• Polymer(Korea)
• /
• v.26 no.6
• /
• pp.812-820
• /
• 2002

The positive temperature coefficient (PTC) characteristics of polymer composites were investigated with the nano-sized carbon black particles using solution tasting and melt compounding methods. The polymeric PTC composites should the electrical threshold at 35 wt% for the melt compounding method and 40 wt% for the solution casting method. The ethylene vinylacetate copolymer (EVA) composite showed a gradual increase of resistance as a function of temperature and showed a maximum at the polymer molting point. The resistance of the high-density polythylene (HDPE) composite remains unchanged with temperature but started to Increase sharply near the melting point of HDPE and showed a maximum resistance at the melting point of HDPE. The dispersion of nano-sized carbon black particles was investigated by scanning electron microscopy (SEM) and low resistance after electrical threshold, and both methods exhibited a well dispersed morphology. When the electric current was applied to the PTC composites, the resistance started increasing at the curie temperature and further increased until the trip temperature was roached. Then the resistance remained stable over the trip temperature. The secondary increase started at T$\sub$m/ of matrix polymer and kept increasing up to the trip temperature.

• Proceedings of the Korean Magnestics Society Conference
• /
• 2002.12a
• /
• pp.126-127
• /
• 2002

현재 광 자기 디스크에 대한 연구는 두 층으로 구성된 기록 층들을 이용하여 기록 층에 기록된 매우 작은 마크(0.1 um이하)를 리드아웃 층에서 도메인을 확장하여 재생 시 큰 신호를 얻는 도메인 확장형 광자기디스크(Magnetic AMpligying Magneto-Optical disk)에 대한 연구가 진행되고 있다[1]. 신호 재생시 레이저빔을 디스크에 집속시키면, 리드아웃 층의 스팟의 온도가 큐리 온도(Curie Temperature)까지 올라가게 되며, 이때 기록 층으로부터의 누설 자장에 의해 기록 마크 크기의 도메인이 리드아웃 층에 형성된다. (중략)

• Proceedings of the Korean Magnestics Society Conference
• /
• 1998.10a
• /
• pp.102-103
• /
• 1998

• The Transactions of the Korean Institute of Electrical Engineers C
• /
• v.55 no.8
• /
• pp.392-398
• /
• 2006

The properties of tunable dielectric materials on RF frequency band are important high tunability and low loss for RF variable devices, variable capacitor, phased array antenna and other components application. Various composite of BST(barium strontium titanate) ratio combined with other non-electrical active oxide ceramics have been formulated for such uses. We present the tunable properties and Curie temperature on BST thick films. The grain growth of the weight ratio of $BaTiO_3$ increased. This can be explained by the substitute $Sr^{2+}$ ion for $Ba^{2+}$ ion in the $BaTiO_3$ system. The Curie temperature was shifted to lower temperature with increasing $SrTiO_3$in the $BaTiO_3-SrTiO_3$ system, because of decreasing the lattice constant. Also, the dielectric constant, tunability and K-factor of $(Ba_xSr_{1-x})TiO_3$ at over the Curie temperature decreased, at over the $60^{\circ}C$ fixation, maximum dielectric constant at Curie temperature and hence sharper phase transformation occurred at Curie temperature. The result were interpreted as a process of internal stress relaxation resulting form the increase of $90^{\circ}$ domains induced the BST. As a result, It is concluded that over the Curie temperature, frequency response and DC field effect for the tunable properties of BST thick film are suppressed by the transition broadening. For the application of tunable devices, that the curie temperature was investigated to be increased.

• Journal of the Korean Magnetics Society
• /
• v.2 no.2
• /
• pp.114-118
• /
• 1992

아크로를 이용하여 제작한 NdF $e_{12-x}$ $Ti_{x}$ (1 .leq. x .leq. 2) 합금의 상분석 결과 이들 합금은 ThM $n_{12}$ 구조의 경자성상(1-12상) 과 반강자성의 F $e_{2}$Ti 및 연자성의 .alpha. -Fe 등으로 구성되며, x=1.3 인 NdF $e_{10.7}$ $Ti_{1.3}$ 조성에서 단상에 가까운 ThM $n_{2}$ 구조가 얻어짐이 밝혀졌다. 한편, 합금중의 1-12 상은 50 .mu. m - 100 .mu. m 의 사각주 형태로 생성되며, FeTi은 1-12상의 결정립계에 고립된 입자의 형태로 존재한다. NdF $e_{10.7}$ $Ti_{1.3}$ 합금을 질화처리할 경우 단위포의 체적, 자화, 이방성자장 및 큐리온도가 증가하며, 이합금을 500 .deg. C 에서 15분간 질화처리한 NdF $e_{10.7}$ $Ti_{1.3}$ $N_{x}$ 의 비포화자화, 이방성자장 및 큐리온 도는 각각, .sigma. $_{s}$ =128 A $m^{2}$/kg $H_{A}$=6400 kA/m (80 kOe) 및 Tc=470 .deg. C로 질화처리 전에 비하여 크게 증가한다.크게 증가한다. 증가한다.

• Korean Chemical Engineering Research
• /
• v.43 no.1
• /
• pp.71-75
• /
• 2005

$La_{0.5}Ca_{0.5}MnO_3$ colossal magnetoresistance (CMR) powders and pellets were synthesized by sol-gel process. The structural changes were investigated by FT-IR, CP/MAS $^{13}C$ solid state NMR spectroscopy and XRD. The particle characterization, microstructure of sintered samples, and cation composition of gel powders were studied by FE-SEM/EDS, TEM and ICP-AES. The structure refinement reveals that $La_{0.5}Ca_{0.5}MnO_3$ has orthorhombic, perovskite type unit cell. The magnetic characterizations were identified through measurement of magnetic moment by VSM.

• Electrical & Electronic Materials
• /
• v.5 no.3
• /
• pp.329-336
• /
• 1992

본 논문은 이방성 Sr.페라이트의 자기특성의 개선에 관하여 연구한 것이다. 시편은 SrO.nFe$_{2}$O$_{3}$의 기본조성으로서 비화학양론적 영역인 n=5.9를 택하였다. 그리고 보자력을 증가시키기 위하여 기본첨가제로서 0.7wt% CaCO$_{3}$와 0.3% wt% SiO$_{2}$를 첨가하여 하소시킨 다음 $Na_{2}$SiO$_{3}$의 량을 변화시키면서 복합첨가하였다. 한편, 위의 시료(기본첨가제와 0.5wt% $Na_{2}$SiO$_{3}$)에 Cr$_{2}$O$_{3}$ 및 $Al_{2}$O$_{3}$를 단독 및 복합첨가한 결과, 0.5wt% $Al_{2}$O$_{3}$가 단독첨가되었을 경우, 좋은 자기특성을 나타내었다. 본 연구에서 시행한 복합첨가방식에 의한 Sr.페라이트의 자기특성의 조사를 통하여 등방성의 경우, 기본조성과 기본첨가제와 0.5wt% $Na_{2}$SiO$_{3}$와 0.5wt% $Al_{2}$O$_{3}$조성에서 (BH)$_{max}$=1.15MGOe, 그리고 이방성의 경우, (BH)$_{max}$=3.23MGOe를 얻었으며 시료를 이방성화하므로서 자기특성면에서 등방성인 경우의 2~3배의 개선효과를 얻었다. 그리고 소결온도는 1210.deg.C에서 가장 좋은 특성을 나타내었으며 큐리온도는 등방성의 경우 T$_{c}$=410~420.deg.C에서 이방성의 경우 T$_{c}$=439~445.deg.C로서 약 30.deg.C가 향상되었다.

• Electrical & Electronic Materials
• /
• v.8 no.5
• /
• pp.640-647
• /
• 1995

In this study, the BaTiO$\sub$3/ capacitor add to MnO$\sub$2/ like depressor and shifter were investigated for temperature or voltage compensation by structural and electrical analysis. The relative density of BCTM, generating poly crystall and formation of lattice defect, has a 90[%] over as the CaTiO$\sub$3/ come out to control grain size. The current density of BCTM2 increased non-ohmic in high-electric field but that BCTM3 and BCTM4 had a few changing. The BCTM3 and BCTM4 unformated grain boundary shown temperature compensation properties, so that the dielectric constant was low value. The curie point was near 140[.deg. C] in BCTM1 and BCTM4, but BCTM3 and BCTM4 not shown the curie point. It is found that the charging energy of BCTM4 was changed 6[%] according to rising temperature from room temperature to 417[K]. The formation of BaMnO$\sub$3/ was low dielectric constant to change frequency and temperature.

• Korean Journal of Materials Research
• /
• v.7 no.4
• /
• pp.287-294
• /
• 1997

(NdㆍDy)-(FeㆍCoㆍAIㆍM)-B 합금에 Sn,Mo등을 첨가하여 그에 따른 미세구조와 열적안정성 및 자기적 특성 변화를 조사하였다. Sn과 Mo의 첨가는 (NdㆍDy)-(FeㆍCoㆍAIㆍM)-B 합금리본의 큐리온도를 크게 향상시켰으며 자기특성, 특히 보자력을 1KOe이상 증가시켰다. 그리고 이러한 현저한 보자력 증가는 입계형 defect인 disturbed grain boundary defect에 기인하는 것이라 판단되었다. 또한 Sn과 Mo 첨가원소는 irreversible loss를 각각 4%와 6% 감소시켜 리본자석의 열적안정성을 향상시켰다. 이는 Sn과 Mo의 첨가가 보자력을 크게 증가시켰기 때문이다. 한편 (NdㆍDy)-(FeㆍCoㆍAIㆍM)-B 리본자석들의 열저항온도(heat resistance temperature)는 irreversible loss와 직선관계를 이루었다.

• Proceedings of the KIEE Conference
• /
• 1988.07a
• /
• pp.828-830
• /
• 1988

This paper considered temperature-sensitive characteristics on the basis of curie tempeature and quenching method in the process of manufacturing Mn-Cu-Zn Fersite. The results are as follow. Curie tempeature drops according as the content of CuO and ZnO increases. It also decreases according as sintering temperature increases when the content of ZnO in fixed. Curie temperature drops more in quenching than in slow cooling and activation energy diminishes were too. On the basis of curie tempeature, activation energy is greater in paramagnetic region than in ferrimagnetic region. As its voltage-crrent characteristics is similar to that semiconductors, the temperature-sensitive ferrite is expeated to be appied in the area of power electronics.