Phase relationships in the Na<Subscript>2</Subscript>ZnP<Subscript>2</Subscript>O<Subscript>7</Subscript>–LiKZnP<Subscript>2</Subscript>O<Subscript>7</Subscript> system

The phase relationships in the Na₂ZnP₂O₇–LiKZnP₂O₇ system are studied. They are represented by a mixture of the starting components in the subsolidus region. The eutectic was found at a temperature of 640°C and composition of 0.5LiKZnP₂O₇. The phase formation of this system is compared with the previously studied NaKZnP₂O₇–LiKZnP₂O₇ system. It is shown that a structural factor affects the geometry of the state diagrams.     

Exploring the Redox Behavior of La<Subscript>0.6</Subscript>Sr<Subscript>0.4</Subscript>Mn<Subscript>1−x</Subscript>Al<Subscript>x</Subscript>O<Subscript>3</Subscript> Perovskites for CO<Subscript>2</Subscript>-Splitting in Thermochemical Cycles

Mixed oxides with perovskite structure have been proposed as promising alternative for the solar fuel production via thermochemical redox cycles. For this work, the system La_0.6Sr_0.4Mn_1?xAl_xO₃ (x?=?0 to 0.8) was selected according to its high thermal stability and rapid oxidation kinetics, and the influence of the Al/Mn ratio on the redox properties was investigated. The characterization of the five oxides samples with different Al content confirmed the high redox capacity and the favorable behavior of these materials in consecutive cycles, as analyzed thermogravimetrically. The results show that following reduction at 1300?°C in inert atmosphere up to 0.32 mmol g^?1 of O₂ are released, while a 10-cycle reaction test confirms the feasibility of long term operation with these perovskites. It was observed that the reduction extent was enhanced with increasing the Al-content, but the oxidation degree is maximum for compositions near x?=?0.5, corresponding to an O₂ release of 0.318 mmol g^?1 (δ?=?0.132). After selecting the compositions with more promising redox properties, additional reactions were performed in a lab-scale fixed bed reactor with injection of CO₂ in the oxidation step at 900?°C in order to generate CO. In these tests, the most interesting results were obtained for the perovskite La_0.6Sr_0.4Mn_0.6Al_0.4O_3, with reduction extent of 0.266 mmol?g^?1, but the production of CO is in comparison significantly lower (0.114 mmol?g^?1). Further studies are required to determine the best operation conditions for thermochemical cycles using those materials.     

Photon interaction parameters for some ZnO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>–P<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses

Some photon interaction parameters such as mass attenuation coefficient, effective atomic number, half value layer, mean free path and electron density for 15ZnO–(17.5–x)Al₂O₃–xFe₂O₃–67.5P₂O₅ glass system (x = 0, 7.5, 12.5, 17.5) and 15ZnO–(25–x)Al₂O₃–xFe₂O₃–60P₂O₅ glass system (x = 0, 25) have been investigated in the photon energy range of 1 keV to 100 GeV. It has been observed that all the photon interaction parameters for the selected glass systems vary with the photon energy. Among the selected glass systems, the sample 15ZnO–25Fe₂O₃–60P₂O₅ glass system shows maximum values for mass attenuation coefficients, effective atomic numbers, electron densities and minimum values for mean free path and half value layer in the entire energy grid.     

Structural heterogeneity of SiO<Subscript>2</Subscript>–Na<Subscript>2</Subscript>O–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> glass

It is shown that the phase heterogeneity of SiO₂–Na₂O–Al₂O₃ glass has a liquation and crystallization nature, the balance between which is determined by the conditions of their synthesis. An increase in the aluminum oxide content decreases the number of liquation and crystallization sites, and also the linear sizes of the crystalline formations without eliminating the phase separation due to the liquation. The area of metastable immiscibility in the SiO₂–Na₂O–Al₂O₃ system, which is determined by scanning electron microscopy, is probably wider than the area detected by the optical methods.     

Hydroisomerization of Benzene-Containing Gasoline Fraction on Pt/B<Subscript>2</Subscript>O<Subscript>3</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and Pt/WO<Subscript>3</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Catalysts

The effect of the hydroisomerization conditions of the benzene-containing fraction of catalytic reforming gasoline on the yield and composition of products is studied on Pt/B₂O₃–Al₂O₃ and Pt/WO₃–Al₂O₃ catalysts. These catalysts allow benzene to be completely removed from the raw material. At the same time, the greatest yields of liquid products are obtained with minimal losses of the octane number at 2 MPa, a mass feedstock hourly space velocity (MFHSV) of 2 h^?1, and 325°C: 96.3 and 95.4 wt % on Pt/B₂O₃–Al₂O₃ and Pt/WO₃–Al₂O₃ catalysts, respectively. The activity of the catalysts is maintained for 100 h during their operation.     

Magneto Optical Properties of FeB<Subscript>x</Subscript>Fe<Subscript>2−x</Subscript>O<Subscript>4</Subscript> Nanoparticles

In this study, FeB_xFe_2?xO₄ nanoparticles (NPs) were synthesized by the polyol method. The M–H hysteresis curves exhibit superparamagnetic characteristics that are both coercivity and remanent magnetization values are negligible. The particle size dependent Langevin function was applied to calculate the magnetic particle dimensions around 9 nm. The measured magnetic moments of NPs are in range of (1.52–2.2) µ_B and almost half or less with respect to 4 µ_B of bulk Fe ferrite. Magnetic anisotropy was specified as uniaxial and calculated effective anisotropy constants (K _eff ) are between 43.3 × 10⁴ and 19.4 × 10⁴ emu/g. The UV–Vis diffuse reflectance spectroscopy and Kubelka–Munk theory were used to determine the optical properties. The estimated optical band gap values (2.15–2.48 eV) of FeB_xFe_2?xO₄ NPs are bigger with respect to reported values (1.88–2.12 eV) for Fe₃O₄ NPs in the literature. The bigger E _g values are mainly attributed to B concentration and partly to quantum confinement effect.     

Magnetic Properties of FeMn<Subscript>y</Subscript>Co<Subscript>y</Subscript>Fe<Subscript>2−2y</Subscript>O<Subscript>4</Subscript>@Oleylamine Nanocomposite with Cation Distribution

In this study, oleylamine (OAm) capped FeMn_yCo_yFe_2?2yO₄ (0.0?≤?y?≤?0.4) nanocomposites (NCs) were prepared via the polyol route and the impact of bimetallic Co³⁺ and Mn³⁺ ions on the structural and magnetic properties of Fe₃O₄ was investigated. The complete characterization of FeMn_yCo_yFe_2?2yO₄@OAm NCs were done by different techniques such as XRD, SEM, TGA, FT-IR, TEM, and VSM. XRD analyses proved the successful formation of mono-phase MnFe₂O₄ spinel cubic products free from any impurity. The average crystallite sizes were calculated in the range of 9.4–26.4 nm using Sherrer’s formula. Both SEM and TEM results confirmed that products are nanoparticles like structures having spherical morphology with small agglomeration. Ms continued to decrease up to Co³⁺ and Mn³⁺ content of y?=?0.4. Although Mössbauer analysis reveals that the nanocomposites consist three magnetic sextets and superparamagnetic particles are also formed for Fe₃O₄, Co_0.2Mn_0.2Fe_2.6O₄ and Co_0.4Mn_0.4Fe_2.2O₄. Cation distributions calculation was reported that Co³⁺ ions prefer to replace Fe²⁺ ions on tetrahedral side up to all the concentration while Mn³⁺ ions prefer to replace Fe³⁺ ions on the octahedral.     

Direct-hydrothermal synthesis of LiFe<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>PO<Subscript>4</Subscript> cathode materials

Carbon free LiFe_1−x Mn _x PO₄ (x = 0, 0.05, 0.1, 0.2, 0.4) cathode materials were prepared by a direct-hydrothermal process at 170 °C for 10 h. The structural and electrochemical properties of the samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), charge–discharge experiments, cyclic voltammetry (CV) and alternating current (AC) impedance spectroscopy. The electrochemical performance of LiFePO₄ prepared in this manner showed to be positively affected by Mn²⁺-substitution. Among the Mn²⁺-substitution samples, the LiFe_0.9Mn_0.1PO₄ exhibited an initial discharge capacity of 141.4 mA h g⁻¹ at 0.1 C, and the capacity fading is only 2.7% after 50 cycles.     

Zn<Superscript>2+</Superscript>-exchange kinetics and antimicrobial properties of synthetic zirconium umbite (K<Subscript>2</Subscript>ZrSi<Subscript>3</Subscript>O<Subscript>9</Subscript>·H<Subscript>2</Subscript>O)

Zirconium umbite, K₂ZrSi₃O₉·H₂O, is a microporous framework ion exchanger whose potential as a carrier for Zn²⁺ ions in antimicrobial formulations has not yet been investigated. Accordingly, batch Zn²⁺-exchange kinetics of synthetic zirconium umbite (K-UM) and the subsequent antimicrobial action of the zinc-bearing phase (Zn-UM) against Staphylococcus aureus and Escherichia coli are reported. Nonstoicheiometric over-exchange of Zn²⁺ for K⁺ was observed and attributed to hydrolysis and complexation reactions of Zn²⁺ within the umbite framework. The exchange process, which was described by a simple pseudo-first-order model (k ₁ = 2.69 × 10⁻⁴ min⁻¹, R ² = 0.992), did not achieve equilibrium within 120 h at 25 °C, by which time the uptake of zinc was found to be 1.04 mmol g⁻¹. The minimal bactericidal concentrations of Zn-UM for E. coli and S. aureus were found to be >10 g cm³ and <1.0 g cm³, respectively.     

Fe-doping effects on the structural and electrochemical properties of 0.5Li<Subscript>2</Subscript>MnO<Subscript>3</Subscript>·0.5LiMn<Subscript>0.5</Subscript>Ni<Subscript>0.5</Subscript>O<Subscript>2</Subscript> electrode material

With the aim of achieving a high-performance 0.5Li₂MnO₃·0.5LiMn_0.5Ni_0.5O₂ material, a series of 0.5Li₂MnO₃·0.5LiMn _x Ni _y Fe_(1−x−y)O₂ (0.3 ≤ x ≤ 0.5, 0.4 ≤ y ≤ 0.5) samples with low Fe content was synthesized via coprecipitation of carbonates. Its crystal structure and electrochemical performance were characterized by means of powder X-ray diffraction, field emission scanning electron microscopy, X-ray photoelectron spectroscopy, galvanostatic charge/discharge testing, cyclic voltammetry, and electrochemical impedance spectra. Rietveld refinements with a model integrating R [`3] \overline{3} m and Fm [`3] \overline{3} m indicate that a low concentration of Fe incorporated in 0.5Li₂MnO₃·0.5LiMn_0.5Ni_0.5O₂ decrease a disordered cubic domain of the composite structure. The preferential distribution of Fe in cubic rock-salt contributes to an unimaginable decrease of c-axis parameter of the predominant layered structure as the Fe content increases. Moreover, including Fe as a dopant can kinetically improve crystallization and also change the ratio of Mn³⁺/Mn⁴⁺ and Ni³⁺/Ni²⁺. As a result, 0.5Li₂MnO₃·0.5LiMn_0.4Ni_0.5Fe_0.1O₂ exhibits lower Warburg impedance and higher reversible capacity than the undoped material.     

An EPR study of Cu adsorption by clinoptilolite from Cl<Superscript>−</Superscript>, NO<Stack><Subscript>3</Subscript><Superscript>−</Superscript></Stack> and SO<Stack><Subscript>4</Subscript><Superscript>2−</Superscript></Stack> solutions

The concentration and the type of Cu²⁺ species adsorbed on a natural zeolite (Clinoptilolite) was measured and studied by using Electron Paramagnetic Resonance Spectroscopy (EPR). The EPR results together with macroscopic sorption data indicate that the solution ionic strength as well as, the type of electrolyte anion (Cl⁻, NO₃⁻ and SO₄²⁻ ions were examined) affect the amount of Cu adsorbed and the type of Cu surface complexes. The increasing in solution pH affects Cu adsorption quantitatively whereas; the type of surface complexes formed depends mainly on solution ionic strength. For low solution ionic strength, when the inhibition from solution species is limited, the adsorbed Cu is characterized by more than one type of chemical environment. On the contrary, for high solution ionic strength the Cu adsorption is inhomogeneous and EPR spectra show only one type of surface complex. When the anions of the background electrolytes are different, but of equal normality, the results indicate that in the presence of SO₄²⁻ discernible Cu surface complexes are formed whereas, for Cl⁻ and NO₃⁻ these surface formations are obtained only for high Cu adsorbed concentrations.     

Synthesis and proton incorporation in BaCe<Subscript>0.9−<Emphasis Type="Italic">x</Emphasis></Subscript>Zr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Y<Subscript>0.1</Subscript>O<Subscript>3−δ</Subscript>

BaCe_0.9−x Zr _x Y_0.1O_3−δ powders were synthesized by a solid-state method at 1,400 °C. Two compositions were studied (x = 0.3 and x = 0.7). Pellets were prepared and conventionally sintered in air at 1,700 °C. Then, the samples were heated at 600 °C for 3 h in different reducing atmospheres: dry hydrogen, wet hydrogen and wet deuterium. After each treatment, the proton diffusion depth profile was obtained using Secondary Ion Mass Spectroscopy (SIMS). Protons were not incorporated in the material when the gas was not wet, and the isotope effect suggests that protons present in the pellet come from water and not from hydrogen.     

Thermal expansion and phase transitions in K<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Cs<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>BSi<Subscript>2</Subscript>O<Subscript>6</Subscript> borosilicate solid solutions

Solid solutions K_{1 − x} Cs _x BSi₂O₆ (x (atomic fraction) = 0.00, 0.20, 0.30, 0.35, 0.40, 0.80, 0.90,1.00) have been prepared by solid-phase synthesis and crystallization of glasses in the KBSi₂O₆-CsBSi₂O₆ borosilicate series. The thermal behavior of the solid solutions has been investigated using the annealing and quenching techniques, dilatometry, and high-temperature X-ray powder diffraction. It has been shown that solid solutions with x = 0.00–0.35 and 0.40–1.00 correspond to space groups I $ \bar 4 $ \bar 4 3d and I a $ \bar 3 $ \bar 3 d, respectively. The cubic-cubic phase transition I $ \bar 4 $ \bar 4 3d ai Ia $ \bar 3 $ \bar 3 d occurs in the composition range x = 0.35−0.40 at room temperature. In the series of solid solutions with x = 0−0.30, the reversible cubic-cubic polymorphic transition I $ \bar 4 $ \bar 4 3d ai ia $ \bar 3 $ \bar 3 d with an increase in the temperature has been revealed, the temperature of the polymorphic transition has been determined, and the thermal expansion in both polymorphic modifications has been studied using high-temperature X-ray diffraction and dilatometry. The solid solutions belonging to the space group Ia $ \bar 3 $ \bar 3 d are characterized by a lower thermal expansion than the solid solution belonging to the space group I $ \bar 4 $ \bar 4 3d. According to the calculations, the equivalents α/γ for the space groups I $ \bar 4 $ \bar 4 3d and Ia $ \bar 3 $ \bar 3 d are 0.03 and 0.02 (in cesium atomic fractions per degree Celsius), respectively.     

Composite WSi<Subscript>2</Subscript>–<Emphasis Type="Italic">Me</Emphasis><Superscript>V</Superscript>B<Subscript>2</Subscript> materials in W–Si–<Emphasis Type="Italic">Me</Emphasis><Superscript>V</Superscript>–B systems

Sections are constructed for WSi₂–Me ^VB₂ of the quaternary systems W–Si–(V, Nb, Ta)–B described by eutectic diagrams of state with T _eut (1940 ± 20), (1980 ± 20) and (2020 ± 30)°C and a boride content in the eutectics of 35, 20 and 15 mol.% respectively. Translated from Novye Ogneupory, No. 3, pp. 41 – 44, March 2009.     

Effects of ZnO–B<Subscript>2</Subscript>O<Subscript>3</Subscript> addition on sintering behaviors and microwave dielectric properties of Ba<Subscript>4</Subscript>Sm<Subscript>9.33</Subscript>Ti<Subscript>18</Subscript>O<Subscript>54</Subscript> ceramics

Effects of ZnO–B₂O₃ (ZB) addition on the densification, phase evolution and microwaves dielectric properties of Ba₄Sm_9.33Ti₁₈O₅₄ (BST) ceramics for low-temperature fired applications have been investigated. The sintering temperature of BST ceramics can be effectively lowered to about 1000°C with introduction of ZB. Tungsten bronze like single phase is observed in the BST ceramics with 0.5 and 1.0% ZB. However, Sm₂Ti₂O₇ secondary phase appears when ZB addition reaches 2%, and Sm₂Ti₂O₇ phase gradually increases with the increase ZB addition. Microwave dielectric properties of the present ceramics are strongly dependent on phase constitution and density. Optimal microwave dielectric properties of ε = 63.4, Qf = 2830 GHz, τ _f =–8.8 ppm/°C is obtained for BST ceramics with 1% ZB addition.     

Spatial localization of holes in La<Subscript>2 − <Emphasis Type="Italic">x</Emphasis></Subscript>Sr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>CuO<Subscript>4</Subscript>

The parameters of the tensor of the electric field gradient (EFG) in cation sites of the La_{2 ? x} Sr _x CuO₄ lattice have been determined by the method of emission Mössbauer spectroscopy on ⁵⁷Co(^57m Fe), ⁶⁷Cu(⁶⁷Zn), ⁶⁷Ga(⁶⁷Zn), and ¹⁵⁵Eu(¹⁵⁵Gd) isotopes. There is no quantitative agreement between the calculated (the pointcharge model) and experimental values of the main component of the tensor EFG V _zz , which is explained by the absence of the reliable data on the Sternheimer coefficients for Fe³⁺, Zn²⁺, and Gd³⁺ ions. Based on the comparison of the calculated and experimental dependences of V _zz on x it was shown that the holes appearing during the substitution of La³⁺ for Sr²⁺ are localized preferably on the oxygen atoms that are in the same plane as the copper atoms, which is in agreement with the model discussed in the literature and assumes that the mechanism responsible for the high-temperature superconductivity of solid solutions La_{2 ? x} Sr _x CuO₄ is the interaction between the conductivity electrons and two-atomic two-electron centers with negative correlation energy.     

Mechanical,Structural and Thermal Properties of Transparent Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–ZnO–TeO<Subscript>2</Subscript> Glass System

Oxide based optical glass materials has important potential material in many applications from fiber optic to sensor due to the high transparency and amourphous structures. The objective of this study is to synthesize the novel optical glass materials based on the bismuth and aluminum contents to be able to determine the physical, chemical and mechanical properties by considering the systematic experimental steps. In this study, Bi₂O₃–Al₂O₃ based tellurite optical glasses have been prepared by using conventional melt quenching method as a function of the both Bi₂O₃ and Al₂O₃ compositions. There is a strong interactions between the glass former and modifier ions that might effect on the structure and mechanical properties. During the experimental steps, thermal, structural and mechanical properties of the prepared glass materials have been determined considering the DTA/DSC, FT-IR spectroscopy, SEM and Vicker’s hardness techniques, respectively. Thermal parameters, like glass transition, T_g, onset, T_x, crystallization, T_p, and melting, T_m, temperatures were obtained by using DTA scan.