Electrochemical investigation of the P2–NaxCoO2 phase diagram

Sodium layered oxides NaxCoO2 form one of the most fascinating low-dimensional and strongly correlated systems; in particular P2–NaxCoO2 exhibits various single-phase domains with different Na+/vacancy patterns depending on the sodium concentration. Here we used sodium batteries to clearly depict the P2–NaxCoO2 phase diagram for x≥0.50. By coupling the electrochemical process with an in situ X-ray diffraction experiment, we identified the succession of single-phase or two-phase domains appearing on sodium intercalation with a rather good accuracy compared with previous studies. We reported new single-phase domains and we underlined the thermal instability of some ordered phases from an electrochemical study at various temperatures. As each phase is characterized by the position of its Fermi level versus the Na+/Na couple, we showed that the synthesis of each material, even in large amounts, can be carried out electrochemically. The physical properties of the as-prepared Na1/2CoO2 and Na2/3CoO2 ordered phases were characterized and compared. Electrochemical processes are confirmed to be an accurate route to precisely investigate in a continuous way such a complex system and provide a new way to synthesize materials with a very narrow existence range.     

Influence of the microstructure evolution of ZrO2 fiber on the fracture toughness of ZrB2–SiC nanocomposite ceramics

ZrB₂–SiC nanocomposite ceramics toughened by ZrO₂ fiber were fabricated by spark plasma sintering (SPS) at 1700 °C. The content of ZrO₂ fiber incorporated into the ZrB₂–SiC nanocomposites ranged from 5 mass% to 20 mass%. The content, microstructure, and phase transformation of ZrO₂ fiber exhibited remarkable effects on the fracture toughness of the ZrO_2(f)/ZrB₂–SiC composites. Fracture toughness of the composites greatly improved to a maximum value of 6.56 MPa m^1/2 ± 0.3 MPa m^1/2 by the addition of 15 mass% of ZrO₂ fiber. The microstructure of the ZrO₂ fiber exhibited certain alterations after the SPS process, which enhanced crack deflection and crack bridging and affected fracture toughness. Some microcracks were induced by the phase transformation from t-ZrO₂ to m-ZrO₂, which was also an important reason behind the improvement in toughness.     

Effect of cyclic heat treatment parameters on the grain refinement of Ti–48Al–2Cr–2Nb alloy

This work presents the influence of individual parameters of a cyclic heat treatment, i.e. upper cycle temperature, heating and cooling rates between room temperature and an upper temperature and number of cycles, on the grain refinement of a Ti–48Al–2Cr–2Nb alloy. The grain size as determined by the value of the average plane section diameter and indices describing its distribution (standard deviation) is sufficient to define grain refinement when the refinement obtained as a result of the treatment concerns the whole section of a sample. In the event when the refinement process only takes place partially or locally it becomes necessary to present distributions of the grain plane section area as a function of the frequency of occurrence and area fraction. The paper presents a possible mechanism of grain refinement of Ti–48Al–2Cr–2Nb alloy. The use of cyclic heat treatment provides an increase in the mechanical parameters of the alloy.     

Effect of atmosphere on the electrical properties of TiO2–SnO2 varistor systems

This work illustrates the advancement of research on TiO₂-based electroceramics. In this work will be presented that the addition of different dopants, as well as thermal treatments at oxidizing and inert atmosphere, influences of the densification, the mean grain size and the electrical properties of the TiO₂-based varistor ceramics. Dopants like Ta₂O₅, Nb₂O₅, and Cr₂O₃ have an especial role in the barrier formation at the grain boundary in the TiO₂ varistors, increasing the nonlinear coefficient and decreasing the breakdown electric field. The influence of Cr_Ti is to increase the O and O₂ adsorption at the grain boundary interface and to promote a decrease in the conductivity by donating electrons to O₂ adsorbed at the grain boundary. In this paper, TiO₂ and (Sn,Ti)O₂-based studies of polycrystalline ceramics, which show a non-linear I–V electrical response typical of low voltage varistor systems are also presented. All these systems are potentially promising for varistor applications.     

Prediction of the temperature dependence of fracture toughness of 12Cr–2Ni–Mo refractory steel

We study the influence of temperature and the size of the specimens on the characteristics of static crack resistance of 12Cr–2Ni–Mo refractory steel. It is shown that, in the temperature range 20–450°C, the increase in the thickness of specimens leads to an insignificant increase in fracture toughness obtained along a 5% secant line according to the standards of evaluation of the characteristics of crack resistance. The evaluation of the characteristics of crack resistance of 12Cr–2Ni–Mo steel with regard for the scale effect according to an earlier developed numerical-experimental model reveals the existence of satisfactory agreement with the experimental data in the entire investigated temperature range. Translated from Problemy Prochnosti, No. 4, pp. 78–88, July–August, 2009.     

Synthesis of W–Zr–Ti Alloy via Combustion in the WO3–ZrO2–TiO2–Mg System

Inorganic Materials - We have studied the self-propagating high-temperature synthesis (SHS) process due to the combustion of a WO3 + ZrO2 + TiO2 + Mg multicomponent mixture. The ratio of the oxide...     

The influence of mechanochemical treatment of the Bi2O3–ZrO2 system on the structural and dielectric properties of the sintered ceramics

A powder mixture of -Bi₂O₃ and ZrO₂, both monoclinic, in the molar ratio 2 : 3, was mechanochemically treated in a planetary ball mill in an air atmosphere for up to 20 h, using steel vial and hardened-steel balls as the milling medium. Mechanochemical reaction leads to the gradual formation of an amorphous phase. After 5 h of milling the starting -Bi₂O₃ and ZrO₂ were transformed fully into a non-crystalline phase. After milling for various times the powders were compacted by pressing and isothermal sintering. The pressed and sintered densities depended on the milling time. Depending on the duration of the mechanochemical treatment and sintering temperature, the phases: -Bi₁₂(Zr _x Fe_1–x )O₂₀; Bi(Zr _x Fe_1–x )O₃ and Bi₂(Zr _x Fe_1–x )₄O₉ were obtained by reactive sintering, whereby the Fe originates from vial and ball debris. The dielectric permittivity of the sintered samples significantly depends on the milling time. Samples milled for 10 and 15 h and subsequently sintered at 800 °C for 24 h exhibit a hysteresis dependence of the dielectric shift (in altering electric fields higher than 10 kV/cm at room temperature), confirming that the synthesized materials possess ferroelectric properties.     

Ti K-edge XANES study of the local environment of titanium in bioresorbable TiO2–CaO–Na2O–P2O5 glasses

Ti K-edge XANES (X-ray absorption near edge structure) spectroscopy has been used to study the local coordination of titanium in biocompatible and bioresorbable TiO₂–CaO–Na₂O–P₂O₅ glasses. Both conventional melt-quenched glasses of composition (TiO₂) _x (CaO)_0.30(Na₂O)_(0.20−x)(P₂O₅)_0.50, where x = 0.01, 0.03 and 0.05, and sol–gel derived (TiO₂)_0.25(CaO)_0.25(P₂O₅)_0.50 glass have been studied. The results show that in all the materials studied, titanium is surrounded by an octahedron of oxygen atoms. Further analysis reveals that the TiO₆ site in the amorphous samples is not heavily distorted relative to that in rutile, anatase or CaSiTiO₅. The spectra from the (TiO₂)_0.25(CaO)_0.25(P₂O₅)_0.50 sol–gel samples reveal greater distortion in the TiO₆ site in the dried gel compared to the heat-treated sol–gel glass. The XANES spectra from melt-quenched glass samples soaked in distilled water for various times do not shown any evidence of degradation of the titanium site over periods of up to 14 days.     

BaWO4–BaCuO2–Y2Cu2O5–“1010” Section of the Y2O3–BaO–WO3–CuO System

The phase region of cubic perovskite-like solid solutions (a = 8.28–8.40 Å) in the Y₂O₃–BaO–WO₃–CuO system is outlined, and the phase compatibility diagram of the BaWO₄–BaCuO₂–Y₂Cu₂O₅–1010 (1010 = Y₂WO₆ + Y₂W₃O₁₂) is constructed.     

Computer Simulation of Noncrystalline Ionic–Covalent Oxides in the SiO2–CaO–FeO System

Molecular dynamics simulations were used to study self-diffusion in noncrystalline SiO₂–CaO–FeO oxides at 1873 K. The simulations were carried out in the purely ionic and ionic–covalent approximations. In the latter case, use was made of the semiclassical molecular dynamics simulation method proposed earlier for studying ionic–covalent oxide systems. At SiO₂ contents below 40 mol %, the self-diffusion coefficients of the constituent ions depend little on the oxide composition and the assumed character of bonding. As the SiO₂ content increases to 40 mol % and above, the ion mobility drops sharply. The thermodynamic and structural parameters derived from the ionic–covalent simulations of the ternary oxides are in reasonable agreement with experimental data.     

Effect of TiO2 on the sintering temperature and dielectric properties of Li2O–MgO–ZnO–B2O3–SiO2 ceramic composites for LTCC applications

Journal of Materials Science: Materials in Electronics - The effects of injecting TiO2 to a Li2O–MgO–ZnO–B2O3–SiO2 (LMZBS) microwave dielectric composite on sinterability,...     

Structure-Sensitive Properties of Melts and Thermal Properties of Glasses in the B2O3–CaO–Al2O3–PbO System

Inorganic Materials - The devitrification, “cold” crystallization, and glass transition temperatures and melting point of samples in the B2O3–CaO–Al2O3–PbO system have...     

Control of the coating layer thickness of TiO2–SiO2 core–shell hybrid particles by liquid phase deposition

This paper describes control of the coating layer thickness and the crystallite size of the core–shell hybrid particles by controlling the process parameter. The core–shell hybrid particles were prepared using liquid phase deposition (LPD). We confirmed that the homogeneous coating was attained from the result of the zeta potential and the transmission electron microscope (TEM) observation. Furthermore, the coating layer microstructure was estimated using Brunauer–Emmett–Teller (BET) method. The obtained coating layer of titania was estimated using the band gap energy. Results indicate that the blue shift of the band gap energy signifies that the physical property of the hybrid particles was controlled by the coating layer thickness and the crystallite size, which are determined by the processing parameters.     

Prediction of the mechanical properties of forged Ti–10V–2Fe–3Al titanium alloy using FNN

In this paper, a fuzzy neural network (FNN) prediction model has been employed to establish the relationship between processing parameters and mechanical properties of Ti–10V–2Fe–3Al titanium alloy. In establishing these relationships, deformation temperature, degree of deformation, solution temperature and aging temperature are entered as input variables while the ultimate tensile strength, yield strength, elongation and area reduction are used as outputs, respectively. After the training process of the network, the accuracy of fuzzy model was tested by the test samples and compared with regression method. The obtained results with fuzzy neural network show that the predicted results are much better agreement with the experimental results than regression method and the maximum relative error is less than 7%. And the optimum matching processing parameters can be quickly selected to achieve the desired mechanical property based on the fuzzy model. It proved that the model has a good precision and excellent ability of predicting.     

Influence of yttrium addition on the corrosion behaviour of as-cast Mg–8Li–3Al–2Zn alloy

The influence of yttrium on the microstructure and corrosion behaviour of as-cast Mg–8Li–3Al–2Zn–xY alloys was investigated. The results show that Y addition leads to the formation of Al₂Y particles and the transformation of α-Mg from the long needle-like to the round-like. The noble Al₂Y particles on the grain boundary inhibit the galvanic corrosion between β-Li phase and α-Mg phase, and also weaken the corrosion occurrence inside β-Li phase due to the decrease of the AlLi phase. With Y addition, the corrosion resistance is improved gradually, especially when the content of Y is up to 1.5 wt-%. Moreover, Y addition makes the corrosion film become more compact, which can prevent the base materials from being attacked continuously.     

Analysis of the ellipse of polarization by the senarmont method as the phase difference varies in the range 0–2π

An analysis of the Senarmont method is performed using Müller marices and Stokes, vectors. It is proved that the traditional undrstanding of the Senarmont method is applicable in the case of phase differences not exceeding one-half wave. For measurements of phase differences in the range 0–2π, a preliminary identification of the rapid and slow axes of the phase plate is required. A method is presented by means of which it is possible to distinguish the axes on the basis of the direction of the rotation of the resultant plane oscillations in the case of continuous variation of the phase differences. Translated from Izmeritel'naya Tekhnika, No. 11, pp. 22–25, November, 1999.     

Thermodynamics of the System MgCl2–NaCl–H2O to 573 K: New Measurements of Heat of Mixing and Heat of Dilution

Heats of mixing of NaCl(aq) with MgCl₂(aq) at 373.15, 423.15, 473.15, 523.15, and 573.15 K for ionic strengths of 0.5 to 3.8 mol·kg^–1, and heats of dilution of MgCl₂(aq) at 523.15 and 573.15 K for ionic strengths of 0.3 to 4.6 mol·kg^–1, have been measured at 20.5 MPa. These experimental data are combined with published heat of mixing data at 298 and 373 K to provide a comprehensive Pitzer ion-interaction treatment for the thermodynamic properties of the system to 573 K. The treatment includes a general equation valid to 523 K, incorporating the published equations for NaCl(aq) and MgCl₂(aq), and equations for MgCl₂(aq) and the mixed system valid at 573 K.