Nitrate Route Research Articles

Processing and oxygen permeation studies of asymmetric multilayer Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3− δ membranes

The oxygen transport studies of dense Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3− δ (BSCF) ceramic membranes, prepared via glycine–nitrate route, demonstrated that the permeation rate is predominantly controlled by surface exchange kinetics when the membrane thickness is smaller than 1.00 mm. In order to improve oxygen exchange, an asymmetric membrane concept including two porous and one dense layer was implemented. The amount of graphite as a pore-forming additive, powder compaction and sintering conditions were optimized to produce three-layer membranes having appropriate mechanical strength and microstructure. Comparison of the data on oxygen permeation through three-layer and dense 1.00 mm thick symmetric membranes indicated that a moderate improvement of the overall performance was achieved due to asymmetric architecture. The oxygen fluxes through membrane with 170 μm thick dense and porous layers with thicknesses of 1.05 mm and 100 μm at 1173 K were found to be ∼1.5–1.8 times higher than those for a 1.00 mm thick symmetric membrane. The variation of oxygen flux changes with pressure and the values of the activation energies for oxygen permeation suggest significant gas diffusion limitations in the porous layers, whilst the role of other factors is still significant. Microstructure of the porous layers requires further optimization for successful application of the oxygen exchange catalysts.

Epitaxial Growth of La<SUB>2</SUB>Zr<SUB>2</SUB>O<SUB>7</SUB> Buffer Layer on Textured Ni5W Substrate by the Nitrate Route

采用硝酸盐为前驱盐制备涂层导体结构中的La 2 Zr 2 O 7 (LZO)过渡层. 实验通过对前驱盐粉体热分解行为的分析, 以及前驱盐溶液在铝酸镧(LAO)单晶和Ni5W合金基底上外延生长LZO膜层工艺的比较研究, 经优化获得了采用硝酸盐为前驱盐, 适用于Ni5W合金基底的低温两步热处理结合高温快速热处理制备LZO的工艺路线. 研究发现, 硝酸盐热分解过程及中间产物分解对外延织构的生成起着重要的作用. 取向分析显示LZO膜层(222)phi扫描和(400)ω扫描的半高宽分别为8.5°和8.1°, 这表明LZO膜层形成了较好的立方织构. SEM分析显示该工艺制备的膜层均匀致密, 没有裂纹和孔洞. 以上研究表明硝酸盐法可以应用于LZO过渡层的制备.

Micro‐Raman investigation of nanosized zinc ferrite: effect of crystallite size and fluence of irradiation

AbstractZinc ferrite nanoparticles of different sizes ranging from 12 to 62 nm were synthesized by using the nitrate route. These nanoparticles were irradiated by a 100 MeV oxygen beam at two fluences: 1 × 1013 and 5 × 1013 ions/cm2. It was observed that modes corresponding to cubic spinel phase were retained after the irradiation in all the systems. The variation in the parameters of various modes follows phonon confinement, while this effect seems to violate in irradiated specimen. It was found that the irradiation‐induced changes in the modes F2g(2) and F2g(3) depend on whether the crystallite size of the pristine sample is less than, equal to or greater than the phonon confinement length, while this length is not dominant for the irradiation‐induced changes in the mode A1g. The changes in various parameters of the modes are attributed to the combined effect of the restructuring of the chemical species and ion‐induced defects. Copyright © 2011 John Wiley & Sons, Ltd.

Photocatalytic reduction of Cr(VI) on the new hetero-system CuAl2O4/TiO2

Visible light driven HCrO4− reduction was successfully achieved over the new hetero-system CuAl2O4/TiO2. The spinel, elaborated by nitrate route, was characterized photo electrochemically. The optical gap was found to be 1.70eV and the transition is directly allowed. The conduction band (−1.05VSCE) is located below that of TiO2, more negative than the HCrO4−/Cr3+ level (+0.58VSCE) yielding a thermodynamically feasible chromate reduction upon visible illumination. CuAl2O4 is stable against photo corrosion by holes consumption reaction involving salicylic acid which favors the charges separation. There is a direct correlation between the dark adsorption and the photo activity. A reduction of more than 95% of chromate was achieved after 3h irradiation at pH 2 with an optimal mass ratio (CuAl2O4/TiO2) equal to 1/3. The reduction follows a first order kinetic with a half life of ∼1h and a quantum yield of 0.11% under polychromatic light. Prolonged illumination was accompanied by a deceleration of the Cr(VI) reduction thanks to the competitive water discharge. The hydrogen evolution, an issue of energetic concern, took place with a rate of 3.75cm3 (gcatalyst)−1h−1.

Preparation and characterization of CuFe2O4 bulk catalysts

This work is devoted to the investigation of the influence of the preparation process on the physical–chemical properties of a copper spinel applied as catalyst for hydrocarbon (HC) oxidation. Samples of CuFe2O4 mixed oxide belonging to the inverted spinel type structure have been obtained by high temperature solid state reaction and by wet chemical synthesis methods, applying nitrate and citrate precursor procedures, within the thermal range from 150 to 700°C.The bulk catalysts were characterized by XRD, TPR, FTIR, SEM-EDX, TEM and Mössbauer spectroscopy. Propane combustion was performed as a reaction test.In this work it is demonstrated that the calcination temperature and chemical synthesis affect the crystal properties and cation distribution in the spinel structure, microstructure, surface area and reducibility; which are among the most relevant physical chemical properties for the catalytic activity. The materials obtained by wet chemical procedure, through nitrate and citrate routes, are better suited for propane combustion. This feature is assigned to the microstructure, to the presence of nanometric size particles and also to the cation distributions in the spinel sublattices of these materials.

Preparation of Y0.5[Yb1−x Nd x ]0.5Ba2Cu3O z Superconductors Using Nitrate Routes

The chemical solution nitrate route was used to prepare Y0.5[Yb1−xNdx]0.5Ba2Cu3Oz superconducting phase with x=0.1, 0.2 and 0.3. Different calcination temperatures from 870 to 900 °C were used. Both XRD and DSC techniques were utilized in monitoring the Y0.5[Yb1−xNdx]0.5Ba2Cu3Oz superconducting phase and the non-superconducting impurity phases such as BaCuO5, CuO and RE2BaCuO5. These two techniques were used to study the effect of impurity phases on the decomposition temperature of Y0.5[Yb1−xNdx]0.5Ba2Cu3Oz superconducting phase. The value of x, the Nd amount, and the calcination temperature both influenced the type and number of impurity phases, which resulted in changing the eutectic and peritectic reaction temperatures.

Synthesis of SrTiO<sub>3</sub> Nanoparticles by a pH-Varying Sol-Gel Process

SrTiO3 is one of the most technologically important dielectric ceramics. In this paper, SrTiO3 nanoparticles were synthesized by a simple sol-gel route using NaOH to adjust the pH of the system. Three different strontium-containing starting precursors (Sr(NO3, SrCl2.6H2O and Sr(CH3COO)2.0.5H2O) were employed. Thermogravimetric analysis (TGA) showed complete decomposition of organics at approximately 800°C; this temperature was chosen as a calcination temperature. At 800°C, 6 hours, only the nitrate route with pH = 10 gives single-phase SrTiO3. Other conditions yield various impurities, most likely due to the incompletion of the reaction although they still contain very broad XRD peaks corresponding to SrTiO3, signifying the probable phase formation capability at these conditions. The obtained SrTiO3 powders are in the nanoscale range of 10 to 40 nm with isotropic morphology.

Hydrogen photo-evolution over the spinel CuCr 2O 4

The photocatalytic H 2 evolution over CuCr 2O 4 has been studied in connection with some physical properties. The black oxide is classified as a narrow band gap semiconductor crystallizing in the normal spinel structure. The photoactivity is dependent on the preparative conditions through the surface area of the powder and CuCr 2O 4 has been synthesized by nitrate route. The conductivity varies exponentially with temperature indicating an extrinsic conductivity between mixed valences states Cr 3+/4+ located in octahedra sharing common corners. The oxide exhibits p-type conductivity with an activation energy of 0.20 eV and a hole mobility of 2.14 × 10 −8 cm 2/V s thermally activated. CuCr 2O 4 shows an excellent chemical stability, a corrosion potential of −0.775 V SCE and an exchange current density of 16 μA cm −2 have been determined from the semilogarithm plot. The capacitance measurement (C −2−V), performed in basic electrolyte, exhibits a linear behavior from which a flat band potential of 0.48 V SCE was obtained. CuCr 2O 4 is photoelectrochemically stable by hole consumption reactions involving X 2− (= SO 3 2 - and S 2 O 3 2 - ) as hole scavengers. The best catalytic performance for H 2-photoproduction was obtained in (NaOH 0.5 M, Na 2S 2O 3 0.025 M) with an average rate of 0.013 cm 3 h −1 (mg catalyst) −1 and a quantum efficiency of 0.2% under polychromatic light. S 2 O 3 2 - is oxidized to SO 3 2 - and subsequently to SO 4 2 - as proven by the dual slopes in the Tafel plot. The system shows a tendency towards saturation whose deceleration is the result of the competitive reductions of the end products namely S 2 O 6 2 - and S 2 O 4 2 - with the water discharge.

Synthesis and characterization of nanocrystalline forsterite through citrate–nitrate route

Nanocrystalline forsterite, Mg 2SiO 4, powder was synthesized according to the citrate–nitrate technique using an aqueous solution of magnesium nitrate, colloidal silica, citric acid, and ammonia. The dried precursor and the powders calcined at different temperatures were characterized by X-ray diffraction (XRD), simultaneous thermal analysis (STA), field emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). The initial crystallization temperature of forsterite was around 770 °C while fully crystallized forsterite was obtained at 860 °C with a crystallite size of about 30 nm.

Characterization and electrochemical performances of Ba 2− xSr xFeO 4+ δ as a novel cathode material for intermediate-temperature solid oxide fuel cells

Novel cathode materials, Ba 2− x Sr x FeO 4+ δ ( x = 0.5, 0.6, 0.7, 0.8, 1.0), for intermediate-temperature solid oxide fuel cells on a samaria-doped ceria (SDC) electrolyte were prepared by the glycine–nitrate route and characterized by X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), thermogravimetric (TG) analysis, electrochemical impedance spectroscopy and steady-state polarization measurement. SEM results showed that the electrode formed a good contact with the SDC electrolyte after sintering at 1000 °C for 2 h. The value of δ in Ba 1.0Sr 1.0FeO 4+ δ materials was calculated from the TG results. The electrochemical impedance spectra revealed that Ba 2− x Sr x FeO 4+ δ had a better electrochemical performance than that of Ln 2NiO 4 (Ln = La, Pr, Nd, Sm). In the Ba 2− x Sr x FeO 4+ δ ( x = 0.5, 0.6, 0.7, 0.8, 1.0) family, the composition Ba 1.0Sr 1.0FeO 4+ δ exhibited the best electrochemical activity for oxygen reduction. The polarization resistance of Ba 1.0Sr 1.0FeO 4+ δ on SDC electrolyte was 1.11 Ω cm 2 at 700 °C, which was less than half that reported for Ln 2NiO 4 at the same temperature.

Development of MgAl 2O 4 spinel coating on graphite surface to improve its water-wettability and oxidation resistance

Low water-wettability and oxidation resistance of graphite have limited its application in carbon containing refractory castables. The aims of this study are the improvement of water-wettability and the oxidation resistance of natural flaky graphite by applying an oxide coating on its surface. To develop the coating, magnesium aluminate spinel sol was formulated via a citrate–nitrate route and graphite powder was then added to the sol. The mixture was heat treated in appropriate temperature and atmosphere to get the polycrystalline MgAl 2O 4 coating on graphite particles surface. The microstructure of coating was studied by X-ray diffractometer, SEM and TEM. The water-wettability was evaluated by measuring the water drop contact angle and plotting the zeta potential vs. pH. The results showed the development of a stable nanocrystalline MgAl 2O 4 spinel coating which improved the water-wettability and oxidation resistance of graphite significantly. Also, characterization of the coating is explained with emphasis on its application importance.

Photocatalytic removal of M 2+ ( [dbnd]Ni 2+, Cu 2+, Zn 2+, Cd 2+, Hg 2+ and Ag +) over new catalyst CuCrO 2

The metal ions M 2+ (Ni 2+, Cu 2+, Zn 2+, Cd 2+, Hg 2+ and Ag +) are potentially toxic. Their electro deposition has been carried out in aqueous air-equilibrated CuCrO 2 suspension upon visible illumination. The delafossite CuCrO 2 is p-type semiconductor characterized by a low band gap (1.28 eV) and a long-term chemical stability. The corrosion rate is found to be 10 −2 μmol m −2 month −1 in aqua regia. The oxide has been elaborated through nitrate route where the specific surface area is increased via the surface/bulk ratio. A correlation exists between the dark M 2+ adsorption, the redox potential of M 2+/0 couple and the conduction band of CuCrO 2 positioned at −1.06 V SCE. Ag + cannot be photoreduced because of its positive potential located far above the valence band. By contrast, Zn 2+ is efficiently deposited due to the large driving force at the interface. The improved photoactivity of copper with a deposition percentage (90%) is attributed to the strong dark adsorption onto the surface catalyst. The results indicate a competitive effect with the water reduction; it has been observed that the M 2+ deposition goes parallel with the hydrogen evolution. Such behavior is attributed to the low H 2 over voltage when ultra fine aggregate of M islands are photodeposited onto CuCrO 2 substrate.

Low temperature processing of dense samarium-doped CeO2 ceramics: sintering and intermediate temperature ionic conductivity

Samarium-doped Ceria powders for solid electrolyte ceramics were synthesized by a combustion process. Cerium nitrate and samarium nitrate were used as the starting materials, and glycine was used as fuel. Decomposition of unburned nitrogen and carbon residues was investigated by simultaneous thermogravimetry analysis and differential thermal analysis experiments. The X-ray diffraction results showed that the single-phase fluorite structure forms at a relatively low calcination temperature of 800 °C. X-rays patterns of the SDC powders revealed that the crystallite size of the powders increases with increasing calcination temperature. The sintering behavior results showed that more than 96% of the relative density is obtained for powders sintered at 1,100 °C for 8 h. The alternating current impedance spectroscopy results showed that the SDC15 sample sintered at 1,100 °C has ionic conductivity of 0.015 Scm−1at 650 °C in air. The present work results have indicated that glycine–nitrate route is a relatively low-temperature preparation technique to synthesize SDC powders with a high sinterability and a good ionic conductivity.

Effect of γ-irradiation on the transport and structural properties of polycrystalline Bi1.2 Pb0.33 Sr1.54 Ca2.06 Cu3 O10+δ superconductor

The effect of γ-irradiation on the transport and structural properties of polycrystalline Bi1.2 Pb0.33 Sr1.54 Ca2.06 Cu3 O10+δ superconductor, synthesized by nitrate route is studied. The sample has been irradiated by γ-ray upto a dose 400 MR using a 60Co isotope source of 2 kCi strength with a dose-rate of 6.26 Gy/min. Its X-ray diffraction pattern, resistivity–temperature behaviour as well as elemental and morphological analyses using scanning electron microscope have been examined before and after the irradiation. It is observed that the normal state resistivity increases as the dose is increased. The transition width of the sample is found to get broadened with the increasing dose. Using the theories of Aslamazov–Larkin and Maki–Thompson, we present an analysis of the excess conductivity of our sample and the effect of γ-irradiation on it. It is found that the coherence length of the sample gets increased with the increase of the irradiation dose.

Phase equilibria and crystal structures of phases in the La-Fe-Ni-O system at 1370 K in air

The phase equilibria in the La-Fe-Ni-O system have been studied at 1370 K in air, and the La-Fe-Ni-O phase diagram at constant temperature and pressure has been constructed. Based on x-ray diffraction results for samples prepared by standard solid-state reactions and via citrate and nitrate routes, the following solid solutions have been shown to exist at 1370 K in air: LaFe1 − xNixO3 − δ (0 < x ≤ 0.4, sp. gr. Pbnm; 0.6 ≤ x ≤ 0.8, sp. gr. R-3 c), La4(Ni1 − yFey)3O10 − δ (0 < y ≤ 0.3), La3(Ni1 − zFez)2O7 − δ (0 < z ≤ 0.05), La2Ni1 − vFevO4 + δ (0 < v ≤ 0.05), NikFe3 − kO4 (0.81 ≤ k ≤ 1.05), Ni1 − mFemO (0 < m ≤ 0.05), and Fe2 − pNipO3 (0 < p ≤ 0.04). The lattice constants and structural parameters of single-phase samples have been refined by the Rietveld profile analysis method.

Citrate - Nitrate route for the synthesis and characterization of TAG using sol-gel techniques

Terbium Aluminum Garnet (TAG) is an important optically active material and is one of the best materials known for the fabrication of optical isolators. TAG has a large Verdet constant and has good transmission in the region of 350–1500 nm of the electromagnetic spectrum. It is also known that TAG melts incongruently at 1840°C. This makes efficient synthesis of TAG important and challenging and forms the motivation of the present work to develop techniques for the synthesis of TAG at lower temperatures. In the present work we report the synthesis of TAG using sol-gel techniques following the citrate-nitrate route. The prepared sample is sintered at various temperatures in presence of air and characterized using X-ray diffraction, FT-IR spectroscopy, energy dispersive X-ray Analysis and the morphology is observed using the scanning electron microscopy.

Combined in situ FT-IR and TRM analysis of the NO x storage properties of Pt-Ba/Al 2O 3 LNT catalysts

The storage of NO 2 and NO/O 2 in the presence and in the absence of CO 2 was investigated at 350 °C on Pt-Ba/Al 2O 3 LNT catalysts and on the reference Ba/Al 2O 3 system, by coupling in situ FT-IR spectroscopy and transient response method (TRM). Experiments were performed by admitting NO 2/CO 2 or NO/O 2/CO 2 mixture (CO 2/NO x ratios in the range 1–7) or, in alternative, by admitting NO 2 or NO/O 2 on catalysts previously saturated by flowing CO 2. In the case of NO 2/CO 2 adsorption, it was found that NO 2 was efficiently stored as nitrate species according to a disproportion reaction, which occurs with evolution of NO, as in the absence of CO 2. In the case of NO/O 2/CO 2 adsorption it was confirmed that two pathways operated simultaneously as in the absence of CO 2: the “nitrite route”, involving the initial formation of surface nitrite and their subsequent evolution to nitrates, and the “nitrate route”, involving NO oxidation to NO 2 over Pt and its subsequent adsorption on Ba in the form of nitrates. The presence of CO 2 inhibits to some extent the “nitrite route”, whereas the “nitrate route” proceeds as in the absence of CO 2.

Nano and micro structural studies of thin films of ZnO

Zinc oxide thin films grown by sol–gel and RF sputtering methods have been characterized. The characterization techniques used involve ellipsometry, optical absorption, scanning tunneling microscopy, scanning and transmission electron microscopy. The films grown by sol–gel spin method which followed zinc acetate route exhibited a smoother texture than the films, which were deposited by using zinc nitrate route. The later type of films showed a dendritic character. Nano-structured fine grains of size ranging from 20 to 60 nm were observed with zinc nitrate precursor film. Individual grains show a sharp contrast with different facets and boundaries. Crystal planes and lattice parameters calculated by electron diffraction and X-ray diffraction are quite close and in agreement with the reported values in literature. Scanning tunneling microscopy has been used for measuring the average roughness of the surface and estimating the lattice constants. The STM studies of RF sputtered films, although showing a ZnO structure, exhibited a disturbed lattice. This was presumably due to the fact that after deposition the films were not annealed. Nanographs of 2D and 3D view of atomic positions of ZnO have been presented by using scanning tunneling microscopy.

High temperature thermal expansion and electrical conductivity of Ln 0.95MnO 3+ δ (Ln = La, Nd or Gd)

The rare earth deficient manganites Ln 0.95MnO 3+ δ (Ln = La, Nd or Gd) have been prepared by conventional ceramic method as well as by wet chemical methods like nitrate route and sol–gel route. Structural transformation, thermal expansion and electrical conductivity at elevated temperature were investigated on Ln 0.95MnO 3+ δ . The X-ray diffraction studies revealed that crystal symmetry of all the rare earth deficient manganites prepared either by sol–gel or solid-state route showed orthorhombic symmetry except lanthanum manganite prepared by solid-state route and the nitrate route. The thermal expansion behavior was studied using thermo-dilatometry and high temperature XRD techniques. The electrical conductivity studies of Ln 0.95MnO 3+ δ showed a clear phase transformation in case of La 0.95MnO 3+ δ synthesized by solid state route which was missing in all other rare earth manganites prepared by solid state and nitrate routes and wet chemical method. A comparative study on their linear thermal expansion behavior indicates that the value of coefficient of thermal expansion ( α) reduces to half as it goes from La to Gd. The electrical conductivity of sample synthesized by nitrate route was more as compared to sample prepared by other route like ceramic or sol–gel.

NO x removal catalysis under lean conditions

The storage-reduction of NO x over Pt–Ba/Al 2O 3 samples is analyzed in this work. It is pointed out that the storage of NO in the presence of excess oxygen proceeds through two parallel routes: (i) the “nitrate route” where NO is oxidized to NO 2 on Pt sites followed by NO 2 disproportionation on Ba sites to form nitrates with evolution of gaseous NO; (ii) the “nitrite route”, where NO is oxidized on Pt sites and directly stored on Ba neighbouring sites in the form of nitrites that are then oxidized to nitrates. The latter route possibly dominates at high Ba loadings. Concerning the reduction of the stored NO x , the bulk of data indicates that the process under isothermal conditions is not initiated by the release of NO x in the gas phase but occurs through a Pt-catalysed reduction of adsorbed NO x species. This route requires the co-presence of Pt and Ba on the same support. It is speculated that H 2 is activated on Pt sites and spills on the alumina support towards nitrate ad-species where it operates the reduction, although alternative explanations are possible.