Papers by Author: Doo Won Seo

Abstract: Silicon nitride ceramics were prepared by new nitrided pressureless sintering (NPS) process in this study. The microstructures, strengths and thermal properties of the NPS silicon nitride ceramics containing three types of Al2O3 and Y2O3 sintering additives were investigated. Additionally, we have investigated the effect of silicon metal contents changing with 0, 5, 10, 15 and 20 wt% in each composition. The silicon nitride was successfully densified using NPS process, particularly at the starting composition of 5 wt.% Al2O3, 5 wt.% Y2O3, and 5 wt.% Si addition. The maximum flexural strengths and relative densities of these specimens were 500 MPa and 98%, respectively. The flexural strength of sintered specimens after the thermal shock test between 30oC and 1300oC for 20,000 cycles was maintained with the original laboratory strength of 500MPa by low thermal expansion coefficient, 2.9 × 10-6/oC, and high thermal conductivity, 28 W/m⋅oC.

Abstract: Two different types of carbon fibre bundles were used for filament winding to obtain C/C preforms. C/C-SiC composites were produced from the C/C preforms by a silicon melt infiltration technique. The effect of the type of carbon fibre bundle on the mechanical and thermal properties of the resultant C/C-SiC composites was compared. The spun fiber preform yields C/C-SiC composites of better mechanical properties than the unidirectional continuous fiber preform. The strength of the composites from the SFP was 1.8 times higher than that from the CFP. The flexural strength and the O-ring strength of the composites from the SFP with a density of 2.35 g/cm3 were about 160 MPa and 170 MPa, respectively.

Abstract: Strength degradations of porous silicon carbide hot gas filters bonded with clay and calcium carbonate are investigated in the simulated condition of the pressurized fluidized bed combustion (PFBC). Thermal cycling, static fatigue, thermal shock, and hot corrosion tests are conducted to differentiate the independent parameter that affects the strength degradation during the filtration using silicon carbide filter in PFBC condition. The results indicate that hot corrosive gas mainly causes the strength reduction because of the degradation of grain boundary region.

Abstract: The Ministry of Commerce, Industry and Energy has contracted with the KIER including the ceramics company to localize of the ceramic heat exchanger tubes and its components. The basic objective of this paper is to develop a ceramic formulation and process which would yield a cost-effective and long-life Si/SiC tube materials by extrusion and reaction sintering process. Thus,KIER is currently developed and localized heat exchanger tubes with 40mm out diameter, 1500mm length. This paper was tested the mechanical and thermal properties of the localized Si/SiC tubes obtained from reaction sintering. Also, the effect of energy savings of the heat exchanger after exposure to forging furnace with hot corrosive environment was investigated.

Abstract: Surface modification effects have been investigated for perovskite-type mixed ionic-electronic conductors. As the mixed conducting oxides show both ionic and electronic conductivity, these can be applied as oxygen permeable membranes. We have coated surfaces of the perovskite-type mixed conductors, LaSrCoFeO3 and LaSrGaFeO3, with LaSrCoO3 and investigated the effects on oxygen permeability. Enhanced oxygen permeability was achieved when the LaSrGaFeO3 membrane was surface-modified with LaSrCoO3. However, there was no effect on oxygen permeability of LaSrCoFeO3 even when the surface of which was modified. The morphological factors related with electrochemical reactions have also been discussed