• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.05a
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• pp.254-257
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• 2007

In this study, hydroformability and mechanical properties of pre- and post- heat treated Al6061 tubes at different extrusion type were investigated. For the investigation, as-extruded, full annealed and T6-treated Al 6061 tubes at different extrusion type were prepared. To evaluate the hydroformability, uni-axial tensile test and free bulge test were performed at room temperature and $200^{\circ}C$. Also mechanical properties of hydroformed part at various pre- and post-heat treatments were estimated by tensile test. And the tensile test specimens were obtained from hexagonal prototype hydroformed tube at $200^{\circ}C$. As for the heat treatment, hydroformability of full annealed tube is 25% higher than that of extruded tube. The tensile strength and elongation were more than 330MPa and 12%, respectively, when hydroformed part was post-T6 treated after hydroforming of pre- full annealed tube. However, hydroformed part using T6 pre treated tube represents high strength and low elongation, 8%. Therefore, the T6 treatment after hydroforming for as-extruded tube is cost-effective. Hydroformability of Al6061 tube showed similar value for both extrusion types. But flow stress of seam tube showed $20{\sim}50MPa$ lower value.

• Food Science and Preservation
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• v.12 no.6
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• pp.552-557
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• 2005

Effect of pre- and post-mild heat treatment on quality of fresh-cut potatoes was investigated with the focus on surface color, firmness, phenolics, vitamin C and sensory characteristics. As the pre-heat treatment before cutting of potatoes, dried hot air (DH) and hot water (WH) treatment were conducted at $45^{\circ}C$ for 60 min, respectively. As a post-heat (CH) treatments, potato cubes were dipped into water of $55^{\circ}C$ for 45 seconds after cutting. The potato cubes were packed in 15 cm x 20 cm LDPE pouches $30^{\mu}m$ thick and then stored at $5{\pm}1^{\circ}C$. The respiration rate of fresh-cut potatoes was decreased by mild heat treatment Especially, the rate of cubes treated with DH was decreased by $20\%$ compared to that of the non-heat treated. L value of cubes treated with DH showed higher value than that of others. Firmness and free phenolics had no significant difference between the treatments. The fresh-cut potatoes prepared with non-heat treatment showed higher vitamin C content than that of the heat treated. In sensory visual color, CH treated cubes marked the best quality. Conclusively, mild heat treatment, especially CH treatment, showed positive effect on browning inhibition and quality enhancement of fresh-cut potatoes.

• Journal of the Korean Society for Heat Treatment
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• v.18 no.1
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• pp.24-28
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• 2005

New post plasma nitriding can achieve a high uniformity that have been difficult in DC nitriding and have a high productivity comparable to gas nitriding. However, it has not a enough high nitriding potential for a rapid nitriding, because surface activation or ion etching in the general plasma nitriding cannot be expected. Thus, in this study, the effects of pre-treatments with oxidation and reduction gas have been investigated to improve the nitriding kinetics of post plasma nitriding. An effective pre-treatment consisting of oxidation and reduction resulted in the increase of surface energy of STD 11. This induced the surface hardness and the effective nitriding depth of STD 11. It is thought that the increase of the surface energy and the surface area with pre-treatment promote the nucleation of nitriding layer.

• Journal of the Korean Society for Heat Treatment
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• v.4 no.4
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• pp.24-33
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• 1991

The effects of thermomechanical treatments on microstructure and fatigue properties of 7050 Al alloy were investigated. The precipitation kinetics changed to a faster rate due to cold deformation employed in this special TAHA thermomechanical treatments including pre-aging, plastic deformation and two step final-aging. The G.P. zones in the under-aged condition were cut by dislocations and dissolved during the plastic deformation. During the low cycle fatigue, the T6' condition showed cyclic hardening behavior whereas the TMT5, TMT27 and T76 conditions showed cyclic softening at above 0.7% total strain amplitudes. The ${\Delta}K_{th}$ value of TMT27 was improved more than two times, compared with that of T76 condition. The T6' with small shearable precipitates resulted in the markedly high ${\Delta}K_{th}$ value. This is thought to be resulted from dislocation reversibility and roughness-induced crack closure due to planarity of slip.

• Progress in Superconductivity and Cryogenics
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• v.1 no.1
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• pp.7-14
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• 1999

Wekk oriented $Bi_{2} Sr_{2} CaCu_{2} O_{8}$ suppercondcting thick films were fabricared on copper tape by LiReac-PreCu (liquid reaction between a Cu-free precousor and Cu tape) method. Cu-free precursor power which is composed of $Bi_{2}Sr_{2}Ca_{5}$ was printed on a copper tape by screen printing and was heat-treated. The speciment were partially in a molten state at the heat treatment temperature (85$0^{\circ}C$~87$0^{\circ}C$). The heat heat treatments for the reaction were performed in air or low oxygen pressure in several stages. XRD analyses of the resulting Bi2Sr2CaCu2O8 superconducting tapes show that the $Bi_{2} Sr_{2} CaCu_{2} O_{8}$ phase is dominant and a small amount of $Bi_{2} Sr_{2} Cu_{2} O_{6}$ phase is detected. Both phases are aligned in the c-axis direction.

• Journal of the Korean Society for Precision Engineering
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• v.5 no.4
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• pp.48-58
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• 1988

This study was undertaken to observe the formation behavior of ferro- magnetic phase in Mn-Al-Cu Alloys. The alloy selected for this investigation was 70% Mn-29% Al-1% Cu. This pre-allyed pig was prepared to the cylinderical castings using an Induction furnace after homogenizing at $1100^{\circ}C$ for 2hr, the specimens were cooled by cooling methods. Subwequent isothermal heat treatments were followed at $550^{\circ}C$ for various periods of time at predetermined(1-1000min). The formation behavior of ferromagnetic phase was investigated by measurements of magnetic properties of the specimens at each stage of heat treatment, and optical microscopic esamination and X-Ray diffraction analyses were also employed. By this basic experimental results, the conclusions are as follows 1) In order to obtain much amount of ferromagnetic phase, the optimum average cooling rate was about 7.35-$16.4^{\circ}C$/sec($1100^{\circ}C$-$600^{\circ}C$). 2) We verified the decomposition of {\tau} phase to {\beta} -Mn and {\gamma} , as the specimens were homogenized at $1100^{\circ}C$ for 12hr, then heat-treased at $550^{\circ}C$ for 1-1000min. 3) A condition of optimum heat treatments in Mn-Al-Cu permanent mag-netic alloys showed that after homogenizing at $1100^{\circ}C$ for 2hr, the speciments were cooled in air or furnace(A) and subsequent heat treatments at $550^{\circ}C$ for 1-30min. The maximum magnetic properties were measured as follows: Air cooling; Br=1200(Gause), bHc=100(oe), (BH)max=0.07(MGOe) Furnace cooling(A);Br=950(Gauss), bhe=80(Oe), (BH)max=0.05(MGOe)

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.11
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• pp.1010-1015
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• 2008

In this study, the characteristics of aluminum tube hydroformed products at different extrusion type and heat treatment conditions were investigated. For the investigation, as-extruded, full annealed and T6-treated Al 6061 tubes at different extrusion type were prepared. To evaluate the hydroformability, free bulge test was performed at room temperature to $300^{\circ}C$. Also mechanical properties of hydroformed products at various pre- and post-heat treatments were estimated by hexagonal prototype hydroforming test at $250^{\circ}C$. And the tensile test specimens were obtained from hexagonal prototype hydroformed tube. As a results, hydroformability of full annealed tube is $5{\sim}8%$ higher than that of extruded and T6-treated tube. The tensile strength and elongation of T6-post heat treated indirect extrusion tube were more than 330MPa and 12%, respectively. However, T6 pre treated hydroformed product represents high strength, 330MPa and low elongation, 8%. Therefore, Hydroformability of Al6061 tube showed similar value for both extrusion types. However flow stress of direct tube showed $20{\sim}50MPa$ lower value than indirect tube.

• The Journal of Korean Academy of Prosthodontics
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• v.35 no.1
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• pp.130-143
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• 1997

A heat-pressed technique(IPS-Empress, Ivoclar) has been described to construct single unit crown, inlay/onlay and veneers using a partially pre-cerammed and pre-colored glass-leucite ingot that has the greateast strength by the combination of heat-pressed procedure through the smalldiameter sprue and heat treatment procedure. The purpose of this study was to evaluate the flexure strength of a heat-pressed ceramic material(IPS-Empress) without simulated firing treatments according to pontic designs. Two groups of 9 disks(1.4mm thick, 14mm in diameter) each using two types of sprues with different diameters($({\Phi}2.8\;,{\Phi}1.8)$) and numbers were prepared. The specimens were mounted in the testing jig. The flexural strengths were determined, by means of the bi-axial bending test, by loading the center of disk to failure using a universal testing machine(Zwick 145141, Zwick, Germany) at a cross-head speed of 1.0 mm/min. The means flexural strength value of one group using a sprue with ${\Phi}2.8$ was $140.4{\pm}8.0Mpa$. That of the other group using two sprues with ${\Phi}1.8$ was $151.8{\pm}10.3Mpa$. After analysis, results showed that there was a statistical difference between groups(t=2.33m p<0.05). No clnical implications were drawn from these data because of absence of simulated firing treatment.

• Food Science and Preservation
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• v.15 no.5
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• pp.731-735
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• 2008

The coliform group, Salmonella typhimurium and Staphylococcus were analyzed for eliminating of microorganism spore which could be embeded in honey and eradication of studied for heat resistance of thermoacidophilic bacteria was studied for marketing of honey after producing honey drink. The method for analyzing of heat resistance thermoacidophilic bacteria was membrane-seperated cell culture with $0.45\;{\mu}m$ micro-filter and vacuum aspirator. The results of bacteria, coliform group, Salmonella typhimurium and Staphylococcus was negative, but normal method such as sterilization with electrolyzed water, normal micro-filter, high-temperature heating and microwave did not have effect on heat resistance thermoacidophilic bacteria. Also, absolute type micro-filter of $0.45\;{\mu}m$ and $0.8\;{\mu}m$ microfilteration showed higher effect on heat resistance thermoacidophilic bacteria than micro-filter of normal type, showing negative results at all treatments.

• Food Science of Animal Resources
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• v.31 no.2
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• pp.158-165
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• 2011

A sensitive reverse transcriptase-PCR (RT-PCR) method to detect viable Escherichia coli O157:H7 in milk was established. The primer sets were designed based on the nucleotide sequences of the rfbE (per) and wbdN genes in the O157 antigen gene cluster of E. coli O157:H7. RT-PCR using five different primer sets yielded DNA with sizes of 655, 518, 450, and 149-bp, respectively. All five of the E. coli O157:H7 strains were detected by RT-PCR, but 11 other bacterial species were not. The sensitivity of RT-PCR was improved by adding yeast tRNA as a carrier to the crude RNA extract. The RT-PCR amplifying the 149-bp DNA fragment was the most sensitive for detecting E. coli O157:H7 and the most refractory to the bactericidal treatments. Heat treatment at $65^{\circ}C$ for 30 min was the least inhibitory of all bactericidal treatments. Treatment with RNase A strongly inhibited the RT-PCR of heated milk but not unheated milk. This study described RT-PCR methods that are specific and sensitive with a detection limit of 10 E. coli O157:H7 cells, and showed that pre-treating milk samples with RNase A improved the specificity to detect viable bacteria by RT-PCR.