• Economic and Environmental Geology
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• v.45 no.2
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• pp.195-204
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• 2012

Biomineralization has been explored for geochemical cycles and microbial tolerance mechanisms to metal toxicity. Here, we are introducing NanoFermentation which enables economic, environmentally friendly, requiring low input energy, and scalable manufacturing of nano-dimensioned magnetite. We are also focusing on controlling factors of crystallite size which can determine superparamagnetism and ferrimagnetism. Controlling factors are such as microbial species, temperature, incubation time, medium composition, substituted elements and their concentration, precursor type, reaction volume, precursor concentration density and their combinations. Crystallite size distribution of biomagnetite depends on the balance between nuclei generation and crystal growth. Biomineralization will elucidate elemental cycles on earth crust and microbial ecology as well as it will be applied to material sciences and devices via massive production of nanomaterials.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.9 s.240
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• pp.1013-1021
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• 2005

In this work, $TiO_2$ nanoparticles were synthesized using a N2-diluted hydrogen coflow diffusion flame. The effects of flame temperature on the crystalline structure and the size of formed nanoparticles were investigated. The maximum centerline temperature of the flame ranged from 1,920K for $H_2-only$ flame to 863k for $81\%\;N_2-diluted$ flame. The morphology and the crystal structure of $TiO_2$ nanoparticles were analyzed by a TEM and a XRD, respectively. The particle size distribution was also measured by using a scanning mobility particle size. (SMPS). The mean particle diameter was calculated from the TEM images depended on the flame temperature, having minimum at about 1,look. Based on the SMPS measurements, the mean particle diameter of $TiO_2$ nanoparticles at flame temperatures > 1,300K was smaller than that at flame temperatures < 1,300K. From the XRD analysis, it was evident that the anatase fraction increased with decreasing the flame temperature. The portion of anatase phase in $TiO_2$ nanoparticles might be greater than $80\%$ when the flame temperature was lower than 1,000K.

• Journal of the Korean Ceramic Society
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• v.30 no.4
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• pp.325-331
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• 1993

Aqueous solutions of metallic salts, ZrO(NO3)2.2H2O and Y(NO3)3.5H2O were used as raw materials to synthesize crystalline submicron spherical powders of Zr0.94Y0.06O1.97 with tetragonal crystal phase. Each aqueous solution was mixed on the magnetic stirrer to homogenize for 12 hours. The concentration of the mixed solutionwas changed from 0.01mol/$\ell$ to 0.1mol/$\ell$ calculated as the concentration of Zr0.94Y0.06O1.97. Ultrafine droplets of starting mixed solution were sprayed by the ultrasonic vibrator and carried into the furnace kept at 55$0^{\circ}C$, $650^{\circ}C$, 75$0^{\circ}C$ and 85$0^{\circ}C$ using carrier gas of air (10$\ell$/min) and pyrolysed to form Y-TZP fine powders. The results of this exeriment were as follows. 1) Synthesized powders were nonagglomerated and spherical type. 2) Particle size distribution was narrow between 0.1${\mu}{\textrm}{m}$ and 1${\mu}{\textrm}{m}$. 3) Forming reaction Y-TZP was finished above synthetic temperature 75$0^{\circ}C$. 4) As the synthetic temperature rised from 55$0^{\circ}C$ to 85$0^{\circ}C$, the mean particle size decreased from 0.35${\mu}{\textrm}{m}$ to 0.22${\mu}{\textrm}{m}$ in the concentration of starting solution with 0.02mol/$\ell$. 5) At 75$0^{\circ}C$ of synthetic temperature, the concentration changes of starting solution from 0.01mol/$\ell$ to 0.1mol/$\ell$ increased the mean particle size from 0.24${\mu}{\textrm}{m}$ to 0.38${\mu}{\textrm}{m}$. 6) Chemical compositions of each synthesized particle were homogeneous nearly.

• Journal of Industrial Technology
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• v.23 no.A
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• pp.199-206
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• 2003

The charcoal-encapsulated methyl silica microcapsules were prepared by a O/W microemulsion sol-gel method, and the adsorption properties on aquatic humic acid were investigated. The capsules prepared were spherical, $100{\sim}1000{\mu}m$ in size. The size distribution was controllable by adjusting the size of charcoal powder, charcoal/methyl silica ratio, and agitating speed in O/W sol-gel process. Adsorption efficiency of charcoal for aquatic humic acid was decreased after encapsulation by methyl silica shell. The decreased adsorption efficiency can be dependent on the decrease of the BET surface area and pore volume after encapsulation. Diffusion properties of humic acid through the capsule shell also played an important role on adsorption efficiency. Therefore, the reasonable target pollutants for the capsules can be VOC or odor molecules which can overcome diffusion barrier through shell of capsules in air condition. Functionalization methods for the charcoal-encapsulated $CH_3(SiO)_n$ microcapsules by incorporation of $TiO_3$ as a phtocatalytic function and by incorporation of inorganic pigment as a color function were also investigated. $TiO_2$ coating properties were controllable by adjusting pH, temperature, and the concentration of $TiOSO_4$. In XRD measurement, the crystal form of the coated $TiO_2$ was anatase. For the colorization of the capsules, inorganic pigments were more efficient than organic dyes, and various color was introduced to the capsules using inorganic pigments.

• Journal of Powder Materials
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• v.28 no.5
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• pp.423-428
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• 2021

Here, we report the development of a new and low-cost core-shell structure for lithium-ion battery anodes using silicon waste sludge and the Ti-ion complex. X-ray diffraction (XRD) confirmed the raw waste silicon sludge powder to be pure silicon without other metal impurities and the particle size distribution is measured to be from 200 nm to 3 ㎛ by dynamic light scattering (DLS). As a result of pulverization by a planetary mill, the size of the single crystal according to the Scherrer formula is calculated to be 12.1 nm, but the average particle size of the agglomerate is measured to be 123.6 nm. A Si/TiO₂ core-shell structure is formed using simple Ti complex ions, and the ratio of TiO₂ peaks increased with an increase in the amount of Ti ions. Transmission electron microscopy (TEM) observations revealed that TiO₂ coating on Si nanoparticles results in a Si-TiO₂ core-shell structure. This result is expected to improve the stability and cycle of lithium-ion batteries as anodes.

• Proceedings of the Materials Research Society of Korea Conference
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• 2012.05a
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• pp.68.1-68.1
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• 2012

The best part of graphene is - charge-carriers in it are mass less particles which move in near relativistic speeds. Comparing to other materials, electrons in graphene travel much faster - at speeds of $10^8cm/s$. A graphene sheet is pure enough to ensure that electrons can travel a fair distance before colliding. Electronic devices few nanometers long that would be able to transmit charge at breath taking speeds for a fraction of power compared to present day CMOS transistors. Many researches try to check a possibility to make it a perfect replacement for silicon based devices. Graphene has shown high potential to be used as interconnects in the field of high frequency electrical devices. With all those advantages of graphene, we demonstrate characteristics of electrical and optical properties of graphene such as the effect of graphene geometry on the microwave properties using the measurements of S-parameter in range of 500 MHz - 40 GHz at room temperature condition. We confirm that impedance and resistance decrease with increasing the number of graphene layer and w/L ratio. This result shows proper geometry of graphene to be used as high frequency interconnects. This study also presents the optical properties of graphene oxide (GO), which were deposited in different substrate, or influenced by oxygen plasma, were confirmed using different characterization techniques. 4-6 layers of the polycrystalline GO layers, which were confirmed by High resolution transmission electron microscopy (HRTEM) and electron diffraction analysis, were shown short range order of crystallization by the substrate as well as interlayer effect with an increase in interplanar spacing, which can be attributed to the presence of oxygen functional groups on its layers. X-ray photoelectron Spectroscopy (XPS) and Raman spectroscopy confirms the presence of the $sp^2$ and $sp^3$ hybridization due to the disordered crystal structures of the carbon atoms results from oxidation, and Fourier Transform Infrared spectroscopy (FTIR) and XPS analysis shows the changes in oxygen functional groups with nature of substrate. Moreover, the photoluminescent (PL) peak emission wavelength varies with substrate and the broad energy level distribution produces excitation dependent PL emission in a broad wavelength ranging from 400 to 650 nm. The structural and optical properties of oxygen plasma treated GO films for possible optoelectronic applications were also investigated using various characterization techniques. HRTEM and electron diffraction analysis confirmed that the oxygen plasma treatment results short range order crystallization in GO films with an increase in interplanar spacing, which can be attributed to the presence of oxygen functional groups. In addition, Electron energy loss spectroscopy (EELS) and Raman spectroscopy confirms the presence of the $sp^2$ and $sp^3$ hybridization due to the disordered crystal structures of the carbon atoms results from oxidation and XPS analysis shows that epoxy pairs convert to more stable C=O and O-C=O groups with oxygen plasma treatment. The broad energy level distribution resulting from the broad size distribution of the $sp^2$ clusters produces excitation dependent PL emission in a broad wavelength range from 400 to 650 nm. Our results suggest that substrate influenced, or oxygen treatment GO has higher potential for future optoelectronic devices by its various optical properties and visible PL emission.

• Korean Journal of Heritage: History & Science
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• v.45 no.4
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• pp.114-125
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• 2012

The purpose of this study is to analysis chromaticity, granulometry, main chemical composition and mineral crystal structure of wall soils excavated from Poongnatoseong Earthen Castle using color reader, XRD, particla size analyzer. The analysed soils of Poongnatoseong Earthen Castle were yellowish brown and isabella. All samples were sands or sands including silty soil(SW~SC) and showed similar granulometry, chemical composition and mineral crystal structure, which were characteristics of construction materials suitable for modern road or airstrip. As resulting in comparison with 4 factors from chromaticity, granulometry, main chemical composition and mineral crystal structure, we decided that the control soils(PNS) near by Poongnatoseong Earthen Castle were not to be used for the castle wall construction We presumed that there was a huge soil distribution area for the wall construction around Poongnatoseong Earthen Castle. For further study, we will make a comparison analysis all kinds of soil characteristics. And then we can understand correctly about wall soils producing area, construction method, repair method and time of Poongnatoseong Earthen Castle.

• Applied Chemistry for Engineering
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• v.22 no.2
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• pp.133-137
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• 2011

In this study, illite was size-reduced using a wet-ball-milling treatment to improve its dispersion. Changes in illite particle size, size distribution, and dispersion characteristics after varying the treatment period were investigated. And the dispersion and dispersion stability of illite solution after 2 h wet ball milling treatment with different pH conditions were also evaluated. The illite particle size significantly decreased as the treatment time increased and the size reduction effect of wet ball milling deteriorated above 2 h treatment time. In addition, illite particle size was more evenly distributed as the treatment time increased. X-ray diffraction (XRD) analysis showed that no crystal structural changes of illite were induced, but the characteristic peak of illite the weaker due to the size reduction and exfoliation, as the treatment time increased. Zeta potential analysis showed that the illite dispersion improved, as the treatment time increased. The illite wet-ball-mill treated at pH 2 had the lowest dispersion stability. Illite dispersion and dispersion stability increased as pH increased, due to the increase in surface ionization. Hence, the results showed that as the treatment time increased, the illite particle size decreased, and dispersion and dispersion stability improved due to the increase in surface energy and repulsion force between particles.

• Journal of the Korean Electrochemical Society
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• v.2 no.4
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• pp.221-226
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• 1999

Two needle cokes (NC-A and NC-B) that differ in both the texture and impurity content to each other were graphitized at $2000-3000{\circ}C$, and the average particle size, size distribution and surface area were compared after milling. Their anodic properties in Li secondary batteries were also analyzed. Two materials showed a higher degree of graphitization with an increase in the preparation temperature, however, the NC-B series was less graphitized than NC-A due to the presence of impurities and less ordered mosaic texture. The mein particle size of the milled powder was proportional to the degree of graphitization, but the surface area showed the opposite trend. The highly graphitized materials yielded powders of lower uniformity in the size distribution. The discharge capacity of the resulting carbons steadily decreased in the temperature range of 1000 to $2000^{\circ}C$ due to the depletion of carbonaceous interlayers that contain crystal defects. A later increase in the discharge capacity was observed at $>2000^{\circ}C$, which arises from the formation of graphitic interlayers. The milling process gave rise to a sloping discharge curve at >1.0 V, but this was converted to a plateau at <0.25V after a repeated cycling or additional heat-treatment at $1000^{\circ}C$. The discharge at >1.0V likely comes from the disordered surface structure formed during the milling process. The evolution of a plateau at <0.25 V suggests that this disordered structure transforms to a more ordered graphitic one upon a cell cycling or heat-treatment.

• Applied Chemistry for Engineering
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• v.9 no.5
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• pp.654-660
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• 1998

In preparing PSZT powder by hydrothermal synthesis, effects of reaction temperature, concentration of raw materials and mineralizer on crystallinity, particle size distribution, and dielectric constant were investigated. By varying the concentration of mineralizer and the ratio of Pb to Sr or Zr to Ti, crystalline PSZT powder, having the mean particle size of $0.3{\sim}15{\mu}m$, was prepared by hydrothermal synthesis in the temperature range of $120{\sim}200^{\circ}C$ for a 2h reaction. PSZT ceramics, having dielectric constant of 1000~3000, were prepared at $1150^{\circ}C$ for a 2h sintering reaction of the PSZT powders. Experimental results showed that the weight mean particle size of $0.5{\mu}m$ was obtained when the concentration of KOH in the solution was 10 wt % and the ratio of Pb to Sr was 0.95/0.05, that of Zr to Ti was 0.52/0.48. It also showed that the ceramics of dielectric constant of 2900 were prepared through sintering of this PSZT powder. Size of PSZT particles became smaller with its narrow distribution as the concentration of KOH increased up to 10 wt %. However, it came to be larger at this concentration and above. By adding small amount of Sr that would not affect that crystallinity of particles we can improve dielectric property of sintered materials. Addition of Zr may shift the major crystal phase of synthetic PSZT powder from tetragonal to rhombohedral phase.