• Journal of the Korean Society for Heat Treatment
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• v.9 no.1
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• pp.1-11
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• 1996

Mechanical alloying is an effective process to finely distribute inert dispersoids in an Al-TM(TM is a transition metal) system. It has been considered that high melting point aluminides are formed by precipitation from supersaturated Al(Ti) powder. This analysis is based on the fact that much higher content of TM than the solubioity can be dissolved in alpha aluminum during the high energy ball milling. Thus, decomposition behavior of Ti in the Al(Ti) was considered very important. But it is confirmed that the higher portion of Ti than Al(Ti) solid solution is existed as nano-sized Ti particles in the MA powders by high energy ball nilling from the XRD spectrum and TEM analysis in this study. Therefore, the role of undissolved TM particles affect the formation of aluminides should be suitably considered. In this study, we present experimental observation on the formation of $Al_3Ti$ fron mechanical alloyed Al-Ti alloys in the hyperperitectic region. This study showed that, in the mechanically alloyed Al-20wt%Ti specimen, intermediate phase of cubic $Al_3Ti$ and tetragonal $Al_{24}Ti_8$ formed at $300{\sim}400^{\circ}C$ and $400{\sim}500^{\circ}C$, respectively, before the MA state reaches to equilibrium at higher temperatures. The formation behavior of $Ll_2-Al_3Ti$ is interpreted by interdiffusion of Al and Ti in solid state based on the fact that large amount of nano-sized Ti particles exist in the milled powder. Present analysis indicated undissolved Ti particles of nanosize should have played an important role initiation the formation of $Al_3Ti$ phase during annealing.

• International Journal of Advanced Culture Technology
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• v.3 no.2
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• pp.100-109
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• 2015

Environmental problems from petroleum-based plastic wastes have been rapidly increasing in recent years. The alternative solution is focus on the development of environmental friendly plastic derived from renewable resource. Poly(lactic acid) (PLA) is a biodegradable polymer synthesized from biomass having potential to replace the petroleum-based non-degradable polymers utilizations. PLA can be synthesized by two methods: (1) ring-opening of lactide intermediate and (2) direct polycondensation of lactic acid processes. The latter process has advantages on high yields and high purity of polymer products, materials handling and ease of process treatments. The polymerization process of PLA synthesis has been widely studied in a laboratory scale. However, the mass scale production using direct polycondensation of lactic acid has not been reported. We have investigated the kinetics and scale-up process of direct polycondensation method to produce PLA in a pilot scale. The order of reaction is 2 and activation energy of lactic acid to lactic acid oligomers is 61.58 kJ/mol. The pre-polymer was further polymerized in a solid state polymerization (SSP) process. The synthesized PLA from both the laboratory and pilot scales show the comparable properties such as melting temperature and molecular weight. The appearance of synthesized PLA is yellow-white solid powder.

• Composites Research
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• v.12 no.2
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• pp.91-100
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• 1999

The manufacture of high strength polyethylene(HSPE) tape yarns has been accomplished by a solid state processing(SSP) method as the compaction of ultra-high molecular weight polyethylene(UHMWPE) powders and drawing of the compacted film under the melting point without any organic solvents. In this study, the characteristics of HSPE tape yarns produced by SSP which is desirable for production cost and environmental aspect were analyzed. As the results, tensile strengths of HSPE tape yarns increased with increasing the draw ratio and the fracture morphology of highly drawn HSPE tape yarns showed more fibrillar shape than the low drawn one. Interfacial shear strengths of HSPE tape yarns with vinylester resin increased by $O_2$ plasma treatment and maximum interfacial shear strength was obtained in the plasma treatment condition of 100W and 5min. In addition, mechanical properties of HSPE tape yarn reinforced composites were investigated and compared with those of the gel spun HSPE fiber reinforced composites.

• Archives of Pharmacal Research
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• v.20 no.6
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• pp.560-565
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• 1997

The physicochemical properties of melatonin (MT) in propylene glycol (PG) and 2-hydroxypropyl-.betha.-cyclodextrin $(2-HP{\beta}CD)$ vehicles were characterized. MT was endothermally decomposed as determined by differential scanning calorimetry (DSC). Melting point and heat of fusion obtained were $116.9{\pm}0.24^{\circ}C $.and $7249{\pm}217 cal/mol$., respectively. MT as received from a manufacture was very pure, at least 99.9%. The solubility of MT in PG solution increased slowly until reaching 40% PG and then steeply increased. Solubility of MT increased linearly as concentration of $2-HP{\beta}CD$ without PG INCREASED$(R^2=0.993)$. MT solubility in the mixtures of pg and $2-HP{\beta}CD$ also increased linearly but was less than the sum of its solubility in $2-HP{\beta}CD$ and PG individually. The MT solubility was low in water, simulated gastric or intestinal fluid but the highest in the mixture of PG(40v/v%) and $2-HP{\beta}CD$ (30w/v%) although efficiency of MT solubilization in $2-HP{\beta}CD$ decreased as the concentration of PG increased. MT was degraded in a fashion of the first order kinetics $(r^2>0.90)$. MT was unstable in strong acidic solution (HCl-NaCl buffer, pH 1.4) but relatively stable in other pH values of 4-10 at $70^{\circ}C$. In HCl-NaCl buffer, MT in 10% PG was more quickly degraded and then slowed dpwm at a higher concentration. However, the degradation rate constant of MT in 2-HP.betha.CD was not changed significantly when compared to the water. The current studies can be applied to the dosage formulations for the purpose of enhancing percutaneous absorption or bioavailability of MT.

• Korean Journal of Materials Research
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• v.31 no.3
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• pp.156-161
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• 2021

Cr-Si based alloys are not only excellent in corrosion resistance at high temperatures, but also have good wear resistance due to the formation of Cr3Si phase, therefore they are promising as metallic coating materials. Aluminum is often added to Cr-Si alloys to improve the oxidation resistance through which stable alumina surface film is formed. On the other hand, due to the addition of aluminum, various Al-containing phases may be formed and may negatively affect the heat resistance of the Cr-Si-Al alloys, so detailed investigation is required. In this study, two Cr-Si-Al alloys (high-Si & high-Al) were prepared in the form of cast ingots through a vacuum arc melting process and the microstructural changes after high temperature heating process were investigated. In the case of the cast high-Si alloy, a considerable amount of Cr3Si phase was formed, and its hardness was significantly higher than that of the cast high-Al alloy. Also, Al-rich phases (with the high Al/Cr ratio) were not found much compared to the high-Al alloy. Meanwhile, it was observed that the amount of the Al-rich phases reduced by the annealing heat treatment for both alloys. In the case of the high temperature heating at 1,400 ℃, no significant microstructural change was observed in the high Si alloy, but a little more coarse and segregated AlCr phases were found in the high Al alloy compared to the cast state.

• Nuclear Engineering and Technology
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• v.54 no.8
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• pp.3051-3058
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• 2022

In the present work, untreated Iraqi sand with grain sizes varied between 100 and 200 ㎛ was used to produce a colored glass sample that has shielding features against the low gamma-ray energy. Therefore, a weight of 70-60 wt % sand was mixed with 9-14 wt% B₂O₃, 8-10 wt% Na₂O, 4-6 wt% of CaO, 3-6 wt% Al₂O₃, in addition to 0.3% of Co₂O₃. After melting and annealing the glass sample, the X-ray diffraction spectrometry was applied to affirm the amorphous phase of the fabricated glass samples. Moreover, the X-ray dispersive energy spectrometry was used to measure the chemical composition, and the MH-300A densimeter was applied to measure the fabricated sample's density. The Makishima-Makinzie model was applied to predict the mechanical properties of the fabricated glass. Besides, the Monte Carlo simulation was used to estimate the fabricated glass sample's radiation shielding capacity in the low-energy region between 22.1 and 160.6 keV. Therefore, the simulated linear attenuation coefficient changed between 10.725 and 0.484 cm^-1, raising the gamma-ray energy between 22.1 and 160.6 keV. Also, other shielding parameters such as a half-value layer, pure lead equivalent thickness, and buildup factors were calculated.

• Nuclear Engineering and Technology
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• v.44 no.3
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• pp.237-248
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• 2012

Corium behavior in the lower plenum of the reactor vessel during a severe accident is very important, as this affects a failure mechanism of the lower head vessel and a thermal load to the outer reactor vessel under the IVR-ERVC (In-Vessel corium Retention through External Reactor Vessel Cooling) condition. This paper discusses the state of the art and technical issues on corium behavior in the lower plenum, such as initial corium pool formation characteristics and its transient behavior, natural convection heat transfer in various geometries, natural convection heat transfer with a phase change of melting and solidification, and corium interaction with a lower head vessel including penetrations of the ICI (In-Core Instrumentation) nozzle are discussed. It is recommended that more detailed analysis and experiments are necessary to solve the uncertainties of corium behavior in the lower plenum of the reactor vessel.

• Bulletin of the Korean Chemical Society
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• v.33 no.9
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• pp.2949-2954
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• 2012

Nano ZnO with an average size of 8 nm was prepared by thermal decomposition of zinc oxalate at $450^{\circ}C$. A series of based composite polymer electrolyte PEO-$LiClO_4$ and nano ZnO as a filler have been synthesized using solution cast technique, with varying the filler ratio systematically. XRD, DSC and FTIR studies have been conducted to investigate the structure and interaction of different groups in the composite polymer electrolyte. Effect of nano ZnO ceramic filler concentration on the structure of composites and their electrical properties (DC-conductivity, AC-conductivity, dielectric constant, dielectric loss and impedance) at different frequencies and temperatures was studied. Melting temperature ($T_m$) of PEO decreased with the addition of both $LiClO_4$ salt and nano ZnO filler due to increasing the amorphous state of polymer. All composite samples showed an ionic conductivity. The maximum room temperature ionic conductivity is found for $(ZnO)_{0.5}(PEO)_{12}(LiClO_4)$ composite sample. All the results are correlated and discussed.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.29A no.11
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• pp.106-112
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• 1992

In this paper, we analyze the structure characteristics of $As_{40}Se_{50-x}S_{x}Ge_{10}$ system bulk and thin films. As the results of XRD patterns, it identified amorphous state. In order to find the glass transition temperature($T_g$), crystallization($T_c$) and melting point ($T_m$)of bulk sample, it ascertained that TS1gT is 238$^{\circ}C$ in $As_{40}Se_{15}S_{35}Ge_{10}$, and 231$^{\circ}C$ in $As_{40}Se_{25}S_{25}Ge_{10}$ & $As_{40}Se_{50}Ge_{10}$ following the thernal analysis by DSC, DTA, & TGA method. Also it was confirmed the phase seperation of continuous phase and dispertion phase by the optical texture of polarizing microscope and $T_g$ near 20$0^{\circ}C$ in thin film. Therefore, it was found that it occurs the phase seperation of Ge-rich dontinuous phase and Se-rich dispersion phase following the EDS analysis of thin film and the surface SEM photograph.

• Proceedings of the KIEE Conference
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• 1991.11a
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• pp.269-273
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• 1991

High Tc oxide superconductor with a Tc above 100 K has been successfully prepared by solid state reaction method in added-Pb BiSrCaCuO system. As compared with 123 compound, the formation reaction of the high Tc requires long time heat treatment. It is due to the transformation from the low Tc phase to high Tc phase. The sintering just below the melting point of the calcined powder mixture is effective on the formation of the high Tc phase in BiSrCaCuO system to be added with Pb. The growth of the high Tc superconducting phase has a thin plate shape, which is characterized by the c parameter of 37${\AA}$. The formation kinetics is also investigated in the samples with different Bi/Pb ratio and the 30% Pb addition is most preferable for the formation of the high Tc phase. The formation of the high Tc phases is delayed by the excessive addition of Pb. The lattice parameter(c) of the unit cell(both the low and high Tc phases) is increased with increase of Pb.