Elusive super-hard B6C accessible through the laser-floating zone method

Boron carbide is among the most promising ceramic materials nowadays: their mechanical properties are outstanding, and they open potential critical applications in near future. Since sinterability is the most critical drawback to this goal, innovative and competitive sintering procedures are attractive research topics in the science and technology of this carbide. This work reports the pioneer use of the laser-floating zone technique with this carbide. Crystallographic, microstructural and mechanical characterization of the so-prepared samples is carefully analysed. One unexpected output is the fabrication of a B6C composite when critical conditions of growth rate are adopted. Since this is one of the hardest materials in Nature and it is achievable only under extremely high pressures and temperatures in hot-pressing, the use of this technique offers a promising alternative for the fabrication. Hardness and elastic modulus of this material reached to 52¿GPa and 600¿GPa respectively, which is close to theoretical predictions reported in literature

Cation-driven electrical conductivity in Ta-doped orthorhombic zirconia ceramics

This paper is devoted to the study of the electrical conductivity of tantalum-doped zirconia ceramics prepared by spark plasma sintering. In this study, the temperature dependence of conductivity in as-prepared specimens and in those previously annealed in air is determined and compared. A semi-empirical model, which is based on the oxidation states of the cations, has been developed and successfully assessed. According to this, the conductivity is basically controlled by the diffusion of tetravalent zirconium cations in both cases, although the concentration of these species varies drastically with the amount of induced oxygen vacancies. This is a quite unexpected fact, since conductivity is normally controlled by anionic diffusion in zirconia ceramics. This option is forbidden here due to the presence of substitutional pentavalent cations. Therefore, conductivity values are much lower than those reported in trivalent or divalent substitutional cation doped zirconia ceramics

Removal of copper ions from dilute sulfuric acid solutions: Effect of solution composition and applied potential

Removal of copper from synthesized and real dilute sulfuric acid solutions was investigated. Effects of copper, iron concentrations and applied potential were studied. In pure copper solutions, increasing the Cu2+ concentration from 1000 to 5000 mg.L-1 increased the copper recovery from about 30-300% depending on the cathode potential and decreased the energy consumption by about 30%. Also, with increasing the acid concentration from 15 to 50 g.L-1 an about 25% increase in copper recovery and a 30% decrease in energy consumption were observed. The addition of Fe2+ to the solution improved the ionic conductivity and so that the copper recovery. The specified energy consumption for the real leaching solutions increased to 31-47 KWh.kg-1. The diffusion coefficients for several synthesized and real copper electrowinning electrolytes were determined. Moreover, the maximum value of the diffusion coefficient (D) was obtained 2.27*10-4 cm2.s-1 for the pure copper solution at a concentration of 1000 mg.L-1 Cu2+ which was higher than impure and real solutions

Silicon carbide- from synthesis to application: a review

This paper provides a review of the synthesis techniques that are used to produce nanostructured silicon carbide. The synthesis methods, consisting of carbothermal reduction, chemical vapor deposition, laser ablation, sol-gel and microwave heating are described. The silicon carbide properties and application are also explained. The paper then discusses the limitations of previous studies which involved complicated equipment and processes, that limit their further application and act as a barrier to further research and development in many fields

A New Class of Banach Spaces and Its Relation with Some Geometric Properties of Banach Spaces

By introducing the concept of L-limited sets and then L-limited Banach spaces, we obtain some characterizations of it with respect to some well-known geometric properties of Banach spaces, such as Grothendieck property, Gelfand-Phillips property, and reciprocal Dunford-Pettis property. Some complementability of operators on such Banach spaces are also investigated

Limited pp-converging operators and relation with some geometric properties of Banach spaces

summary:By using the concepts of limited $p$-converging operators between two Banach spaces $X$ and $Y$, $L_p$-sets and $L_p$-limited sets in Banach spaces, we obtain some characterizations of these concepts relative to some well-known geometric properties of Banach spaces, such as $*$-Dunford--Pettis property of order $p$ and Pelczyński's property of order $p$, $1\leq p<\infty$

Fixed Point Methods in the Stability of the Cauchy Functional Equations

By using the fixed point methods, we prove some generalized Hyers-Ulam stability of homomorphisms for Cauchy and CauchyJensen functional equations on the product algebras and on the triple systems