• 한국세라믹학회지
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• 제29권5호
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• pp.367-376
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• 1992

The powder characteristics of seeded alumina prepared from alkoxide by sol-gel method were studied. When ${\alpha}$-Al2O3 seeded powders used, these ${\alpha}$ phase transformation temperatures decreased than those of unseeded powders by 110$^{\circ}C$ and fine powders under 0.1 $\mu\textrm{m}$ could be obtained. When Fe-nitrate added powders used, fast transformation rate resulted from ionic effects of Fe3+, but hard aggregated morphology exhibited. When ${\alpha}$-Al2O3 and Fe nitrate simultaneously added, these powders represented lower transformation temperature but resulted in microstructure with aggregated particles.

• Bulletin of the Korean Chemical Society
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• 제31권10호
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• pp.2943-2948
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• 2010

Silica monolith powders were prepared by a new procedure where ground powders of proper size distribution were obtained without sieving. An initiator was attached to this ground monolith and polystyrene was bound by reversible addition-fragmentation chain transfer polymerization to give a new stationary phase. The separation efficiency of this phase was found better than that of the polystyrene bound phase based on conventional silica particles and that of the C18 bound silica monolith powders.

• 한국세라믹학회지
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• 제40권5호
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• pp.488-493
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• 2003

유기용매를 함유하는 염화니켈 수용액으로부터 Ni 미분말을 제조하였고 Ni 분말형성에 미치는 유기용매 첨가의 영향을 검토하였다. 모든 생성물들은 0.1~l.0 $\mu\textrm{m}$ 범위의 구형입자들이었고 입자들간의 응집은 관찰되지 않았다. 1-propanol이 40 vol% 첨가된 경우 분말의 입경감소와 균일성이 현저하였다. 이들 분말에 대한 평균입경과 비표면적은 각각 0.3 $\mu\textrm{m}$와 16.4 m$^2$/g이었다. 1-propanol의 첨가량이 증가함에 따라 hydrazine에 의한 환원반응시간은 감소하였고, 1-propanol이 40 vol%가 첨가된 경우 환원시간은 약 5분이었다. Ni 합성 분말은 32$0^{\circ}C$ 부근에서 산화되었고, 30$0^{\circ}C$ 부근에서의 중량 감소는 Ni(OH)$_2$의 탈수에 기인한 것이다.

• 센서학회지
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• 제4권1호
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• pp.35-42
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• 1995

NASICON 분말을 합성하기 위하여 볼밀링법을 사용하였다. 사용된 원료 분말은 3종류 였으며, 이것은 $ZrO_{2}\;+\;Na_{3}PO_{4}\;+\;SiO_{2}$의 미세 및 조립 분말, 그리고 $ZrSiO_{4}\;+\;Na_{3}PO_{4}$의 미세 분말이다. 미세 분말은 $1100^{\circ}C$ 혹은 그 이상의 온도에서 쉽게 반응하여 원하는 생성물로 바뀌었지만, 조립 분말을 사용하면 $1170^{\circ}C$에서도 불완전한 반응이 일어났다. NASICON 전해질을 제조할 때, 원료 분말의 입도가 작을수록 소결 후의 밀도는 높아졌다. 이론적인 밀도($3.27g/cm^{3}$)의 95% 이상의 단일상 NASICON 전해질은 $1150{\sim}1170^{\circ}C$에서 $40{\sim}60$시간 소결할 때에 얻어질 수 있었다.

• 한국세라믹학회지
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• 제33권5호
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• pp.563-571
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• 1996

In order to fabricate solid electrolyte CaO-stabilized ZrO2 of high density sintered body economically 13 mol% CaO-stabilized ZrO2 powders were synthesized by the coprecipitation method. The characteristics and sintering behavior of fine powder were investigated. The precipitates has the specific surface area of 193 m2/g and apperaed to be fine and spherical primary particles with a size of approximately 5nm. The crystalliza-tion temperture of CaO-stabilized ZrO2 was 462$^{\circ}C$. The tetragonal phase was stable in the low calcining tempe-rature regions and the cubic zirconia solid solution was formed from above 120$0^{\circ}C$ through an intermediate stage of formation of CaZrO3 By introducing fine powders washed with alcohol and ball-milling process after calcination the sintered body was possible to attain the value of above 92% of the theoretical density at low temperature of 120$0^{\circ}C$.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2005년도 춘계학술대회
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• pp.310-313
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• 2005

The conical fluidizing system of a binary mixture of Geldart C powders and Geldart A particles was defined as the conical powder-particle fluidized bed. We used a cold conical powder-particle fluidized bed model having a 0.104m-I.D. and 0.6m-high with an apex angle of $10^{\circ}$ for fluidization of a binary powder-particle mixture of 50 $vol\%$ fine carbon black powders (HI-900L, Korea Carbon Black Co.) and coarse alumina particles $(90{\mu}m)$ under different superficial gas velocities (0-0.1 m/s). The differential bed pressure drop increases with increasing gas velocity, and it goes from zero to a maximum value with increasing or decreasing gas velocity. In the conical fluidized beds of fine powders, demarcation velocities of the partial fluidization, full fluidization, partial defluidization was not observed.

• 한국세라믹학회지
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• 제28권2호
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• pp.146-152
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• 1991

Ultra fine and homogeneous (Ni0.4Zn0.6)Fe2O4 ferrite powders were prepared by direct-wet, Hydrothermal and coprecipitation methods. In case that specific surface areas of Ni-Zn ferrite powders were over 220㎡/g, 100㎡/g, 30㎡/g individually direct-wet, hydrothermal and coprecipitation methods. The Ni-Zn ferrite magnetic fluids of which Solvents were benzene or kerosene was prepared by making cation surfactant adsorbed on the surface of the (Ni0.4Zn0.6)Fe2O4. The results that measured dispersion and viscosity by making cation surfactant adsorbed were as follows. 1. The adsorption amount of Oleric acid be proportioned the specific surface area of powders. 2. The maximum amount of Oleric acid was 36wt% of dried powders which has 220㎡/g of specific surface area. 3. The stability of fluid by direct-wet synthesis emthod in benzene or kerosene solvent excellent.

• 한국세라믹학회지
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• 제34권10호
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• pp.1009-1014
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• 1997

Ammonia gas was blown into the solution of zirconium ion to induce precipitation of supersaturated zirconium ion at gas-liquid interface with increase in pH. The influence of pH on the phase and particle size of precipitate and calcined powders has been investigated. At pH 4.5 of zirconium solution, maximum yield of 98.7% was obtained. Above pH 4.5, there was no more increase of yield. Above pH 5.5, large aggregates consisting of primary particles were observed in precipitate and calcined powders. At pH 4.5, almost aggregate-free fine spherical zirconia powders were obtained.

• 한국세라믹학회지
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• 제29권1호
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• pp.74-82
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• 1992

Ultra-fine calcium phosphate powders were synthesized by the reaction of Ca(OH)2 suspension with various phosphoric aqueous solutions such as (NH4)2HPO4, H4P2O7 and H3PO4, and the characterization of powders was examined for each synthetic condition. When (NH4)2HPO4 and H3PO4 were used, hydroxyapatite powders with poor crystallinity were obtained. In the case of H4P2O7, amorphous calcium phosphate was obtained up to 0.3 mol/ι Ca(OH)2 suspension, but above the concentration, poor crystalline hydroxyapatite was produced. Crystalline phases of powders heat-treated at 80$0^{\circ}C$ were hydroxyapatite, $\beta$-tricalcium phosphate and $\beta$-tricalcium phosphate for the case of (NH4)2HPO4, H4P2O7 and H3PO4, respectively. SEM observation revealed that the shapes of synthesized powders were vigorously agglomerated spherical with the size below 100 nm, but TEM observation revealed that primary shapes of particles were rod for (NH4)2HPO4 and H3PO4 and were sphere for H4P2O7. There was no dependence of the concentration of Ca(OH)2 suspension. In the case that reaction temperature and pH of the suspension were raised, the inclination to the hydroxyapatite were remarkable. The amorphous calcium phosphate synthesized in this experiment contained water about 20% , and was crystallized to $\beta$-tricalcium phosphate at 69$0^{\circ}C$.

• 한국분말재료학회지
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• 제3권3호
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• pp.181-187
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• 1996

Cobalt and VC powders were ball milled with M2 grade high speed steel powders under various ball to powder ratios. The powders milled under higher ball to powder ratio become finer, more irregular and have a broader size distribution, and thus possess a lower compressibility and a better sinterability regarding densification. Increasing the ball to powder ratio lowered the sintering temperature to obtain the density level necessary to isolate all the pores. Lowering the sintering temperature is very critical to maintain fine microstructure since grain and carbide coarsening are accelerated by higher sintering temperature due to more liquid phase formation. The powders obtained by ball milling at 20 to 1 ratio has the lowest compressibility but has the best sinterability, almost compatible to unmilled pure M2 powders. A sintered body over 97% theoretical density with fine microstructures having average grain size of ~10 microns was obtained from the powder by sintering at 1260 $^{\circ}C$ for 1 hour in vacuum. XRD results indicate that two types of carbides are mainly present in the sintered structure, MC and $M_{6}C$ type. The MC type carbides are more or less round shaped and mainly located at the grain boundaries whereas the $M_{6}C$ type are angular shaped and mainly located inside the grains.