• Journal of the Korean Electrochemical Society
• /
• v.24 no.3
• /
• pp.52-64
• /
• 2021

The effect of Fe and BO₃ doping on structure, thermal, and electrical properties of Li_1+xFe_xTi_2-x(PO₄)_3-y(BO₃)_y (x = 0.2, 0.5)-based glass and glass ceramics was investigated. In addition, their crystallization behavior during sintering and ionic conductivity were also investigated in terms of sintering temperature. FT-IR and XPS results indicated that Fe²⁺ and Fe³⁺ ions in Li_1+xFe_xTi_2-x(PO₄)_3-y(BO₃)_y glass worked as a network modifier (FeO₆ octahedra) and also as a network former (FeO₄ tetrahedra). In the case of the glass with low substitution of BO₃, boron formed (PB)O₄ network structure, while boron preferred BO₃ triangles or B₃O₃ boroxol rings with increasing the BO₃ content owing to boic oxide anomaly, which can result in an increased non-bridging oxygen. The glass transition temperature (GTT) and crystallization temperature (CT) was lowered as the BO₃ substitution was increased, while Fe²⁺ lowered the GTT and raised the CT. The ionic conductivity of Li_1+xFe_xTi_2-x(PO₄)_3-y(BO₃)_y glass ceramics were 8.85×10^-4 and 1.38×10^-4S/cm for x = 0.2 and 0.5, respectively. The oxidation state of doped Fe and boric oxide anomaly were due to the enhanced lithium ion conductivity of glass ceramics.

• Journal of the Korean Ceramic Society
• /
• v.40 no.1
• /
• pp.81-86
• /
• 2003

Microwave dielectric properties have been investigated in the$(1-x)CaTiO_3-xYAlO_3$ (x=0.1~1.0) solid solution system. The mixtures of $CaTiO_3$ and $YalO_3$using solid state method were sintered at various temperatures. Their dielectric constants and related temperature coefficients were strongly depend on the composition of the solid solution. The optimum properties were recorded as for ${\varepsilon}_r=47,$ $Q{\times}f_0$=35000 and ${\tau}_f=+11ppm/^{\circ}C$ without sintering agent. Even at $1200^{\circ}C$ full densification has been achieved with addition of $CaB_2O_4$ in the $0.75CaTiO_3-0.25YalO_3$ composition. The sample of $0.3 wt%-CaB_2O_4$ added $ 0.75CaTiO_3-0.25YalO_3$ sintered at $1300^{\circ}C$ for 3 h showed optimum microwave dielectric properties of ${\varepsilon}_r=47$, $Q{\time}f_0=37000$ and ${\tau}_f=+17ppm/^{\circ}C$, which demonstrates the promising candidates for microwave dielectric materials covering 5~7 GHz range.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.20 no.3
• /
• pp.147-152
• /
• 2010

In this study, the artificial coarse aggregate was manufactured by using coal ash and low grade clay. The characteristics of a coal ash-clay system were investigated using XRD, XRF, TG-DTA, SEM and Dilatometer with various coal ash contents. The chemical compositions are the fly ash, bottom ash and clay, $Al_2O_3$ are 28.5 wt%, 32.4 wt% and 18.1 wt%, and $SiO_2$ are 33.0 wt%, 53.7 wt% and 68.4 wt% in weight ratio, respectively. The shrinkage of specimens started at around $850^{\circ}C$ and changed little up to $1100^{\circ}C$, but increased markedly at above $1100^{\circ}C$. The shrinkage rate is strongly related to the decarbonization amount of coal ash. At the sintering temperature $1150^{\circ}C$, it was found that quartz, mullite, anorthite and albite phase exist in all specimens. It was found that bottom-clay system specimen sintered at $1150^{\circ}C$ had a good compressive strength of 87.5 kg/$cm^2$, and the compressive strength of bottom-clay specimen was higher than that of fly-clay system specimen. The reusability of coal ash as a raw material in the process of shotcrete resources such as artifical coarse aggregate is highly expected.

• Journal of the Korean Ceramic Society
• /
• v.34 no.1
• /
• pp.102-108
• /
• 1997

ZrO2 powders stabilized with Y2O3 and CeO2 of various compositions were prepared by the coprecipitation of water-soluble ZrOCl2.8H2O, YCl3.6H2O and Ce(NO3)3.6H2O, and their compacts were pressurelessly sintered at 1400 and 150$0^{\circ}C$ for 2hrs in air. 2mol% Y2O3-ZrO3 showed the most superior strength (1003MPa) and microhardness (12.6GPa), while 10 mol%CeO2-ZrO2 had the hightest toughness (13.3 MPa.m1/2) after sintering at 140$0^{\circ}C$. The addition of Y2O3 into Y2O3-ZrO3 decreased mean grain size and increased strength and hardness but decrease toughness. On the other hand, the addition of CeO2 into Y2O3-ZrO2 enhanced the stability of tetragonal phase during low-temperature aging for a long time under hydrothermal atmosphere.

• Journal of the Korean Magnetics Society
• /
• v.21 no.2
• /
• pp.77-82
• /
• 2011

The use of soft magnetic materials have been increasing in the various industrial fields according to the increasing demand for high performance, automatic, miniaturing equipments in the recent our life. In this study, we investigated the effect of factors on the core loss and magnetic properties of electrical steel and soft magnetic composites. Furthermore, we reviewed the major efforts to reduce the core loss and improve the soft magnetic properties in the two main soft magnetic materials. Domain purification which results from reduced density of defects in cleaner electrical steels is combined with large grains to reduce hysteresis loss. The reduced thickness and the high electrical conductivity reduce the eddy current component of loss. Furthermore, the coating applied to the surface of electrical steel and texture control lead to improve high permeability and low core loss. There is an increasing interest in soft magnetic composite materials because of the demand for miniaturization of cores for power electronic applications. The SMC materials have a broad range of potential applications due to the possibility of true 3-D electromagnetic design and higher frequency operation. Grain size, sintering temperature, and the degree of porosity need to be carefully controlled in order to optimize structure-sensitive properties such as maximum permeability and low coercive force. The insulating coating on the powder particles in SMCs eliminates particle-to-particle eddy current paths hence minimizing eddy current losses, but it reduces the permeability and to a small extent the saturation magnetization. The combination of new chemical composition with optimum powder manufacturing processes will be able to result in improving the magnetic properties in soft magnetic composite materials, too.

• The Journal of Engineering Research
• /
• v.3 no.1
• /
• pp.181-187
• /
• 1998

Hydroxyapatite was used as implant materials, because it has a good biocompatibility and is similar to human bone. However it is not expected to have a high strength as implant materials because of a low fracture strength after sintering of HAp. Alumina ($\alpha$-alumina) shows a stable chemical properties and high strength in physiological environments. Thus it was tried to use a HAp coatings on Alumina substrate as implant materials. In this study, HAp was coated on Alumina substrate by lon Beam Assisted Deposition(IBAD). Then Ag was impregnated on HAp coating layer, which showed antimicrobial effects. To carry out the ion exchange of $Ag^+$ with $Ca^{2+}$ in HAp on the surface, HAp coated alumina substrate was immersed in 20ppm, 100ppm $AgNO_3$ solution at room temperature for 48 hours. Antimicrobial test was studied by using bacteria, which normally caused periprosthetic infections. The follwing bacteria was used in antimicrobial test. Escherichia coli, Pseudomonas aeruginosa (gram negative) and staphylococcus epidermidis (gram positive). Ag impregnated HAp shows very good antimicrobial effects against these bacteria. The surface structure of sample, which was treated in $AgNO_3$ solution was studied by SEM, XRD. Ag release curve was studied in Simulated Body Fluid (SBF) solution.

• Korean Journal of Materials Research
• /
• v.23 no.6
• /
• pp.309-315
• /
• 2013

$GdBa_2Cu_3O_{7-y}$(Gd123) powders were synthesized by the solid-state reaction method using $Gd_2O_3$ (99.9% purity), $BaCO_3$ (99.75%) and CuO (99.9%) powders. The synthesized Gd123 powder and the Gd123 powder with $Gd_2O_3$ addition ($Gd_{1.5}Ba_2Cu_3O_{7-y}$(Gd1.5)) were used as raw powders for the fabrication of Gd123 bulk superconductors. The Gd123 and Gd1.5 bulk superconductors were fabricated by sintering or a top-seeded melt growth (TSMG) process. The superconducting transition temperature ($T_{c,onset}$) of the sintered Gd123 was 93 K and the transition width was as large as 20 K. The $T_{c,onset}$ of the TSMG processed Gd123 was 82 K and the transition width was also as large as 12 K. The critical current density ($J_c$) at 77 K and 0 T of the sintered Gd123 and TSMG processed Gd123 were as low as a few hundreds A/$cm^2$. The addition of 0.25 mole $Gd_2O_3$ and 1 wt.% $CeO_2$ to Gd123 enhanced the $T_c$, $J_c$ and magnetic flux density (H) of the TSMG processed Gd123 sample owing to the formation of the superconducting phase with high flux pinning capability. The $T_c$ of the TSMG processed Gd1.5 was 92 K and the transition width was 1 K. The $J_cs$ at 77 K (0 T and 2 T) were $3.2{\times}10^4\;A/cm^2$ and $2.5{\times}10^4\;A/cm^2$, respectively. The H at 77 K of the TSMG-processed Gd1.5 was 1.96 kG, which is 54% of the applied magnetic field (3.45 kG).

• Journal of the Mineralogical Society of Korea
• /
• v.22 no.3
• /
• pp.261-277
• /
• 2009

This study is aimed to emphasize the significance of ore selection in lime manufacturing through the evaluation of applied-mineralogical impact factors of crude ores controlling calcination characteristics for some domestic limestones used currently for lime manufacturing. To do this work, systematic characterization and determination were carried out for the limestone ores and their calcination products in a fixed calcining condition (target temperature: $1000^{\circ}C$, retention time: 30 minutes, 2, 4, 10, 16 hours), and the results were correlated and discussed. Selected high-Ca limestones in this study are as much as > 98 wt%, but they are somewhat diverse in crystallinity, texture, and impurity composition. Synthesized quicklimes are varied depending on such a difference in ore characters. The Pungchon limestone has relatively very low calcination rate, and the limestones from the Gabsan formation and the Jeongseon formation exhibit good quality in calcination rate and decrepitation. Among these samples, the limestone ore from the Jeongseon formation is evaluated to be the best for crude ore in manufacturing of highly-reactive quicklime. In addition, it is characteristic that the Gabsan limestone comparative rich in Fe-bearing mineral such as pyrite and goethite is more conspicuous in sintering effect.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2008.06a
• /
• pp.306-306
• /
• 2008

기계적 에너지를 전기적 에너지로 변환하는 에너지 변환소자인 압전 세라믹스는 액추에이터, 변압기, 초음파모터, 초음파 소자 및 각종 센서로 응용되고 있으며, 그 응용분야는 크게 증가하고 있다. 최근에는 이러한 압전 소자를 앞으로 도래하는 ubiquitous, 무선 모바일 시대의 휴대용 전자제품, robotics, MEMS 분야 등의 대체 에너지원으로 응용하기 위한 연구가 진행되고 있다. 특히 인간의 걷기 운동 등과 같은 일상적인 동작으로 필요한 전력을 얻을 수 있고, 세라믹 소자를 이용하기 때문에 전자노이즈가 발생되지 않을 뿐 아니라 반영구적으로 사용할 수 가 있어서, 기존 이차전지를 대체 또는 보완 할 수 있는 방안도 검토되고 있다. PZT계 세라믹스는 높은 유전상수와 우수한 압전특성으로 전자세라믹스 분야에서 가장 널리 사용되어지고 있지만 $1200^{\circ}C$ 이상의 높은 소결온도 때문에 $1000^{\circ}C$ 부근에서 급격히 휘발되는 PbO로 인한 환경오염과 기본조성의 변화로 인한 압전 특성의 저하가 문제시 되고 있다. 또한 적층 세라믹스의 제작 시 구조적 특성상 내부전극이 도포된 상태에서 동시 소결이 필요한데, 융점이 낮은 Ag전극 대신 값비싼 Pd나 Pt가 다량 함유된 Ag/Pd, Ag/Pt 전극이 사용되고 있어 경제성이 떨어지는 단점을 갖게 된다. 순수 Ag 전극을 사용하거나 Ag의 비율이 높은 내부전극을 사용하기 위해서는 $900^{\circ}C$ 이하에서 소결되고 우수한 전기적 특성을 보이는 압전 세라믹스를 개발 하는 것이 필요하다. 따라서 본 연구에서는 압전특성이 우수한 $(Pb_{1-x}Cd_x)(Ni_{1/3}/Nb_{2/3})_{0.25}(Zr_{0.35}/Ti_{0.4})O_3$ 계의 조성을 설계하고, 소걸온도를 낮추기 위해서 2 단계 하소법을 이용하였다. 또한 $MnCO_3$, $SiO_2$, $Pb_3O_4$ 등을 소량 첨가하여 액상 소결 특성을 부여하여 소결 온도를 감소시키려는 시도도 하였다. 분말을 볼 밀링 (ball milling)을 통해 24시간 동안 혼합하고, 혼합된 분말은 $800^{\circ}C$에서 2시간 동안 하소하였다. 하소한 분말을 다시 72시간 동안 볼 밀링 하여 최종 분말을 얻었다. 최종 분말에 PVB를 첨가하여 직경 15mm의 디스크 형태로 성형한 후, 850~$975^{\circ}C$ 범위에서 온도를 변화시키면서 소결을 하였다. 최종 분말 및 소결된 시편을 XRD분석을 통하여 상을 확인하였고, SEM을 이용하여 미세조직을 관찰 하였다. 전기적 특성을 평가하기 위하여 두께를 1mm로 연마한 시편에 Ag 전극을 도포하여 $650^{\circ}C$에서 열처리한 후, 분극처리 하였다. 압전특성은 $d_{33}$-meter로 측정하였고, impedance analyzer를 이용하여 압전 특성 (전기기계결합계수 및 기계적품질계수)을 측정 하였다. 또한 강유전체 특성 평가 장치 (Precision-LC)를 이용하여 분극-전계 특성을 평가하였다. 이상의 연구를 통하여 소결 온도가 $900^{\circ}C$인 경우에서도 양호한 압전 특성을 확보 할 수 있었다.

• Korean Journal of Materials Research
• /
• v.11 no.3
• /
• pp.178-184
• /
• 2001

Transparent and highly oriented KLN thin films have been grown by an rf- magnetron sputtering deposition method. A homogeneous and stable KLN target was prepared by calcine and sintering process. For KLN target, stoichiometry and composition excess with K of 30% and 60%, and Li of 15% and 30% respectively, was prepared. The targets were sintered at low temperature to prevent vaporization of K and Li. KLN thin films were fabricated by rf-magnetron sputtering method using those targets. In this experiment, using the target of composition excessed with K of 60% and Li of 30%, single phase KLN thin film was produced. KLN thin film has excellent crystallinity and highly c-axis oriented on Corning 1737 substrate. Transmittance of thin film in visible range was 90%, absorption edge is 333 nm and refractive index at 632.8 nm was 1.93.