Materials Science Forum Vol. 724

Abstract: Biomorphic hydroxyapatite (Bio-HA) was fabricated using extracted beech wood that was impregnated with HA sol followed by sintering at 600~1300 °C for 2 hours. The extraction using boiling 5% ammonia solution was helpful to bring more pores to benefit to impregnation of the HA sol into wood templates. The weight changes of the exacted wood sample with HA gel, phase formation and microstructures evolution of resulting products were investigated by TGA, XRD and SEM. The main weight loss occurred below 600 °C. The biomorphic HA sintered at 1100~1300 °C were three dimensions and connective pores structure, in which the main tracheid pores with diameter of 60~80 μm derived from beech wood template and the small pores with 1~8 μm in the strut walls resulted from the sintering process. Bio-HA faithfully retained the woods porous structure. The method provided a novel candidate for fabricating a porous scaffold suitable for bone tissue engineering applications.

Abstract: Group B^I(Cu, Ag)-, B^II(Zn)- and B^III(Al, In)-doped Mg₂Si compounds were synthesized by solid state reaction and mechanical alloying. Electronic transport properties (Hall coefficient, carrier concentration and mobility) and thermoelectric properties (Seebeck coefficient, electrical conductivity, power factor, thermal conductivity and figure of merit) were examined. Mg₂Si powder was synthesized successfully by solid state reaction at 773 K for 6 h and doped by mechanical alloying for 24 h. It was fully consolidated by hot pressing at 1073 K for 1 h. The electrical conductivity increased by doping due to an increase in the carrier concentration. However, the thermal conductivity did not changed significantly by doping, which was due to much larger contribution of the lattice thermal conductivity over the electronic thermal conductivity. Group B^III(Al, In) elements were more effective to enhance the thermoelectric properties of Mg₂Si.

Abstract: Cell performance was measured for four types of Ni (40 vol%)-Gd-doped ceria (GDC) anode-supported solid oxide fuel cells with GDC electrolyte (40-120 μm thickness) of Ce_1-xGd_xO_2-x/2 compositions (x = 0.05, 0.1, 0.15 and 0.2) at 773-1073 K using a H₂ fuel. (La_0.8Sr_0.2)(Co_0.8Fe_0.2)O₃ cathode was printed on the GDC films. The open circuit voltage and maximum power density at 873-1073 K showed a maximum at x = 0.1. The maximum power density at x = 0.1 was 166 and 506 mW/cm² at 873 and 1073 K, respectively. The excess oxygen vacancy at x = 0.1-0.2, which does not contribute to the oxide ion conductivity, reacts with a H₂ fuel to form electrons (H₂ + V_O 2H⁺ + V_O^×, V_O^× V_O + 2e^-). This reaction reduces the cell performance.

Abstract: Two kinds of Ag-pastes were prepared for integrating the bulk Si solar cell. One is the Ag-paste mixed with Pb-based glass frit and the other is that mixed with Pb-free glass frit. The major components in the silver paste were 84 wt% Ag, 2 wt% glass frit, 11 wt% solvent of buthyl-cabitol acetate, and 2 wt% the other additives. After fabricating the Ag-pastes, they were coated on the SiN_x/n⁺/p^- stacks of a commercial mono-Si substrate. The solar cell efficiency was 17.6% in case of the silver paste mixed with Pb-based glass frit, which was one of the world-best records in the technology. By the way, the efficiency was 16.2% in the solar cell integrated with the silver paste mixed with Pb-free glass frit. The lower performance in the Pb-free Ag-paste was caused by the higher serial resistance and the lower shunt resistance in comparison with the Pb-containing Ag paste.

Abstract: ZnO nanorod/TiO₂ nanoparticle composite films were prepared by a sol-gel method, in which the slurry of TiO₂ nanoparticles (NPs) were penetrated into ZnO nanorod arrays. The agglomerate size of TiO₂ NPs was controlled with tetraethylammonium hydroxide. Lowering ZnO nanorod array density was an effective way to fill TiO₂ NPs in the space of ZnO nanorod array. The presence of ZnO and TiO₂ was confirmed by scanning electron microscopy and X-ray diffraction. Triblock copolymer (P123) was added as a template agent to obtain high specific surface area, and the solar cell performance was improved. However, the viscosity of the TiO₂ slurry was increased by addition of P123, and TiO₂ content in the composite film was reduced. Low concentration TiO₂ slurry was preferable to be penetrated into ZnO nanorod array and solar cell performance was further improved.

Abstract: Spherical carbon nanoparticles were synthesized by sol-gel polymerization of resorcinol and formaldehyde in the presence of CTAB(cetyltrimethyl ammonium bromide) and subsequent carbonization at 900 in N₂ atmosphere. It is found that the amount of CTAB, water and catalyst showed a significant impact on the morphology and size of carbon nanoparticles. The magnesia-carbon (MgO-C) bricks containing 1~4 wt% nanocarbon were prepared by adding various types of carbon black (CB), multi walled carbon nanotubes (CNT) and synthesized nanocarbon. The mechanical properties, oxidation resistance and corrosion resistance of the MgO-C brick in which the nanocarbon is added was investigated. The MgO-C refractories were characterized by Field Emission Scanning Electron Microscope (FE-SEM, MIRA II LMH), Cold Crush Strength (CCS).

Abstract: Membrane distillation (MD) is a special evaporation process to produce fresh water from seawater or contaminated water using membranes. MD has advantages over other evaporation technologies such as multi-stage flash vaporization (MSF) and multi-effect distillation (MED) due to its relatively low energy requirements, allowing the use of solar energy as its heat source. Nevertheless, lack of membrane materials for MD process hinders its practical implementation for desalination and water treatment. In this study, membranes made of carbon nanotube (CNT) are presented for MD. Flat sheet hydrophobic membranes made of polyvinylidene fluoride (PVDF) were selected as supports for bucky-paper membranes, allowing formation of CNT bucky-paper without chemical reactions. Laboratory-scale systems were used to evaluate their potential and performance in direct contact MD. Water permeability and salt rejection were analyzed for each case. D.I water and synthetic feed water were used for the lab-scale tests. It was demonstrated that the physical immobilization of CNT on a hydrophobic membrane changed led to an increase in vapor permeability while improving salt rejection.

Abstract: Sulfonated poly (diphenyl ether ketone sulfone) s, SPDPEKSs were successfully synthesized for proton exchange membranes (PEMs). Poly (diphenyl ether ketone sulfone) s, PDPEKSs were prepared by the polycondensation of 4,4'-sulfonyldiphenol with 1,2-bis (4-fluorobenzoyl)-3,6-diphenylbenzene (BFBDPB) and 4-fluorophenylsulfone respectively, at 210 °C using anhydrous potassium carbonate as catalyst in sulfolane. PDPEKSs were followed by sulfonation using chlorosulfonic acid and concentrated sulfuric acid at two step reactions. Different contents of sulfonated unit of SPDPEKS (25, 35, 45 mol% of BFBDPB) were studied by FT-IR, ¹H NMR spectroscopy, and thermogravimetric analysis (TGA). The ion exchange capacity (IEC), water uptake and proton conductivity of SPDPEKS were evaluated with increase of degree of sulfonation.

Abstract: Sulfonated poly (ethersulfone) s (S-PDHTPEs) were prepared from 4,4-(2,2-diphenylethenylidene) bisphenol (DHTPE), 4,4-sulfonyldiphenol, 4-fluorophenylsulfone using potassium carbonate, and followed sulfonation reaction with conc. sulfuric acid. DHTPE is a conjugated structure, which enables to form planar conformation between aromatic rings, and selectively sufonated on phenyl rings of polymer side chain. Composite membranes were prepared with copolymers and SiO₂ nanoparticles (20 nm, 4~10%wt). The composite membranes were cast from DMSO. A series of composite membranes structures and characteristic were evaluated by the ¹H-NMR spectroscopy, and thermal stabilities. The membranes were performed by ion exchange capacity (IEC), water uptake and proton conductivity as a function of degree of sulfonation.

Abstract: The effect of different factors, such as carbon fiber content, temperature, electrifying time and frequency, power density on the electrothermal properties of the composite papers with different carbon fiber content was researched. The results show that the resistivity of the composite papers decreases with the increasing of carbon fibers. The current-voltage relationship is in good conformity with the Ohm's law. The negative temperature coefficient and good reversibility are shown during the heated and cooled process of the papers. The resistance of the papers decreases gradually with electrifying time and trends to stable after several hours. On-off electrifying times on its resistance have little effect in the long term. The curve of power density and surface temperature shows a good linear behavior.