• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.27 no.7
• /
• pp.452-457
• /
• 2014

Copper manganite thin films were fabricated on $SiN_x/Si$ substrate by metal organic decomposition (MOD) process. They were burned-out at $400^{\circ}C$ and annealed at various temperatures ($400{\sim}800^{\circ}C$) for 1h in ambient atmosphere. Their micro-structure and negative temperature coefficient of resistance (NTCR) characteristics were analyzed for micro-bolometer application. The copper manganite film with a cubic spinel structure was well developed at $500^{\circ}C$ which confirmed by XRD and HRTEM analysis. It showed a low resistivity ($47.5{\Omega}{\cdot}cm$) at room temperature and high NTCR characteristics of $-4.12%/^{\circ}C$ and $-2.15%/^{\circ}C$ at room temperature and $85^{\circ}C$, implying a good thin film for micro-bolometer application. Furthermore, its crystallinity was enhanced with increasing temperature to $600^{\circ}C$. However, the appearance of secondary phase at temperatures higher than $600^{\circ}C$ lead to deteriorate the NTCR characteristics.

• Journal of Korean Ophthalmic Optics Society
• /
• v.8 no.2
• /
• pp.25-29
• /
• 2003

Nickel-ferrite $Ni_xFe_{3-x}O_4$ thin films with several composition for Ni on glass substrate was prepared by ferrite plating method in order to make sunglass which cut off ultraviolet and shield electromagnetic field. It has single phase of polycrystalline spinel structure and has gloss as mirror and has high hardness which is no scratch while scraping by using nail. The transmittance of nickel-ferrite thin film is lowered to zero below 400 nm manifestly. And it shows that the nickel-ferrite thin film in nickel composition rate x = 0.09 was most cut oil ultraviolet when compared with goods of other company in the cut off effect of ultraviolet. Therefore, sunglasses coated with $Ni_xFe_{3-x}O_4$ thin film can be used in removing ultraviolet and electromagnetic field.

• Advances in materials Research
• /
• v.3 no.2
• /
• pp.105-116
• /
• 2014

The microwave dielectric properties of $CeO_2$ nanoparticles (0.5, 1.0 & 1.5wt%) doped $Mg_2TiO_4$ (MTO) ceramics have been investigated at cryogenic temperatures. The XRD patterns of the samples were refined using the full proof program reveal the inverse spinel structure without any secondary phases. The addition of $CeO_2$ nanoparticles lowered the sintering temperature with enhancement in density and grain size as compared to pure MTO ceramics. This is attributed to the higher sintering velocity of the fine particles. Further, the microwave dielectric properties of the MTO ceramics were measured at cryogenic temperatures in the temperature range of 6.5-295 K. It is observed that the loss tangent ($tan{\delta}$) of all the samples increased with temperature. However, the $CeO_2$ nanoparticles doped MTO ceramics manifested lower loss tangents as compared to the pure MTO ceramics. The loss tangents of the pure and MTO ceramics doped with 1.5 wt% of $CeO_2$ nanoparticles measured at 6.5K are found to be $6.6{\times}10^{-5}$ and $5.4{\times}10^{-5}$, respectively. The addition of $CeO_2$ nanoparticles did not cause any changes on the temperature stability of the MTO ceramics at cryogenic temperatures. On the other hand, the temperature coefficient of the permittivity increased with rise in temperature and with the wt% of $CeO_2$ nanoparticles. The obtained lower loss tangent values at cryogenic temperatures can be attributed to the decrease in both intrinsic and extrinsic losses in the MTO ceramics.

• Journal of the Korean Applied Science and Technology
• /
• v.17 no.1
• /
• pp.55-61
• /
• 2000

$Zn_{x}Fe_{3-x}O_{4}(0.00.<X<0.08)$ was synthesized by air oxidation method for the decomposition of carbon dioxide. We investigated the characteristics of catalyst, the form of methane by gas chromatograph after decomposition of carbon dioxide and kinetic parameter. $Zn_{x}Fe_{3-x}O_{4}(0.00.<X<0.08)$ was spinel type structure. The surface areas of catalysts($Zn_{x{Fe_{3-x}O_{4}(0.00.<X<0.08)$) were $15{\sim}27$ $m^{2}/g$. The shape of $Zn_{0.003}Fe_{2.997}O_{4}$ was sphere. The optimum temperature for the decomposition of carbon dioxide into carbon was $350^{\circ}C$. $Zn_{0.003}Fe_{2.997}O_{4}$ showed the 85% decomposition rate of carbon dioxide and the degree of reduction by hydrogen(${\delta}$) of $Zn_{0.003}Fe_{2.997}O_{4}$ was 0.32. At $350^{\circ}C$, the reaction rate constant and activation energy of $Zn_{0.003}Fe_{2.997}O_{3.68}$ for the decomposition of carbon dioxide into carbon were 3.10 $psi^{1-{\alpha}}/min$ and 0.98 kcal/mole respectively. After the carbon dioxide was decomposed, the carbon which was absorbed on the catalyst surface was reacted with hydrogen and it became methane.

• Korean Journal of Materials Research
• /
• v.8 no.7
• /
• pp.616-620
• /
• 1998

Zn_{0.994}Mn_{0.006}Ga_2O_4$ green phosphor powders were synthesized using polymerized complex and solution combustion methods, and their powder and luminescence properties were characterized by XRD, SEM, BET, PL, etc. The properties were compared with those of the powders prepared by a solid state reaction method. The powders prepared by polymerized complex and solution combustion methods showed only a single spinel phase at 50$0^{\circ}C$ and 40$0^{\circ}C$, respectively. Their particle sizes were smaller than that of a solid state reaction method. Emission intensity of the phosphor powders prepared by both methods were highest at 90$0^{\circ}C$ and 40$0^{\circ}C$, respectively.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.24 no.6
• /
• pp.256-260
• /
• 2014

This study was carried on the phenomena in reactivity with the clay surface according to the thickness of the cobalt component coating. In the coated specimen, it was observed that the cobalt component was spreaded to diffuse with a constant thickness from the surface of it and the diffusion layer at the white porcelain soil was more increased with the increase of the amount of cobalt sulfate than at the celadon porcelain one. It was evaluated that the color of the surface on the coated specimen at the white porcelain soil was changed from grayish blue to blue and the $L^*$ value was decreased from 51.78 to 37.61 and also in the case of the coated specimen in celadon porcelain soil, $L^*$ value was from 53.91 to 38.93 and the color was from dark olive gray to dark gray. The physical properties of the specimen were characterized by X-ray diffraction, Scanning electron microscope, Dilatometer, TG-DTA, UV-vis spectrophotometer and HRDPM.

• Journal of the Korean Magnetics Society
• /
• v.17 no.2
• /
• pp.71-75
• /
• 2007

Ultrasonic irradiation in a solution during the chemical reaction may accelerate the rate of the reaction and the crystallization at low temperature. We have synthesized nanometer sized zinc ferrite particles using chemical co-precipitation technique through a sonochemical method with surfactant such as oleic acid. The thermal behaviour of the zinc ferrite was determined by the thermoanalytical techniques (TGA-DSC). Powder X-ray diffraction measurements show that the samples have the spinel structure. Magnetic properties measurement were performed using a superconducting quantum interference device (SQUID) magnetometer.

• Bulletin of the Korean Chemical Society
• /
• v.28 no.12
• /
• pp.2288-2292
• /
• 2007

The catalytic activities of nickel-based catalysts were estimated for oxidizing acetaldehyde of VOCs exhausted from industrial facilities. The catalysts were prepared by sol-gel methods of SiO2 and SiO2-TiO2 as a xerogel followed by impregnating Al2O3 powder with the nickel nitrate precursor. The crystalline structure and catalytic properties for the catalysts were investigated by use of BET surface area, X-ray diffraction (XRD), Xray photoelectron spectroscopy (XPS) and temperature programmed reduction (TPR) techniques. These results show that nickel oxide is transformed to NiAl2O4 spinel structure at the calcination temperature of 400 °C in response to the steps with after- and co-impregnation of Al2O3 powder in sol-gel process. The NiAl2O4 could suppress the oxidation reaction of acetaldehyde by catalysts. The NiO is better dispersed on SiO2-TiO2/Al2O3 support than SiO2/Al2O3 and SiO2-TiO2-Al2O3 supports. From the testing results of catalytic activities for oxidation of acetaldehyde, Catalysts showed a big difference in conversion efficiencies with the way of the preparation of catalysts and the loading weight of nickel. The catalyst of 8 wt.% Ni/TiO2-SiO2/Al2O3 showed the best conversion efficiency on acetaldehyde oxidation with 100% conversion efficiency at 350 °C.

• Carbon letters
• /
• v.28
• /
• pp.87-95
• /
• 2018

This study examined the influence of operating parameters on the electrosorptive recovery system of lithium ions from aqueous solutions using a spinel-type lithium manganese oxide adsorbent electrode and investigated the electrosorption kinetics and isotherms. The results revealed that the electrosorption data of lithium ions from the lithium containing aqueous solution were well-fitted to the Langmuir isotherm at electrical potentials lower than -0.4 V and to the Freundlich isotherm at electrical potentials higher than -0.4 V. This result may due to the formation of a thicker electrical double layer on the surface of the electrode at higher electrical potentials. The results showed that the electrosorption reached equilibrium within 200 min under an electrical potential of -1.0 V, and the pseudo-second-order kinetic model was correlated with the experimental data. Moreover, the adsorption of lithium ions was dependent on pH and temperature, and the results indicate that higher pH values and lower temperatures are more suitable for the electrosorptive adsorption of lithium ions from aqueous solutions. Thermodynamic results showed that the calculated activation energy of $22.61kJ\;mol^{-1}$ during the electrosorption of lithium ions onto the adsorbent electrode was primarily controlled by a physical adsorption process. The recovery of adsorbed lithium ions from the adsorbent electrode reached the desorption equilibrium within 200 min under reverse electrical potential of 3.5 V.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2004.07b
• /
• pp.898-901
• /
• 2004

[ $ZnCr_2O_4$ ]를 모물질로 하고 MgO, $TiO_2$를 몰비로 2:1, 4:1, 6:1, 및 8:1이 되게 정량적으로 조합한 후, 조사하였다. $ZnCr_2O_4$-MgO와 $ZnCr_2O_4-TiO_2$를 X-선 분석한 결과 Spinel 결정구조를 형성하였으며, 또한 SEM과 EDX 분석결과 각각 $Li_2CrO_4$와 $Li_3VO_4$의 형성으로 인하여 저항 특성이 나타나는 것을 알 수 있었다. $ZnCr_2O_4-MgO$, $ZnCr_2O_4-TiO_2$에서 MgO의 양이 증가할수록 저항값은 약간 감소하는 반면, $TiO_2$의 양이 증가할수록 저항값이 급격히 증가하는 특성을 나타내었고, 감습 특성에서도 M??보다 TiO2가 더 높게 나타내었다. 습에 따른 복원 특성의 경우 $700^{\circ}C$에서 소결한 ($ZnCr_2O_4:MgO=4:1$)과 ($ZnCr_2O_4:TiO_2=6:1$) 조성의 센서가 가장 양호하였다.