Low-density interconnected ionic material foams and methods of manufacture

Abstract

Ultralow density ionic material 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 dispersed into a freezable liquid through a suitable fluid exchange. Surface treatments ensure that nanowires remain sufficiently metallic and physically separated. Wire-liquid 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. Sintering or oxidation and reduction treatment of the foam material at elevated temperatures is used to connect the nanowires into an interconnected metallic foam. Metals of the metal foams are then processed into ionic materials including oxides, nitrides, chlorides, hydrides, fluorides, iodides and carbides.

What is claimed is: 
     
         1 . A method for fabricating low density and ultralow density nanostructured ionic material foams, the method comprising:
 (a) forming a liquid dispersion of metal nanowires in a freezable fluid;   (b) freezing the liquid dispersion to form an ice-nanowire structure;   (c) sublimating the ice-nanowire structure to expose a free standing nanowire foam structure;   (d) binding the nanowire foam structure at points of contact to form an interconnected metal foam monolith; and   (e) converting the metals of the metal foam monolith into an ionic material selected from the group of materials consisting of a nitride, an oxide, a chloride, a hydride, a fluoride, an iodide and a carbide to produce an ionic material foam.   
     
     
         2 . The method of  claim 1 , further comprising:
 treating nanowire surfaces with an acid to remove oxide contaminants; and   dispersing treated nanowires in a freezable liquid.   
     
     
         3 . The method of  claim 1 , further comprising:
 treating nanowire surfaces with a surfactant to separate nanowires from each other; and   dispersing treated nanowires in a freezable liquid.   
     
     
         4 . The method of  claim 1 , wherein said metal nanowires are formed from a metal selected from the group of metals consisting of Al, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Ga, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Sn, Sb, La, Nd, Sm, Dy, Pt, Au, Pb, and Bi, and alloys based on one or more of these metals. 
     
     
         5 . The method of  claim 1 , wherein said metal nanowires have an aspect ratio of length vs. diameter within the range of 2 to 1,000,000. 
     
     
         6 . The method of  claim 1 , wherein said dispersion contains wires diluted in volume by a factor of 2 to 10,000. 
     
     
         7 . The method of  claim 1 , further comprising:
 depositing the liquid dispersion in one or more molds; and   freezing the liquid dispersion in the molds.   
     
     
         8 . The method of  claim 1 , wherein said binding of points of contact of the ice-nanowire structure is performed by sintering. 
     
     
         9 . The method of  claim 1 , wherein said binding of points of contact of the ice-nanowire structure is performed by one or more oxidation and reduction cycle(s) performed at elevated temperatures. 
     
     
         10 . A method for fabricating low density and ultralow density nanostructured ionic material foams, the method comprising:
 (a) preparing a nanoporous membrane template;   (b) applying an electrode to one side of the nanoporous membrane template:   (c) forming nanowires within the nanoporous membrane template by electrodeposition;   (d) releasing the formed nanowires from the membrane template;   (e) forming a liquid dispersion of metal nanowires in a freezable fluid;   (f) freezing the liquid dispersion to form an ice-nanowire structure;   (g) sublimating the ice-nanowire structure to expose an interlocked nanowire structure;   (h) binding the interlocked nanowire structure at points of contact between nanowires to form an interconnected metal foam; and   (i) converting the metals of the interconnected metal foam into an ionic material selected from the group of materials consisting of a nitride, an oxide, a chloride, a hydride, a fluoride, an iodide and a carbide to produce an ionic material foam.   
     
     
         11 . The method of  claim 10 , wherein said releasing of formed nanowires comprises:
 etching the membrane template to remove the electrode;   disintegrating the membrane template to release nanowires;   dispersing the released nanowires in a freezable fluid; and   agitating released nanowires to separate and randomize nanowires in the freezable fluid.   
     
     
         12 . The method of  claim 10 , wherein said nanoporous membrane template comprises an anodized aluminum oxide (AAO) membrane, a polycarbonate membrane, a porous mica membrane or a nanochannel glass membrane. 
     
     
         13 . The method of  claim 10 , further comprising:
 treating nanowire surfaces with an acid to remove oxide contaminants; and   dispersing treated nanowires in a freezable liquid.   
     
     
         14 . The method of  claim 10 , further comprising:
 treating nanowire surfaces with a surfactant to separate nanowires from each other; and   dispersing treated nanowires in a freezable liquid.   
     
     
         15 . The method of  claim 10 , further comprising:
 depositing the liquid dispersion in one or more molds; and   freezing the liquid dispersion in the molds.   
     
     
         16 . The method of  claim 10 , wherein said metal nanowires are formed from a metal selected from the group of metals consisting of Al, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Ga, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Sn, Sb, La, Nd, Sm, Dy, Pt, Au, Pb, and Bi, and alloys based on one or more of these metals. 
     
     
         17 . The method of  claim 10 , wherein said metal nanowires have an aspect ratio within the range of 2 to 1,000,000. 
     
     
         18 . The method of  claim 10 , wherein said liquid dispersion contains wires diluted in volume by a factor of 2 to 10,000. 
     
     
         19 . The method of  claim 10 , wherein said binding of points of contact of the interlocked nanowire structure is performed by sintering. 
     
     
         20 . The method of  claim 10 , wherein said binding of points of contact of the interlocked nanowire structure is performed by one or more oxidation and reduction cycle(s) performed at elevated temperatures. 
     
     
         21 . An ionic material foam structure having a bulk density and comprising:
 (a) an interconnected nanoscale ionic material network structure of an ionic material selected from the group of materials consisting of a nitride, an oxide, a chloride, a hydride, a fluoride, an iodide and a carbide to produce an ionic material foam;   (b) wherein the network structure has a density of about 0.1% of the bulk density.   
     
     
         22 . The ionic material foam structure of  claim 21 , wherein the network structure has a density from about 20 g/cm 3  to about 1 mg/cm 3 . 
     
     
         23 . The ionic material foam structure of  claim 21 , wherein said ionic material network structure is formed from one or more metals selected from the group of metals consisting of consisting of Al, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Ga, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Sn, Sb, La, Nd, Sm, Dy, Pt, Au, Pb, and Bi, and alloys based on one or more of these metals.