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.Ministerio de Economía y Competitividad (Government of Spain) and FEDER Funds under Grants Nos MAT2015-71411-R and MAT2016-77769-

Superplastic Deformation of Alumina Composites Reinforced with Carbon Nanofibers and with Graphene Oxide Sintered by SPS—Experimental Testing and Theoretical Interpretation

The superplastic behavior of alumina-based nanostructured ceramics (Al2O3) is an important issue in the world of materials. The main body of this paper is an analysis of the creep behavior of polycrystals, with grain boundary sliding as the main deformation mechanism at high temperatures. Concomitant accommodation of grain shapes to preserve spatial continuity has a comparatively small effect on the strain rate. The constitutive equations for small deformations, relating strain and strain rate, derived from two models for grain sliding, are compared with the experimental data with their respective uncertainties. The data follow from experiments on the plastic deformation of alumina composites reinforced, on the one hand by graphene oxide, and on the other hand by carbon nanofibers sintered by SPS. The results show good agreement between experiment and theory for these advanced ceramics, particularly for one of the assumed models. The values obtained of ξ2 for model A were in the interval 0.0002–0.1189, and for model B were in the interval 0.000001–0.0561. The values obtained of R2 for model A were in the interval 0.9122–0.9994, and for model B were in the interval 0.9586–0.9999. The threshold stress was between (3.05 · 10−15–25.68) MPa.Junta de Andalucía the regional projects P18-RTJ1972 and P20-01121España Ministerio de Economía y Competitividad and Fondo Europeo de Desarrollo Regional funds through the projects MAT2015-71411-R and RTI2018-099033-B-C33Universidad de Sevilla “VI Plan Propio de Investigación y Transferencia-US 2017España Ministerio de Ciencia, Innovación y Universidades The projects PGC2018-094952-B-I00 (MCIU/AEI/FEDER, UE) and PID2019- 103847-RJ-I0

The prolific polytypism of silicon carbide

A worked example of polytypism is presented, aimed at assisting undergraduates in the learning and instructors in the teaching of this topic. In particular, this crystallography concept, not necessarily obvious for beginners, is illustrated pedagogically using to that end the model case of the prolific polytypism of silicon carbide (SiC). On the basis of concepts that are easily assimilated by students (i.e. simple topological constraints) this article first presents a unified description of the polytypism phenomenon in SiC that allows one to understand without difficulty the existence of its numerous polytypic variants and how they develop. Then the various notations used to designate these different polytypes are described, and finally the crystal structures of the most common are discussed. This worked example is thus expected to contribute to motivating undergraduates in the study of a crystallography topic that often is not treated in sufficient depth in class.Ministerio de Ciencia y Tecnología MAT2010-1684

Rietveld analysis and mechanical properties of in situ formed La-β-Al2O3/Al2O3 composites prepared by sol-gel method

In this work, the crystal evolution of α-Al2O3 composites reinforced with LBA platelets were monitored by XRD Rietveld. In addition, the mechanical properties of totally densified specimens were researched by Vickers and Knoop indentations. These composite materials were prepared by a sol-gel process from alumina seeded boehmite sol and lanthanum nitrate. X-ray diffraction data have been studied by Rietveld refinements and line profile analyses, paying attention to the LBA formation, the evolution of vol%, and crystallite size of the different phases. It has been observed that the appearance of the LBA phase happens at a lower temperature than in samples prepared by a conventional solid state reaction. Indentation tests revealed that the presence of LBA microplatelets in the sol-gel samples leads to a significant increase of their indentation fracture resistance, in comparison to the conventional samples

An Interpretation of Article 24 of the Constitution of Japan: Reconsidering the Principle of \u27\u27Gender Equality\u27\u27 from the Perspective of \u27\u27the Dilemma of Difference\u27\u27

This paper presents a novel methodology to calculate cation diffusion coefficients and activation energies in cubic Y2O3–ZrO2 by Molecular Dynamics. The calculation is based upon modulating the interaction potential to promote cation mobility within the lattice. The technique was calibrated by measuring static properties and oxygen self-diffusion characteristics, and then applied to cation diffusion. The respective activation energies and diffusion coefficients agree well with experimental findings. Preliminary results about grain boundary cation diffusion are presented for the first time as a proof of the potentiality of the procedureMinisterio de Ciencia e Innovación MAT2009-14351-C02-01, MAT2009-14351-C02-02Agencia Española de Cooperación Internacional y Desarrollo 53687

Spinel Ferrite Catalysts for CO2 Reduction Via Reverse Water Gas Shift Reaction

The production of CO via Reverse Water Gas Shift (RWGS) reaction is a suitable route for CO2 valorization. In this study a series of modified spinels AB2O4 (A site = Ni, Zn and Cu and B site=Fe) are investigated as RWGS catalysts and their structure-to-function relationships derived from the changes on the A-site cation are rationalized. For all ferrite systems, the RWGS reaction the process main activity and selectivity is governed by the B-site cation, but the variations on the A-site metals determines catalysts' structural features and stability in the reaction. Among the catalyst series, superior RWGS performance displayed the ferrites modified with Cu and Ni associated to the greater oxygen vacancy population for those spinels enabled by the partial allocation on Fe3+ cations into the tetrahedral sites.Junta de Andalucía US-1263288Ministerio de Ciencia e Innovación TI2018-096294-B-C