Solid solutions in the MgO-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> system

Coexisting solid solutions with spinel and corundum structure were synthesized at 1773 K and two pressures, 1 bar and 25 kbar. Samples were analyzed by electron microprobe analysis and X-ray powder diffraction. Pressure and temperature were shown to affect the properties of the solid solutions in different ways. Pressure governs the composition of the defect spinel Mg_1−xAl₂O₄, and temperature changes the cation distribution between coexisting phases. This allows one to separate the effects of cation exchange and magnetic contribution to the heat capacity in thermodynamic modeling. The defect spinel itself can form only because γ-Al₂O₃ exists, polymorph with spinel structure.     

Modeling and optimizing toughness and rigidity of PA6/SBR: Using compatibilizer and response surface methodology

The improvement of miscibility between toughened Polyamide-6 (PA6) and Styrene-Butadiene Rubber (SBR) was carried out using grafted Glycidyl Methacrylate (SBR-g-GMA). At first, the compatibilizers were prepared using different comonomers, Styrene, and N-vinyl pyrrolidone. Central composited design (CCD) was distinctly applied to study the influence of Glycidyl Methacrylate (GMA) content and comonomer/GMA on the process of compatibilizer preparation. Four models were developed for Gel content and Degree of grafting for both comonomers using Design-expert software. The models were used to calculate the optimum operating conditions and according to the Flory-Huggins parameter and obtained results, SBR-co-NVP-g-GMA was chosen as an effective compatibilizer. Afterward, another CCD was employed to scrutinize the effect of various amounts and grafting degree of compatibilizer on morphology and mechanical properties of PA6/SBR. The Interparticle distance and polydispersity were studied using a Scanning electron microscope (SEM) and also the Izod impact test inspected in order to evaluate the mechanical properties. Finally, modulus and impact strength were optimized to minimize the former and maximize the latter. Also, the most practical terms in the fitted model are statistically specified using F-value. The root causes for the improvement of blend properties were attributed to a chemical reaction between epoxy groups in SBR-g-GMA and both the carboxylic and amine groups in PA6. Impact strength (539.8 J/m) and modulus (2017.2 N/mm²) of the optimum blend indicate an excellent agreement with the amounts predicted by the models.     

Oxygen redistribution in ZrO<Subscript>2</Subscript>-Y<Subscript>2</Subscript>O<Subscript>3</Subscript> system

This work represents the results of oxygen redistribution studies at quantitative and isotopic levels in synthesis and thermal treatment of ZrO - (0 to 35 mol %) Y₂O₃ solid solution crystals. The crystals were grown by directed melt crystallization method in a cold container using direct high-frequency heating. The crystal oxygen content and isotopic composition data was collected with respect to stabilizer concentration and technological conditions of synthesis. The temperature and frequency relationships of crystal electroconductivity were also studied. Some strength and tribological characteristics of the given materials were represented. The solid state formation by directional melt crystallization was shown to involve oxygen isotopic exchange interaction between the melt, growing crystal, and gas phase.     

Oxygen dependence of NO adsorption on Hollandite-type K<Subscript>x</Subscript>Ga<Subscript>x</Subscript>Sn<Subscript>8–<Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>16</Subscript> thin film

Thin films of hollandite-type K_1.9Ga_1.9Sn_6.1O₁₆ (KGSO) were prepared by a spin-coating method. The films were colorless and transparent, 100-150 nm thick, and consisted of KGSO fine particles of about 20 nm in average size. The adsorption behavior of NO on the KGSO surface was examined by diffuse reflectance infrared fourier transform (DRIFTS). The KGSO was preheated at 968 K in a gas mixture of N₂ and O₂ prior to NO adsorption. As the oxygen ratio in the gas mixture increased up to 40%, absorption bands emerged and became stronger around 1400 cm^-1. Those bands were assigned to NO₂ species in chelating and nitrito form. It was found that the coexistence of oxygen remarkably improves the adsorption ability of NO on KGSO surface.     

Synthesis and X-ray diffraction of Cd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Hg<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript> Te solid solutions

The Cd _x Hg_{1 − x} Te solid solutions were synthesized by combining two methods: immersion of CdTe single crystals in liquid mercury and thermal homogenization in mercury vapors. The samples obtained were studied by X-ray diffraction and X-ray fluorescence analyses. Nonstoichiometric cadmium microinclusions were shown to present in the initial CdTe single crystals and the solid solutions synthesized. The samples annealed in mercury vapors have smaller unit cell volumes than unannealed samples.     

Solubility isotherm for the Na<Subscript>2</Subscript>MoO<Subscript>4</Subscript>-Na<Subscript>2</Subscript>SO<Subscript>4</Subscript>-H<Subscript>2</Subscript>O system

Solubility in the Na₂MoO₄-Na₂SO₄-H₂O system was studied using isothermal saturation at 5–100°C. The boundaries of crystallization fields were determined for sodium sulfate and sodium molybdate. Solid solutions were not observed within the range of the temperatures studied. The density, refractive index, and dynamic viscosity of the saturated solutions of the system were determined, and these data were used to calculate the molar volume, kinematic viscosity, and apparent molar volume of the sum of salts in these solutions. All property isotherms of solutions are in a strict correlation with the solubility in the system; this correlation is represented as an isobaric-isothermal diagram.     

Reaction of methylpheophorbides <Emphasis Type="Italic">d</Emphasis> and <Emphasis Type="Italic">b</Emphasis> with amines

A series of formyl analogs of chlorin e₆ 13-amides were synthesized in high yields by reaction under mild conditions of primary and secondary amines with methylpheophorides b and d. In contrast with the secondary 13-amides, tertiary 13-amides were found as two isomers differing in the orientation of the amide plane relative to the plane of the chlorin ring. Methylpheophorbides b and d were more reactive toward the amines than methylpheophorbide a.     

Polysaccharides from <Emphasis Type="Italic">Crotalaria alata</Emphasis>

Water-soluble polysaccharides, pectinic substances, and hemicellulose were isolated from various organs of Crotalaria alata cultivated in Uzbekistan. Water-soluble polysaccharides that were present in seeds were found to be galactomannans.     

Phase equilibria in the K<Subscript>2</Subscript>O-Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> system

Phase equilibria in the potassium oxide-niobium oxide system were studied by oscillation phase-analysis and thermal analysis on 35 samples with compositions lying the range from 24.9 to 66.4 mol % Nb₂O₅. The melting temperatures and melting types of the compounds of the system were refined. The composition of crystallizing phases was shown to depend on the thermal history of the sample.     

Y<Subscript>2</Subscript>O<Subscript>3</Subscript>-Ga<Subscript>2</Subscript>O<Subscript>3</Subscript> phase diagram

Phase relations in the Y₂O₃-Ga₂O₃ system were studied by the anneal-and-quench technique in air within 1000–2300°C, and a phase diagram was plotted. Three compounds were found to form: Y₃GaO₆, Y₄Ga₂O₉, and Y₃Ga₅O₁₂; the temperature and concentration bounds of stability were determined for these compounds. Indexing results for Y₃GaO₆ are given.     

Influence of pressure on the electrical and electrochemical behaviour of high-temperature steam electrolyser La<Subscript>0.6</Subscript>Sr<Subscript>0.4</Subscript>Co<Subscript>0.2</Subscript>Fe<Subscript>0.8</Subscript>O<Subscript>3</Subscript> anode

This paper is dedicated to the impact of pressure on the electrochemical behaviour of LSCF (La_1-xSr_xCo_yFe_1-yO_3-δ) anode in high-temperature electrolysers. This study was carried out with symmetrical cells associating LSCF electrodes to a 3YSZ (yttrium-stabilised zirconia) electrolyte. Impedance spectroscopy measurements were performed using a three-electrode configuration, at temperature as high as 700 to 800 °C, in a pressure range from 1 to 30 bar. A clear improvement in terms of electrode resistance decrease is highlighted, mainly due to faster oxygen adsorption/desorption kinetics and a better supply of gas to electrochemical reaction sites. Other assumptions were considered and analysed, such as the impact of pressure on LSCF electrical conductivity and on the mechanical contacts. Thus, three contributions were determined as limiting steps at low pressure, up to 5 bar, whilst for higher pressure, the optimised conditions in operation are reached. This study completes a previous one related to a modelling approach.     

Eu<Superscript>3+</Superscript>-fluorescence properties in nano-crystallized SnO<Subscript>2</Subscript>-SiO<Subscript>2</Subscript> glass-ceramics

Fluorescence and spectral hole burning properties of Eu³⁺ ions were studied in nanocrystals-precipitated SnO₂-SiO₂ glasses. The glasses were prepared to contain various amount of Eu₂O₃ using the sol-gel method, in which SnO₂ nanocrystals were precipitated by heating in air. In the glasses containing Eu₂O₃ less than 1%, the Eu³⁺ ions were preferentially doped in the SnO₂ nanocrystals and their fluorescence intensities were enhanced by the energy transfer due to the recombination of electrons and holes excited in SnO₂ crystals. The SnO₂ nanocrystals-precipitated glasses exhibited the persistent spectral holes with the depth of ∼25% of the total fluorescence intensities of the Eu³⁺ ions. With the increasing Eu₂O₃ concentration, the amount of SnO₂ nanocrystals decreased and the Sn⁴⁺ ions formed the random glass structure together with the silica network. This structure change induced the fluorescence intensities and the hole depth to decrease.     

Magnetic and thermal analysis of <Emphasis Type="Italic">M</Emphasis>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> (<Emphasis Type="Italic">M</Emphasis> = Co,Mn, Zn) nanoparticles

Magnetic nanoparticles were prepared by a wet chemical method. Precursors of MFe₂O₄ (M = Co, Mn, Zn) were prepared from a mixture of metal chloride and metasilicate nonahydrate aqueous solutions. The precipitates obtained in the wet chemical method were calcined to obtain MFe₂O₄ nanoparticles encapsulated by amorphous SiO₂. The blocking temperatures T _B’s were between 20 and 320 K, in this temperature range, the anisotropy energy of the particles decreased below their thermal energy. T _B increased with the particle size. In order to clarify the nanoparticle formation process, differential thermal analysis and thermogravimetric (TG-DTA) measurements were performed for the as-prepared samples.     

The synthesis and properties of solid solutions based on Ba<Subscript>4</Subscript>Ca<Subscript>2</Subscript>Nb<Subscript>2</Subscript>O<Subscript>11</Subscript>

(Ba_{1 ? x} Ca _x )₆Nb₂O₁₁ solid solutions were synthesized. The compositions were shown to be single-phase at 0.23 ≤ x ≤ 0.47 and have a double perovskite cubic structure with an incomplete oxygen sublattice. The interaction of solid solutions with water vapor and their electrical properties were studied. In dry atmosphere, these complex oxides were mixed oxygen-hole conductors. In humid atmosphere, they intercalated water and exhibited protonic conductivity. The influence of Ba/Ca isovalent substitution, the dynamics of the oxygen sublattice, and the concentration of intercalated water on the value and contribution of protonic and hole conductivity was analyzed.     

Physicochemical properties of KOH-H<Subscript>2</Subscript>O<Subscript>2</Subscript>-H<Subscript>2</Subscript>O solutions

Density, viscosity, and surface tension of KOH-H₂O₂-H₂O solutions used to synthesize potassium superoxide in sprayer apparatus were studied with various relative amounts of the components in the temperature range 0–30°C. Analytical dependences of the above-mentioned quantities on temperature and solvent (water) content of the system were found.     

Synthesis of highly dispersed super-refractory tantalum-zirconium carbide Ta<Subscript>4</Subscript>ZrC<Subscript>5</Subscript> and tantalum-hafnium carbide Ta<Subscript>4</Subscript>HfC<Subscript>5</Subscript> via sol-gel technology

Nanocrystalline powders of super-refractory complex carbides Ta₄HfC₅ and Ta₄ZrC₅ were synthesized using a hybrid method comprising sol-gel technology for preparing highly dispersed metal oxidescarbon starting mixtures and a relatively low-temperature (1300–1500°C) carbothermal synthesis under a dynamic vacuum (P = 1 × 10⁻³ to 1 × 10⁻⁵ MPa). The elemental and phase compositions of the products and average crystallite sizes were determined. TEM was used to study particle morphology and dispersion. Microstructures were observed by SEM. BET specific surface areas were determined for powders prepared at 1400°C.     

σ<Superscript>H</Superscript>-Adducts of <Emphasis Type="Italic">N</Emphasis>-alkylpyrazinium and quinoxalinium salts with nucleophiles. The <Superscript>1</Superscript>H and <Superscript>13</Superscript>C NMR spectra and the crystal structures of P-adducts

The previously unknown addition products of P-nucleophiles to 5-aryl- and 5-hetaryl- 2,3-dicyano-1-ethylpyrazinium salts and to 5-aryl- and 5-hetaryl-14nethylquinoxalinium salts were synthesized. The three-dimensional structures of the P- σ^H-adducts of the 1,4-diazine series were established by X-ray diffraction.     

The La(CCl<Subscript>3</Subscript>COO)<Subscript>3</Subscript>-NaCCl<Subscript>3</Subscript>COO-H<Subscript>2</Subscript>O system at 298 K

The ternary lanthanum trichloroacetate-sodium trichloroacetate-water system was studied by the isothermal solubility method at 298 K. The compositions of solid phases were established by the Schkreinemakers’ wet residue method. The liquid refractive indexes, specific volumes, and viscosities were determined. The system was found to be eutonic.     

The thermodynamic properties of fullerene hydrides C<Subscript>60</Subscript>H<Subscript>2<Emphasis Type="Italic">n</Emphasis></Subscript>

The equilibrium geometric parameters and normal vibration frequencies of the C₆₀H₂, C₆₀H₁₈, and C₆₀H₆₀ molecules were determined using density functional theory at the B3LYP/6-31G* level. The results were used to calculate the thermodynamic properties of the substances in the ideal gas state. The heat capacity of crystalline hydrofullerenes was modeled and the enthalpies of their sublimation estimated. The thermodynamic parameters of the hydrogenation of fullerene C₆₀ were analyzed.     

Transition metal salts of H<Subscript>4</Subscript>PMo<Subscript>11</Subscript>VO<Subscript>40</Subscript> for efficient H<Subscript>2</Subscript>S removal in the liquid redox process

Several transition metal (Cu²⁺, Fe³⁺, Zn²⁺, Mn⁴⁺, and Cr⁶⁺) salts of H₄PMo₁₁VO₄₀ were prepared and their solutions were used initially for H₂S removal in the liquid redox process. H₂S removal tests were performed by dynamic absorption experiments. Among these polyoxometalates, that with the Cu²⁺ cation was found to have pronounced H₂S removal performance with the removal efficiency of up to 98%. The relevant oxidative desulfurization mechanism and the role of Cu²⁺ were studied.