Effect of gamma-irradiation on surface and catalytic properties of CuO−ZnO/Al2O3 system

A copper, zinc and aluminium mixed oxides sample having the nominal composition 0.25 CuO/0.03 ZnO/Al₂O₃ was prepared by impregnating Al(OH)₃ with copper and zinc nitrate solutions, drying at 100 °C then heating in air at 600 °C. The obtained solid was exposed to different doses of -rays (20–160 Mrad). The surface characteristics namelyS _BETV_P andr of different treated adsorbents were determined from N₂ adsorption isothems measured at –196 °C. The catalytic activity of various irradiated solids was determined by following up the kinetics of CO-oxidation by O₂ at 150–200 °C. The results showed that the doses up to 80 Mrad resulted in no significant change in theS _BET but increased slightly theV _P (20%) of the treated adsorbents. The irradiation at 160 Mrad caused an increase of 20% in theS _BET of the irradiated solid sample. The catalytic activity increased progressively by increasing the dose, a dose of 160 Mrad brought about an increase of 140% in the catalyst's activity. The apparent activation energy of the catalytic reaction decreased monotonically by increasing the absorbed dose of -rays which was attributed to a parallel induced decrease in the value of pre-exponential term of the Arrhenius equation. The observed increase in the catalytic activity due to -irradiation has been interpreted as a result of increasing the concentration of catalytically-active sites contributing in chemisorption and catalysis of CO-oxidation via a possible fragmentation of CuO crystallites.     

Thermodynamic stability of solid phases in the system Cu–O–Al2O3 by means of the EMF and DSC-TGA techniques

Journal of Solid State Electrochemistry - Thermodynamic properties of solid phases in the Cu–O–Al2O3 system were measured by means of the EMF method with oxygen concentration galvanic...     

Behavior and bioactive properties of aqueous L-cysteine–AgNO3 solution at different pH

Polypeptide-like supramolecular aggregates are formed in aqueous cysteine–AgNO₃ solution. At low pH, their positively charged shell consists of several layers of cysteine–Ag⁺ complexes held by hydrogen bonds; with an increase in pH, the particles aggregate at isoelectric point; while at higher pH, the shell acquires negative charge and starts being destroyed. The pH control has been demonstrated for cytotoxic effect of the solution against MCF-7 breast cancer cells     

Structure and properties of glasses in the system Li2O–SnO–B2O3

Glasses in the system Li₂O–SnO–B₂O₃ system were prepared by a melt-quenching method. Thermal and viscous properties and local structure of these glasses were investigated. The SnO–B₂O₃ glasses exhibited relatively low glass-transition temperatures (T_g) around 350 °C and excellent thermal stability against crystallization. Viscosity measurements in the vicinity of T_g indicated that the glasses were considerably fragile compared to alkali borate glasses. Fraction of four-coordinated boron was maximized at the composition with 50 mol% SnO and that of nonbridging oxygen, which is not purely ionic in alkali borate systems but partially covalent, augmented with an increase in the SnO content. Correlation between glass properties and structure was discussed in the SnO–B₂O₃ binary system.     

Mechanochemical synthesis and thermal stability of phases in the Y2O3–Yb2O3 system

Substitutional, continuous solid solution of the general formula Y_2–xYb_xO₃ was obtained from the mixture of Y₂O₃ and Yb₂O₃ oxides, for the first time by the mechanochemical method in a high-energy ball milling. The monophasic samples of nanocrystalline solid solution for x?>?0.00 and x?<?2.00 were examined by the methods: XRD, DTA, SEM, IR and UV–Vis–DR. As follows from the results, the solid solution crystallizes in cubic system and is isostructural with Y₂O₃ and Yb₂O₃. The solution is stable in the air atmosphere up to at least 900°C, and its decomposition temperature decreases with the increase in x, that is, with decreasing number of Yb³⁺ ions replacing Y³⁺ ions in the crystal lattice of Y₂O₃. The energy band gap estimated for the solid solution varies from?~?5.30 eV for x?=?0.50 to?~?4.90 eV for x?=?1.50, which means that it is an insulator.

     

Thermodynamic properties of the system NH4NO3–KNO3–H2O at 298.15 K

The water activity and osmotic coefficients of the system {y NH₄NO₃+(1-y) KNO₃}(aq) has been measured at total molalities from 0.2 mol kg⁻¹ to about saturation of one of the solutes for different ionic-strength fractions y of NH₄NO₃ with y=0.2, 0.5 and 0.8 at the temperature 298.15 K using the hygrometric method. The obtained data allow the deduction of the thermodynamic parameters. From these measurements, new Pitzer ionic mixing parameters are determined and used to predict the solute activity coefficients in the mixture. The results obtained are used to calculate the excess Gibbs energy at total molalities for different ionic-strength fractions of NH₄NO₃.     

Dilational properties of gemini surfactant/polymer systems at the air–water surface

The surface properties of mixed system containing gemini anionic surfactant 1,2,3,4-butanetetracarboxylic sodium, 2,3-didodecyl ester and partly hydrolyzed polyacrylamide were investigated by surface tension measurements and oscillating bubble methods. The influences of surfactant concentration, dilational frequency, temperature, pH, as well as salts on dilational modulus were explored. Meanwhile, the interfacial tension relaxation method was employed to obtain the characteristic time of surface relaxation process. The polymers play important roles in changing the interfacial properties especially at lower surfactant concentration. The possible mechanism of the polymer in changing the interfacial properties is proposed. Both the hydrophobic and electrostatic interaction among the surfactants and polymers dominate the surface properties of mixed system. These dynamic properties are of fundamental interest in understanding the structure of adsorption layers, dynamics of surfactant molecules, and their interaction with polymers at the surface.     

Synthesis and selected properties of a new solid solution in the Zn2FeV3O11–Mg2FeV3O11 system

The binary Zn₂FeV₃O₁₁?CMg₂FeV₃O₁₁ system has been studied by XRD, DTA, IR, and SEM methods. A new continuous substitution solid solution with the formula Zn_2?x Mg _x FeV₃O₁₁ has been obtained by high-temperature synthesis. The DTA investigations were used to choose the heating temperatures as well as for determination of thermal stability of the new triclinic phase. The influence of the degree of Mg²⁺ ion incorporation on the unit cell volume as well as on the position of the IR absorption bands of the solid solution have been determined. The morphology of crystals of the new phase is presented.     

Study of the system Pr2O3-SeO2-H2O at 100°C and the properties of the compounds obtained

The solubility of the system Pr₂O₃-SeO₂-H₂O at 100°C was studied. The fields of crystallization of Pr₂(SeO₃)₃·H₂O, PrH(SeO₃)₂, Pr(HSeO₃)₃ were established. The compounds obtained were identified by means of chemical, X-ray and thermal analysis. The thermal decomposition of Pr₂(SeO₃)₃·H₂O, PrH(SeO₃)₂, and Pr(HSeO₃)₃ was determined.This revised version was published online in November 2005 with corrections to the Cover Date.     

Influence of SrO content on microstructure and crystallization of glazes in the SiO2–Al2O3–CaO–MgO–K2O system

The effect of the SrO addition on the microstructure and structure of the glazes from the SiO₂–Al₂O₃–CaO–MgO–K₂O system was investigated in this study. The results were obtained by testing the ability of the frits crystallization, the stability of the crystallizing phases during the single-step fast-firing cycle depending on their chemical composition and the effect of addition of strontium oxide. Differential scanning calorimetry (DSC) curves showed that all glazes crystallized, and diopside and anorthite were mainly identified as dominant phases in the obtained glazes, while the size and amount of each depended on the amount of SrO introduced. The thermal characteristic of the frits was carried out using DSC, and crystalline phases were determined by X-ray diffractometry. The glaze microstructure was investigated by scanning electron microscopy and transmission electron microscopy. Additional information on the microstructure of frits was derived from spectroscopic studies in the mid-infrared range.

     

Effects of nano-YAG (Y3Al5O12) crystallization on the structure and photoluminescence properties of Nd3+-doped K2O–SiO2–Y2O3–Al2O3 glasses

Nd³⁺-doped precursor glass in the K₂O–SiO₂–Y₂O₃–Al₂O₃ (KSYA) system was prepared by the melt-quench technique. The transparent Y₃Al₅O₁₂ (YAG) glass–ceramics were derived from this glass by a controlled crystallization process at 750 °C for 5–100 h. The formation of YAG crystal phase, size and morphology with progress of heat-treatment was examined by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and Fourier transformed infrared reflectance spectroscopy (FT-IRRS). The crystallite sizes obtained from XRD are found to increase with heat-treatment time and vary in the range 25–40 nm. The measured photoluminescence spectra have exhibited emission transitions of ⁴F_3/2 → ⁴I_J (J = 9/2, 11/2 and 13/2) from Nd³⁺ ions upon excitation at 829 nm. It is observed that the photoluminescence intensity and excited state lifetime of Nd³⁺ ions decrease with increase in heat-treatment time. The present study indicates that the incorporation of Nd³⁺ ions into YAG crystal lattice enhance the fluorescence performance of the glass–ceramic nanocomposites.     

Study of ceramic pigments based on cobalt doped Y2O3–Al2O3 system

Ceramic pigments based on Y₂O₃–Al₂O₃ system doped by cobalt as a colourant agent were synthesized by solid-state reaction at temperatures up to 1,400 °C. The reactivity of initial mixtures of components was improved by the mineralizer LiF and the mechanical activation in a planetary ball mill. The temperature region of the product formation was followed by the method of thermal analysis. The effect of the synthetic method on the phase composition of the products was studied by X-ray diffraction analysis. Studied pigment-application properties of the product include the measurement of optical properties in the visible region of light and particle size distribution. The simple solid-state reaction led to the formation of turquoise samples that contain mainly blue CoAl₂O₄ spinel and next to it also YAlO₃ perovskite and Y₃Al₅O₁₂ garnet phases. The mineralizer LiF promotes the formation of yttrium aluminium double oxides of sandy-yellow to grey–brown colour hue, although the samples also contain small amount of blue CoAl spinel phase. Intensive milling process did not results in CoAl spinel phase and the samples contain yttrium aluminium perovskite and cobalt oxide. Evaluation of Kubelka–Munk absorption as a function of the pigment concentration was found that hiding is complete by adding of 5 mass% of pigment to the ceramic glaze. Resulting colour hue of all pigment applications into ceramic glaze is blue. The size of particles lies in the range of 7–26 μm.     

Synthesis and some properties of a new compound in the Al–Sb–V–O system

A new compound in the Al?CSb?CV?CO system of the composition AlSbVO₆ was successfully synthesized by a solid-state reaction and characterized by powder XRD diffraction. The structural and thermal properties of AlSbVO₆ were investigated. The infra-red spectrum of the new phase is presented.     

Bulk and surface properties of ZnTe–ZnS system semiconductors

Physicochemical studies of a new ZnTe–ZnS semiconductor system are conducted. It is found that at certain ratios of binary components, substitutional solid solutions with a cubic sphalerite structure are formed in this system. Interrelated laws governing changes in the bulk (crystal chemical, structural) and surface (acid–base) properties with varying system composition are identified. It is assumed they can be attributed to the nature of the active (acid–base) sites. The presented data, observed patterns, and an interpretation of them are used not only to confirm earlier proposed mechanisms of atomic–molecular interaction on diamond-like semiconductors, but to search for promising materials for use in highly sensitive selective sensors for environmental and medical purposes as well.     

Phase equilibria in the solid state and colour properties of the CuO–In2O3 system

Phase equilibria up to solidus line in CuO?CIn₂O₃ system have been investigated using XRD and DTA/TG methods. According to the results, only one compound of the formula Cu₂In₂O₅ formed in the system studied. Its thermal stability was determined in the air and argon proving that the compound did not melt but underwent decomposition. The decomposition of Cu₂In₂O₅ in the air atmosphere began at 1080?°C, while in argon at 835?°C. Additional studies were undertaken to determine the hitherto unknown colour properties of samples representing the CuO?CIn₂O₃ system in the equilibrium state.     

Thermodynamic properties of the system MgSO4–MnSO4–H2O at 298.15 K

The mixed aqueous electrolyte system magnesium and manganese sulfate has been studied with the hygrometric method at the temperature 298.15 K. The relative humidity of this system is measured at total molalities from 0.2 mol kg⁻¹ to about saturation of one of the solutes for different ionic-strength fractions y of MgSO₄ with y=0.2, 0.5 and 0.8. The obtained data allow the deduction of new thermodynamic parameters. The experimental results are compared with the predictions of ZSR rule. From these measurements, the new Pitzer mixing ionic parameters are determined and used to predict the solute activity coefficients in the mixture. The obtained results are used to calculate the excess Gibbs energy at total molalities for different ionic-strength fractions y of MgSO₄.     

Effect of Fe2O3 as an accelerator on the reaction mechanism of Al–TiO2 nanothermite system

Thermite reactions between aluminum and metal oxides could lead to the formation of intermetallic matrix composites used in high-temperature industrial applications. Thermite reaction in Al–TiO₂ system needs a considerable amount of energy to take place by mechanochemical or by the combustion synthesis (CS) method due to the low amount of reaction enthalpy in Al–TiO₂ system. In this study, Fe₂O₃ was chosen as a accelerator for this system, to generate a high amount of heat which could be released between Fe₂O₃ and Al, leading to a more convenient reaction between Al and TiO₂ in the CS process. The results of XRD, SEM, and DSC analyses indicated that both the mechanical activation of Al–TiO₂ system in a high-energy ball mill and the Fe₂O₃ addition led to considerable effects of reduction in the reaction temperature and increase in the reaction intensity in Al–TiO₂ nanothermite system. Finally, it was shown that Fe₃Al intermetallic compounds as well as γ-AlTi and alumina phases in the final products were formed after the CS of the milled powders.