Application of the levitation technique for investigation of metal alloys and phase equilibria in slags

Experimental methods, based on electromagnetic levitation, have been developed for preparation and investigation of copper-rich alloys, and for the determination of oxide-metal phase equilibria. These techniques involve high-temperature equilibration, rapid quenching and chemical analysis of the phases using electron probe X-ray microanalysis. The experiments can be carried out in the temperature range 1373-1873 K (= 1100 degrees C-1600 degrees C). A developed calibration method, using phase equilibria data in known oxide systems, was applied for pyrometric temperature measurements. Described methods of the application of the electro-magnetic levitations were used for in-situ formation of Cu-based alloys and for formation of Ca-ferrite slags equilibrated with metallic copper

Methods of Introduction of MgO Nanoparticles Into Bi-2212/Ag Tapes

The effect of addition of ultra-fine MgO particles, obtained by Mg combustion, in Bi-2212/Ag tapes was investigated. Bi-2212/Ag tapes were prepared by coating and partial melt processing. Four different methods of MgO particles embedment were applied in green tape preparation; settlement of MgO in Bi-2212, pre-mixing of MgO in the solvent, deposition of the MgO into the solvent, and deposition of MgO onto the surface of Bi-2212. Microstructural studies of processed tapes show that uniformity of MgO particles distribution in Bi-2212 matrix depends on the methods of tape preparation. MgO particles, introduced in Bi-2212 matrix by all applied methods, significantly enhanced transport properties of the tapes. The Jc degradation with the increase of magnetic field and/or temperature in all doped samples was significantly lower compared to un-doped Bi-2212 samples. The best improvement was achieved when MgO particles were introduced into Bi-2212 matrix by settlement method of the tape coating. The improvement also depends on a magnitude of the magnetic field and operating temperatures

Re-melting of Bi-2212/Ag laminated tapes by partial melting process

Bi-2212 tapes are prepared by a combination of dip-coating and partial melt processing. We investigate the effect of re-melting of those tapes by partial melting followed by slow cooling on the structure and superconducting properties. Microstructural studies of re-melted samples show that they have the same overall composition as partially melted tapes. However, the fractional volumes of the secondary phases differ and the amounts and distribution of the secondary phases have a significant effect on the critical current. Critical current of Bi-2212/Ag tapes strongly depends on the maximum processing temperature. Initial J(c)'s of the tapes, which are partially melted, then slowly solidified at optimum conditions and finally post-annealed in an inert atmosphere, are up to 10.4 x 10(3) A/cm(2). It is found that the maximum processing temperature at initial partial melting has an influence on the optimum re-heat treatment conditions for the tapes. Re-melted tapes processed at optimum conditions recover superconducting properties after post-annealing in an inert atmosphere: the J(c) values of the tapes are about 80-110% of initial J(c)'s of those tapes

The effect of Yb addition in Bi2Sr2Ca1-xY bxCu2Oy partial melted thick films

To study the phase relations in the Bi-2212 and Yb2O3 system, Bi2Sr2Ca1-xYbxCu 2Oy thick films are prepared by partial melt processing via an intermediate reaction between Bi-2212 and Yb2O3. When Bi-2212 and Yb2O3 are partially melted and then slowly cooled, solid solutions of Bi2Sr2Ca 1-xYbxCu2Oy, form by reactions between liquid and solid phases which contain Yb. Following these reactions, Ca is partially replaced in Bi-2212 matrix and participates in the formation of secondary phases, such as Bi-free, (Ca, Sr)Ox and CaO. Variation of the Bi-2212-Yb2O3 ratios and processing parameters changes the balance between the phases and leads to different Yb:Ca ratios in the Bi-2212 matrix of processed thick films. When the partial melting process is optimized for each sample to minimize the growth of secondary phases, x = 0.42-0.46 for the samples prepared at pO2 = 0.01 atm, x = 0.24-0.29 for the samples prepared at pO2 = 0.21 atm, x = 0.18-0.23 for the samples prepared at pO2 = 0.99 atm are obtained regardless to the starting compositions. It is found that superconducting properties of Bi 2Sr2Ca1-xYbxCu2O y thick films strongly depend on the processing conditions, because the conditions result in different Yb content in the Bi-2212 matrix and the volume fraction of the secondary phases. The highest Tc(0) of 77, 90 and 91 K were obtained for the samples processed at 0.01, 0.21 and 0.99 atm of O2, respectively

Material Challenges and Hydrogen Embrittlement Assessment for Hydrogen Utilisation in Industrial Scale

Hydrogen has been studied extensively as a potential enabler of the energy transition from fossil fuels to renewable sources. It promises a feasible decarbonisation route because it can act as an energy carrier, a heat source, or a chemical reactant in industrial processes. Hydrogen can be produced via renewable energy sources, such as solar, hydro, or geothermic routes, and is a more stable energy carrier than intermittent renewable sources. If hydrogen can be stored efficiently, it could play a crucial role in decarbonising industries. For hydrogen to be successfully implemented in industrial systems, its impact on infrastructure needs to be understood, quantified, and controlled. If hydrogen technology is to be economically feasible, we need to investigate and understand the retrofitting of current industrial infrastructure. Currently, there is a lack of comprehensive knowledge regarding alloys and components performance in long-term hydrogen-containing environments at industrial conditions associated with high-temperature hydrogen processing/production. This review summarises insights into the gaps in hydrogen embrittlement (HE) research that apply to high-temperature, high-pressure systems in industrial processes and applications. It illustrates why it is still important to develop characterisation techniques and methods for hydrogen interaction with metals and surfaces under these conditions. The review also describes the implications of using hydrogen in large-scale industrial processes

Transformation of mineral matter during pyrolysis, gasification and combustion of biosolid chars

During thermochemical processing of biosolids in sewage sludge, different forms of phosphorus-containing compounds are generated in biosolid chars (biochars). This study examines the effects of biochar processing conditions on the mineral compounds produced during the pyrolysis, gasification, and combustion of biosolids, and the major determinants of phase formation kinetics. Our results show identified phase transformations through experiments in a laboratory tube furnace followed by X-ray diffraction analysis (XRD). Additionally, a synchrotron powder diffraction study was conducted to verify XRD results of the laboratory processed samples and to observe in situ phase transformations in biochars. It was found that under a neutral atmosphere, crystalline oxide phases are formed at lower temperatures and much faster than iron phosphide, while gasification and combustion conditions led to the formation of crystalline phases in phosphate forms. These forms of phosphorus compounds in by-products of biosolids thermochemical treatment can be used as agricultural fertilizers

Oriented Sm-doped CeO<inf>2</inf> thin films on biaxially textured Ni-W substrate produced by ultrasonic spray deposition

A new method of producing Sm-doped CeO2 thin films on metal substrates using an ultrasonic nebuliser has been developed and experimentally verified. Sm-doped CeO2 films with a thickness down to 50 nm and the required properties were consistently and cost effectively produced on Ni-W textured substrates. High film uniformity and c-axis crystal orientation were confirmed by electron microscopy and X-ray diffraction. Characteristics of films and elements valence states are discussed. Our results suggest that the techniques used are promising for further development of buffer layer formation for textured high-temperature superconducting tape applications

Synthesis and characterisation of nanoscale magnesium oxide powders and their application in thick films of Bi2Sr2CaCu2O8

Nanoscale MgO powder was synthesized from magnesite ore by a wet chemical method. Acid dissolution was used to obtain a solution from which magnesium containing complexes were precipitated by either oxalic acid or ammonium hydroxide, The transformation of precipitates to the oxide was monitored by thermal analysis and XRD and the transformed powders were studied by electron microscopy. The MgO powders were added as dopants to Bi2SrCa2CuO8 powders and high temperature superconductor thick films were deposited on silver. Addition of suitable MgO powder resulted in increase of critical current density, J(c), from 8,900 Acm(-2) to 13,900 Acm(-2) measured at 77 K and 0 T. The effect of MgO addition was evaluated by XRD, electron microscopy and critical current density measurements. (C) 1998 Elsevier Science B.V

Application of spray deposition techniques for fabrication of Sm-doped CeO<inf>2</inf> thin films on biaxially textured Ni-W substrate

Chemical and thermo-resistant buffer layers are commonly used to separate metal substrates and high-temperature superconductors (HTS). This ensures that no reaction occurs between the superconductor's precursor materials and the substrate metal during high-temperature HTS tape processing. Various materials and coating procedures are available, with each combination of buffer layers requiring specific characteristics. This paper reports a feasibility study into the development and use of simple, aerosol-based production methods of samarium-doped cerium thin films for subsequent use as a buffer layer between a Ni substrate and yttrium barium copper oxide (YBCO) superconductor. The suggested methods are very cost effective and hence attractive for commercial use. It was shown that different types of aerosol nebulisers can produce textured, pinhole-free films of high integrity and uniformity. Thickness of the films could be precisely controlled by the deposition time enabling achieving any required value starting from 40. nm. It was found that that the optimum film thickness is between 120 and 180. nm, and higher film thickness led to the surface cracking. Microstructural and crystallographic characteristics, and chemical composition of fabricated films are also reported and discussed