• Korean Journal of Materials Research
• /
• v.1 no.1
• /
• pp.37-45
• /
• 1991

In order to control the microstructures, the sintering behavior and abnormal grain growth with Ba/Ti ratio variation of $BaTiO_3$were investigated. The $BaTiO_3$powders used in this study were prepared by conventional calcination of $BaCO_3$ and $TiO_2$. The onset temperatures of the sintering were lowered and the densification was enhanced with increasing amounts of $TiO_2$ excess. These results are because of decrease of calcined particle sizes. A eutectic melt above temperature of $1320^{\circ}C$ did not assist the densification. Grain growth was strongly inhibited with increasing amounts of $TiO_2$ excess. The inhibition of grain growth caused abnormal grain growth due to inhomogeneous distribution of Ti-rich second phase.

• Journal of the Korean Ceramic Society
• /
• v.35 no.8
• /
• pp.857-863
• /
• 1998

The BaTiO3 powders extensively used as MLCC (Multilayer ceramic capacitor) in electronic ceramic in-dustry were synthesized by GNP (Glycine-Nitrate process) The powders were prepared using carbonate and alkoxide as starting materials and nitric acid was used as a solvent for starting materials as well as an oxidant for combustion. The BaTiO3 powders were synthesized using different amounts of glycine as a fuel for combustion. The characteristics of synthesized powders were examined with helium pycnometer X-ray diffraction(XRD) Brunauer-Emmett-Teller with N2 adsorption and scanning electron microscopy(SEM). It was found that single phase BaTiO3 could be formed when the as-synthesized powders were heat-treated at 100$0^{\circ}C$ When the glycine/cation molar ratio was 1,2 specific surface area was 24m2/g

• Proceedings of the Korean Vacuum Society Conference
• /
• 2013.08a
• /
• pp.165-165
• /
• 2013

희토류 발광 물질은 4f 껍질에 위치하는 전자의 독특한 특성 때문에 발광 소자와 디스플레이에 그 응용성을 확장하고 있다. 본 연구에서는 고효율의 적색과 주황색 형광체를 합성하기 위하여 모체 격자 CaNb2O6에 희토류 이온인 유로퓸과 사마륨을 치환 고용하여 최적의 합성 조건을 조사하였다. Ca1-1.5xNb2O6:REx3+ (RE=Eu, Sm) 형광체 분말 시료는 고상반응법을 사용하여 활성제 이온인 Eu3+와 Sm3+의 농도비를 0, 0.01, 0.05, 0.10, 0.15, 0.20 mol 로 변화시키면서 합성하였다. 초기 물질 CaO, Nb2O5, Eu2O3와 Sm2O3을 화학 적량으로 측정하고, 400 rpm의 속도로 24시간 밀링 작업을 수행한 후에, 건조기 $60^{\circ}C$에서 28시간 건조하고, 시료를 막자 사발에서 갈아 세라믹 도가니에 담아 튜브형 전기로에서 분당 $5^{\circ}C$의 비율로 승온시켜 $500^{\circ}C$에서 5시간 동안 하소와 $1,100^{\circ}C$에서 6시간 소결하여 합성하였다. Eu3+가 도핑된 경우에, 발광 스펙트럼은 Eu3+ 이온의 농도비에 관계없이 강한 적색 발광 스펙트럼이 616 nm에서 관측되었다. 이외에도, 596 nm와 708 nm에서 상대적으로 발광 세기가 약한 주황색 발광과 적색 발광 신호가 검출되었으며, 541 nm에서는 매우 약한 녹색스펙트럼이 관측되었다. Eu3+ 이온의 농도비에 0.01 mol에서 0.15 mol로 증가함에 따라 주발광 신호의 세기는 점점 증가하였으며, 0.15 mol에서 최대 발광 세기를 나타내었다. Eu3+ 이온의 농도비가 0.20 mol 로 더욱 증가함에 따라 주 피크의 세기는 농도 소강 현상에 의하여 현저히 감소함을 보였다. 한편, 주된 흡광 스펙트럼은 279 nm에서 나타났는데, 이것은 전하전달밴드 신호이다. Sm3+가 도핑된 형광체 분말의 발광 스펙트럼은 모든 시료의 경우에 613 nm에서 강한 적주황색 발광 스펙트럼이 관측되었고, 상대적으로 세기가 약한 570 nm와 660 nm에 피크를 갖는 황색과 적색 발광 스펙트럼이 발생하였다. 흡광과 발광 스펙트럼의 최대 세기는 0.05 mol에서 나타났으며, Sm3+ 이온의 농도비가 더욱 증가함에 따라 흡광과 발광 세기는 급격하게 감소하였다.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.31 no.6
• /
• pp.240-246
• /
• 2021

In the ceramic industry, a drastic decrease in crystalline formation was found even among the glazes well known for their high crystalline productivity when the ceramic glaze was stored in wet conditions over a period. This study aimed to investigate the reason for decreasing willemite crystals during storage. As the starting materials ZnO, calcined ZnO and frit 3110 are selected; the composition for zinc crystalline glazes was set through a three-component system with the materials. The firing condition was used from previous studies. The study was observed how wet conditions affected the crystallization of zinc crystalline glazes from a day to 24 weeks. The results were obtained by particle size analysis, XRD, Raman spectroscopy and SEM analysis. The results indicated that ZnO is advantageous in terms of willemite crystalline development and growth; however, Zn(OH)₂ cluster, formed by the reaction with water during the storage, caused the decrease in ZnO level in the glaze. The reduction of ZnO in the glaze eventually interfered the willemite development and growth.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.18 no.5
• /
• pp.200-204
• /
• 2008

Mechano Chemical Process (MCP) skips the calcinations steps at an intermediate temperature that is always required in the conventional solid-state reaction because forming phase from raw powder is activated by mechanical energy. In this study, we prepared (Pb, La)$TiO_3$ nanopowder with perovskite structure by only high energy MCP. Especially, the PLT nanopowder was synthesized without any thermal treatment using oxides, not salts as raw powder. This process is also very simple due to dry milling method, unnecessary to dry of powder. The oxide powder was milled up to 12 hr at intervals of an hour using MCP and the pure PLT phase of perovskite structure was formed after milling time of 3 hr. And the average particle size was 20 nm with narrow distribution after milling time of 3 hr from raw powder of several $\mu m$ with inhomogeneous distribution.

• Journal of the Korean Ceramic Society
• /
• v.39 no.1
• /
• pp.68-73
• /
• 2002

The dielectric properties and synthesis of $LaAlO_3$ ceramics from mixtures of $La_2O_3-Al_2O_3$ (LAO) and $La_2O_3-Al(OH)_3$(LAH) via grinding process were investigated. The single phase $LaA1O_3$of LAO and LAH powders were formed at $1300^{\circ}C$ and $1000^{\circ}C$, respectively. A non-reacted $La_2O_3$ existing in calcined powder was changed to La(OH)$_3$by moisture in the air, and their samples were worse than those of the samples made from a $LaA1O_3$single phase powder. The densities of LAO samples sintered at 150$0^{\circ}C$ for 4 h and LAH samples sintered at $1400^{\circ}C$ for 4 h were 97.3% and 98.3% of theory density, respectively. Grains of LAH sample showed uniformity and their sizes were 0.75 ${\mu}{\textrm}{m}$, and LAO samples showed non-uniformity and their sizes were 4-5 ${\mu}{\textrm}{m}$. Dielectric constant of LAO and LAH samples were the same value (≒22), however dielectric loss of LAH sample (0.0003) were lower than that of LAO sample(0.001)due to grain size.

• Applied Chemistry for Engineering
• /
• v.16 no.1
• /
• pp.45-51
• /
• 2005

$K^+-{\beta}^{{\prime}{\prime}}-Al_2O_3$ in the $K_2O-Li_2O-Al_2O_3$ ternary system was synthesized using aluminum nitrate solution as a starting material. For the synthesis of pure $K^+-{\beta}^{{\prime}{\prime}}-Al_2O_3$, raw materials with chemical composition of $0.84K_2O{\cdot}0.082Li_2O{\cdot}5.2Al_2O_3$ were mixed in solution state. The effects of dispersant and solution-pH were investigated in minimizing the particle size and on the synthesis of pure $K^+-{\beta}^{{\prime}{\prime}}-Al_2O_3$. Ethanol was used for a dispersant, and $NH_4OH$ solution and nitric acid were added for pH adjustment. The solution pH was increased from 1.0 to 7.5 by 0.5 increments. Each sample was calcined at $1200^{\circ}C$ for 2 h and characterized with X-ray diffraction and particle size analyzer. The pH of solution significantly effected both particle size and phase formation, while the addition of ethanol only effected particle size. The synthesis of pure $K^+-{\beta}^{{\prime}{\prime}}-Al_2O_3$ was favored by addition of nitric acid (for pH control).

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.20 no.2
• /
• pp.93-100
• /
• 2010

The calcium to phosphate ratio (Ca/P) in biphasic calcium phosphates powders using X-ray diffraction analysis (XRD) was characterized. The BCP powders with various stoichiometric Ca/P molar ratio were synthesized with coprecipitation process and calcination. Compositions of the powders with Ca/P molar ratio between 1.5 and 1.67 were subjected to starting Ca/P molar ratio, pH = 10, and thermal treatment up to $900^{\circ}C$. The structural, morphological and chemical characterizations for BCP powders with stoichiometric Ca/P ratio were carried out with scanning electron microscope (SEM) and inductively coupled plasma atomic emission spectroscopy (ICP-AES) and a phase quantification was investigated by XRD. The solubility of HAp, $\beta$-TCP, and BCP powders was tested in the phosphate buffer solution (PBS) at $36.5^{\circ}C$ and pH = 7.4.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.22 no.3
• /
• pp.139-146
• /
• 2012

Natural hydroxyapatite powder was obtained from the calcination of bovine bones and its porous compacts were fabricated by pressureless sintering at 1100 and $1200^{\circ}C$ for 1h. To evaluate and compare their biocompatibility with porosity, we investigated the support of osteoblast cells growth and cytotoxicity using the MG-63 cell line model in vitro. Sintered hydroxyapatite ceramics have a porous microstructure with a relative density of 65 % at $1100^{\circ}C$ and 82 % at $1200^{\circ}C$. Cells adherence to the surface of hydroxyapatite ceramics was observed in a day after the cell culture, and the spreading of cytoplasm around the nucleus was shown after 3 day cell culture. Most of cells were extended to the surface of hydroxyapatite through the wide area. Cell viability was nearly the same till 3 days culturing. But the rate of cell growth is higher in the specimen sintered at $1100^{\circ}C$ than that of $1200^{\circ}C$. It indicates that the porosity is an important factor to enhance the cell viability in the porous hydroxyapatite ceramics derived from bovine bones.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2011.08a
• /
• pp.314-315
• /
• 2011

최근에 $Eu^{3+}$ 이온이 첨가된 적색 형광체에 대한 연구가 활발히 진행되고 있다. 현재 상업적으로 이용 가능한 적색 형광체와 비교하여 $GdVO_4$를 모체로 갖는 적색 형광체는 우수한 열적 안정성과 광학적 특성을 나타낸다. 본 연구에서는 고효율의 적색 형광체를 개발하기 위하여 고상 반응법을 사용하여 $Gd_{1-x}VO_4$ : $Eu_x^{3+}$ 형광체를 합성하였다. $Gd_{1-x}VO_4$ : $Eu_x^{3+}$ 형광체 분말 시료는 활성체인 $Eu^{3+}$의 함량을 0, 0.05, 0.10, 0.15, 0.20 mol로 변화시키며, 초기 물질 $Gd_2O_3$ (99.99%), $H_3BO_3$ (99.99%), $Eu_2O_3$ (99.9%)를 화학 적량으로 준비하였다. 분말은 볼밀과 건조 작업을 거친 후, 500$^{\circ}C$ 전기로에서 5시간 동안 하소 공정, 1,100$^{\circ}C$에서 6시간 동안 소성시켰다. 합성된 형광체 분말의 XRD 측정한 결과에 의하면, $Eu^{3+}$의 함량비에 관계없이 모든 분말 시료들에서 주 피크는 24.7$^{\circ}$와 33.2$^{\circ}$에 최대값을 갖는 (200)와 (112)면의 회절 신호들이 관측되었고, 상대적으로 약한 회절 세기를 갖는 (101), (211), (301), (103), (312)와 (420)면의 회절 신호들은 각각 18.6$^{\circ}$, 31.1$^{\circ}$, 40.1$^{\circ}$, 44.6$^{\circ}$, 49.2$^{\circ}$와 57.1$^{\circ}$에서 나타났다(Fig. 1). 이결과를 JCPDS(86-0996)와 비교함으로써, 합성된 형광체 분말의 결정 구조는 정방정계임을 확인할 수 있었다. $Eu^{3+}$의 함량비가 0.05 mol에서 0.15 mol로 증가함에 따라 주 피크인 (200)면의 회절 신호의 세기는 증가한 반면, 0.20 mol에서는 급격하게 감소하였으며, 이 경우에 반치폭의 크기는 0.16$^{\circ}$이었다. 결정 입자의 크기를 결정하기 위하여 (200)면의 회절 피크에 대한 정보를 잘 알려진 Scherrer의 식에 대입하여 계산한 결과, $Eu^{3+}$의 함량비가 0 mol인 경우에, 평균 크기는 48 nm이었다. $Eu^{3+}$ 함량비를 증가함에 따라 결정 입자의 크기도 비례하여 증가하였으며, 0.15 mol에서 최대값을 나타내었으나, 농도 억제 효과로 인하여 0.20 mol 에서는 현저히 감소하였다. 표면 형상의 변화를 관측한 SEM 측정 결과에 의하면, $Eu^{3+}$의 함량비가 0 mol에서 0.15 mol로 증가함에 따라 결정 입자의 모양은 사다리꼴 형태에서 모서리가 둥글게 깎인 구형으로 변형되는 것을 관측할 수 있었으며 평균 크기는 500 nm이었다(Fig. 2). $Eu^{3+}$의 함량이 0.20 mol인 경우에 결정 입자의 형상은 더욱 구형에 접근하였으나, 평균 크기는 최소값을 나타내었다. 실험 결과로부터, 적절한 함량비를 갖는 $Eu^{3+}$ 이온을 첨가함으로써 적색 형광체 $Gd_{1-x}VO_4$ : $Eu^{3+}$ 분말의 결정 크기와 발광 세기를 제어할 수 있음을 제안한다.