Low-density interconnected metal foams and methods of manufacture

Abstract

Ultralow density pure metal foams, with density approaching 0.1% of the bulk density, and synthesis methods using interconnected metallic nanowires are provided. Nanowires of various sizes and metals are synthesized by electrodeposition into nanoporous templates such as anodized aluminum oxide or polycarbonate. The templates are etched away and the nanowires are dispersed into water through a suitable fluid exchange. Surface treatments ensure that nanowires remain sufficiently metallic and physically separated. Wire-water solutions can be dropped directly into liquid nitrogen in the form of droplets or placed into molds of various shapes. A freeze drying technique is employed to turn the resulting ice-wire mixture into a freestanding, low-density foam composed of interlocked nanowires. Finally, sintering or oxidation and reduction treatment of the foam material at elevated temperatures is used to connect the nanowires into an interconnected metallic foam, greatly improving the strength of the structure.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application is a 35 U.S.C. § 111(a) continuation of PCT international application number PCT / US2016 / 064218 filed on Nov. 30, 2016, incorporated herein by reference in its entirety, which claims priority to, and the benefit of, U.S. provisional patent application Ser. No. 62 / 261,211 filed on Nov. 30, 2015, incorporated herein by reference in its entirety. Priority is claimed to each of the foregoing applications.[0002]The above-referenced PCT international application was published as PCT International Publication No. WO 2017 / 095925 on Jun. 8, 2017, which publication is incorporated herein by reference in its entirety.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT[0003]This invention was made with Government support under BRCALL08-Per3-C-2-0006, awarded by the Defense Threat Reduction Agency; under DMR-1008791, awarded by the National Science Foundation; and under Contract DE-AC04-94AL85000 between Sandia Corporation ...

AI Technical Summary

Benefits of technology

The present technology describes a way to make low cost, ultralow density pure metal foams using interconnected metallic nanowires. These materials have highly porous foam structures with scalable and macroscopic overall sizes. The nanowires are formed using a template and electrodeposition, which allows for the synthesis of a wide variety of metallic nanowires as the building blocks for the fo�. The nanowires are then bonded to form the final foam without significantly increasing the density. This technology can be used for exploration of lightweight materials, coatings, photovoltaics, thermoelectrics, heat exchangers, hydrogen storage and catalysts, and may have transformative impacts in advanced materials and energy research. The nanowire surface treatments with L-ascorbic acid help ensure that the nanowires remain sufficient metallic, which facilitates the subsequent bonding processes during sintering.

Problems solved by technology

Although a number of methods for preparing pure metal nanoparticles exist, there are relatively few synthetic processes for producing bulk, monolithic forms of nanostructured metals that have been developed.

Conventional methodologies for fabricating monolithic metallic nanoporous materials or foams have limited practical applications and are difficult to adapt to large scale production because of their complicated procedures and use of expensive materials.

Although selective dealloying approaches have been effective for fabricating some nanoporous metallic structures, the diffusion-controlled processes of electrochemical or acid etching limit the practical dimensions of the structure that can be formed.

This further limits the size and morphology of the starting structure and final metal foam.

Additionally, many metals are readily oxidized in air at room temperature resulting in the formation of oxides.

Oxides may form on the surfaces of the metal structure that may interfere with the functionality of the final foam.

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