Materials Science Forum Vols. 544-545

Abstract: We have studied the effect of pH on the dispersion stability of aqueous suspensions of Fe2O3 powders over a wide pH range in the presence of the poly (acrylic acid) (PAA). In order to investigate the ionization behavior of the PAA, pH of PAA solutions was measured. Sedimentation and zeta-potential measurements were conducted on aqueous Fe2O3 suspensions to characterize the dispersion stability of the suspensions. The PAA was ionized over a wide pH range and the quantity of ionization was abruptly increased at pH > 10. Thus, the dispersion of the Fe2O3 powders was observed even in acidic solutions and the dispersion stability of the suspensions increased as pH of the solutions increased. The magnitude of zeta-potential values increased with increasing pH.

Abstract: In this work we have evaluated the effect of platinum (Pt) pre-coating on microstructure evolution of MCrAlY coating during isothermal oxidation, to improve high temperature oxidation and corrosion resistance of the nickel-based superalloy MAR M247-DS. Pt was deposited on the superalloy by electroplating before the MCrAlY coating by a vacuum plasma spray, which was compared to the superalloy without Pt pre-coating. The samples were subjected to isothermal oxidation in a box furnace at 1100°C for 25–150 hrs. The weight gain and loss caused by the oxidation of samples was recorded, and the variation of surface layer and interface morphology were observed before and after the oxidation tests. The length decrement of cross section is remarkably low on according to the precipitation of (Ni,Pt)Al phase by Pt pre-coating. Also, the amount of voids at interface between the coating and the superalloy, which would be introduced as a processing defect, is reduced by Pt pre-coating.

Abstract: The enhancement of physical properties of porous honeycomb filter for air purification was investigated using cordierite with the addition of pore former and zirconia additive. Because cordierite honeycomb has porous body, binder formulation was varied using graphite for a pore forming agent as well as lubricating agent during the extrusion process. Also, the effect of zirconia additives on the resultant physical properties of honeycomb filter such as porosity, thermal expansion coefficient and mechanical strength was investigated.

Abstract: Influence of nitrogen and oxygen annealing atmospheres on the carrier concentration, carrier mobility, electrical resistivity and PL characteristics as well as the crystallinity of ZnO films deposited on sapphire substrates by atomic layer deposition (ALD) were compared. X-ray diffraction (XRD) and photoluminescence (PL) analyses, and Hall measurement were performed to investigate the crystallinity, optical properties and electrical properties of the ZnO thin films, respectively. The UV emission intensity for oxygen annealing is stronger than that for nitrogen annealing in the case of annealing at 600°C, but the difference decreases with the Increase of annealing temperature. The strongest UV emission is obtained by oxygen annealing at 800°C. However, from the viewpoint of electrical resistivity annealing at 1,000°C in either an oxygen or a nitrogen atmosphere is more desirable. Taking both the PL and electrical properties into consideration it may be concluded that optimum annealing condition for ZnO thin films grown on the sapphire substrate by ALD is an annealing temperature of 900°C and an annealing atmosphere of oxygen although the effects of annealing atmosphere on the optical and electrical properties are not so significant.

Abstract: The purpose of this work is to influence of CaO concentrations of 5.0 wt.% and 10.0 wt.%, slurry feeding rate of 200~400
/min, rotating rate of drum of 5,000 and 10,000 rpm, inlet and outlet temperature on the synthesis of Ca(OH)2 powder, and the synthesis of precipitated calcium carbonate by carbonation process using Ca(OH)2 prepared by spray drying method. As the feeding rate of slurry was increased, the particle size of Ca(OH)2 was decreased. Regardless of rotating rate of drum, when the concentration of CaO was 5.0 wt.% and 10.0 wt.%, the morphology of Ca(OH)2 showed spherical shape of 10~30 μm and 20~60 μm, respectively. The specific surface area of synthesized Ca(OH)2 was 27~30 m2/g. When the initial reaction temperature was 11 °C and 30 °C, the shape and particle size of precipitated calcium carbonate synthesized in the carbonation process showed the rectangular shape of 0.1~0.4 μm and the spindle shape of 0.5~1.0 μm, respectively.

Abstract: 0.03Pb(Sb0.5Nb0.5)O3-0.03Pb(Mn1/3Nb2/3)O3-(0.94-x)PbTiO3-xPbZrO3 ceramics doped with Y2O3 were synthesized by conventional bulk ceramic processing technique. Phases analysis, microstructures and piezoelectric properties were investigated as a function of Y2O3 contents (0.03, 0.05, 0.1 0.3, 0.5 and 0.7 wt.%). Microstructures and phases information were characterized using a scanning electron microscope (SEM) and an X-ray diffractometer (XRD). Relative dielectric constant (K33 T) and coupling factor (kp) were obtained from the resonance measurement method. Both K33 T and kp were shown to reach to the maximum at 0.1wt.% Y2O3. In order to evaluate the stability of resonance frequency and effective electromechanical coupling factor (Keff) as a function of Y2O3 contents under strong electric field, the variation of resonance and anti-resonance frequency were also measured using a high voltage frequency response analyzer(FRA5096) under various alternating electric fields from 10V/mm to 80V/mm. It was shown that the effective electromechanical coupling factor was stabilized along with increasing Y2O3 contents.

Abstract: A novel organic/inorganic composite material which can work as a pressure sensor has been synthesized. This composite basically contains nano-sized carbon particles as conductive filler into an elastomer matrix to achieve pressure sensitive function. The superior pressure sensitive effect was showed at 0.88vol% of carbon particles while in the previous study the micro-sized carbon particle was required above 30vol%. In addition, nano-sized silica particles were added to reinforce electrical insulation properties and to improve the pressure sensing reliability of the composite. The addition of the surface modified silica improved better both the sensing performance and the mechanical strength than the composite containing non-modified silica particles. These polymer-based sensors have economical advantage due to low cost production regardless of the high performance.

Abstract: P-type thermoelectric material Si0.8Ge0.2 was fabricated by mechanical alloying(MA) and Hot-Press Process(HP) The effect of Boron(0.25~2wt%) addition on the thermoelectric properties of p-type Si0.8Ge0.2 alloy was reported. Experiments showed that the electrical conductivity decreased with Boron content at temperature ranging from 500K to 1250K. The carrier concentration measured by the Hall effect measurement also decreased as a function of doping level. With increasing temperature, the Seebeck coefficient and the power factor increased with boron content. Based on measured results, the Figure of Merit (Z) value of 0.5 wt% Si0.8Ge0.2 alloy increased with the small addition of Boron, and reached maximum rapidly; the Z value was 0.9×10-3/K, the highest value among the prepared alloys.

Abstract: In this work, we report on the fabrication process of alumina (Al2O3) microtubes using carbon fibers and aluminum/alumina (Al/Al2O3) mixed powder via a solid-vapor (SV) reaction. Al and Al2O3 (α-Al2O3) were mixed in a 1:1 molar ratio, and heated to generate an AlO vapor. The carbon fibers were heat-treated in the pre-carburized Al2O3 crucible at 1400°C for 9h with a heating rate of 5°C/min in flowing argon (Ar) gas at 200 ml/min. Any carbon residues remaining in the core after the heat treatment at 1400°C were burned off by subsequent calcination at 700°C for 3 h in air. A post-heat treatment was conducted to convert the product to Al2O3. As a result, Al2O3 microtubes are successfully synthesized via the SV reaction between carbon fibers and Al/Al2O3 mixed powder. The TGA study shows that the AlO vapor is generated at temperatures above 750°C. As the calcination temperature increases, carbon residues and Al4C3 peaks disappear in XRD patterns. Al2O3 microtubes are synthesized at 1200°C, and show thinner wall thickness and undulating outer and inner surfaces arising from the partial decomposition of Al2O3 microtubes.

Abstract: The organic-inorganic field effect transistors (OIFETs) with ZnS active layer were fabricated on the ITO/glass substrate using cross-linked PVP (poly-4-vinylphenol) as a gate insulator. ZnS semiconductor films were prepared by the atomic layer deposition method. In the case of cross-linked PVP film, the leakage current and capacitance were about 1× 10-8 A and 12 nF/cm2, showing good gate insulation property. The carrier concentration and mobility of ZnS film deposited on SiO2/Si wafer was found to be -9.4×1015 cm-3 and 49.0 cm2/ V·sec, respectively. For the OIFET devices with ITO/PVP/ZnS/Ti:Au structure, the carrier mobility was about 1.9 cm2/V·sec. From the AFM images, lower mobility in the OIFET device compared with ZnS film on SiO2/Si substrate may be attributed to a rough surface morphology of ZnS film.