• Journal of the Korean Crystal Growth and Crystal Technology
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• v.18 no.1
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• pp.5-9
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• 2008

Cordierite has a very low thermal expansion coefficient, but has problem that it has a weak mechanical strength and is apt to be attacked by acid such as sulfur for using as a diesel particulate filter support. The physical properties of $ZrTiO_4$ modified with $SiO_2,\;Al_2O_3$, MoOx, $Cr_2O_3\;and\;Nb_2O_5$ were investigated with XRD, SEM, UTM and thermal expansion, etc. in this paper. $ZrTiO_4$ powder was synthesized as a monoclinic structure with processes that starting materials of $TiO_2\;and\;ZrO_2$ were mixed with ball mill and calcined above $1240^{\circ}C$ for 3 hr. Additive modified $ZrTiO_4$ specimens for flexural strength and thermal expansion measurement were obtained by mixing $ZrTiO_4$ powder with additives, pressing and firing at $1300^{\circ}C$ for 3 hr. The porosity of additive modified $ZrTiO_4$ decreased monotonically with increasing additive content by 5 wt% regardless of additive types and saturated for further increase of additive by 10wt. The flexural strength of $Al_2O_3$ (5, 10 wt%) modified $ZrTiO_4$ shows a large increase, but that of other additives modified $ZrTiO_4$ decreased. The thermal expansion coefficient of additive modified $ZrTiO_4$ except $Nb_2O_5$ decreased continuously with the content of additive. In particular, the lowest thermal expansion coefficient of $ZrTiO_4$ was obtained for the additive of $SiO_2$.

• Journal of Powder Materials
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• v.11 no.3
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• pp.193-201
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• 2004

1960년 Au-Si계 합금에서 처음으로 비정질상이 급속 응고법에 의해 보고된 이래/sup 1)/ 지난 40년 간 많은 합금계에서 비정질상이 보고되어졌다. 대표적으로 Fe-, Ni-, Co기 합금 등 많은 합금계에서 비정질상이 보고되었으나, 비정질상의 형성을 위해서는 약 105 K/s이상의 높은 냉각속도를 필요로 하였다. 1980년대 수백 K/s의 낮은 냉각속도 하에서도 비정질상이 형성될 수 있는 다원계 합금(multi-component alloy)이 Mg-Ln-(Ni, Cu, Zn), Ln-Al-TM 합금에서 보고되어 졌으나 많은 관심을 받지 못하다가 1993년 Zr-Ti-Ni-Cu-Be 합금에서 수 ㎝ 크기의 비정질합금 제조가 보고되면서 전 세계적으로 많은 관심을 받게 되었다. Zr-Ti-Ni-Cu-Be계 벌크 비정질 합금이 보고된 후 Zr-(Nb,Pd)-Al-TM, Pd-Cu-Ni-P, Fe-Co-Zr-Mo-W-B, Ti-Zr-Ni-Cu-Sn등 여러 합금계에서 벌크 비정질 합금이 보고되었다. (중략)

• The Journal of the Petrological Society of Korea
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• v.11 no.1
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• pp.17-28
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• 2002

This study has been designed to elucidate the petrography and geochemical characteristics of the Taeheung-ri lava in southeastern Jeju Island. The lava is divided into the alkaline basalt and tholeiitic basalt. More than 4 layers of tholeiitic basalt are overlain by layers of alkaline basalt. Compared with alkaline basalt, tholeiitic basalt has lower contents of $K_2O$, $P_2O_5$, Ba and Ta, but slight higher contents of $SiO_2$ and CaO. The contents of Ba and Rb of all basalts are enriched, but those of Ni and Cr are depleted compared with primitive mantle compositions. All basalts show inclined chondrite-normalized REE patterns with LREE enriched more than HREE and alkaline basalt has relatively higher. The basalts of this study area are plotted in the field of within plate basalt on the tectonomagmatic discrimination diagram. Tholeiitic basalt has higher ratios of Zr/Nb, Y/Nb, and $Al_2O_3/P_2O_5$ than alkaline basalt. Both tholeiitic and alkaline basalt are similar in their K/Ba ratios. The geochemical data suggest that the parental magma of both basalts might be produced by different degrees of partial melting of similar source mantle. The tholeiitic basalt formed by higher degree of partial melting than the alkaline basalt.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.279-279
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• 2007

비휘발성 메모리 Fe-RAM은 빠른 정보처리 속도와 전원공급이 차단되었을 때도 계속 정보를 유지할 수 있는 비휘발성 특징과 더불어 저전압, 저전력 구동의 장점이 있어서, 차세대 메모리로 많은 주목을 받고 있다. FeRAM에 사용되는 강유전체는 주로 Pb(Zr,Ti)$O_3$가 적용되었는데, 최근에는 비납계 강유전체의 연구도 활발히 이루어지고 있다. 이러한 비납계 강유전체 중에서 가장 특성이 우수한 물질은 $(Bi,La)_4Ti_3O_{12}$ (BLT) 이다. 그런데 BLT는 결정 방향에 따른 강한 이방성의 강유전 특성을 나타내기 때문에 BLT 박막을 이용하여 Fe-RAM 소자 등을 제작하기 위해서는 결정의 방향성을 세심하게 제어하는 것이 매우 중요하다. 지금까지 연구된 BLT 박막의 방향성 조절결과를 보면, BLT 박막을 스핀 코팅 법 (spin coating method)으로 증착하고, 핵생성 열처리 단계를 조절하여 무작위 방향성을 갖는 박막을 제조하는 방법이 일반적이었다. 그런데 이러한 스핀 코팅법에서의 핵생성 단계의 제어는 공정 조건 확보가 너무 어려운 단점이 있다. 이러한 어려움을 극복할 수 있는 대안은 스퍼터링 증착법(sputtering deposition method), PLD (pulsed laser deposition)법 등과 같은 PVD (physical vapor deposition) 법의 증착방법을 적용하는 것이다. PVD 법으로 증착하는 경우에는 이미 박막 내에 무수한 결정핵이 존재하기 때문에 핵생성 단계가 필요가 없게 된다. PVD 증착법의 적용을 위해서는 타겟의 제조 및 평가 실험이 선행되어야 한다. 그런데 벌크 BLT 재료의 소결공정 조건과 전기적 특성에 관한 연구 결과는 거의 발표가 되지 않고 있다. 본 실험에서는 $Bi_2O_3,\;TiO_2,\;La_2O_3,\;Nb_2O_5\;and\;Al_2O_3$ 분말들을 이용하여 최적의 조성을 구하기 위하여 $Nb^{+5}$ 와 $Al^{+3}$을 $Ti^{+4}$ 자리에 소량 치환시켜 제조하였다. 혼합된 분말을 하소 후 pellet 형태로 성형하여 소결을 실시하였다. 시편을 1mm 두께로 연마하고, 양면에 silver 전극을 인쇄하여 전기적 특성을 측정하였다. 측정결과 $Ti^{+4}$ 자리에 $Nb^{+5}$를 치환하여 제조한 시편에서 $2P_r{\sim}31\;{\mu}c/cm^2$정도의 매우 우수한 특성을 얻었다.

• Proceedings of the Korean Fiber Society Conference
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• 1996.10a
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• pp.124-130
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• 1996

The hydrocarbons containing more than 10 carbons(0.1% of total volume, C10+), residue of aromatization from aliphatic hydrocarbons, were condensated in the presence of catalyst aluminumchloride and cocatalyst nitrobenzene(NB) to be pitchs with desirable properties. The properties of pitch were affected by the concentration of cocatalyst chosen 20 and 30wt.%. The pitch with 30wt.% NB showed higher carbon yield and lower crystallinity than that with 20wt.% NB. The two pitches were heat treated at 1000C and measured of charge/discharge capacity of the carbon as an anode. The carbon prepared at 20wt.% NB exhibited excellent cyclic stability with a capacity of 218mAh/.g and that at 30wt.% exhibited rather low cyclic stability with higher capacity of 235mAh/g.

• Korean Journal of Materials Research
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• v.21 no.7
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• pp.384-390
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• 2011

Ti-6Al-4V ELI (Extra Low Interstitial) alloy has been widely used as an alternative to bone due to its excellent biocompatibility. However, it still has many problems, including a high elastic modulus and toxicity. Therefore, nontoxic biomaterials with a low elastic modulus should be developed. However, the fabrication of a uniform coating is challenging. Moreover, the coating layer on Ti and Ti alloy substrates can be peeled off after implantation. To overcome these problems, it is necessary to produce bulk Ti and Ti alloy with hydroxyapatite (HA) composites. In this study, Ti, Nb, and Zr powders, which are biocompatible elements, were milled in a mixing machine (24h) and by planetary mechanical ball milling (1h, 4h, and 6h), respectively. Ti-35%Nb-7%Zr and Ti-35%Nb-7%Zr-10%HA composites were fabricated by spark plasma sintering (SPS) at $1000^{\circ}C$ under 70MPa using mixed and milled powders. The effects of HA addition and milling time on the biocompatibility and physical and mechanical properties of the Ti-35%Nb-7%Zr-(10%HA) alloys have been investigated. $Ti_2O$, CaO, $CaTiO_3$, and $Ti_xP_y$ phases were formed by chemical reaction during sintering. Vickers hardness of the sintered composites increases with increased milling time and by the addition of HA. The biocompatibilty of the HA added Ti-Nb-Zr alloys was improved, but the sintering ability was decreased.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.11
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• pp.1139-1145
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• 2011

An automated anastomotic ring-pin system consisting of both the anastomotic ring-pin system and the coupler device has eliminated the drawbacks of the suture method. High density polyethylene (HDPE), a material with outstanding biocompatibility and injection molding capability, was used in the ring. SUS316 stainless steel, Ti-6Al-4Nb, Ti-6Al-4V, and unalloyed titanium were used in FEM simulations of the micropin. The authors categorized the microvascular anastomotic ring micropins into short neck (SN) and long neck (LN) groups in order to evaluate the effect of the micropin's fillet radius and neck length on the von Mises stress. The micropins were further divided into those with and without fillet. On the basis of the fillet radius rate (FRR), which represents the rate of change in the von Mises stress with respect to the availability and shape of the fillet, and the neck length rate (NLR), which represents the rate of change in the von Mises stress with respect to changes in the length of the neck within the fillet shape, it can be concluded that the SN-3 neck design is the most stable.

• Korean Journal of Materials Research
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• v.14 no.4
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• pp.293-299
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• 2004

Transition metal ions doped $TiO_2$ nanostructured powders were prepared with simply heating aqueous $TiOCl_2$ solutions, contained various metal ions (Ni, Al, Fe, Zr, and Nb) of 1.47 mol% added as metal-chlorides, at $100^{\circ}C$ for 4 hrs by homogeneous precipitation process under suppressing conditions of water vaporization. The characterizations for prepared $TiO_2$ powders were carried out to observe doping of metal ions, their concentrations and microstructures using XRD, UV-VIS (DRS), XPS, SEM, TEM and ICP. Also, photo-oxidative abilities were evaluated by decomposition of 4-chlorophenol (4CP) under ultraviolet light irradiations. No secondary oxide phases were formed in all the $VTiO_2$ powders, showing doping with various transition metal ions. When adding ions ($Ni^{2+}$ or$ Al^{3+ }$ and $Zr^{4+}$ ) having valance states or ionic radii greatly different from those of $Ti^{4+}$ , the $TiO_2$ powders of mixed anatase and rutile phases were formed, whereas in the case of additions of $^Fe{3+ }$ and $Nb^{ 5+}$ as well as no addition of metal ion the powders with pure rutile phase alone were formed. Among the prepared $TiO_2$ powders, Ni$^{2+}$ doped $TiO_2$ powders, containing a small amount of anatase phase, showed excellent photo-oxidative ability in 4CP decomposition because of relative decreases in electron-hole recombination and poisoning of $TiO_2$ surface during the photoreaction.n.

• Journal of Powder Materials
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• v.3 no.2
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• pp.97-103
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• 1996

The densification of the compacts of pure Co, Fe+50%.Co and Fe+25% Co sintered under H$_2$ gas or in vacuum was investigated. The effects of AL, Nb, Ti, and V additions on the densification were also studied. The sintered compact of Co was fully-dense when the density of the compact was lower than $Dg^c$. However, above $Dg^{c}$, it was never fully-dense regardless of sintering atmosphere, temperature, and time. The densification of sintered compacts of Fe-50% Co and Fe-25% Co were always incomplete. While the addition of AL made all compacts fully-dense, the addition of Ti was effective for the compacts of Co and Fe-25% Co. V was effective only for the Fe-25% Co. These results tell us that the particle size of Co powder, the amount of Fe, and the amount of additives forming stable oxides play on important role for the complete densification. Therefore it is desirable to reduce or eliminate the equilibrium pressure of H$_{2}$O or CO in isolated pores to obtain a fully-dense sintered compact.

• Progress in Superconductivity
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• v.3 no.2
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• pp.151-158
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• 2002

We developed a useful SQUID magnetometer for biomagnetic applications, magnetoencepha-logram(MEG) and magnetocardiogram(MCG), etc. The SQUIDs are based on Double Relaxation Oscillation SQUID(DROS). DROS consists of two SQUIDs(signal SQUID and reference SQUID) in series, and a relaxation circuit of an inductor and a resistor. Specially we used single reference junction instead of the reference SQUID. The SQUIDs are based on hysteretic $Nb/AlO_{x}$Nb junctions, fabricated by using a simple four level process. Because DROS magnetometer has large flux-to-voltage transfer coefficient, we can use simple flux-locked loop electronics fur SQUID operation. When the DROS magnetometer was operated inside a magnetically shielded room, its average magnetic field noise was about 3 (equation omitted) at 100 Hz. This noise level is low enough to measure biomagnetic fields. In this paper, we describe noise characteristics of DROS magnetometer, depending on the operation condition . .