Electric arc furnace | EPFL Graph Search

An electric arc furnace (EAF) is a furnace that heats material by means of an electric arc. Industrial arc furnaces range in size from small units of approximately one-tonne capacity (used in foundries for producing cast iron products) up to about 400-tonne units used for secondary steelmaking. Arc furnaces used in research laboratories and by dentists may have a capacity of only a few dozen grams. Industrial electric arc furnace temperatures can reach , while laboratory units can exceed . In electric arc furnaces, the charged material (the material entered into the furnace for heating, not to be confused with electric charge) is directly exposed to an electric arc, and the current from the furnace terminals passes through the charged material. Arc furnaces differ from induction furnaces, in which the charge is heated instead by eddy currents. In the 19th century, a number of people had employed an electric arc to melt iron. Sir Humphry Davy conducted an experimental demonstration in 1810; welding was investigated by Pepys in 1815; Pinchon attempted to create an electrothermic furnace in 1853; and, in 1878–79, Sir William Siemens took out patents for electric furnaces of the arc type. The first successful and operational furnace was invented by James Burgess Readman in Edinburgh, Scotland, in 1888 and patented in 1889. This was specifically for the creation of phosphorus. Further electric arc furnaces were developed by Paul Héroult, of France, with a commercial plant established in the United States in 1907. The Sanderson brothers formed The Sanderson Brothers Steel Co. in Syracuse, New York, installing the first electric arc furnace in the U.S. This furnace is now on display at Station Square, Pittsburgh, Pennsylvania. Initially "electric steel" produced by an electric arc furnace was a specialty product for such uses as machine tools and spring steel. Arc furnaces were also used to prepare calcium carbide for use in carbide lamps. The Stassano electric furnace is an arc type furnace that usually rotates to mix the bath.

Multi-physical characterization of cellular ceramics for high-temperature applications

Ehsan Rezaei

The use of cellular ceramics in enhancing the performance of a high-temperature latent heat thermal energy storage unit was investigated. A detailed design methodology is presented, which consists of a combined analytical-numerical analysis followed by a multi-objective optimization. This optimization indicated that within the selected design space, effectiveness values as large as 0.95 and energy densities as large as 810 MJ/m3 could be achieved. Motivated by the results of this study, new porous structures were investigated. As the classical computer aided design tools are not optimized for quick and efficient design of cellular structures with large number of geometrical features, new design approaches were presented: two methods to design structured and unstructured lattices and a Voronoi-based design approach to create structures consisting of different unit-cells combined together. We then used a combined experimental-numerical approach to investigate the effect of the cell morphology on the heat and mass transport behavior of the porous structures. Different morphologies, namely tetrakaidecahedron, Weaire-Phelan, rotated cube and random foam, were investigated. These structures were designed in cylindrical forms, 3D printed and then manufactured in SiSiC via replica technique followed by silicon reactive infiltration. Permeability and Forchheimer coefficients of the structures were experimentally measured by pressure drop tests at room temperature. The volumetric convective heat transfer coefficients were estimated using temperature measurements and fitting a thermal non-equilibrium heat and fluid flow model to these experiments. It was observed that for the same porosity and cell density the cubic lattice and the random foam exhibited lower pressure drops but also lower heat transfer rates. Undesirable manufacturing anomalies such as pore clogging, was observed for tetrakaidecahedron and Weaire-Phelan structures, which led to a tortuosity larger than calculated, causing additional pressure drop. Finally, the mechanical and degradation behavior of five SiSiC cellular structures, namely simple cube, rotated cube, tetrakaidecahedron, modified octet-truss and random foam, was experimentally investigated in early stage oxidation conditions at 1400 °C. The samples were oxidized in two different environments: in a radiant burner and inside an electric furnace. The results revealed different mechanisms, namely silicon alloy bead formation and H2O/CO2-based corrosion, simultaniously degrading the specimens. It is shown that different lattice architectures led to different oxidation behavior on the struts resulting from the changing gas flow paths inside each ceramic architecture. The effect of the morphology on the elastic behavior of lattice structures was studied in more detail by adapting a numerical approach consisting of a unit-cell model with periodic boundaries. The elastic anisotropies of the lattices were explored by calculating the elastic modulus in different directions. The results revealed that all the studied lattices, and in particular the cubic lattice, have an anisotropic elastic behavior. A new strategy is presented to obtain unit-cells with high elastic modulus and controled anisotropy.

EPFL2020

Dye sensitised solar cells with nickel oxide photocathodes prepared via scalable microwave sintering

Ulf Anders Hagfeldt, Muhammad Awais

Photoactive NiO electrodes for cathodic dye-sensitized solar cells (p-DSCs) have been prepd. with thicknesses ranging between 0.4 and 3.0 μm by spray-depositing pre-formed NiO nanoparticles on fluorine-doped tin oxide coated glass substrates. The larger thicknesses were obtained in sequential sintering steps using a conventional furnace (CS) and a newly developed rapid discharge sintering method. The latter procedure is employed for the first time for the prepn. of p-DSCs. In particular, rapid discharge sintering represents a scalable procedure that is based on microwave-assisted plasma formation that allows the prodn. in series of mesoporous NiO electrodes with large surface areas for p-type cell photocathodes. Rapid discharge sintering possesses the unique feature of transmitting heat from the bulk of the system towards its outer interfaces with controlled confinement of the heating zone. The use of rapid discharge sintering results in a drastic redn. of processing times with respect to other deposition methods that involve heating/calcination steps with assocd. reduced costs in terms of energy. P1-dye sensitized NiO electrodes obtained via the rapid discharge sintering procedure have been tested in DSC devices and their performances have been analyzed and compared with those of cathodic DSCs derived from CS-deposited samples. The highest conversion efficiencies (0.12%) and incident photon-to-current conversion efficiencies (50%) were obtained with sintered NiO electrodes having thicknesses of about 1.5-2.0 μm. In all the devices, the photogenerated holes in NiO live significantly longer (τh ∼1 s) than have previously been reported for P1-sensitized NiO photocathodes. In addn., P1-sensitized sintered electrodes give rise to relatively high photovoltages (up to 135 mV) when the triiodide-iodide redox couple is used.

2013

Multi-physical characterization of cellular ceramics for high-temperature applications

Ehsan Rezaei

EPFL2020