Estremera-Pérez, Elvin G.

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    Fabrication and characterization of porous aluminum and zinc via selective dissolution of AI-Zn alloys
    (2013) Estremera-Pérez, Elvin G.; Suárez, O. Marcelo; College of Engineering; Hernández-Maldonado, Arturo J.; Quintero, Pedro; Pérez, Néstor; Department of Mechanical Engineering; Morales, Alfredo
    Chemical dealloying can be used to fabricate porous metals by removing one or more of the species out of an alloy. Generally, a corrosive electrolyte is used to selectively dissolve a noble element. Alloy concentration, microstructure, applied electric potentials and corrosive medium are the main aspects affecting the morphology of porosity. By controlling these parameters, scientists have been able to design the size of porosity to the extent of creating nanoporous metals. Pores can be tuned between less than 2 nanometers up to the submicron range. Because of their high surface area, these materials can be used as skeletal catalysts. Some metals, like gold, become chemically active once they become nanoporous, while others can be functionalized with a more noble metal to produce catalysts with low precious metal loading. Porous zinc and porous aluminum have been successfully fabricated via selective dissolution of various Al-Zn alloys. Different Al-Zn alloys ranging from 15 to 70 at. % zinc were cast with fast cooling rates to promote finer microstructure. The alloy specimens were cut and polished prior to the selective corrosion to favor a uniform dealloying process. Sodium hydroxide (NaOH) and nitric acid (HNO3) solutions were used to selectively remove the aluminum and zinc atoms respectively. An electrical potential was applied to the samples to increase corrosion energy and help promote porosity formation. Concentration and cooling rate were varied to observe their effect on the attained pore size. The microstructure of the resulting porous sponge was characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The presence and distribution of zinc and aluminum along dendrites were analyzed using energy dispersive X-ray spectroscopy (EDS). Our results revealed that porosity depends highly on Zn concentration and precursor microstructure resulting from cooling rate upon alloy fabrication. A complete removal of zinc crystals was achieved when Al-Zn alloys were treated with HNO3. Moreover, a complete removal of aluminum phase was observed when the alloys were corroded in NaOH. EDS results evinced the preferential distribution of zinc around aluminum rich dendrites with some zinc atoms dissolved into the dendrites. This directly affected the morphology of porosity.