• 한국분말재료학회지
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• 제9권6호
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• pp.449-454
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• 2002

$MnxZn_{1-x}Fe_2O_4$ (x=0.69~0.74) powders synthesized by the thermal decomposition of organic acid salts. The obtained powders were uniform in composition and ultra-fine particle with about 400 nm. The amount of spinel phase of these powders was about 50% in X-ray diffraction patterns. The calcination of powder was carried out at $900^{\circ}C$ for 2 hours in air. After the powders were calcined. the mean size of powder was about 500 nm and the amount of spinel phase was increased over about 65%. The maximum amount of spinel phase was about 75% in the specimen of X=0.72. The magnetic properties of calcined $Mn_{0.72}Zn_{0.28}Fe_2O_4$ powders were the best among the different among the different compositions.

• 한국재료학회지
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• 제16권12호
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• pp.719-724
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• 2006

Ultrafine mullite powder was prepared from aluminium-secbutoxide and tetraethyl orthosilicate(TEOS) in the molar $Al_2O_3/SiO_2$=3/2. Sol-gel method by partial hydrolysis technique, as it were, first, TEOS was partially hydrolysized and then mixed with Al-secbutoxide for complete hydrolysis was used. X-ray diffraction, infrared spectroscopy and transmission electron microscopy, etc. confirmed that the mullite powder prepared by this method is in the stoichiometric $Al_2O_3/SiO_2$ ratio. Al-Si spinel was formed at $980^{\circ}C$ and ultrafine mullite powder with about 20 nm particle size was obtained above $1,200^{\circ}C$. Also mullite powders calcined at $1,600^{\circ}C$ had a stoichiometric composition, $3Al_2O_3{\cdot}2SiO_2$ and the lattice constants of the mullite powders calcined above $1,200^{\circ}C$ were almost coincided with theoretical values.

• Archives of Metallurgy and Materials
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• 제66권3호
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• pp.799-802
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• 2021

The nano-sized Y₂O₃ dispersed W composite powder is prepared by ultrasonic spray pyrolysis of a tungsten precursor using ammonium metatungstate hydrate and a polymer addition solution method using Y-nitrate. XRD analysis for calcined powder showed the formation of WO₂ phase by partial oxidation of W powder during calcination in air. The TEM and phase analysis for further hydrogen reduction of calcined powder mixture exhibited that the W powder with a uniform distribution of Y₂O₃ nanoparticles can be successfully produced. These results indicate that the wet chemical method combined with spray pyrolysis and polymer solution is a promising way to synthesis the W-based composites with homogeneous dispersion of fine oxide particles.

• 환경위생공학
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• 제15권1호
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• pp.62-68
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• 2000

This study was investigated to the recovery of alumina from the first calcined waste pottery using alkaline sintering. This study was based on calcination result of a commercial ${\alpha}-Al2_O_3$ with NaOH powder. $NaAlO_2$ was formed by calcination of ${\alpha}-Al_2O_3$ with NaOH and conversion of $NaAlO_2$ from ${\alpha}-Al_2O_3$ was 91.4% at calcination condition ; weight ritio of $NaOH/{\alpha}-Al2_O_3$ 1.5, $800^{\circ}C$, and 90min. The first calcined waste porrery from the manufacturing Procedure of H Ltd. was grinded to 170/270mesh by a ball mill and calcined over $500^{\circ}C$ with NaOH powder. The calcined sample was dissolved in $25^{\circ}C$ water and sodiumaluminosilicate solid was formed. After filtration, the contained aluminum was leached out by dissolving sodiumaluminosilicate solid in 1N HCl. We estimated the efficiency of Al extraction from waste pottery by ICP analysis and NaOH was added to the filtrate and then aluminum compound was precipitated with $Al(OH)_3$ and recovered. The investigation was carried out with the variables ; the calcination temperature($500-900^{\circ}C$), the calcination time(30~90min), and the weight ratio of NaOH/waste pottery(0.5~1.5). The treatment efficiency of the waste pottery and the recovery of Al as 97.9%, 91.9% were obtained under the optimum conditions as followed ; the weight ratio of NaOH/waste pottery was 1.5 and the calcination conditions were $900^{\circ}C$ and 60min.

• 에너지공학
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• 제26권2호
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• pp.39-49
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• 2017

Coffee is one of the most popular and consumed beverages in the world, which leads to a high contents of solid residue known as spent coffee grounds (SCG). As is known, coffee beans contain several classes of health related chemicals, including phenolic compounds, melanoidins, diterpenes, xanthines and carotenoids. The waste water coming out of coffee industries has high concentration of organic pollutants and is very harmful for surrounding water bodies, human health and aquatic life if discharged directly into the surface waters. Hence it is essential to treat and manage the coffee waste. Oyster shells are a waste product from mariculture that creates a major disposal problem in coastal regions of southeast Korea. In the study, the oyster shell waste was used to treat the coffee waste and its effluents. Oyster shells are calcined at $1000^{\circ}C$ for 2 h, and allowed to test the calcined CaO powder ability to inhibit the growth of bacteria in different aging coffee wastes. Calcined oyster shell powder showed anti-bacterial effect that inhibited cell growth of Escherichia coli and other bacterial forms. The antimicrobial activity of calcium oxide from oyster shell waste for biological treatment and utilization as a fertilizers with economic ecofriendly in nature.

• 한국세라믹학회지
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• 제31권11호
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• pp.1378-1386
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• 1994

The characteristic of calcined BaTiO3 powder and sintered PTC ceramics was investigated varing with calcination temperature and time of BaTiO(C2O4)2.4H2O synthesized from BaCl2.2H2O, TiCl4, oxalic acid and ethanol by oxalic acid method. When the particle size was less than 0.1 ${\mu}{\textrm}{m}$ by controlling calcination temperature and time, the resistance at room temperature was measured very high (above M{{{{ OMEGA }}). However, when the calcined particle sizes ranged from 0.2 to 0.3 ${\mu}{\textrm}{m}$, the resistance was 100 {{{{ OMEGA }} (After sintering, the grain size was 10~30 ${\mu}{\textrm}{m}$ homogeneously with the addition of dopant in sintering, the resistivity, resistance, $\alpha$ value and jumped to were 110{{{{ OMEGA }}.cm, 24$^{\circ}C$/% and 106{{{{ OMEGA }}, respectively.

• 한국세라믹학회지
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• 제20권1호
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• pp.49-54
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• 1983

The main object of this study is to investigate the effect of Al powder as an additive on the sintering of calcined alumina comparing with that of calcined alumina alone. The degree of Al oxidation is calculated by measuring the weight increase during the firing Water absorption bulk density and compressive strength of the $Al_2O_3+Al$ system at each temperature are compared with those of $Al_2O_4$ alone. The $Al_2O_3+Al$ system shows better physical propeties than Al2O3 alone and it seems by the SEM observation that the fine oxidized Al particles(fine $Al_2O_3$ particles submicron unit) fill the interstices of the original $Al_2O_3$ par-ticles and thus result in the well-close-packed arrangement of the particles.

• 한국세라믹학회지
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• 제27권6호
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• pp.777-782
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• 1990

The sintering behavior of cordierite powders synthesized using a sol-gel method of metal alkoxides Si(OC2H5)4, Al(OC3H71)3 and Mg(OC2H5)2 was investigated. Densification of the powder compacts fabricated using the precursor powders calcined at 900$^{\circ}C$ for 2hrs was improved over the sintering temperature range of 800 to 980$^{\circ}C$. The powder compacts, fabricated using the calcined precursor powders and sintered at 1300$^{\circ}C$ for 2hrs, showed relative density of 97-98%, 3-point bending strength of 120-140Mpa, KIC of 2.4-3.7 Mpam1/2, and thermal expansion coefficient of 1.48-1.66${\times}$10-6/$^{\circ}C$.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2014년도 춘계 학술논문 발표대회
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• pp.280-281
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• 2014

Recently, it is certain that the increase of heating and cooling energy consumption by radical change in climate condition has caused serious problems related to environmental and energy concerns associated with increase of fossil fuel usage and carbon dioxide production as well as global warming. Therefore, various actions to reduce greenhouse gas and energy consumption have been prepared by world developed countries. The energy consumption by buildings approximately reaches 25% of total korea energy consumption. The greatest part in the buildings of the energy consumption is building facade. But a few research projects on concrete comprising more than 70% of outsider of buildings has been tried. This research is structural insulation concrete what improved insulation performance using micro form admixture and calcined diatomite powder and lightweight aggregate.

• 한국세라믹학회지
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• 제29권6호
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• pp.489-495
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• 1992

The continuous compaction response of zirconia powders prepared by different processing treatments was investigated. Though the yield point could be or not below 1 MPa, the change of slope was always observed at high pressure range around 60 MPa. Powder compaction was mainly governed by second compaction stage and compaction rate was decreased with increasing forming pressure. Rotary vacuum dried powder favored a high compaction density, whereas freeze dried and calcined powders favored an increase in the pressing efficiency. In order to extract more reliable information about powder compaction, it was necessary to use not only compaction response diagram but also compaction rate diagram.