Complexing Sol Gel Process Research Articles

Self-Assembled Triple (H+/O2-/e-) Conducting Nanocomposite of Ba-Co-Ce-Y-O into an Electrolyte for Semiconductor Ionic Fuel Cells.

Triple (H+/O2−/e−) conducting oxides (TCOs) have been extensively investigated as the most promising cathode materials for solid oxide fuel cells (SOFCs) because of their excellent catalytic activity for oxygen reduction reaction (ORR) and fast proton transport. However, here we report a stable twin-perovskite nanocomposite Ba-Co-Ce-Y-O (BCCY) with triple conducting properties as a conducting accelerator in semiconductor ionic fuel cells (SIFCs) electrolytes. Self-assembled BCCY nanocomposite is prepared through a complexing sol–gel process. The composite consists of a cubic perovskite (Pm-3m) phase of BaCo0.9Ce0.01Y0.09O3-δ and a rhombohedral perovskite (R-3c) phase of BaCe0.78Y0.22O3-δ. A new semiconducting–ionic conducting composite electrolyte is prepared for SIFCs by the combination of BCCY and CeO2 (BCCY-CeO2). The fuel cell with the prepared electrolyte (400 μm in thickness) can deliver a remarkable peak power density of 1140 mW·cm−2 with a high open circuit voltage (OCV) of 1.15 V at 550 °C. The interface band energy alignment is employed to explain the suppression of electronic conduction in the electrolyte. The hybrid H+/O2− ions transport along the surfaces or grain boundaries is identified as a new way of ion conduction. The comprehensive analysis of the electrochemical properties indicates that BCCY can be applied in electrolyte, and has shown tremendous potential to improve ionic conductivity and electrochemical performance.

Preparation by the double extraction process with preliminary neutron irradiation of yttria or calcia stabilised cubic zirconium dioxide microspheres

A modern approach to nuclear energy involves reprocessing like transmutations of spent nuclear fuel products to reduce their radiotoxicity and time needed for their storage. For this purpose, they are immobilized in inert matrices made of zirconia and can be "burned" in fast neutron reactor or Accelerator Driven System. These matrices in spherical form can be obtained by sol-gel process. The paper presents a method of microspheres fabrication based on the combined Complex Sol-Gel Process and double extraction process consisting in the preparation of zirconium-ascorbate sol and simultaneous extraction of water and nitrates. The procedure allows obtaining gel microspheres with a diameter of 50 μm, which after heat treatment are processed into the final product. The synthesis of zirconia microspheres with Yttrium by internal gelation process is well known for over a decade now. However, the explanation and characterization of synthesis of such material by extraction of water process is rarely found. Parameters such as: pH, viscosity, shape, sphericity and crystal structure have been determined for synthesized products and semi-products. In addition, preliminary research consisting in irradiation of the obtained materials in fast and thermal neutron flux was carried out. The obtained results are presented and described in this work.

Microspheres and Pellets of UO2 Prepared Via ADU by Complex Sol-Gel Process and ICHTJ Process

Microspheres and Pellets of UO2 Prepared Via ADU by Complex Sol-Gel Process and ICHTJ Process

Synthesis and Characterization of Zr Doped BaCeO3 by Citrate-EDTA Complexing Sol-Gel Process for Solid Oxide Fuel Cell

Synthesis and Characterization of Zr Doped BaCeO3 by Citrate-EDTA Complexing Sol-Gel Process for Solid Oxide Fuel Cell

Citrate complexing sol–gel process of lead-free (K,Na)NbO3 ferroelectric films

The citrate complexing sol–gel process to fabricate lead-free (K,[Formula: see text]Na)NbO3 ferroelectric thin films was studied. Soluble niobium source of niobium–citric acid (Nb–CA) solution was utilized as a raw material to synthesize (K,[Formula: see text]Na)NbO3 thin films, by pyrolyzing at 450–550[Formula: see text]C and annealing at 650[Formula: see text]C. The film pyrolyzed at 450[Formula: see text]C shows poor crystallization with porous morphology, whereas the film pyrolyzed at 550[Formula: see text]C appear to be well-crystallized and denser, and the ferroelectricity was also proved by the [Formula: see text]–[Formula: see text] hysteresis loop measurement.

The Complex Sol–Gel Process for producing small ThO2 microspheres

Thorium based fuels offer several benefits compared to uranium based fuels thus they might be an attractive alternative to conventional fuel types. This study is devoted to the synthesis and the characterization of small thorium dioxide microspheres (Ø <50 μm). Their application involves using powder-free process, called the Complex Sol–Gel Process. The source sols used for the processes were prepared by the method where in the starting ascorbic acid solution the solid thorium nitrate was dissolved and partially neutralized by aqueous ammonia under pH control. The microspheres of thorium-ascorbate gel were obtained using the ICHTJ Process (INCT in English). Studies allowed to determine an optimal heat treatment with calcination temperature of 700 °C and temperature rate not higher than 2 °C/min which enabled us to obtain a crack-free surface of microspheres. The main parameters which have a strong influence on the synthesis method and features of the spherical particles of thorium dioxide are described in this article.

Preparation of microspheres of carbon black dispersion in uranyl-ascorbate gels as precursors for uranium carbide

A novel technique to fabricate precursors of carbide-ceramic nuclear fuel via synthesis of spherical particles (with a diameter below 150 μm) of carbon black dispersion in uranyl-ascorbate gels by a combination of the Complex Sol–Gel Process and the Double Extraction Process has been elaborated. Applying of ascorbic acid as complexing agent in the Complex Sol–Gel Process allows to obtain stable and uniform dispersion of carbon in an uranyl-ascorbate sol. Traditionally, the dispersability is improved by employment of dispersing agents – surfactants. In the presented Complex Sol–Gel Process, a dispersing agent is needless. The ascorbate sols perfectly wet carbon black and do not form agglomerates. In the Double Extraction Process, dispersion of carbon black in sols is emulsified by drops in the organic phase consisting of 2-ethylhexanol-1 and 1 volume % of Primene JM-T. The microspheres are created by gelation of droplets, through simultaneous extraction of water with 2-ethylhexanol-1 and nitrate ions with Primene JM-T. The elaboration of the optimal gelation conditions requires considering many issues which are described in this paper.

Enhanced oxygen permeability of novel Cu-containing CO2-tolerant dual-phase membranes

Dense dual-phase membranes 40% Sm0.5Sr0.5Cu0.2Fe0.8O3−δ – 60% Ce0.8Sm0.2O2−δ (SmSrCF5528-CSO) and 40% Sm0.3Sr0.7Cu0.2Fe0.8O3−δ – 60% Ce0.8Sm0.2O2−δ (SmSrCF3728-CSO) were prepared via the citric acid/EDTA complexing sol–gel process. The phase composition and the microstructure of the membranes were characterized by XRD, SEM and EDXS analysis. The newly developed cobalt-free membranes SmSrCF5528-CSO and SmSrCF3728-CSO (0.6mm thick) exhibited high oxygen fluxes of 1.12 and 1.15cm3min−1cm−2, respectively, at 1000°C with pure CO2 as the sweep gas. The long-term CO2 stability of each membrane was studied in the temperature range of 900–1000°C for more than 200h on stream. The SmSrCF5528-CSO membrane displayed very good stability at all temperatures. The oxygen permeation fluxes of the Sr-rich membrane SmSrCF3728-CSO were stable at 1000 and 950°C.

Carbonization of solid uranyl-ascorbate gel as an indirect step of uranium carbide synthesis

Abstract The studies of the synthesis of uranium carbide from uranyl-ascorbate gels using the complex sol-gel process (CSGP) have been carried out. The synthesis of uranyl-ascorbate mixture as liquid sol from uranium trioxide and ascorbic acid and solid gel by extraction of water from sol were carefully examined. Ascorbic acid was used as a complexing agent in complex sol-gel process and as a carbon source. The crucial step to obtain final uranium carbides from the aforementioned substrates is the carbonization process. The thermal behavior of ascorbic acid and uranyl-ascorbate gels in a nitrogen atmosphere in the temperature range of 25-900°C were investigated using TG-DTG. Furthermore, the products of the carbonization of uranyl-ascorbate gels in nitrogen, argon and vacuum atmosphere were identified by X-ray diffraction. TG-DTG was used also as a method for determining of carbon residues in the samples.

Nanomechanical Properties and Fracture Behaviors of Ba1–xKxCe0.6Zr0.2Y0.2O3–δ Electrolytes by Nanoindentation

The nanomechanical characteristics and fracture behaviors of the Ba1−xKxCe0.6Zr0.2Y0.2O3− (K-doped BCZY, 0.0 ≤ x ≤ 0.15) oxides were investigated by using nanoindentation techniques. The BKCZY samples were prepared by the citrate-ethylenediaminetetraacetic acid (EDTA) complexing sol–gel process, followed by uniaxial pressure pressing and sintering at 1600 C for 4 h. The XRD results indicated that the BKCZY samples occurred predominantly in perovskite-type cubic structures. The hardness and Young’s modulus of BKCZY samples were measured by a Berkovich nanoindenter operated in continuous contact stiffness measurements (CSM) mode. Results indicated that the hardness and Young’s modulus of BKCZY sample decreased substantially with increasing the K doping concentration, presumably due to doping-enhanced grain growth. Furthermore, the SEM observations indicated that Berkovich nanoindentation-induced fracture mode was mostly transgranular and the fracture toughness exhibited a similar doping dependence as that of the hardness and Young’s modulus.

Isothermal formation kinetics of nanocrystals in LiNb0.5Ta0.5O3 glass

We report an isothermal formation kinetics of nanocrystals in LiNb0.5Ta0.5O3 (LNT) glass prepared by the polymerized complex sol–gel process with no addition of glass former. It is observed that the LNT glass transforms into rhombohedral LNT crystal at an elevated temperature and most crystal grains are confined within the size of ∼30nm. We have determined that the formation mechanism of nanocrystals is the diffusion-controlled growth with a constant nucleation rate, based on the Avrami exponent n ∼2.5 in Johnson–Mehl–Avrami equation.

Preparation of dense La0.5Sr0.5Fe0.8Cu0.2O3−δ–(Li,Na)2CO3–LiAlO2 composite membrane for CO2 separation

Dense La0.5Sr0.5Fe0.8Cu0.2O3−δ–(Li,Na)2CO3 and La0.5Sr0.5Fe0.8Cu0.2O3−δ–(Li,Na)2CO3–LiAlO2 composite membranes were prepared for CO2 separation. The La0.5Sr0.5Fe0.8Cu0.2O3−δ (LSFCu) was prepared via the combined EDTA–citrate complex sol–gel process according to a previous study and then used in the synthesis of the dual phase membrane. XRD characterisation of the La0.5Sr0.5Fe0.8Cu0.2O3−δ sample showed it is orthorhombic structure with space group Pnma(62), a=5.4784(5)Å, b=7.7456(7)Å, c=5.5014(5)Å, and V=233.44(4)Å3.Dense composite membrane was obtained after carbonate treatment. Mixed CO2/N2, CO2/O2 and CO2/air gases were used for CO2 permeation experiments. At 750°C, high CO2 permeation rate of 1.55mlcm−2min−1 was observed for the LSFCu–(Li,Na)2CO3–LiAlO2 composite membrane when 20% CO2/80% O2 mixture was used as the feed gas. Introduction of ~10wt% LiAlO2 in the oxide–carbonate composite results in increased CO2 permeation rates which is likely due to the enhancement in surface reaction.The dominant pathway for CO2 permeation in the LSFCu–(Li,Na)2CO3–LiAlO2 composite membrane was believed through the coherent interaction between O2− and CO32− ions. Increased oxygen partial pressure in the feed gas can facilitate CO2 permeation. Due to the low O2 concentration in real flue gases, potentially the LSFCu–(Li,Na)2CO3–LiAlO2 dual phase membrane will separate CO2 only which provides an alternative technology for CO2 separation.

BaZr0.2Ce0.8−xYxO3−δ solid oxide fuel cell electrolyte synthesized by sol–gel combined with composition-exchange method

This study reports the synthesis of proton-conducting BaZr0.2Ce0.8−xYxO3−δ (x = 0–0.4) oxides by using a combination of citrate-EDTA complexing sol–gel process and composition-exchange method. Compared to those oxides prepared from conventional sol–gel powders, the sintered BaZr0.2Ce0.8−xYxO3−δ pellets synthesized by sol–gel combined with composition-exchange method are found to exhibit improved sinterability, a higher relative density, higher conduction, and excellent thermodynamic stability against CO2. Moreover, the Pt/electrolyte/Pt single cell using such a BaZr0.2Ce0.6Y0.2O3−δ electrolyte shows an obviously higher maximum powder density in the hydrogen-air fuel cell experiments. Based on the experimental results, we discuss the improvement mechanism in terms of calcined particle characteristics. This work demonstrates that the BaZr0.2Ce0.8−xYxO3−δ oxides synthesized by sol–gel combined with composition-exchange method would be a promising electrolyte for the use in H+-SOFC applications. More importantly, this new fabrication approach could be applied to other similar ABO3-perovskite material systems.

Nuclear waste immobilization into structure of zirconolite by Complex Sol Gel Process

ABSTRACTZirconolite (CaZrTi2O7) is one of the components of Synroc materials, which are regarded throughout the world nuclear as the second generation of high-level nuclear waste forms. The zirconolite phase was synthesized by a sol-gel method, with one variant of the method making use of ascorbic acid as a strong complexing agent. Into the structure of the zirconolite was incorporated 10 mol% Sr. Undoped and doped samples were examined by thermal analyses and X-ray diffraction. Addition of ascorbic acid to the sols lowered the firing temperature and promoted formation of the zirconolite phase.

Perovskite synthesis via complex sol–gel process to immobilize radioactive waste elements

Synroc (Synthetic Rocks) materials have been regarded as the second generation of high level waste forms in the world. It allows incorporating into their crystal structures almost all of the elements present in high-level radioactive waste. One of the components of Synroc-C is perovskite (CaTiO3) which immobilize mainly fission products, but also allow immobilizing in his structure long-lived actinides such as plutonium (Pu). Perovskite phase has been fabricated by a sol–gel route. In the present work complex sol–gel process (CSGP Polish Patent PL 172618, 1997) and method of synthesis Me-titanates (Polish Patent PL 198039, 2001) were adapted to prepare of perovskite. Additions of 10 % molar Sr, Co, Cs and Nd into Ti–Ca–nitrate sols were carried out by CSGP. Gels obtained by evaporation of sols under reduced pressure were thermal treated according thermogravimetric (TG, DTA) analysis. Transformation of ascorbat–nitrate gels into doped orthorhombic perovskite phases was definitely lower (about 650 °C) than those pure nitrate gels (approx. 700 °C). All structures were confirmed by X-ray diffraction analyses. Surrogates were homogeneously distributed into crystalline structure of perovskite. It means that elaborated process can be applied for synthesis Synroc materials and it might be competitive to vitrification process.

Synthesis of microspheres of triuranium octaoxide by simultaneous water and nitrate extraction from ascorbate-uranyl sols.

A new method for synthesis of uranium oxide microspheres (diameter <100 μm) has been developed. It is a variant of our patented Complex Sol–Gel Process, which has been used to synthesize high-quality powders of a wide variety of complex oxides. Starting uranyl-nitrate-ascorbate sols were prepared by addition of ascorbic acid to uranyl nitrate hexahydrate solution and alkalizing by aqueous ammonium hydroxide and then emulsified in 2-ethylhexanol-1 containing 1v/o SPAN-80. Drops of emulsion were firstly gelled by extraction of water by the solvent. Destruction of the microspheres during thermal treatment, owing to highly reactive components in the gels, requires modification of the gelation step by Double Extraction Process—simultaneously extraction of water and nitrates using Primene JMT, which completely eliminates these problem. Final step was calcination in air of obtained microspheres of gels to triuranium octaoxide.

Proton-conducting Ba1−xKxCe0.6Zr0.2Y0.2O3−δ oxides synthesized by sol–gel combined with composition-exchange method

Abstract This study reports the synthesis of proton-conducting Ba1−xKxCe0.6Zr0.2Y0.2O3−δ (x=0.025–0.075) ceramics by using a combination of citrate–EDTA complexing sol–gel process and the composition-exchange method. Compared to the sintered oxides of similar composition prepared from conventional sol–gel powders, Ba1−xKxCe0.6Zr0.2Y0.2O3−δ oxides synthesized by sol–gel combined with the composition-exchange method are found to exhibit improved sinterability, higher conductivity, more homogeneous phase, and excellent chemical stability against CO2. Among all sintered oxides in this study, the Ba0.925K0.075Ce0.6Zr0.2Y0.2O3−δ pellet fabricated by this new method has the highest conductivity, 0.0094 S/cm at 800 °C, which is higher than those pressed from conventional sol–gel powders in the K doping range of 0–15%. Based on the experimental results, we discuss the mechanism for improvement in these properties in terms of calcined particle characteristics. This work demonstrates that Ba1−xKxCe0.6Zr0.2Y0.2O3−δ oxides synthesized by sol–gel combined with the composition-exchange method would be a promising electrolyte for H+-SOFC applications. More importantly, this new fabrication approach may be applied to other similar material systems, such as Sr-doped Ba(Ce,Zr)O3 ceramics.

The chemical stability and conductivity improvement of protonic conductor BaCe0.8 − x Zr x Y0.2O3 − δ

A series of BaCe0.8 − x Zr x Y0.2O3 − δ (BCZYx) (x = 0, 0.2, 0.4, 0.6, 0.8) powders were prepared by EDTA–citrate complexing sol–gel process in this paper. The electrical conducting behavior, as well as chemical stability, was investigated. X-ray diffraction (XRD) results reveal that all samples are homogenous perovskite phases. Observed from XRD patterns and thermogravimetric curves, the samples with x ≥ 0.4 survive in the pure CO2, while samples with various Zr contents all present structurally stable against steam at 800 °C. The Zr-free sample of BaCe0.8Y0.2O3 − δ possesses the maximum bulk conductivity, 4.25 × 10−2 S/cm, but decomposes into Ba(OH)2 and Ce0.8Y0.2O3 − δ in steam. A negative influence of increasing Zr content on the conductivity of BCZYx can be observed by impedance tests. Considering the effect of temperature on the bulk conductivity, BCZY0.4 is preferred to be applied in SOFC as a protonic conductor, ranging from 1.52 × 10−4 to 1.51 × 10−3 S/cm (500–850 °C) with E a = 0.859 eV, which is proved to be a good protonic conductor with t H+ ≥ 0.9.

Transition from anatase to rutile phase in titanium dioxide (TiO2) nanoparticles synthesized by complexing sol–gel process: effect of kind of complexing agent and calcinating temperature

In this work, the structural and optical properties of titanium dioxide (TiO2) nanopowders are studied. The TiO2 nanoparticles were synthesized by complexing sol–gel process and effect of complexing agents on transition of the anatase phase to rutile phase during the heat treatment have been investigated. In addition, we have studied the grain size of TiO2 powders and their dependence on the type of complexing agent. The analysis of the XRD patterns, FT-IR and UV–Vis spectroscopy, BET surface area and TEM images show that the synthesis of nanoparticles with acetyl acetone (AcAc) as complexing agent yielded the smallest size of nanoparticles about 22–35 nm. Our results indicate that with increasing the calcinating temperature, the size of the nanoparticles is increased and the energy gap reduced, too. Also, the optical band gap was obtained in the range of 3.4–4.1 and 3.06–3.74 eV for anatase and rutile phases, respectively.

Vitrification of Nuclear Wastes by Complex Sol-Gel Process

For synthesis of silica glasses designed to contain high-level nuclear wastes，a patented complex sol-gel process has been used. Surrogates of the nuclear waste elements Cs, Sr, Co, and Nd (generically denoted Me) were used. Gels in the forms of powders and sintered compacts were prepared by hydrolysis and polycondensation of tetraethoxide/Me nitrate solutions, which contained ascorbic acid as a catalyst. Transformation to final products was studied by thermogravimetric analysis, infrared spectroscopy, and X-ray diffraction. Preliminary testing of Me leaching was also completed in water. Most of the final products were porous; only a single dense form was resistant to leaching.