Evaluation of Formation and Evolution of Microporosity in Anodic Copper Solidification Processes: Simulation and Experim
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CHANICAL and electrical properties of metal products depend on the phenomena occurring during their manufacturing and specifically in solidification. Defects formed during each stage of production can persist over a period of time or modify the behavior of the metal during subsequent processing steps. Therefore, insuring that an appropriate microstructure is formed at each stage with minimal defects has always been a focus in the study of metal production. During casting of anodic copper, the hydrogen, the oxygen, and the dissolved sulfur react and precipitate as water vapor (H2O) and sulfur dioxide (SO2) principally. Carbon is totally insoluble in liquid copper, which implies the inexistence of a thermodynamic equilibrium between it and oxygen; this is the reason why CO and CO2 are not considered in the current study.[1,2] JORGE SEBASTIAN ROMERO, Professor, is with Universidad de Atacama Sede Vallenar, Atacama, Chile. Contact e-mail: jorgerom_met@ yahoo.com MARCELA ANDREA CRUCHAGA, Professor, is with the Departamento de Ingenierı´ a Meca´nica, Universidad de Santiago de Chile, Santiago. DIEGO JAVIER CELENTANO, Professor, is with the Departamento de Ingenierı´ a Meca´nica y Metalu´rgica, Pontificia Universidad Cato´lica de Chile, Santiago. Manuscript submitted June 12, 2012. Article published online March 13, 2013. 624—VOLUME 44B, JUNE 2013
When this process is not controlled properly, severe gas evolution and precipitation may occur during solidification in the metallic piece causing an unacceptable quality in the product, because of, mainly, the high levels of microporosity. This phenomenon will produce several operational problems during the next process of electrorefining. Microporosity causes a decrease in the electrical conductivity of anodes, and therefore it is necessary to utilize a greater current density with the corresponding operational cost.[3,4] Besides, the release of pores during anodic dissolution increases the amount of acid mist produced in the electrolytic cell, which is highly toxic for operators. For the above reasons, it is important to take into account that porosity is an important parameter during the casting of anodic copper. Therefore, developing a model to predict the formation of microporosity in solidifying metal castings is one way of helping casting designers to obtain the best physical and microstructural properties. The modeling of gas porosity is developed from the description of bubble growth from supersaturated liquids to the study of fluid flow through porous media. The analytic and numerical modeling of these processes within metal solidification has been reviewed by Lee et al.[5] Most models related to porosity formation and evolution have been formulated for aluminum alloys, METALLURGICAL AND MATERIALS TRANSACTIONS B
where some of them were focused on relating the shrinkage pressure and hydrogen concentration to either the percentage of porosity formed or to an average equivalent spherical radius.[6] However, it should be noted that in these models, the pores size was not explici
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