• Title/Summary/Keyword: Nb addition

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Vinyl Addition Copolymerization of Norbornene/5-Vinyl-2-norbornene with Cationic $\eta^{3_}$-Allyl Palladium Catalyst and Their Post-Reaction (양이온성 $\eta^{3_}$알릴 팔라듐 촉매를 사용한 노보넨/5-비닐-2-노보넨의 비닐 부가 공중합과 이를 이용한 고분자 후반응)

  • 안재철;박수현;이광희;박기홍
    • Polymer(Korea)
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    • v.27 no.5
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    • pp.429-435
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    • 2003
  • Vinyl addition copolymerizations of norbornene (NB) and 5-vinyl-2-norbomene (VNB) were carried out using a cationic η$^3$-allyl palladium catalyst in the various mole ratio of comonomers. The copolymers could be obtained in good yield (65∼85%) with high weight-average molecular weights (M$_{w}$ > 760,000). Depending on increasing VNB contents, the molecular weight and yield of the copolymers decreased. FT-IR analysis confirmed that actual contents of VNB in polymer were proportional to the feeding content of VNB. From $^1$H-NMR spectroscopy, we found that both exo and endo VNB isomer were copolymerized with NB. Thermal stabilities of NB-VNB copolymers were independent on the VNB content and their initial decomposition temperatures were about 300 C. The NB-VNB copolymers were followed by epoxidation by using m-CPBA and hydroxylation by 9-BBN, respectively, and these post-polymers were characterized by FT-IR spectroscopy and $^1$H-NMR analysis..

Investigation on the Effects of Hydrogen Charging on Oxidation Behavior of Ultrahigh-Strength Automotive Steels (초고강도 자동차용 강의 환원정전류인가에 따른 산화 거동 변화 연구)

  • Ha, Heon-Young;Kim, Hye-Jin;Moon, Joonoh;Lee, Tae-Ho;Jo, Hyo-Haeng;Lee, Chang-Geun;Yoo, Byung-Kil;Yang, Won-Seog
    • Corrosion Science and Technology
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    • v.16 no.6
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    • pp.317-327
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    • 2017
  • The change in the oxidation behavior of three types of B-added ultrahigh strength martensitic steels containing Ti and Nb induced by applying constant cathodic current was investigated. In a 3% NaCl+0.3% $NH_4SCN$ solution, the overall polarization behavior of the three alloys was similar, and degradation of the oxide film was observed in the three alloys after applying constant cathodic current. A significant increase in the anodic current density was observed in the Nb-added alloy, while it was diminished in the Ti-added alloy. Both Ti and Nb alloying decreased the hydrogen overpotential by forming NbC and TiC particles. In addition, the thickest oxide film was formed on the Ti-added alloy, but the addition of Nb decreased the film thickness. Therefore, it was concluded that the remarkable increase in the anodic current density of Nb-added alloy induced by applying constant cathodic current density was attributed to the formation of the thinnest oxide film less protective to hydrogen absorption, and the addition of Ti effectively blocked the hydrogen absorption by forming TiC particles and a relatively thick oxide film.

Effects of Alloying Elements on the Surface Characteristics of Fe-38Al Intermetallic Compounds (Fe-38 at.% Al계 금속간화합물의 표면특성에 미치는 합금원소의 영향)

  • 최한철
    • Journal of the Korean institute of surface engineering
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    • v.37 no.2
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    • pp.128-136
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    • 2004
  • Effects of alloying elements on the surface characteristics of Fe-38Al intermetallic compounds were investigated using potentiostat. The specimens were casted by the vacuum arc melting. The subsequent homogenization and the stabilization led to the homogeneous DO$_3$ structure of the specimen. After the corrosion tests, the surface of the tested specimen was observed by the optical microscopy and scanning electron microscopy(SEM). For Fe-38 at.% Al intermetallic compound, the addition of Cr and Mo proved to be beneficial in decreasing the grain boundary attack by decreasing the active current density. Addition of Band Nb resulted in a higher active current density and also a higher passive current density. These results indicated the role of Cr and Mo in improving the pitting corrosion resistance of Fe-38 at.%Al intermetallic compound. Band Nb addition to Fe-38 at.%Al accelerated the granular corrosion. Fe-38 at.%Al containing Cr and Mo showed remarkably improved pitting corrosion resistance in comparison with Band Nb addition to Fe-38 at. %Al.

Effects of Sintering Atmosphere and Dopant Addition on the Densifcation of $SnO_2$ Ceramics (첨가제와 소결분위기가 $SnO_2$ 요업체의 치밀화에 미치는 영향)

  • 정재일;김봉철;장세홍;김정주
    • Journal of the Korean Ceramic Society
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    • v.34 no.12
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    • pp.1221-1226
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    • 1997
  • The effects of sintering atmosphere and dopant addition on the behavior of densification and grain growth of SnO2 ceramics were investigated with consideration of defect chemistry. CoO and Nb2O5 were chosen as dopants, and oxygen and nitrogen were used for controlling of sintering atmospheres. With the decrease of oxygen partial pressure, densification was depressed due to evaporation of SnO2 ceramics. In the case of SnO2 sintering, the addition of CoO, which produced oxygen vacancy in SnO2 ceramics, led to acceleration of densification and grain growth. On the contrary, when Nb2O5 as a dopant producing Sn vacancy was added to SnO2 ceramics, densification and grain growth were simultaneously retarded. As results, it was conformed that diffusion of oxygen ions was rate determinant in densification and grain growth of SnO2 ceramics.

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The Effects of Flux on the Microstructure and Memory Core Characteristics of Lithium Ferrites (Flux가 Lithium Ferrite의 미세구조 및 메모리코어 특성에 미치는 영향)

  • 임호빈
    • Journal of the Korean Ceramic Society
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    • v.16 no.1
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    • pp.26-30
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    • 1979
  • The microstructures and memory core characteristics of substituted lithium ferrites with addition of $Bi_2O_3$, $V_2O_5$, $Nb_2O_3$, and $P_2O_5$ were investigated. The effects of composite flux on the sintering of the substituted lithium ferrites were also studied. The results show that the addition of $Bi_2O_3$, $V_2O_5$, and $Nb_2O_5$ enhances sintering whereas $Sb_2O_3$ and $P_2O_5$ inhibits it, and that the addition of $Nb_2O_5$ results in uniform grain size while the addition of $Bi_2O_3$ or $V_2O_5$ results in non-uniformity in grain size. When $P_2O_5$ was added with $V_2O_5$ or $Bi_2O_3$, however, it results in uniform grain size and improved memory core properties.

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Effect of V2O5 Addition on the Microstructure and Electrical Properties of Pb(In1/2Nb1/2)O3-PbTiO3 Ceramics (Pb(In1/2Nb1/2)O3-PbTiO3계의 미세구조와 전기적 물성에 미치는 V2O5 첨가의 영향)

  • 박현욱;이응상
    • Journal of the Korean Ceramic Society
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    • v.25 no.4
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    • pp.335-340
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    • 1988
  • The change in microstructure and the electrical properties of Pb(In1/2Nb1/2)O3-PbTiO3 Ceramics caused by V2O5 addition were studied. The results are ; 1. interability was increased because the mass transport through the second phase formed by V2O5 addition increased. 2. ith addition of V2O5, tetragonality and Curie temperature increased. The maximum value of kp was observed when 0.5wt% of V2O5 was added. 3. he second phase formed by V2O5 accelerated the grain growth, and existed in grain boundary. Electrical properties were changed by corelations between tetragonality and the amount of second phase.

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Physical Properties and Out-put Characteristics of Piezoelectric Transformer of $Pb(Mg, Te, Mn, Nb)O_3-PZT$ Ceramics with Addition of $CeO_2$ ($CeO_2$을 첨가한 $Pb(Mg, Te, Mn, Nb)O_3-PZT$계 세라믹스의 물리적 성질과 압전트랜스의 출력특성)

  • 박순태;정수태;이종헌
    • Journal of the Korean Ceramic Society
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    • v.30 no.9
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    • pp.761-767
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    • 1993
  • Electrical and mechanical properties of Pb(Mg, Te, Mn, Nb)O3-PZT ceramics are investigated as a function of CeO2 addition (0 to 0.3wt%), and the output characteristics of piezoelectric transformer are also presented. The grain size decreased and the shapes of particles were more uniform with the addition of CeO2. The coercive electric field(9500V/cm), mechanical quality factor (2500) and bend strength (1065kg/$\textrm{cm}^2$) were improved by addition of CeO2 0.2wt%. After repetition of a number of stress cycles, the degradation of k33 was not found in this sample. The voltage step-up ratio (Vdc/Vrms) of piezoelectric ceramic transformer (half wavevoltage doubler, load resistor 100M.ohm) was about 950 in a linear region, its value was relatively higher than other materials.

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Influence Nb Addition and Transformation Temperature on Impact Properties of Low-Carbon Steels (Nb 첨가에 따른 저탄소강의 충격 특성에 미치는 변태 온도의 영향)

  • Lee, Sang-In;Kang, Jun-Young;Hwang, Byoungchul
    • Korean Journal of Materials Research
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    • v.26 no.11
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    • pp.590-597
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    • 2016
  • In this study, six kinds of low-carbon steel specimens with different ferrite-pearlite microstructures were fabricated by varying the Nb content and the transformation temperature. The microstructural factors of ferrite grain size, pearlite fraction, interlamellar spacing, and cementite thickness were quantitatively measured based on optical and scanning electron micrographs; then, Charpy impact tests were conducted in order to investigate the correlation of the microstructural factors with the impact toughness and the ductile-brittle transition temperature (DBTT). The microstructural analysis results showed that the Nb4 specimens had ferrite grain size smaller than that of the Nb0 specimens due to the pinning effect resulting from the formation of carbonitrides. The pearlite interlamellar spacing and the cementite thickness also decreased as the transformation temperature decreased. The Charpy impact test results indicated that the impact-absorbed energy increased and the ductile-brittle transition temperature decreased with addition of Nb content and decreasing transformation temperature, although all specimens showed ductile-brittle transition behaviour.

Effects of Tungsten Addition on Tensile Properties of a Refractory Nb-l8Si-l0Ti-l0Mo-χW (χ=0, 5, 10 and 15 mot.%) In-situ Composites at 1670 K

  • 김진학;Tatsuo Tabaru;Hisatoshi Hirai
    • Transactions of Materials Processing
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    • v.8 no.3
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    • pp.233-233
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    • 1999
  • To investigate the effect of tungsten addition on mechanical properties, we prepared refractory (62χ)Nb-18Si-l00Mo-l0Ti-χW (χ=0, 5, 10 and 15 mol.%) in-situ composites by the conventional arc-casting technique, and then explored the microstructure, hardness and elastic modulus at ambient temperature and tensile properties at 1670 K. The microstructure consists of relatively fine (Nb, Mo, W, Ti)/sub 5/Si₃, silicide and a Nb solid solution matrix, and the fine eutectic microstructure becomes predominant at a Si content of around 18 mol.%. The hardness of (Nb, Mo, W, Ti(/sub 5/Si₃, silicide in a W-free sample is 1680 GPa, and goes up to 1980 GPa in a W 15 mol.% sample. The hardness, however, of Nb solid solution does not exhibit a remarkable difference when the nominal W content is increased. The elastic modulus shows a similar tendency to the hardness. The optimum tensile properties of the composites investigated are achieved at W 5 mol.% sample, which exhibits a relatively good ultimate strength of 230 MPa and an excellent balance of yield strength of 215 MPa, and an elongation of 3.7%. The SEM fractography generally indicates a ductile fracture in the W-free sample, and a cleavage rupture in W-impregnated ones.

Low Temperature Sintering and Dielectric Properties of $Bi_2(Zn_{1/3}Nb_{2/3})_2O_7$ with (ZBS, BZBS) glasses (붕규산염 유리 첨가에 따른 $Bi_2(Zn_{1/3}Nb_{2/3})_2O_7$의 저온 소결 및 유전 특성)

  • Kim, Kwan-Soo;Park, Jong-Guk;Yoon, Sang-Ok;Kim, Shin;Kim, Yun-Han;Kang, Suk-Young
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2008.06a
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    • pp.342-342
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    • 2008
  • The low temperature sintering and microwave dielectric properties of ceramic/glass composites which were composed of ceramics in the $Bi_2(Zn_{1/3}Nb_{2/3})_2O_7$ and zinc borosilicate glass/bismuth-zinc borosilicate glass were investigated with a view to applying the microwave dielectrics to low temperature co-fired ceramics. The $Bi_2(Zn_{1/3}Nb_{2/3})_2O_7$ addition of 5 wt% ZBS and BZBS glass ensured a successful sintering below $900^{\circ}C$. In addition, pyrochlore phase was observed in the all composition. $Bi_2(Zn_{1/3}Nb_{2/3})_2O_7$ with 5 wt% BZBS glasss demonstrated 70 as the dielectric constant ($\varepsilon_r$), 2,500 GHz as the Q$\times$f value, and -40 ppm/$^{\circ}C$ as TCF.

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