Designing, Processing and Properties of Advanced Engineering Materials

Volumes 449-452

doi: 10.4028/

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Authors: Dong Seok Seo, Hwan Kim, Jong Kook Lee
Abstract: Three types of calcium phosphate ceramics, i.e. tricalcium phosphate, biphasic calcium phosphate and near stoichiometric hydroxyapatite, were prepared by sintering at 1200oC for 2 h in air with moisture protection. Their dissolution processes were investigated by taking microstructural observations after immersion in distilled water for 3 or 7 days. It was found that the surface dissolution of the ceramics was initiated at grain boundaries and generated many separated grains. In case of the materials with high porosity, the residual pores on the surface appeared to be a primary defect site where the dissolution starts although the soluble compound was existed on the matrix.
Authors: J.S. Lee, K.H. Shin, Min Chul Shin, D.H. Cho, Hyung Seok Lee
Abstract: Porous filter was manufactured using cordierite powder and it was loaded with V2O5 catalyst by vacuum impregnation method. The removal efficiency of NOX and simultaneous removal efficiency of NOX /Dust were measured by passing NO and dust through catalystloaded ceramic filter. The cordierite porous filter had the apparent porosity of 61.6%, the compressive strength of 12.3 MPa and the pressure drop of 1200 Pa at the face velocity of 5 cm/sec, at 400oC. NOX removal efficiency of filter loaded only V2O5 catalyst was 80% and it could be improved up to 90% by the acid treatment (which increased specific surface area of filter elements); then this result is equal to the removal efficiency of the commercial V2O5/TiO2 catalyst, which was used at SCR(Selective Catalytic Reduction) process. Dust & NOX simultaneous removal efficiency of filter loaded V2O5 catalyst was about 99.6% of dust and 90% of NOX. Crack generated by thermal shock or pressure was not found. We found that catalytic cordierite filter is good candidate for simultaneous removal of particulate and hazardous gas from this result.
Authors: Jeong Won Kang, Ho Jung Hwang
Abstract: We have investigated the single-wall boron-, aluminum- and gallium-nitride nanotubes using atomistic simulations based on the Tersoff potential. The Tersoff potential for III-nitride effectively describes the properties of III-nitride nanotubes. Structures, energetic and nanomechanics of III-nitride nanotubes were investigated and compared with each other. Young’s moduli of III-N nanotubes were lower than that of CNT. Though the graphite-like sheet formation of AlN was very difficult, since the elastic energy per atom to curve the sheet into cylinder for AlN was very low, if graphite-like sheets of AlN were formed, the extra cost to produce the tubes would be very low
Authors: Se Young Choi, Il Seok Park, Deuk Yong Lee, Jung Suk Han, Dae Joon Kim
Abstract: Aqueous alumina tapes were prepared by a doctor blade using polyvinyl pyrrolidone (PVP) as a binder and gelatin and polyvinyl alcohol (PVA) as additional binders to improve drying rate and mechanical properties of the tapes containing PVP. As binder was prepared by mixing 89.5 wt% of PVP, 10 wt% of PVA, and 0.5 wt% of gelatin, tape properties were optimized showing complete drying in 3h, tensile strength of 1 MPa, and high flexibility. Marginal gap of all-ceramic dental crowns prepared using the tapes was about 56 µm indicating the tape cast alumina dental crowns are clinically applicable.
Authors: Ju-Woong Jang, Byung Soo Kim, Hak Kwan Kim, Deuk Yong Lee
Abstract: 16 different lanthanum-aluminosilicate glasses were prepared to evaluate the effect of alkalis (Na2O, K2O) and alkaline earths (MgO, CaO) on thermal expansion coefficients (CTEs) of the glasses. Analysis was performed with an aid of the Taguchi method and orthogonal arrays to elucidate four factor interactions between 4 two-level factors using two level L16(215) orthogonal arrays. The observed CTEs were in the range of 6.29×10-6 C-1 to 8.22×10-6 C-1. The addition of alkalis was more influential to CTE of the glass than that of alkaline earth, however, co-addition of the mixed alkalis was detrimental to CTEs of the glasses due to the crystallization caused by the mixed alkali effect. However, the highest strength of the glass infiltrated alumina composite was observed at a CTE of 6.4×10-6 C-1 due to the compressive stress caused by the thermal mismatch, indicating that CTE difference between the glass and the alumina should be above 1.0×10-6 C-1.
Authors: Dong Bok Lee, S.J. Park, Yun Soo Lim, Jae Chun Lee
Abstract: Carbon nanofibers were reacted with SiO vapor generated from a mixture of Si and SiO2 to produce silicon carbide nanofibers at 1350oC for 2 h under vacuum. The obtained SiC nanofibers with a diameter ranging 100~200 nm had the specific surface area as high as 124 m2/g. The SiC nanofibers were not oxidation resistant, showing nearly complete oxidation at 1000 oC after about 60 h in air, though the oxidation product was amorphous silica which was generally considered to be oxidation resistant. The poor oxidation resistance was attributed to the inherent nanoporous nature of the fibers resulted from the gas-solid reaction.
Authors: Min Seong Cho, Hyoung Jin Choi
Abstract: Composite particles (CIPMMA) of carbonyl iron (CI) and poly (methyl methacrylate) (PMMA) were prepared by a suspension polymerization method using CI dispersions in MMA monomer, and these were adopted as dispersed phase of magnetorheological (MR) fluids. The CIPMMA can resolve several problems of MR fluids having CI alone such as severe sedimentation and poor dispersion stability. Flow and viscelastic properties of the MR fluids were analyzed via a rotational rheometer equipped with a magnetic field supplier using measuring system of a parallel plate. The MR characteristics like yield stress were affected by the CI contents in the composite particles.
Authors: S.T. Lim, Hyoung Jin Choi
Abstract: Organically modified layered silicate was introduced into miscible poly(ethylene oxide) (PEO) / poly(methyl methacrylate) (PMMA) blends for the synthesis and characterization of polymer/clay nanocomposite through solvent casting method. As a part of our continuous efforts on the study of nanoscopic internal structures and changes of material properties caused by the presence of organically modified layered silicate, we systematically investigated the characteristic morphological changes and internal structures with scanning electron microscope (SEM) and transmission electron microscopy (TEM). Various factors such as clay concentration, thermal history, and shear history were employed to give rise to the changes of morphological and internal structures.
Authors: Noh Yu Kim, Hwan Seon Nah
Abstract: Acoustic impedance of aging epoxy coating in nuclear plant is measured for evaluation of the degradation of the epoxy coating using a new ultrasonic measurement technique that uses a specially designed conical acoustic lens to determine the reflection coefficient (reflectance) of the epoxy coating. Reflection waves measured at two different vertical positions slightly apart from each other are subtracted and used to calculate the acoustic impedance of the epoxy coating. Epoxy coated concrete specimens are fabricated and degraded artificially under accelerated aging conditions to determine the acoustic impedance of the films. Experimental results show that the acoustic impedance is very sensitive to the degradation of coating and can be applied to evaluate the quality of the epoxy coating quantitatively.
Authors: Sung Tag Oh, Yong Ho Choa, Young Do Kim
Abstract: An optimum route to fabricate the Al2O3/Cu nanocomposites with sound microstructure and improved mechanical properties was investigated. Three powder mixtures of Al2O3 and Cu, CuO or Cu-nitrate were used to obtain Al2O3/5 vol% Cu composites. Microstructural investigations for the composite from Al2O3/Cu-nitrate showed that fine Cu particles, about 150 nm in diameter, were homogeneously distributed within the Al2O3 matrix grains and at the grain boundaries. Fracture toughness of 4.8 MPam and strength of 953 MPa were measured for the Al2O3/5 vol% Cu nanocomposites prepared from Al2O3/Cu-nitrate mixture. The toughening and strengthening of the composites are explained by the crack bridging/deflection and the refinement of the microstructure, respectively.

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