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A dense gadolinia-doped ceria (GDC) interdiffusion barrier layer as thin as 300 nm was successfully fabricated on a rigid anode/electrolyte bilayer substrate using the chemical solution deposition (CSD) process for intermediate temperature solid oxide fuel cells (SOFCs). Drying-related macro-defects were removed by employing drying control chemical additives (DCCA), which effectively relieved drying stresses. The major process flaws caused by the constraining effects of the rigid substrate were completely eliminated by the addition of GDC nanoparticles into the chemical solution, which suppressed the generation of microstructural anisotropy by mitigating the predominant bi-axial substrate constraints. As a consequence, a thin film GDC interlayer was successfully deposited with a high volumetric density, effectively preventing the chemical interaction between the electrolyte and cathode during the fabrication process and subsequent operation. The cell test and microstructural analysis confirmed excellent electrochemical performance and structural and chemical stability. The CSD process presented in this paper is considered to be a promising technology for the practical preparation of GDC thin film barrier layers for intermediate temperature SOFCs based on the film quality, processing costs and potential for large-scale production.

An extremely thin bilayer electrolyte consisting of yttria-stabilized zirconia (YSZ) and gadolinia-doped ceria (GDC) is successfully fabricated on a sintered NiO-YSZ substrate. Major processing flaws are effectively eliminated by applying local constraints to YSZ nanoparticles, and excellent open circuit voltage and cell performance are demonstrated in a solid oxide fuel cell (SOFC) at intermediate operating temperatures.

A solvothermal method is described for preparing nanomaterials of titanium dioxide (TiO2) while controlling the growth of rod-shaped nanomaterials. Titanium (IV) isopropoxide (TTIP) and butyl ether were chosen as the precursor and solvent, respectively. Oleic acid and decanoic acid were used as the surfactant. TiO2 nanospherical particles and nano-rods were synthesized in mass quantities by adjusting the kind of surfactant, the concentration of the precursor, and the solvothermal reaction temperature. The synthesized TiO2 nanospherical particles and nanorods were uniform and transparent in the toluene. The TiO2 nanospherical particles were about 3.5 nm in size. The TiO2 nanospherical particles and nanorods were of a highly crystalline anatase structure. The direction of growth of the TiO2 nanorods was [001] and the band gap energy of the TiO2 nanorods, evaluated by optical absorption, was 3.34 eV.

The mechanism of apatite formation on the surface of novel PDMS modified SiO2-CaO- P2O5 hybrids is presented. The bioactive hybrids with different P2O5 content were synthesized by sol-gel method and soaked in the simulated body fluid (SBF) for different periods. The surface and the cross-section of the specimens were examined by use of Fourier transform infrared reflection spectroscopy, thin-film X-ray diffraction technique and scanning electron microscopy. The PDMS-SiO2-CaO-P2O5 hybrid containing 0.03 mole ratio of TEP(triethyl phosphate) / TEOS (tetraethoxysilane) exhibited faster apatite formation compared to P2O5-free hybrids. This composition resulted in the thickest apatite layer (~6µm) and this might be attributed to faster formation of the silica hydrogel on the surface of the P2O5-containing hybrids than on the surface of the P2O5-free hybrids. Resultingly, the apatite nucleation on the surface of the P2O5-containing hybrids is effectively induced by the hydrated silica at a lower degree of supersaturation. Changes in concentrations of the calcium, silicon and phosphorus in the SBF and the SEM-EDS line analysis depicting the variation of Si, Ca and P elements for the bulk, the interface and the apatite are reported. These were found to be quite correlative with each other. The rate of the concentration changes for the P2O5-containing hybrids is higher than that of the P2O5-free hybrids. The increases in the calcium and silicon concentrations are attributed to dissolution of the calcium and silicate ions from the hybrids, and the decrease in the phosphorus concentration is ascribed to formation of the amorphous calcium phosphate and crystalline apatite on the surface of hybrids by consuming the phosphate ion from the fluid.

Fourier transform infrared (FT-IR) and FT-Raman Spectroscopy have been utilized to characterize the structure of physical and chemical bonded ORMOSILs (organically modified silicates) and to compare with the physical properties, reported earlier. The classic and sono ORMOSILs were synthesized by sol–gel method via traditional- and sono-catalysis routes, respectively. The physical and chemical bonding is established by Poly(ethylene glycol) (PEG) and Poly(dimethoxysilane) (PDMS), respectively. Existence of band at 560 cm 1 (FT-IR) and 490 cm 1 (FT-Raman) for the sono and classic gels with 5–10 wt% of PEG indicates the presence of structural defect due to the four-membered siloxane rings. Application of long molecular PEG chain and PDMS increases this defect. Modification in the intensity and peak position of siloxane (Si–O–Si) bands is found correlative with the physical properties. The xerogels with 5–10 wt% of PEG possess a large number of residual surface silanol groups than the xerogels with long molecular PEG chains and PDMS and is found related with the m(OH) band at 3470 cm 1 . These results are attributed to the way of hydro

Nanophase silica-titania particles were prepared by two different synthetic routes, namely, sol–gel and hydrothermal processing. The crystallinity and crystallographic phases, particle size and surface area of the materials were controlled by varying the calcination temperature, and/or the ratio of Si to Ti. It was determined by XRD that the crystallite sizes of SiO2-TiO2 prepared by sol–gel and hydrothermal processing decreased from 11 to 6 nm and 12 to 9 nm, respectively, as the mole fraction of silica was increased from 0.1 to 0.4. It is proposed that the presence of the amorphous silica suppresses the growth of anatase TiO2 grains and their phase transformation to rutile. The photocatalytic decomposition rate of 1,4-dichlorobenzene (DCB) in aqueous solution with the sol–gel derived SiO2-TiO2 powder prepared at 750 °C was about 10 ± 5% higher than that observed with Degussa P25, whereas the SiO2-TiO2 samples prepared by hydrothermal processing at 250 °C showed a slightly lower decomposition rate than P25.

Donor doped BaTiO3 (n-BaTiO3) ceramics were fabricated by adding polyethylene glycol (PEG) at 20 wt %. The effects of reducing and oxidizing atmospheres on the PTCR characteristics of the porous n-BaTiO3 ceramics were investigated. The PTCR characteristics of the porous n-BaTiO3 ceramics is strongly affected by chemisorbed oxygen at the grain boundaries and are recovered as the atmosphere is changed from the reducing gas to oxidizing gas. The low room-temperature resistivity of the porous n-BaTiO3 ceramics in reducing atmospheres may be caused by the decrease in potential barrier height, which originates from an increase in the number of electrons owing to the desorption of chemisorbed oxygen atoms at the grain boundaries. In addition, the high room-temperature resistivity of the porous n-BaTiO3 ceramics in oxidizing atmospheres may be caused by the increase in potential barrier height, which results from the adsorption of chemisorbed oxygen atoms at the grain boundaries.

mole), are reported. BET, UV-visible spectroscopy and SEMwere used for characterizations. The increase in acid or base concentration increased the size of pores andaggregated silica particles. The samples with pH ≤ 2.5 were transparent and attributed to the small size of pores(~20 A) and silica particles. The samples with pH > 2.5 were translucent or opaque due to non-uniform poresystem formed by voids and large aggregated silica particles. The surface area was found a key factorcontrolling the interactions between the gel matrix and the dye. The OS samples with the highest dyeconcentration exhibited the minimal values of pore size, surface area and silica particle size, resulting in theconcentration-quenching phenomenon. Key Words : Physical properties, Microstructure, Organic dye, ORMOSILIntroductionThe organic dye doped ORMOSILs (organically modifiedsilicates) attract widespread interests in recent years due totheir wide application as gain media in laser materials, non-linear optical materials, photochemical hole burning,luminescence solar concentrator, chemical sensor, pH sensor,etc.

Poly(dimethylsiloxane) (PDMS) modified silica xerogels were prepared by two-step acid/base catalyzed sol-gel process. By keeping the acid amount and hydrolysis period in acidic environment fixed, and adding different amounts of base to the sol afterwards, attempts had been made to study the effect of the different amounts of base catalyst on the micro-structure and physical properties of the prepared ORMOSILs. DTA, SEM, BET, FTIR were performed to characterize the derived specimens. The microstructure and physical properties are greatly influenced by the amount of base added to the sol. With increasing base content the crystallite size and porosity increase and the pore size distribution takes a broad spectrum. Whereas, the glass transition temperature seems to decrease with increasing of base catalyst amount. This is explained in terms of the change in the relative amounts of hydrolysis and condensation reactions due to the addition of different amount of base catalyst, which predominantly influences the condensation reactions. The results are reported in this communication along with possible explanations behind the observations.

Organically modified silicates (ORMOSIL) have been prepared by incorporating poly(dimethylsiloxane) (PDMS) into silica xerogels, with tetraethyl orthosilicate (TEOS) as the starting inorganic material, by (i) one-step acid- or base-catalyzed process and (ii) two-step acid/base-catalyzed sol–gel process. The condensation between PDMS and TEOS have been studied to get an idea how experimental parameters control them by using thermal analysis (differential thermal analysis (DTA) and thermal gravimetric analysis (TGA)). It has been found that a base environment enhances the co-condensation between the PDMS and TEOS, whereas an acidic environment has more influence on the hydrolysis reactions. The results are reported in this communication along with possible explanations behind the observations.

†The formation temperature for the perovskite lead zirconate titanate [Pb(Zr,Ti)O 3, PZT] derived from sol-gel route was lowered by more than 100 o C with the addition of crystallographically suitable seed particles, such as barium titanate (BT) or PZT. We investigated the effect of seeding on the crystallization of perovskite phase and on the microstructure of the sol-gel derived PZT powder by varying the concentration, size and chemical species of seed particles. The phase transition as a function of temperature was monitored by DTA, XRD, and Raman spectroscopy, and the interface between the seed particle and grown PZT layer was analyzed by SEM and high resolution TEM techniques. It was found that both the heterogeneous and homogeneous nucleation contributes competitively in the formation of perovskite PZT grains.

An inorganic-organic hybrid system, silica-poly(ethylene glycol) songel is reported. This system was prepared via sol-gel method by varying varous processing variables. e.g. ultrasonic radiation time, gelling temperanture, PEG content and its molecular weight. Various experimental techniques wee employed to analyze the morphological, mechanical and optical properties of the system. The results were discussed in the light of existing theories. The sonogel system exhibited the common features of inorganic-organic hybrids. wt% PEG sonogel exhibited the morphological and optical properties superior to those reported earlier for the classic gels and found suitable for device applications.

Inorganic–organic hybrids or organically modified silicates (ORMOSILs), with tailorable optical and electrical properties depending on the inorganic and organic components chosen, processing conditions, etc., offer many new exciting properties that lead to different applications. In this study, tetraethoxysilane (TEOS) and poly(dimethylsiloxane) (PDMS) were chosen as the inorganic and organic components respectively, to prepare ORMOSIL matrix. Silanol-terminated PDMS can condense with oxide precursors to produce metal–O–Si bond and is known for its superior relaxation. The effects of H 2 O/TEOS ratio, PDMS molecular weight and different reaction schemes (i.e. reaction order) on the microstructures and mechanical properties of the SiO 2 –PDMS ORMOSILs have been studied. Attempts are made to explain the results in the light of presently available theories.

Doping of classical silicate glass prepared by sol–gel technique by Ag or other nanometer size metal particles have made a major stride in past decade. But studies of metallic particle incorporated organically modified silicates (ORMOSIL) are quite scarce. The present work attempts to study the effects of Ag doping on the structural and physical properties of poly(dimethylsiloxane) (PDMS) modified silica xerogels. The choice of tetraethoxysilane (TEOS) and PDMS as the starting inorganic and organic components, respectively, for the preparation of ORMOSIL was dictated by the similarity in their backbone structure (SiO). Ag nano particles were incorporated by two routes: (i) directly into the sol by adding calculated amount of AgNO 3 prior to gelation, and (ii) in this case preformed porous matrix was obtained first and then Ag doping was done by immersion of that matrix in AgNO 3 solution for several days and subsequent heat treatment. Microstructures (SEM, TEM, XRD), particle size distribution, infrared response (FTIR) and density have been studied. It was found that the Ag particles in the sample prepared by the second route were less prone to aggregation compared with that prepared using first route. The merits and demerits of the two methods have been discussed. It was observed that when exposed to humid air, the samples changed the optical state from transparency to opacity to various degrees depending on the amount of Ag incorporation. However, transparency could be brought back by treating the sample at a temperature above 300 °C. This phenomenon exhibits its potential to be used as humidity sensor and/or optical switches.

The effect of ultrasonic radiation is reported for silica-poly(ethylene glycol) system prepared without the solvent using sol-gel processing by varying various parameters such as ultrasonic irradiation time, PEG content and HCl/TEOS molar ratio. The property of sonogel is compared with classic gel which has been prepared with ethanol as a solvent by traditional sol-gel processing. SEM, BET, DTA-TGA, density and Vickers hardness measurements are carried out for analyzing the samples. The gelation time is found strongly dependent on radiation time, PEG content and pH value, and has been discussed on the basis of existing theories. The SiO₂-10 &20 wt% PEG sonogel exhibited superior optical, physical and gel properties as compared to the classic gel, hence, found suitable for device applications. The ultrasonic radiation increased the density and surface area, and also reduced the pore size which is well supported by the shift in the peak of DTA curve. The DTA thermogram was found similar to that of pure silica gel.

The purpose of the present work is to study the effect of silver (Ag) incorporation on the structural and physical properties of poly(dimethylsiloxane) (PDMS) modified silica xerogels. PDMS was chosen as the organic component because of its similarity of backbone structure (–Si–O–) with tetraethyl orthosilicate, the inorganic component of organically modified silicates. In the present work silver was incorporated by two routes: (i) directly in the sol and (ii) silver doping was done after preformed porous matrix was obtained. The microstructures, particle size distribution, infrared spectra, and optical coloration have been studied. The utility of two methods has been discussed. It was found that the particle size was much smaller compared with that of classical gels with dispersed Ag particles. For the indirect method of silver doping the particle size distribution was found to follow log-normal distribution function. Upon exposure to humid air the samples change optical state from transparency to opacit...

A promising candidate material for a H 2 permeable membrane is SiC due to its many unique properties. Ahydrogen-selective SiC membrane was successfully fabricated on the outer surface of an intermediate multilayer γ-Al 2 O 3 witha graded structure. The γ-Al 2 O 3 multilayer was formed on top of a macroporous α-Al 2 O 3 support by consecutively dipping intoa set of successive solutions containing boehmite sols of different particle sizes and then calcining. The boehmite sols wereprepared from an aluminum isopropoxide precursor and heated to 80 o C with high speed stirring for 24 hrs to hydrolyze theprecursor. Then the solutions were refluxed at 92 o C for 20 hrs to form a boehmite precipitate. The particle size of the boehmitesols was controlled according to various experimental parameters, such as acid types and acid concentrations. The topmost SiClayer was formed on top of the intermediate γ-Al 2 O 3 by pyrolysis of a SiC precursor, polycarbosilane, in an Ar atmosphere. Theresulting amorphous SiC-on-Al