Kwang-Young Lim

Effects of Additive Composition and Content on Sintered Density and Compressive Strength of Cordierite Ceramics

Cordierite ceramics were fabricated via a reaction sintering process using ceramics-filled polysiloxane as a precursor for cordierite ceramics. In this study, the effects of the additive composition, additive content, and sintering temperature on the sintered density and compressive strength of cordierite ceramics have been investigated. The sintered densities of reaction-sintered cordierite ceramics containing TiO₂ as an additive were insensitive to the additive composition, additive content, and sintering temperature and ranged from 1.92 g/㎤ to 2.06 g/㎤. In contrast, the cordierite ceramics containing Y₂O₃ showed a maximal density of 2.21 g/㎤ at 5 wt% addition and at a sintering temperature of 1400℃. The compressive strength of cordierite ceramics showed the same tendency with the density. Typical compressive strength of cordierite ceramics containing 5 wt% Y₂O₃ as a sintering additive and sintered at 1400℃ was~480 ㎫.

Effect of Carbon Source on Porosity and Flexural Strength of Porous Self-Bonded Silicon Carbide Ceramics

Porous self-bonded silicon carbide (SBSC) ceramics were fabricated at temperatures ranging from 1700 to 1850℃ using SiC, silicon (Si), and three different carbon (C) sources, including carbon black, phenol resin, and xylene. The effects of the Si:C ratio and carbon source on porosity and strength were investigated as a function of sintering temperature. Porous SBSC ceramics fabricated from phenol resin showed higher porosity than the others. In contrast, porous SBSC ceramics fabricated from carbon black showed better strength than the others. Regardless of the carbon source, the porosity increased with decreasing the Si:C ratio whereas the strength increased with increasing the Si:C ratio.

Frit 함량이 다공질 Frit-Bonded 알루미나 세라믹스의 미세조직과 꺾임강도에 미치는 영향

Porous frit-bonded alumina ceramics were fabricated using alumina and frit as raw materials. The effects of frit content and sintering temperature on microstructure, porosity, and flexural strength were investigated at low temperature of 750~850℃. Increased addition of frit content or higher sintering temperature resulted in improved flexural strength of porous frit-bonded alumina ceramics. It was possible to produce frit-bonded alumina ceramics with porosities ranging from 35% to 40%. A maximum strength of 52㎫ was obtained at a porosity of ~38% when 90 wt% alumina and 10 wt% frit powders were used.

Effect of Aluminum Addition on Porosity and Flexural Strength of Porous Self-Bonded Silicon Carbide Ceramics

Porous self-bonded silicon carbide (SBSC) ceramics were fabricated at temperatures ranging from 1750 to 1850℃ using SiC, Si, C as starting materials and Al as an optional sintering additive. The effect of Al addition on the porosity and strength of the porous SBSC ceramics were investigated as functions of sintering temperature and Si:C ratio. The porosity increased with decreasing the Si:C ratio and increasing the sintering temperature. It was possible to fabricate SBSC ceramics with porosities ranging from 37% to 44% by adjusting the Si:C ratio and the sintering temperature. Addition of Al additive promoted densification and necking between SiC grains, resulting in improved strength. Typical flexural strengths of SBSC ceramics with and without Al addition were 44 ㎫ and 34㎫, respectively.

Effect of Si:C Ratio on Porosity and Flexural Strength of Porous Self-Bonded Silicon Carbide Ceramics

Porous self-bonded silicon carbide (SiC) ceramics were fabricated at temperatures ranging from 1750 to 1850℃ using SiC, silicon (Si), and carbon (C) powders as starting materials. The effect of the Si :C ratio on porosity and strength was investigated as a function of sintering temperature. It was possible to produce self-bonded SiC ceramics with porosities ranging from 36% to 43%. The porous ceramics showed a maximal porosity when the Si :C ratio was 2 : 1 regardless of the sintering temperature. In contrast, the maximum strength was obtained when the ratio was 5:1.

Fabrication of SiC Fiber-SiC Matrix Composites by Reaction Sintering

This paper presents a new process for producing SiC fiber-SiC matrix (SiC/SiC) composites by reaction sintering. The processing strategy for the fabrication of the SiC/SiC composites involves the following: (1) infiltration of the SiC fiber fabric using a slurry consisting of Si and C precursors, (2) stacking the slurry-infiltrated SiC fiber fabric at room temperature, (3) cross-linking the stacked composites, (4) pyrolysis of the stacked composites, and (5) hot-pressing of the pyrolyzed composites. It was possible to obtain dense SiC/SiC composites with relative densities of ＞ 96% and a typical flexural strength of ~400 ㎫.

Preparation and Sintering Characteristics of Gd-Doped CeO 2 Powder by Oxalate Co-Precipitation

GDC20() powder was synthesized by oxalate co-precipitation and milling and its thermal decomposition, phase formation, and sinterability were investigated. As-prepared precipitates were non-crystalline due to the milling process and completely decomposed at 400 The powder calcined at 800 for 2 h contained fine p]sty particles with an average size of 0.69 m. Attrition milling of the calcined powder for 2 h had a little milling effect, resulting in a slight decrease in the particle size to 0.45 m. The milled powder consisted of small spherical primary particles and some large particles, which had been agglomerated during calcination. Due to the excellent sinterability of the powder, sintering of the powder compacts for 4 h showed relative densities of 78.7% at 1000 and 97.8% at 1300, respectively. Densification was found to almost complete at temperature above 1200 and a dense and homogeneous microstructure was obtained. A rapid grain growth occurred between 1200 and 1300. Grains in 0.10.5 m sizes at 1200 grew to 0.22 m and their size distribution became broader at 1300.

Effect of the Processing Parameters on the Densification and Strength of 2D SiC Fiber-SiC Matrix Composites Fabricated by Slurry Infiltration and Stacking Process

2D SiC fiber-SiC (SiC/SiC) composites were fabricated via slurry infiltration and a stacking process. The effects of the additive composition and content in SiC slurries and the effect of the sintering time on the sintered density and strength of SiC/SiC composites were investigated. A slurry containing Al₂O₃-Y₂O₃-MgO (AYM) additives led to a higher strength compared to a slurry containing Al₂O₃-Y₂O₃-CaO (AYC) additives. The sintered density increased as the sintering time increased and showed a maximum (＞98%) at 4 h. In contrast, the flexural strength increased as the sintering time increased and showed a maximum (615 ㎫) at 6 h. The relative density and flexural strength increased as the additive content increased.

SOFC 음극 제조를 위한 NiO가 코팅된 YSZ 분말의 합성

NiO-coated YSZ powder was prepared using heterogeneous precipitation of Ni hydroxides on YSZ particle surface and high energy milling. The powders were characterized by TG/DTA, XRD, XPS, and SEM. Amorphous Ni precipitate completely decomposed into NiO at 500℃ and the growth of NiO crystallites was constrained by the core particles. Nanocrystalline NiO-coated YSZ core-shell structure powder could be obtained after calcination at 800℃ for 2 h. A core-shell powder compact, due to high sinterability, showed a near theoretical density at 1350℃. After reduction at 900℃, interpenetrating Ni-YSZ microstructure with very uniformly distributed fine Ni and YSZ grains and pores was observed. In contrast, the mechanically mixed oxide sample showed less uniform distribution of pores and larger discontinuous Ni particles as compared with the core-shell samples.