Specific Features of the Formation of Crystalline Phases of the W—C—N System in a Cumulative Process

Results of x–ray diffractometric studies of coatings and powders of the W—C, W—N, and W—C—N systems that were obtained under conditions of a shaped–charge explosion are reported. The dependence of the phase composition on the experimental conditions is investigated. Diffusion of nitrogen to the initial polycrystalline tungsten is shown.     

Improvement of the magnetoelectric response in NiFe2O4−Sr0.5Ba0.5Nb2O6 composites using LiNbO3 as sintering additive

Magnetoelectric (NiFe₂O₄)_0.3−(Sr_0.5Ba_0.5Nb₂O₆)_0.7 composites with addition of LiNbO₃ as sintering additive were prepared by a classical mixed-oxide method. XRD patterns of ceramics sintered between 1000 and 1200 °C show the desired Sr_0.5Ba_0.5Nb₂O₆ and NiFe₂O₄ phases. SEM investigations confirm the 0–3 connectivity of the composite ceramics. The addition of 10 and 20 mol% LiNbO₃ improves the densification of the composite ceramics and leads to an increase of the size of the Sr_0.5Ba_0.5Nb₂O₆ grains. Magnetic measurements show hystereses with low coercivities. Dielectric measurements were carried out depending on temperature and frequency. The samples with the LiNbO₃ addition show significantly higher resistivity values (σ_DC). Magnetoelectric measurements were carried out in dependence of the magnetic DC-field, temperature, and frequency. The maximum magnetoelectric coefficient (α_ME) rises with the addition of LiNbO₃ from 180 to 803 µV Oe⁻¹ cm⁻¹ (@900 Hz). Temperature dependent measurements show a continuously decreasing of α_ME with lower temperature.     

Synthesis,Characterization and Application of a Multi-Site Phase Transfer Catalyst in Radical Polymerization of n-Butyl Methacrylate—A Kinetic Study

The multi-site phase transfer catalyzed radical polymerization of n-butyl methacrylate (n-BMA) using newly synthesized and characterized 1,1,2,2-tetramethyl-1-benzyl-2-n-propylethylene-1,2-diammonium bromide chloride (TMBPEDBC) as a multi-site phase transfer catalyst was investigated in an aqueous-organic two-phase system at 60 ± 1°C under nitrogen circumstances. The kinetics and effects of various operating variables (monomer, initiator, catalyst, temperature, acid, and ionic strength) on the rate of polymerization (Rp) were examined in detail. The order with respect to monomer, initiator and multi-site phase transfer catalyst was found to be 0.50. A suitable kinetic reaction scheme has been proposed to account for experimental observations, and its significance is discussed.     

Subsolidus phase equilibria in the La2O3–Fe2O3–Sb2O5 system and characterization of layered ternary oxide LaFe0.5Sb1.5O6

Phase equilibria in the La₂O₃-Fe₂O₃–Sb₂O₅ system have been studied. The isothermal section was constructed at T=900 °С. The existence of the ternary oxide LaFe_0.5Sb_1.5O₆ was confirmed. The structure of this compound was solved using Rietveld refinement of synchrotron radiation-based powder XRD data. LaFe_0.5Sb_1.5O₆ crystallizes in a trigonal layered structure relating to PbSb₂O₆ type (space group P-31m, a=b=5.2446(3) Å, c=5.1930(3) Å, Z=1). The fine powder of LaFe_0.5Sb_1.5O₆ was prepared by molten salt synthesis. The compound was characterized by diffuse reflection and Mossbauer spectroscopy, magnetic measurements, scanning electron microscopy and photocatalytic tests. The magnetic behavior of LaFe_0.5Sb_1.5O₆ in the applied magnetic field H=5000 Oe is entirely paramagnetic. By contrast, in the small magnetic field H=100 Oe the magnetic data of LaFe_0.5Sb_1.5O₆ indicates an unusual critical behavior near phase transition at T<2 K.     

Polymerization of Butyl Acrylate using Potassium Peroxy Disulfate as Initiator in the Presence of Phase Transfer Catalyst—A Kinetic Study

The kinetics and mechanism of free radical polymerization of butyl acrylate (BA), using potassium peroxydisulfate (K₂S₂O₈) as initiator in the presence of propiophenonebenzyldimethylammonium chloride (PPBDMAC) as phase transfer catalyst (PTC) has been studied. The reactions were carried out under inert, unstirred conditions and at a constant temperature of 60°C in cyclohexanone/water biphase media. The dependence of the rate of polymerization (R_p) on various experimental conditions such as different concentrations of monomer, initiator, phase transfer catalyst, varying acid and ionic strength, temperature, and volume fraction of aqueous phase were studied. The order with respect to monomer, initiator, and the phase transfer catalyst were found to be 1.5, 0.5, and 0.5, respectively. The rate of polymerization was independent of acid and ionic strength. Based on the results, a mechanism has been proposed for the polymerization reaction.     

Effect of composite methods on the phase transition and microwave performances of ZnZrNb1.99(Sn0.5W0.5)0.01O8–TiO2 system

Tri-layer ZnZrNb_1.99(Sn_0.5W_0.5)_0.01O₈–TiO₂–ZnZrNb_1.99(Sn_0.5W_0.5)_0.01O₈ and random distribution ZnZrNb_1.99(Sn_0.5W_0.5)_0.01O₈@TiO₂ ceramics with different mass fractions of TiO₂ were initially synthesized. The effects of the laminated cofiring and the random distribution processes on the crystal structure and microwave dielectric properties of the composite ceramics were investigated. The advantages of the unique tri-layer architecture were fully demonstrated. It not only allows the effects of the chemical reactions between ZnZrNb_1.99(Sn_0.5W_0.5)_0.01O₈ and TiO₂ can be effectively limited to a narrow region (∼20 μm in width) within the ZnZrNb_1.99(Sn_0.5W_0.5)_0.01O₈/TiO₂ interfaces, and acts as the “glues” to bond each layer well. The layers are well connected and the possibility of deterioration of Q× f values during the modification process can be greatly reduced. When compared with ZnZrNb_1.99(Sn_0.5W_0.5)_0.01O₈@TiO₂ ceramics with random distribution type, the tri-layer design can produce a roughly 60% improvement in Q× f value with no noticeable loss in dielectric constant while maintaining temperature stability. After sintering at 1340°C for 6 h, ZnZrNb_1.99(Sn_0.5W_0.5)_0.01O₈–TiO₂–ZnZrNb_1.99(Sn_0.5W_0.5)_0.01O₈ tri-layer ceramics exhibited excellent dielectric properties (ε_r = 30.29, Q× f = 56,880 GHz, and τ_f = −5.73 ppm/°C) with 0.05 wt% TiO₂, and the cooperative optimization of microwave dielectric properties was achieved. The current research provides a strategy for synthesizing microwave dielectric devices with high dielectric properties for applications in 5G network communications.     

The solid-state rearrangement of the Wells-Dawson K6P2W18O62·10H2O to a stable Keggin-type heteropolyanion phase: a catalyst for the selective oxidation of isobutane to isobutene

The thermal and structural stability of the Wells-Dawson-type heteropoly compound K₆P₂W₁₈O₆₂·10H₂O was examined by FT-IR spectroscopy, X-ray powder diffraction, thermogravimetric analysis and HRTEM. It was found that calcination at temperatures higher than 850 K led to the formation of a Keggin-type compound K₃PW₁₂O₄₀, containing small amounts of an additional phase originated from the high-temperature interaction between potassium phosphate (K₃PO₄ formed during the decomposition of the K₆P₂W₁₈O₆₂·10H₂O) and the Keggin-type compound itself. The Keggin-type product showed a higher activity in the selective oxidative dehydrogenation of isobutane to isobutene compared to both the Wells-Dawson precursor and to pure, authentic K₃PW₁₂O₄₀. This higher activity can be tentatively attributed to the presence of an amorphous layer of unknown stoichiometry at the surface of the thermally rearranged Wells-Dawson compound.     

Relationship between the Bond Valence and the Temperature Coefficient of the Resonant Frequency in the Complex Perovskite (Pb1−xCax)[Fe0.5(Nb1−yTay)0.5]O3

The temperature coefficient of the resonant frequency (TCF) of complex perovskite (Pb_1−xCa_x)[Fe_0.5(Nb_1−yTa_y)_0.5]O₃ ceramics (x= 0.5, 0.55; 0.0 ≤y≤ 1.0) was investigated, relative to the bond valence of the A- and B-site ions in the ABO₃ perovskite structure (such as the barium-, strontium-, and calcium-based complex perovskites). The TCF of these complex perovskite compounds varied with the bond valence of the A- and B-sites and the tolerance factor (t) in the perovskite structure. In the tilted region (t < 1.0), the tilting of the oxygen octahedra increased and the TCF decreased, because of the increased bond valence of the B-site. Also, the dependence of TCF on the bond valence of the A-site was similar to its dependence on t.     

Improving the electrochemical performance of single crystal LiNi0.5Mn1.5O4 cathode materials by Y–Ti doping and unannealing process

In recent years, due to the rising price of cobalt, people have been increasingly interested in LiNi_0.5Mn_1.5O₄ (LNMO) cathode materials, and many studies researches have been carried out on the preparation and modification of LNMO. However, the codoping of Y and Ti and the choice of annealing and unannealing processes after doping are less explored. In this study, single-crystal LNMO particles and Y, Ti-doped LiNi_0.45Mn_1.45O₄ particles were prepared by a simple sol-gel method under annealing and unannealing processes, respectively. Four samples were analyzed by X-ray powder diffraction, Raman spectra, Fourier transform infrared spectroscopy and electron paramagnetic resonance. By these means, it was found that the samples doped and not annealed had the largest amount of disordered structures and oxygen vacancies (OVs). Scanning electron microscopy showed that the doped and unannealed samples had more exposed (100) crystal planes than the other samples, and after multiple cycles, this sample had the smoothest surface morphology. Electrochemical tests show that the doped and unannealed samples exhibit excellent electrochemical performance, with a Coulombic efficiency of 93.94% in the first cycle, a specific capacity of 126.74 mAh?g^?1 after 500 cycles at a rate of 1 C, and a specific capacity of 126.74 mAh?g^?1 at a rate of 5 C. After 500 cycles, the specific capacity is 111.1 mAh?g^?1.     

Catalytic Activity of Multi-metallic Perovskite-Type Oxide Prepared by the Thermal Decomposition of Heteronuclear Cyano Complex, Sm[Fe x Co1−x (CN)6] · nH2O

The perovskite-type SmFe _x Co_1?x O₃ oxides were prepared by the thermal decomposition of heteronuclear cyano complexes, Sm[Fe _x Co_1?x (CN)₆] ? nH₂O. XRD studies demonstrated that SmFe _x Co_1?x O₃ catalyst prepared by the thermal decomposition of heteronuclear cyano complex at 1,273 K showed orthorhombic structure in whole range of x. The catalytic activity for CO oxidation was dependent on x in SmFe _x Co_1?x O₃; the maximum activity was obtained for SmFe_0.5Co_0.5O₃.     

Improving the electrochemical performance of Ni-rich cathode materials using a fast ion conductor coating of Li2O–B2O3–LiBr

The high-Ni layered metal oxide, LiNi_0.8Co_0.1Mn_0.1O₂ (LNCM811), has received widespread attention in the energy field because of its high specific capacity, but its large-scale applications are hindered due to severe capacity fading. Herein, a uniform and thin Li₂O–B₂O₃–LiBr-glass (LBBrO-glass) coating was deposited on LNCM811 by a liquid-phase coating and thermal treatment method. The experimental results suggested that the LBBrO-glass coating acted as a protective layer that inhibited transition metal dissolution and side reactions, which helped improve the electrochemical properties of LNCM811. Remarkably, after 200 cycles, the 2 wt% coating (LBBrO@LNCM-2) delivered a superior capacity retention of 88.9%, while only 71.8% was obtained for the pristine material (LNCM811). The discharge capacity of LBBrO@LNCM-2 was 163.5 mAh g^?1 at 5C, while it was only 139 mAh g^?1 for the pristine material.     

Influences of B2O3/CuO additions on the sintering behavior,microstructure and microwave dielectric properties of 6Nd[(Zn0.7Co0.3)0.5Ti0.5]O3–4(Na0.5Nd0.5)TiO3 ceramics

B₂O₃ and CuO were codoped into 6Nd[(Zn_0.7Co_0.3)_0.5Ti_0.5]O₃–4(Na_0.5Nd_0.5)TiO₃ (abbreviated as 6NZCT–4NNT) ceramics as sintering aids. The influences of the sintering aids on the sintering characteristics, microstructure and microwave dielectric properties of the 6NZCT–4NNT ceramics were systematically investigated as a function of the proportion of B₂O₃ and CuO. Codoping could greatly reduce the sintering temperature from 1410 °C to 1150 °C, indicating that B₂O₃/CuO are good sintering aids for 6NZCT–4NNT ceramics. The B₂O₃/CuO sintering aids had no significant impact on the phase purity of the investigated ceramics, even though a solid solution was formed due to Cu²⁺ ion substitution. However, they had evident influences on the surface morphology and grain size. The average grain size was enlarged with increasing amounts of CuO in the B₂O₃/CuO sintering aids. Remarkable deterioration of the microwave dielectric properties for 6NZCT-4NNT ceramics was not observed when codoping an appropriate amount of B₂O₃ and CuO. The 6NZCT–4NNT ceramics codoped with 2.0 mol% B₂O₃ and 2.0 mol% CuO sintered at 1150 °C for 3 h exhibited a homogeneous microstructure and promising microwave dielectric properties: an appropriate dielectric constant (ε_r = 49.37), a high quality factor (QF = 47,295 GHz), and a near-zero temperature coefficient of resonant frequency (TCF = +0.9 ppm/^°C).     

On-Board Hydrogen Production Through Catalytic Exhaust-Gas Reforming of Isooctane: Efficiency of Mixed Oxide Catalysts Ce2Zr1.5Me0.5O8 (Me = Co, Rh, or Co–Noble Metal)

Isooctane reforming under conditions which are set by exhaust gas can be built on to generate hydrogen on-board. Isooctane reforming reactivity tests have been performed with bimetallic catalysts Co–Noble Metal/ceria–zirconia. Variable activity of noble metals doped catalysts, depending on the nature of the noble metal, its loading, and affected by the activation process, is discussed.     

Cationic Polymerization of β-Pinene Using B(C6F5)3 as a Lewis Acid for the Synthesis of Tackifiers in Pressure Sensitive Adhesives

β-pinene is a well-known bio-based monomer that can be polymerized via cationic polymerization to give low molecular weight resins that find use commercially as tackifiers. However, the controlled synthesis of these polymers by cationic polymerization is challenging due to the reactivity of commonly used Lewis acid catalysts and the propagating carbocationic species with water. Here, the cationic polymerization of β-pinene under mild conditions using the water stable Lewis acid tris(pentafluorophenyl)borane is demonstrated. It is shown that when combined with a suitable alcohol initiator the molecular weight of the polymer can be tuned while the kinetics are largely controlled by the concentration of tris(pentafluorophenyl)borane. The final poly(β-pinene) is shown to perform well as a tackifier in the formation of pressure sensitive adhesives based on polystyrene-b-polyisoprene-b-polystyrene triblock copolymers.     

Synthesis of Pd（C4H2O4）（C4H8N2）0.5 Complex and the Catalytic Activity for Oxidative Carbonylation of Phenol

A novel complex Pd（C4H2O4）（C4H8N2）0.5 has been synthesized by solvent thermal synthesis and used as a heterogeneous catalyst for direct synthesis of diphenyl carbonate （DPC） by oxidative carbonylation of phenol. In the reaction system of Pd（C4H2O4）（C4H8N2）0.5/Cu（OAc）2/ tetrabutylammonium bromide/ hydroquinone/ 4A molecular sieves, the effect of reaction temperature, time and CO pressure on catalytic activity were investigated, and the results revealed that the catalyst could catalyze oxidative carbonylation of phenol effectively. Under suitable reaction conditions of T=90℃, t=4 h, p（O2）=0.3 MPa, p（CO）=3.9 MPa and CH2Cl2 as solvent, the turnover number （TON） of diphenyl carbonate can reach about 13.50 （mol-DPC/mol-Pd）, which is higher than the TON for oure PdCl2 under the same reaction conditions.     

Living Anionic Polymerization of <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>–Dimethylacrylamide and Copolymerization with Methyl Methacrylate in the presence of Bulky Aluminum Phenoxide

Summary Anionic polymerization of N,N–dimethylacrylamide (DMAAm) was examined in toluene with tert–butyllithium (t–BuLi)/bis(2,6–di–tert–butylphenoxy)ethylaluminum [EtA1(ODBP)₂]. In the presence of excess amounts of the aluminum compound over t–BuLi, the polymerization proceeded in a living manner. Sequential block copolymerization of DMAAm and methyl methacrylate (MMA) with the same initiator underwent smoothly in both directions, that is, polymerization of MMA by poly(DMAAm) living anions and vice versa. Moreover, the copolymerization of an equimolar mixture of DMAAm and MMA proceeded in a monomer–selective manner to give a block–like copolymer; DMAAm was polymerized first followed by MMA polymerization through selective activation of DMAAm by the coordination of EtA1(ODBP)₂.     

Observation of Sublattice Disordering of the Catalytic Sites in a Complex Mo–V–Nb–Te–O Oxidation Catalyst Using High Temperature STEM Imaging

A Mo–V–Nb–Te–O oxidation catalyst has been imaged using scanning transmission electron microscopy at 780 K, which is slightly above its operating temperature. We observe a sublattice disordering of the corner-sharing octahedra forming the catalytic sites containing V⁵⁺ while the edge-sharing pentagonal bipyramidal {Nb(Mo₅)} sublattice remains structurally more rigid and thereby maintains the overall structural integrity of the catalyst. Imaging the termination of the edges of the [001] basal zones at room temperature reveal a preference for presence of a closed network of secondary structural {Nb(Mo)₅} units providing further evidence of the stability of this sublattice structure. We propose that sublattice disordering of catalytic sites enables structural flexibility to accommodate different oxidation states during multistep chemical reactions within a more rigid superstructure and presents a new paradigm for compositionally and structurally complex catalysts.