• Journal of the Korean Chemical Society
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• v.26 no.3
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• pp.188-193
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• 1982

Four new thermotropic copolyesters were prepared and their liquid crystal properties were investigated by differential scanning calorimetry and on a hot-stage of a polarizing microscope. Three copolyesters had same mesogenic unit, triad aromatic ester structure, interconnected through a random combination of either odd-even, or odd-odd, or even-even number of methylene groups in the polymethylene flexible spacers. Another random copolyester consisted of mesogenic units of 1 : 1 mixture of central methyl-and bromohydroquinone moieties with two flanking p-oxybenzoate units connected by decamethylene spacer. All of the polyesters formed nematic liquid crystal phase upon melting. The transitions for melting and nematic ${\to}$ isotropic transformations could be reversibly observed by DSC as well as by microscopic study. The thermodynamic properties for their liquid crystal ${\to}$ isotropic phase transitions were discussed in relation to their chemical structures.

• Journal of Powder Materials
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• v.25 no.4
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• pp.340-345
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• 2018

Additive manufacturing by electron beam melting is an affordable process for fabricating near net shaped parts of titanium and its alloys. 3D additive-manufactured parts have various kinds of voids, lack of fusion, etc., and they may affect crack initiation and propagation. Post process is necessary to eliminate or minimize these defects. Hot isostatic pressing (HIP) is the main method, which is expensive. The objective of this paper is to achieve an optimum and simple post heat treatment process without the HIP process. Various post heat treatments are conducted for the 3D-printed Ti-6Al-4V specimen below and above the beta transus temperature ($996^{\circ}C$). The as-fabricated EBM Ti-6Al-4V alloy has an ${\alpha}^{\prime}$-martensite structure and transforms into the ${\alpha}+{\beta}$ duplex phase during the post heat treatment. The fatigue strength of the as-fabricated specimen is 400 MPa. The post heat treatment at $1000^{\circ}C/30min/AC$ increases the fatigue strength to 420 MPa. By post heat treatment, the interior pore size and the pore volume fraction are reduced and this can increase the fatigue limit.

• Textile Coloration and Finishing
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• v.35 no.3
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• pp.159-168
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• 2023

Polyolefin elastomer (POE) is widely used in a variety of applications, particularly in the manufacture of composites, due to its excellent mechanical properties, chemical resistance, and flexibility. However, POE has a high processing temperature, which causes damage to the fiber during the manufacturing process when impregnating the fiber. Therefore, ethylene vinylacetate (EVA), which has a low melting point and excellent adhesion properties, is blended with POE to reduce the processing temperature, and POE-g-MAH (Polyolefin elastomer-grafted-maleic anhydride) is used as a compatibilizer to further improve the POE/EVA blend properties. The compatibility of POE/EVA blends is observed by SEM, and the interaction between each polymer is confirmed by DSC and FT-IR. In addition, the effect of adding the compatibilizer is analyzed through mechanical properties such as tensile strength and elongation. The optimal content of compatibilizer for POE/EVA blends considering physical properties and moldability is sought, and 20 phr is determined to be the most appropriate.

• Korean Journal of Food Science and Technology
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• v.23 no.3
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• pp.341-348
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• 1991

Physicochemical properties and gelatinization patterns of defatted and lipid-reintroduced moist (Hwangmi) and dry (Suwon 147) type sweet potato starches were investigated. Starch granules of sweet potato were polygonal and round, and the sizes of starch granules ranged $5{\sim}13\;{\mu}m$. All starches showed Ca type in X-ray diffraction but relative crystallinity was decreased by defatting and reintroduction. The amylose content of defatted starches increased, but that of lipid-reintroduced starches decreased. The swelling power and solubility at each temperature increased by defatting, but decreased by reintroduction. Transmittance of Hwangmi and Suwon 147 showed a rapid increase at $60,\;65^{\circ}C$, respectively. The initial pasting temperature by amylograph of Hwangmi and Suwon 147 were $67.5^{\circ}C\;and\;72.7^{\circ}C$, respectively. The peak viscosity and the height at $50^{\circ}C$ on amylogram of Hwangmi were lower than those of Suwon 147. Hot paste viscosity and setback decreased by defatting but setbak and consistency drastically increased by reintroduction. The peak temperature for gelatinization by the DSC was $65.7^{\circ}C$ for Hwangmi and $68.5^{\circ}C$ for Suwon 147. The gelatinization temperature and enthalpy of the DSC decreased and amylose-lipid melting peak was lost by defatting. The gelatinization temperature and enthalpy decreased by reintroduction.

• Journal of Radiation Protection and Research
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• v.4 no.1
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• pp.14-20
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• 1979

For accurate and easily shielding irregular shaped organ, its minimized penumbra region and a low melting point alloy 'Lead Y' and synchronizing instrument have been developed. The 'Lead Y' is the quaternary eutectic alloy and it is composed of Lead 30.0% Tin 11.5% Bismuth 48 5% Cadmium 10.0% The density of its at $22^{\circ}C$ is $9.8g/cm^3$ and the melting temperature has $40^{\circ}C\;to\;68^{\circ}C$. The thickness of 'Lead Y' for perfect shielding of Co-60 gamma ray and LINAC 10MeV x-ray is 6cm and 7cm respectively. The 'Lead Y' shielding block is casted directly on the styrofoam from which is cut with hot wire of synchronizer device. The special features and advantages of the Lead Y shielding block could be summarized as follows; 1. The shielding block for radiotherapy is rapidly processed only with boiling water and styrofoam. 2. It is not injure one's health and not danger of a fire, because of not generating of any metals vapor and evil smelling. 3. It is very effective to minimize secondary penumbra for the protection of healthy tissue from unnecessary ionizing radiation regardless of the magnification source to skin distance. 4. The HVL of the Lead Y is 1.2cm for Co-60 gamma ray and it's shielding effect is almost same as the pure lead block. 5. The hardness of Lead Y is 1.5 times higher than lead block. 6. It's reavailability is higher than lead block and then one block of Lead Y is reavailable about 30 to 40 times. 7. It is usefull for shielding of x-ray, gamma ray, beta-ray, electron and neutron radiation. 8. The materials for Lead Y are easy to acquire with reasonable price and tractable.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.29 no.5
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• pp.681-688
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• 1996

To investigate the effort of drying methods on the physicochemical properties of agar, gel strength, viscosity, melting and setting point, and phase transition by differential scanning calorimetery (DSC) during its heating were determined. In addition the structural differences of agar powder by scanning electron microscope (SEM) was examined. The most shortest onset temperature of gel strength increase was extruding method among any other methods. Viscosity of agar with hot air method, 400.00 cps at $45^{\circ}C$, was markedly increased, but with spraying and extruding ones were little change. The melting and setting point, and the temperature for maximum endothermic and enthalpy for agar with extruding one, $80.01^{\circ}C,\;36.05^{\circ}C\;and\;61.72^{\circ}C,\;0.73\;cal/g$, respectively, were lowest among the drying ones. But in the case of reheating after gelling, there were little change in all methods. Observing the surface structure of agar with SEM, extruding method showed the most unstable with absorptive property.

• Korean Journal of Food Science and Technology
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• v.16 no.1
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• pp.78-82
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• 1984

Effects of various drying conditions of agar gel on the physico-chemical properties of dried agar were investigated. For drying of the agar gel$(1.0{\times}1.0{\times}34.0cm)$ by means of sun drying, simple solar drying, hot-air drying ($30^{\circ}C$, control, natural convection), hot-air drying ($30^{\circ}C$, pretreatment, natural convection) and freeze drying, it took 96, 75, 67, 50 and 21 hours, respectively. The gel strengths of dried agar gel prepared by sun drying, solar drying, freeze drying and spray drying were320, 370, 270 and $360g/cm^2$, respectively and that of hot air-dried agar gel was influenced by drying temperature, pretreatment an mode of heat transfer. The gel strength, the gelation temperature and other quality index of spray-dried agar were not inferior to those of sun-dried agar, but it was not expected to be economical because of it recovery rate. In case of hot air drying, the gel strength value of agar increased as the drying rate increased. No significant differences among various products were noted in the gelation temperature, the melting temperature, the ash and $SO_3$ content.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.15 no.2
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• pp.75-78
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• 2005

Silicon boride ($SiB_6$) is very promising for use as thermoelectric materials at high temperature because of its high melting point and relatively large Seebeck coefficient. In the present work, spark plasma sintering (SPS) was applied for preparing dense $SiB_6$ ceramics, and their thermoelectric properties were investigated, together with their microstructural evaluation. The SPS process was found to be effective in densifying a $SiB_6$ ceramic, typically 99 % of the theoretical density at low temperature of $1500^{\circ}C$. In comparison with $SiB_6$ specimen prepared by hot-pressing, the SPS-processed specimen exhibited the significantly improved Seebeck coefficient, resulting in the higher power factor.

• Journal of the Korean Ceramic Society
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• v.23 no.1
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• pp.51-59
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• 1986

It was the first time the MgO-C brick was developed for the lining materials in the hot spots in electric are furnace in 1972. MgO-C brick is high registant to thermal and structural spalling. Futhermore for the reason that carbon is hard to react with slag and MgO is high fireproof MgO-C brick shows a high corrosion registance to slag attack compared with conventional basic refractories. Owing to their excellent properties the use of MgO-C refractories are being developed widely in the field of shaped refractories and even in that of monolithic refractories. In this paper the oxidation of carbon the infiltration of slag into the brick texture and effects of additions were investigated. The results obtained were as follows : 1) The use of fused MgO-clinker and high purity carbon as raw materials increased the corosion registance and hot modulus of rupture of MgO-C brick. 2) As the oxidation reaction of the carbon proceeded the slag infiltrated into the brick texture. And then the slag components reacted with the MgO grains and formed low melting point compounds particulary CaO.MgO.$SiO_2$ and 3CaO.MgO.$2SiO_2$ that resulted in the wear of the brick. 3) It is recongnized the Al, Si, $B_3C$ effects on the oxidation registant properties of MgO-C brick by contribu-ting to the decrease of permeability according to the formation of $Al_4C_3$, SiC, $B_2O_3$ and the decrease of open pores relating to the formation of MgO.Al2O3, $SiO_2$, 3MgO.$B_2O_3$ at the decarbonized layer.

• Journal of Sensor Science and Technology
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• v.9 no.2
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• pp.141-145
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• 2000

In order to measure the thickness of the slag layer on the molten metal in the melting vessels for steel making foundaries, we manufactured the slag-thickness measuring system consisting of the probe and its driving system, which is based on the principle of detecting the change in the electrical resistivity. Experimental results show that there is a very wide difference of the electrical resistivity by the order of about $10^3$ between the molten metal and the hot slag and, hence, the air/slag and slag/molten metal interface can be exactly detected with the use of the probe which can be moved toward the melt. Therefore, it can be concluded that the proposed scheme of the slag measurement system in this study is Proven to be excellent in its efficiency and accuracy.