• 폴리머
• /
• 제27권5호
• /
• pp.429-435
• /
• 2003

양이온η$^3$-알릴 팔라듐 촉매를 사용하여 환상형 올레핀 단량체인 노보넨 (NB)과 5-비닐-2-노보넨(VNB)을 조성별로 비닐 부가 공중합하였다. 공중합체는 고수율과 고분자량 (M$_{w}$ > 760000)으로 얻을 수 있었다. VNB 함량이 많아질수록 공중합체의 분자량과 수득율은 감소하였으며, 첨가한 공단량체의 양과 공중합한 후 함유된 단량체의 양이 비례함을 FT-IR 분광분석으로 확인하였다. $^1$H-NMR 분석 결과 VNB는 exo, endo 이성체 모두 중합에 참여하는 것을 알 수 있었다. NB-VNB 공중합체의 분해 개시 온도는 약 300 $^{\circ}C$이었고, 열안정성은 VNB 함량과 관계없이 유사한 거동을 나타내었다. 합성된 NB-VNB 공중합체의 곁사슬 비닐기는 m-CPBA를 이용하여 에폭시화 하였고, 또한 9-BBN을 이용하여 수산화기를 도입하였다. 조성별 공중합체에 각각의 치환기가 도입된 것은 FT-IR, $^1$H-NMR 분석으로 확인하였다..

• Corrosion Science and Technology
• /
• 제16권6호
• /
• pp.317-327
• /
• 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.

• 한국표면공학회지
• /
• 제37권2호
• /
• pp.128-136
• /
• 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.

• 한국세라믹학회지
• /
• 제34권12호
• /
• pp.1221-1226
• /
• 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.

• 한국세라믹학회지
• /
• 제16권1호
• /
• pp.26-30
• /
• 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.

• 한국세라믹학회지
• /
• 제25권4호
• /
• pp.335-340
• /
• 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.

• 한국세라믹학회지
• /
• 제30권9호
• /
• pp.761-767
• /
• 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.

• 한국재료학회지
• /
• 제26권11호
• /
• pp.590-597
• /
• 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.

• 소성∙가공
• /
• 제8권3호
• /
• pp.233-233
• /
• 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.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2008년도 하계학술대회 논문집 Vol.9
• /
• pp.342-342
• /
• 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.