Self-propagating Room Temperature Synthesis Research Articles

Self-propagating room temperature synthesis of Ce0.8SmXM0.2-xO1.9(M= Gd, Nd, 0≤x≤0.2) co-doped ceria oxide-ion conductor ceramics for solid oxide fuel cells

Ce0.8SmXM0.2-xO1.9 (M = Gd, Nd, 0≤x ≤ 0.2) co-doped cerium oxide ionic conductor ceramics are prepared for the first time by a simple and time-saving self-propagating room temperature (SPRT) method. The uncalcined ceramic powders and the microstructure of the pellets sintered at 1400 °C are characterized by thermogravimetric analysis, Fourier-transformed infrared spectroscopy, scanning electron microscopy, and X-ray diffractometry. The density of the pellets is determined using the Archimedes method. The oxygen ion conductivity properties of the electrolytes are measured by electrochemical impedance spectroscopy. Impurity-free, non-porous electrolytes with high-density (>95 %) are successfully prepared. We report that the influence of dopant type and composition on the physical properties of the electrolytes prepared by the SPRT method is insignificant, with the total dopant concentration kept constant at 20 %. The dopant type and composition mainly influence the lattice parameters, grain interior conductivity of the grains, and the activation energy of the internal conductivity of the grains. Maximum oxygen ion conductivities are demonstrated with Ce0.8Sm0.1Nd0.1O1.9 and Ce0.8Sm0.15Gd0.05O1.9 samples for the Nd and Gd series, respectively. The highest ionic conductivity of 0.0677 S cm−1 and the lowest activation energy of 0.75 eV is achieved at a value of 10%Nd-10%Sm.

Confined space self-propagating room temperature synthesis of carbon-encapsulated Fe3O4 nanocrystals and its lithium storage performance

A self-propagating reaction between ferrocene and iron nitrate nonahydrate that is initiated at room temperature is discovered. Amorphous carbon-encapsulated Fe3O4 nanocrystals (Fe3O4@C) can be one-step prepared in an autoclave through this reaction. The equiaxed Fe3O4 nanocrystals have typical dimensions in the range of 5–60 nm with a median size of 24.1 nm, and their weight percent is up to 82.3%. The course of the reaction is recorded, and the formation mechanism of Fe3O4@C with the core–shell structure is proposed. The scaling-up synthesis is also achieved, and 52.1 g of the Fe3O4@C can be obtained in a single batch. The shock wave appeared in the fast gas release self-propagating reaction in confined space plays a decisive role in the preparation of homogeneous Fe3O4@C with a core–shell structure. The Fe3O4@C anode shows excellent capacity retention with a high specific capacity of 494 mAh g−1 at 1 A g−1 in the 200th cycle.

Nanocrystalline CeO2-δ as effective adsorbent of azo dyes.

Ultrafine CeO2-δ nanopowder, prepared by a simple and cost-effective self-propagating room temperature synthesis method (SPRT), showed high adsorption capability for removal of different azo dyes. Batch type of adsorption experiments with fixed initial pH value were conducted for the removal of Reactive Orange 16 (RO16), Methyl Orange (MO), and Mordant Blue 9 (MB9). The equilibrium adsorption data were evaluated using Freundlich and Langmuir isotherm models. The Langmuir model slightly better describes isotherm data for RO16 and MO, whereas the Freundlich model was found to best fit the isotherm data for MB9 over the whole concentration range. The maximum adsorption capacities, determined from isotherm data for MO, MB9, and RO16 were 113, 101, and 91 mg g(-1) respectively. The adsorption process follows the pseudo-second-order kinetic model indicating the coexistence of chemisorption and physisorption. The mechanism of azo dye adsorption is also discussed.

Electrical and microstructural properties of Yb-doped CeO2

Nanopowdered Ce1−xYbxO2−δ solid solutions (0 ≤ x ≤ 0.2) were synthesized by a self-propagating room temperature synthesis. XRD and SEM were used to study the properties of these materials as well as the Yb solubility in CeO2 lattice. Results showed that all the obtained powders were solid solutions with a fluorite-type crystal structure and with nanometric particle size. The average size of Ce1−xYbxO2−δ particles was approximately 3 nm. Electrochemical impedance spectroscopy for the sintered pellets depicted that it was possible to separate Rbulk and Rgb in the temperature interval of 550–800 °C. The activation energy for the bulk conduction was 1.03 eV and for grain boundary conduction was 1.14 eV. Grain boundary resistivity dominates over the other resistivities. These measurements confirmed that Yb3+-doped CeO2 material had a potential as electrolyte for intermediate-temperature solid oxide fuel cell applications.

Effect of preparation route on the microstructure and electrical conductivity of co-doped ceria

Abstract Dense Ce 0.8 Sm 0.1 Gd 0.1 O 2− δ electrolytes were fabricated by sintering of CeO 2 solid solutions which were prepared from metal nitrates and NaOH using self propagating room temperature synthesis (SPRT). Three different routes were employed to obtain CeO 2 solid solution powders: (I) hand mixing of reactants, (II) ball milling of reactants and (III) ball milling of Ce 0.8 Sm 0.2 O 2− δ and Ce 0.8 Gd 0.2 O 2− δ solid solutions previously prepared by ball milling of corresponding nitrates and NaOH. Density measurements showed that ball milling, which is more convenient than hand mixing, is an effective way to obtain almost full dense samples after presureless sintering at 1550 °C for 1 h. These samples had larger grain size and consequently higher conductivity than the samples obtained by hand mixing. The highest conductivity of 2.704×10 −2 (Ω cm) −1 was measured at 700 °C in a sample prepared by route II. It was found that reduced grain size in samples obtained by hand mixing leads to a decrease in grain boundary conductivity and therefore decrease in the total conductivity. The results showed that mixing of single doped ceria solid solutions improved densification and inhibited grain growth.

Nanometric solid solutions of the fluorite and perovskite type crystal structures: Synthesis and properties

In this paper a short review of our results on the synthesis of nanosized CeO2, CaMnO3 and BaCeO3 solid solutions are presented. The nanopowders were prepared by two innovative methods: self propagating room temperature synthesis (SPRT) and modified glycine/nitrate procedure (MGNP). Different types of solid solutions with rare earth dopants in concentrations ranging from 0-0.25 mol% were synthesized. The reactions forming solid solutions were studied. In addition, the characteristics of prepared nanopowders, phenomena during sintering and the properties of sintered samples are discussed.

Synthesis and characterization of Cu-doped ceria nanopowders

Nanopowdered solid solution Ce 1− x Cu x O 2− γ samples (0 ≤ x ≤ 0.15) were synthesized by self-propagating room temperature synthesis (SPRT). Raman spectroscopy and XRD at room temperature were used to study the vibration properties of these materials as well as the Cu solubility in ceria lattice. The solubility limit of Cu 2+ in CeO 2 lattice was found to be lower than published in the literature. Results show that obtained powders with low dopant concentration are solid solutions with a fluorite-type crystal structure. However, with Cu content higher than 7.5 mass%, the phase separation was observed and two oxide phases, CeO 2 and CuO, coexist. All powders were nanometric in size with high specific surface area.

Synthesis and characterization of ceria based nanometric powders

Nanopowdered solid solution Ce1−xFexO2−δ samples (0 ≤ x ≤ 0.1) were synthesized by a self-propagating room temperature synthesis (SPRT). XRD and Raman spectroscopy at room temperature were used to study the vibrational properties of these materials as well as the Fe solubility in ceria lattice. Results show that all obtained powders are solid solutions with a fluorite-type crystal structure and all powders were nanometric in size. The average size of Ce1−xFexO2−δ particles lies about 5 nm. The results of electrical properties of the sintered samples investigated by an ac impedance spectroscopy are also presented and discussed. It was confirmed that Fe3+ doped ceria material has a potential as electrolyte for intermediate-temperature solid oxide fuel cell applications.

Raman study of Ba-doped ceria nanopowders

A series of Ce1-xBaxO2-y (5?x?0.20) nanometric powders were synthesized by selfpropagating room temperature synthesis. XRD and Raman scattering measurements were used to characterize the samples at room temperature. All the samples are solid solutions with fluorite type structure with an average crystallite size about 5 nm. The redshift and asymmetric broadening of the Raman F2g mode can be well explained with combined confinement and strain effects because of the nanocrystalline powders nature. The appearance of the additional peaks at ~ 560 cm-1 and ~ 600 cm-1, are attributed to extrinsic and intrinsic O2- vacancies in ceria lattice. Raman spectra of temperature treated Ce0.80Ba0.20O2-d sample revealed the instability of this system.

Reaction of Ce<sub>1-x</sub>Re<sub>x</sub>O<sub>2-δ</sub> Nanopowders Synthesis

One of the methods for powder synthesis that is both cost and time effective is the selfpropagating room temperature synthesis. We applied this method to synthesize rare earth doped ceria nanopowders. Since they exhibit very high ionic conductivity at intermediate temperatures these compositions are attractive for a new generation of nanostructured ceramics applicable in solid oxide fuel cells as electrolytes. In this paper we paid our attention to the reaction based on methathetical pathway, whereby solid solution nanopowders of rare earth elements with ceria were obtained at room temperature. Compositions of Ce1-xRexO2-δ (Re = Y , Nd) were synthesized with x ranging from 0 to 0.20. The reaction course is discussed and the properties of the obtained powders are presented.

The size and strain effects on the Raman spectra of Ce 1− xNd xO 2− δ (0≤ x≤0.25) nanopowders

Ultrafine Ce 1− x Nd x O 2− δ ( x=0–0.25) powders were synthesized by self-propagating room temperature synthesis. Raman spectra were measured at room temperature in the 300–700 cm −1 spectral range. The shift and asymmetric broadening of the Raman F 2g mode at about 454 cm −1 in pure and doped ceria samples could be explained with combined size and inhomogenous strain effects. Increased concentration of O 2− vacancies with doping is followed by an appearance of new Raman feature at about 545 cm −1.

Self-propagating room temperature synthesis of nanopowders for solid oxide fuel cells (SOFC)

Ceria based solid solutions are promising ceramic electrolytes for SOFC which will be able to function at intermediate temperatures. In accordance with common trends to decrease the production and operating costs of new generation of SOFC materials the reaction based on metathetical pathway is described, whereby solid solution powders of rare earth doped ceria in the nanoscale range were obtained at room temperature. By simple hand mixing of reactants the reaction was enhanced, propagating afterwards by itself. Nanometric ceria powders doped with Y or Nd, as well as co doped with both cations were synthesized. Composition of Ce 1 − x Me x O 2 − y ranged from x = 0–0.25. The reaction course is described in detail and the properties of the obtained powders are presented.