• Journal of the Korean Ceramic Society
• /
• v.50 no.6
• /
• pp.446-450
• /
• 2013

TRISO coated particles with a ZrC barrier layer were fabricated by a fluidized-bed chemical vapor deposition (FBCVD) method for a use in a very high temperature gas-cooled reactor (VHTR). The ZrC layer was deposited by the reaction between $ZrCl_4$ and $CH_4$ gases at $1500^{\circ}C$ in an $Ar+H_2$ mixture gas. The amount of free carbon codeposited with in ZrC was changed by controlling the dilution gas ratio. Near-stoichiometric ZrC phase was also deposited when an impeller was employed to a $ZrCl_4$ vaporizer which effectively inhibited the agglomeration of $ZrCl_4$ powders during the deposition process. A near-stoichiometric ZrC coating layer had smooth surface while ZrC containing the free carbon had rough surface with tumulose structure. Surface roughness of ZrC increased further as the amount of free carbon increased.

• Journal of the Korean Ceramic Society
• /
• v.50 no.6
• /
• pp.434-438
• /
• 2013

Monodispersed 3Y-$ZrO_2$ spherical agglomerates were synthesized by thermal hydrolysis process followed by crystallization processes (hydrothermal treatment and calcination). The crystallization process affected the properties of the final particles, such as the primary particle size, the agglomeration state, and the fraction of $ZrO_2$ monoclinic phase. The hydrothermal treated spherical particles were porous microstructures (weak agglomerates) composed of small primary particles with a size of 14 nm, but the calcined spherical particles had a dense microstructure due to the hard aggregation between primary particles. While the calcined particles had a low green density due to the hard aggregation, hydrothermal treated ones were soft agglomerates and had a deflection point at 50 MPa due to the rearrangement of secondary spherical particles and the filling of the interstices with the primary particles. Finally, the green density of hydrothermally treated $ZrO_2$ particles was 58% at 200 MPa.

• Journal of the Korean Ceramic Society
• /
• v.50 no.6
• /
• pp.390-395
• /
• 2013

Nanocrystalline CrN films were deposited on Si (100) substrates by means of asymmetric pulsed DC reactive magnetron sputtering. We investigated the growth behavior, corrosion resistance and mechanical properties of CrN films with a change in the duty cycle and pulse frequency. The grain size of the CrN films decreased from 25.4 nm to 11.2 nm upon a decrease in the duty cycle. The corrosion potentials for the CrN films by DC sputtering was approximately - 0.6 V, and it increased to - 0.3 V in the CrN films which underwent pulsed sputtering. The nanoindentation hardness of the CrN films also increased with a decrease in the duty cycle. This enhancement of the corrosion resistance and mechanical properties of pulsed sputtered CrN films could be attributed to the densification and surface smoothness of the microstructure of the films.

• Journal of the Korean Ceramic Society
• /
• v.55 no.5
• /
• pp.480-491
• /
• 2018

Calcium phosphates (CaP) were prepared by a wet chemical method. Micro-crystalline dicalcium phosphate (DCPD) was precipitated at $37^{\circ}C$ and pH 5.0 using $Ca(OH)_2$ and $H_3PO_4$. The precipitated DCPD solution was kept at $37^{\circ}C$ for 96 h. Artificial bone cement was composed of DCPD, $Ca(H_2PO_4)_2{\cdot}H_2O$ (MCPM), and $CaSO_4{\cdot}1/2H_2O$, $H_2O$ and aqueous poly-phosphoric acid solution. The wet prepared CaP powder was used as a matrix for the bone cement recipe. With the addition of aqueous poly-phosphoric acid, the cement hardening reaction was started and the CaP bone cement blocks were fabricated for the mechanical strength measurement. For the tested blocks, the mechanical strength was measured using a universal testing machine, and the microstructure phase analysis was done by field emission scanning electron microscopy and X-ray diffraction. The cement hardening reaction occurred through the decomposition and recrystallization of MCPM and $CaSO_4{\cdot}1/2H_2O$ added on the surface of the wet prepared CaP, and this resulted in grain growth in the bone cement block.

• Journal of the Korean Ceramic Society
• /
• v.56 no.5
• /
• pp.453-460
• /
• 2019

To reduce residual pores of composites and obtain a dense matrix, SiC_f/SiC composites were fabricated by chemical vapor deposition (CVI) using SiC nanorods. SiC nanorods were uniformly grown in the thickness direction of the composite preform when the reaction pressure was maintained at 50 torr or 100 torr at 1,100℃. When SiC nanorods were grown, the densities of the composites were 2.57 ~ 2.65 g/㎤, higher than that of the composite density of 2.47 g/㎤ for non-growing of SiC nanorods under the same conditions; grown nanorods had uniform microstructure with reduced large pores between bundles. The flexural strength, fracture toughness and thermal conductivity (room temperature) of the SiC nanorod grown composites were 412 ~ 432 MPa, 13.79 ~ 14.94 MPa·m^1/2 and 11.51 ~11.89 W/m·K, which were increases of 30%, 25%, and 25% compared to the untreated composite, respectively.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.15 no.5
• /
• pp.202-207
• /
• 2005

We have investigated the relationship between a viscosity of the slip prepared from kaolin, quartz, $Mg(OH)_2$, etc and its influence on the speed of slip casting and the microsturcture of a sintered body. The speed of slip casting decreases as a viscosity of a slip decreases. The optimized viscosity range of a slip was found to be around $3.0\~17.0\;cP$. By careful controlling a viscosity of slip, homogeneous microstructure of outer surface layers, inner surface layers, intermediate layers, and inside layers were obtained by casting process. The specimen sintered at $1350^{\circ}C$ consists of a cordierite crystalline phase only as a constituent mineral.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.13 no.5
• /
• pp.383-389
• /
• 2000

The relationship between the DC degradation characteristics of the ZnO varistor and the ambient sintering-process is investigated in this study. ZnO varistors made o matsuoka’s composition were fabricated by standard ceramic techniques. The ambient sintering-process is performed at the extraordinary electrical-furnace which is equipped with the vacuum system. Gases used in sintering process were oxygen nitrogen argon and air. Using XRD and SEM the phase and microstructure of samples were analyzed respectively. The conditions of DC degradation tests were conducted at 115$\pm$2$^{\circ}C$ for 13 h. Current-voltage analysis is used to determine nonlinear coefficients($\alpha$). Frequency analysis are performed to understand electrical properties as DC degradation test. From above analysis it is found that the ZnO varistor sintered in oxygen atmosphere showed superior properties at the DC degradation test and degradation phenomenon of ZnO varistor is caused by the change of electrical properties in grain boundary. These results are in accordance with Gupta’s degradation model.

• Journal of the Korean Ceramic Society
• /
• v.29 no.8
• /
• pp.587-592
• /
• 1992

Sheets of SiC-SiC whisker maxed matrix were prepared from the mixed slurry of SiC whisker and SiC matrix by the rolling method. With the increase of SiC whisker, the pore size, the porosity and the phosphoric acid absorbency of the matrix were increased, while the bubble pressure was decreased. The activation energy for the transfer of H+ ion was decreased with the increase of mixing ratio of SiC whisker to the SiC matrix from the measurement of hydrogen ion conductivity. The activation energy was evaluated as 0.25 eV when the mixing ratio of SiC whisker to the SiC matrix was 1 : 2 and the activation energy was 0.16 eV for the 2 : 1 matrix. It means that SiC whisker matrix contributes to attain a better microstructure for the diffusion of hydrogen ion. From the measurement of single cell performance of matrix with various mixing ratio, it is concluded that if SiC-SiC whisker maxed matrix has a sufficient bubble pressure to prevent the crossover of H2 gas, the current density of a fuel cell is increased with the increase of acid absorbency of the matrix. Current density was improved from 140 mA/$\textrm{cm}^2$ for 0.25 mm thickness of matrix to 170 mA/$\textrm{cm}^2$ for the 0.20 mm one at 700 mV.

• Journal of the Korean Ceramic Society
• /
• v.40 no.3
• /
• pp.234-240
• /
• 2003

Hardened cement pastes of OPC which contains 10 wt% CSA type expansive additives were immersed in aqueous solution of 10 wt% MgS $O_4$.7$H_2O$ and then investigated by compressive strength, XRD. SEM and DSC etc.. According to the results including the hydration products and the microstructure of the hardened paste, the case of CSA type expansive additives［No. 6(C/(equation omitted) : 2.29, A/(equation omitted) : 0.16)] prepared from raw materials increased the resistance to $Mg^{2＋}$, S $O_4$$^{2-}$ ion diffusion than that of OPC paste due to the densification by the formation of fine ettringite in the first stage and the hydrates according to $\beta$-C$_2$S hydration in the late period.

• Journal of the Korean Ceramic Society
• /
• v.40 no.3
• /
• pp.309-316
• /
• 2003

EAF(Electric Arc Furnace) Dust classified as special wastes containing heavy metal contaminants may cause to damage an environment such as underground water contamination if they were not treated properly. The possibility of producing the porous sintered body made from EAF Dust/clay composition system was studied. Mixing of EAF Dust and clay was carried out using wet-mixing process and two different sintering methods such as rapid and normal heat treatment were tried. By observing density, porosity and microstructure of sintered bodies, it was found that the bloating phenomenon depend on the contents of C, where the liquid phase occur or not during the sintering process. To obtain a light-aggregate of porous body due to bloating, the rapid heating was better than the normal heating at sintering process.