• Resources Recycling
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• v.12 no.6
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• pp.38-46
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• 2003

In this study, nano-sized Ni-ferrite and $Fe_2$$O_3$＋NiO powder was fabricated by spray pyrolysis process in the condition of 1kg/$\textrm{cm}^2$ air pressure using the Fe-Ni complex waste acid solution generated during the manufacturing process of shadow mask. The average particle size of the produced powder was below 100 nm. The effects of the reaction temperature, the concentration of raw material solution and the nozzle tip size on the properties of powder were studied. As the reaction temperature increased from $800 ^{\circ}C$ to $1100^{\circ}C$, the average particle size of the powder increased from 40 nm to 100 nm, the structure of the powder gradually became solid, yet the distribution of the particle size appeared more irregular. Along with the increase of the reaction temperature, the fraction of the Ni-ferrite phase were also on the rise, and the surface area of the powder was greatly reduced. As the concentration of Fe in solution increased from 20g/l to 200g/l, the average particle size of the powder gradually increased from 30 nm to 60 nm, while the distribution of the particle size appeared more irregular. Along with the increase of the concentration of solution, tie fraction of the Ni-ferrite phase was on the rise, and the surface area of the powder was greatly reduced. Along with the increase of the nozzle tip size, the distribution of the particle size appeared more irregular, yet the average particle size of the powder showed no significant change. As the nozzle tip size increased from 1 mm to 2 mm, the fraction of the Ni-ferrite phase showed no significant change, while the surface area of the powder slightly reduced. As the nozzle tip size increased to 3 mm and 5 mm, the fraction of the Ni-ferrite phase gradually reduced, and the surface area of the powder slightly increased.

• The Journal of the Petrological Society of Korea
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• v.3 no.1
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• pp.1-19
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• 1994

We present petrography, mode and chemistry data for Fe-Ti oxide minerals from the Mesozoic granitoids in South Korea. Magnetites from the Daebo Uurassic) granites are nearly pure $Fe_3O_4$, while those from the Bulgugsa (Cretaceous) granites contain considerable amounts of Mn and Ti. This is probably related to rapid cooling of the Bulgugsa granites compared with slow cooling of Daebo granites, which is supported by geologic relations and hornblende geobarometry results of Cho and Kwon (1994) on the emplacement depth for these granites. The composition of ilmenite does not shew appreciable difference between the Daebo and Bulgugsa granites. However, $Fe_2O_3$ contents are higher for the ilmenites coexisting with magnetite than for those without magnetite. In the temperature vs. oxygen fugacity diagram, the Bulgugsa granites plot near Ni-NiO and QFM buffer curves, although only two samples show greater than the granite solidus temperature. The mode data suggest that both magnetite- and ilmenite-series exist in Daebo and Bulgusa granites from the Kyonggi massif, Ogcheon belt and Youngnam massif, while only magnetite-series exists in Bulgugsa granites from the Kyongsang basin. Many ilmenite-series granites occur in the Ogcheon belt, which might be related to assimilation of carboniferous sediments in the belt. The proportion (44 : 56) between ilmenite- and magnetite-series for the Daebo granites is significantly different from that of Ishihara et al. (1981) who showed, using magnetic susceptibility data, predominance of ilmenite-series (more than 70%) for the Daebo granites, which can be mainly attributed to preference in sampling and to wrong assignment of age for some plutons. We also found magnetite in weakly-magnetized Kanghwa granite which was formerly classified as ilmenite-series by Ishihara et al. (1981). The proportion of ilmenite-series increases in the order of hornblende biotite granite, biotite granite and two mica granite. We conclude from these observations that the ilmeniteseries granites might have originated from contamination of carboniferous crustal material and/or such source material.

• Journal of the Korean Magnetics Society
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• v.10 no.3
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• pp.106-111
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• 2000

The magnetic thin films can be prepared without vacuum process and under the low temperature (<100 $^{\circ}C$) by ferrite plating. We have performed ferrite plating of M $n_{x}$Z $n_{0.22}$F $e_{2.78-x}$ $O_4$(x=0.00~0.08) films and N $i_{x}$Z $n_{0.22}$F $e_{*}$2.78-x/ $O_4$(x=0.00~0.15) films on cover glass at the substrate temperature 90 $^{\circ}C$. The crystal structure of the samples has been identified as a single phase of polycrystal spinel structure by x-ray diffraction technique. The lattice constant in the M $n_{x}$Z $n_{0.22}$F $e_{2.78-x}$ $O_4$films increases but in the N $i_{x}$Z $n_{0.22}$F $e_{*}$2.78-x/ $O_4$films decrease with the composition parameter, x. The saturation magnetization in the M $n_{x}$Z $n_{0.22}$F $e_{2.78-x}$ $O_4$films does not greatly change, in agreement with observations on bulk samples.k samples.k samples.

• Korean Chemical Engineering Research
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• v.49 no.6
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• pp.720-725
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• 2011

Gold catalysts supported on metal-oxides were prepared by co-precipitation using the various metal nitrates and chloroauric acid as precursors, and effect of water addition on the catalytic activity in CO oxidation was investigated. Among the various supported gold catalysts, Au/$Co_{3}O_{4}$ and Au/ZnO catalysts showed the excellent activity for CO oxidation. Water in the reactant gas had a negative effect on the oxidation activity over Au/$Co_{3}O_{4}$ catalysts and a positive effect on that over Au/ZnO, which means the activity depends strongly on the nature of support. It was also confirmed that no significant change in the particle size of gold was observed after reaction both in dry and wet conditions. This fact suggested that the deactivated catalyst due to a carbonate species could be regenerated by water addition in the reactant gas.

• Composites Research
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• v.29 no.4
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• pp.179-185
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• 2016

A self-charging supercapacitor is constructed through simple integration of the energy storage and photo exited materials at the photo electrode. The large band gap of $NiO/Fe_3O_4$ heterostructure generates photo electron at the photo electrode and store the charges through redox mechanism at the counter electrode. Sulfanilic acid azocromotrop/reduced graphene oxide layer at the photo electrode trapped the photo generated hole and store the charge by forming double layer. The solar supercapacitor device is charged within 400 s up to 0.5 V and exhibited a high specific capacitance of ~908 F/g against 1.5 A/g load. The solar illuminated supercapacitor shows a high energy and power density of 33.4 Wh/kg and 385 W/kg along with a very low relaxation time of ~15 ms ensuring the utility of the self charging device in the various field of energy storage and optoelectronic application.

• Korean Journal of Materials Research
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• v.13 no.6
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• pp.365-368
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• 2003

Small amounts of additives such as mol % 0.13 NiO and mol % 0.01 $CaCO_3$were added to Cu-Zn-Mg ferrites. Basic composition of the Cu-Zn-Mg ferrites was $Cu_{Cu}$X/$Fe_{0.054}$ /$Zn_{0.486}$$Mg_{0.407}$ $Fe_{1.946}$ $O_4$(group A) and $Cu_{0.263}$$Fe_{0.027}$ $Zn_{0.503}$ $Mg_{0.262}$ $Fe_{1.973}$ $O_4$(group B). Specimens were sintered at different temperatures (1010, 1030, $1050^{\circ}C$) for 2 hours in air followed by an air cooling. Then, effects of various composition and sintering temperatures on the microstructure and the magnetic properties such as inductions, coercive forces, and initial permeabilities of the Cu-Zn-Mg ferrites were investigated. The average grain size increased with the increase of sintering temperature. The magnetic properties obtained from the aforementioned Cu-Zn-Mg ferrite specimens were 1,724 gauss for the maximum induction, 1.0 oersted for the coercive force, and 802 for the initial permeability. These magnetic properties indicated that the specimens could be utilized as the core of IFT (intermediate frequency transformer) and antenna in the amplitude modulation.

• Journal of the Korean institute of surface engineering
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• v.20 no.2
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• pp.49-59
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• 1987

The properties of $Cr_2O_3-Al_2O_3-SiO_2$ composite oxide coatings on steel surface were investigated. The results obtained were as follows: The microhardness of oxide coating layer increased with increasing heat-treatment temperature and $Cr_2O_3$ content in coating layer. The hardness showed the highest value (850Hv) treated at 700$^{\circ}C$ for $SiO_2:Al_2O_3:Cr_2O_3$=1:1:4. Increasing heat-treatment temperature, corrosion current density became lower and coating layer became denser. The corrosion current density showed the lowest value $(6.5{\times}10^{-5}\;Acm^2)$ treated at 750$^{\circ}C\;for\;SiO_2:Al_2O_3:Cr_2O_3$=1:1:3. These results were explained by protective layer which was formed during heat-treatment. The bonding between matrix and coating layer is expected to be made mechanically and chemically by the inter diffusion of Ni and Fe. The composite oxide coating was formed by softening of the binder with increasing heat-treatment temperature. The strengthening of coating layer is to be resulted from the dispersion of major oxide particles.

• Journal of the Korean Ceramic Society
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• v.15 no.2
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• pp.79-84
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• 1978

$Zn_{0.105}Co_{0.025}Li_{0.435-1/2x}Ni_x Fe_{2.435-1/2x-y }Mn_y O_4$ 조성의 메모리코어 특성과 $Nb_2O_5$ 및 $V_2O_5$의 소량 첨가가 square-loop성질에 주는 영향을 연구하였다. 위의 조성에서 닉켈의 양 x는 0에서 0.15까지, 그리고 망간의 양 y는 0.05에서 0.25까지 변화시켰다. $Nb_2O_5$와 $V_2O_5$의 양은 각각 위의 화학식에 대하여 0.005에서 0.015까지 변화시켰다. 실험결과에 의하면 $Mn^{+3}$를 octahedral자리에 첨가하였을 때에는 잡음이 감소되었고 메모리코어 squareness와 보자련의 온도계수가 증가하였다. 닉켈을 첨가하였을 때에는 메모리코어의 squareness와 잡음이 증가하였다. $Nb_2O_5$를 소량 첨가하였을 때에는 square-loop성질이 개선되었음에 비하여 $V_2O_5$를 소량 첨가하였을 때에는 square-loop성질이 나빠졌다.

• Journal of Sensor Science and Technology
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• v.22 no.6
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• pp.379-386
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• 2013

The influences of the load resistance $R_L$ on the magnetoelectric (ME) characteristics of $NiZnFe_2O_4+PZT$ composite were investigated in the non-resonance frequency range. The ME coefficient peak increases with increasing $R_L$, but the frequency indicating the ME coefficient peak decreases with increasing $R_L$. The maximum output power peak is approximately $9.3{\times}10^{-10}mW/Oe$ near $R_L=3.3M{\Omega}$ at f=280 Hz, and the ME coefficient seems to be saturated at $R_L&gt;20M{\Omega}$. This frequency shift effect of $R_L$ shows that the frequency range for an ME sensor application can be modulated with the appropriate value of $R_L$. The ME output voltage has a good linear response to the ac field Hac and shows fair stability over a range of temperatures. The measured non-linearity of this sample is approximately 0.8%. This sample will allow for a low-strength magnetic ac-field sensor. The result from this sample will serve as basic data for a signal-processing circuit system.

• Journal of the Korean institute of surface engineering
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• v.24 no.3
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• pp.144-150
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• 1991

The stainless steel 304 oxidized at $70^{\circ}C$ in 2.5M CrO3/5.0M H2SO4 solution and at $200^{\circ}C$ , $300^{\circ}C$, and $400^{\circ}C$ in the air are analyzed with X-ray Photoelectron Spectroscopy (XPS) to obtain depth composition profile of the surface region. It is confirmed that the surface region has a quite different composition from that of the bulk. This is due to a difference in the outward diffusion rates of the oxidized species in the surface region. The order of diffusion rates is Fe > Cr > Ni in the experimental temperature range. In spite of the inferior rate of diffusion, Cr is enriched in the surface when it is oxidized in the CrO3/H2SO4 solution. This is due to preferential dissolution of oxidized Fe.