Kinetic and thermal studies of removal of CrO 4 2− ions by ettringite

Ettringite was prepared in the presence of various dosages of CrO ₄ ^2? ions at three different temperatures. X-ray diffraction (XRD) and differential scanning calorimetery (DSC) results showed shift in the peaks characterized to ettringite as the result of formation of Cr-substituted ettringite. Substitution of SO ₄ ^2? by CrO ₄ ^2? ions in ettringite crystal resulted in delay in the rate of its formation, as well as reduction in the crystal diameters. However, the crystal diameters and rate of formation of both ettringite and Cr-substituted ettringite were increased by increasing temperature of preparation, and this was confirmed by scanning electron microscope (SEM) micrographs. The thermodynamic parameters: the enthalpy, entropy, and Gibbs free energy changes for substitution process were studied. It is concluded that the removal of chromate ions by ettringite is an endothermic spontaneous process. The positive value of ΔS° suggests increasing in randomness during the removal process.     

Ferrimagnetic spinels in hydrothermal and thermal treatment of MnxFe2−2x(OH)6−4x

Products of hydrothermal treatment of the initial amorphous system Mn_xFe_2–2x(OH)_6–4x for 0x1 in 0.1x intervals, and products of their further thermal treatment, were examined by chemical analysis, X-ray, IR, and DTA techniques supported by magnetic measurements. After hydrothermal growth for lowx, hematite and goethite phases occurred. Although the goethite phase was still identifiable atx=0.6, formation of a solid solution with the isostructural groutite was not found. The ferrimagnetic spinel phase, which resists heating up to 400C, was present at 0.5x0.9. At higher temperatures, it transformed into the rhombohedral hematite type phase or into the cubic bixbyite phase. AtT900C, a ferrimagnetic spinel structure reappeared up tox=0.8. For x=0.9, the low- and high-temperature forms of the hausmannite phase occurred, forx= 1 passing from one form into another through Mn₅O₈ and partritgeite.For a primary mixture Mn_0.5Fe(OH)₄, corresponding to the manganese ferrite structure, the lattice parameter of which passes from 8.43 å through 8.33 å to 8.50 å, the probable crystallochemical formula was suggested.We are grateful to KBN (The State Committee for Scientific Research, Poland) for grant No. 3 T09A 064 08, which contributed substantially to the materialization of this project.     

Structural Features and Electrical Properties of Chlorine-Substituted Proton Conductors Ba4In2+2xZr2−2xO11−x

Russian Journal of General Chemistry - Chlorine-substituted perovskite Ba3.95In2Zr2O10.9Cl0.1 was synthesized for the first time, and its single-phase nature was confirmed by X-ray diffraction...     

Synthesis and characterization of the ZnxCd1−xIn2S4 pseudoternary solid solution

We have synthesized several compounds of the Zn_xCd_1−xIn₂S₄ family by solid phase reactions and chemical transport reactions using iodine. The reaction products have been characterized as to composition, structure, and lattice dynamics. Here we discuss and compare the different results obtained by the two synthesis methods.     

Hydrothermal processing and characterization of Ce1−xPbxO2−δ solid solutions

Nanocrystals of Ce_1?xPb_xO_2?δ (x = 0.00, 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, and 0.35) were prepared by a hydrothermal reaction route. During the formation reaction, buffer solutions were explored as an effective additive to retain the initial molar ratio. With increasing the Pb²⁺ content, the average crystallite size was slightly retarded. Morphologies observed by transmission electron microscope indicated that the particles were spherical-like and highly uniformed. Pb²⁺ ions are homogenously distributed in the solid solutions. Analyses using X-ray diffraction, Raman and UV spectroscopies showed that the solid solubility limit of Pb²⁺ in CeO₂ was about x = 0.20. For x < 0.20, with increasing the Pb²⁺ content, the bulk conductivity increased, and the oxygen storage capacity was enhanced as followed by a decrease in reduction temperature.     

Electrocrystallization of PrO2 and TbO2−x from alkali hydroxide melts and characterization of the fluorite-related TbO2−x

Single crystals of PrO₂ and of the oxygen deficient fluorite related phase TbO_2−x have been obtained by anodic electrocrystallization from alkaline hydroxide melts containing PrCl₃ and TbCl₃, respectively. Magnetic measurements, X-ray diffraction data and TEM investigations confirm the identity of the products. PrO₂ crystallizes in a fluorite type of structure with a=5.3945(3) Å and shows paramagnetic behaviour with a magnetic moment as expected for Pr⁴⁺ (μ_eff=2.49μ_B, Θ=−109 K, T_N=10 K). According to precession photographs and an examination with an area sensitive X-ray detector, TbO_2−x exhibits a superstructure of fluorite with a pseudocubic subcell with a_f=5.2810(1) Å. This lattice constant is intermediate between those of TbO₂ and Tb₂O₃ (C-type), the same is true for its paramagnetic behaviour (μ_eff=8.58μ_B, Θ=−22 K, T_N=5 K). The supercell was found to be hexagonal with a=25.836(1) Å and c=36.672(2) Å, the symmetry of the intensity distribution being monoclinic. Electron diffraction revealed a cubic cell with a=10.6 Å, space group Ia-3, indicating reduction of the material in the electron beam.     

Structural characterization,thermal investigation,and liquid crystalline behavior of 4-[(4-chlorobenzyl)oxy]-3,4′-dichloroazobenzene

Using the Williamson method, a new dye 4-[(4-chlorobenzyl)oxy]-3,4′-dichloroazobenzene (CODA) with liquid crystalline properties was synthesized. The structure and the thermal behavior of CODA were investigated by means of nuclear magnetic resonance, X-ray diffraction, differential scanning calorimetry, and light polarized optical microscopy techniques. The thermophysical processes were monitored by heating–cooling cycles, but the formation of liquid crystal phases were exhibited only for small values of the cooling rates. For the first heating–cooling cycle, the melting and the solidification processes, thus the characteristic temperatures, are shifted to higher values when compared to the following cycles.     

Synthesis,characterization and photocatalytic properties of Mg1−xZnxAl2O4 spinel nanoparticles

Mg_1−xZn_xAl₂O₄ spinel nanoparticles with x = 0, 0.05, 0.10, 0.15 and 0.20 were prepared via the chemical coprecipitation method. The obtained samples were characterised by thermal gravimetric and differential scanning calorimetry, X-ray diffraction, Fourier transform infrared spectroscopy, UV–Vis diffuse reflection spectrum, transmission electron microscopy and ²⁷Al MAS-NMR spectroscopy. Mg_1−xZn_xAl₂O₄ spinel powders with the mean crystallite size of around 11 nm–14 nm were obtained. The crystallinity of the MgAl₂O₄ samples increases with the increase in the calcination temperature. At the same calcination temperature, higher amount of Zn²⁺ substitution leads to the higher level of crystallinity, but has no apparent influence on the mean crystallite size of the samples. The photocatalytic activity of the obtained Mg_1−xZn_xAl₂O₄ spinel nanoparticles was evaluated by monitoring the degradation of methylene blue under UV light. The degradation rates of methylene blue using the MgAl₂O₄ nanoparticles prepared at the calcination temperatures of 700 °C and 800 °C are much higher than those prepared at 900 °C and 1000 °C. The photocatalytic activities of the spinel powders with lower level of Zn²⁺ substitution such as Mg_0.95Zn_0.05Al₂O₄ are inferior to that of MgAl₂O₄. Results of ²⁷Al MAS-NMR spectroscopy analysis and the first principle total density of state calculations reveal that this is probably due to the substitutions of Zn²⁺ decreasing the degree of Al³⁺ ions inversion over the sites of tetrahedral and octahedral coordination. With the increase in the amounts of Zn²⁺ substitution, the effects of Zn²⁺ additions on the photocatalytic activities become gradually predominant, leading to the increases in the degradation rates. The methylene blue degraded by 99% within 4 h using the Mg_0.8Zn_0.2Al₂O₄ spinel powders.     

Synthesis, characterization, infrared studies, and thermal analysis of Mn0.6Zn0.4Fe2(C4H2O4)3·6N2H4 and its decomposition product Mn0.6Zn0.4Fe2O4

Manganese zinc ferrous fumarato–hydrazinate precursor, Mn_0.6Zn_0.4Fe₂(C₄H₂O₄)₃·6N₂H₄ was synthesized for the first time and characterized by chemical analysis, infrared spectral studies, and thermal analysis. Infrared studies show band at 977 cm^?1 indicating bidentate bridging nature of the hydrazine in the complex. Thermogravimetric (TG) studies show two steps dehydrazination followed by two steps total decarboxylation. The precursor on touching with burning splinter undergoes self propagating autocatalytic decomposition yielding ultrafine Mn_0.6Zn_0.4Fe₂O₄. XRD studies confirms single phase formation as well as nanosize nature of “as prepared” Mn_0.6Zn_0.4Fe₂O₄. The saturation magnetization of the “as prepared” Mn_0.6Zn_0.4Fe₂O₄ was found to be 31.46 emu gm^?1, which is lower than the reported, confirms the ultrafine nature of the oxide.     

Synthesis and electrochemical characterization of LiMn2−xAlxO4 powders prepared by mechanical alloying and rotary heating

LiMn_2−xAl_xO₄ (0.0⩽x⩽0.10) intercalation powders have been synthesized by mechanical alloying followed by rotary heating. The precursor of LiMn_2−xAl_xO₄ has been prepared using LiOH · H₂O, MnO₂, and Al₂O₃ by mechanical alloying, which ensured a high level of homogeneity in the chemical composition of the precursor and resulted in a reduction in the synthesis temperature and heating time. Highly crystallized LiMn_2−xAl_xO₄ powders were obtained by subsequent rotary heating of the precursor at 600 °C for 3 h. Rotary heating enhanced the experimental control in particle size distribution of the final products. The synthesized LiMn_2−xAl_xO₄ powder has a narrow particle size distribution, high discharge capacities and good cycleability. Compared with the conventional solid-state reaction process, the present method of mechanical alloying combined with rotary heating should be a suitable technique of decreasing synthesis temperature and shortening heating time, and enhancing the uniformity of particle size of the product.     

Structural characterization and ionic conductivity of Co2+-stabilized β″-alumina

Single crystals of Co²⁺-stabilized β″-alumina were synthesized by a flux growth technique using Bi₂O₃ as the flux and subsequent X-ray crystallographic studies showed that the Co²⁺ ions substitute only at the Al(2) sites. Optical absorption spectroscopic measurement also supports the concept that the dopant ions are in distorted tetrahedral environment. Co²⁺-doped β-alumina crystals were made by a skull melting technique. Chemical analysis of these two materials indicated that the Co²⁺ ion concentration may be important in the formation of one phase over the other. The temperature-dependent ionic conductivity of Co²⁺-stabilized β″-alumina, Co²⁺-doped β-alumina, and undoped β-alumina has been measured and compared between 25 and 450°C. The detailed conductivity analysis was made by a phase-synchronous detection system in the frequency range 100 Hz-10 MHz. The conductivity is highest in the stabilized β″-alumina and lowest in the undoped β-alumina. For Co²⁺-doped β-alumina, a slight bend in the conductivity at around 200°C is noted. The analysis of the conductivity and the effect of the dopant Co²⁺ ions on the resulting conductivity is discussed.     

Structural characterization of a sodium perchlorate−acridino-18-crown-6 ether complex

This paper describes the X-ray crystal structure of a complex of acridino-18-crown-6 ether (S,S)-2 and sodium perchlorate. The structure shows a homodimer in the crystal and suggests the potential for π–π bonded interactions between the monomers. The average distance of the two tricyclic units (3.49 ± 0.1 Å) may indicate a considerably strong π–π interaction. Fluorescence titration was performed in order to determine the stoichiometry and stability constant (K _s) of the sodium ion-(S,S)-2 complex. Based on the global fitting of the fluorescence spectra, we suggest the formation of a complex with 1:1 ligand to metal ion ratio, and the logK value determined by nonlinear regression analysis was 5.23.     

Concentration determination of I2 and I− formed by thermal and radiolytic decomposition of NaIO3

Journal of Radioanalytical and Nuclear Chemistry - As a part of the evaluation of radioactive iodine behavior under the severe accident condition of nuclear power plant, we measured the...     

Excitation and luminescence spectra of UO2F2−4

The luminescence and excitation spectra of [(CH₃)₄]₂UO₂F₄, M₃UO₂F₅ (M = K and Rb) and Cs₂SnCl₆:UO₂Cl²⁻₄ have been recorded at temperatures down to 10 K. The excitation spectrum of [(CH₃)₄]₂UO₂F₄ is unique because the electronic origin is located at the lowest energy reported for any uranyl compound. The analysis of the excitation spectrum is consistent with a D_4h, but not a D_5h coordinated uranyl chromophore. A detailed interpretation of the vibronic structure of the spectrum enables the lower excited states of the uranyl ion to be located, and the symmetries of these are consistent with the model of Denning. A comparison with the excitation spectra of salts of the UO₂F³⁻₅ anion is made.     

Synthesis and physical and chemical characterization of Ca10−xAgx(PO4)6(OH)2−xx apatites

The synthesis of calcium-silver hydroxyapatites of composition Ca_10−xAg_x(PO₄)₆(OH)_2−xx is discussed, together with their physical and chemical properties. Samples prepared both by dry process and by double decomposition were characterized using a variety of analytical techniques (chemical analysis, X-ray diffraction, infrared spectroscopy). The lattice parameters a and c increase linearly with the amount of silver added. The increase is attributed to the preferential substitution of the silver ion in site me (I) of these apatites.     

Structural characterization and physicochemical properties of quercetin–Pb complex

Flavonoids are a large group of ubiquitous molecules synthesized by plants. These molecules possess antioxidant activities which prevent free radical damage to biological molecules and can also be metal chelators. This article describes the synthesis of a Pb(II)–quercetin complex and characterization by UV–visible, infrared, ¹H nuclear magnetic resonance spectroscopy, thermogravimetric analysis, and differential thermal analysis. The formation of quercetin and Pb(II) complex ratio 1?:?1 was confirmed by UV–visible spectroscopy. The composition of the complex does not change with pH. Antimicrobial activities were evaluated by using Gram-positive and Gram-negative bacteria. The antioxidant properties of quercetin and the complex was evaluated by using 2,2′-diphenyl-1-picrylhydrazyl radical scavenging method. The quercetin–Pb complex was less effective than quercetin in antimicrobial and antioxidant activity.