Effect of preparation conditions on the phase composition of the MoVTe(Nb) oxide catalyst for the oxidative conversions of propane

The replacement of expensive propylene by propane, which requires the development of catalysts for the direct oxidation of propane into acrylonitrile, is an important and insufficiently studied problem. Multicomponent Mo _m V _n Te _k Nb _x oxide systems are promising in one-stage ammoxidation of propane to acrylonitrile. Despite considerable attention of various authors to the preparation methods for these catalysts, the reproducibility of their physicochemical and catalytic properties is low. To optimize the technology of catalyst synthesis, we studied the effect of drying method (evaporation or spray drying) for the aqueous suspension of the initial compounds on the formation of the Mo1V_0.3Te_0.23(Nb_0.12) oxide catalyst. It is shown that the method of drying determines the chemical and phase composition of solid catalyst precursors and the phase composition of the final catalyst in high-temperature treatment. The use of spray drying provides the required physicochemical characteristics of the catalyst (the specific surface area and the phase composition) that determine the high activity and selectivity in the selective conversion of propane. These catalysts contain two crystalline phases: orthorhombic M1 and hexagonal M2 in an optimal ratio of 3: 1.     

Effect of small additions of Li2O on phase separation and crystallization of barium-silicate glasses

It is known that the addition of Li₂O to 33.3BaO-66.7SiO₂ glass, whose composition is the same as BaSi₂O₅, promotes crystallization of BaSi₂O₅. In this study, in order to clarify the effect of a smaller amount of Li₂O, xLi₂O-(30-x)BaO-70SiO₂[mol%] (x = 0, 0.2, 0.5) glasses were prepared. The main crystalline phases in the heat treatments near the maximum crystallization peak temperature, were high-BaSi₂O₅ and low-BaSi₂O₅ which transformed from high-BaSi₂O₅. It is found that the introduction of only 0.2 mol% and 0.5 mol% Li₂O significantly changes the crystallization behavior. In the composition without Li₂O, only high-BaSi₂O₅ was formed after heat treatment even for 24 h. For compositions containing Li₂O, low-BaSi₂O₅ was formed within 1 h of heat treatment. In these compositions, it is found that the addition of Li₂O enhances phase separation in the early stage of heat treatment, resulting in the formation of Si-rich droplet phases and Ba-rich phases. The composition of the Ba rich glass phase would be close to the stoichiometric composition of BaSi₂O₅, suggesting a significant change in crystallization behavior.     

Structural,magnetic, electrical,and electrochemical properties of Sr–Co–Ru–O: A hybrid‐capacitor application

In this study, we report the synthesis of SrCo_1?xRu_xO_3?δ nominal compositions, where x = 0.0‐1.0, using solid‐state reaction technique. XRD analysis confirms the structure of x = 0 sample as hexagonal Sr₆Co₅O₁₅. As the Co ions are substituted by Ru, a two‐phase structure (hexagonal R32 and orthorhombic Pbnm) emerges up to x ≤ 0.5. As the Ru content is increased further, the hexagonal R32 phase disappears completely and an orthorhombic Pbnm phase becomes the main phase. SEM images show that grain size of the samples decreases with increasing Ru content. Temperature‐dependent electrical conductivity studies indicate upon Ru substitution in the nominal SrCo_1?xRu_xO_3?δ compounds, resistivity decreases due to appearance of metallic SrRuO₃ phase. The cyclic voltammogram (CV) of the samples show capacitive properties upon Ru substitution. The cycle measurements of the capacitors yield promising results for potential supercapacitor applications.     

Phase relation studies in the CeO2-La2O3 system at 1100-1500 °C

Materials based on CeO₂-La₂O₃ system are promising candidates for a wide range of applications, but the phase relationship has not been studied systematically previously. To address this challenge, the subsection of the phase diagram for 1100 and 1500 °C have been elucidated. Samples of different compositions have been prepared from nitrate acid solutions using conventional ceramic techniques; evaporation, drying, and calcinations. The phase relations in the binary CeO₂-La₂O₃ system at 1100-1500 °C were studied from the heat treated samples using X-ray diffraction analysis, petrographic investigation and scanning electron microscopy in the overall concentration range. It was established that in the binary CeO₂-La₂O₃ system there exist fields of solid solutions based on hexagonal (A) modification of La₂O₃, and cubic modification of CeO₂ with fluorite-type structure (F). The systematic study that covered whole composition range excluded formation of new phases. The refined lattice parameter of the unit cell and the boundaries of the homogeneity fields for solid solutions were determined.     

Synthesis of spherical LiMn2O4 microparticles by a combination of spray pyrolysis and drying method

Lithium manganese oxide (LiMn₂O₄) has been synthesized by a spray pyrolysis method from the precursor solution; LiNO₃ and Mn(NO₃)₂·6H₂O were stoichiometrically dissolved into distilled water. The synthesized LiMn₂O₄ particles exhibited a pure cubic spinel structure in the X-ray diffraction (XRD) patterns, however they were spherical hollow spheres for various concentrations of precursor solution. Thus, the as-prepared LiMn₂O₄ particles were then ground in a mortar and dispersed into distilled water. To make a well dispersed slurry solution, a dispersion agent was also added into the slurry solution. The LiMn₂O₄ microparticles with a spherical nanostructure were finally prepared by a spray drying method from the slurry solution. The tap density of the LiMn₂O₄ microparticle prepared by a combination of spray pyrolysis and drying method was larger than that by a conventional spray pyrolysis method.The as-prepared samples were sintered at 750 °C for 1 h in air and used as cathode active materials for lithium batteries. Test experiments in the electrochemical cell Li|1 M LiClO₄ in EC:DEC = 1:1|LiMn₂O₄ demonstrate that the sample prepared by the present method is a promising cathode active material for 4 V lithium-ion batteries at high-charge-discharge and elevated temperature operation. The LiMn₂O₄ compounds by the combination of spray pyrolysis and drying method are superior to that by the conventional spray pyrolysis method in terms of electrochemical characteristics and tap density.     

Synthesis and characterization of Cu–Co–Fe hydrotalcites and their calcined products

A series of new Cu–Co–Fe compounds with the general formula Cu _x Co_2−x Fe₁HT (x = 0, 0.5, 1, 1.5 and 2) has been prepared by hydrotalcite coprecipitation method. The presence of hydrotalcite phase is revealed by XRD analysis for x values of 0, 0.5 and 1. When the copper quantity is higher than 1, the malachite phase is preferentially formed. These results are confirmed by TG-DTA, FT-IR and XPS analysis. After calcination at 500 °C in air of all samples, XRD analysis reveals the presence of spinel phases such as Co₃O₄, CoFe₂O₄, CuFe₂O₄, Cu _x Co _y O₄ in the solids, monoclinic CuO phase when the copper content is greater or equal to 1 and haematite phase for the sample where x is equal to 2. The presence of these phases is also confirmed by XPS results. For comparison, a Co₂Fe₁OH sample has been synthesized by classical coprecipitation method and although Co₂Fe₁HT sample and Co₂Fe₁OH form a similar phase after calcination at 500 °C, Co₂Fe₁HT500 presents a higher BET value than Co₂Fe₁OH500 sample.     

Effect of Synthesis pH and H2O Molar Ratio on the Structure and Morphology of Aluminum Phosphate (AlPO-5) Molecular Sieves

AlPO-5 molecular sieves were prepared by the hydrothermal reaction of a gel mixture with the following compositions: Al₂O₃ : P₂O₅ : Et₃N : H₂O = 1:1:1.5:x, where x is between 100 and 750 H₂O molar ratio. The structure and morphology of the AlPO-5 molecular sieves depend on the gel mixture's composition, hydrothermal temperature, hydrothermal reaction time, and pH. Without pH control, the AlPO-5 structure changed from a spherical shape at H₂O = 100 to a hexagonal pillar shape at H₂O = 450. With pH control in the range of about 2.5-3.5, the hexagonal pillar crystals began to form at H₂O = 100 and an island of hexagonal pillars with radiation form appeared at H₂O = 300-450 due to the formation of a tridymite type of dense AlPO₄ phase. It appears that the formation rate of hexagonal pillar crystals to form a dense AlPO₄ phase is favorable under acidic conditions, and an amorphous AlPO-5 structure forms under basic conditions. Thus, the H₂O concentration and pH value have a dramatic effect on the AlPO-5 structure.     

Investigation of phase composition and microwave dielectric properties of MgO‐Ta2O5 ceramics with ultrahigh Qf value

Four MgO‐Ta₂O₅ ceramics with the MgO/Ta₂O₅ mole ratio x = 1, 2, 3, and 4 were prepared by traditional solid‐state reaction method, and the influence of x on the phase composition, microstructure, and dielectric properties (the dielectric constant ε_r, the temperature coefficient of resonant frequency τ_f and the quality factor Qf) of the materials was investigated using XRD, SEM, etc. The results indicated that the ceramics were composed of two crystalline phases MgTa₂O₆ and Mg₄Ta₂O₉ in the composition range studied, and that the dielectric properties ln ε, 1/Qf, and τ_f changed proportionally to the fraction of main crystal phases, which meet perfectly with the mixing model proposed in this study. It is obvious that the proportion of the two crystal phases could be precisely controlled by x, and thereby, the dielectric properties can be conveniently and precisely tailored. Our research provided a new microwave dielectric ceramic with the composition of 2MgO‐Ta₂O₅, which has an ultrahigh Qf value (211 000 GHz), low dielectric constant ε_r (19.9), and near zero temperature coefficient of resonant frequency τ_f (8 ppm/°C).     

Structural, thermal and crystallization kinetics of ZnO–BaO–SiO2–B2O3–Mn2O3 based glass sealants for solid oxide fuel cells

Glass compositions in the system 40SiO₂–30BaO–20ZnO–(x)Mn₂O₃–(10 − x)B₂O₃ glasses have been synthesized and the thermal, structural and crystallization kinetic properties characterized. The lower concentration of Mn₂O₃ in place of B₂O₃ acts as a network former and suppressed the tendency of phase separation in glasses. On the other hand, concentration of Mn₂O₃ > 7.5 mol% induce phase separation in the glass matrix. The highest activation energy for crystallization is observed in the composition without B₂O₃ (INM4) (355 kJ/mol). The values of thermal expansion coefficient (TEC) and viscosity of this glass is 8 × 10⁻⁶ K⁻¹ and 10^4.2dPa s (850 °C), respectively. After long heat treatment (800 °C for 100 h), thermodynamically stable hexacelsian and monoclinic phases are formed. These phases are not detrimental to SOFC application.     

A low external temperature method for synthesis of active electrode materials for Li batteries – Part B: Synthesis of lithium iron oxides Li x Fe y O z

Anode materials for lithium-ion batteries based on iron oxides were synthesized using two different methods: a Low External Temperature Method (LETM) and a conventional Solid State Reaction Method (SSRM). Both methods lead to the formation of final products representing a mixture of two phases: approximately 75% LiFeO₂ and 25% Li_−x Fe₅O₈ (0  <  x ≤ 0.1). When compared with the ordinary solid state synthesis, LETM creates conditions for carrying out the synthesis at a lower external calcination temperature (200 °C) over a shorter period. The properties of the Li _x Fe _y O _z obtained by the LETM were compared with those of the same compound obtained by SSR at 700 °C. Higher initial discharge capacity was displayed by the sample synthesized by the SSR method, while a superior cycling stability was shown by the sample synthesized by the LETM. The latter shows approximately double capacity at the 30th cycle as compared with the sample synthesized by SSRM.     

Phase Evolution and Microstructural Studies in CaZrTi2O7–Nd2Ti2O7 System

A series of compositions with general stoichiometry Ca_1?xZr_1?xNd_2xTi₂O₇ has been prepared by high‐temperature solid‐state reaction of component oxides and characterized by powder X‐ray diffraction and electron probe for microanalyses (EPMA). The phase fields in CaZrTi₂O₇–Nd₂Ti₂O₇ system and distribution of ions in different phases have been determined. Four different phase fields, namely monoclinic zirconolite, cubic perovskite, cubic pyrochlore, and monoclinic Nd₂Ti₂O₇ structure types are observed in this system. The 4M‐polytype of zirconolite structure is stabilized by substitution of Nd³⁺ ion. The addition of Nd³⁺ ions form a cubic perovskite structure‐type phase and thus observed in all the compositions with 0.05 ≤ x ≤ 0.80. Cubic pyrochlore structure‐type phase is observed as a coexisting phase in the nominal composition with 0.20 ≤ x ≤ 0.90. Only a subtle amounts of Ca²⁺ and Zr⁴⁺ are incorporated into the perovskite‐type Nd₂Ti₂O₇ structure. EPMA analyses on different coexisting phases revealed that the pyrochlore and perovskite phases have Nd³⁺‐rich compositions.     

Structural,morphological, and magnetic characterization of bulk and thin films Y3Al5–xFexO12 (YAIG): From the perspective of aqueous sol–gel processing

An aqueous sol–gel method was used for the preparation of bulk Y₃Al_5–xFe_xO₁₂ (yttrium aluminum–iron garnet, YAIG) with the composition of x?=?0.0, 1.0, 2.0, 2.5, 3.0, 4.0, 5.0 and thin films with the composition of x?=?0, 3.0, 4.0, 5.0. The dip-coating technique was used for the preparation of Y₃Al_5–xFe_xO₁₂ films on a silicon (Si) substrate. The phase composition and surface morphology of both bulk and coatings were determined and compared. The synthesized powder samples were investigated by X-ray diffraction analysis, infrared spectroscopy, scanning electron microscopy, and Mössbauer spectroscopy. The data provide evidence that some sol–gel-derived powder specimens consist of magnetically ordered component, while others show paramagnetic behavior depending on the composition of the product. It was also shown that sol–gel processing route could be successfully used for the preparation of mixed-metal YAIG thin films.     

Plasma sprayed nanostructured GdPO4 thermal barrier coatings: Preparation microstructure and CMAS corrosion resistance

Nanostructured GdPO₄ thermal barrier coatings (TBCs) were prepared by air plasma spraying, and their phase structure evolution and microstructure variation due to calcium–magnesium–alumina–silicate (CMAS) attack have been investigated. The chemical composition of the coating is close to that of the agglomerated particles used for thermal spraying. Nanozones with porous structure are embedded in the coating microstructure, with a percentage of ~30%. CMAS corrosion tests indicated that nanostructured GdPO₄ coating is highly resistant to penetration by molten CMAS at 1250°C. Within 1 hour heat treatment duration, a continuous dense reaction layer forms on the coating surface, which are composed of P–Si apatite based on Ca_2+xGd_8?x(PO₄)_x(SiO₄)_6?xO₂, anorthite and spinel phases. This layer provides effective prevention against CMAS further infiltration into the coating. Prolonged heat treatment densifies the reaction layer but does not change its phase composition.     

Spray Drying,a Versatile Synthetic Method to Control Purity in Single Phases and Mixed Phases of Bismuth Molybdates

The synthesis of pure bismuth molybdates (α, β and γ phases) using a novel method — spray drying — has been studied and successfully applied. It is shown that it is possible to control the synthesis of mixtures of different bismuth molybdates using spray drying. The influence of the relative molar ratio of bismuth to molybdenum constituents on the formation of different bismuth molybdate phases has been investigated. Starting from spray‐dried precursors, thermal details of the phase diagram of the Bi₂O₃‐MoO₃ system can be accurately reproduced and very pure phases can be easily obtained. Spray‐drying is compared to conventional precipitation and solid‐state reaction and the obtained products were characterized by XRD, IR, Raman, SEM, BET and DTA.     

Thermoelectric properties of plasma sprayed of calcium cobaltite (Ca2Co2O5)

The thermoelectric properties of calcium cobaltite deposits produced by the plasma spray process are investigated from room-temperature to 873 K. Synthesis of Ca₃Co₂O₆ and Ca₂Co₂O₅ powders were prepared by the solid-state reaction from CaO and CoO_x starting powders. During their subsequent plasma spray Ca particles experience preferential evaporation within the plasma, resulting in a complex interplay among process conditions, stoichiometry, and resultant phases. The as-sprayed material predominantly contains amorphous and secondary phases. Upon annealing, the deposits show sensitivity to phase evolution and therefore thermoelectric properties. Through screening studies, optimal annealing conditions were identified which show a p-type Seebeck coefficient value of 180 μV K^?1, electrical conductivity of 1.09 × 10⁴ S m^?1, thermal conductivity of 1.16 W m^-1 K^-1 at 873 K. The resultant figure of merit value reached 0.266 for this combination of processing and thermal treatment and is in line with data reported from other techniques for this system.     

The effect of B-site Y substitution on cubic phase stabilization in (Ba0.5Sr0.5)(Co0.8Fe0.2)O3−δ

The cubic phase mixed ionic-electronic conductor (Ba_0.5Sr_0.5)(Co_0.8Fe_0.2)O_3−δ (BSCF) is well-known for its excellent oxygen ion conductivity and high catalytic activity. However, formation of secondary phases impedes oxygen ion transport and consequentially a widespread application of BSCF as oxygen transport membrane. B-cation substitution by 1, 3 and 10 at.% Y was employed in this work for stabilization of the cubic BSCF phase. Secondary phase formation was quantified on bulk and powder samples exposed to temperatures between 640 and 1100°C with annealing time up to 44 days. The phase composition, cation valence states, and chemical composition of all samples were analyzed by high-resolution analytical electron microscopic techniques. Y doping effectively suppresses the formation of Ba_n+1Co_nO_3n+3(Co₈O₈) (n ≥ 2) and Co_xO_y phases which would otherwise act as nucleation centers for the highly undesirable hexagonal BSCF phase. This work validates for 10 at.% Y cation substitution perfect stabilization of the cubic BSCF phase at temperatures ≥800°C, while a negligible small volume fraction of the hexagonal BSCF phase was found at lower temperatures. A newly developed model describes the effect of Y doping on the formation of secondary phases and their effective suppression with increasing Y concentration.     

The dielectric property and phase transition of Sr-doping effect of Ba1−xSrxTi0.9Mn0.1O3-δ ceramic

In this work, we prepare Ba_1−xSr_xTi_0.9Mn_.01O_3-δ (x = 0.00, 0.01, 0.03, 0.05, and 0.07) ceramics by the mixed oxide method and study the relationship between phase transition and dielectric property of the ceramics. The phase of the samples transformed from a hexagonal phase to mixed phases due to the increase in Sr doping amount. The X-ray diffraction (XRD) profiles and Raman spectra of the samples also show the same phase transformation due to increasing Sr doping amount. The XRD pattern of the undoped sample indicates a single h-BaTiO₃ phase with P6₃/mmc symmetric space group, while the samples with high Sr doping amounts have a mixed phase with t-BaTiO₃ with P₄mm symmetric space group. The scanning electron microscopy images show two types of BaTiO₃ grains, which grew with increasing sintering temperature. With increasing Sr concentration, the K-values (relative dielectric constant) of the ceramics increased, while the Q_xf values (the quality factor multiplied by frequency) decreased, which indicate that the microwave dielectric property is related to phase transformation.     

Effect of weak reductant on properties of electroless copper polyacrylonitrile nanocomposites for electromagnetic interference shielding

In this work, the electroless copper method with different reductant compositions (NaHSO₃/Na₂ S₂O₃·5H₂O and Na₂S₂O₃·5H₂O) without sensitizing and activating, was used to deposit copper‐sulfide deposition on the polyacrylonitrile (PAN) surface for electromagnetic interference (EMI) shielding materials. The weak reductant, NaHSO₃, in the electroless copper method was used to control the phase of copper‐sulfide deposition. The Cu_x(x=1–1.8)S was deposited on the PAN (Cu_xS‐PAN) by reductant composition (NaHSO₃/Na₂S₂O₃·5H₂O) and the Cu_x(x=1–1.8)S deposition of Cu_xS‐PAN possesses three kinds of copper‐sulfide phases (CuS, Cu_1.75S and Cu_1.8S). However, the electroless copper with reductant was only Na₂S₂O₃·5H₂O (without weak reductant, NaHSO₃), the hexagonal CuS deposition was plated on the PAN (CuS‐PAN) and increased the EMI shielding effectiveness of CuS‐PAN composites about 10–15 dB. In this study, the best EMI SE of CuS‐PAN and Cu_xS‐PAN composites were about 27–30 dB and 15–17 dB respectively, as the cupric ion concentration was 0.24 M. The volume resistivity of CuS‐PAN composite was about 1000 times lower than that of Cu_xS‐PAN composite and lowest volume resistivity of CuS‐PAN composites was 0.012 Ω cm, as the cupric ion concentration was 0.24 M. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Electromagnetic wave reflection loss and magnetic properties of M-type SrFe12−x(Mn0.5Sn0.5)xO19 hexagonal ferrite nanoparticles in the Ku microwave band

Ferrimagnetic nanoparticles of SrFe_12−x(Mn_0.5Sn_0.5)_xO₁₉ was synthesis by controlling the effective processing parameters of sol-gel techniques. Microwave, magnetic properties and structure of nanosize, high purity sol-gel synthesized SrFe_12−x(Mn_0.5Sn_0.5)_xO₁₉ hexaferrite ferrimagnetic nanoparticles were investigated by vector network analysis, vibrating sample magnetometry, EDS and XRD. 57Fe Mössbauer spectroscopy was employed to find the occupancy sites of incorporated cations. The position of manganese and tin in 12k sites caused reduction in coercivity and magnetization saturation. The values of coercivity and magnetization saturation show that superparamagnetism did not occur in the synthesized products. Results demonstrate that additions of manganese and tin to hexagonal ferrite enhance bandwidth and reflection loss. Such composition could be proposed as a suitable electromagnetic wave absorber in microwave frequencies.