In-Hyuck Song

The effect of a dilution agent on the dipping exothermic reaction process for fabricating a high-volume TiC-reinforced aluminum composite

Abstract A synthesis of in situ formed TiC/Al composites utilizing the reaction between molten aluminum and preforms consisting of Ti, C, Al and TiC powder was studied. The addition of TiC powder as a dilution agent controlled the explosive exothermic reaction and played a key role in the homogeneous distribution of reinforcement.

Low Temperature Processing and Properties of Porous Frit-Bonded SiC Ceramics

Porous frit-bonded SiC ceramics were successfully prepared at a temperature as low as 800 o C from SiC, frit, and microbeads (glass or polymer). The effects of SiC starting particle size and microbead addition on microstructure, porosity, and flexural strength were investigated. The addition of hollow glass microbead improved the strength of frit-bonded SiC ceramics without the loss of porosity by acting additional binder phase between SiC grains. The 65 μm-sized SiC resulted in lower porosity and higher strength than 50 μmsized SiC because of higher packing density. Typical flexural strengths of frit-bonded SiC were 23 MPa at 46% porosity and 19 MPa at 49% porosity.

Investigation of Ti3AlC2 in the in situ TiC–Al composite prepared by the exothermic reaction process in liquid aluminum

Abstract The synthesis of in situ formed TiC–Al composites utilizing the reaction between molten aluminum and preforms consisting of Ti, C and Al powders was studied. Whisker-shaped Ti 3 AlC 2 as an intermediate phase was clearly observed in the in situ TiC–Al composite fabricated by the combustion-wave arresting technique. It was the first time to observe Ti 3 AlC 2 with the whisker shape during the reaction sequences of the Ti–C–Al system. In addition, the formation mechanism of Ti 3 AlC 2 was suggested in this study.

Synthesis of Microcellular Cordierite Ceramics Derived from a Preceramic Polymer

In this study, a novel-processing route for producing microcellular cordierite ceramics has been developed. The proposed strategy for making the microcellular cordierite ceramics involves three steps: (ⅰ) fabricating ceramic-filled preceramic foams by heating a mixture of polysiloxane, expandable microspheres, talc, and alumina in a mold, (ⅱ) cross-linking the foamed body, and (ⅲ) transforming the body into microcellular cordierite ceramics by sintering. Cu jig was used for near net shaping in the foaming step. The experimental variables such as the shape of foaming jig and the content of expendable microsphere were investigated. By controlling the content of expendable microsphere, it was possible to make the porous cordierite ceramics with cell density of ~1.0×10? cells/㎤.

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.

Microstructure and Permeability Property of Si Bonded Porous SiC with Variations in the Carbon Content

The achievement of high gas permeability is a key factor in the development of porous SiC ceramics for applications of hot gas filter, vacuum chuck, and air spindle. However, few reports on the gas permeability of porous SiC ceramics can be found in the literature. In this paper, porous SiC ceramics were fabricated at temperatures ranging from 1600℃ to 1800℃ using the mixing powders of SiC, silicon, carbon and boron as starting materials. In some samples, expanded hollow microspheres as a pore former were used to make a cellular pore structure. It was possible to produce Si bonded SiC ceramics with porosities ranging from 42% to 55%. The maximum bending strength was 58㎫ for the carbon content of 0.2 wt% and sintering temperature of 1700℃. The increase of air permeability was accelerated by addition of hollow microsphere as a pore former.

CERAMIC MEMBRANES PREPARED FROM A SILICATE AND CLAY-MINERAL MIXTURE FOR TREATMENT OF OILY WASTEWATER

The application of ceramic membranes is limited by the high cost of raw materials and the sintering process at high temperatures. To overcome these drawbacks, the present study investigated both the preparation of ceramic membranes using cost-effective raw materials and the possibility of recycling the membranes for the treatment of oily wastewater. Ceramic membranes with a pore size of 0.29–0.67 μm were prepared successfully at temperatures as low as 1000–1100°C by a simple pressing route using lowcost base materials including diatomite, kaolin, bentonite, talc, sodium borate, and barium carbonate. The typical steady-state flux, fouling resistance, and oil-rejection rate of the low-cost virgin membranes sintered at 1000°C were 2.5 × 10−5 m3m−2s−1 at 303 kPa, 63.5%, and 84.1%, respectively, with a feed oil concentration of 600 mg/L. A simple burn-out process of the used membranes at 600°C in air resulted in >95% recovery of the specific surface area (SSA) of the virgin membranes, a significantly increased steady-state flux, decreased fouling resistance, and increased oil-rejection rate. The typical steady-state flux, fouling resistance, and oil-rejection rate of the low-cost ceramic membrane sintered at 1000°C and subsequently heat treated at 600°C for 1 h in air after the first filtration were 5.4 × 10−5 m3m−2s−1 at 303 kPa, 27.1%, and 92.9%, respectively, with a feed oil concentration of 600 mg/L. The present results suggest that the low-cost ceramic membranes used for oily wastewater filtration can be recycled by simple heat-treatment at 600°C in air. As the fouling resistance of the low-cost ceramic membranes decreased with a decrease in pore size, the preferred pore size of the membranes for oily wastewater filtration is <0.4 μm.

Effect of Process Conditions on the Microstructure of Particle-Stabilized Al 2 O 3 Foam

foam is an important engineering material because of its exceptional high-temperature stability, low thermal conductivity, good wear resistance, and stability in hostile chemical environment. In this work, foams were designed to control the microstructure, porosity, and cell size by varying different parameters such as the amount of amphiphile, solid loading, and stirring speed. Particle stabilized direct foaming technique was used and the particles were partially hydrophobized upon the adsorption of valeric acid on particles surface. The foam stability was drastically improved when these particles were irreversibly adsorbed at the air/water interface. However, there is still considerable ambiguity with regard to the effect of process parameters on the microstructure of particle-stabilized foam. In this study, the foam with open and closed-cell structure, cell size ranging from to having single strut wall and porosity from 75% to 93% were successfully fabricated by sintering at for 2 h in air.

The Synthesis and Pore Property of Hydrogen Membranes Derived from Polysilazane as Inorganic Polymer

We investigated the pore properties of inorganic membranes applied for hydrogen separation industry. Inorganic membranes were derived from polysilazanes. The thermal reactions involved were studied using thermogravimetry(TG) and IR spectroscopy(FTIR) of the solids. To determine the thermal effect of pore properties, polysilazanes were pyrolysed in inert atmosphere. Pore volume and BET surface area showed the maximum value at a pyrolysis temperature of 500℃. For amorphous SiCN membrane derived from polysilazanes, selectivity of H₂/N₂ was 4.81 at 600℃.

Characterization of Pore Structures for Porous Sintered Reaction-Bonded Silicon Nitrides with Varied Pore-Former Content

The effect of pore former content on both porosity and pore structure was investigated for porous sintered reaction-bonded silicon nitrides (SRBSNs). A spherical PMMA with d 50 =8 μm was employed as a pore-former. Its amount ranged from 0 to 30 part. Porous SRBSNs were fabricated by post-sintering at various temperatures where the porosity was controlled at 12~52%. The strong tendency of increasing porosity with PMMA content and decreasing porosity with sintering temperature was observed. Measured pore-channel diameter increased (0.3→1.1 μm) with both PMMA content and sintering temperature.