• 한국주조공학회지
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• 제12권4호
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• pp.335-345
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• 1992

Aluminum alloy matrix composites reinforced with various amounts of SiC particles have been produced by rheo-compocasting followed by hot extrusion. A relatively uniform distribution of SiC particles in the composites was obtained. The amounts of pore and SiC particles cluster were relatively small in the composites. Particle free zones were observed in the hot extruded composites when the amount of SiC particles was less than 20 vol%. However, the width of particle free zone decreases with the increase of SiC particle content. Eutectic Si phase play an important role for improving bonding between SiC particle and matrix. Tensile and yield strength increased with the increase of SiC particle content. the strenthening effect of SiC particle addition was effective even at relatively high temperature of 573 K.

• 한국식품조리과학회지
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• 제14권5호
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• pp.584-588
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• 1998

Red pepper powders with variuos seed contents (0%, 10%, 20%) and particle sizes were stored at 0$^{\circ}C$, 20$^{\circ}C$, and 30$^{\circ}C$ for 90 days, and the changes in their characteristics were monitored. The initial moisture content was about 13%, and the powders were packed in 0.1 mm-thick polypropylene (PP) bags. Moisture content of each power remained constantly, so PP bags appeared to be effective to prevent moisture transmission. All the values of L＊, a＊ and b＊ were higher in fine particles than in coarse particles. Storage at 0$^{\circ}C$ did not change any color values, however, overall color values devreased apparently when stored at 30$^{\circ}C$ for 90 days. Capsanthin contents decreased gradually at all storage temperatures and more rapidly at higher temperature. The contents of capsaicinoids in fine particles (49∼59 mg%) were twic as much as those in coarse particles (15∼36 mg%), and they did not change throughout the storage.

• Korean Chemical Engineering Research
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• 제59권3호
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• pp.455-466
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• 2021

Micro and nanoparticles of Finasteride were prepared by gas-antisolvent method. The influence of process parameters such as pressure (100, 130 and 160 bar), temperature (308, 318 and 328 K) and solute concentrations (10, 25 and 40 mg/ml) on mean particle size was studied by Box-Behnken design. As ANOVA results indicated, the highest influence in production of smaller particles was attributed to the pressure. Optimum condition leading to the smallest particle size was as follows: initial solute concentration, 10 mg/ml; temperature, 308 K and pressure, 160 bar. The particles were evaluated with FTIR, SEM, DLS, XRD as well as DSC. The analyses revealed a size decrease in the precipitated Finasteride particles (232.4 nm, on mean) via gas-antisolvent method, as compared to the original particles (55.6 ㎛).

• Journal of Korean Society for Atmospheric Environment
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• 제22권E2호
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• pp.78-88
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• 2006

In order to study the characteristics of cloud, a real-scale experiment for cloud generation was carried out using an extinct vertical mine (430 m height) located in the northeastern Honshu, Japan. The dry particles generated from the three-step concentrations of NaCl solutions were used for cloud generation. The number size distributions of initial dry particles and cloud droplets were monitored by Scanning Mobility Particle Sizer (SMPS) and Forward Scattering Spectrometer Probe (FSSP) at bottom and upper sites of pit, respectively. The polymeric water absorbent film (PWAF) method was employed to measure liquid water content ($W_L$) as a function of droplet size. Moreover the chemical properties of individual droplet replicas were determined by micro-PIXE. The CCN number concentration shows the lognormal form in dependence of the particle size, while the number size distributions of droplets are bimodal showing the peaks around $9{\mu}m$ and $20{\mu}m$ for every case. In comparison to background mineral particles, right shifting of size distribution line for NaCl particles was occurred. When NaCl solutions with three-step different concentrations were neulized, $W_L$ shows the strong droplet size dependence. It varied from $10.0mg\;m^{-3}$ up to $13.6mg\;m^{-3}$ with average $11.6mg\;m^{-3}$. A good relationship between $W_L$ and cloud droplet number concentration was obtained. Both chemical inhomogeneities (mixed components with mineral and C1) and homogeneities (only mineral components or C1) in individual droplet replicas were obviously observed from micro-PIXE elemental images.

• 대한금속재료학회지
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• 제46권5호
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• pp.304-309
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• 2008

Magnesium alloys containing $Mg_2Si$ particles, as a promising cheap heat-resistant magnesium alloy for automobile power train parts applications, are attracting more attention of both material scientists and design engineers. Modification of the Chinese script shape $Mg_2Si$ particle is a key for using this alloy in sand or permanent mould casting. In the present work, the modification effect of Sr and Sb on the corrosion properties of the Mg-5Al-2Si alloy was investigated. Sr or Sb addition promoted the formation of fine polygonal shape $Mg_2Si$ particles by providing the nucleation sites. Sr was more effective element than Sb for shape modification of Chinese script shape $Mg_2Si$. Such improved microstructure of the modified alloy resulted in large improvement in corrosion resistance as compared to unmodified Mg-5Al-2Si alloy.

• 열처리공학회지
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• 제29권4호
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• pp.168-175
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• 2016

Influence of trace amount of Ca addition on the corrosion resistance was comparatively investigated in solutionized Mg-4%Zn and Mg-4%Zn-0.1%Ca alloys. In as-cast state, the alloys were characterized by primary ${\alpha}-(Mg)$ dendrite with MgZn intermetallic compound particles. After solution-treatment, both alloys consisted of single ${\alpha}-(Mg)$ phase by dissolution of the compound particles into the matrix. It was found from the immersion and electrochemical corrosion tests that the Mg-4%Zn alloy had better corrosion resistance than the Mg-4%Zn-0.1%Ca alloy. Morphological and compositional analyses on the surface corrosion products indicate that the incorporation of Ca oxide with low PBR value into the surface corrosion products would be responsible for the decreased corrosion resistance of the Ca-containing alloy.

• 한국대기환경학회지
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• 제24권5호
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• pp.594-603
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• 2008

A single particle analytical technique, named low-Z particle electron probe X-ray microanalysis, was applied to characterize four samples collected at an underground shopping area connected to Dongdeamun subway station, in January and May 2006. Based on the analysis of their chemical compositions of the samples, many distinctive particle types are identified and the major chemical species are observed to be soil-derived particles, iron-containing particles. sulfates. nitrates, and carbonaceous particles. which are encountered both in coarse and fine fractions. Carbonaceous particles exist in carbon-rich and organic. Soil derived particles such as aluminosilicates, AlSi/C, $CaCO_3\;and\;SiO_2$ are more frequently encountered in spring samples than winter samples. Nitrate- and sulfate-con taming particles are more frequently encountered in winter samples, and those nitrate- and sulfate-containing particles mostly exist in the chemical forms of $Ca(CO_3,\;NO_3),\;Ca(NO_3,\;SO_4),\;(Na,\;Mg)NO_3\;and\;(Mg,\;Na)(NO_3,\;SO_4)$. Fe-containing particles which came from nearby subway platform are in the range of about 10% relative abundances for all the samples. It is observed that nitrate- and sulfate-containing particles and carbonaceous particles are much more frequently encountered in indoor aerosol samples than in outdoor aerosols, implying that $NO_x,\;SO_x$, and VOCs at the underground shopping area were more partitioned into aerosol phase.

• 상하수도학회지
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• 제32권1호
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• pp.47-53
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• 2018

This study investigated phosphorus removal from secondary treated effluent using coagulation-membrane separation hybrid treatment to satisfy strict regulation in wastewater treatment. The membrane separation process was used to remove suspended phosphorus particles after coagulation/settlement. Membrane separation with $0.2{\mu}m$ pore size of micro filtration membrane could reduce phosphorus concentration to 0.02 mg P/L after coagulation with 1 mg Al/L dose of polyaluminum chloride (PACl). Regardless of coagulant, the residual concentration of phosphorus decreased as the dose increased from 1.5 to 3.5 mg Al/L, while the target concentration of 0.05 mg P/L or less was achieved at 2.5 mg Al/L for the aluminum sulfate (Alum) and 3.5 mg Al/L for PACl. Moreover, alum showed better membrane flux as make bigger particles than PACl. Alum showed a 40% of flux decrease at 2.5 mg Al/L dose, while PACl indicated a 50% decrease of membrane flux even with a higher dose of 3.5 mg Al/L. Thus, alum was more effective coagulant than PACl considering phosphorus removal and membrane flux as well as its dose. Consequently, the coagulation-membrane separation hybrid treatment could be mitigate regulation on phosphorus removal as unsettleable phosphorus particles were effectively removed by membrane after coagulation.

• 열처리공학회지
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• 제6권4호
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• pp.237-242
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• 1993

The fatigue behaviors of mechanically alloyed Al-4Mg alloys dispersed with either $Al_2O_3$ or $MgAl_2O_4$ oxide particles were investigated. This study maily concerned with the role of coherency of dispersed particles with the matrix on the fatigue behavior of the alloys. The $MgAl_2O_4$ which has a spinel structure with the lattice parameter of exactly the twice of Al showed the habit relation with the matrix. The mechanically alloyed Al-4Mg alloys showed stable stress responses with fatigue cycles from start to failure regadless of strain amplitudes and of existence of dispersoids. The Al-4Mg alloy dispersed with $MgAl_2O_4$ showed not only the better static mechanical properties but also the better low cycle fatigue resistance than that with $Al_2O_3$, i.e., much higher plastic strain energy dissipated to failure, at low strain amplitude. However, this alloy showed inferior fatigue resistance to that dispersed with $Al_2O_3$ or that without dispersion at high strain amplitude. These results imply that $MgAl_2O_4$ may promote lowering the stacking fault energy of the alloy inherited from the coherency with the matrix so that dislocations shuttle back and forth on the same slip plane without cross slipping to other planes during fatigue at low strain amplitude resulting in long fatigue life.

• 한국분말재료학회지
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• 제16권1호
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• pp.43-49
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• 2009

Titanium carbides are widely used for cutting tools and grinding wheels, because of their superior physical properties such as high melting temperature, high hardness, high wear resistance, good thermal conductivity and excellent thermal shock resistance. The common synthesizing method for the titanium carbide powders is carbo-thermal reduction from the mixtures of titanium oxide($TiO_2$) and carbon black. The purpose of the present research is to fabricate nano TiC powders using titanium salt and titanium hydride by the mechanochemical process(MCP). The initial elements used in this experiment are liquid $TiCl_4$(99.9%), $TiH_2$(99.9%) and active carbon(<$32{\mu}m$, 99.9%). Mg powders were added to the $TiCl_4$ solution in order to induce the reaction with Cl-. The weight ratios of the carbon and Mg powders were theoretically calculated. The TiC and $MgCl_2$ powders were milled in the planetary milling jar for 10 hours. The 40 nm TiC powders were fabricated by wet milling for 4 hours from the $TiCl_4$+C+Mg solution, and 300 nm TiC particles were obtained by using titanium hydride.