• Applied Chemistry for Engineering
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• v.19 no.4
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• pp.370-375
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• 2008

Optimum synthesis conditions were investigated for the non-aqueous dispersion (NAD) polymerization of environmentally-friendly acrylic resin. The optimum amount of stabilizer was observed to be 20 wt% to prevent flocculation of the synthesized polymer particles. The optimum ratio of aliphatic solvents to aromatic solvents turned out to be 80 to 20 in order to obtain a stabilized NAD resins. The viscosity of NAD resins was affected not only by the reaction time but also by the amount of initiator and the impeller rpm. Also, the particle size and the size distribution were influenced by the amount of stabilizers and initiators. Since the stability of NAD resin was devastated by the increase in particle size when all the monomers were fed at the beginning of polymerization, the monomers need to be put into the reactor step by step throughout the entire polymerization process.

• Journal of Powder Materials
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• v.20 no.3
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• pp.180-185
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• 2013

The iron oxides nanoparticles and iron oxide with other compounds are of importance in fields including biomedicine, clinical and bio-sensing applications, corrosion resistance, and magnetic properties of materials, catalyst, and geochemical processes etc. In this work we describe the preparation and investigation of the properties of coated magnetic nanoparticles consisting of the iron oxide core and organic modification of the residue. These fine iron oxide nanoparticles were prepared in air environment by the co-precipitation method using of $Fe^{2+}$: $Fe^{3+}$ where chemical precipitation was achieved by adding ammonia aqueous solution with vigorous stirring. During the synthesis of nanoparticles with a narrow size distribution, the techniques of separation and powdering of nanoparticles into rather monodisperse fractions are observed. This is done using controlled precipitation of particles from surfactant stabilized solutions in the form organic components. It is desirable to maintain the particle size within pH range, temperature, solution ratio wherein the particle growth is held at a minimum. The iron oxide nanoparticles can be well dispersed in an aqueous solution were prepared by the mentioned co-precipitation method. Besides the iron oxide nanowires were prepared by using similar method. These iron oxide nanoparticles and nanowires have controlled average size and the obtained products were investigated by X-ray diffraction, FESEM and other methods.

• Journal of Powder Materials
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• v.17 no.1
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• pp.13-22
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• 2010

The unique features of spark plasma sintering process are the possibilities of a very fast heating rate and a short holding time to obtain fully dense materials. $\beta$-SiC powder with 0, 2, 6, 10 wt% of $\alpha$-SiC particles (seeds) and 4 wt% of Al-B-C (sintering aids) were spark plasma sintered at $1700-1850^{\circ}C$ for 10 min. The heating rate, applied pressure and sintering atmosphere were kept at $100^{\circ}C/min$, 40 MPa and a flowing Ar gas (500 CC/min). Microstructural development of SiC as function of seed content and temperature during spark plasma sintering was investigated quantitatively and statistically using image analysis. Quantitative image analyses on the sintered SiC ceramics were conducted on the grain size, aspect ratio and grain size distribution of SiC. The microstructure of SiC sintered up to $1700^{\circ}C$ consisted of equiaxed grains. In contrast, the growth of large elongated SiC grains in small matrix grains was shown in sintered bodies at $1750^{\circ}C$ and the plate-like grains interlocking microstructure had been developed by increasing sintering temperature. The introduction of $\alpha$-SiC seeds into $\beta$-SiC accelerated the grain growth of elongated grains during sintering, resulting in the plate-like grains interlocking microstructure. In the $\alpha$-SiC seeds added in $\beta$-SiC, the rate of grain growth decreased with $\alpha$-SiC seed content, however, bulk density and aspect ratio of grains in sintered body increased.

• Applied Chemistry for Engineering
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• v.9 no.5
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• pp.768-773
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• 1998

A mathematical model of discharge mechanism of metal-hydride (MH) electrode was presented. A computer simulation program was developed in order to predict the variation of electrode potential and the distribution of hydrogen concentration within MH particles during discharge. By investigating the effects of the discharge current density, the size of MH particle, the diffusivity of hydrogen in MH particle, and the porosity of the electrode, it was found that these factors exerted a collective effect on the discharge characteristic of the electrode and the utilization of hydrogen in the MH particle. It was confirmed that and optimization of design factors of an MH electrode is necessary in order to execute a high-rate discharge and to improve the utilization of hydrogen in MH particle.

• Korean Chemical Engineering Research
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• v.54 no.5
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• pp.659-664
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• 2016

In order to resolve the AAEM species migration routes and the interaction relationship between biochar structure and AAEM species during biomass pyrolysis, experiments were performed in an entrained flow reactor with $N_2$ at $500{\sim}900^{\circ}C$. ICP-AES, XPS and SEM-EDX were used to examine content and distribution of AAEM species and the physicochemical structures of biochar. The results show that at $500{\sim}700^{\circ}C$, the precipitation rate of AAEM species is relatively high. At high temperature (>$700^{\circ}C$), the AAEM species continue to migrate from interior to exterior, but little precipitation from biochar surface. And the migration of AAEM species is mainly realized by the C-O bond as the carrier medium. The AAEM species on biochar surface are mainly Na, Mg and Ca (<$700^{\circ}C$), while changing to K, Mg and Ca (${\geq}700^{\circ}C$). From $500^{\circ}C$ to $900^{\circ}C$, the biochar particle morphology gradually changes from fibers to porous structures, finally to molten particles. At $700{\sim}900^{\circ}C$, Ca element is obviously enriched on the molten edge of the biochar porous structures.

• Geomechanics and Engineering
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• v.22 no.4
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• pp.361-374
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• 2020

This paper is concerned with the thermoelastic bending of FG beams resting on two-layer elastic foundations. One of these layers is Winkler springs with a variable modulus while the other is considered as a shear layer with a constant modulus. The beams are considered simply supported and subjected to thermo-mechanical loading. Temperature-dependent material properties are considered for the FG beams, which are assumed to be graded continuously across the panel thickness. The used theories contain undetermined integral terms which lead to a reduction of unknowns functions. Several micromechanical models are used to estimate the effective two-phase FG material properties as a function of the particles' volume fraction considering thermal effects. Analytical solutions for the thermo-mechanical bending analysis are obtained based on Navier's method that satisfies the boundary conditions. Finally, the numerical results are provided to reveal the effect of explicit micromechanical models, geometric parameters, temperature distribution and elastic foundation parameters on the thermoelastic response of FG beams.

• Journal of Conservation Science
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• v.32 no.1
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• pp.75-88
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• 2016

In this study, 5 mural paintings in the Buddhist temples of Joseon era were researched for component analysis on the soil contained in the walls. The results of particle size analysis showed that the ratio of particle contents were different in each layer. In the finishing layer, the distribution of the middle sand fraction is higher than that of the middle layer. The results of XRD analysis showed that quartz, feldspar, and clay mineral are the main components of sand, suggesting similar mineral composition to that of ordinary soil component. It seems weathered rocks were used for construction of the walls. The main chemical components detected from EDX analysis were Si, Al, Fe, and K. Also the SEM images showed sand or clay sized minerals. In conclusion, the walls of the buddhist mural paintings in Joseon Dynasty had been constructed by using the loess, and had been produced by using mixture of clay and sand particles of different sizes for each layer. This study identified the characteristics of the materials and the manufacturing technologies used on the walls of mural paintings of Buddhist temples in Joseon era.

• Journal of Animal Science and Technology
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• v.63 no.5
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• pp.1182-1193
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• 2021

The aims of this study were to develop a milk protein-based probiotic delivery system using a modified rennet-induced gelation method and to determine how the skim milk powder concentration level and pH, which can affect the rennet-induced intra- and inter-molecular association of milk proteins, affect the physicochemical properties of the probiotic delivery systems, such as the particle size, size distribution, encapsulation efficiency, and viability of probiotics in simulated gastrointestinal tract. To prepare a milk protein-based delivery system, skim milk powder was used as a source of milk proteins with various concentration levels from 3 to 10% (w/w) and rennet was added to skim milk solutions followed by adjustment of pH from 5.4 or 6.2. Lactobacillus rhamnosus GG was used as a probiotic culture. In confocal laser scanning microscopic images, globular particles with a size ranging from 10 ㎛ to 20 ㎛ were observed, indicating that milk protein-based probiotic delivery systems were successfully created. When the skim milk powder concentration was increased from 3 to 10% (w/w), the size of the delivery system was significantly (p < 0.05) increased from 27.5 to 44.4 ㎛, while a significant (p < 0.05) increase in size from 26.3 to 34.5 ㎛ was observed as the pH was increased from 5.4 to 6.4. An increase in skim milk powder concentration level and a decrease in pH led to a significant (p < 0.05) increase in the encapsulation efficiency of probiotics. The viability of probiotics in a simulated stomach condition was increased when probiotics were encapsulated in milk protein-based delivery systems. An increase in the skim milk powder concentration and a decrease in pH resulted in an increase in the viability of probiotics in simulated stomach conditions. It was concluded that the protein content by modulating skim milk powder concentration level and pH were the key manufacturing variables affecting the physicochemical properties of milk protein-based probiotic delivery systems.

• Corrosion Science and Technology
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• v.15 no.3
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• pp.120-124
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• 2016

The effect of alloying element Ca (0, 1, and 2 wt%) on corrosion resistance and bioactivity of the as-received and anodized surface of rolled plate AM60 alloys was investigated. A plasma electrolytic oxidation (PEO) was carried out to form anodic oxide film in $0.5mol\;dm^{-3}\;Na_3PO_4$ solution. The corrosion behavior was studied by polarization measurements while the in vitro bioactivity was tested by soaking the specimens in Simulated Body Fluid (1.5xSBF). Optical micrograph and elemental analysis of the substrate surfaces indicated that the number of intermetallic particles increased with Ca content in the alloys owing to the formation of a new phase $Al_2Ca$. The corrosion resistance of AM60 specimens improved only slightly by alloying with 2 wt% Ca which was attributed to the reticular distribution of $Al_2Ca$ phase existed in the alloy that might became barrier for corrosion propagation across grain boundaries. Corrosion resistance of the three alloys was significantly improved by coating the substrates with anodic oxide film formed by PEO. The film mainly composed of magnesium phosphate with thickness in the range $30-40{\mu}m$. The heat resistant phase of $Al_2Ca$ was believed to retard the plasma discharge during anodization and, hence, decreased the film thickness of Ca-containing alloys. The highest apatite forming ability in 1.5xSBF was observed for AM60-1Ca specimens (both substrate and anodized) that exhibited more degradation than the other two alloys as indicated by surface observation. The increase of surface roughness and the degree of supersaturation of 1.5xSBF due to dissolution of Mg ions from the substrate surface or the release of film compounds from the anodized surface are important factors to enhance deposition of Ca-P compound on the specimen surfaces.

• Journal of the Korean Ceramic Society
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• v.46 no.1
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• pp.116-121
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• 2009

The constituent phases in Ti($C_{0.7}N_{0.3}$)-xWC-20Ni (wt%, x=5, 15, 25) cermets were characterized using nanoindentation in conjunction with observation of microstructure. The microstructure of cermet is composed of hard phase and binder phase, which gave rise to a wide range of hardness distribution when nanoindentation was carried out on the polished surface of cermets. Because of the inhomogeneous nature of cermet microstructure, observation of indented surface was indispensable in order to separate the hardness of each constituent phase. The measured values of hardness using nanoindentation were ${\sim}14\;GPa$ for the binder phase and ${\sim}24$ to 28 GPa for the hard phase, of which nanoindentation hardness was decreased with the addition of WC into Ti($C_{0.7}N_{0.3}$)-Ni system. In addition, the nanoindentation hardness of Ni binder phase was much higher than reported Vickers hardness, which could result from confined deformation of binder phase due to the surrounding hard phase particles.