for $20{\sim}180\;hrs$ exhibit two broad exothermic heat releases around $220^{\circ}C$ and $570^{\circ}C$. On the other hand, MA sample ball-milled far 260 hrs exhibits only a sharp exothermic peak at $230^{\circ}C$ Single phase Mg2Si powder can be obtained by MA of $Mg_{66.7}Si_{33.3}$ mixture for 60 hours and subsequently heated up to $620^{\circ}C$. Sintering of the MA powders was performed in a spark plasma sintering (SPS) machine using graphite dies at $800{\sim}900^{\circ}C$ under 50 MPa. The shrinkage of sintering sample during SPS was significant at about $200^{\circ}C$. All compact bodies have a high relative density above 94% with metallic glare on the surface.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.19 no.6
• /
• pp.288-292
• /
• 2009

Hydrophobic/hydrophilic patterned substrates were fabricated on a glass substrate by a liquid phase deposition (LPD) method. Hydrophobic surface was obtained by modifying ZnO thin films with a rough surface using a fluoroalkyltrimethoxysilane (FAS) and hydrophilic surface was prepared by decomposing FAS on an exposed to UV light. The hexagonal ZnO rods were perpendicularly grown by LPD method on glass substrates with a ZnO seed layer. The diameter and thickness of hexagonal ZnO rods were increased as a function of increases of immersion time. The surface morphology, thickness, crystal structure, transmittance and contact angle of prepared ZnO thin films were measured by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), UV-visible spectrophotometer (UV-vis) and contact angle measurement. Hydrophilic ZnO thin films with a contact angle of $20^{\circ}{\sim}30^{\circ}$ were changed to a hydrophobic surface with a contact angle of $145^{\circ}{\sim}161^{\circ}$ by a FAS surface treatment. Prepared hydrophobic surface was pattered by an irradiation of UV light using shadow mask with $300\;{\mu}m$ or 3 mm dot size. Finally, the hydrophobic surface exposed to UV light was changed to a hydrophilic surface.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.15 no.11
• /
• pp.923-932
• /
• 2002

A stoichiometric mixture of evaporating materials for CdIn$\_$2/S$\_$4/ single crystal thin films was prepared from horizontal furnace. To obtain the single crystal thin films, CdIn$\_$2/S$\_$4/ mixed crystal was deposited on thoroughly etched semi-insulating GaAs(100) substrate by hot wall epitaxy(HWE) system. The source and substrate temperatures were 630 $\^{C}$ and 420 $\^{C}$, respectively. The crystalline structure of single crystal thin films was investigated by the photoluminescence and double crystal X-ray diffraction(DCXD). The carrier density and mobility of CdIn$\_$2/S$\_$4/ single crystal thin films measured from Hall effect by van der Pauw method are 9.01$\times$10$\^$16/ cm$\^$-3/ and 219 ㎠/V$.$s at 293 K, respectively. From the optical absorption measurement, the temperature dependence of energy band gap on CdIn$\_$2/S$\_$4/ single crystal thin films was found to be Eg(T) ＝ 2.7116 eV - (7.74 $\times$ 10$\^$-4/ eV) T$\^$2//(T＋434). After the as-grown CdIn$\_$2/S$\_$4/ single crystal thin films was annealed in Cd-, S-, and In-atmospheres, the origin of point defects of CdIn$\_$2/S$\_$4/ single crystal thin films has been investigated by the photoluminescence(PL) at 10 K. The native defects of V$\_$cd/, V$\_$s/, Cd$\_$int/ and S$\_$int/ obtained by PL measurements were classified as donors or accepters type. And we concluded that the heat-treatment in the S-atmosphere converted CdIn$\_$2/S$\_$4/ single crystal thin films to an optical p-type. Also, we confirmed that In in CdIn$\_$2/S$\_$4/GaAs did not from the native defects because In in CdIn$\_$2/S$\_$4/ single crystal thin films existed in the form of stable bonds.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2008.11a
• /
• pp.66-66
• /
• 2008

본 연구에서는 ITO/Ag/ITO 다층 박막을 유기발광소자와 플렉시블 광전소자의 전극으로 적용하기 위하여 선형 대항 타겟 스퍼터(Linear facing target sputter) 시스템을 이용하여 성막하였고, ITO/Ag/ITO 다층박막의 전기적, 광학적, 구조적 특성을 분석하였다. 선형 대항 타겟 스퍼터 시스템은 강한 일방항의 자계와 타겟에 걸린 음극에 의해 전자의 회전, 왕복 운동이 가능해 마주보는 두 ITO 타겟 사이에 고밀도의 플라즈마를 구속 시켜 플라즈마 데미지 없이 산화물 박막을 성막시킬 수 있는 장치이다. 대항 타겟 스퍼터 시스템을 이용하여 성막한 ITO 전극을 DC power, working pressure, Ar/O2 ratio 에 따른 특성을 각각 분석하였다. glass 기판위에 최적화된 ITO 전극을 bottom layer로 두고, bottom ITO layer 위에 thermal evaporation 을 이용하여 Ag 박막을 6~20nm의 조건에 따라 두께를 다르게 성막하고, Ag 박막을 성막한 후에 다시 bottom ITO 전극과 같은 조건으로 ITO 전극을 top layer로 성막 하였다. 두 비정질의 ITO 전극 사이에 매우 앓은 Ag 박막을 성막 함으로 해서 glass 기판위에 ITO/Ag/ITO 다층 박막전극은 매우 낮은 저항과 높은 투과도를 나타낸다. ITO/Ag/ITO 박막의 전기적 광학적 특성을 보기 위해 hall measurement와 UV/visible spectrometer 분석을 각각 진행하였다. ITO/Ag/ITO 다층 박막 전극이 매우 얇은 두께임에도 불구하고 $4\Omega$/sq.의 낮은 면저항과 85%의 높은 투과도를 나타내는 이유는 ITO/Ag/ITO 전극 사이에 있는 Ag층의 표면 플라즈몬 공명 (SPR) 현상으로 설명할 수 있다. ITO/Ag/ITO 전극의 Ag의 거동을 분석 하기위해 FESEM분석과 synchrotron x-ray scattering 분석을 하였다. ITO/Ag/ITO 전극의 Ag층이 islands의 모양에서 연속적으로 연결되는 변화과정 중에 SPR현상이 일어남을 알 수 있다. 여기서, 대항 타겟 스퍼터 시스템을 이용하여 성막한 ITO/Ag/ITO 다층박막을 OLED 또는 inverted OLEDs의 top 전극으로의 적용 가능성을 보이고 있다.

• Journal of the korean academy of Pediatric Dentistry
• /
• v.34 no.2
• /
• pp.183-191
• /
• 2007

Through out the world dental caries seems to be decreased as it is difficult to make an accurate diagnosis for dental caries. The traditional diagnostic method which is probing and x-ray taking has many limitations to diagnose the early caries, so there were recommendations for the needs of new equipments such as laser fluorescence(LF), digital imaging fiber-optic trans-illumination(DIFOTI), and quantitative light fluorescence (QLF) which were developed from various study results. Also confocal laser scanning microscopy(CLSM) and ultrasonics are used for research progression. This study is to evaluate whether it is possible to monitor accurately for remineralization amount of enamel surface early caries using DIFOTI or LF After inducing artificial caries to bovine teeth to 10 participants remineralization was enhanced by 0 ppm and 500 ppm fluoride mouth rinse solution for 3 weeks. Then they were cross sectioned and analyzed using gold standard of the lesion depth measured by CLSM. The following results were obtained: 1. The measured percentage of light intensity(luminosity ratio) by DIFOTI increased with remineralization period, and showed significant reverse correlation with lesion depth measured by CLSM (p<0.01). 2. The measurement of laser fluorescence increased with remineralization period, and showed significant correlation with lesion depth measured by CLSM (p<0.01). 3. To the result for CLSM, 500 ppm fluoride mouth rinse group showed rapid rate for decreased tendency of lesion depth than 0 ppm fluoride mouth rinse group. In conclusion DIFOTI system was used to measure accurately for the remineralization amount of early surface caries, it is a very useful equipment to detect precisely the changes for early enamel caries remineralization during treatments.

• Journal of muscle and joint health
• /
• v.5 no.1
• /
• pp.83-109
• /
• 1998

This study was carried out to identify the Important modifiable risk factors for reduced bone mass and to construct prediction model which can classify women with either low or high bone mass. Through the literature review, individual characteristics such as age, body weight, height, education level, family history, age of menarche, postmenopausal period, gravity, parity, menopausal status, and breast feeding period were identified and factors of life style such as past milk consumption, past physical activity, present daily activity, present calcium intake, alcohol intake, cigarette smoking, coffee consumption were identified as influencing factors of reduced bone mass in women. Four hundred and eighty women aged between 28 and 76 who had given measurement bone mineral density by dual energy x-ray absortiometry in lumbar vertebrae and femur from July to October, 1997 at 4 general hospitals in Seoul and Pusan were selected for this study. Women were excluded if they had a history of any chronic illness such as rheumatoid arthritis, diabetes mellitus, hyperthroidism, & gastrointestinal disorder and any medication such as calcium supplements, calcitonin, estrogen, thyroxine, antacids, & corticosteroids known affect bone. As a result of these exclusion criteria, four hundred and seventeen women were used for analysis. Multiple logistic regression model was developed for estimating the likelihood of the presence or absence of reduced bone mass. A SAS procedure was used to estimate risk factor coefficient. The results are as follows For lumbar spine, the variables significant were age, body weight, menopause status, daily activity, past milk consumption, and past physical activity(p<0.01), while for femoral Ward's triangle, age, body weight, level of education, past milk consumption, past physical activity(p<0.001). Past physical activity, present daily activity and past milk consumption are the most powerful modifiable predictors in vertebrae and femur among the predictors. When the model performance was evaluated by comparing the observed outcome with predicted outcome, the model correctly identified 74.1% of persons with reduced bone mass and 84.5% of persons with normal bone mass in the lumbar vertebrae and 82.9% of persons with reduced bone mass and 75.0% of persons with normal bone mass in the femoral Ward's triangle. On the basis of these results, a number of recommendations for the management of reduced bone mass may be made : First, those woman who are classified as high risk group of the reduced bone mass in the prediction model should examine the bone mineral density to further examine the usefulness of this model. Second, the optimal amount of milk consumption and a regular weight bearing exercise in childhood, adolescence, and early adult should be ensured.

• Progress in Medical Physics
• /
• v.7 no.2
• /
• pp.19-28
• /
• 1996

It is important that the precise decision of the region and the accurate delivery of radiation dose required for treatment in the stereotactic radiosurgery. In this research, radiosurgery was carried with Leksell streotactic frame(LSF) which is especially developed water phantom to verify in experiment. Leksell Gamma Knife and LSF are used in radiosurgery is the spherical water phantom has the thickness of 2 mm, the radius of 160mm. The film for target localization and ionchamber for dose delivery was used in measurement instruments We compare the coordinate of target which is initialized by biplannar film with simple X-ray to the coordinate of film measured directly. The calculated dose by computer simulation and the measured dose by ionization chamber are compared. In this research, the target localization has the range ${\pm}$0.3mm for the acceptable error range and the absolute dose is :${\pm}$0.3mm for the acceptable error range. This research shows that the values measured by using the especially manufactured phantom are included the acceptable error range. Thus, this water phantom will be used continuously in the periodic quality assurance of Gamma Knife Unit and Leksell Stereotactic Frame.

• Journal of the Korean Society of Radiology
• /
• v.9 no.5
• /
• pp.323-329
• /
• 2015

This study is aimed at assessing whether dynamic wedge filters are appropriate to be used instead of physical wedge filters. The X-ray energy generated from linear accelerator is commercialize 6 MV and 10 MV. $15^{\circ}$, $30^{\circ}$, $45^{\circ}$, and $60^{\circ}$ of physical wedge filter was irradiated by dose rate 100, 200, 300, 400, 500, and 600 MU/min for each angle and for comparison with a dynamic wedge filter, irradiate 96 times under the same conditions. The measurement conditions are as 100 cm source-film distance and $10{\times}10cm$ irradiated surface. A developed film was scanned and analyzed after a calibration through a dose analysis program and the dose rate was compared after calculating the standard deviation. Dynamic wedge filters make dose, scattered rays and treatment time reduced and very useful due to less irradiated doses to patients. The errors at each dose rate under the same conditions were irrelevant. Thus, treatment based on a high dose rate depending on the patient is expected to be feasible.