Kinetic demixing/decomposition of Ba0.5Sr0.5CoxFe1−xO3−δ (x = 0.2 and 0.8)

Microstructural changes due to kinetic demixing within sintered BSCF ceramics (Ba_0.5Sr_0.5Co_xFe_1?xO_3?δ, x = 0.2 and 0.8: BSCF5528 and BSCF5582, respectively) have been investigated. When the specimens were subjected to 2 A/cm² at 1000 °C and pO₂ = 10^?5 atm, there was a significant enhancement of grain growth as well as 2nd phase formation observed in BSCF5528. At the anode, cobalt deficient aggregates within the grains; and, at the cathode, cobalt rich 2nd phase particles were observed on the grain surfaces of the microstructure. Such phenomena were not observed in BSCF5582, even under higher current density (7 A/cm²) and longer delay time. These results were explained by the kinetic demixing/decomposition.     

Microwave absorption properties of (1 − x)La0.85Ag0.15MnO3/x graphene (x = 0, 3, and 5 wt.%) composites

Composite of (1 − x)La_0.85Ag_0.15MnO₃/x graphene (x = 0, 3, and 5 wt.%) and epoxy resin with a ratio of 4:1 were prepared to investigate the influence of the addition of graphene in (1 − x)La_0.85Ag_0.15MnO₃/x graphene on real and imaginary parts of permittivity, permeability, as well as microwave reflection loss (RL), using a vector network analyzer in the 8–18 GHz of the frequency range. It is found that the value of RL is smaller at x = 3 wt.% (−20.74 dB at 14.85 GHz) and 5 wt.% (−14.81 at 16.50 GHz) compared to at x = 0 wt.% (−8.89 dB at 15.90 GHz). The result indicates that microwave absorption properties significantly improved as a result of the addition of graphene. It is suggested that the addition of graphene enhanced the dielectric loss–related mechanism such as interfacial polarization and conduction loss resulting in an improvement of microwave absorption performance for both x = 3 wt.% and x = 5 wt.% samples. It also shows that the observed enhanced microwave absorption properties may also be influenced by the resistivity of the sample as x = 3 wt.% sample exhibits enhanced microwave absorption properties and the lowest resistivity among the studied samples.     

Determination of the initial heat treatment temperature in the two-step sintering of xAl–ZnO (x = 1, 2, and 3 wt.%)

The application of a two-step sintering route successfully decreased the sintering temperature of Al-doped ZnO transparent conducting oxide target. The two-step sintering consisted of initial heat treatment (IHT) at 800–1000 °C under mild (<2 MPa) external pressure, and pressureless final sintering at 1250–1350 °C in a separate furnace. The optimum IHTs for effective densification depended on the Al doping. The 800 °C IHT was effective for 1 wt.% Al doping, and the 1000 °C IHT, for 3 wt.% Al doping. As a result of the effective IHT, the volume of the micron sized pore decreased with the fragmentation into submicron pores. This suggests that cohesion of the secondary particles occurred during the effective IHT. The IHT temperature for achieving cohesion increased in the 3 wt.% Al doping. The criterion for determining the IHT in the two-step sintering was identified as the minimum temperature at which the cohesion of secondary particles can be achieved.     

Se4CuX,Te4CuX and Cu2Se7X2 (X = GaCl4) — Coordination compounds of neutral infinite chalcogen chains

The reactions of selenium and tellurium in molten GaCl₃ with SbCl₃ and copper(II) or copper(I) chloride yielded CuSe₄[GaCl₄] (1), CuTe₄[GaCl₄] (2), and Cu₂Se₇[GaCl₄]₂ (3). EPR measurements show no resonances, implying the presence of monovalent Cu ions. The structures consist of discrete infinite neutral chalcogen chains of helical shape. Cu(I) ions are coordinated to the Se and Te chains via three chalcogen atoms for the isotypic 1 and 2, and via two Se atoms for 3. The coordination tetrahedron for Cu is completed by coordination of Cl atoms of neighboring [GaCl₄]⁻ anions.     

Kinetic role of C/Zr ratio in the reaction process,combustion behavior,and synthetic product of 70 wt.% (xC–Zr)–30 wt.% Cu

The kinetic role of C/Zr ratio in the reaction processes, combustion behaviors, and synthesized products of 70 wt.% (xC–Zr)–30 wt.% Cu was investigated. Results indicated that ZrC particles were produced by the replacement reaction between carbon atoms and Zr–Cu melt. With an increase in C/Zr ratio, more carbon atoms combined with the zirconium atoms in Zr–Cu liquid. As a result, the formation rate of massive ZrC enhanced, which shortened the ignition time of combustion reaction. On the other hand, the quantity, the lattice parameter, and the x value of synthetic ZrC_x increased, while the byproduct Cu_yZr_x compounds decreased. These effects contributed to an increase in the burning temperature and ZrC_x particle size. Moreover, it is also revealed that the formation of ZrC_x is a multistep process, which leads to an inhomogeneous distribution of the particle size. Results from this work offer a theoretical reference for the kinetic research of combustion synthesis and related techniques, and provide a valuable guide to the in situ synthesis of composite materials containing ZrC.     

Catalytic performance of NO oxidation over LaMeO3 (Me = Mn,Fe, Co) perovskite prepared by the sol–gel method

The catalytic performance of LaMeO₃ (Me = Mn, Fe, Co) perovskite prepared by a sol–gel method was studied. These catalysts were characterized by X-ray diffraction (XRD), N₂ adsorption (BET), H₂ temperature programmed reduction (TPR), NO temperature programmed desorption (TPD) and CO–O₂ pulse. LaCoO₃ exhibited the best activity than that of LaFeO₃ and LaMnO₃ even after hydrothermal ageing. The activity sequence is in accordance with the reducibility of the samples. The activated oxygen species and adsorbed NO play key roles in the NO oxidation reaction.     

Etherification of n-butanol to di-n-butyl ether over H3PMo12 − xWxO40 (x = 0, 3, 6, 9, 12) Keggin and H6P2Mo18 − xWxO62 (x = 0, 3, 9, 15, 18) Wells–Dawson heteropolyacid catalysts

Etherification of n-butanol to di-n-butyl ether was carried out over H₃PMo_12 − xW_xO₄₀ (x = 0, 3, 6, 9, 12) Keggin and H₆P₂Mo_18 − xW_xO₆₂ (x = 0, 3, 9, 15, 18) Wells–Dawson heteropolyacid (HPA) catalysts. Acid strength of H₃PMo_12 − xW_xO₄₀ Keggin and H₆P₂Mo_18 − xW_xO₆₂ Wells–Dawson HPA catalysts was determined by NH₃-TPD (temperature-programmed desorption) measurements. The correlations between desorption peak temperature (acid strength) of the HPA catalysts and catalytic activity revealed that conversion of n-butanol and yield for di-n-butyl ether increased with increasing acid strength of the catalysts, regardless of the identity of HPA catalysts (without HPA structural sensitivity).     

Dependence of dielectric properties on structural characteristics of (Zn1/3A2/3)0.5 (Ti1−xBx)0.5O2 (A = Nb5+, Ta5+, B = Ge4+, Sn4+) ceramics at microwave frequencies

The effects of structural characteristics on the dielectric properties of (Zn_1/3A_2/3)_0.5(Ti_1?xB_x)_0.5O₂ (A = Nb⁵⁺, Ta⁵⁺, B = Ge⁴⁺, Sn⁴⁺) (0.1 ≤ x ≤ 0.3) ceramics were investigated at microwave frequency. The sintered specimens showed solid solutions with a tetragonal rutile structure within the solid solution range of compositions. With an increase of BO₂, the temperature coefficient of resonant frequency (TCF) and dielectric constant (K) decreased with a decrease of oxygen octahedral distortion and dielectric polarizabilites, respectively. However, the quality factor (Qf) of the sintered specimens was increased with BO₂ due to the reduction of Ti⁴⁺ ions. The Qf value of the specimens with A = Ta was higher than that of the specimens with A = Nb.     

Selective acetylation of glycerol over CeO2–M and SO42−/CeO2–M (M = ZrO2 and Al2O3) catalysts for synthesis of bioadditives

The feasibility of acetylation of glycerol with acetic acid was investigated employing CeO₂–ZrO₂, CeO₂–Al₂O₃, SO₄^2?/CeO₂–ZrO₂, and SO₄^2?/CeO₂–Al₂O₃ solid acid catalysts to synthesize monoacetin, diacetin and triacetin having interesting applications as bioadditives for petroleum fuels. Intensive physicochemical and surface characterization of the prepared catalysts were performed using XRD, BET surface area, ammonia-TPD and Raman spectroscopy techniques. Characterization results revealed that impregnated sulfate ions strongly influence the physicochemical characteristics of the investigated mixed oxide catalysts. Among various catalysts investigated, the SO₄^2?/CeO₂–ZrO₂ combination catalyst exhibited superior catalytic activity under mild conditions. The effect of various parameters such as reaction temperature, molar ratio of acetic acid to glycerol, catalyst wt% and time-on-stream were studied over the SO₄^2?/CeO₂–ZrO₂ catalyst to optimize the reaction conditions. Catalyst reusability was also carried out to understand its stability.     

MgTiO3–Ca1−xSm2x/3TiO3 (x = 0.2–0.5) microwave dielectric composites with greatly improved temperature stability

MgTiO₃–CaTiO₃ composite is one of the most important commercial microwave dielectric ceramics. However, the significant nonlinear change in resonant frequency with temperature and the temperature dependence of its temperature coefficient of resonant frequency (τ_f) severely deteriorate the temperature stability of MgTiO₃–CaTiO₃ composite. In this study, the Ca²⁺ in CaTiO₃ was partially substituted with Sm³⁺ to prepare a series of (1 − y)MgTiO₃–yCa_1−xSm_2x/3TiO₃ (x = 0.2–0.5) composites that was subsequently characterized. With increasing x from 0 to 0.5, the y value for obtaining the near-zero average τ_f between 20 and 80°C increases from 0.07 to 0.23; the dielectric constant of the composite correspondingly increases from 21.5 to 27.1, whereas the Qf value first increases and then decreases. Notably, (1 − y)MgTiO₃–yCa_1−xSm_2x/3TiO₃ composites with greatly improved temperature stability are realized, and the nonlinearity of the change in resonant frequency with temperature and the rate of change of τ_f with temperature are reduced by 48%–73%, relative to those of 0.93MgTiO₃–0.07CaTiO₃ composite. These results are attributed to the significantly reduced temperature dependence of τ_f for the constituent phase of Ca_1−xSm_2x/3TiO₃. This study sheds light on the development of temperature-stable microwave dielectric composites featuring constituent phases with τ_f of opposite signs.     

Catalytic cracking of rubber seed oil using basic mesoporous molecular sieves K<Subscript>2</Subscript>O/MeO-SBA-15 (Me = Ca,Mg or Ba) as heterogeneous catalysts for the production of liquid hydrocarbon fuels

Liquid hydrocarbon fuels obtained from the catalytic cracking animal fats and plant oils have become one kinds of the attractive fuels because of their possible environment benefits and the current concern over the depletion of fossil fuel sources. In this work, using the combined methods of one-pot synthesis and wetness-impregnation, some basic mesoporous molecular sieves K₂O/MeO-SBA-15 (Me?=?Ca, Mg or Ba) were prepared, characterized and used in the catalytic cracking of rubber seed oil (RSO). The results indicated that the catalysts K₂O/MeO-SBA-15 had better catalytic performances than MeO-SBA-15, assigning to their stronger basicity. The catalyst K₂O/MgO-SBA-15 obtained with 15 wt% KNO₃ impregnation concentration showed the excellent catalytic performance with about 93.2% conversion and 78.3% yield of liquid hydrocarbon biofuel. The obtained liquid biofuel had similar chemical composition to diesel-based fuels and showed good cold flow property, high calorific and low acid value. Importantly, the catalyst K₂O/MgO-SBA-15 was of excellent reusability, and it was reused with negligible loss in its catalytic performance for five times, attributing to the MgO layer between silicon skeleton and potassium species which prevents the reaction between silicon in the framework and potassium species.

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Improved dielectric strength and energy storage density in Ba6−3xLa8+2xTi18O54 (x = 0.5, 2/3, and 0.75) ceramics

Dielectric strength and energy storage density in Ba_6−3xLa_8+2xTi₁₈O₅₄ (x = 0.5, 2/3, and 0.75) ceramics were investigated as functions of composition and microstructure. With increasing x, although the dielectric constant decreased from 113 to 102, the energy storage density increased from 2.3 J/cm³ to 3.2 J/cm³ due to the increased dielectric strength for ceramics prepared by conventional sintering. The energy storage was further improved to 4.2 J/cm³ in ceramics prepared by spark plasma sintering under an electric field of 1058 kV/cm. Both dielectric strength and energy storage density in the present ceramics indicated the strong processing and microstructure dependence. The optimum dielectric strength and energy storage density were achieved in the dense ceramics with fine grains, while both dielectric strength and energy storage density decreased in the ceramics with coarse columnar grains.     

Terbium-oxalate-pyridinedicarboxylate coordination polymers suggesting the reductive coupling of carbon dioxide (CO2) to oxalate (C2O42−):[Tb2 (3,5-PDC)2(H2O)4(C2O4)]·2H2O and [Tb(2,4-PDC)(H2O)(C2O4)0.5] (PDC = pyridinedicarboxylate)

Under hydrothermal conditions, Tb(NO₃)₃·5H₂O reacted with 3,5-pyridinedicarboxylic acid (3,5-PDCH₂) to give a 3-D coordination polymer with the empirical formula of [Tb₂ (3,5-PDC)₂(H₂O)₄(C₂O₄)]·2H₂O (1). Tb(NO₃)₃·5H₂O also reacted with 2,4-pyridinedicarboxylic acid (2,4-PDCH₂) to give another 3-D coordination polymer [Tb₂ (2,4-PDC)₂(H₂O)₂(C₂O₄)] (2). The structures of both polymers have been determined by X-ray diffraction. X-ray structure analyses show that both polymers contain bridging oxalate (C₂O₄²⁻) ligands, which might have been formed by the reductive coupling of CO₂ molecules released from the PDC²⁻ ligands through the C–C bond cleavage.