• Journal of Powder Materials
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• v.22 no.3
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• pp.208-215
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• 2015

Fe-TiC composite powders were fabricated by planetary ball mill processing. Two kinds of powder mixtures were prepared from the starting materials of (a) (Fe, TiC) powders and (b) (Fe, $TiH_2$, Carbon) powders, respectively. Milling speed (300, 500 and 700 rpm) and time (1, 2, and 3 h) were varied. For (Fe, $TiH_2$, Carbon) powders, an in situ reaction synthesis of TiC after the planetary ball mill processing was added to obtain a homogeneous distribution of ultrafine TiC particulates in Fe matrix. Powder characteristics such as particle size, size distribution, shape, and mixing homogeneity were investigated.

• Journal of the Korean Ceramic Society
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• v.31 no.10
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• pp.1231-1239
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• 1994

In this study, gel powder which had relatively high hydration reactivity in CaO and P2O5 rich composition of CaO-P2O5-SiO2-H2O system was prepared by sol-gel process and its hydrated specimen was manufactured. The it was investigated to appropriate calcination temperature in sol-gel process which hydrated specimen of gel powder have proven to strength and the effect of factors influenced strength in hydration process. The major product of before and after hydration reaction was hydroxyapatite, and crystalline phase of C-S-H was already formed during gelation process. After hydration reaction of pressed specimen, crystalline phase of C-S-P-H was formed. It was hydrated product of silicocarnotite (5CaO.P2O5.SiO2). Gel phases of C-S-H and C-S-P-H occured as a result of partial substitution of amorphous silica by P2O5 was formed. The strength of hydrated hardened body is developed by strong bonding and bridging between the gel phases of C-S-H or C-S-P-H and the crystalline products such as hydroxyapatite, Ca(OH)2 C-S-H and C-S-P-H. In addition, the ultrafine gel powder have an great effect on increase of hydration reaction.

• Journal of the Korean Ceramic Society
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• v.37 no.2
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• pp.164-167
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• 2000

Flue gases in the iron foundry consist of 15~20% CO2 as an air pollution gas whose emission should be mitigated in order to protect the environment. In the present study, ultrafine powders of NixZn1-xFe2O4 as a potential catalyst for the CO2 decomposition were prepared by the coprecipitation methods. Oxygen deficient ferrites (MeFe2O4-$\delta$) can decompose CO2 as C and O2 at a low temperature of about 30$0^{\circ}C$. The XRD result of synthesized ferrites showed the spinel structure of ferrites and ICP-AES and EDS quantitative analyses showed the composition similar with initial molar ratios of the mixed solution prior to reaction. The BET surface area of the (Ni, Zn)-ferrites was about 77~89.5$m^2$/g and their particle size was observed about 10~20 nm. The CO2 decomposition efficiency of the oxygen deficient (Nix, Zn1-x)-ferrites was the highest at x=0.3, and the ternary (Ni, Zn)-ferrites was better than that of binary Ni-ferrites.

• Korean Journal of Materials Research
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• v.11 no.9
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• pp.797-801
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• 2001

In this study, the solution combustion method was employed to synthesize stoichiometric mullite, and hence the attrition process was employed to prepare ultrafine mullite particles with nano size. The thermal decomposition behavior and partial pressure of equilibrium species of both oxidizer and fuel were considered during solution combustion process. The synthesized product was mullite phase with 40 nm crystalline size, and the alumina contents of the product by TEM/EDS quantity analysis was 3.12$\pm$04 mole. The result showed that the synthesized mullite was almost close to the it's stoichiometric composition. For attrition process, the dispersion behavior of the mullite suspension was controlled and was comminuted with the condition of 800 rpm for 4 hours using 0.3 mm zirconia ball media. As a result of comminution, the mean particle size was 80 nm.

• Journal of Environmental Science International
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• v.16 no.7
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• pp.793-798
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• 2007

During May of 2003, smoke from fires in the Yucatan Peninsula was transported across the Gulf of Mexico and into Texas where it caused significant enhancement in measured aerosol concentrations and reduced visibility. During this event, the formation and growth of aerosol particles has been observed by a differential mobility analyzer (DMA) / tandem differential mobility analyzer (TDMA) system to characterize the size distribution and size-resolved hygroscopicity of the aerosol. The most number concentration is by the particles smaller than 100 nm, but the integrated number concentrations for over 100 nm increased due to the aerosol growth. Hygroscopic growth factor increase from 1.2 to 1.4 for 25, 50, and 100 nm particles during the nucleating period. This distribution and the aerosol properties derived from the TDMA data were used to calculate the growth rate. Particle growth rates were in the range 1-12 nm/hr.

• Journal of Powder Materials
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• v.27 no.4
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• pp.293-299
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• 2020

W₂C is synthesized through a reaction-sintering process from an ultrafine-W and WC powder mixture using spark plasma sintering (SPS). The effect of various parameters, such as W:WC molar ratio, sintering temperature, and sintering time, on the synthesis behavior of W₂C is investigated through X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM) analysis of the microstructure, and final sintered density. Further, the etching properties of a W₂C specimen are analyzed. A W₂C sintered specimen with a particle size of 2.0 ㎛ and a relative density over 98% could be obtained from a W-WC powder mixture with 55 mol%, after SPS at 1700℃ for 20 min under a pressure of 50 MPa. The sample etching rate is similar to that of SiC. Based on X-ray photoelectron spectroscopy (XPS) analysis, it is confirmed that fluorocarbon-based layers such as C-F and C-F2 with lower etch rates are also formed.

• Journal of Radiation Protection and Research
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• v.20 no.2
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• pp.79-83
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• 1995

A number of investigators have reported formation of radiolytic ultrafine particles produced by the interaction of ionizing radiation with atmospheric trace gases. Previous studies have suggested that a very high localized concentration of the hydroxyl radical produced by the radiolysis of water can react with atmospheric trace gases such as $SO_2$ and produce lower vapor pressure compounds that can subsequently nucleate. To determine the trace gas and water vapor concentration dependence of the active, positively charged, first decayt product of radon (Po-218), a well-controlled radon chamber was used in this research. The mobility spectrum of the decay products in the range of $0.07-5.0cm^2/V\;sec$ from the radon chamber was measured using alpha track detector installed inside a specially-designed electrostatic spectrometer. Measurements were taken for different concentrations (0.5ppm to 5ppm) of $SO_2$ in Purified, Compressed air. A kinetics Study following the clustering of $SO_2$ around the $PoO_x^+$ ion in an excess of $SO_2$ for interpretation of the reaction processes was performed.

• Journal of the Korean Ceramic Society
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• v.40 no.12
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• pp.1202-1207
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• 2003

Using a recently developed Hybric Plasma-Particle Accelerating Impact Deposition (HP-PAID) process, synthesis of nanostructured silicon coatings has been investigated by injecting vapor-phase TEOS (tetraethosysilane, (C$_2$H$\_$5/O)$_4$Si) into an Ar hybrid plasma. The plasma jet with reactants was expanded through nozzle into a deposition chamber, with the pressure dropping from 700 to 10 torr. Ultrafine particles accelerated in the free jet downstream of the nozzle, deposited by an inertial impaction onto a temperature controlled substrate. By using this process, nanostructured amorphous silicon coatings with grain size smaller than 10 nm could be synthesized. These samples were annealed in an Ar and crystallized at 900$^{\circ}C$ for 30 min. TEM analysis showed that the annealed coatings were also composed of nanoparticles smaller than 10 nm, which showed a good consistency that the average grain size of 7 nm was also estimated from a peak shift of 2.39 cm$\^$-1/ and Full Width at Half Maximum (FWHM) 5.92 cm$\^$-1/ of Raman analysis. The noteworthy is that a strong PL peak at 398 nm was also obtained for this sample, which indicates that the deposited coatings also contained 3∼4 nm nanostructured grains.

• Korean Journal of Materials Research
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• v.8 no.9
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• pp.813-818
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• 1998

Ultrafine powders of $\textrm{In}_{2}\textrm{O}_{3}$-doped $\textrm{SnO}_{2}$ were synthesized by a coprecipitation method and the effects of pH value and the amount of In2Q addition on particle size were investigated. The influence of pH value on particle size could be negligible, whereas the amount of $\textrm{In}_{2}\textrm{O}_{3}$ has influenced on particle size and specific surface area. The gas sensitivity to hydrocarbOn($\textrm{C}_{3}\textrm{H}_{8}$, $\textrm{C}_{4}\textrm{H}_{10}$) increased with $\textrm{In}_{2}\textrm{O}_{3}$ addition and reached a maximum at 3wt.% addition. From the results of impedance analysis and I-V characteristics. it was showed that the agglomeration structure of particles and the boundaries between agglomerates were the important factors to determine the gas sensing mechanism.

• Food Science and Preservation
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• v.21 no.1
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• pp.75-81
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• 2014

In this study, the biological activity of water and ethanol extracts from Saururus chinensis by ultra-fine grinding for functional food source are examined. It is more effective to use ethanol than water when extracting phenolic compounds. Approximately 2.5 times higher extraction yield were shown when it was ultra-fine grinded because the particle size decreases, thereby increasing the extraction yield. Normal grinded sample extracts showed 69.8% of DPPH inhibition effect, while fine grinded and ultra-fine grinded sample extracts showed 70.7% and 83.8% each, respectively. Normal extract, as well as fine grinded and ultra-fine grinded extracts, showed over 97% of ABTS inhibition effect, thereby indicating only a slight difference in the anti-oxidative activity with the grinding method. Higher PF was determined with fine grinded and ultra-fine grinded extracts than the normal grinded extract, while ultra-fine grinded 50% ethanol extracts showed the highest anti-oxidative activity value of 1.8 PF. The fine grinded and ultra-fine grinded particle sizes are smaller than the normal grinded particle size, thus increasing the inhibition rate of the TBARS. Furthermore, the ethanol extract was revealed to have a higher effect than the water extracts. The xanthin oxidase inhibition, on the other hand, was identified as ultra-fine grinded that led to the increase in the enzyme inhibition effect. In the angiotensin-converting enzyme, water extracts with normal grinding did not show inhibition activity, while 50% ethanol extracts showed 24% inhibition activity. Moreover, the ethanol extracts showed higher inhibition effect compared to the water extracts. Ultra-fine grinded 50% ethanol extracts showed a slight antibacterial effect on the Staphylococcus aureus and Escherichia coli, while the other extracts showed none. The result suggests that Saururus chinensis extracts by ultra-fine grinding may be more useful than normal grinding as potential sources due to anti-oxidation, angiotensin converting enzyme and xanthine oxidase inhibition.