Personnel: S. Yuan, P. Soral, H. Larson, B. Schroeder, R. Mizia and U. Pal
Sponsorship: National Science Foundation, INEL-University Consortium
Short circuited solid electrolyte cells have been used in the laboratory to deoxidize molten steel and copper down to 2 ppm oxygen content. The solid electrolyte cell consisted of a one end closed stabilized zirconia tube which conducted oxygen ions. The tube interior was flushed with a reducing gas and the tube was immersed in the molten metal. A layer of porous cermet electrode deposited on the inner wall of the tube served as the anode while the molten metal was the cathode. The melt was deoxidized by short circuiting the cermet electrodes and the melt. The process was modeled and it was found that the kinetics can be improved by stirring the melt well, reducing the external resistance involved in short circuiting, lowering the electrode contact resistance and increasing the interfacial area of the electrolyte per unit mass of the melt. Based on these findings, we have designed possible scale-up structures of the cell that can be used for either a batch or continuous deoxidation process. We are evaluating these structures for their deoxidation performance in a copper casting facility at ``Reading Tube Corporation'' in PA. We will also conduct lab experiments to extend this methodology and modeling for deoxidizing molten super alloys, nickel and silicon.
Personnel: F. Patsiogiannis, K. Chou and U. Pal
Sponsorship: Molten Metal Technology
A synthetic flux based on mayenite (12CaO.7Al2O3) was developed for both removing oxygen in the form of alumina inclusions and sulfur from steel melts. The final slag which is a product of the refining treatment was employed for maximum incorporation of chlorine and sulfur into its structure. A single chlorine phase can be produced as a result of the replacement of one oxygen atom of mayenite by two chlorine atoms.
Personnel: S. Britten, V. Stancovski, U. Pal and J. Oakley
Sponsorship: National Science Foundation
The ability to measure the concentrations and transport properties of easily dissociable oxides within a 40%CaO.40%SiO2.20%Al2O3 steelmaking slag by means of an in-situ solid-state amperemetric technique will be determined. The technique consists of using a yttria partially stabilized zirconia (PSZ) oxygen ion conducting electrolyte to separate a reference gas compartment from the steelmaking slag. Using a potentiostat, a direct current potential sweep is applied between the inner and outer compartments of the electrolyte driving oxygen ions from the slag into the reference gas. The current is measured as both a function of time and potential in order to determine the concentration and transport properties of the dissociable oxides within the slag. The potential indicates the type of oxide while the current indicates its transport property and relative concentration.
Personnel: D. Woolley, H. Larson and U. Pal
Sponsorship: National Science Foundation
In smelting operations, ionic melts such as slags, fluxes or mattes react with gases and metals. These reactions are electrochemical in nature involving charge transfer between ionic and electronic species and are often diffusion limited in the slag phase. Since slags, fluxes and mattes are primarily ionic melts the diffusion process is controlled by the slower moving electronic species. By providing an electronic pathway through the slag and/or imposing an electric field with a plasma the migration of electronic species in the slag can be accentuated which in turn would also increase the rate of reaction and quickly drive the process towards chemical equilibrium. For instance, it has been shown in the laboratory that by providing an electronic pathway in the slag with an inert metallic foil or an electronic refractory, an Fe-C melt can be completely and rapidly decarburized with a 2-5 % iron oxide containing calcia-alumina-silica slag and without the electronic pathway the complete decarburization required 30-40% FeO in the slag, similar to what is presently encountered in steelmaking processes. The objective of this work is to enhance slag-metal reactions encountered in processing ferrous melts (such as decarburization, desulfurization, dephosphorization, deoxidation and alloy additions) by using various electronic pathways in the slag including plasma/electric arcs and assess the magnitude of its impact in terms of lowering FeO content and volume of the slag, and increasing yield, refractory life and recovery of alloying elements. If successful, this could revolutionize steelmaking and open other new opportunities in metals processing such as copper and zinc removal from ferrous scraps, matte smelting of copper, etc., all of which would have a major economic impact.
Personnel: P. Soral, S. Yuan, W. Worrell and U. Pal
Sponsorship: Chipman Chair (MIT), ALCOA Foundation
Transport phenomena involving one mobile ionic specie (oxygen ions) and electronic carriers (electrons and holes) in single and multi-layers of different mixed conducting oxides under the influence of external load and oxygen chemical potential gradient are analyzed. The analysis utilizes the intrinsic ionic and electronic transport properties of the oxide layers and explicitly computes the ionic and electronic fluxes, voltage drop across the layers and variation of chemical potential through the layers. Some limiting cases are being solved to illustrate the generality of the analysis. Based on this analysis, the accuracy, limitations, and physical significance of using an equivalent circuit to define transport in such devices is being investigated. Finally, the engineering implication of the analysis in terms of designing efficient stable devices with layered structures for fuel cells, sensors, separation membranes, batteries, etc., will be provided. The EVD process, described below is being used to synthesize these multi-layer structures.
Personnel: A. Gouldstone, K.C. Chou and U. Pal
Sponsorship: Chipman Chair (MIT), ALCOA Foundation
This is a modified vapor deposition process which is presently used at Westinghouse to deposit yttria stabilized zirconia electrolyte films for solid oxide fuel cells. The research being conducted at MIT will extend the use of this process to deposit other various important ionic, mixed conducting, semi-conducting and compositionally graded films for applications in solid oxide fuel cells and help in gaining a fundamental understanding of the defect structure and the solid state transport properties of these materials. Briefly, the vapor deposition process consists of passing gaseous halides of the cations over one side of a porous substrate and oxygen over the other side of the substrate. The gases diffuse and react within the porous substrate and the pores get filled with the desired solid oxide. Subsequent solid state transport through the oxide maintaining electroneutrality continues the reaction and the film grows over the substrate.
Personnel: S. Seetharaman, W. Worrell, V. Stancovski and U. Pal
Sponsorship: Electric Power Research Institute
The effects of ionic (fully stabilized zirconia), electronic (Ni, Pt) and mixed conductors (fully stabilized zirconia doped with titania, ceria doped with yttria, etc.) on electrocatalytic steam reforming of methane at temperatures between 750-1000C are being studied. The parameters considered are surface areas of the different phases, three phase boundary lengths, fuel composition (methane/steam ratio) and temperature. The experimental techniques being used include I-V characterestics, current interruption, impedance spectroscopy, and gas analysis with quadropole mass spectrometer.
New Methods of Fe-Si Alloy Production
Personnel: A. Agarwal, H. Larson, K. Chou and U. Pal
Sponsorship: Griffin Pipe Products Company - Amstead Industries
The program will experimentally demonstrate the feasibility of producing Fe-Si alloys from various silicon sources including slags using a combination of carbothermic and metallothermic reduction at high temperatures corresponding to conditions that exist in iron cupola furnace. The experimental work will establish reaction mechanisms and parameters which enhances the formation of Fe-Si alloys. The process will be mathematically modeled to support the experimental findings and assist in the development and commercialization of the process.
Personnel: Dan Simon, M. Cevdet Celenligil, Adam Powell, G. Trapaga and
U. Pal
Sponsorship: GE, Pratt & Whitney, AT&T, Sandia National Laboratories
Process models will be established for the key process characterestics that control melting, evaporation, transport of the coating species, and deposition and growth of the coating. Experimental coating trials will be conducted to refine and demonstrate capabilities of each model.
Prof. Uday Pal