Mixed Oxide Powders Research Articles

Synthesis and characterization of a nano-scaled barium cerate perovskite powder using starch as polymerization agent

The preparation of nano-sized BaCeO 3 powder using starch as a polymerization agent is described herein. Phase evolution during the decomposition process of a (BaCe)-gel was monitored by XRD. A phase-pure nano-sized BaCeO 3 powder was obtained after calcining of the (BaCe)-gel at 920 °C. The resulting powder has a specific surface area of 15.4 m 2/g. TEM investigations reveal particles mainly in the size range of 30 to 65 nm. The shrinkage and sintering behavior of resulting powder compacts were studied in comparison to a coarse-grained mixed-oxide BaCeO 3 powder ( S BET = 2.1 m 2/g). Dilatometric measurements show that the beginning of shrinkage of compacts from the nano-sized powder is downshifted by 300 °C compared to mixed-oxide powder. Compacts from the nano-sized powder reach a relative density of 91% after sintering at 1450 °C for 10 h.

Time-resolved Measurements of Loading Ratios and Heat Evolution in D2 (and H2)-Pd·Zr Mixed-oxide Systems

Using a twin system for hydrogen absorption, we have studied heat evolution and high-energy particle generation by D2 and H2 gas absorption into nano-sized mixed oxide powders of palladium and zirconium. We have found very large energy of hydrogen absorption by Pd·Zr oxide compounds exceeding 1.0 eV/D (or H) together with a very high D/Pd loading ratio, exceeding 1.0. The system has been improved to enable time-dependent measurements of the gas flow rate and loading ratio simultaneously with the output heat. It has been revealed that the first phase is divided into two sub-phases; the 1a-phase, where most of the anomalously large output energy is produced with a very high loading, D/Pd ≈ 1.2, and the 1b-phase, where much smaller power is produced as loading increases further by a ratio of about 0.5 with a difference in pressure between deuterium and hydrogen.

Synthesis of bismuth mixed oxide by thermal decomposition of a coprecipitate precursor

Bismuth mixed oxide powders were prepared by oxalate coprecipitation process. The thermal decomposition behaviour of the coprecipitate precursors has been followed by thermal analysis (TG-DTA) and FTIR spectroscopy. During the decomposition of the precursor, several intermediates species were detected and a mechanism of formation of mixed oxide by this method is proposed. After the thermal treatment, the precursor obtained of suggested formula Ca3[Bi6O6(C2O4)4(OH)3NO3]0.5H2O, has led to the formation of CaBi2O4 at shorter reaction time than the traditional ceramic method. In order to consolidate the results, the coprecipitation in absence of oxalic precipitant under the same conditions was examined. XRD and scanning electron spectroscopy were used to study particles sizes and morphology.

The Influence of Sintering Time of Feedstock Powders on the Electrical Properties of La10(SiO4)6O3 Electrolyte Coatings

Electrical properties of apatite-type La10(SiO4)6O3 electrolyte coatings as a new class of the fast oxide ion conductors were investigated in this study. The feedstock powders were prepared by sintering the mixed oxide powders in different sintering times. The ceramic coatings with a typical composition of La10(SiO4)6O3 were deposited by atmospheric plasma spraying (APS). The highest conductivity of the dense composite electrolyte coatings reaches 6.8×10-6 S•cm-1 at 435 ºC in air which is comparable to other apatite-type lanthanum silicate (ATLS) conductors.

Synthesis and characterization of nano-structured Th1−x Ce x O2 mixed oxide

GEL combustion technique was applied to obtain oxides of thorium and cerium from their respective nitrate solutions using citric acid as the gelating agent. The dried samples were characterized by IR and TG studies. Intermediate and final products during TG studies have been isolated and characterized by XRD studies. All the TG runs during heating of thorium and cerium nitrate with citric acid dried Gels showed a two step process. The weight loss at each step and the X-ray data of the product at each step, helped in suggesting a possible mechanism. Kinetic study was carried out independently for each step. The reaction mechanism as observed during interactive procedure was found to be diffusion controlled. The kinetic parameters (activation energy and pre-exponential factor) for each step in all reactions have been calculated. Observations from XRD studies show that with increase in cerium concentration in the oxides, the lattice parameter values have shown a decreasing trend for all the five compositions studied. It was observed that in TG studies with increase in cerium concentration, the final temperature of the reactions have shown a decreasing trend. SEM studies of the powders reveal that synthesized oxides have a tendency to form agglomerate of varying size ranging from 50 to 100 μm in case of mixed oxides but the size of thorium oxide powder so synthesized have pore size 10–100 μm. SEM images shows that GEL combustion may result in agglomeration, if the temperature is not properly controlled to the desired value. SEM studies also reveal that each agglomerate contains approximately 10–100 individual particles. Surface area of the mixed oxide powders were determined using Gas adsorption technique. The surface area was found to be in the range of 3–17 m2/g in all cases. Specific surface area of thorium oxide was found to be lesser than cerium oxide but in case of mixed oxides surface area decreases with increase in cerium content. Majority of pores, indicating the particle size are in the range of 0.01–0.04 cm3/g.

Improvement of electrochemical properties of layered LiNi 1/3Co 1/3Mn 1/3O 2 positive electrode material by zirconium doping

To improve the electrochemical properties of LiNi 1/3Co 1/3Mn 1/3O 2, powders of Zr-doped mixed transition metal oxides, LiNi 1/3Co 1/3Mn 1/3-xZr xO 2 (x = 0, 0.01, 0.025, 0.05) (LNCMZ), are synthesized via a thermal polymerization method. Their structure and electrochemical properties are investigated by X-ray diffraction, galvanostatic charge–discharge of LNCMZ/Li half cells, galvanostatic intermittent titration technique (GITT), direct current resistance measurement and AC impedance spectroscopy. All of the prepared LNCMZ samples have a hexagonal α-NaFeO 2 structure whose lattice parameters increase monotonously with the Zr content. The Zr doping results in higher lithium diffusion coefficient in LNCMZ and more stable resistance during the electrochemical cycling of LNCMZ/Li cells so that the Zr-doped samples show notable improvement of cycling performance and rate capability. The sample LiNi 1/3Co 1/3Mn 1/3-0.01Zr 0.01O 2 exhibits the best electrochemical performance with capacity retention of 92.7% during 100 cycles and a capacity of 133.9 mAh g −1 at 8 C rate, corresponding to 71.5% of its capacity at 0.1 C.

Enhanced Electrode Activity of Ni/(CeO2)1−x(TiO2)x Anode in Electrochemical Oxidation of Methane

The electrode activity of a newly developed Ni/(CeO2)1−x(TiO2)x cermet anode has been investigated at intermediate temperatures. (CeO2)1−x(TiO2)x mixed oxide powders were synthesized by the sol-gel method. A single cell, Ni/(CeO2)1−x(TiO2)x|Sm0.2Ce0.8O3|Sm0.5Sr0.5CoO3, was fabricated using a samarium-doped ceria disk. The effect of incorporating TiO2 into the CeO2 matrix was studied with the goal of improving the anode micro structure. The modified micro structure of the new Ni/(CeO2)0.8(TiO2)0.2 cermet anode, which consists of fine Ni particles distributed on (CeO2)0.8(TiO2)0.2 mixed oxide particles, enhances the electrode activity in methane oxidation.

Preparation of zirconium–manganese oxide/polyacrylonitrile (Zr–Mn oxide/PAN) composite spheres and the investigation of Sr(II) sorption by experimental design

Zirconium–manganese oxide/polyacrylonitrile (Zr–Mn oxide/PAN) composite spheres were prepared to remove strontium ions from aqueous solution. Zr–Mn mixed hydrous oxide powder was synthesized via co-precipitation and then mixed with polyacrylonitrile (PAN) as a binding material to form a Zr–Mn oxide/PAN composite spheres. The surface of the composite spheres was modified with 1 M NaOH. The effect of pH, temperature, initial strontium concentration and shaking time on strontium sorption were investigated via experimental design method using central composite design (CCD). Central composite design, with seven replicates at the centre points and thus a total of 31 experiments were employed in this study. A second-order polynomial equation related to the model was obtained and 3 dimensioned surface contour plots were drawn. The characterization of the adsorbent was performed by XRD, SEM, surface area and porosity analysis. Chemical stability of the composite spheres was tested against acidic media. Sorption data have been interpreted in terms of Freundlich, Langmuir and Dubinin–Radushkevich isotherms. Thermodynamic parameters for the sorption system have been determined.

5d–4f and 4f–4f emissions in Ln-doped sesquioxide ceramics

In this study, various lanthanide and mixed lanthanide oxides (Ln 2O 3 with Ln = La, Lu, Lu 0.5Gd 0.5) powders have been synthesized by a coprecipitation method. The luminescence properties and/or the quenching mechanisms of different dopants (europium, cerium, praseodymium) have been studied. Luminescence mechanisms of Ce:Ln 2O 3 and Pr:Ln 2O 3, are closely related to the 5d and 4f energy levels positions of the dopant versus materials bandgap and crossing effect between dopant energy levels. Energy level positions have been analyzed through optical spectroscopy and their effect on the luminescence is presented. Eu:Lu 2O 3 and Eu:LuGdO 3 have also been prepared as transparent ceramics and radioluminescence properties are presented.

Magnetic properties of nano-clusters lanthanum chromite powders doped with samarium and strontium ions synthesized via a novel combustion method

Abstract A novel approach to synthesize a single-phase orthorhombic perovskite lanthanum chromite LaCrO3 clusters doped with Sm3+ and Sr2+ ions via gel combustion route was reported. The producing materials were synthesized using metal nitrates as oxidizers and triethanol amine (TEA), N-butyl amine (NBA) or ethylene diamine (EDA) as a fuel. The effect of the annealing temperature, type of organic fuel and the variation of the samarium and/or strontium substitution and its impact on crystal structure, crystallite size, microstructure and magnetic properties of the LaCrO3 powders formed was systematically studied. The results revealed that a well crystalline single phase of pure LaCrO3 can be achieved at annealing temperature from 800 to 1000 °C for 2 h. Moreover, each organic carrier materials exhibited a different degree of effectiveness in the synthesis of the mixed oxide powders. The crystal structure was influenced by doped Sm3+ and/or Sr2+ ions. The crystallite size of the produced powders was increased with the increase the annealing temperature, increasing the Sm3+ ion and the decrease of Sr2+ ion substitution. The microstructures of the produced powders were found to be nanoclusters octahedra-like shaped. The saturation magnetization of the LaCrO3 powders increased continuously with an increase in the Sm3+ ion concentration and it decreased with an increase in the Sr2+ ion up to 0.3 at annealing temperature of 1000 °C for 2 h. The maximum saturation magnetization (0.279 emu/g) was achieved at the Sm3+ ion molar ratio 0.3 and annealing temperature 1000 °C. Moreover, wide coercivities can be obtained at different synthesis conditions (49.25 to 522 Oe).

Sol−Gel Based Chemical Synthesis of Nd2Fe14B Hard Magnetic Nanoparticles

Nd2Fe14B hard magnetic nanoparticles were synthesized by chemical synthesis techniques. Nd−Fe−B gel was prepared using NdCl3·6H2O, FeCl3·6H2O, H3BO3, citric acid, and ethylene glycol (EG) by a Pechini type sol−gel method. This gel was subsequently annealed to produce mixed oxide powders. Nd2Fe14B nanoparticles were prepared from these oxides by a reduction−diffusion process. The phase analysis, structure, and magnetic properties were determined by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), transmission electron microscope (TEM), and vibrating sample magnetometer (VSM) techniques. The mechanism of Nd2Fe14B formation was investigated by differential scanning calorimetry (DSC), XRD, and thermodynamic free energy change data. Our experimental and modeling results showed that the reduction−diffusion of the Nd−Fe−B mixed oxide was a three step process. The reduction of Fe2O3 to Fe and B2O3 to B o...

Synthesis of Nanosized Ag<sub>0.9</sub>Na<sub>0.1</sub>(Nb<sub>0.7</sub>Ta<sub>0.3</sub>)O<sub>3</sub> Ceramic Powder and Investigation on its Property

In this communication, Ag0.9Na0.1(Nb0.7Ta0.3)O3（ANNT） mixed oxide powder was synthesized by citrate wet chemical method. TG-DTA, XRD and TEM analyses showed that the reaction temperature was 800°C, the calcining time was three hours, and the product was pure ANNT in well-dispersed grain structure (35nm in average).

Selective methanation of CO in hydrogen-rich gases involving large amounts of CO 2 over Ru-modified Ni-Al mixed oxide catalysts

Selective methanation of CO was investigated in hydrogen-rich gas streams involving 20% CO 2 over a Ru-modified Ni-Al mixed oxide catalyst. The Ni-Al mixed oxide was prepared by the solution-spray plasma technique, by which fine powders of homogeneous mixed oxides can be easily synthesized. By the addition of a small amount of Ru, the catalytic activity and selectivity of the Ni-Al mixed oxide catalyst for CO methanation was improved dramatically. The added Ru enhanced the formation of nano-sized Ni metal particles via reduction of the mixed oxide by spill-over-hydrogen during reduction treatment, even at low temperature. Kinetic measurements revealed that the methanation of CO took place predominantly over the Ni metal sites. Selectivity for the CO methanation was also improved significantly by the addition of Ru due to suppression of CO 2 dissociation over the Ni metal sites.

Fabrication of Mg Ferrite/permalloy Magnetic Nano-composites

Dense {Mg(Fe1-xMnx)2O4/53Fe-47Ni permalloy (0≤x≤0.4)} magnetic nano-composites consisting of spinel and alloy phases have been fabricated from N2-atomized metal particles and fine-powder mixtures of MgO/α-Fe2O3/MnO using a combination of pulsed electric current pressure sintering (PECPS) and hot isostatic pressing (HIP). Fe-Ni permalloy particles were coated with the mixed metal oxide powders homogeneously by passing these mixtures through a narrow gap (1 mm) under high shear compression in Ar. Mixed powder compacts of permalloy with the fine metal oxides were densified into the green bodies having relative densities of 83-85 % under isostatic high pressure of 1 GPa at room temperature. Then green powder compacts were pre-sintered at 823 K for 3 min under a uniaxial pressure of 100 MPa in Ar using a PECPS. The pre-sintered bodies composed of spinel ferrite and permalloy revealed the relative densities of 94-96 %; the mixed metal oxides changed into magnesium spinel ferrites Mg(Fe1-xMnx)2O4 during a short heating time. Then hot isostatic pressing (HIP: (1123 K/6 h/200 MPa-Ar)) was adopted to sinter the pre-sintered bodies into a near full density without an encapsulation, however, a sintering atmosphere control was performed using a ferrite muffle in order to maintain the both phase. Sintered nano-composites with the relative density more than 99.5 % have a saturation magnetization density ≥1 T and moderate permeability values of 30-35 at 10 MHz, which values have been expected from a material design.

Feasibility Study on a Simplified MOX Pellet Fabrication Process, the Short Process, for Fast Breeder Reactor Fuel

Technological feasibility of a simplified mixed-oxide (MOX) pellet fabrication process, the short process, was studied. About 300 g of microwave heating denitrated (MH)-MOX powder with adjusted plutonium content to 30% could be successfully processed by a tumbling granulator for subsequent pelletizing and sintering processes. The granulated 30%PuO2-MOX powder could be pressed into green annular pellets directly and smoothly when using a die wall lubrication method. The pellet tensile strengths were compared for a granulated molybdenum powder that has similar characteristics to those of granulated 30%PuO2-MOX powder, and they were higher for pellets obtained when using the die wall lubrication method than when using the conventional powder mixing method. The amount of additives in the green pellets could be controlled at a low value of 0.06 wt% in this process. It is, therefore, possible to carry out dewaxing and sintering of green pellets in the same furnace. By controlling the average particle sizes of granulated 30%PuO2-MOX powders, pellets with more than 95% theoretical density could be obtained after sintering at 1700°C for 2 h.As a result, it can be concluded that the short process is technologically feasible to fabricate MOX annular pellets.

Phase characterization of Sm–Lu mixed oxide powders prepared by sintering and radio frequency plasma spraying

Abstract Radio frequency plasma spraying is a promising technique to prepare rare earth oxide nano-particles. Applying this method after sintering of pellets at T = 1600 °C and subsequent grinding, Sm2O3—Lu2O3 mixed oxide powders of various compositions were synthesized. Analyzing the ground powders, the phase field can be divided into three regions: (1) Sm-rich monoclinic B-type solid solutions, (2) Lu-rich cubic C-type solid solutions, and (3) a diphasic region for Lu contents 0.33 ≤ x Lu ≤ 0.54. In the single phase areas, the volume for one formula unit of the rare earth sesquioxide is found to depend linearly on the cubed average cation radius. Plasma spraying of the Lu-rich powders leads to a second monoclinic B-type phase. Excluding the solubility gap, the monoclinic lattice parameters show quadratic dependencies on the Lu content and the molecular volume is a function of third order on the cation radius.

Electrocatalytic Activity of an SOFC Anode Consisting of Nickel, Cerium Oxide, and Titanium Oxide for the Oxidation of Methane

Ti-doped CeO2 mixed oxide powders (CeO2-TiO2) were synthesized by a sol-gel method with varying amount of Ti. The XRD patterns of CeO2-TiO2 (10 and 20 mol% Ti) powders calcined at 800°C for 4 h did not show the TiO2 phase. The electrical conductivity of CeO2-TiO2 mixed oxide was higher than that of CeO2 between 650 and 750°C under reducing atmosphere. The electrocatalytic activity of Ni/CeO2 and Ni/CeO2-TiO2 cermet anodes were examined under the oxidation of methane for solid oxide fuel cells (SOFCs). The Ni/CeO2-TiO2 (20 mol% Ti) anode showed a higher power density than that Ni/CeO2 in both H2 and CH4 fuels. The enhancement of methane oxidation was most likely to be caused by the higher electrical conductivity of the mixed ionic and electronic CeO2-TiO2 oxide cermet. The electrode polarization of the Ti-doped CeO2 anode was lower than that of the non-doped CeO2 anode.

Silica–zirconia mixed oxide samples by an hybrid materials based innovative preparation procedure: Influence of preparation procedure and composition on active sites

Abstract In this work, the interaction of amorphous silica–zirconia mixed oxide samples obtained from inorganic–organic silica-based hybrid materials with pyridine and CO2 was studied to investigate their acid/base character. Several silica–zirconia mixed oxide powders characterized by different [Zr/Si] atomic ratios were prepared and treated at increasing temperatures both in a conventional muffle and with microwave technology. The powder samples were characterized with Diffuse Reflectance Infrared Fourier Transform (DRIFT) and X-ray Photoelectron (XP) spectroscopies. The surface acidic and basic active sites were investigated (with DRIFT spectroscopy) by chemisorbing probe molecules (pyridine, carbon dioxide). The obtained results revealed the presence of both Lewis and Bronsted acidic sites on the amorphous silica–zirconia mixed oxide powder surfaces. Several acidic sites characterized by different strength were observed; the acidic sites distribution is markedly influenced by the sample composition and by the heat treatment: more numerous acidic sites form on the surface of the samples treated with microwaves with respect to the muffle treated ones; the increment of the temperature and the decrease of the zirconium content cause a significant decrement of the acidic sites. No basic sites were revealed.

Effective thermal conductivity of MOX raw powder

The radial temperature distribution of plutonium and uranium mixed oxide powder loaded into a cylindrical vessel was measured in air and argon gas, and the effective thermal conductivity was calculated from the measured temperature distribution and the decay heat. The effective thermal conductivities were small values of 0.061–0.13 W m –1 K –1 at about 318 K, and changed significantly with O/M, bulk density and atmospheric gas. The results in this work were analyzed by the model of Hamilton and Crosser and a new model for the effective thermal conductivity of the powder was derived as functions of powder properties and thermal conductivity of atmospheric gas.

Screen printing of sol–gel-derived electrolytes for solid oxide fuel cell (SOFC) application

The idea of using the sol–gel technique for producing low-cost components for solid oxide fuel cell (SOFC) application has attracted great interest. Besides its economic advantages, the sol–gel technique additionally offers the chance to reduce either the thickness of the electrolyte and therefore to reduce ohmic resistances or to lower the sintering temperature of single components like the electrolyte layer, due to the clearly reduced particle sizes of colloidal distributed particles in the sol. The work presented here deals with the development of sols and their application in combination with yttria fully stabilized zirconia mixed-oxide powders for the preparation of screen-printing pastes. Besides physical, chemical and thermal characterization of the sols, variations of the composition of the sol as well as of the pastes composed of sol and mixed-oxide powder were evaluated for preparing dense, gas-tight layers sintered at various temperatures, resulting in sufficient gas-tightness to ensure high power density SOFCs. Additionally, technological screen-printing parameters were studied. Single cell tests (50 mm × 50 mm) revealed current densities of approx. 1 A/cm 2. These values are comparable to current densities obtained by cells based on normal electrolyte layers, which were prepared in parallel.