Effect of Bottom Blowing Mode on Fluid Flow and Mixing Behavior in Converter

Bottom blowing agitation plays a crucial role in improving the reaction kinetics condition of molten bath during the steelmaking process. Herein, the influence of bottom blowing mode on the flow and mixing characteristics of molten bath and the abrasion characteristics of refractory lining in a 6:1 scaled-down model of a 100 t converter were investigated using physical and numerical simulations together. Eight bottom blowing modes were designed (uniform, three-point linear co-direction, three-point linear unco-direction, two-point linear, circumferential linear, A-type, V-type, and triangle alternating). The results indicated that bottom blowing mode has a significant effect on the local flow field at the inner ring of bottom tuyeres, the velocity interval distribution, and the turbulent kinetic energy, which in turn determines the tracer diffusion path and rate as well the mixing time of molten bath. Reasonable non-uniform bottom blowing modes promote the interaction between the various stirring sub-zones of the molten bath. Among them, the three-point linear co-direction mode and A-type mode have the highest mixing efficiency under the conditions of bottom blowing and combined blowing, respectively, which is superior to the uniform mode. In addition, the bottom blowing mode changed the location and degree of abrasion of the refractory lining, and the total abrasion of the non-uniform mode was reduced. The average value and fluctuation degree of integral wall shear stress for the A-type mode were minimal.

Diffusion in Metallic Glasses and in Oxide Glasses - An Overview

We remind the reader to some common features of metallic and oxide glasses. We then introduce the radiotracer method for diffusion studies, which can be applied for both types of glasses. We provide an overview on diffusion in metallic glasses in which we consider both types of metallic glasses – conventional and bulk metallic glasses. In the last part we discuss diffusion and ionic conduction in oxide glasses. For ionic glasses, conductivity measurements are an important complement to tracer diffusion studies. We remind the reader to the method of impedance spectroscopy. We discuss results for soda-lime silicate glasses, single alkali borate glasses and mixed alkali borate glasses and present evidence for collective jump processes in glasses.

Lithium Tracer Diffusion in Sub-Stoichiometric Layered Lithium-Metal-Oxide Compounds

Cathode materials based on lithium-metal-oxide compounds are an essential technical component for lithium-ion batteries, which are still being researched and continuously improved. For a fundamental understanding of kinetic processes at and in electrodes the Li diffusion is of high relevance. Most cathode materials are based on the layered LiCoO2 (LCO) and LiNi0.33Mn0.33Co0.33O2 (NMC333). In the present study Li tracer self-diffusion is investigated in polycrystalline sintered bulk samples of sub-stoichiometric Li0.9CoO2 at 145 °C ≤ T ≤ 350 °C and compared to Li0.9Ni0.33Mn0.33Co0.33O2 in the temperature range between 110 and 350 °C. For analysis, stable 6Li tracers are used in combination with secondary ion mass spectrometry (SIMS). The Li tracer diffusivities D* of both compounds with a sub-stoichiometric Li concentration are identical within error limits and can be described by the Arrhenius law with an activation enthalpy of (0.76 ± 0.13) eV for LCO and (0.85 ± 0.03) eV for NMC333, which is interpreted as the migration energy of a single Li vacancy. This means that a modification of the transition metal (M) layer composition within the LiMO2 structure does not significantly influence lithium diffusion in the temperature range investigated.

Cooperative excitations in superionic PbF 2

Links between dynamical Frenkel defects and collective diffusion of fluorides in β -PbF 2 are explored using Born–Oppenheimer molecular dynamics. The calculated self-diffusion coefficient and ionic conductivity are 3.2 × 10 −5 cm 2 s −1 and 2.4 Ω −1 cm −1 at 1000 K in excellent agreement with pulsed field gradient and conductivity measurements. The calculated ratio of the tracer-diffusion coefficient and the conductivity-diffusion coefficient (the Haven ratio) is slightly less than unity (about 0.85), which in previous work has been interpreted as providing evidence against collective ‘multi-ion’ diffusion. By contrast, our molecular dynamics simulations show that fluoride diffusion is highly collective. Analysis of different mechanisms shows a preference for direct collinear ‘kick-out’ chains where a fluoride enters an occupied tetrahedral hole/cavity and pushes the resident fluoride out of its cavity. Jumps into an occupied cavity leave behind a vacancy, thereby forming dynamic Frenkel defects which trigger a chain of migrating fluorides assisted by local relaxations of the lead ions to accommodate these chains. The calculated lifetime of the Frenkel defects and the collective chains is approximately 1 ps in good agreement with that found from neutron diffraction. This article is part of the Theo Murphy meeting issue ‘Understanding fast-ion conduction in solid electrolytes’.

Lithium tracer diffusion in near stoichiometric LiNi0.5Mn1.5O4 cathode material for lithium-ion batteries

The compound LiNi0.5Mn1.5O4 is used as novel cathode material for Li-ion batteries and represents a variant to replace conventional LiMn2O4. For a further improvement of battery materials it is necessary to understand kinetic processes at and in electrodes and the underlying diffusion of lithium that directly influences charging/discharging times, maximum capacities, and possible side reactions. In the present study Li tracer self-diffusion is investigated in polycrystalline sintered bulk samples of near stoichiometric LiNi0.5Mn1.5O4 with an average grain size of about 50–70 nm in the temperature range between 250 and 600 °C. For analysis, stable 6Li tracers are used in combination with secondary ion mass spectrometry (SIMS). The tracer diffusivities can be described by the Arrhenius law with an activation enthalpy of (0.97 ± 0.05) eV, which is interpreted as the sum of the formation and migration energy of a thermally activated Li vacancy.

Modelling the Diffusion Coefficients of Dilute Gaseous Solutes in Hydrocarbon Liquids

In this work, we present a model, based on rough hard-sphere theory, for the tracer diffusion coefficients of gaseous solutes in non-polar liquids. This work extends an earlier model developed specifically for carbon dioxide in hydrocarbon liquids and establishes a general correlation for gaseous solutes in non-polar liquids. The solutes considered were light hydrocarbons, carbon dioxide, nitrogen and argon, while the solvents were all hydrocarbon liquids. Application of the model requires knowledge of the temperature-dependent molar core volumes of the solute and solvent, which can be determined from pure-component viscosity data, and a temperature-independent roughness factor which can be determined from a single diffusion coefficient measurement in the system of interest. The new model was found to correlate the experimental data with an average absolute relative deviation of 2.7 %. The model also successfully represents computer-simulation data for tracer diffusion coefficients of hard-sphere mixtures and reduces to the expected form for self-diffusion when the solute and solvent become identical.