• Journal of Powder Materials
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• v.20 no.6
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• pp.474-478
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• 2013

The most general photocatalyst, $TiO_2$ and $WO_3$, are acknowledged to be ineffective in range of visible light. Therefore, many efforts have been directed at improving their activity such as: band-gap narrowing with non-metal element doping and making composites with high specific surface area to effectively separate electrons and holes. In this paper, the method was introduced to prepare a photo-active catalyst to visible irradiation by making a mixture with $TiO_2$ and $WO_3$. In the $TiO_2-WO_3$ composite, $WO_3$ absorbs visible light creating excited electrons and holes while some of the excited electrons move to $TiO_2$ and the holes remain in $WO_3$. This charge separation reduces electron-hole recombination resulting in an enhancement of photocatalytic activity. Added Ag plays the role of electron acceptor, retarding the recombination rate of excited electrons and holes. In making a mixture of $TiO_2-WO_3$ composite, the mixing route affects the photocatalytic activity. The planetary ball-mill method is more effective than magnetic stirring route, owing to a more effective dispersion of aggregated powders. The volume ratio of $TiO_2(4)$ and $WO_3(6)$ shows the most effective photocatalytic activity in the range of visible light in the view point of effective separation of electrons and holes.

• Advances in nano research
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• v.10 no.1
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• pp.77-90
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• 2021

In the present study, novel chitosan coated magnetic magnetite (Fe3O4) nanoparticles were successfully biosynthesized from mushroom, Agaricus campestris, extract. The obtained bio-nanocomposite material was used to investigate ultra-fast and highly efficient for removal of Ni2+ ions in a fixed-bed column. Chitosan was treated as polyelectrolyte complex with Fe3O4 nanoparticles and a Fungal Bio-Nanocomposite Material (FBNM) was derived. The FBNM was characterized by using X-Ray Diffractometer (XRD), Scanning Electron Microscopy-Energy Dispersive X-Ray Spectroscopy (SEM-EDS), Fourier Transform Infrared spectra (FTIR) and Thermogravimetric Analysis (TGA) techniques and under varied experimental conditions. The influence of some important operating conditions including pH, flow rate and initial Ni2+ concentration on the uptake of Ni2+ solution was also optimized using a synthetic water sample. A Central Composite Design (CCD) combined with Response Surface Modeling (RSM) was carried out to maximize Ni2+ removal using FBNM for adsorption process. A regression model was derived using CCD to predict the responses and analysis of variance (ANOVA) and lack of fit test was used to check model adequacy. It was observed that the quadratic model, which was controlled and proposed, was originated from experimental design data. The FBNM maximum adsorption capacity was determined as 59.8 mg g-1. Finally, developed method was applied to soft drinks to determine Ni2+ levels. Reusability of FBNM was tested, and the adsorption and desorption capacities were not affected after eight cycles. The paper suggests that the FBNM is a promising recyclable nanoadsorbent for the removal of Ni2+ from various soft drinks.

• Composites Research
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• v.20 no.5
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• pp.43-48
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• 2007

The absorption and the interference shielding of electromagnetic wave have been very important issues for commercial and military purposes. The stealth technique is one of the most typical applications of electromagnetic wave absorption technology. This study has started for the development of composite fillers containing dielectric and magnetic lossy materials. To improve the electromagnetic characteristics of conductive nano fillers, carbon nanofibers (CNFs) with nickel-phosphorous (Ni-P) or nickel-iron (Ni-Fe) have been fabricated by the electroless plating process. Observations by the electron microscopy (SEM/TEM) and element analyzer (EDS/ELLS) showed the uniform Ni-P and Ni-Fe coated CNFs. The compositions of the plating layers were about Ni-6wt%P and Ni-70wt%Fe, respectively. The average thicknesses of the plating layers were about $50\;{\sim}\;100\;nm$.

• Composites Research
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• v.36 no.6
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• pp.408-415
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• 2023

The formation of bonding configurations such as pyridinic-N, pyrrolic-N, and graphitic-N by nitrogen doping plays a crucial role in imparting distinct physical properties to carbon nanomaterials. In this study, we propose a simple and cost-effective approach to regulate nitrogen dopant configurations in carbon nanotubes (CNTs) by mixing melamine as a dopant source. We employed three distinct mechanical mixing techniques, namely magnetic stirring, bath sonication and tip sonication. The higher the ratio of melamine to CNT, the higher the ratio of Pyrrolic-N, and when mixed through stirring, the highest ratio of Pyridinic-N was shown. The facile method proposed in this study, which can easily form various types of nitrogen dopants in carbon nanotubes, is expected to facilitate the application of nitrogen-doped carbon nanomaterials.

• Journal of Gastric Cancer
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• v.3 no.3
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• pp.151-157
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• 2003

Purpose: In this study, we attempted to ascertain the proton magnetic resonance spectroscopy (${1}^H$ MRS) peak characteristics of human gastric tissue layers and finally to use the metabolic peaks of MRS to distinguish between normal and abnormal gastric specimens. Materials and Methods: Ex-vivo ${1}^H$ MRS examinations of thirty-five gastric specimens were performed to distinguish abnormal gastric tissues invaded by carcinoma cells from normal stomach-wall tissues. High-resolution 400-MHz (9.4-T) ${1}^H$ nuclear magnetic resonance (NMR) spectra of two gastric layers, a proper muscle layer, and a composite mucosasubmucosa layer were compared with those of clinical 64- MHz (1.5-T) MR spectra. Three-dimensional spoiled gradient recalled (SPGR) images were used to determine the size and the position of a voxel for MRS data collection. Results: For normal gastric tissue layers, the metabolite peaks of 400-MHz ${1}^H$ MRS were primarily found to be as follows: lipids at 0.9 ppm and 1.3 ppm; alanine at 1.58 ppm; N-acetyl neuraminic acid (sialic acid) at 2.03 ppm; and glutathione at 2.25 ppm in common. The broad and featureless featureless spectral peaks of the 64-MHz MRS were bunched near 0.9, 1.3, and 2.0, and 2.2 ppm in human specimens without respect to layers. In a specimen (Borrmmann type III) with a tubular adenocarcinoma, the resonance peaks were measured at 1.26, 1.36 and 3.22 ppm. All the peak intensities of the spectrum of the normal gastric tissue were reduced, but for gastric tumor tissue layers, the lactate peak split into 1.26 and 1.39 ppm, and the peak intensity of choline at 3.21 ppm was increased. Conclusion: We found that decreasing lipids, an increasing lactate peak that split into two peaks, 1.26 ppm and 1.36 ppm, and an increasing choline peak at 3.22 ppm were markers of tumor invasion into the gastric tissue layers. This study implies that MR spectroscopy can be a useful diagnostic tool for gastric cancer.

• Journal of the Korean Ceramic Society
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• v.42 no.2 s.273
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• pp.132-139
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• 2005

Sintering behavior of $BaO-Nd_{2}O_3-TiO_2$ with a Pb-based glassceramics frit were investigated in order to understand an effect of glassceramics as a low temperature sintering agent on dielectric ceramics. A green sheet form was fabricated through tape casting method with the glassceramic fut added $BaO-Nd_{2}O_3-TiO_2$. The dispersion properties, rheological properties and final density of dielectric composit slurry as a function of amount and composition of organic additives was examined. The dispersants' addition was effective in controlling dispersion of the ceramics in solution. The addition of excessive dispersant showed adverse effect on dispersion. The prepared slurries, containing ceramic : powders, glass-ceramics and various kinds of organic viechles, exhibited typical shear thinning behavior. The best properties of tape casting appeared powder to solvent ratio 65 : 35 and amount of the binder 6 wt$\%$ and plasticizer 3 wt$\%$. The viscosity of the slurry was 677 cps and green/sintered density in the tape was $3.3 g/cm^3,\;5.56 g/cm^3$ respectively.

• Journal of the Korean Magnetics Society
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• v.15 no.2
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• pp.67-75
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• 2005

For th aim of lightweight microwave absorbers, conductive and magnetic microspheres are fabricated by plating of Co films on hollow ceramic microspheres of low density. Metal plating was carried out in a two-step electroless plating process (pre-treatment of activation and plating). Uniform coating of the film with about $2{\~}3{\cal}um$ thickness was identified by SEM. High-frequency magnetic and microwave absorbing properties were determined in the rubber composites containing the Co-coated microspheres. Due to conductive and ferromagnetic behavior of the Co thin films, high dielectric constant and magnetic loss can be obtained in the microwave frequencies. Due to those electromagnetic properties, high absorption rate (25 dB) and thin matching thickness ($2.0{\~}2.5{\cal}mm$) are predicted in the composite layers containing the metal-coated microspheres of low density (about 0.84 g/cc) for the electromagnetic radiation in microwave frequencies.

• The Korean Journal of Quaternary Research
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• v.11 no.1
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• pp.57-68
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• 1997

Climatic change of the late-Quaternary period has been record-ed in the loess deposits of the central Great plains and the record of such change is extractable using a number of approaches and parameters. The stratigraphy of loess deposits which have been investigated on Fort Riley exhibits the same sequence of loess units and intercalated buried soils as is found elsewhere in the re-gion but adds detail unique to the reservation Upland late-Qua-ternary composite stratigraphy preserved on the reservation con-sists of the basal Sangamon soil of the Last interglacial(c. 120-110ka), Gilman Canyon Formation(c. >40 -20ka), Peoria loess(c. 20 -10ka) Brady soil(c. 11 -10ka) Bignell loess(c. 9-\ulcornerka). and mod-ern surface soil. Application of magnetic analyses has provided proxy data sets that represent a time series of climatically regulated pedogenesis/weathering and botanical composition. magetic data have yielded an impression of the variation in climate from Sangamon time to the late Holocene through a reconstruction of the history of pedogenesis/weathering. Sangamon soil formation dominated the reservation durin the Last interglacial as indicated by magnetic parameters. During Gil-man Canyon time loess influx was usually sufficiently slow as to permit pedogenesis which appears to have been at a maximum twice during that time. Warm season grasses were important dur-ing soil formation but diminished in importance during the peri-ods of more rapid loess fall which were cooler and perhaps wet-ter. Peoria loess fall a function of the deterioration of climate during the last Glacial Maximum thinly blanketed the reservation with thickest accumulations occurring to the north-west(Bala Cemetery site)proximal to the source region. Long-term surface stability did not apparently occur within Peoria time but short-term stability may be indicaed by the presence of thin weathering zones(incipient soils) in the Peoria loess. Re-gional landscape stability prevailed during the environmental shift at the Pleistocene/Holocene transition resulting in forma-tion of the well expressed Brady soil. One or more weak soils developed in the Bignell loess as it ac-cumulated. A notable feature of the Bignell loess is the appear-ance of the Altithermal dry period: the loess experienced little weathering and was dominated by warm season grasses until the latter of the Holocene.

• Composites Research
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• v.21 no.5
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• pp.9-14
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• 2008

Carbon nanofibers (CNFs) were used as dielectric lossy materials and NiFe particles were used as magnetic lossy materials. Total twelve specimens for the three types such as dielectric, magnetic and mixed radar absorbing materials (RAMs) were fabricated. Their complex permittivities and permeabilities in the range of $2{\sim}18$ GHz were measured using the transmission line technique. The parametric studios for reflection loss characteristics of each specimen to design the single-layered RAMs were performed. The mixed RAMs generally showed the improved absorbing characteristics with thinner matching thickness. One of the mixed RAMs, MD3with the thickness of 2.00 mm had the 10 dB absorbing bandwidth of 4.0 GHz in the X-band ($8.2{\sim}12.4$ GHz). It also showed very broad 10 dB absorbing bandwidth as wide as 6.0 GHz in the Ku-band ($12.0{\sim}18.0$ GHz) with the thickness tuning to 1.49 mm. The experimental results for selected several specimens were in very good agreements with simulation ones in terms of the overall reflection loss characteristics and 10 dB absorbing bandwidth.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.34 no.4
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• pp.125-130
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• 2024

Preparation of ferromagnetic powders for the mixture of hematite and pure Mg powders by ball milling has been investigated. Also, consolidation of the ball-milled powders was performed in a spark plasma sintering machine at 800-1,000℃. It is found that a ferromagnetic Fe-MgO composite powders are obtained by ball milling of hematite and pure Mg powders before 1 hour. The magnetization and coercivity of ball-milled samples change at the results of the solid state reaction of hematite by pure Mg during ball milling. The saturation magnetization of ball-milled samples increases with increasing ball milling time and reaches to a maximum value of 93.4 emu/g after 5 hours of ball milling. Shrinkage change after sintering of ball-milled sample for 5 hours was significant above 300℃ and gradually increased with increasing temperature up to 800℃. X-ray diffraction result shows that the average grain size of Fe in Fe-MgO bulk sample sintered at 900℃ is 50 nm. It can be also seen that the coercivity of bulk sample sintered at 900℃ is still high value of 90 Oe, indicating that the grain growth of magnetic Fe phase during sintering process tend to be suppressed.