Electrochemical Deoxidation of Titanium Foam in Molten Calcium Chloride
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INTRODUCTION
METALLIC foams (also known as cellular metals), because of the presence of a high-volume fraction of interconnected network of voids/pores, are increasingly being used for a variety of purposes such as (1) load/ sound absorbing material, (2) sandwich material in the construction industry, (3) heat-transfer media (fluid filters), (4) flame retardants, (5) catalytic supports, and (6) bio-medical implants.[1–3] Although in many cases these materials look like typical polymer foams, they differ from them in metallic characteristics such as ductility, electrical conductivity, and weldability.[4] Aluminum and nickel foams are being routinely used for a variety of applications, such as ‘‘crash protection,’’ electrodes, and current collectors;[5] steel and titanium foams, on the other hand, have emerged as potentially new materials for many commercial applications. Steel foams are being developed as suitable materials for civil building and construction projects.[6] Alternately, titanium foams, which have been found to be better efficient materials over solid titanium[6] in many applications (especially as a bio-mimetic material), offer promising applications both as a construction material and in the field of bio-medical/bone-implant engineering. Titanium foams, because of the combination of a series of attractive properties such as (1) low density as well as stiffness, (2) high porosity and permeability, (3) PRABHAT K. TRIPATHY, formerly with the Department of Materials Science and Metallurgy, University of Cambridge, Cambridge CB2 3QZ, United Kingdom, is with the Materials Processing Division, Bhabha Atomic Research Centre, Trombay, Mumbai, 400 085, India. Contact e-mail: [email protected] MAXIME GAUTHIER is with the Industrial Materials Institute, National Research Council of Canada, Boucherville, PQ, Canada J4B 6Y4. DEREK J. FRAY is with the Department of Materials Science and Metallurgy, University of Cambridge, Cambridge CB2 3QZ, United Kingdom. Manuscript submitted March 16, 2007. Article published online October 23, 2007. METALLURGICAL AND MATERIALS TRANSACTIONS B
good mechanical strength, (4) low modulus, (5) excellent corrosion resistance, and (6) superior bio-compatibility, are classified under ‘‘high performance’’ materials.[6] A relatively higher working temperature, comparable specific strength (as that of aluminum foams), superior fracture toughness, and better energy absorbing ability (than that of aluminum foams) favor the potential use of these foams in rocket construction and in military and aerospace applications.[6] Furthermore, it is predicted that these materials can offer effective gains in the ship-building industry (luxury boat hulls), car industry (car body as well as its interior), and armor.[6] From a medical application perspective, titanium foams, in the form of porous scaffolds (that can mimic the human bone), have recently emerged as excellent bio-mimetic materials.[7] These foams provide the necessary support to cells to proliferate and maintain their differential functions, and thus
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