• 한국세라믹학회지
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• 제41권11호
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• pp.842-850
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• 2004

BaO$_2$-TiO$_2$-환원제-입자제어제계에서 자전연소합성법을 이용한 BaTiO$_3$ 분말의 제조에 대하여 고찰하였다. 환원제로서 C, Mg를 사용하였고, 입자제어제로서 NaCl을 사용하였다. 자전연소합성법을 이용한 BaTiO$_3$ 분말의 제조에 있어 최적의 반응계에서 환원제의 종류와 농도, 입자제어제, 반응량의 변화에 따른 생성물의 영향을 조사하였다. 최적의 반응계 및 조성은 Ae반응 분위기에서 BaO$_2$+TiO$_2$+0.1Mg+0.2C+0.75NaCl이었다. 희석제로서 첨가된 NaCl은 연소온도의 조절 뿐 아니라 반응생성물의 입도를 제어하는 효과를 나타냄을 알 수 있었다. 최적의 조건에서 제조된 순수 BaTiO$_3$ 분말의 입도는 약 0.5 $mu extrm{m}$ 이하였으며, 반응량을 증가시킬수록 균일한 반응성을 나타내었다 제조된 BaTiO$_3$ 분말의 유전특성을 측정하기 위하여 130$0^{\circ}C$, 2시간동안 대기중에서 소결실험을 행하였고 이때 상온에서의 유전상수는 약 2290이었고, 큐리점(129$^{\circ}C$)에서의 유전상수는 약 13800을 나타내었다.

• 한국분말재료학회지
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• 제31권2호
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• pp.146-151
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• 2024

Pure SnO₂ has proven very difficult to densify. This poor densification can be useful for the fabrication of SnO₂ with a porous microstructure, which is used in electronic devices such as gas sensors. Most electronic devices based on SnO₂ have a porous microstructure, with a porosity of > 40%. In pure SnO₂, a high sintering temperature of approximately 1300℃ is required to obtain > 40% porosity. In an attempt to reduce the required sintering temperature, the present study investigated the low-temperature sinterability of a current system. With the addition of TiO₂, the compositions of the samples were Sn_1-xTi_xO₂-CoO(0.3wt%)-CuO(2wt%) in the range of x ≤ 0.04. Compared to the samples without added TiO₂, densification was shown to be improved when the samples were sintered at 950℃. The dominant mass transport mechanism appears to be grain-boundary diffusion during heat treatment at 950℃.

• 한국세라믹학회지
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• 제45권5호
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• pp.263-267
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• 2008

$(Bi_{1/2}Na_{1/2})TiO_3$-based ceramics have been intensively studied as lead-free piezoelectric ceramics. In this study, the piezoelectric properties and phase transition behaviors of BNT based solid solution $(Bi_{0.5}Na_{0.5})_{1-x}Ca_xTiO_3$ ($X=0.01{\sim}0.25$) were investigated. The morphotropic phase boundary(MPB) zone which BNT is transformed from rhombohedral to cubic structure was appeared by adding $CaTiO_3$ with 0.12 mol by the measurement of permittivity and X-ray diffraction. The behavior which ferroelectric BNT with adding $CaTiO_3$ was changed to antiferroelectric and paraelectric state was confirmed by the measurement ofhysterisis loop and depolarization temperature as a function of temperature. As $CaTiO_3$ concentration was increased, the phase transition temperature was decreased. The piezoelectric properties were highest at 0.01 mol of $CaTiO_3$ concentration. The electromechanical coupling factor($K_t$) and mechanical quality factor($Q_m$) were 42% and 254, respectively.

• 한국재료학회지
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• 제20권11호
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• pp.575-580
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• 2010

The microstructure and positive temperature coefficient of resistivity (PTCR) characteristics of 0.1 mol%$Na_2Ti_6O_{13}$ doped $0.94BaTiO_3-0.06(Bi_{0.5}Na_{0.5})TiO_3$ (BBNT-NT001) ceramics sintered at various temperatures from $1200^{\circ}C$ to $1350^{\circ}C$ were investigated in order to develop eco-friendly PTCR thermistors with a high Curie temperature ($T_C$). Resulting thermistors showed a perovskite structure with a tetragonal symmetry. When sintered at $1200^{\circ}C$, the specimen had a uniform microstructure with small grains. However, abnormally grown grains started to appear at $1250^{\circ}C$ and a homogeneous microstructure with large grains was exhibited when the sintering temperature reached $1325^{\circ}C$. When the temperature exceeded $1325^{\circ}C$, the grain growth was inhibited due to the numerous nucleation sites generated at the extremely high temperature. It is considered that $Na_2Ti_6O_{13}$ is responsible for the grain growth of the $0.94BaTiO_3-0.06(Bi_{0.5}Na_{0.5})TiO_3$) ceramics by forming a liquid phase during the sintering at around $1300^{\circ}C$. The grain growth of the BBNT-NT001 ceramics was significantly correlated with a decrease of resistivity. All the specimens were observed to have PTCR characteristics except for the sample sintered at $1200^{\circ}C$. The BBNT-NT001 ceramics had significantly decreased $\tilde{n}_{rt}$ and increased resistivity jump with increasing sintering temperature at from $1200^{\circ}C$ to $1325^{\circ}C$. Especially, the BBNT-NT001 ceramics sintered at $1325^{\circ}C$ exhibited superior PTCR characteristics of low resistivity at room temperature ($122\;{\Omega}{\cdot}cm$), high resistivity jump ($1.28{\times}10^4$), high resistivity temperature factor (20.4%/$^{\circ}C$), and a high Tc of $157.9^{\circ}C$.

• 열처리공학회지
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• 제28권3호
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• pp.134-138
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• 2015

Ag intermediated $TiO_2$ films were deposited by RF and DC magnetron sputtering and then vacuum annealed at 100, 200 and $300^{\circ}C$ for 30 minutes to investigate the effect of annealing temperature on the structural and optical properties of the films. For all depositions, the thickness of the $TiO_2$ and Ag films were kept constant at 24 and 15 nm by controlling the deposition time. As-deposited $TiO_2/Ag/TiO_2$ trilayer films have a weak crystalline and an optical reflectance in a near infrared wavelength region of 77.8%, while the films annealed at $300^{\circ}C$ show the polycrystalline structure and an increased mean optical reflectance of 80.4%. From the experimental results, it can be concluded that increasing the annealing temperature enhanced the structural and optical properties of the $TiO_2/Ag/TiO_2$ films.

• 열처리공학회지
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• 제28권6호
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• pp.291-295
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• 2015

IGZO single layer and $IGZO/TiO_2$ bi-layered films were deposited on glass substrate at room temperature with radio frequency magnetron sputtering to investigate the effect of $TiO_2$ buffer layer on the electrical and optical properties of the films. For all deposition, the thickness of IGZO and $TiO_2$ Buffer layer was kept at 100 and 5 nm, respectively. In a comparison of figure of merit, IGZO films with a 5-nm-thick $TiO_2$ buffer layer show the higher figure of merit ($8.40{\times}10^{-5}{\Omega}^{-1}$) than that of the IGZO single layer films ($6.23{\times}10^{-5}{\Omega}^{-1}$) due to the enhanced optical transmittance and the decreased sheet resistance of the films. The observed results mean that a 5 nm thick $TiO_2$ buffer layer in the $IGZO/TiO_2$ films results in better electrical and optical performance than conventional IGZO single layer films.

• 한국세라믹학회지
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• 제41권8호
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• pp.599-604
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• 2004

무선 이동통신 산업에서 소형화와 RF모듈을 구현하기 위해 저온 동시 소성 세라믹(LTCC)기술이 부각되고 있다. LTCC용 재료는 90$0^{\circ}C$ 이하의 온도에서 소성이 되어야 한다 본 연구는 BaO-N $d_2$ $O_3$-Ti $O_2$ (BNT：20∼40wt%) 세라믹과 L $a_2$ $O_3$- $B_2$ $O_3$-Ti $O_2$ (LBT：80∼60wt%) 유리를 혼합하여 유리를 결정화시킴으로, 나타나는 부수적인 효과를 얻고자 하였다. 이에 소결 거동, 결정상 분석, 상대밀도 그리고 유전특성을 평가하였다 80wt% 유리의 첨가는 90%에 가까운 상대밀도를 갖는 복합체로서 15에 가까운 유전율과 10000GHz의 품질계수와 같은 우수한 유전특성을 보였다. 이와 같은 결과는 유리 결정화를 이용하여 LTCC용 유전체에 적용될 수 있는 가능성을 부여하였다.

• Advances in materials Research
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• 제9권2호
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• pp.99-107
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• 2020

Reinforced aluminum alloy base composites have become increasingly popular for engineering applications, since they usually possess several desirable properties. Recently, Warm Accumulative Roll Bonding (WARB) process has been used as a new novel process to fabricate particle reinforced metal matrix composites. In the present study, TiO₂ particles are used as reinforcement in aluminum metal matrix composites fabricated through warm accumulative roll bonding process. Firstly, the raw aluminum alloy 1060 strips with TiO₂ as reinforcement particle were roll bonded to four accumulative rolling cycles by preheating for 5 min at 300℃before each cycle. The mechanical and bonding properties of composites have been studied versus different volume contents of TiO₂ particles by tensile test, peeling test and vickers micro-hardness test. Moreover, the fracture surface and peeling surface of samples after the tensile test and peeling test have been studied versus different amount of TiO₂ volume contents by scanning electron microscopy. The results indicated that the strength and the average vickers micro-hardness of composites improved by increasing the volume content of TiO₂ particles and the amount of their elongation and bonding strength decreased significantly.

• 한국결정성장학회지
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• 제24권2호
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• pp.70-76
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• 2014

아연결정유약에 Anatase 형 $TiO_2$에 의해 생성되는 $Zn_2TiO_4$가 효과적인 결정 생성제로 나타났다. 이에 저온에서 생성되는 $Zn_2TiO_4$를 인위적으로 합성하여 유약의 미치는 효과를 규명하였다. 첨가 $Zn_2TiO_4$는 저온에서 생성되는 결정으로 아연결정 W의 핵으로 작용하는 것으로 밝혀졌다. 합성된 $Zn_2TiO_4$를 유약에 5 wt% 첨가하면 유약 내에 결정생성이 증가하며 안정적으로 유지된다. 특히, $Zn_2TiO_4$ 합성 시 발색제로 CoO, NiO, CuO를 각각 고용시켜 유약에 첨가하면 발색제의 고용효과가 커져 Willemite 결정의 다양한 발색에 큰 효과를 얻을 수 있다.

• 한국재료학회지
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• 제24권8호
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• pp.423-428
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• 2014

We synthesized Fe-doped $TiO_2/{\alpha}-Fe_2O_3$ core-shell nanowires(NWs) by means of a co-electrospinning method and demonstrated their magnetic properties. To investigate the structural, morphological, chemical, and magnetic properties of the samples, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy were used, as was a vibrating sample magnetometer. The morphology of the nanostructures obtained after calcination at $500^{\circ}C$ exhibited core/shell NWs consisting of $TiO_2$ in the core region and ${\alpha}-Fe_2O_3$ in the shell region. In addition, the XPS results confirmed the formation of Fe-doped $TiO_2$ by the doping effect of $Fe^{3+}$ ions into the $TiO_2$ lattice, which can affect the ferromagnetic properties in the core region. For comparison, pure ${\alpha}-Fe_2O_3$ NWs were also fabricated using an electrospinning method. With regard to the magnetic properties, the Fe-doped $TiO_2/{\alpha}-Fe_2O_3$ core-shell NWs exhibited improved saturation magnetization(Ms) of approximately ~2.96 emu/g, which is approximately 6.1 times larger than that of pure ${\alpha}-Fe_2O_3$ NWs. The performance enhancement can be explained by three main mechanisms: the doping effect of Fe ions into the $TiO_2$ lattice, the size effect of the $Fe_2O3_$ nanoparticles, and the structural effect of the core-shell nanostructures.