Frontiers Of Dealloying - Novel Processing For Advanced Materials

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dc.contributor.advisorHemker, Kevin J.
dc.contributor.committeeMemberWeihs, Timothy P.
dc.contributor.committeeMemberEl-Awady, Jaafar A.
dc.contributor.committeeMemberCammarata, Robert C.
dc.contributor.committeeMemberErlebacher, Jonah D.
dc.creatorMcCue, Ian Daniel
dc.date.accessioned2016-12-15T07:38:17Z
dc.date.available2016-12-15T07:38:17Z
dc.date.created2015-12
dc.date.issued2015-10-21
dc.date.submittedDecember 2015
dc.date.updated2016-12-15T07:38:17Z
dc.description.abstractDealloying is the selective dissolution in a liquid environment of one or more component sfrom a multicomponent metal alloy, leaving behind a material enriched in the remaining component(s). This process can be broken down into two competing kinetic reactions: surface roughening from dissolution, and surface smoothening from diffusion of the remaining component(s) along the metal/liquid interface. When both rates are approximately equal porosity evolution can occur, leading to the formation of a porous metal with a characteristic ligament and pore size. Previous work in this field has heavily focused on using the dissolution rate to control porosity evolution, but in this dissertation we study how surface diffusivity affects dealloying and use it as a dial to control the resulting structure. Starting with finite systems we use kinetic Monte Carlo simulations to study how particle size affects porosity evolution. Dealloying is used extensively to fabricate next-generation catalysts, however this process isn’t well-understood at small particle sizes. We report that changes to the chemical potential due to high curvatures increases the surface diffusivity, making it more difficult to evolve porosity in nanoparticle systems. It follows that higher dealloying potentials are required to overcome this increased surface diffusion rate. We then turn to the fabrication of porous refractories where the surface diffusivity is very low. Electrochemical dealloying of refractory alloys does not lead to porosity evolution because the homologous temperature (reaction temperature normalized by the melting point of the remaining component) is too low. To solve this we extended the concept of dealloying to a liquid melt where we can reach much higher temperatures in order to fabricate porous structures. We studied the morphology, dealloying rate and ligament size as functions of composition, temperature, and time, and developed a model for liquid metal dealloying. Lastly, in addition to studying the kinetics of porosity evolution we used this new technique to fabricate refractory-based composites and report the first bicontinuous metal/metal composite materials. We were able to fabricate bulk quantities (~ 1 cm3) and studied their base mechanical properties, e.g. the yield strength. The materials show size-dependent strengthening and provide a new processing route to fabricate bulk nanostructured materials.
dc.format.mimetypeapplication/pdf
dc.identifier.urihttp://jhir.library.jhu.edu/handle/1774.2/39631
dc.languageen
dc.publisherJohns Hopkins University
dc.publisher.countryUSA
dc.subjectNanomaterials
dc.subjectPhysical Metallurgy
dc.subjectKinetics and Phase Transformations
dc.titleFrontiers Of Dealloying - Novel Processing For Advanced Materials
dc.typeThesis
dc.type.materialtext
thesis.degree.departmentMaterials Science and Engineering
thesis.degree.disciplineMaterials Science & Engineering
thesis.degree.grantorJohns Hopkins University
thesis.degree.grantorWhiting School of Engineering
thesis.degree.levelDoctoral
thesis.degree.namePh.D.
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