• Proceedings of the Korea Association of Crystal Growth Conference
• /
• 2000.06a
• /
• pp.233-242
• /
• 2000

Cordierite/ZrO$_2$ composites with 5 to 25wt% ZrO$_2$ were fabricated by prssureless sintering, and their densification behavior, fracture strength, fracture toughness, microstructure and thermal expansion behavior were studied. The ZrO$_2$ addition into cordierite matrix affects the densification behavior and mechanical properties of the composites. By dispersing 25wt% ZrO$_2$, densified cordierite/ZrO$_2$ composite with a relative density of 98.5% was obtained at optimum sintering condition of 144$0^{\circ}C$/2H. Both fracture strength and toughness were increased from 140 to 290MPa and from 1.6 to 3.5 MPam$\frac{1}{2}$, respectively, by dispersing 25wt% ZrO$_2$ into the cordierite matrix. ZrO$_2$ particles were homogenously dispersed into cordierite matrix, which intragranular particles were fine(<100nm) and intergranular particles were coarse. The toughening mechanisms in the present composites were mainly attributed to martensitic transformation toughening. Then, the addition of ZrO$_2$ is likely to have little deleterious effect upon thermal expansion coefficient of cordierite.

• Journal of the Korean Ceramic Society
• /
• v.34 no.11
• /
• pp.1187-1197
• /
• 1997

Dry gel composed of primary particles more homogeneous than starting boehmite powder was prepared by dispersing and gelling the boehmite powder. The transformation temperatures of boehmite powder, dry gel seeded with 0, 1, 3, 5 wt% $\alpha$-Al2O3, and ball milled gel were 1192$^{\circ}C$, 1184$^{\circ}C$, 1141$^{\circ}C$, 1119$^{\circ}C$, 1117$^{\circ}C$, and 1106$^{\circ}C$, respectively. Sintering behavior of dry gel without seed was similar to that of boehmite powder, but the sintered density of dry gel was improved as much as 10%~15% than boehmite powder. In the case of dry gel seeded with 5 wt% $\alpha$-Al2O3, sintering behavior was much improved. The relative density of the gel seeded with 5 wt% $\alpha$-Al2O3 was 96% when sintered at 140$0^{\circ}C$ for 1h. On the other hand, ball milling of the non-seeded sol for 48h resulted in the relative density of 97% when sintered at 130$0^{\circ}C$ for 1h. The size and amount of $\alpha$-Al2O3 particles added by ball milling were 0.107 ${\mu}{\textrm}{m}$ and 0.5 wt%.

• Korean Journal of Metals and Materials
• /
• v.49 no.1
• /
• pp.32-39
• /
• 2011

The present investigation was performed on the die compaction and sintering behavior of Fe micro-nano mixed powder with a mixed binder for powder injection molding. Warm die compaction of the feedstock for simulation of the static injection molding process was conducted using a cylindrical mold of 10 mm diameter at $100^{\circ}C$ under 4MPa. The die compaction of the micro-nanopowder feedstock underwent a uniform molding behavior showing a homogeneous distribution of nanopowders among the micropowders without porosity and distortion. After debinding, the powder compact maintained a uniform structure without crack and distortion, leading to a high green density of 64.2% corresponding to the initial powder loading of 65%. The sintering experiment showed that the micro-nanopowder compact underwent a near full and isotropic densification process during sintering. It was observed that the nanopowders effectively suppressed the growth of micropowder grains during densification process. Conclusively, the use of nanopowder for PIM feedstock might provide a new concept for processing a full density PIM parts with fine microstructure.

• Journal of the Korean Ceramic Society
• /
• v.31 no.7
• /
• pp.739-744
• /
• 1994

The B4C-C system was investigated to gain an understanding of the sintering behaviors of B4C. In order to get sintered density of 97% TD, sintering temperature of 225$0^{\circ}C$ was necessary. Since such a high temperature operation is actually difficult on a commercial basis, our objective was to examine the possibility of decreasing the sintering temperature by adding SiC. The addition of SiC in B4C increases the sintering rate about at 210$0^{\circ}C$ and results in a fine microstructure with more than 98% relative density on 55 wt% B4C-40wt% SiC-5 wt% C composition. The probability of liquid phase sintering was investigated, but the evidences of liquid phase formation were not observed with XRD and TEM observation. It was proposed that the addition of SiC and carbon to B4C reduce interface energy during sintering, which results in enhanced grain-boundary diffusion. Thus, the enhanced grain-boundary diffusion and retarded grain growth by SiC improve densification.

• Journal of the Korean Ceramic Society
• /
• v.33 no.3
• /
• pp.259-268
• /
• 1996

In the present study the effect of the addition of Fe on the pressureless and hot press sintering behavior was studied under Ar atmosphere. Pressureless sintering was performed 1900~220$0^{\circ}C$ under. Ar atmosphere. The addition of 1 wt% Fe was increased effectively of the sintered density. However it was impossible to obtain high density higher than 90%,. Zr-Fe-B compound in liquid phase was observed from the EDS and WDS analysis. It was considered that sinterability was enhanced due to the mass transfer through Fe based liquid phase formed at the sintering temperature. Hot pressing was performed at 1600~1$700^{\circ}C$ under Ar atmos-phere for 1 hr. It was possible obtain 95% relative density of ZrB2 specimen which is higher density at pressure-less sintering. It could be thought that ZrB2 particles was rearranged through liquid phase by applied pressure during initial stage of sintering.

• Journal of Ceramic Processing Research
• /
• v.19 no.6
• /
• pp.467-471
• /
• 2018

Diatomite powder, a naturally occurring porous raw material, was used to make ceramic materials with porosity and high strength. The sintering behavior of the diatomite powder at various sintering temperatures suggests that diatomite monoliths with a high porosity and strength can be prepared at $1100^{\circ}C$. The compressive strength of the sintered diatomite monoliths increased as the sintering temperature increased, and the molding pressure of 2 MPa and the binder of 18.6 wt.% were excellent. When the sintering temperature rises, the diatomite powder is melted, and its pores gradually disappear. SEM images show that strengthening begins with the formation of inter-particle bonds at a low sintering temperature.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.23 no.11
• /
• pp.875-879
• /
• 2010

In this study, we have characterized the roles of $Cr_2O_3$ on the sintering and electrical properties of ZnO. The densification and grain growth of Cr-doped ZnO (ZCr) system was mainly influenced by Cr contents. In the beginning of sintering, the densification of ZnO was retarded as reducing the Zni concentration in ZnO lattice with Cr doping. And the densification and grain growth of ZnO was more retarded due to a formation of spinel phase with increasing the Cr contents. ZCr system revealed varistor behavior with nonlinear coefficient $\alpha$ of 3~23 depending on the sintering temperature, implying double Schottky barrier formation on the grain boundary of ZnO. Especially the best varistor characteristics should be developed with 0.1~0.5 at% Cr contents and under $1100^{\circ}C$ in ZCr systems.

• Korean Journal of Materials Research
• /
• v.10 no.1
• /
• pp.83-89
• /
• 2000

$Si_3N_4$ powder with 2wt% $Al_2O_3$ and 6wt% $Y_2O_3$ additives was sintered by gas pressure sintering (GPS) technique. The variations in the unlubricated wear behavior depending on sintering time were compared. Tribological properties depending on sintering time are associated with fracture toughness as well as flexural strength of materials. When increasing the sintering time, the larger elongated grains were formed as a result of exaggerated grain growth. As the fracture toughness and flexural strength decreased, the wear volume increased. On the basis of these experimental results, the unlubricated wear properties of silicon nitride were found to be governed mostly by both the fracture toughness and the flexural strength of the material.

• Journal of Powder Materials
• /
• v.17 no.2
• /
• pp.101-106
• /
• 2010

In this study, we successfully synthesized a nano-sized lanthanum-modified lead-titanate (PLT) powder with a perovskite structure using a high-energy mechanochemical process (MCP). In addition, the sintering behavior of synthesized PLT nanopowder was investigated and the sintering temperature that can make the full dense PLT specimen decreased to below $1050^{\circ}C$ by using $Bi_2O_3$ powder as sintering agent. The pure PLT phase of perovskite structure was formed after MCP was conducted for 4 h and the average size of the particles was approximately 20 nm. After sintered at 1050 and $1150^{\circ}C$, the relative density of PLT was about 93.84 and 95.78%, respectively. The density of PLT increased with adding $Bi_2O_3$ and the specimen with the relative densitiy over 96% were fabricated below $1050^{\circ}C$ when 2 wt% of $Bi_2O_3$ was added.

• Journal of Powder Materials
• /
• v.10 no.3
• /
• pp.172-175
• /
• 2003

Mechanically-alloyed NiAl powder was sintered by Spark-Plasma Sintering (SPS) process. Densification and behavior mechanical property were determined from the experimental results and analysis ,such as changes in linear shrinkage, shrinkage rate, microstructure, and phase during sintering process, Victors hardness, and transver.ie-rupture-strength (TRS). Above 97% relative density was obtained after sintering at 115$0^{\circ}C$ for 5 min. Crystallite size determined by the Scherrer method was approximately 50 nm. From the X-ray diffraction analysis it was confirmed that the sintered bodies were composed mainly of NiAl phase together with Ni$_3$Al phase. Measured Vickers hardness and TRS value were 555$\pm$10 $H_v$ and 1393$\pm$75 MPa , respectively.