• Journal of Korean Society of Environmental Engineers
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• v.31 no.9
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• pp.735-742
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• 2009

The bone of spinal animals has a hydroxylapatite ($Ca_{10}(PO_4)_6(OH)_2$, HAp) structure which is well known as an excellent inorganic ion exchanger for various heavy metal ions in solutions. In this study, the reusability of cow-bone, pig-bone and fish-bone as a potential material for the removal of heavy metals in solutions was evaluated from the removal of Cu(II) ion in batch tests. The surface properties of three bones, calcined at different temperatures, were measured with SEM, XRD, FT-IR analyses. From the SEM analysis, a clear development of heterogeneity as well as pores having small diameter was observed as the calcination temperature increased. The results of X-ray diffraction analysis showed well developed crystallinity on the surface of calcined bones obtained at higher temperatures, suggesting a transform of amorphous type to crystalline type. Fourier transform infrared (FT-IR) analysis showed disappearance of water molecule on the surface of HAp and organic functional groups of the HAp with increasing the calcination temperatures. Cu(II) removal in the control test was below 15%. By the way, additional 40% increase of Cu(II) removal was observed in the presence of calcined bones. For three bones, Cu(II) removal was decreased as the calcined temperature increased. Cu(II) removal was increased as the solution pH increased due to a favorable condition for the cation exchange as well as precipitation.

• Korean Journal of Materials Research
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• v.6 no.2
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• pp.175-181
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• 1996

Ti(i-OC3H7)와 Ba(OH)2.8H2Or 그리고 공통용매로서 2-Methoxy Ethanol을 이용하여 균일 용액을 제조하고, 이로부터 미세하고 조성비가 균일한 BaTiO3분말을 제조하였다. 이러한 졸-겔법으로 제조된 분말을 TG-DTA와 XRD 분석으로 결정화 및 상변화를 관찰하였다. 각 온도별로 하소된 분말에서 (111)쌍정의 생성여부를 TEM을 이용해 관찰한 결과, 합성된 BaTiO3 분말에서는 하소중(111)쌍정의 생성이 활발히 일어나지 않는 것으로 판단되었다. 특히(111) 쌍정판은 합성된 겔을 120$0^{\circ}C$에서 하소한 후 이를 140$0^{\circ}C$에서 소결한 경우에만 관찰할 수 있었다. 이러한 하소온도의 영향은 원료분말의 입자크기나 형상이 쌍정 생성에 큰 영향을 미침을 의미하는 것으로, 본 연구에서는 이를 근거하여 (111) 쌍정의 생성에 대해서 고찰하였다.

• Composites Research
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• v.36 no.5
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• pp.289-296
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• 2023

In this study, we investigated the electromagnetic properties and microwave absorption characteristics of M-type hexagonal ferrites, which are known as millimeter-wave absorbing materials, according to their calcination temperature. The M-type ferrites synthesized using a molten salt-based sol-gel method exhibited a single-phase M-type crystal structure at calcination temperatures above 850℃. The synthesized particle size increased as well with the calcination temperature. Saturation magnetization increased gradually with increasing calcination temperature, but coercivity reached a maximum at 1050℃ and then rapidly decreased. After preparing a thermoplastic polyurethane (TPU) composite containing 70 wt% of M-type ferrites, we measured the complex permittivity and permeability in the Q-band (33-50 GHz) and V-band (50-75 GHz) frequency ranges, where ferromagnetic resonance occurred. Strong magnetic loss from ferromagnetic resonance occurred in the 50 GHz band for all composite samples. Based on the measured results, we calculated the reflection loss of the TPU/M-type ferrite composite. By calculating the reflection loss of the M-type ferrite composite, the M-type ferrite calcined at 1250℃ showed excellent electromagnetic wave absorption performance of more than -20 dB at 52 GHz with a thickness of about 0.5 mm.

• Journal of the Korean Ceramic Society
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• v.38 no.8
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• pp.749-754
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• 2001

마이크로파 추출 및 하소 공정을 통하여 카올린으로부터 베타 알루미나 전구체 및 베타 알루미나 분말을 합성하였다. 황산 알루미늄 및 가성소다의 혼합 용액을 교반되는 에탄올 용액 중에 적하시켜서 $Al_2$(SO$_4$)$_3$.17$H_2O$ 및 $Na_2$SO$_4$.10$H_2O$의 균일한 침전물을 얻었다. $\beta$- 및 $\beta$\"-Al$_2$O$_3$상으로 구성된 베타 알루미나를 얻기 위하여 재래식 및 마이크로파 하소법으로 주어진 온도에서 약 2h 동안 침전물 시료를 하소하였다. 재래식 하소된 시료에 비하여 마이크로파 하소된 시료는 $\beta$\"-Al$_2$O$_3$상이 상대적으로 많이 존재하였다. 또한, 재래식 하소된 시료와 마이크로파 하소된 시료의 미세구조는 매우 상이하였다. 매우 상이하였다.

• Journal of the Korean Ceramic Society
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• v.40 no.1
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• pp.31-36
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• 2003

In this study, nano-sized NiCuZn-ferrites for the multi-layered chip inductor application were prepared by a coprecipitation method and its electromagnetic properties were analyzed. Also, the property of low temperature sintering were studied with the initial heat treatment of powder.$(Ni_{0.4-x}Cu_xZn_{0.60})_{1+w}(Fe_2O_4)_{1-w}$ (x=0.2, w=0.03) were calcined at $300^{circ}C~750^{circ}C.$ The sintered NiCuZn-ferrites at $900^{\circ}C$ showed good apparent density $4.90g/cm^3,$ and magnetic properties of initial permeability 164 and quality factor 72. As the calcination temperature increase, the grain size of NiCuZn-ferrite increased with irregular grain distribution and its magnetic properties were deteriorated.

• Korean Journal of Crystallography
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• v.3 no.1
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• pp.1-8
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• 1992

The morphology of lead titanate powders prepared by sol-gel and coprecipitation techniques was investigated as a function of firing temperature and soaking time. PbTiO3 precursor powders were derived from a mixed solution of lead nitrate and titanium tetrachloride at 40℃ to 43℃ and pH of 9.0 to 9.7, and fired at temperatures 350-1000℃ for 1-10h in air. An increase of particle size and agglomeration with increasing calcination temperature and duration could be observed. By annealing sol-gel derived powder at 700℃, the tially-formed acicular(and/or prismatic) primary particles transformed to polyhedral shape with soaking time, and further soaking caused coarsening the polyhedral particles with rounded edges. However, the morphology of the coprecipitated powders was not varied during crystallization.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.05a
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• pp.304-307
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• 1999

The Mg($_{1-x}$ )S $r_{x}$Ti $O_3$(x=0.1,0.2,0.3) ceramics were prepared by the conventional mixed oxide method. The structural properties were investigated with calcining temperature and composition ratio by XRD and DT-TGA. Increasing the calcining temperature from 80$0^{\circ}C$ to 100$0^{\circ}C$, second phase was decreased and average particle size was increased. The SrTi $O_3$ ceramics of calcined at 100$0^{\circ}C$ had a structure of polycrystalline perovskite without the secondary phases. The average particle size of the $Mg_{0.9}$S $r_{0.1}$Ti $O_3$ ceramics calcined at 100$0^{\circ}C$ were 0.67${\mu}{\textrm}{m}$..>......

• Proceedings of the Materials Research Society of Korea Conference
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• 1997.10a
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• pp.62-62
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• 1997

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.32 no.4
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• pp.128-135
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• 2022

The inside of a quartz glass crucible for semiconductor processing, called a transparent layer, is manufactured using synthetic silica powder. Bubbles existing in the transparent layer of the crucible cause a problem of reducing the quality of the crucible as well as the yield of the silicon ingot. Therefore, the main goal of the synthetic silica powder, which is the raw material of the transparent layer, is to minimize the bubble generation factor. For this purpose, in the case of synthetic silica powder, it is necessary to minimize silanol groups, carbon and pores. In this study, synthetic silica gel was prepared using the sol-gel method, and changes in carbon content and specific surface area were investigated according to calcination temperature and dwelled time in a two-stage calcination process. The first-stage calcination process was performed between 500℃ and 600℃ and the second-stage calcination process was performed between 1000℃ and 1100℃. The dwelled time was carried out from 10 minutes to a maximum of 12 hours. The carbon content of the powder calcined at 1000℃ for 1 hour was 0.0031 wt.%, and the specific surface area of the powder calcined at 1100℃ for 12 hours was 16.6 m²/g.

• Journal of the Korean Ceramic Society
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• v.34 no.3
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• pp.289-295
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• 1997

Effect of ceramic processing was investigated on the microstructure and electronic properties of low loss Mn-Zn ferrite. Addition of CaO and SiO2 to calcined powder rather than to raw materials mixtured resulted in finer-grained microstructure. Higher oxygen pressure during sintering caused microstructural inhomogeneity and the increase in power loss and disaccommodation factor. Relatively low power loss was found for sintering up to 130$0^{\circ}C$ from powders calcined at high temperature and milled shortly. It was caused by slow densification rate and normal grain growth up to 130$0^{\circ}C$. Calcination at low temperature and prolonged milling enhanced den-sification, which gave a fine grained microstructure and low powder loss at sintering temperture below 120$0^{\circ}C$. Sintering temperature above 125$0^{\circ}C$, however, showed abnormal grain growth.