Physicochemical properties of precursors of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–ZrO<Subscript>2</Subscript> oxide ceramics prepared by electrochemical method

Scanning electron microscopy, X-ray, and thermal analysis are used to examine the structure and properties of dispersive systems based on aluminum and zirconium oxides prepared electrochemically. The effect the conditions of synthesis have on the structure and morphology of Al₂O₃–ZrO₂ particles is studied. It is shown that the effect of an electric field on the reaction medium allows us to adjust the physicоchemical properties and morphology.     

Synthesis and properties of γ-Ga<Subscript>2</Subscript>O<Subscript>3</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> solid solutions

The textural and structural properties of mixed oxides Ga₂O₃–Al₂O₃, obtained via impregnating γ-Al₂O₃ with a solution of Ga(NO₃)₃ and subsequent heat treatment, are studied. According to the results from X-ray powder diffraction, gallium ions are incorporated into the structure of aluminum oxide to form a solid solution of spinel-type γ-Ga₂O₃–Al₂O₃ up to a Ga₂O₃ content of 50 wt % of the total weight of the sample, accompanied by a reduction in the specific surface area, volume, and average pore diameter. It is concluded that when the Ga₂O₃ content exceeds 50 wt %, the β-Ga₂O₃ phase is observed along with γ-Ga₂O₃–Al₂O₃ solid solution. ⁷¹Ga and ²⁷Al NMR spectroscopy shows that gallium replaces aluminum atoms from the tetrahedral position to the octahedral coordination in the structure of γ-Ga₂O₃–Al₂O₃.     

Glass Formation in the Al<Subscript>2</Subscript>(SO<Subscript>4</Subscript>)<Subscript>3</Subscript>–(CH<Subscript>3</Subscript>)<Subscript>2</Subscript>SO–H<Subscript>2</Subscript>O System

The glass formation in the Al₂(SO₄)₃–(CH₃)₂SO–H₂O system was found for the first time. The competitive ability of ligands, dimethyl sulfoxide and water (which are strong donors), for entering the first coordination sphere of aluminum is considered. The possibility of mixed coordination of (CH₃)₂SO (via sulfur and oxygen atoms) in the first coordination sphere of aluminum with retention of the glass-forming ability of the sample was suggested on the basis of IR spectral study.     

Modifying additives affect the properties of Y<Subscript>2</Subscript>O<Subscript>3</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript> system

The effects caused by modifying additives, namely nonionic surfactants (Tween 80 and Neonol AF 9-6) and oxides (B₂O₃ and HfO₂), on the rheology, film formation, and phase formation in the yttrium aluminum silicate system prepared by sol–gel technology were studied. The effect of 1 wt % HfO₂ additions on the activation energy of crystallization was studied.     

Porous xerogels with a bifunctional surface layer of the composition ≡Si(CH<Subscript>2</Subscript>)<Subscript>3</Subscript>SH/≡Si(CH<Subscript>2</Subscript>)<Subscript>2</Subscript>H<Subscript>3</Subscript>

The sol-gel method with ethanol as a solvent and fluoride ion as a catalyst was used to prepare polysiloxane xerogels containing both 3-mercaptopropyl and n-propyl groups in the surface layer. An increase in the relative amount of n-propyltriethoxysilane in the initial reaction solution was found to result in the formation of xerogels with developed porous structures, which was accompanied by an increase in the specific surface area from 370 to 550 m²/g; simultaneously, other porous structure parameters such as sorption volume and pore size exhibited a tendency to increase. Atomic-force microscopy was used to show that the xerogels synthesized comprised aggregates of mean size 30 nm. An analysis of the IR and ¹³C cross-polarization magic angle spinning NMR data led us to conclude that the surface layer of bifunctional xerogels contained not only 3-mercaptopropyl and n-propyl groups but also silanol groups, part of nonhydrolyzed alkoxy groups, and H-bonded water molecules. The ²⁹Si cross-polarization magic angle spinning NMR spectra revealed the presence of structural units of the compositions T¹ [(≡SiO)Si(OR’)₂(CH₂CH₂CH₃) and/or (≡SiO)Si(OR’)₂(CH₂)₃SH, R’ = H, OCH₃, or OC₂H₅], T² [(≡SiO)₂Si(OR’)(CH₂CH₂CH₃) and (≡SiO)₂Si(OR’)(CH₂)₃SH], and T³ [(≡SiO)₃SiCH₂CH₂CH₃ and (≡SiO)₃Si(CH₂)₃SH] in the xerogels synthesized.     

Synthesis and properties of magnetic superhydrophobic mesoporous Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript> composites

Ways to obtain Fe₂O₃–SiO₂ iron-containing silica composites with organized mesoporous structure (MCM-41) and large specific surface area (up to 1476 m² g^–1) were considered. The influence exerted by the method used to synthesize the materials on their structure, texture characteristics, particle size, and magnetic properties were studied. The aggregative stability of samples was examined. It was shown that treatment of the resulting composites with compounds from the chlorosilane group affects their hydrophobic properties.     

Polytherm of the CO(NH<Subscript>2</Subscript>)<Subscript>2</Subscript>–KNO<Subscript>3</Subscript>–H<Subscript>2</Subscript>O phase diagram

The crystallization polytherm of the ternary CO(NH₂)₂–KNO₃–H₂O system is plotted for the first time via visual polythermal analysis and calculating ternary eutonics characteristics from data on the boundary elements of two-component systems. The ternary eutonics modeling error does not exceed 3.5%. In addition to the crystallization fields of individual components, the field of the redox reaction that occurs in the system between potassium nitrate and carbamide is shown in the CO(NH₂)₂–KNO₃–H₂O diagram by a dashed outline.     

Selective Hydrogenation of Acetylene and Physicochemical Properties of Pd–Fe/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Bimetallic Catalysts

The selective hydrogenation of acetylene on Pd–Fe/Al₂O₃ catalysts prepared by decomposition of ferrocene on reduced Pd/Al₂O₃ was studied. The effect of the conditions of treatment of the Pd–ferrocene/ Al₂O₃ precursor on the catalyst activity and selectivity was investigated, and the optimum conditions were determined at which the Pd–Fe/Al₂O₃ catalyst has higher selectivity than Pd/Al₂O₃ without any loss of activity.     

Catalytic properties of Fe/SiO<Subscript>2</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> systems,obtained via sol–gel method

The high efficacy of iron-containing catalysts based on SiO₂–Al₂O₃ systems obtained via sol–gel method in the oxidative destruction of carmoisine azo dye in aqueous solutions is demonstrated. It is found that the stability of the catalysts with respect to the leaching of iron ions into a solution during catalysis grows along with the aluminum content in the composition of aluminosilicate supports. It is concluded that the synthesized catalysts are promising materials for purifying wastewaters contaminated with organic dyes.     

A Raman Spectroscopic Study of Aqueous La(CH<Subscript>3</Subscript>CO<Subscript>2</Subscript>)<Subscript>3</Subscript> Solutions and La(CH<Subscript>3</Subscript>CO<Subscript>2</Subscript>)<Subscript>3</Subscript>·1.5 H<Subscript>2</Subscript>O(cr)

Aqueous solutions of La(CH₃CO₂)₃, NaCH₃CO₂ and La(ClO₄)₃ were studied using Raman spectroscopy. In dilute NaCH₃CO₂ solution, acetate is fully hydrated and forms only minor amounts of ion pairs. The characteristic Raman bands are discussed and assigned. In fairly dilute La(ClO₄)₃ solutions, the La³⁺(aq) ion occurs as the nonahydrate. The separation of the carboxylate bands, ν_as – ν_s (Δ-value), in NaCH₃CO₂(cr) compared to La(CH₃CO₂)₃·1.5H₂O(cr) correlates with the bonding type of acetate which is “ionic” in the former but bidentate chelating/tridentate chelating in the latter. Other acetate bands such as the deformation mode of the CO₂ moiety, δ CO₂, and the two rocking vibrations (ρ), as well as the C–C stretch show marked differences in their band positions in NaCH₃CO₂(cr) compared to the ones in La(CH₃CO₂)₃·1.5H₂O(aq). In a ternary solution of La(CH₃CO₂)₃/LaCl₃ with a molar ratio La³⁺(aq): \( {\text{CH}}_{3} {\text{CO}}_{2}^{ - } \)(aq) = 3.87: 1.00), the bands of the bound acetate on La³⁺ were characterized and compared to those of fully hydrated acetate, \( {\text{CH}}_{3} {\text{CO}}_{2}^{ - } \left( {\text{aq}} \right) \). In this solution, almost all acetate is ligated to La³⁺ in a bidentate fashion and two complex species could be identified (molar ratios La³⁺: \( {\text{CH}}_{3} {\text{CO}}_{2}^{ - } \)  = 1:1 and 1:2, respectively). In La(CH₃CO₂)₃ solutions in H₂O and D₂O strong acetato complexes are formed and the bands of the bound acetate were characterized and compared with the ones of the fully hydrated acetate modes. A dilution series down to 0.0037 mol·L^?1 in La(CH₃CO₂)₃(aq) and to 0.0150 mol·L^?1 in La(CH₃CO₂)₃(D₂O) showed that two acetate complexes are formed in these solutions. Again, it was shown that in these solutions the bound acetates on La³⁺ exist as bidentate ligands. DFT frequencies of the acetate on clusters {La(OH₂)₇O₂CCH₃)}²⁺ and {La(OH₂)₅(O₂CCH₃)₂}⁺ compared well with the measured values. By determining the ligation number, \( \bar{n} \), it can be established that in dilute solutions, below 0.04 mol·L^?1, a complex with a 1:1 stoichiometry (La³⁺: \( {\text{CH}}_{3} {\text{CO}}_{2}^{ - } \)) exists in equilibrium with “free” acetate while in more concentrated solutions a 1:2 complex also forms. La³⁺(aq) hydrolysis is slight and very small equilibrium concentrations of CH₃COOH were detected (C–C stretch at 893 cm^?1). From quantitative Raman measurements, K ₁ was determined to be 160 ± 10 at 22 °C.     

Characterization of gold supported on Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–CuO–Mn<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts obtained by thermal decomposition of aerosols

The purpose of this work was to employ the differential thermal analysis (DTA) technique to compare variations in the collapse energy of the zeolite Y crystalline structure in a fresh catalyst and in the same catalyst impregnated with nickel and vanadium. A small exothermic signal in the DTA curve at 950–1150 °C indicated the collapse of the crystalline structure. The areas of the exothermic signals in the DTA curves of the two samples indicated a reduction in the curve of the metal impregnated catalyst. These results were compared with X-ray data, leading to the conclusion that metal impregnation affects the zeolite Y crystalline structure and that the DTA technique is a potentially useful tool for measuring the integrity of zeolite Y in catalysts.     

Thermal properties of Ga<Subscript>2</Subscript>O<Subscript>3</Subscript>–PbO–P<Subscript>2</Subscript>O<Subscript>5</Subscript> glass system

Thermal behavior of xGa₂O₃–(50 − x)PbO–50P₂O₅ (x = 0, 10, 20, and 30 mol.% Ga₂O₃) and xGa₂O₃–(70 − x)PbO–30P₂O₅ (x = 0, 10, 20, 30, and 40 mol.% Ga₂O₃) glassy materials were studied by thermo-mechanical analysis (TMA) and differential thermal analysis (DTA). Replacement of PbO for Ga₂O₃ is accompanied by increasing glass-transition temperature (263 ≤ T _g/°C ≤ 535), deformation temperature (363 ≤ T _d/°C ≤ 672), crystallization temperature (396 ≤ T _c/°C ≤ 640) and decreasing of coefficient of thermal expansion (5.1 ≤ CTE/ppm K⁻¹ ≤ 16.7). Values of Hruby parameter were determined (0.1 ≤ K _H ≤ 1.3). The thermal stability of prepared glasses increases with increasing of concentration of Ga₂O₃.     

Thermal analysis of the (Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>)<Subscript>1−x</Subscript>(Y<Subscript>2</Subscript>O<Subscript>3</Subscript>)<Subscript>x</Subscript> pigments

The synthesis of new compounds based on Bi₂O₃ is investigated because they can be used as new ecological inorganic pigments. Chemical compounds of the (Bi₂O₃)_1−x(Y₂O₃)_x type were synthesized. The host lattice of these pigments is Bi₂O₃ that is doped by Y³⁺ ions. The incorporation of doped ions provides the interesting colours and contributes to a growth of the thermal stability of these compounds. The simultaneous TG-DTA measurements were used for determination of the temperature region of the pigment formation and thermal stability of pigments. This paper also contains the results of the pigment characterization by X-ray powder diffraction and their colour properties.     

Atmospheric control of gel-oxide transformation in sol–gel derived Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-Y<Subscript>2</Subscript>O<Subscript>3</Subscript> fibers

Via sol–gel processing metal–organic fibers were produced and dried up to 140 °C. For these gel fibers the influence of a treatment in different atmospheres was investigated for the temperature range of 200–850 °C. The atmospheres were nitrogen, water vapor, evaporated nitric and hydrochloric acid and evaporated hydrogen peroxide. In the presence of moisture and especially with acidic moisture fibers were transformed almost completely to their oxide composition (82 mol% Al₂O₃·18 mol% Y₂O₃). In these inorganic amorphous structures considerable differences were observed on several structural levels. On the atomic scale, the coordination of Al ions was investigated by ²⁷Al MAS NMR and skeletal density by He-pycnometry. Porosity in the nm scale was characterized by N₂-sorption. As a macroscopic effect of different treatment atmospheres, the longitudinal shrinkage was observed. For fibers treated at 500 °C the relative shrinkage varied by 100% (comparing water vapor and nitrogen atmosphere). No simple correlation between the release of organic constituents, the formation of porosity and the shrinkage could be found. These aspects were controlled by the rigidity of the inorganic network against atomic reconstitution. The kind of atmosphere was found to be an effective parameter to control various aspects of the xerogel structure.     

Hydrocracking of vacuum gas oil in the presence of catalysts NiMo/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–amorphous aluminosilicates and NiW/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–amorphous aluminosilicates

Supported nickel–molybdenum and nickel–tungsten hydrocracking catalysts prepared using a support that consists of 70% Al₂O₃ and 30% amorphous aluminosilicate were characterized by nitrogen and mercury porosimetry, IR spectroscopy of adsorbed CO, and high-resolution electron microscopy. The catalytic tests in hydrocracking of vacuum gas oil containing 3.39% sulfur showed that the nature of the hydrogenating component (NiMo or NiW) only slightly influences the vacuum gas oil conversion and the diesel fraction yield, but noticeable influences the properties of the diesel fraction obtained. The catalyst NiMo/Al₂O₃–amorphous aluminosilicates, compared to NiW/Al₂O₃–amorphous aluminosilicates, ensures lower sulfur content in the diesel fraction obtained, whereas the catalyst NiW/Al₂O₃–amorphous aluminosilicates allows obtaining a diesel fraction with lower content of polyaromatic compounds.     

Formation of solid solutions of multiferroics in the Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–Nd<Subscript>2</Subscript>O<Subscript>3</Subscript>–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> system

The sequence of phases appearance during the formation of Bi_1–xNd_xFeO₃ solid solutions in powder oxides mixtures of bismuth, neodymium, and iron has been determined. It has been shown that the closeness of the reaction mixture composition to that of the individual compound (BiFeO₃ or NdFeO₃) is essential for the realization of the series of phase transformations yielding solid solutions of multiferroics Bi_1–xNd_xFeO₃ as the final product, due to the prevalence of various interphase contacts in the starting reaction zone.     

Sol–gel synthesis and characterization of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–TiO<Subscript>2</Subscript> nanocrystalline powder

Al₂O₃–TiO₂ nanocrystalline powders were synthesized by sol–gel process. Aluminum sec-butoxide and titanium isopropoxide chemicals were used as precursors and ethyl acetoacetate was used as chelating agent. Thermal and crystallization behaviors of the precursor powders were investigated by thermal gravimetric-differential thermal analysis, Fourier-transform infrared spectrum and X-ray diffraction. The average crystalline size of heat treated Al₂O₃–TiO₂ powders at 1,100 °C is ~100 nm.     

Crystal structure of Na<Subscript>3</Subscript>(NH<Subscript>4</Subscript>)<Subscript>2</Subscript>[Ir(SO<Subscript>3</Subscript>)<Subscript>2</Subscript>Cl<Subscript>4</Subscript>]·4H<Subscript>2</Subscript>O

The complex Na₃(NH₄)₂[Ir(SO₃)₂Cl₄]·4H₂O was examined with single crystal X-ray diffraction and IR spectroscopy. Crystal data: a = 7.3144(4) Å, b = 10.0698(5) Å, c = 12.3748(6) Å, β = 106.203(1)°, V = 875.26(8) ų, space group P2₁/c, Z = 2, d _calc = 2.547 g/cm³. In the complex anion two trans SO ₃ ^2? groups are coordinated to iridium through the S atom. The splitting of O-H bending vibrations of crystallization water molecules and N-H ones of the ammonium cation is considered in the context of different types of interactions with the closest neighbors in the structure.