• Journal of the Korean Ceramic Society
• /
• v.34 no.11
• /
• pp.1165-1172
• /
• 1997

ZrB2 powders were prepared from a mixture of ZrO2, B2O3 and Mg by self-propagating high temperature synthesis method. The combustion product was successfully obtained from a mixture of ZrO2:B2O3:Mg=1:2:8.5 molar ratio. By-product, MgO was effectively removed by leaching with 1M HCl solution at 9$0^{\circ}C$ for over 5hours. After leaching, the Mg content was 0.86~1.42 wt%, and the mean particle size was 4.72${\mu}{\textrm}{m}$. The addition of 7.5 wt%(14Ni:1.0C) as a sintering aid greatly densified ZrB2 bodies compared with that of only Ni. The ZrB2 sintered bodies containing 7.5 wt%(14Ni:1.0C) was 94.3% of the theoretical density. In this case, ZrB2 existed as a major phase and had a bend strength of 300 MPa and a vickers hardness of 2000 kg/$\textrm{mm}^2$.

• Journal of the Korean Ceramic Society
• /
• v.42 no.7 s.278
• /
• pp.503-508
• /
• 2005

A simple and effective method for the synthesis of LiMn$_{2}$O$_{4}$ powder as a cathode material for lithium secondary battery is reported. Micrometer size LiMn$_{2}$O$_{4}$ was prepared by combustion synthesis technique employing initial mixture of l.l LiNO$_{3}$ -1.3Mn-0.7MnO$_{2}$-1NaCl composition. Parametric study of the combustion process including molar ratio of Mn/MnO$_{2}$ and NaCl concentration were carried out under air atmosphere. The combustion products obtained were additionally heat treated at the temperature 900$^{\circ}C$ and the washed by distilled water. The results of charging-discharging characteristics revealed that LiMn$_{2}$O$_{4}$ cell synthesized in the presence of NaCl had a high capacity and much better reversibility than one formed without NaCl An approximate chemical mechanism for LiMn$_{2}$O$_{4}$ formation is proposed.

• Journal of the Korean Ceramic Society
• /
• v.42 no.7 s.278
• /
• pp.509-515
• /
• 2005

Interfacial reactions at LSGM electrolyte and NiO-GDC anode interfaces were thoroughly investigated with Environmental Scanning Electron Microscopy (ESEM-PHlLIPS XL-30) and Energy Dispersive X-ray (EDX-Link XL30). According to the analysis, serious reaction zone was observed at LSGM/NiO-GDC interface. It was found that the reaction layer was originated from the chemical reaction between NiO and LSGM. The reaction products were identified as La deficient form of LSGM based perovskite and Ni-La-O compounds such as LaSrGa$_{3}$O$_{7}$ and LaNiO$_{3}$ from the X-Ray Diffraction (XRD, Philips) analysis. According to the electrical characterization, interfacial layer was very electrically resistive which would be the cause of high internal resistance and low power generating characteristic of the unit cell.

• Journal of the Korean Ceramic Society
• /
• v.26 no.1
• /
• pp.100-108
• /
• 1989

Aluminum hydroxides were prepared by the alkoxide hydrolysis method using Al-isopropoxide as a starting material and NH4OH as a catalytic agent. When Al-isopropoxide was hydrolyzed in a H2O-NH3 system, only Al(OH)3 was obtained over all pH values. However, AlOOH was formed besides Al(OH)3 when Al-isopropoxide was hydrolyzed in a H2O-NH3-isopropyl alcohol system. The AlOOH/Al(OH)3 ratio was increased as the isopropyl alcohol content was increased. The hydroxides, Al(OH)3 and AlOOH, obtained in this study and the commerical products, $\alpha$-Al2O3 and AlOOH were subjected to the carbothermal reduction and nitridation reaction to product AlN powder, using carbon black as a reducing agent under N2 atmosphere at various temperatures. AlN was synthesized from the obtained Al(OH)3 and the commercial AlOOH at 145$0^{\circ}C$, however, synthesized from the obtained AlOOH and the commercial alpha-alumina at 135$0^{\circ}C$. The temperature difference is assumed to be attributed to the reactivity of those powders. AlN powder prepared from the Al-isopropoxide was observed to have the narrower particle size distribution than that prepared from the commercial $\alpha$-Al2O3 or AlOOH.

• Journal of the Korean Ceramic Society
• /
• v.44 no.10
• /
• pp.580-584
• /
• 2007

The ZrC layer instead of SiC layer is a critical and essential layer in TRISO coated fuel particles since it is a protective layer against diffusion of fission products and provides mechanical strength for the fuel particle. In this study, we carried out computational simulation before actual experiment. With these simulation results, Zirconium carbide (ZrC) films were chemically vapor deposited on $ZrO_2$ substrate using zirconium tetrachloride $(ZrCl_4),\;CH_4$ as a source and $H_2$ dilution gas, respectively. The change of input gas ratio was correlated with growth rate and morphology of deposited ZrC films. The growth rate of ZrC films increased as the input gas ratio decreased. The microstructure of ZrC films was changed with input gas ratio; small granular type grain structure was exhibited at the low input gas ratio. Angular type structure of increased grain size was observed at the high input gas ratio.

• Journal of the Korean Ceramic Society
• /
• v.35 no.2
• /
• pp.185-195
• /
• 1998

This experiment carried out in order to investigate the effect of the chemical activators for acceleration of hydration the system of Fly ash-Cao The paste was consisted of 80wt% Fly ash and 20wt% CaO with 1. 3. 5wt% of 4 activators(N{{{{ alpha _2 }}S{{{{ OMICRON _4 }}, CaC{{{{ {l }_{2 } }}, NaOH, Ca(N{{{{ OMICRON _3 {)}_{2 } }} and W/S ratio of 0.42 After curing for 1, 3, 7, 14, 28 days the paste hydration was characterized by the measurement of compressive strength XRD analysis SEM observation the combined water and the reaction amount of Ca(OH)2 determination. As a result of this ex-periment all of the system which involved Na2SO4 or NaOH had a god compressive strength. In the case of 7 days curing a system which added CaCl2 showed the highest compressive strength among all especially NaOH system showed a high increase in strength as a dosage of it increased. Hydration products were different according to activatores added. Only C-S-H was observed in NaOH system. As the reaction amount of Ca(OH)2 and combined water were increased the compressive strength increased. There were few differences in the comparision of strength between ignited loss 3.1% and loss 9.3% of fly ash.

• Journal of the Korean Ceramic Society
• /
• v.22 no.5
• /
• pp.47-53
• /
• 1985

In view of innovated utilization of Korean clay resources conventional techniques for pulverization are reviewed in comparison with fluid energy milling processes of fluidized-bed type. Throughout experiment indigenous halloysite ores (white grade) after usual pretreatment are employed as typical sample. It is evidenced that grinding by means of porcelain ball mills has limitation in reducing clay particles to less than 10${\mu}{\textrm}{m}$ in diameter regardless of whether it is processed in dry or wet. Upon use of tungsten carbide bull mill particulation to submicron sizes could be effected with relative ease but severe coloration in grey is attended indicating metallic contamination possibly from friction of the grinding apparatus itself. In contrast the modified fluid en ergy milling enables particulation to $\leq$10${\mu}{\textrm}{m}$ in diameter with simultaneous classification int olimited ranges of particle size distributions. Since this technique is in principle based on the interparticle collisions rather than on the frictions between particles and mill surfaces minimum impurity attendance would be an additional advantage. Evidence leads to the conclusion that the fluidized-bed type milling is regarded as highly effective in puverization as well as fractionation of the clay minerals under examination. This is especially so in contemplating high-value and/or high-purity clay products.

• Journal of the Korean Ceramic Society
• /
• v.41 no.3
• /
• pp.242-246
• /
• 2004

Nano-sized a-alumina with a narrow distribution was prepared by using Flame Spray Pyrolysis (FSP). The microemulsion of water in oil (W/O) was prepared to make ultrafine droplets for FSP process. Kerosene (fuel) as a continuos phase and Al(NO$_3$)$_3$$.$9$H_2O$ (oxidizer) aqueous solution as a dispersed phase were prepared for microemulsification. The microemulsion with dispersion stability was obtained by adjusting the composition of 80 vol% kerosene, 10 vol% aqueous solution, and 10 vol% emulsifying agent. Microemulsion was sprayed onto the flame by using two-fluid nozzle spray gun under the condition of 0.03 ㎫ air pressure. The synthesized products were $\alpha$-alumina phase with the size of 20 to 30 nm.

• Journal of the Korean Ceramic Society
• /
• v.45 no.7
• /
• pp.418-422
• /
• 2008

The preparation of FeB by SHS in $B_2O_3-Mg-Fe-Fe_3O_4$ system was investigated in this study. In the preparation of FeB, the effects of the initial pressure of inert gas in reactor, the content of Mg and $Fe_3O_4$ in mixture on the reactivity and reaction products was investigated. The minimum initial pressure of inert gas in reactor for SHS reaction in this system was 25 atm, and as the pressure increased, the concentration of unreacted Mg decreased and combustion temperature increased. At the initial inert gas pressure in reactor of 25 atm, the optimum composition for the preparation of pure FeB was $1.5B_2O_3$+3.43Mg+ 1.7Fe+$0.1Fe_3O_4$. The FeB synthesized in this condition had an irregular shape and the particle size of $5\;{\mu}m$.

• Journal of Korea Foundry Society
• /
• v.36 no.6
• /
• pp.208-214
• /
• 2016

Casting defects, which are closely related to entrapped air bubbles and metallic oxides, occur very frequently in the casting process. Many researchers have shown that these defects can be reduced by adopting an appropriate gating system design. But, it is difficult for field engineers to identify a specific gating system that is more appropriate for their products. In this study, we tried to draw a comparison of gating system designs with and without ceramic foam filters. A ceramic foam filter was added to the horizontal runner just after the sprue to prevent air bubble generation and to reduce turbulence without change of the gating system design. To verify the effects of initial pouring velocity, the experiment was conducted with four different amounts of water volume in the reservoir. Results of the water modeling experiment applying the filter showed remarkably changed flow characteristics. Although the study confirmed that use of the filter may change the flow characteristics, it needs to be noted that only filter use alone cannot solve all the problems caused by a poorly designed gating system.