• Korean Journal of Materials Research
• /
• v.21 no.4
• /
• pp.225-231
• /
• 2011

The effect of ferrous/ferric molar ratio on the formation of nano-sized magnetite particles was investigated by a co-precipitation method. Ferrous sulfate and ferric sulfate were used as iron sources and sodium hydroxide was used as a precipitant. In this experiment, the variables were the ferrous/ferric molar ratio (1.0, 1.25, 2.5 and 5.0) and the equivalent ratio (0.10, 0.25, 0.50, 0.75, 1.0, 2.0 and 3.0), while the reaction temperature ($25^{\circ}C$) and reaction time (30 min.) were fixed. Argon gas was flowed during the reactions to prevent the $Fe^{2+}$ from oxidizing in the air. Single-phase magnetite was synthesized when the equivalent ratio was above 2.0 with the ferrous/ferric molar ratios. However, goethite and magnetite were synthesized when the equivalent ratio was 1.0. The crystallinity of magnetite increased as the equivalent ratio increased up to 3.0. The crystallite size (5.6 to 11.6 nm), median particle size (15.4 to 19.5 nm), and saturation magnetization (43 to 71 $emu.g^{-1}$) changed depending on the ferrous/ferric molar ratio. The highest saturation magnetization (71 $emu.g^{-1}$) was obtained when the equivalent ratio was 3.0 and the ferrous/ferric molar ratio was 2.5.

• Korean Journal of Materials Research
• /
• v.26 no.5
• /
• pp.246-249
• /
• 2016

Nickel powders were prepared under solvothermal condition by precipitation from metal nitrates with aqueous ammonium hydroxide. The powders were obtained at in a temperature range of $190-250^{\circ}C$ for 6h. The morphology and size of nickel powders were studied as a function of reaction temperature. The synthesis of nickel crystalline particles is possible under a solvothermal conditions in ethylene glycol solution. Characterization of the synthesized nickel powders were studied by XRD, SEM(FE-SEM) and TG/DSC. X-ray diffraction analysis of the synthesized powders indicated the formation of nickel structure after reaction. The average crystalline sizes of the synthesized nickel powders were in the range of 200-1000 nm; and the distribution of the powders was broad. The shape of the synthesized nickel particles was almost spherical. The morphology of synthesized nickel powders changed with reaction condition. It was possible to synthesize nickel powders directly in ethylene glycol without reducing agent.

• Advances in nano research
• /
• v.2 no.4
• /
• pp.187-198
• /
• 2014

Magnetite nanoparticles (MNPs) of different sizes were synthesized by solvothermal process maintaining their stoichiometric composition and unique structural phase. Utilizing hydrated ferric (III) chloride as unique iron precursor, it was possible to synthesize sub-micrometric magnetite clusters of sizes in between 208 and 381 nm in controlled manner by controlling the concentration of sodium acetate in the reaction mixture. The sub-micrometer size nanoclusters consist of nanometric primary particles of 19 - 26.3 nm average size. The concentration of sodium acetate in reaction solution seen to control the final size of primary MNPs, and hence the size of sub-micrometric magnetite nanoclusters. All the samples revealed their superparamagnetic behavior with saturation magnetization ($M_s$) values in between 74.3 and 77.4 emu/g. $M_s$. The coercivity of the nanoclusters depends both on the size of the primary particles and impurity present in them. The mechanisms of formation and size control of the MNPs have been discussed.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.31 no.5
• /
• pp.345-350
• /
• 2018

Nanomaterials have considerable potential to solve several key challenges in various electrochemical devices, such as fuel cells. However, the use of nanoparticles in high-temperature devices like solid-oxide fuel cells (SOFCs) is considered problematic because the nanostructured surface typically prepared by deposition techniques may easily coarsen and thus deactivate, especially when used in high-temperature redox conditions. Herein we report the synthesis of a self-regenerated Pd metal nanoparticle on the perovskite oxide anode surface for SOFCs that exhibit self-recovery from their degradation in redox cycle and $CH_4$ fuel running. Using Pd-doped perovskite, $La(Sr)Fe(Mn,Pd)O_3$, as an anode, fairly high maximum power densities of 0.5 and $0.2cm^{-2}$ were achieved at 1,073 K in $H_2$ and $CH_4$ respectively, despite using thick electrolyte support-type cell. Long-term stability was also examined in $CH_4$ and the redox cycle, when the anode is exposed to air. The cell with Pd-doped perovskite anode had high tolerance against re-oxidation and recovered the behavior of anodic performance from catalytic degradation. This recovery of power density can be explained by the surface segregation of Pd nanoparticles, which are self-recovered via re-oxidation and reduction. In addition, self-recovery of the anode by oxidation treatment was confirmed by X-ray diffraction (XRD) and scanning electron microscopy (SEM).

• Bulletin of the Korean Chemical Society
• /
• v.18 no.8
• /
• pp.831-840
• /
• 1997

Core/shell structured composite metal oxides of Fe2O3/MgO were prepared by thermal decomposition of Fe(acac)3 adsorbed on the surface of MgO cores. The morphology of the composites conformed to that of the MgO used as the cores. Broad powder X-ray diffraction peaks shifted toward larger d, large BET surface area (∼350 m2/g), and the size of crystalline domains in nano range (4 nm), all corroborate to the nanocrystallinity of the Fe2O3/MgO composite which was prepared by using nanocrystalline MgO as the core. By use of microcrystalline MgO as the core, microcrystalline Fe2O3/MgO composite was prepared, and it had small BET surface area of less than 35 m2/g. AFM measurements on nanocrystalline Fe2O3/MgO showed a collection of spherical aggregates (∼80 nm dia) with a very rough surface. On the contrary, microcrystalline Fe2O3/MgO was a collection of plate-like flat crystallites with a smooth surface. The nitrogen adsorption-desorption behavior indicated that microcrystalline Fe2O3/MgO was nonporous, whereas nanocrystalline Fe2O3/MgO was mesoporous. Bimodal distribution of the pore size became unimodal as the layer of Fe2O3 was applied to nanocrystalline MgO. The macropores in a wide distribution which the nanocrystalline MgO had were absent in the nanocrystalline Fe2O3/MgO. The decomposition of CCl4 was largily enhanced by the overlayer of Fe2O3 on nanocrystalline MgO making the reaction between nanocrystalline Fe2O3/MgO and CCl4 be nearly stoichiometric. The reaction products were environmentally benign MgCl2 and CO2. Such an enhancement was not attainable with the microcrystalline samples. Even for the nanocrystalline MgO, the enhancement was not attained, if not with the Fe2O3 layer. Without the layer of Fe2O3, it was observed that the nanocrystalline domain of the MgO transformed into microcrystalline one as the decomposition of CCl4 proceeded on its surface. It appeared that the layer of Fe2O3 on the particles of nanocrystalline Fe2O3/MgO blocked the transformation of the nanocrystalline domain into microcrystalline one. Therefore, in order to attain stoichiometric reaction between CCl4 and Fe2O3/MgO core/shell structured composite metal oxide, the morphology of the core MgO has to be nanocrystalline, and also the nanocrystalline domains has to be sustained until the core was exhausted into MgCl2.

• Journal of Korea Technical Association of The Pulp and Paper Industry
• /
• v.41 no.5
• /
• pp.26-32
• /
• 2009

As a part of utilizing the nanocellulose (NC) from lignocellulosic components of wood biomass, this paper reports preliminary results on the products of sulfuric acid hydrolysis. The purpose of this study was to investigate the morphology of both NC and micro-sized cellulose fiber (MCF) isolated by acid hydrolysis from commercial microcrystalline cellulose (MCC). Field emission.scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) were employed to observe the acid hydrolysis suspension, NC, and MCF. The electron microscopy observations showed that the acid hydrolysis suspension, before separation into NC and MCF by centrifugation, was composed of nano-sized NCs and micro-sized MCFs. The morphology of isolated NCs was a whisker form of rod-like NCs. Measurements of individual NCs using TEM indicated dimensions of 6.96$\pm$0.87 nm wide by 178$\pm$55 nm long. Observations of the MCFs showed that most of the MCC particles had de-fibered into relatively long fibers with a diameter of 3-9 ${\mu}m$, depending on the degree of acid hydrolysis. These results suggest that proper technologies are required to effectively realize the potentials of both NCs and MCFs.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.23 no.4
• /
• pp.195-200
• /
• 2013

Novel Sr-Y-Si-Oxynitride yellow phosphors were synthesized and the effect of calcination temperature, reduction temperature and $Eu^{2+}$ concentration on their luminescence properties were studied. Optimal temperature conditions were found to be $1400^{\circ}C$ and $1300^{\circ}C$ for solid-state reaction and reduction, respectively. The synthesized $Ba_9Y_{2+y}Si_6O_{24-3y}N_{3y}:Eu^{2+}$ phosphors showed a single intense broadband emission in the range of 571~587 nm for 450 nm excitation light source. The highest luminescence intensity was obtained with Eu concentration of 3 mol% and concentration quenching was observed beyond 5 mol%. FE-SEM and PSA showed that the synthesized phosphors consists of particles with an average size of ${\sim}8.2{\mu}m$.

• Journal of Power System Engineering
• /
• v.15 no.6
• /
• pp.67-72
• /
• 2011

In the present study, crack healing effect and residual stress of $Al_2O_3$ ceramics were investigated by changing the sintering temperature and heat treatment conditions. And also it was investigated that the influence of different filler loadings of nano-sized SiC particles on the crack healing behavior of $Al_2O_3$ ceramics. The test samples were characterized by three point bend flexural tests to evaluate their mechanical properties. The morphological changes were studied by FE-SEM and EDS. The test results indicated that the $Al_2O_3$ with nano-sized SiC ceramics sintered at $1800^{\circ}C$ were showed highest density. Sintering temperature at $1800^{\circ}C$, the bending strength of heat treatment in air atmosphere specimens showed about 42 % increment in comparison to the un-heat treated specimens. The cracked specimens can be healed by heat treatment in vacuum atmosphere but the crack healing effect of $Al_2O_3$ ceramics, which is heat treated in air atmosphere was higher than that of heat treated in vacuum atmosphere. $Al_2O_3$ with 30 wt% of SiC ceramics indicated higher crack healing ability than that with 15 wt% of SiC ceramics. The FE-SEM images showed that the median cracks and pores were disappeared after heat treatment in air.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2010.08a
• /
• pp.281-281
• /
• 2010

Very low refractive index (<1.4) materials have been proved to be the key factor improving the performance of various optical components, such as reflectors, filters, photonic crystals, LEDs, and solar cell. Highly porous SiO2 are logically designed for ultralow refractive index materials because of the direct relation between porosity and index of refraction. Among them, ordered macroporous SiO2 is of potential material since their theoretically low refractive index ~1.10. However, in the conventional synthesis of ordered macroporous SiO2, the time required for the crystallization of organic nanoparticles, such as polystyrene (PS), from colloidal solution into well ordered template is typical long (several days for 1 cm substrate) due to the low interaction between particles and particle - substrate. In this study, polystyrene - polyacrylic acid (PS-AA) nanoparticles synthesized by miniemulsion polymerization method have hydrophilic polyacrylic acid tails on the surface of particles which increase the interaction between particle and with substrate giving rise to the formation of PS-AA film by simply spin - coating method. Less ordered with controlled thickness films of PS-AA on silicon wafer were successfully fabricated by changing the spinning speed or concentration of colloidal solution, as confirmed by FE-SEM. Based on these template films, a series of macroporous SiO2 films whose thicknesses varied from 300nm to ~1000nm were fabricated either by conventional sol - gel infiltration or gas phase deposition followed by thermal removal of organic template. Formations of SiO2 films consist of interconnected air balls with size ~100 nm were confirmed by FE-SEM and TEM. These highly porous SiO2 show very low refractive indices (<1.18) over a wide range of wavelength (from 200 to 1000nm) as shown by SE measurement. Refraction indices of SiO2 films at 633nm reported here are of ~1.10 which, to our best knowledge, are among the lowest values having been announced.

• Advances in nano research
• /
• v.5 no.3
• /
• pp.253-260
• /
• 2017

We report a simple eco-friendly process for the synthesis of gold nanoparticles (AuNPs) using aqueous extract from Coffea Arabica fruit. The formation of AuNPs was confirmed using absorption spectroscopy and scanning electron microscopy images. FT-IR analysis demonstrates the major functional groups present in Coffee Arabica fruit extract before and after synthesizing AuNPs. The Face Center Cubic (FCC) polycrystalline nature of these particles was identified by X-Ray diffraction (XRD) analysis. Taking into account the contribution of the biomass surrounding the AuNPs, dynamic light scattering (DLS) results revealed an average particle size of ~59 nm.