• 한국재료학회지
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• 제21권7호
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• pp.357-363
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• 2011

In this paper, high temperature oxidation behavior of newly developed alloys, Ti-6Al-4Fe and Ti-6Al-1Fe, is examined. To understand the effect of Fe on the air oxidation behavior of the Ti-Al-Fe alloy system, thermal oxidation tests are carried out at $700^{\circ}C$ and $800^{\circ}C$ for 96 hours. Ti-6Al-4V alloy is also prepared and tested under the same conditions for comparison with the developed alloys. The oxidation resistance of the Ti-Al-Fe alloy system is superior to that of Ti-6Al-4V alloy. Ti-6Al-4V shows the worst oxidation resistance for all test conditions. This is not a result of the addition of Fe, but rather it is due to the elimination of V, which has deleterious effects on high temperature oxidation. The oxidation of the Ti-Al-Fe alloy system follows the parabolic rate law. At $700^{\circ}C$, Fe addition does not have a noticeable influence on the amount of weight gain of all specimens. However, at $800^{\circ}C$, Ti-6Al-4Fe alloy shows remarkable degradation compared to Ti-6Al-1Fe and Ti-6Al. It is discovered that the formation of $Al_2O_3$, a diffusion resistance layer, is remarkably hindered by a relative decrease of the ${\alpha}$ volume fraction. This is because Fe addition increases the volume fraction of ${\beta}$ phase within the Ti-6Al-xFe alloy system. Activities of Al, Ti, and Fe with respect to the formation of oxide layers are calculated and analyzed to explore the oxidation mechanism.

• 한국분말재료학회지
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• 제9권6호
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• pp.394-408
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• 2002

Nanostructured high strength metastable Al-, Mg- and Ti-based alloys containing different amorphous, quasicrystalline and nanocrystalline phases are synthesized by non-equilibrium processing techniques. Such alloys can be prepared by quenching from the melt or by powder metallurgy techniques. This paper focuses on one hand on mechanically alloyed and ball milled powders containing different volume fractions of amorphous or nano-(quasi)crystalline phases, consolidated bulk specimens and, on the other hand. on cast specimens containing different constituent phases with different length-scale. As one example. $Mg_{55}Y_{15}Cu_{30}$- based metallic glass matrix composites are produced by mechanical alloying of elemental powder mixtures containing up to 30 vol.% $Y_2O_3$ particles. The comparison with the particle-free metallic glass reveals that the nanosized second phase oxide particles do not significantly affect the glass-forming ability upon mechanical alloying despite some limited particle dissolution. A supercooled liquid region with an extension of about 50 K can be maintained in the presence of the oxides. The distinct viscosity decrease in the supercooled liquid regime allows to consolidate the powders into bulk samples by uniaxial hot pressing. The $Y_2O_3$ additions increase the mechanical strength of the composites compared to the $Mg_{55}Y_{15}Cu_{30}$ metallic glass. The second example deals with Al-Mn-Ce and Al-Cu-Fe composites with quasicrystalline particles as reinforcements, which are prepared by quenching from the melt and by powder metallurgy. $Al_{98-x}Mn_xCe_2$ (x =5,6,7) melt-spun ribbons containing a major quasicrystalline phase coexisting with an Al-matrix on a nanometer scale are pulverized by ball milling. The powders are consolidated by hot extrusion. Grain growth during consolidation causes the formation of a micrometer-scale microstructure. Mechanical alloying of $Al_{63}Cu_{25}Fe_{12}$ leads to single-phase quasicrystalline powders. which are blended with different volume fractions of pure Al-powder and hot extruded forming $Al_{100-x}$$(Al_{0.63}Cu_{0.25}Fe_{0.12})_x$ (x = 40,50,60,80) micrometer-scale composites. Compression test data reveal a high yield strength of ${\sigma}_y{\geq}$700 MPa and a ductility of ${\varepsilon}_{pl}{\geq}$5% for than the Al-Mn-Ce bulk samples. The strength level of the Al-Cu-Fe alloys is ${\sigma}_y{\leq}$550 MPa significantly lower. By the addition of different amounts of aluminum, the mechanical properties can be tuned to a wide range. Finally, a bulk metallic glass-forming Ti-Cu-Ni-Sn alloy with in situ formed composite microstructure prepared by both centrifugal and injection casting presents more than 6% plastic strain under compressive stress at room temperature. The in situ formed composite contains dendritic hcp Ti solid solution precipitates and a few $Ti_3Sn,\;{\beta}$-(Cu, Sn) grains dispersed in a glassy matrix. The composite micro- structure can avoid the development of the highly localized shear bands typical for the room temperature defor-mation of monolithic glasses. Instead, widely developed shear bands with evident protuberance are observed. resulting in significant yielding and homogeneous plastic deformation over the entire sample.

• 한국재료학회지
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• 제15권3호
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• pp.177-182
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• 2005

Large amounts of the waste SiC sludge containing small amounts of Si and organic lubricant were produced during the wire cutting process of the single silicon crystal ingots. The waste SiC sludge was purified by the washing process and the purified SiC powders were used to fabricate continuously porous $SiC-Si_3N_4$ composites using a fibrous monolithic process, in which carbon, $6wt\%\;Y_2O_3-2\;wt\%\;A1_2O_3$ and ethylene vinyl acetate were added as a pore-forming agent, sintering additives, and binder, respectively. In the burning-out process, carbon was fully removed and continuously porous $SiC-Si_3N_4$ composites were successfully fabricated. The green bodies containing SiC, Si particles and sintering additives were nitrided at $1410^{\circ}C$ in a flowing $N_2+10\%\;H_2$ gas mixture. Continuously porous composites were combined with SiC, ${\alpha}Si_3N_4,\;\beta-Si_3N_4$ and a few $\%$ of Fe phases. The pore size of the 2nd and the 3rd passed $SiC-Si_3N_4$ composites was $260\;{\mu}m$ and $35\;{\mu}m$ in diameter, respectively.

• Preventive Nutrition and Food Science
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• 제11권2호
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• pp.100-104
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• 2006

The in vitro antimicrobial and antioxidant activities of the essential oil and methanol extracts of Ledum palustre L. were investigated. Using GC-MS analysis, we identified 37 compounds in the essential oil, constituting 87.58% of the total oil. There are several monoterpenes, of which sabinene is the major compound ($16{\sim}17%$). There are several oxygenated monoterpenes of which terpinen-4-ol(7.6%) and myrtenal (3.5%) are the main constituents. $\beta$-Selinene, a-selinene, $\gamma$-elemene, a-caryophyllene are the main sesquiterpenes ($2{\sim}6%$ range). The oil strongly reduced the diphenylpicrylhydrazyl radical ($IC_{50}=1.56{\mu}g/mL$) formation and exhibited a hydroxyl radical scavenging effect in the $Fe^{3+}-EDTA-H_2O_2$ deoxyribose system ($IC_{50}=2.7{\mu}g/mL$), and also inhibited the nonenzymatic lipid peroxidation of rat liver homogenate ($IC_{50}=13.5{\mu}g/mL$). The polar phase of the extract showed antioxidant activity. The oil showed antimicrobial activity against Streptococcus pneumoniae, Clostridium perfringens, Candida albicans, Mycobacterium smegmatis, Acinetobacter lwoffii and Candida krusei while the water-insoluble parts of the methanolic extracts exhibited slight or no activity. This study confirms that the essential oil of Ledum palustre L. possesses antioxidant and low antimicrobial properties in vitro.

• 자원환경지질
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• 제30권1호
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• pp.35-49
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• 1997

The coal formation of the Deokpyeong area are interbedded along metapelites of the Ogcheon Supergroup, which are composed mainly of graphite, quartz, muscovite and associated with small amounts of biotite, chlorite, pyrite and barite. The ratios of $SiO_2/Al_2O_3$, $Al_2O_3/Na_2O$ and $K_2O/Na_2O$ of the coaly metapelite are variable and wide range from 1.80 to 10.21, from 27.8 to 388.8 and from 7.6 to 61.8, respectively. These coal formation were deposited in basin of marine environments, and the REE of these rocks are not influenced with metamorphism and hydrothermal alterations on the basis of $Al_2O_3$ versus La, La against Ce, the ratios of La/Ce (0.19 to 0.99) and Th/U (0.02 to 4.75). These rocks also show much variation in $La_N/Yb_N$ (1.19 to 22.89), Th/Yb (0.14 to 21.43) and La/Th (0.44 to 13.67), and their origin is explained by derivation from a mixture of sedimentary and igneous rocks. The wide range in trace and REE element characteristics as Co/Th (0.12 to 2.78), La/Sc (0.33 to 10.18), Sc/Th (0.57 to 5.73), V/Ni (8 to 2347), Cr/V (0.02 to 0.67) and Ni/Co (1.56 to 32.95) of these coaly metapelites argues for inefficient mixing of the various source lithologies during sedimentation. Deep to pale green barium-vanadium muscovites (vanadium-oellacherite) have been found in this coal formations. Modes of occurrence and grain size of muscovite are heterogeneous, but most of the barium and vanadium-bearing muscovites occur along the boundaries between graphite and quartz grains, ranging from 200 to $350{\mu}m$ in length and from 40 to $60{\mu}m$ in width. Results of X-ray diffraction data of the minerals characterized to be monoclinic system with $a=5.249{\AA}$, $b=8.939{\AA}$, $c=20.924{\AA}$ and ${\beta}=95.894^{\circ}$. Representative chemical formula of the muscovite was $(Na_{0.09}K_{1.44}Ba_{0.46})(Al_{2.75}Ti_{0.07}V_{0.56}Fe_{0.08}Mg_{0.50})(Si_{6.12}Al_{1.88})O_{22}$. The V possibly substitute octahedral Al, and the Ba is coupled substitution of $K^+Si^{4+}=Ba^{2+}Na^+Ca^{2+}$, which compositional ranges of V and Ba are from 0.42 to 0.69 and from 0.34 to 0.56 based on $O_{22}$, respectively. Formation mechanism of the barium-vanadium muscovites in the coaly metapelite is shown that the formed by high pressure and temperature from regional metamorphism origanated during diagenesis at the interface between a basinal brine and organic matter.

• 한국문화재보존과학회:학술대회논문집
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• 한국문화재보존과학회 2002년도 제15회 발표논문집
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• pp.45-52
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• 2002

본 연구에서는 KaOH, $K_2CO_3$, Sodium, 그리고 1차 이온수 용액의 $Cl^-$ 이온 추출량과 부식생성물의 생성순위, 부식물 생성, 그리고 부식물 제거에 관하여 관찰하였으며 이 연구로 아래와 같은 결과를 얻었다. $Cl^-$ 이온 추출량에 대한 실험 결과 NaOH은 탈염 초기에는 Cl- 이온을 잘 추출시켰으나 탈염 횟수가 증가하면서 $Cl^-$ 이온의 추출량이 급감하였다. 또한 유물 중량 변화에도 감소폭이 가장 심하였다. $K_2CO_3$은 NaOH나 1차이온수 용액과 비교해 보면 이 방법은 탈염처리동안 $Cl^-$ 이온을 꾸준히 추출시켜 주었으며 다른 탈염용액에 비해 유물 중량변화가 거의 관찰되지 않았다. Sodium 용액은 $K_2CO_3$ 용액과 마찬가지로 탈염처리 동안 $Cl^-$ 이온을 꾸준히 추출시켰으며 다른 탈염 용액에 비해 $Cl^-$ 이온 추출량이 가장 많았다. 하지만 이 용액은 약품 내에 불순물인 $Cl^-$ 이온을 $3\~5\;ppm$을 기지고 있어 보존처리자가 탈염처리를 할 때 좀 더 신중하게 생각해야 할 것 같다. 1차 이온수 용액은 부식인자가 $Cl^-$이온을 완전하게 제거해주지는 못하였지만, pH가 $7.5\~7.9$로 다른 탈염 용액에 비해서 전위차가 낮으며, 별도로 탈알칼리 처리를 하지 않아도 되기 때문에 유물손상은 극소화할 수가 있다. 따라서 이 용액은 부식이 매우 심한 철제 유물이나 균열이 많은 주조 철편과 같은 유물을 처리할 때 적절한 용액이다. 부식생성물 관찰에서는 출토 철기 유물에 생성된 부식물은 주로 인철광$(\gamma-FeOOH)$, 침철광$(\alpha-FeOOH)$, 적금광$(\beta-FeOOH)$, 그리고 자철광$(Fe_3O_4)$이다. 인위적 부식에서는 전부 인철광의 부식물이 생성되었고 자연적 부식에서는 모두 침철광의 부식물이 생성되었다. 특히 철제 표면에 자연적으로 생성된 공식 녹을 XRD 분석한 결과 적금광으로 동정되었다. 이런 모든 시편들을 각 탈염방법에 따라 탈염처리한 후 XRD와 SEM-EDS으로 분석한 결과 인철광과 침철광은 어떠한 변화도 보이지 않았고, 다만 적금광으로 동정된 시편만이 잔존하지 않았다. 철기 제작별 $Cl^-$ 이온 추출량과 탈염효과에 대한 비교 실험은 이온 크로마토그래피 분석 결과와 마찬가지로 단조 철제유물이 주조 철제보다 $Cl^-$ 이온을 많이 가지고 있었으며, 탈염 처리 후에는 $Cl^-$ 이온은 전혀 발견되지 않았다. 이상의 결과 $K_2CO_3$와 Sodium 용액은 탈염처리에서 가장 적합한 탈염처리 용액으로 알수가 있었으며 특히 어떠한 탈염 용액으로 유물을 처리한다 해도 철제유물에 생성된 부식물은 제거되지 않는다는 것을 알게 되었다. 따라서 보존처리자는 유물 표면의 부식 상태만을 보고 처리하기 보다는 철기제작물로 고려하여 처리하는 것이 필요하다. 또한 금속에 부식을 야기시키는 $Cl^-$ 이온과 부식물을 완전하게 제거하여 탈염처리를 하는 것이 유물 부식을 최대한 지연시킬 수 있는 것이라 생각된다.

• Environmental Analysis Health and Toxicology
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• 제22권4호
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• pp.349-355
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• 2007

장수풍뎅이 유충(Allomyrina dichotoma larva, ADL)은 중국의 전통 약재로서, 특히 항산화 효과가 우수하여 항당료 제재로 사용되고 있다. 본 연구에서는 이러한 ADL의 추출물을 이용하여 헴스터 췌장의 ${\beta}$-세포(HIT-T15)에서 Streptozotocin에 의해 유발된 산화적 손상에 대한 보호효과 및 그 작용기전을 조사하였다. ADL추출물은 처리농도 의존적으로 Streptozotocin에 의해 유발된 지질과산화 및 세포 내 자유산 소종의 양을 억제함으로서 ${\beta}$-세포의 산화적 스트레스에 의한 손상을 보호하였다. 또한 DNA laddering 방법을 사용하여 Streptozotocin에 의해 유발된 DNA 손상을 조사한 결과, ADL추출물 처리농도에 비례하여 Streptozotocin에 의해 유발된 DNA 손상이 감소하였다. 이러한 산화적 손상의 억제능 관련 작용 기전을 조사하기 위해 DPPH free radical 소거능을 실시하였다. 그 결과 ADL추출물 자체가 DPPH 자유 레디컬 소거능이 있음을 확인하였으며, 또한 플라스미드를 이용한 Single-strand break 방법을 통한 DNA 손상 보호능을 측정한 결과도 $Fe^{3+}$ 및 $H_2O_2$에 의해 유발된 DNA 손상이 ADL추출물 처리농도에 비례하여 감소하였다. 이러한 결과들을 종합하여 볼 때, 장수풍뎅이 유충의 추출물들이 자체의 레디컬 소거능 및 산화적 손상에 의한 DNA손상을 억제함으로써, Streptozotocin에 의해 유발된 산화적 손상을 억제할 수 있을 것이라 사료된다.

• Environmental Engineering Research
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• 제10권3호
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• pp.138-143
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• 2005

Laboratory batch experiments were conducted to evaluate the Fenton degradation rates of phenanthrene. Fenton reactions for the degradation of phenanthrene were carried out with aqueous and slurry phase, to investigate the effects of sorption of phenanthrene onto solid phase. Various types of surfactants and electrolyte solutions were used to evaluate the effects on the phenanthrene degradation rates by Fenton's reaction. A maximum 90% removal of phenanthrene was achieved in aqueous phase with 0.9% of $H_2O_2$ and 300 mg/L of $Fe^{2+}$ at pH 3. In aqueous phase reaction, inhibitory effects of synthetic surfactants on the removal of phenanthrene were observed, implying that surfactant molecules acted as strong scavenger of hydroxyl radicals. However, use of $carboxymethyl-{\beta}-cyclodextrin$ (CMCD), natural surfactant, showed a slight enhancement in the degradation of phenanthrene. It was considered that reactive radicals formed at ternary complex were located in close proximity to phenanthrene partitioned into CMCD cavities. It was also show that Fenton degradation of phenanthrene were greatly enhanced by addition of NaCl, indicating that potent radical ion ($OCI^-$) played an important role in the phenanthrene degradation, although chloride ion might be acted as scavenger of radicals at low concentrations. Phenanthrene in slurry phase was resistant to Fenton degradation. It might be due to the fact that free radicals were mostly reacting with dissolved species rather than with sorbed phenanthrene. Even though synthetic surfactants were added to increase the phenanthrene concentration in dissolved phase, low degradation efficiency was obtained because of the scavenging of radicals by surfactants molecules. However, use of CMCD in slurry phase, showed a slight enhancement in the phenanthrene degradation. As an alternative, use of Fenton reaction with CMCD could be considered to increase the degradation rates of phenanthrene desorbed from solid phase.

• Bulletin of the Korean Chemical Society
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• 제30권7호
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• pp.1459-1462
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• 2009

Two new flavone glycosides, giraldiin A and B, together with three known compounds, annulatin, myricetin 3-O-$\alpha$- L-rhamnopyranoside and gallic acid, were isolated from the ethanol extract of the root of Pteroxygonum giraldii Damm. et Diels. The structures of giraldiin A and B are designated as 3'-($\alpha$-L-arabinopyranosyloxy)-4',5,5',7- tetrahydroxy-3-methoxyflavone and 4'-($\beta$-D-glucopyranosyloxy)-5,5',7-trihydroxy-2',3-dimethoxyflavone, respectively, on the basis of detailed spectroscopic analyses. The free radical scavenging activity of giraldiin A was evaluated by decolouring spectrophotometry of pentamethine cyanine dye (Cy5) with $Fe^{2+}-H_2O_2$ Fenton radical generating system. The results indicated the hydroxyl free radical scavenging activity of giraldiin A (E$D_{50}$ = 23.7 nmol/mL) is higher than that of some known antioxidants such as rutin, puerarin, daidzein and 2,6-di-tertbutyl-4-methylphenol.

• 자원환경지질
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• 제30권4호
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• pp.303-312
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• 1997

황해 대륙붕의 준고화된 표층퇴적물에서 자생하는 해록석들을 산출상태와 외부조직에 따라 괴상형, 균열형 및 다공질형으로 분류하였다. 이 해록석은 현세의 해침에 의하여 퇴적된 표층의 사질퇴적물내에 산포상으로 산출되며, 보통 0.1~1 mm 크기의 직경을 갖는다. x-선 회절분석 결과로 계산된, 해록석의 단위포와 크기는 $a=5.242{\AA}$, $b=9.059{\AA}$, $c=10.163{\AA}$, ${\beta}=100.5^{\circ}$, $V=474.53{\AA}^3$ 이고, 화학조성과 단위포의 크기로 계산된 밀도는 $2.60{\pm}0.45gm/cc$ 이다. 이 광물은 가열실험시 $10{\AA}$의 회절선이 증가하는 것으로 볼때 일정한 팽윤층을 갖는 것으로 보인다. $O_{10}(OH)_2$를 기준으로 평균조성을 구하면, 팔면체 자리의 Fe 함량은 1.19~2.06 이고, Al 함량은 0.18~0.76 이다. Fe와 Al은 서로 치환관계를 보이며 다공질형에서 괴상형으로 갈수록 Fe의 함량은 증가하고 Al은 감소한다. Mg의 함량은 0.35~0.54로서 Al이 높을수록 Mg의 양도 증가한다. K의 함량은 0.34~0.71의 범위를 보이며 다공질형에서 괴상형으로 갈수록 증가한다. 괴상형 또는 균열형 해록석은 질서/무질서의 혼합층 운모이며, 다공질형의 해록석은 혼합층 일라이트/스멕타이트로서 7~27%의 팽윤층을 포함한다. 이 광물은 표층 퇴적물이 퇴적된후에 극미립의 퇴적입자를 핵으로, 환원환경하에서 발생하는 퇴적물의 분해 및 생물체 파편과의 반응에 따라 자생한 것으로 추정된다.