Sol-gel Preparation of Rutile Type Solid Solution in TiO2-RuO2 System

The preparation of rutile type solid solutions in (TiO₂)_x -(RuO₂)_1−x system in the 0≤x ≤0.7 concentration range is described. The single phase solid solutions are formed by controlled nanocrystallization of amorphous gels prepared by the sol-gel method. The kinetics of this crystallization process has been analyzed. It was found that the crystallization does not correspond to the Johnson-Mehl-Avrami model and it can be described by the two-parameter Šesták-Berggren kinetic model. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermal Studies in Cuo−Cu2O−SnO2 System At Two Oxygen Pressures, As Observed by DTA/TG Experiments

This study reports experimental investigations by DTA/TG analysis of (1−x)SnO₂−xCuO compositions, up to 1773 K and at two oxygen partial pressures (i.e. air and argon). In air, DTA/TG results showed thermal effects due exclusively to CuO presence in the initial mixture. No binary compounds were formed. The reduction process of CuO to Cu₂O over 1273 K as well as the formation over 1373 K of the liquid phase, have been evidenced. In argon atmosphere, CuO to Cu₂O reduction reaction is shifted toward 1205 K, while the liquid phase appears in the studied mixtures over 1473 K. The formation of an eutectic composition between SnO₂−Cu₂O, melting at 1491 K, coordinates:0.932Cu₂O+0.068SnO₂, has been experimentally established in argon. This revised version was published online in August 2006 with corrections to the Cover Date.     

Influence of purity on the thermal stability of solid organic compounds

DSC method was used to study thermal stability of nitrocompounds. It was assumed the model to estimate stability of solid phase in which perfect solid phase is totally stable and amorphous-liquid domains connected with impurities decompose according to the kinetic model determined for the liquid phase above the melting point. The influence of sample purity on relative stability, which is k _l/k _s — ratio of decomposition rate constants in liquid and solid phase, at temperature 20 K below the melting point was predicted. The increase of liquid domains in solid phase causes decrease of k _l/k _s ratio (relative stability) at chosen temperature. This revised version was published online in July 2006 with corrections to the Cover Date.     

Investigation of s, p, d-element Niobates and Their Solid Solution Formation Processes by Thermal Analysis

The binary and ternary systems M'O(M'CO₃)-Nb₂O₅ and M'O(M'CO₃)-MO-Nb₂O₅, where M'=Ca,Sr and Ba and M=Cu, Ni, Cd, Zn and Pb, were investigated by means of thermal analysis in the temperature range 20–1500°C. The boundaries of stability of the solid solutions Sr_2−xMe_xNb₂O₇,Sr_2−xM_xNb₂O₇, Sr_4−xM_xNb₂O₉ and Sr_6−xM_xNb₂O₁₁ were determined by means of X-ray diffraction, and IR and Raman spectroscopy. The possibility of prognostication of the phase fields of stable solid solutions by calculation from the diagrams of the ‘comparative electronegativity of atoms vs. tolerance factor’ was demonstrated. The kinetic parameters of the interactions in theSrCO₃+MO+Nb₂O₅ powder mixtures were established. This revised version was published online in August 2006 with corrections to the Cover Date.     

Studies on Thermal Stability of Titanium Substituted Iron Molybdenum Spinel Oxide

The thermal stability of the solid solutions of Fe₂Mo_1–xTi_xO₄ for x=0.0 to 1.0 in air, had been investigated in the temperature range 303–1173 K using differential thermal analysis and thermogravimetry (DTA and TG). The products obtained by heating the sample in air, at different temperatures, have been characterized by X-ray diffraction and IR-studies. The results show that all the ferrite samples undergo surface oxidation during initial heating. On heating to 823 K, the samples undergo oxidation of the octahedral site cations only and forma cation deficient spinel phase. On further heating in air, the ferrites undergo complete oxidation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal Oxidation Kinetics of Ni100–xPx Powders

The oxidation of Ni_100–xP_x(7.3 at%<x<25.0 at%) powders in air in the temperature range 350–450°C was determined by kinetics and X-ray diffraction. The isothermal kinetics was modeled using theGinstling–Brounstein equations. The oxidation process was found to be thermally activated with activation energy 127.8 kJ mol^–1 for x=7.3 at% to 157.7 kJ mol^–1 for x=25.0 at%. It was found that the rate constants for x=7.3 at% were approximately 100 times lower than those for x=25.0 at%. This revised version was published online in July 2006 with corrections to the Cover Date.     

Liquid flow porous electrode: The effect of local variations in liquid-phase conductivity on its operation efficiency

For one-dimensional model of porous electrode (PE), an equation for the ideal ratio between the local conductivities of liquid phase κ_L(x) and solid phase κ_s(x), which provides uniform distributions of potential and current inside the PE, is obtained. It is shown that the principal possibilities of levering action of both phases are similar; however, the shapes of their ideal conductivity profiles are mirror-opposite. To gain a beneficial effect at the expense of conductivity of liquid phase, κ_L(x) should increase monotonically from the rear current lead to the frontal side of PE provided that the conductivities of phases are equal in the middle of PE. The effect of distortions of ideal κ_L(x) profile is analyzed. It is found that, with regard to the natural upper limit of solution conductivity, the best conditions for the levering action of ideal κ_L(x) profile should be expected in the porous matrices with low conductivity. It is shown that the formation of even few zones with opposite-shaped κ_L(x) profile inside PE (the solution conductivity decreases towards the frontal side of PE) leads to more nonuniform potential distribution and a decrease in the PE operation efficiency (especially at high total current density).     

Structural and calorimetric investigations on nonaqueous liquid crystals and gel phases in the binary system K-behenate/glycerol

Two mixtures of the binary system K-behenate/glycerol, x _KC22 = 0.30 and 0.50 (x = mole fraction), have been investigated as a function of temperature using small- and wide-angle X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The binary phase diagram based on texture observations using polarizing optical microscopy was confirmed. XRD and DSC measurements provided concordant results with respect to the range of the phase regions in the phase diagram. Only differences between the DSC curves for rising and falling temperatures were detected. The recorded XRD and DSC data of the liquid crystals and gel phases observed are also in agreement with previously reported investigations on K-soap/glycerol. The C ⇆ G and G ⇆ L_α phase transitions correlate with a sharp shift in the d value of the first small-angle reflection. The G phase is characterized by a split of the first small-angle reflections. Also, the position and shape of the wide-angle reflections change and the peak intensity is reduced. Received: 5 July 1999 Accepted in revised form: 27 July 1999     

New doped Li-M-Mn-O (M = Al, Fe, Ni) spinels as cathodes for rechargeable 3 V lithium batteries

The electrochemical behaviour of new doped Li-M-Mn-O (M = Al, Fe, Ni) spinel oxides in liquid electrolyte lithium cells was studied. The insertion electrode materials were obtained by heating stoichiometric amounts of thoroughly mixed LiOH and M _x Mn_{1− x} CO₃ (M = Fe, Ni; x = 0.08−0.15) or Al _x Mn_{1− x} (CO₃) (OH) _y , in the case of Al, at 380 °C in air for 20 h. The transition metal-doped samples, particularly those containing Ni or obtained at low temperatures, where the resulting spinel was cation-deficient and highly disordered, exhibited the best cycling performance in the potential window 3.3−2.3 V. Cell capacity was retained by 80% after 200 cycles. Capacity fading was observed on increasing the firing temperature, together with improved crystallinity and the disappearance of cation vacancies. This impaired electrochemical behaviour is ascribed to a Jahn-Teller effect, which induces an X-ray-detectable cubic-tetragonal phase transition upon lithium insertion. The phase transition was undetectable in the low-temperature samples. The influence of the Jahn-Teller distortion is thus seemingly lessened by a highly disordered structure. Received: 25 November 1997 / Accepted: 28 January 1998     

Synthesis and X-ray diffraction study of complex oxides of the Zn2 ? x(ZraSnb)1 ? xFe2xO4 composition

A multicomponent system of complex refractory oxides of the composition Zn_{2 − x} (Zr _a Sn _b )_{1 − x} Fe_2x O₄ (a + b = 1; a: b = 1: 5, 1: 4, 1: 3, 1: 2, 1: 1, 2: 1, 3: 1, 4: 1; x = 0−1.0; Δx = 0.05) was studied by X-ray diffraction. The samples were prepared from oxides of appropriate metals by low-temperature plasma synthesis (hydrogen-oxygen flame). Two phases with wide homogeneity ranges were identified: α phase crystallized in the crystal system of inverse cubic spinel and β phase with the structure of tetragonal spinel. The phase boundaries were found. Structural data are presented for about 100 solid solutions.     

Sorption kinetics for the removal of aldehydes from aqueous streams with extractant impregnated resins

The sorption kinetics for the removal aldehydes from aqueous solutions with Amberlite XAD-16 and MPP particles impregnated with Primene JM-T was investigated. A model, accounting for the simultaneous mass transfer and chemical reaction, is developed to describe the process. It is based on the analogy to the diffusion and reaction in a stagnant liquid sphere, but corrected for the porosity and particle properties influencing the diffusion. The developed model describes the kinetic behavior of the process in the low concentration region rather well. However, in the high concentration region, larger discrepancies are observed. Initially, the influence of the flow rate was investigated to eliminate the effect of the external mass transfer. The influence of the particle morphology was investigated for both physical and reactive sorption. Physical sorption experiments were used to determine the factor τ that takes the particle properties influencing the diffusion into account. It was shown that the diffusion is faster in XAD-16 than in MPP impregnated systems. Reaction rate constant k _x was determined by fitting the model to the experimental data. Sorption of benzaldehyde appears to be significantly slower (k _x ∼10⁻⁴ l/mol s) than the sorption of pentanal (k _x ∼10⁻³ l/mol s) due to the slower chemical reaction. The influence of the particle size was investigated for the sorption of pentanal with XAD-16. It was observed that the particle size does influence the diffusion term, but does not have an effect on the reaction rate. On the other hand, the extractant loading influences the reaction rate slightly in the low concentration region, whereas the initial concentration of the solute has more pronounced effect.     

Characterization of phase transition of Ba2-xSrxIn2O5 by thermal analysis and high temperature X-ray diffraction

The phase transitions of Ba_2-xSr_xIn₂O₅ were investigated with various thermal analyses and high-temperature X-ray diffraction. It was clarified that crystal structure of Ba_2-xSr_xIn₂O₅ with x=0.0~0.4 varies from brownmillerite through distorted perovskite to another distorted perovskite with increase of temperature. The phase transition from brownmillerite to distorted perovskite was revealed to be first order, whereas transition from distorted perovskite to another one was second order. The specimen with x≥0.5 showed only one first order phase transition from brownmillerite to distorted perovskite. The phase diagram of Ba_2-xSr_xIn₂O₅ was established and existence of tricritical point at ~1100°C with x=0.4~0.5 was suggested. This revised version was published online in August 2006 with corrections to the Cover Date.     

Anomalies in Heat Capacity Measurements of RuO2-TiO2 System

DSC was used for heat capacity measurements of pure RuO₂ in the temperature range from 300 to 1170 K of solid solutions corresponding to the compositions of (Ti_1−x Ru_x )O₂ (x ≤0.15 and x ≥0.85) and in the temperature range from 300 to 1550 K of pure TiO2. The analysis of experimental data obtained within ±2% of accuracy has shown that the characteristic temperatures representing the harmonic lattice vibrations do not strongly depend on the chemical composition x . It was demonstrated that non-harmonic heat capacity is strongly correlated to x. The existence of additional excess heat capacity was observed with the mixed oxide solid solution samples of low Ru content and explained by the defect formation model. This revised version was published online in August 2006 with corrections to the Cover Date.     

Heat capacity measurement and DSC study of hafnium hydrides

Heat capacities, electrical conductivities and phase transition temperature of hafnium hydrides, HfH_x (0.99≤x≤1.83), were studied using a direct heating pulse calorimeter and a differential scanning calorimeter from room temperature to above 500 K. The heat capacity of HfH_1.83 was larger than that of pure hafnium and showed no anomaly of heat capacity. In contrast, there were λ-type peaks for the heat capacity and DSC curves for HfH_x (1.1≤x≤1.6) near 385 and 356 K. The anomalies of heat capacity and electrical conductivity of HfH_x (1.1≤x≤1.6) were considered the result of phase transition and order-disorder phase transition for hydrogen in the hafnium hydride lattice for HfH_x (1.1≤x≤1.3).     

Synthesis and Properties of The Solid Solutions Formed in The Fe2V4O13–Cr2V4O13 System

DTA and XRD studies of the Fe₂V₄O₁₃–Cr₂V₄ O₁₃ system have shown that continuous solid solutions of a Fe_2–xCr_xV₄O₁₃ type, bearing a Fe₂ V₄ O₁₃ structure, are formed in the system. With the increasing degree of the Cr3+ ion incorporation into the Fe₂ V₄ O₁₃ structure, a contraction of the solid solution crystal lattice develops. Solid solutions of a Fe_2–x Cr_x V₄ O₁₃ type melt incongruently, their melting temperature increasing from 953 to 1003 K with increase in the degree of the Cr³⁺ ion incorporation. The solid product of melting Fe_2–x Cr_x V₄ O₁₃ solid solutions for 0.2<x >1.2 is the Fe_1–x Cr_x VO₄ solution phase, and for x ≤0.2 and x ≥1.4 – the Fe_1–x Cr_x VO₄ phase as well as FeVO₄ or CrVO₄ , respectively. This revised version was published online in July 2006 with corrections to the Cover Date.     

Review of the thermodynamic and transport properties of EuBr<Subscript>2</Subscript>–RbBr binary system

Differential Scanning Calorimetry was used to study phase equilibrium in EuBr₂–RbBr binary system. It was established that this system includes two eutectics and three stoichiometric compounds. First of them, Rb₂EuBr₄, decomposes peritectically at 778 K. Second one, RbEuBr₃, undergoes the solid–solid phase transition at 732 K and melts incongruently at 852 K. Third compound, RbEu₂Br₅, melts congruently at 888 K. The composition and temperature values of eutectics were determined as x(EuBr₂) = 0.316; T _eut = 776 K and x(EuBr₂) = 0.797; T _eut = 859 K. Mixing enthalpy was measured by direct calorimetry on the whole composition range. The minimum of the mixing enthalpy occurs around the composition x(EuBr₂) ≈ 0.4. The electrical conductivity of liquid mixtures was also investigated over the whole composition range and measured down to temperatures below solidification. The specific conductance (liquid phase) plotted against the mole fraction of EuBr₂ shows a broad minimum at x(EuBr₂) ~ 0.6. The activation energy for conductivity changes with temperature. Results obtained are discussed in terms of possible complex formation.     

Effect of Copper on Thermomechanical Characteristics of Amorphous AsSeyIz

The paper describes results of a study of glasses of the type Cu_x (AsSe_1.4 I_0.2 )_100–x for x =0, l, 5, 10, 15, 20 and 25 at% Cu, by the methods of thermomechanical analysis. Values of the thermal coefficients of linear expansion in solid and visco-plastic phase were determined and the dependence of this parameter on copper concentration was established. The experimental method used enabled the determination of characteristics glass transition temperature and the temperature of the beginning of deformation, and it was found that these parameters increase with increase in the copper content. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis and Properties of Solid Solutions in The FeVMoO7–CrVMoO7 System

X-ray phase analysis (XRD), differential thermal analysis (DTA) and IR spectroscopy have shown that continuous substitution solid solutionsin are formed in the FeVMoO₇–CrVMoO₇ system. With increasing the degree of Cr³⁺ ion incorporation into the FeVMoO₇ structure, a crystal lattice contraction of the Fe_1–xCrxVMoO₇ solid solution arise. Elevation of temperature of its incongruent melting and gradual shifting of the corresponding IR absorption bands towards higher wavenumbers have been noticed, as well. The solid product of incongruent melting for x≤0.5 is the Fe_4–yCr_yV₂ Mo₃ O₂₀ solid solutions phase, whereas for x>0.5 Fe_2–zCr_z(MoO₄)₃ and Fe_2–u Cr_u O₃ solid solutions. This revised version was published online in July 2006 with corrections to the Cover Date.     

Stability of the anatase phase in nanodimensional titanium dioxide doped with europium(III), samarium(III), and iron(III)

lid solutions Ti_1−x M _x O_2−x/2 in the anatase and rutile forms were obtained from the precursors Ti_1−x M _x (OCH₂CH₂O)_2−x/2 at T = 450–900 °C. The temperature and concentration dependence of the phase transformation of anatase to rutile in Ti_1−x M _x O_2−x/2 was investigated by Raman spectroscopy. It was shown that the anatase phase is stabilized most effectively by the Eu³⁺ dopant.     

Electrophysical properties of materials based on BaGdCo2O5 + δ

The phase composition, linear thermal expansion coefficient, electroconductivity (in the temperature interval 600–900°C and partial pressures of oxygen 10⁻⁵–0.21 atm) of solid-oxide materials based on gadolinium-barium cobaltite doped with 3d-elements BaGdCo_{2 − x} Me _x O_{5 + δ}, Me = Cu, Fe; x = 0.0, 0.2, …, 2.0 were investigated. The homogeneity regions of samples were established by means of X-ray phase analysis. It was shown that the linear thermal expansion coefficient of cobaltite decreases with an increase in the copper or iron concentration. It was established that the electroconductivity of BaGdCo_{2 − x} Me _x O_{5 + δ} decreases with an increase in x. We concluded that upon a decrease in p(O₂), the electroconductivity of samples first decreases and then reaches a horizontal plateau.