Hai-Doo Kim

Processing of closed-cell silicon oxycarbide foams from a preceramic polymer

A novel processing route for fabricating closed-cell ceramic foams has been developed. The strategy for making the ceramic foams involves: (i) forming some shapes using a mixture of preceramic polymer and expandable microspheres by a conventional ceramic forming method, (ii) foaming the compact by heating, (iii) cross-linking the foamed body, and (iv) transforming the foamed body into ceramic foams by pyrolysis. By controlling the microsphere content and the pyrolysis temperature, it was possible to adjust the porosity ranging from 56 to 85%.

Fabrication of porous preceramic polymers using carbon dioxide

Porous materials have a unique set of properties— low density, low thermal conductivity, high permeability, high surface area, high thermal shock resistance, high specific strength and high resistance to chemical corrosion—which make them good candidates for both structural and functional applications, such as thermal insulators, lightweight structural components, catalysts, absorbents, and filters [1–3]. The properties of porous materials are influenced by their relative density and the morphology, i.e., the size and distribution of the pores. The porosity characteristics can be varied in a wide range of values depending on the fabrication method [2]. Various processing routes have been proposed for the production of porous ceramics: (1) the immersion of an open-cell polymeric foam into a ceramic slurry and subsequent pressureless

Fabrication of biaxially textured Ni tape for YBCO coated conductor by electrodeposition

Abstract Electrodeposition process under the magnetic field has been investigated to search for simple and economical process in order to produce a biaxially textured Ni tape. The crystal orientations of electrodeposited Ni films were measured by means of X-ray pole figure, ω -scan and φ -scan methods. The texture of electrodeposited Ni film was changed from uniaxial (fiber texture) to biaxial when it was deposited in the presence of magnetic field. Biaxially textured Ni film showed cube texture with good out-of-plane (

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.

Porosity Control of Porous Zirconia Ceramics

A simple pressing process using zirconia and microbead for fabricating porous zirconia ceramics is demonstrated. Effects of microbead content and sintering temperature on microstructure, porosity, compressive and flexural strengths were investigated in the processing of porous zirconia ceramics using microbead as a pore former. By controlling the microbead content and the sintering temperature, it was possible to produce porous zirconia ceramics with porosities ranging from 43% to 70%. Typical compressive and flexural strength values at ~50% porosity were ~150㎫ and ~35㎫, respectively.

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.

Alloying effect of Ag sheath on microstructure and superconducting properties of Bi-2223/Ag tape

Abstract The effect of Cu and Pb addition to Ag sheath on microstructure and superconducting properties was investigated in Bi-2223/Ag composite. The use of Ag-Cu(2.5 and 5% Cu) alloys as sheath materials improved oxide alignment exhibiting good workability and mechanical strength, while no marked deterioration of superconductivity was observed.

Effect of Template Size Ratio on Porosity and Strength of Porous Zirconia Ceramics

Effect of template size ratio on porosity and mechanical properties of porous zirconia ceramics were investigated using two different size (~8 μm and ~50 μm in diameter) of polymethyl methacrylate-coethylene glycol dimethacrylate (PMMA) microbeads as sacrificial templates. Porosity of the porous zirconia ceramics increased with decreasing the template size ratio (8 μm:50 μm) whereas the compressive and flexural strengths of the porous zirconia ceramics increased with increasing the template size ratio. By controlling the template size ratio, sintering temperature and sintering time, it was possible to produce porous zirconia ceramics with porosities ranging from 57% to 69%. Typical flexural and compressive strength values of porous zirconia ceramics with ~60% porosity were~37MPa and ~85MPa, respectively.

Influence of Cu addition on microstructure and transport properties in MgB/sub 2/ tapes

Stainless steel sheathed MgB/sub 2/ tapes with Cu addition were fabricated by PIT method. The influence of Cu content on microstructure and the critical-current density (J/sub c/) of the tapes has been studied. The J/sub c/ value of MgB/sub 2/ tapes was increased from 1500 A/cm/sup 2/ to 4500 A/cm/sup 2/ at 4.2 K and 5 T due to Cu addition. J/sub c/-B curves show enhancement in J/sub c/(B), which suggests that the microstructure and transport properties of MgB/sub 2/ have been improved with Cu addition.

Synthesis of SiAlON Ceramics with Novel Magnetic Properties

This paper presents a study on the magnetic behaviour of selected doped SiAlONs with various compositions including Y, Yb, Sm, Gd, and Er. The resulting crystalline phases were confirmed by X-ray diffraction. The magnetic hysteresis data for the samples were collected at room temperature using a vibrating sample magnetometer. The study revealed that doped SiAlONs experience an appreciable level of magnetic hysteresis. Although the parameters corresponding to hysteresis loops in doped SiAlONs are less than those of common ferrites, their magnetic properties of SiAlONs may open up new potential areas of application as the host SiAlON ceramics have excellent structural properties.