Lockheed Martin Discloses Carbon Nanotube Infused Metal Fiber Materials

In U.S. Patent Application 20100159240, Lockheed Martin Corporation (Bethesda, MD) inventors disclose compositions that include a carbon nanotube (CNT)-infused metal fiber material which includes a metal fiber material of spoolable dimensions, a barrier coating conformally disposed about the metal fiber material, and carbon nanotubes (CNTs) infused to the metal fiber material.

FIG. 1 shows a transmission electron microscope (TEM) image of multi-walled CNTs grown on a stainless steel mesh substrate. 

A continuous CNT infusion process includes: (a) disposing a barrier coating and a carbon nanotube (CNT)-forming catalyst on a surface of a metal fiber material of spoolable dimensions; and (b) synthesizing carbon nanotubes on the metal fiber material, thereby forming a carbon nanotube-infused metal fiber material, according to inventors Tushar K. Shah, Slade H. Gardner, Mark R. Alberding and Harry C. Malecki.

FIG. 2 shows a scanning electron microscope (SEM) image of 20 micron long CNTs grown on stainless steel mesh substrate. 

Fiber materials are used for many different applications in a wide variety of industries, such as the commercial aviation, recreation, industrial and transportation industries. Commonly-used fiber materials for these and other applications include metal fiber, cellulosic fiber, carbon fiber, metal fiber, ceramic fiber and metal fiber, for example.

Metal fiber materials, in particular, are frequently used in composites to impart electrical conductivity. The use of high aspect ratio metal fibers with random orientation in the composite matrix material allows for low fiber loading while achieving good electrical conductivity. Such low level loadings, however, impart little benefit to the tensile strength of the composite, which is almost unchanged relative the parent matrix material. While increasing the loading of metal fiber might improve tensile strength, it can negatively impact the overall weight of the composite material.

It would be beneficial to provide an agent that allows the electrical conductivity properties of metal fiber materials to be realized in a composite while also enhancing the metal fiber-matrix material interface and, ultimately, the tensile strength of the composite material. The present invention satisfies this need and provides related advantages as well. 

 The Lockheed Martin manufacturing process relates to a composition that includes a carbon nanotube (CNT)-infused metal fiber material which includes: a metal fiber material of spoolable dimensions, a barrier coating conformally disposed about the metal fiber material, and carbon nanotubes (CNTs) infused to the metal fiber material. The CNTs are uniform in length and uniform in distribution.

In some aspects, embodiments disclosed herein relate to a continuous CNT infusion process that includes: (a) disposing a barrier coating and a carbon nanotube (CNT)-forming catalyst on a surface of a metal fiber material of spoolable dimensions; and (b) synthesizing carbon nanotubes on the metal fiber material, thereby forming a carbon nanotube-infused metal fiber material. 

The processes allow for the continuous production of carbon nanotubes of uniform length and distribution along spoolable lengths of tow, roving, tapes, fabrics, meshes, perforated metal sheets, solid metal sheets, and ribbons. While various mats, woven and non-woven fabrics and the like can be functionalized by processes of the invention, it is also possible to generate such higher ordered structures from the parent roving, tow, yarn or the like after CNT functionalization of these parent materials.

For example, a CNT-infused chopped strand mat can be generated from a CNT-infused metal fiber roving. The term "metal fiber material" refers to any material which has metal fiber as its elementary structural component. The term encompasses, fibers, filaments, yarns, tows, tapes, woven and non-woven fabrics, plies, mats, and meshes. 

FIG. 3 shows an SEM image of about 1 micron long CNTs in a mat-like arrangement grown on stainless steel mesh, under high magnification. 

FIG. 4 shows an SEM image of about 1 micron long CNTs with a density of within 10% across a stainless steel mesh substrate. 

Without being bound by theory, when growing CNTs on metal fiber materials, the elevated temperatures and/or any residual oxygen and/or moisture that can be present in the reaction chamber can damage the metal fiber material, although standard measures to minimize such exposure are generally practiced. These issues can be considerable when the metal fiber material is a zero-valent metal that is vulnerable to oxidation. Moreover, the metal fiber material itself can be altered by reaction with the CNT-forming catalyst. That is the metal fiber material can form an alloy with the catalyst at the reaction temperatures employed for CNT synthesis. The CNT-forming nanoparticle catalysts are also vulnerable to high temperature sintering on the surface metal fiber material. This is because the surface structure of metals facilitates particle transport at the surface at the high temperatures employed in CNT synthesis. The barrier coating employed in the invention is designed to facilitate CNT synthesis on metal fiber materials, in addition to preventing sintering and/or alloying of the catalyst on the metal surface.

Without being bound by theory, the barrier coating can provide a thermal barrier for use with low melting metal fiber material substrates such as zinc, aluminum, lead, and tin, for example. This thermal protection can also help reduce the formation of alloys. Furthermore, the barrier coating can also provide a physical barrier preventing sintering of the CNT-forming catalyst nanoparticles at the elevated temperatures by restricting movement of the catalyst nanoparticles on the surface of the metal fiber material. Additionally, the barrier coating can minimize the surface area contact between the CNT-forming catalyst and the metal fiber material and/or it can mitigate the effects of the exposure of the metal fiber material to the CNT-forming catalyst at CNT growth temperatures.