Phase equilibria in the Nd2O3–BaO–Fe2O3 system: Crystal structure,oxygen content,and properties of intermediate oxides

The phase equilibria in the ½Nd₂O₃–BaO–½Fe₂O₃ system were systematically studied at 1373 K in air and presented in the form of a phase diagram. By X-ray diffraction (XRD) analysis of quenched samples, the homogeneity ranges and crystal structure were determined for the following intermediate oxides: Nd_1-xBa_xFeO_3-δ with 0.0 ≤ x ≤ 0.05 (space group (SG) Pnma) and with 0.6 ≤ x ≤ 0.7 (SG Pm-3m), Ba_6+yNd_2-yFe₄O_15-δ with 0.0 ≤ y ≤ 0.4 (SG P6₃mc), and Ba_1.1Nd_1.9Fe₂O_7-δ (SG P4₂/mnm). The structural parameters of single-phase oxides were refined by the Rietveld method. The changes in oxygen content for Nd_1-xBa_xFeO_3-δ (0.6 ≤ x ≤ 0.7), Ba₆Nd₂Fe₄O_15-δ, and Ba_1.1Nd_1.9Fe₂O_7-δ versus temperature in air were determined by thermogravimetric analysis. Gradual substitution of neodymium by barium in the Nd_1-xBa_xFeO_3-δ (0.6 ≤ x ≤ 0.7) oxides leads to a decrease of oxygen content. Partial ordering via formation of separate domains with a_p × a_p × 5a_p superstructure in Nd_0.4Ba_0.6FeO_3-δ, which cannot be detected by XRD, noticeably influence its thermal expansion and electrical conductivity.     

Effect of mechanochemical synthesis on the structure,magnetic and optical behavior of Ni1−xZnxFe2O4 spinel ferrites

Ni_1−xZn_xFe₂O₄ (0≤x≤1) nanocrystals were prepared by a soft mechanochemical approach. The structure and morphology were assessed via X-ray powder diffractometery (XRD), infrared spectroscopy (FTIR), Raman spectroscopy, transmission electron microscopy (TEM) and Energy dispersive spectroscopy (EDS). The magnetic characteristics have been evaluated using vibrating sample magnetometer (VSM). The optical properties were explored by diffuse reflectance UV–visible spectrophotometry (DRS). The substitution of Zn into the Ni_1−xZn_xFe₂O₄ nanocrystals increased the mean nanocrystal size from 4 to 19 nm. The FTIR and Raman spectroscopies showed that the substitution with Zn up to x=0.5 in Ni_1−xZn_xFe₂O₄ nanocrystals results in a migration of Fe ions from tetrahedral to octahedral sites, leading to an improvement of the saturation magnetization value to 33.8 emu/g. At the same time, the optical band gap decreased from 2.6 to 1.93 eV due to the increase of the Zn content from x=0 to x=1. These promising characteristics of Ni_1−xZn_xFe₂O₄ nanocrystals make them suitable for the use in the field of magnetically recoverable catalysts including those for energy applications.     

Crystal structure,microstructure, thermal expansion and electrical conductivity of CeO2–ZrO2 solid solution

CeO₂–ZrO₂ solid solution was synthesised by mechanical activation solid-state chemical reaction method and characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM), thermal dilatometer, Hebb–Wagner method and DC van der Pauw method. The effects of CeO₂ content on the crystal structure, microstructure, thermal expansion coefficient (TEC), electronic conductivity and total conductivity were investigated. XRD analysis showed that (25 and 75?mol-%) CeO₂–ZrO₂ solid solutions corresponded to tetragonal and cubic phase, and 50?mol-% CeO₂–ZrO₂ belonged to the mixture of tetragonal and cubic phases. SEM analysis showed that doping CeO₂ was helpful to the sinterability of CeO₂–ZrO₂ samples. The TECs increased from 13.27?×?10^?6 to 14.72?×?10^?6?K^?1 with increasing CeO₂ content. The electronic and total conductivities of 75?mol-% CeO₂–ZrO₂ were largest, reaching 1.02?×?10^?4?S?cm^?1 and 1.02?×?10^?2?S?cm^?1 at 850°C, respectively.     

Erbium activating effect on the photoluminescence,morphology, and structure studies of nano-composite Phospho-silicate SiO2–P2O5

Smart nano-composites Phospho-silicate (SiO₂–P₂O₅) prepared in monolith form containing 16 mol% P₂O₅, and doped with different mol% of Er³⁺ ions between 0.5 and 5 mol%; the composite has been synthesized by Sol-Gel technique, and subsequently annealed at 850 °C.X-ray diffraction patterns show the structural properties of the mentioned prepared samples, giving rise to the crystallite sizes to increase in a range between 18, and 20.8 nm as the molar percent of the Er³⁺ ion increase from 0% to 5%. The morphology, and surface morphology of the prepared samples were characterized using TEM, and FESEM, respectively. The Raman analyses show that the active Raman bands are corresponding to silicate, and phosphate. These bands were enveloped by the strong asymmetric vibrations of Er₂O₃ at 420, and 840 cm⁻¹, their Bose-Einstein corrected intensities increased gradually by increasing the Er³⁺ ions concentration in the regions from 3400 up to 3450 cm⁻¹, and 3550 up to 3700 cm⁻¹. The optical studies show that the refractive index increased by increasing Er³⁺ ions concentration, from 1.7 up to 1.8 for as the concentration of Er³⁺ ions increase. The photoluminescence are exhibiting an emission with splitting at 1545, and 1555 nm, which is related to the intra 4F transition. It has been found that the optimal doping content of Er is 1 mol% then, after quenching caused by OH groups in Er³⁺ ions doped Phospho-silicate at higher concentrations. It is obviously that 1 mol% of Erbium ions is a suitable candidate for photonic applications such as Laser waveguide, and optical amplifier.     

Effects of boron oxide composition,structure, and morphology on B4C formation via the SHS process in the B2O3–Mg – C ternary system

This study investigates the formation of B₄C in the B₂O₃–Mg–C ternary system via a magnesiothermic reduction process using two kinds of boron oxide (B₂O₃) ‒ the commercial B₂O₃ and that synthesized from boric acid via the coupled chemical-thermal process. In addition to the raw materials, the products were subjected to XRD, FTIR, SEM, and FESEM analyses to determine the effects of microstructural and morphological properties of boron oxide as an important raw material, on B₄C formation in the combustion synthesis process. For this purpose, powder mixtures of B₂O₃:Mg:C were prepared at a stoichiometric molar ratio of 2:6:1 and compacted into pellets using a uniaxial hydraulic press, which were subsequently subjected to the combustion synthesis process based on the self-propagating high-temperature synthesis (SHS). Finally, the samples thus obtained were leached in an aqueous hydrochloric acid solution. Analysis of the commercial B₂O₃ revealed the presence of large amounts of such by-products as magnesium borate (Mg₃B₂O₆) and magnesium oxide (MgO) along with relatively small amounts of boron carbide after the leaching process, while those obtained for the chemically-thermally synthesized B₂O₃ showed a relatively large amount of B₄C (from micron-sized particles to nanoparticles) together with a remaining carbon phase and very small amounts of magnesium borate as by-products. It can be, therefore, concluded that the changes in chemical composition and introduction of a hydrous HBO₂ phase in the boron oxide in the B₂O₃–Mg–C mixture as well as its varied microstructure, morphology, and particle size have significant effects on the efficiency of B₄C production through the SHS process.     

In situ synthesis,physical and mechanical properties of ZrB2–ZrC–WB composites

In this study, two composition ZrB₂–ZrC–WB composites were synthesized by reactive hot-pressing of Zr + B₄C + WC powder mixtures at 1900 °C. The microstructure of the resulting composites was characterized by a combination of scanning electron microscopy and X-ray diffraction. It is seen that highly-dense ZrB₂–ZrC–WB composites with a homogenous fine-microstructure were obtained after the sintering. The mechanical behavior of the composites was evaluated using by testing under four-point bend testing at room and high temperatures. The results show that the high-temperature strength of the ZrB₂–ZrC–WB composites was substantially improved, compared to ZrB₂–ZrC-based composites without WB. In addition, the elastic properties, electrical conductivity, hardness and fracture toughness of the composites were measured at room temperature. The results reveal that these properties were comparable to those of ZrB₂–ZrC-based composites without WB.     

The impact of Na2O on the synthesis of α-C2SH with different mineral composition and the stability of intermediate and final products

In this work the effect of Na₂O on the synthesis of α-C₂S hydrate (2CaO·SiO₂·H₂O), named as α-C₂SH, with different mineral composition and the stability of intermediate and final products were investigated. It is worth noting that new results was discovered by evaluating the mineral composition of hydrothermally synthesized α-C₂SH samples (200?°C; 2–72?h). It was found that Na₂O additive significantly influenced the formation and stability of intermediate and final products: within 12?h of hydrothermal treatment together with α-C₂SH a new calcium silicate hydrate phase, killalaite, was obtained in the products. Besides, the mineral composition of formed compounds slightly varied by prolonging the duration of synthesis to 24?h. For the first time it was proved that Na⁺ ions are not incorporated into the crystal structure of the main synthesis product, α-C₂SH. On the contrary, the mentioned ions are intercalated into the crystal structure of other calcium silicate hydrates. Moreover, the investigated alkaline additive reduced the recrystallization temperature of the synthesis products to wollastonite by 50?°C and significantly decreased the values of both specific area and total pore volume of α-C₂SH till 8.496?m²/g and 0.05084?cm³/g, respectively. The synthetic products were characterized by XRD, DSC, SEM/EDX and N₂ adsorption analysis.     

Al2O3–W nanocomposites obtained by colloidal processing and in situ synthesis of nano-metal particles

The preparation process and the properties of Al₂O₃-W nanocomposites obtained by gelcasting are reported. The novelty of the synthesis path is the formation of nano-tungsten particles in an in situ reduction of water-soluble precursor during pressureless sintering. The use of water-soluble salt as a tungsten precursor ensured highly homogenous distribution of reinforcing particles and good adhesion between ceramic and metal phases. The maximum content of tungsten in the composites was approximately 0.5 wt%. The size of the reinforcing particles was less than 100 nm. Presence of metallic tungsten and tungsten carbide (W₂C) in the composites lead to the improvement of mechanical parameters: an increase of hardness by about 10 % and of fracture toughness by about 20 %, compared to the reference sample of pure aluminum oxide.     

Furan fatty acids: Occurrence,synthesis, and reactions. Are furan fatty acids responsible for the cardioprotective effects of a fish diet?

Furan FA (F-acids) are tri-or tetrasubstituted furan derivatives characterized by either a propyl or pentyl side chain in one of the α-positions; the other is substituted by a straight long-chain saturated acid with a carboxylic group at its end. F-acids are generated in large amounts in algae, but they are also produced by plants and microorganisms. Fish and other marine organisms as well as mammals consume F-acids in their food and incorporate them into phospholipids and cholesterol esters. F-acids are catabolized to dibasic urofuran acids, which are excreted in the urine. The biogenetic precursor of the most abundant F-acid, F₆, is linoleic acid. Methyl groups in the β-position are derived from adenosylmethionine. Owing to the different alkyl substituents, synthesis of F-acids requires multistep reactions. F-acids react readily with peroxyl radicals to generate dioxoenes. The radical-scavenging ability of F-acids may contribute to the protective properties of fish and fish oil diets against mortality from heart disease.     

Crystal structure and catalytic studies of heterodinuclear complex [CuZn(μ-OAc)(μ-OH)(μ-OH2)(bpy)2](ClO4)2

The heterodinuclear copper–zinc complex [CuZn(μ-OAc)(μ-OH)(μ-OH₂)(bpy)₂](ClO₄)₂ has been synthesized from solid state reaction and its crystal structure was established. The heterobimetallic complex is quite efficient catalyst for hydrogen peroxide mediated oxidation of alcohols into corresponding carbonyl compounds.     

Controlled delivery of drugs through smart pH-sensitive nanohydrogels for anti-cancer therapies: synthesis,drug release and cellular studies

Nanohydrogels were synthesized by microemulsion polymerization. These nanohydrogels were pre-designed to be pH and temperature stimuli-response materials, using N-isopropylacrilamide as a base monomer and 1-vinyl imidazole as ionizable comonomer. The pH sensitivity was confirmed by measuring the increase or decrease in volume in the nanoparticles by changing the pH of the medium. Nanoparticles were properly characterized by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), nuclear magnetic resonance (NMR) and transmission electron microscopy (TEM). Glass-transition temperature increased with vinyl imidazole content, and nanoparticles with average diameter of 68 nm were obtained. Particle size decreases with the increase in pH. After characterization, nanohydrogels were functionalized with folic acid to take advantage that the folate receptor is overexpressed in different types of cancer cells. The nanoparticles were loaded with the drugs: metformin, terfenadine, and 5-fluorouracil. The amount of drug loaded and released by nanoparticles was measured by UV–vis spectroscopy. Then, cellular viability and internalization studies were performed obtaining promising results.     

NO reduction by CH4over La2O3: temperature‐programmed reaction and in situ DRIFTS studies

The chemistry between NO _x species adsorbed on La₂O₃ and CH₄ was probed by temperature‐programmed reaction (TPR) as well as in situ DRIFTS. During NO reduction by CH₄ in the presence of O₂, NO ₃ ^- does not appear to activate CH₄, thus either an adsorbed O species or an NO ₂ ^- species is more likely to activate CH₄. In the absence of O₂, a different reaction pathway occurs and NO^- or (N₂O₂)^2- species adsorbed on oxygen vacancy sites seem to be active intermediates, and during NO reduction with CH₄ unidentate NO ₃ ^- , which desorbs at high temperature, behaves as a spectator species and is not directly involved in the catalytic sequence. Because reaction products such as CO₂ or H₂O as well as adsorbed oxygen cannot be effectively removed from the surface at lower temperatures, steady‐state catalytic reactions can only be achieved at temperatures above 800 K, even though formation of N₂ and N₂O from NO was observed at much lower temperature during the TPR experiments. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of Al2O3 and K2O content on structure,properties and devitrification of glasses in the Li2O–SiO2 system

The effect of Al₂O₃ and K₂O content on structure, sintering and devitrification behaviour of glasses in the Li₂O–SiO₂ system along with the properties of the resultant glass–ceramics (GCs) was investigated. Glasses containing Al₂O₃ and K₂O and featuring SiO₂/Li₂O molar ratios (3.13–4.88) far beyond that of lithium disilicate (Li₂Si₂O₅) stoichiometry were produced by conventional melt-quenching technique along with a bicomponent glass with a composition 23Li₂O–77SiO₂ (mol.%) (L₂₃S₇₇). The GCs were produced through two different methods: (a) nucleation and crystallization of monolithic bulk glass, (b) sintering and crystallization of glass powder compacts.Scanning electron microscopy (SEM) examination of as cast non-annealed monolithic glasses revealed precipitation of nanosize droplet phase in glassy matrices suggesting the occurrence of phase separation in all investigated compositions. The extent of segregation, as judged from the mean droplet diameter and the packing density of droplet phase, decreased with increasing Al₂O₃ and K₂O content in the glasses. The crystallization of glasses richer in Al₂O₃ and K₂O was dominated by surface nucleation leading to crystallization of lithium metasilicate (Li₂SiO₃) within the temperature range of 550–900 °C. On the other hand, the glass with lowest amount of Al₂O₃ and K₂O and glass L₂₃S₇₇ were prone to volume nucleation and crystallization, resulting in formation of Li₂Si₂O₅ within the temperature interval of 650–800 °C.Sintering and crystallization behaviour of glass powders was followed by hot stage microscopy (HSM) and differential thermal analysis (DTA), respectively. GCs from composition L₂₃S₇₇ demonstrated high fragility along with low flexural strength and density. The addition of Al₂O₃ and K₂O to Li₂O–SiO₂ system resulted in improved densification and mechanical strength.     

Effects of in situ synthesis of CNTs/SiCw on microstructure and properties of Al2O3–SiC–C composites

Al₂O₃–SiC–C composites were prepared using tabular corundum, ball pitch and silicon carbide as the main raw materials. The carbon nanotubes (CNTs) and SiC whiskers (SiC_w) were in situ synthesized and their effects on the thermo–mechanical properties of Al₂O₃–SiC–C composites have been studied. The experimental results indicated that the high yield of SiC_w and CNTs with large aspect ratio could be obtained due to addition of Ni(NO₃)₂·6H₂O as catalyst in the composites. The cold modulus of rupture values were increased by 24% to 7.2 MPa, and the flexural modulus was increased from 19 GPa to 24 GPa. Additionally, the hot modulus of rupture reached a maximum value of 3.6 MPa, which presented a 71% increase over that of composites without catalyst. After three thermal shock cycles, the residual cold crush strength was improved from 57.1% to 76.9%. It is believed that the enhancement in the thermo-mechanical properties of Al₂O₃–SiC–C composites could be attributed to the reinforcement effect of SiC_w and CNTs.     

Self-propagating high-temperature synthesis of advanced ceramics in the Mo–Si–B system: Kinetics and mechanism of combustion and structure formation

The goal of this work is to investigate the combustion mechanisms of reactions in the Mo–Si–B system and to obtain ceramic materials using the SHS method. It is concluded that the following processes are defined by the SHS for Si-rich Mo–Si–B compositions: silicon melting, its spreading over the surfaces of the solid Mo and B particles, followed by B dissolution in the melt, and formation of intermediate Mo₃Si-phase film. The subsequent diffusion of silicon into molybdenum results in the formation of MoSi₂ grains and molybdenum boride phase forms due to the diffusion of molybdenum into B-rich melt. The formation of MoB phase for B-rich compositions may occur via gas-phase mass transfer of MoO₃ gaseous species to boron particles. The stages of chemical interaction in the combustion wave are also investigated. The obtained results indicate the possibility of both parallel and consecutive reactions to form molybdenum silicide and molybdenum boride phases. Thus the progression of combustion process may occur through the merging reaction fronts regime and splitting reaction fronts regime. Molybdenum silicide formation leads the combustion wave propagation during the splitting regime, while the molybdenum boride phase appears later. Finally, targets for magnetron sputtering of promising multi-phase Mo–Si–B coatings are synthesised by forced SHS compaction method.     

Synthesis,spectroscopic studies and structure prediction of the new Tb(3-NH2PIC)3·3H2O complex

The synthesis, spectroscopic properties and structure prediction of the complex of Tb(III) with 3-aminopyridine-2-carboxylic acid (3-NH₂PIC) are described. The complex was characterized by elemental analysis and IR, absorption and emission spectra. The C, H and N elemental analysis consistent with the formulation of the compound as Tb(3-NH₂PIC)₃·3H₂O. This complex exhibits a luminescence intensity that is attenuated to that of its Eu⁺³ congener. The Sparkle model, used for structural computations of lanthanide complexes (SMLC), was applied to the new complex. The calculation used an INDO/S-CI model for determination of the electronic spectrum.     

In situ synthesis of ZrB2–MoSi2 platelet composites: Reactive hot pressing process,microstructure and mechanical properties

Using elemental Zr, B, Mo and Si as raw materials, partially textured ZrB₂–MoSi₂ composites with in situ platelet ZrB₂ grains were fabricated by reactive hot pressing. Synthesized by a combustion reaction, the in situ formed ZrB₂ phase had unique characteristics to grow up to platelet grains, on the surroundings of Mo–Si–B ternary liquid phase at high temperature. Mechanical properties were dependent on grain size and aspect ratio of the ZrB₂ platelets. The rotation and realignment of the platelet ZrB₂ grains under hot pressing led to a partially textured microstructure, which showed anisotropic mechanical properties on different directions of the as-sintered samples. A roadmap of the reaction process, microstructure evolution and texture formation was given to describe the preparation of partially textured ZrB₂–MoSi₂ composites by reactive hot pressing.     

Crystal structure refinement and the magnetic and electro-optical properties of Er3+–Mn2+-substituted Y-type barium hexaferrites

The influence of Er³⁺–Mn²⁺ substitution on the properties of Y-type hexaferrites (chemical composition: Ba_2–xEr_xZn_0.6Co_0.6Cu_0.8Fe_12?yMn_yO₂₂ (x = 0.0, 0.3, and 0.5 and y = 0.0, 0.4, and 0.6)), which were synthesized by the sol-gel autocombustion method, was investigated. The X-ray diffraction spectra were analyzed by the Rietveld refinement method, and hexaferrite was observed to possess a single-phase crystalline structure, whereas the Fourier-transform infrared spectra clarified the formation of the iron oxide base material. The morphology of the grains revealed that they were hexagonal and without agglomeration. The band gap of the samples decreased as the Er³⁺–Mn²⁺ concentration increased. Dielectric and impedance spectroscopies of the prepared samples indicated the role of polarization in the variation in the dielectric and impedance parameters. Particularly, the occurrence of space-charge polarization increased the dielectric constant at lower frequencies. Further, the Cole–Cole plot revealed a semicircle in the lower frequency region, thereby indicating that the grain boundary contributed the most to the dielectric constants. Modulus spectroscopy revealed that the charge mobility increased as the concentration of Er³⁺–Mn²⁺ increased. Additionally, the magnetic analysis indicated that Mn²⁺ preferably replaces Fe³⁺ at the octahedral site, thereby reducing the magnetization of the prepared samples through a reduced superexchange interaction. Furthermore, increasing the coercivity values thermally stabilized the sample, and this is vital for perpendicular magnetic recording.     

Synthesis,structure and properties of the first dinuclear copper(II) complex as a structural model for the phenolic intermediate in tyrosinase–cresolase activity

The synthesis, X-ray crystal structure and spectroscopic and electrochemical properties of the new dinuclear copper(II) complex [Cu₂(Hbtppnol)CH₃COO](ClO₄)₂ (1), employing the novel unsymmetric dinucleating ligand N-(2-hydroxybenzyl)-N,N′,N′-tris(2-pyridylmethyl)-1,3-diaminopropan-2-ol (H₂btppnol), are presented. This complex could be a relevant model for the axial interaction of a phenolic substrate to tyrosinase during cresolase activity.     

Quantitative prediction of the structure and properties of Li2O–Ta2O5–SiO2 glasses via phase diagram approach

Tantalum silicate glasses serve as laser host materials to take advantage of their high refractive index and the ability to tailor their physical properties in the design of high-performance photonic and photoelectric components. However, successful attainment of feature control in tantalum-doped materials remains a longstanding problem due to the limited understanding of local structure around the tantalum ions, a problem that lies at the heart of predicting the micro- and macroscopic properties of these glasses. Herein, we present a novel approach for predicting the local structural environments in tantalum silicate glass based on a phase diagram approach. The phase relations and glass formation region of Li₂O–Ta₂O₅–SiO₂ ternary systems are explored to calculate the structure and additive physical properties of lithium tantalum silicate glasses. These measured and calculated results are in good quantitative agreement, indicating that the phase diagram approach can be applied broadly to Li₂O–Ta₂O₅–SiO₂ ternary glass systems. Using the phase diagram approach, the local structure of tantalum can be directly obtained. Each Ta atom is surrounded by six atoms, and its polyhedron, the TaO₆ octahedron, bonds through oxygen to Li and Ta. As a network modifier, Ta⁵⁺ depolymerizes the silicate glass structure by modulating the local structure of lithium atoms in Li₂O–Ta₂O₅–SiO₂ ternary glass system. The compositional dependence of structure in lithium tantalum silicate glasses is quantitatively determined based on the structure of the nearest neighbor congruent compound through the lever rule. These findings offer a precise prediction of tantalum silicate glass properties with quantitative control over local structural environment of the disordered materials.