Phase equilibria in the Zn-Mn-O system

International audienceDifferent ratios of ZnO and MnCO3 were mixed and processed by ceramic route to investigate phase relations in the Zn-Mn-O system using differential thermal analysis and X-ray powder diffraction techniques. Except for Zn1-xMnxO we detected two different spinel phases in this system. FactSage program was used for the construction of the Zn-Mn-O phase diagram in air and oxygen atmosphere. To verify the composition in several parts of the diagram at the temperature of interest, a number of high-temperature annealings followed by quenching was performed. © 2014 Elsevier Ltd

Phase equilibria in the Zn-Mn-O system

Different ratios of ZnO and MnCO3 were mixed and processed by ceramic route to investigate phase relations in the Zn-Mn-O system using differential thermal analysis and X-ray powder diffraction techniques. Except for Zn1-xMnxO we detected two different spinel phases in this system. FactSage program was used for the construction of the Zn-Mn-O phase diagram in air and oxygen atmosphere. To verify the composition in several parts of the diagram at the temperature of interest, a number of high-temperature annealings followed by quenching was performed. © 2014 Elsevier Ltd

Towards graphene bromide : bromination of graphite oxide

Halogenated graphene derivatives are interesting for their outstanding physical and chemical properties. In this paper, we present various methods for the synthesis of brominated graphene derivatives by the bromination of graphite oxides. Graphite oxides, prepared according to either the Hummers or Hofmann method, were brominated using bromine or hydrobromic acid under reflux or in an autoclave at elevated temperatures and pressures. The influence of both graphite oxide precursors on the resulting brominated graphenes was investigated by characterization of the graphenes, which was carried out using various techniques, including SEM, SEM-EDS, high-resolution XPS, FTIR, STA and Raman spectroscopy. In addition, the resistivity of the brominated graphenes was measured and the electrochemical properties were investigated by cyclic voltammetry. Although the brominated graphenes were structurally similar, they had remarkably different bromine concentrations. The most highly brominated graphene (bromine concentration above 26 wt%) exhibited a C/O ratio above 44 and partial hydrogenation. Brominated graphenes with such properties could be used for reversible bromine storage or as a starting material for further chemical modifications.Published versio

Novel approach for manufacture of single-grain EuBCO/Ag bulk superconductors via modified single-direction melt growth

AbstractDespite the success of top‐seeded melt growth (TSMG) and TSIG, some key aspects of their manufacture need to be addressed including the presence of microstructural defects, inhomogeneities in trapped field and the difficulty of growing large‐diameter bulk monoliths. Recently, a promising new method single‐direction melt growth (SDMG) appears to address the majority of the shortcomings of TSMG and TSIG. Single‐grain EuBCO/Ag bulk with the highest peritectic temperature to date was grown by modified SDMG. This remarkable achievement was made possible by lowering the peritectic temperature of the precursor composition by the addition of silver and by using single‐grain EuBCO fabricated by TSMG as a seed. The EuBCO/Ag bulk grown by SDMG has demonstrated significant improvements in comparison to a reference TSMG sample. A reduction of approximately 30% in defect area (associated primarily with porosity), as well as a significantly enhanced homogeneity of trapped field and critical temperature, was observed. Furthermore, the critical current density curves exhibit a considerable improvement, particularly in the 2–5 T field range. The SDMG technique has considerable potential for scale‐up for the fabrication of large‐diameter bulk single grains, with only growth along the c‐axis involved during the thermal process.</jats:p

Cost-effective isothermal top-seeded melt-growth of single-domain YBCO superconducting ceramics

Abstract In this work, a series of melt processed YBaCuO (YBCO) single-grains have been fabricated by the top-seeded melt growth (TSMG) technique. The melt processing is accepted widely as an effective way to grow bulk, single grain YBCO superconductors; however, this process is extremely complex and every step can affect the final properties of prepared bulk. Therefore, the impact of precursor powder preparation and growth conditions was studied for the first time. Cost-effective in-house made powder and commercially available precursor powders were employed and samples were grown employing top seeded melt growth, following the isothermal and the under-cooling growth techniques. The bulk microstructure including Y2BaCuO5 (Y-211) particle size and distribution, superconducting properties (Tc, Jc) and field trapping potential were investigated. The cost-effective high performance batch processing methodology was optimized. The fabricated YBCO bulks (diameter of 28 mm) exhibited average trapped field of 0.85 T at 77 K. Furthermore, other possibilities to achieve advancement in processing (RE)BCO bulks, are proposed.Czech Ministry of Industry and Trade, project TIP (FR-TI4/184)

Cost-effective isothermal top-seeded melt-growth of single-domain YBCO superconducting ceramics

In this work, a series of melt processed Y–Ba–Cu–O (YBCO) single-grains have been fabricated by the top-seeded melt growth (TSMG) technique. The melt processing is accepted widely as an effective way to grow bulk, single grain YBCO superconductors; however, this process is extremely complex and every step can affect the final properties of prepared bulk. Therefore, the impact of precursor powder preparation and growth conditions was studied for the first time. Cost-effective in-house made powder and commercially available precursor powders were employed and samples were grown employing top seeded melt growth, following the isothermal and the under-cooling growth techniques. The bulk microstructure including Y 2 BaCuO 5 (Y-211) particle size and distribution, superconducting properties (T c , J c ) and field trapping potential were investigated. The cost-effective high performance batch processing methodology was optimized. The fabricated YBCO bulks (diameter of 28 mm) exhibited average trapped field of 0.85 T at 77 K. Furthermore, other possibilities to achieve advancement in processing (RE)BCO bulks, are proposed