Novel Synthesis of CeO2 Nanoparticles Within Formamide/Tri(ethyleneglycol)monododecyl Ether/n-Octane Nonaqueous Microemulsion Systems

The present study evaluates a new method to prepare Cerium oxide (CeO₂) nanoparticles by formamide/tri(ethyleneglycol)monododecyl ether (C₁₂E₃)/n-octane oil-continuous nonaqueous microemulsion. The effect of the polar phase (formamide/water) on the phase behavior, drop size, and conductivity behavior of the reverse microemulsion were investigated. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to characterize the phase and morphology of synthesized CeO₂ nanoparticles. It was found that the CeO₂ powders synthesized within nonaqueous microemulsions and aqueous microemulisons had an average particle size of 30–50 nm and 15–40 nm, respectively. The experimental results indicate the formation mechanism of CeO₂ nanoparticles in formamide nonaqueous microemulsion and aqueous microemulsion is similar, and the formamide nonaqueous microemulsion can be used as nanoreactors for preparation of nanoparticles.     

Colloidal properties of CeO<Subscript>2</Subscript>-ZrO<Subscript>2</Subscript> hydrosols

CeO₂-ZrO₂ hydrosols are synthesized and the size, shape, phase composition, density, and electrophoretic mobility of particles are studied. The pH ranges of the stability of hydrosols and the thresholds of their fast coagulation in the presence of some electrolytes are determined. The nature of the aggregation stability of CeO₂-ZrO₂ hydrosols is discussed.     

Luminescent characteristics and microstructures of Sr<Subscript>2</Subscript>CeO<Subscript>4</Subscript> phosphors prepared via sol–gel and solid-state reaction routes

Blue-light-emitting Sr₂CeO₄ phosphors were synthesized via a sol–gel process and the conventional solid-state method in this study. The developed sol–gel process lowered the synthesis temperature of monophasic Sr₂CeO₄ to as low as 900 °C. In comparison with the solid-state derived powders, the sol–gel derived powders had more uniform morphology and smaller particle sizes. In addition, sol–gel derived Sr₂CeO₄ displayed higher luminescent intensity than that prepared via the solid-state route under the same heating conditions. This is attributed to the improved compositional homogeneity and crystallinity in the sol–gel process. During the heating processes, Sr₂CeO₄ tended to thermally decompose at elevated temperatures. This decomposition reaction resulted in the formation of an impurity phase- SrCeO₃ and thereby a decrease in the luminescent intensity. For obtaining Sr₂CeO₄ phosphors with high luminescent intensity, the heating conditions in both processes need to be well modulated.     

Structural and Electrochemical Properties of Sol-Gel Derived Mo : CeO2, Si : Mo : CeO2 and Si : CeO2 Nanocrystalline Films for Electrochromic Devices

Mo:CeO₂, Si:CeO₂ and Mo:Si:CeO₂ films were made by the sol-gel dip-coating technique. XRD investigations of the analogously prepared powders revealed that particle grain size of CeO₂ with the addition of Mo, Si or both decreased. FT/IR spectra of the corresponding films showed that no separate Mo-oxide phase was formed while the Si containing CeO₂ films had nanocrystallites of ceria as well as amorphous silica. Electrochemical investigations (cyclic voltammetry, chronocoulometry) performed in protic (0.1M LiOH) and aprotic (1M LiClO₄/propylene carbonate(PC)) electrolytes showed that additions of Mo:, Si: and Mo: Si:-to ceria increased ion storage ability. The suitability of films as optically passive counter electrodes was demonstrated by making electrochromic cells with asymmetric and symmetric configurations using a Li⁺ doped ionic conductor (ormolyte^®) and an electrochromic tungstophosphoric acid (WPA)/TiO₂ gel film.     

Synthesis of CeO<Subscript>2</Subscript>-ZrO<Subscript>2</Subscript> hydrosols via peptization at room temperature

A procedure is developed for the synthesis of concentrated CeO₂-ZrO₂ hydrosols based on the peptization of a precipitate obtained by the hydrolysis of a cerium nitrate-zirconium oxynitrate mixture. The time intervals and optimum [H⁺]/[Me ⁿ⁺] molar ratios giving rise the formation of CeO₂-ZrO₂ hydrosols stable to aggregation with a narrow particle size distribution are established. The size, shape, density, and phase composition of the hydrosol particles are determined.     

New In-situ Sampling and Analysis of the Production of CeO<Subscript>2</Subscript> Powders from Liquid Precursors using a Novel Wet Collection System in a rf Inductively Coupled Thermal Plasma Reactor. Part 1: Reactor System and Sampling Probe

A new reactor and a novel in-situ sampling technique were developed for the study of the synthesis of CeO₂ powders produced from dissolved cerium nitrate salts. The conical reactor minimized particle recirculation and provided a highly symmetrical and undisturbed plasma flow suitable for the analysis of the phenomena affecting the formation of CeO₂ powders. Both a calorimetric study of the reactor and a thermodynamic analysis of CeO₂ formation were conducted. The sampling probe is described and near-isokinetic sampling was achieved. The sampled particles were collected using a miniature wet collection system, i.e. a mist atomizer and a custom-made spray chamber. A numerical simulation of the velocity and temperature fields of the plasma gas in the reactor was done using Fluent. A comprehensive droplet-to-particle formation mechanism presented elsewhere is revisited and expanded based on calorimetry, thermodynamics of CeO₂ formation, numerical simulations and collected particles. No traces of other oxidation states other than CeO₂ were found.     

Development of CeO<Subscript>2</Subscript>- and TiO<Subscript>2</Subscript>-incorporated aluminium metal-composite matrix with high resistance to corrosion and biofouling

Cerium oxide (CeO₂) is a potential corrosion inhibitor for aluminium, and titanium oxide (TiO₂) is an efficient anti-fouling agent in the marine environment. The present study explored the possibility of incorporating CeO₂ and TiO₂ in aluminium to prepare a metal matrix composite that could have high corrosion and biofouling resistance under marine conditions. Such incorporation of CeO₂ and TiO₂ in pure aluminium offered high resistance to corrosion and biogrowth under marine conditions as evidenced during different tests. The specimens exhibited more anodic and stable open circuit potential throughout the period of the study. The optimum concentration of CeO₂ and TiO₂ was found to be 0.2 and 0.1%, respectively. The present results lay emphasis on the potential scope of the use of CeO₂- and TiO₂-incorporated aluminium in marine environments.     

Synthesis of highly dispersed super-refractory tantalum-zirconium carbide Ta<Subscript>4</Subscript>ZrC<Subscript>5</Subscript> and tantalum-hafnium carbide Ta<Subscript>4</Subscript>HfC<Subscript>5</Subscript> via sol-gel technology

Nanocrystalline powders of super-refractory complex carbides Ta₄HfC₅ and Ta₄ZrC₅ were synthesized using a hybrid method comprising sol-gel technology for preparing highly dispersed metal oxidescarbon starting mixtures and a relatively low-temperature (1300–1500°C) carbothermal synthesis under a dynamic vacuum (P = 1 × 10⁻³ to 1 × 10⁻⁵ MPa). The elemental and phase compositions of the products and average crystallite sizes were determined. TEM was used to study particle morphology and dispersion. Microstructures were observed by SEM. BET specific surface areas were determined for powders prepared at 1400°C.     

Sintering behavior and ionic conductivity of Ce<Subscript>0.8</Subscript>Gd<Subscript>0.2</Subscript>O<Subscript>1.9</Subscript> with a small amount of MnO<Subscript>2</Subscript> doping

A 20% GdO_1.5 doped ceria solid solution with a small amount of MnO₂ doping (≤5% molar ratio) was prepared via the mixed oxide method from high-purity commercial powders with grain size around 0.2–0.5 μm. X-ray diffraction analysis indicated that all the samples exhibited the fluorite structure, and no new phase was found. The data from dilatometeric measurements and scanning electron microscopy observations revealed that 1% Mn doping reduced the sintering temperature by over 150 °C, and enhanced the densification and grain growth. Mn doping has little effect on grain interior conductivity, but a marked deterioration in grain boundary behavior is observed. This leads to a lower total conductivity in comparison with the undoped Ce_0.8Gd_0.2O_2–δ. Therefore, for solid oxide fuel cells (SOFCs) with Mn-containing compounds as electrodes, optimization of electrode fabrication conditions is needed to prevent the formation of a lower conductivity layer at the electrode/electrolyte interface since Mn will diffuse from the electrode side to the electrolyte during fabrication and operation of SOFCs. Electronic Publication     

Lithium AlPO<Subscript>4</Subscript> composite polymer battery with nanostructured LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> cathode

The borate ester plasticized AlPO₄ composite solid polymer electrolytes (SPE) have been synthesized and studied as candidates for lithium polymer battery (LPB) application. The electrochemical and thermal properties of SPE were shown to be suitable for practical LPB. Nanostructured LiMn₂O₄ with spherical particles was synthesized via ultrasonic spray pyrolysis technique and has shown a superior performance to the one prepared via conventional methods as cathode for LPB. Furthermore, the AlPO₄ addition to the polymer electrolyte has improved the polymer battery performance. Based on the AC impedance spectroscopy data, the performance improvement was suggested as being due to the cathode/polymer electrolyte interface stabilization in the presence of AlPO₄. The Li/composite polymer electrolyte/nanostructured LiMn₂O₄ electrochemical cell showed stable cyclability during the various current density tests, and its performance was found to be quite acceptable for practical utilities at ambient temperature and showed remarkable improvements at 60 °C compared with the solid state reaction counterpart.     

Taguchi Optimization for Combustion Synthesis of Aluminum Oxide Nano-particles

Nano-structured aluminum oxide powders were prepared by a combustion synthesis method utilizing serine as a new fuel. The product was sonicated to obtain nano powders. A Taguchi L-4 statistical design of combustion synthesis was utilized to optimize the production of γ-alumina powder. The product was characterized by XRD, BET, SEM, EDX and LLS. Nano crystalline γ-alumina with crystal sizes between 4.26 and 5.47 nm and α-Al2O3 powders with crystal sizes 24.51 and 28.62 nm were obtained by the combustion synthesis. The specific surface area was measured by a BET method to be 75.21 m2/g. The average particle size after sonication of product, observed by LLS, was 79.32 nm.     

New In-Situ Sampling and Analysis of the Production of CeO<Subscript>2</Subscript> Powders from Liquid Precursors in a rf Thermal Plasma Reactor. Part 2: Analysis of CeO<Subscript>2</Subscript> Powders,Fuel Addition,and Image Analysis

A novel reactor design, sampling probe and wet collection system were used to investigate the combined effects of plasma operating parameters and particle collection mechanisms on the synthesis of CeO₂ particles from liquid precursors. The sampling of particles in-flight and the collection of particles at several reactor regions were used to provide experimental evidence of particle size at different reactor locations at various plasma operating conditions, i.e., power and plasma gas flow rates. This information provided a picture of how CeO₂ particles were formed and how these particles were collected in various locations. The effect of adding water-soluble fuels (alanine and glycine) to the original cerium nitrate solutions was also investigated. Fuel addition decreased the temperature of CeO₂ formation by acting as a local heat source as a result of fuel auto-ignition. Photographs of the particles in-flight were taken using a fast speed CCD camera.     

Preparation and characterization of high specific surface area Mn<Subscript>3</Subscript>O<Subscript>4</Subscript> from electrolytic manganese residue

Mn₃O₄ powders have been produced from Electrolytic Manganese Residue (EMR). After leaching of EMR in sulfuric acid, MnSO₄ solution containing various ions was obtained. Purifying the solution obtained and then adding aqueous alkali to the purified MnSO₄ solution, Mn(OH)₂ was prepared. Two methods were employed to produce Mn₃O₄. One way was oxidation of Mn(OH)₂ in aqueous phase under atmosphere pressure to obtain Mn₃O₄. The other way was roasting Mn(OH)₂ precursors in the range of 500°C to 700°C. The prepared samples were investigated by using several techniques including X-ray powder diffraction (XRD), Fourier Transformation Infra-Red (FTIR) spectra, and Brunauer-Emmett-Teller (BET) specific surface area instrument. Particle distribution and magnetic measurements were carried out on laser particle size analyzer, vibrating sample magnetometer (VSM). Through XRD, FTIR and determination of total Mn content (TMC), the products prepared were confirmed to be a single phase Mn₃O₄. BET specific surface areas can reach to 32 m² g⁻¹. The results indicated that products synthesized by aqueous solution oxidation method had higher specific surface areas and smaller particle size than those prepared by means of roasting. However the products prepared using the above two methods showed no obvious differences in magnetic property.      

Films of certain oxides of rare-earth elements as the activators of platinum electrode on ZrO<Subscript>2</Subscript> + 10 mol % Y<Subscript>2</Subscript>O<Subscript>3</Subscript> electrolyte

The characteristics of porous Pt/YSZ (ZrO₂ + 10 mol % Y₂O₃) electrodes activated with small amounts of either oxides of rare-earth elements (REE) of the cerium subgroup (CeO₂, PrO _x , TbO _x ) or a mixed oxide with the Сe₂Tb₄O₁₁ composition by the procedure of impregnating the electrodes with ethanol solutions of REE nitrates and subsequent heating at 850°С are studied by the impedance method. The studies are carried out for those cases where the REE oxides after thermal treatment form a film on the electrolyte and also where no activator film is formed. The characteristics of films and activated electrodes are compared. Film-activated Pt/YSZ electrodes are discussed within the framework of the model of compact oxide electrodes.     

Effect of Thermal Treatment on the Textural Properties of CeO2 Powders Synthesized in Near‐ and Supercritical Alcohols

CeO₂ nanocrystals (NCs) have attracted increasing interest over the past few years, in particular for their use in catalytic reactions. Syntheses mediated by near‐ and supercritical alcohols have proven to be innovative ways to obtain CeO₂ NCs with controlled crystallite sizes (from 3 to 8 nm depending on the alcohol) and surface functionalities, with alcohol moieties. When submitted to a thermal treatment at 500 °C, required to desorb/degrade surface organic species, these powders displayed different behaviors depending on the alcohol used during the synthesis. Cerium oxide powders synthesized in sc‐MeOH, sc‐EtOH and sc‐iPrOH undergo sintering during treatment at 500 °C, with a decrease of their specific surface area. Conversely, those synthesized in sc‐BuOH, nc‐PentOH and nc‐HexOH keep their initial crystallite sizes and morphology, but show a great enhancement of their specific surface area (up to 200 m² g^?1), which is unprecedented after such a thermal treatment.     

Influence of cerium oxide on properties of glass–ceramic sealants for solid oxide fuel cells

The influence of the cerium oxide concentration on the properties of glasses and glass ceramics of the SiO₂–Al₂O₃–CaO–Na₂O–MgO–K₂O–B₂O₃–CeO₂ system as potential adhesive and sealing materials for solid oxide fuel cells was studied. According to the data of differential scanning calorimetry, variation of the CeO₂ concentration does not appreciably influence the glass transition and crystallization temperatures of glasses. As the cerium oxide concentration is increased, the linear thermal expansion coefficient increases for the glasses but decreases for the partially crystalline samples. The gluing temperature of the glass sealants prepared allows their use for joining YSZ solid electrolytes with interconnectors of Crofer22APU type in solid oxide fuel cells..     

Synthesis of non-agglomerated Ba<Subscript>0.77</Subscript>Ca<Subscript>0.23</Subscript>TiO<Subscript>3</Subscript> nanopowders by a modified polymeric precursor method

In this work, we have studied the influence of the pH on the synthesis and structural properties of the Ba_0.77Ca_0.23TiO₃ nanopowders synthesized by a modified polymeric precursor method, in order to achieve non-agglomerated powders. Synthesis, morphology, thermal reactions, crystallite and average particle size of the synthesized powders were investigated through thermal analysis (DTA/TG), X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM) and Infrared spectroscopy. In summary, Ba_0.77Ca_0.23TiO₃ nanopowders were synthesized for the first time at a relative low temperature (500 °C). It was also found that the alkalinity and acidity of the solution presented a great influence on the powder properties. The best results were obtained from solutions with pH = 8.5 and 11 whose nanopowders presented weakly agglomerate, with homogeneous particle size and a narrow size distribution (30–40 nm). This behavior could be explained based on the FT-IR results in which it was possible to see the increased of the chelation in higher pHs.     

Effects of precipitants and surfactants on catalytic activity of Pd/CeO<Subscript>2</Subscript> for CO oxidation

A series of precipitants and commercial surfactants (soft templates) were employed to synthesize mesoporous/nano CeO₂ by a hydrothermal method. As-prepared CeO₂ was impregnated with palladium and employed for low-temperature catalytic oxidation of CO. It was found that both soft templates and precipitants had significant effects on the morphology, particle size, crystallinity, and porous structure of the CeO₂, having a significant effect on the surface palladium abundance, molar ratios of surface species, and catalytic activity of the final impregnated Pd/CeO₂. Using ammonia as precipitant could facilitate increased surface palladium abundance and surface molar ratios of PdO/Pd _SMSI , Ce³⁺/(Ce³⁺ + Ce⁴⁺), and O_surface/O_lattice. The catalytic activity of the final Pd/CeO₂ catalysts could be enhanced as well. The optimal P123-assisted ammonia-precipitated Pd/CeO₂ catalyst exhibited over 99% catalytic conversion of CO at 50 °C.     

Effect of the microstructure of the supported catalysts CuO/TiO<Subscript>2</Subscript> and CuO/(CeO<Subscript>2</Subscript>-TiO<Subscript>2</Subscript>) on their catalytic properties in carbon monoxide oxidation

The effect of the microstructure of titanium dioxide on the structure, thermal stability, and catalytic properties of supported CuO/TiO₂ and CuO/(CeO₂-TiO₂) catalysts in CO oxidation was studied. The formation of a nanocrystalline structure was found in the CuO/TiO₂ catalysts calcined at 500°C. This nanocrystalline structure consisted of aggregated fine anatase particles about 10 nm in size and interblock boundaries between them, in which Cu²⁺ ions were stabilized. Heat treatment of this catalyst at 700°C led to a change in its microstructure with the formation of fine CuO particles 2.5–3 nm in size, which were strongly bound to the surface of TiO₂ (anatase) with a regular well-ordered crystal structure. In the CuO/(CeO₂-TiO₂) catalysts, the nanocrystalline structure of anatase was thermally more stable than in the CuO/TiO₂ catalyst, and it persisted up to 700°C. The study of the catalytic properties of the resulting catalysts showed that the CuO/(CeO₂-TiO₂) catalysts with the nanocrystalline structure of anatase were characterized by the high-est activity in CO oxidation to CO₂.     

Glycine-nitrate combustion synthesis of CeFeO<Subscript>3</Subscript>-based nanocrystalline powders

Glycine-nitrate combustion method was used to obtain powders based on CeFeO₃ nanocrystals with average crystallite size in the range from 33 ± 3 to 51 ± 5 nm. The influence exerted by parameters of the glycine-nitrate combustion process and, in particular, by the glycine-nitrate ratio (G/N) on the composition and crystallite size of the synthesis products was determined. The optimal G/N ratio at which nanocrystalline cerium orthoferrite is formed with the minimum amount of impurity phases Fe₂O₃ and CeO₂ was found to be 0.8. It was demonstrated that the composition of the starting solution affects the nature of the phase heterogeneity in the resulting product, crystallite size, and porosity of the nanocrystalline powders being formed. The patterns determined in the study make it possible to optimize the technology of nanocrystalline powders based on CeFeO₃ in order to obtain powders with prescribed phase composition and crystallite sizes to enable their use as a basis for photocatalytic materials.