Method for making metal-carbon composites and compositions
A method for making covetic metal-carbon composites or compositions by electron beam melt heating under vacuum (pressure <10 −3 Torr) is described herein. This fabrication method is advantageous, in that it provides oxygen-free covetic materials in a process that allows precise control of the composition of the covetic material to be produced. The method described herein also can be applied to produce multi-element-carbon composites within a metal or alloy matrix, including high melting temperature materials such as ceramic particles or prefabricated nano- or micro-structures, such as carbon nanotubes or graphene compounds. The covetic reaction between metal and carbon takes place under the influence of flowing electrons through the melted metal-carbon precursor. This process creates strong bonding between nanocarbon structure and the metal elements in the melt.
1. A method for preparing a covetic metal-carbon composite material comprising the sequential steps of:
(a) passing an electric current of less than about 1 ampere through a precursor mixture of a metal and a carbon material in an electrically conductive, grounded vessel by irradiating the mixture with an electron beam under vacuum at a pressure of less than about 10 −3 Torr, wherein the electron beam has a sufficient beam energy to heat the mixture to a temperature below the melting point of the mixture at a heating rate in the range of about 1 to about 10° C. per minute (° C./min) to expel dissolved gasses therefrom;
(b) increasing the electron beam energy to a level sufficient to heat the precursor composition at a heating rate in the range of about 10 to about 200° C./min to a temperature sufficient to melt the mixture, cause convention mixing therein, and thereby convert the precursor mixture to a covetic metal-carbon composite material;
(c) terminating the electron beam to allow the mixture to cool to ambient room temperature while maintaining the pressure at less than about 10 −3 Torr; and
(d) recovering the resulting covetic metal-carbon composite material from the vessel at ambient atmospheric pressure.
2. The method of claim 1 , wherein the metal is selected from the group consisting of copper, aluminum, silver, gold, platinum, iron, nickel, and alloys thereof.
3. The method of claim 1 , wherein the metal is in the form of a powder.
4. The method of claim 1 , wherein the metal comprises copper.
5. The method of claim 1 , wherein the carbon material is a particulate carbon material.
6. The method of claim 5 , wherein the particulate carbon material comprises carbon microparticles, carbon nanoparticles, or a combination thereof.
7. The method of claim 1 , wherein the vessel is a grounded graphite crucible.
8. The method of claim 1 , wherein the pressure in steps (a), (b) and (c) is in a range of about 10 −3 Torr to about 10 −7 Torr.
9. The method of claim 1 , wherein the carbon material comprises graphite.
10. The method of claim 1 , wherein the carbon material comprises carbon black.
11. The method of claim 1 , wherein the carbon material is selected from the group consisting of graphene, carbon nanotubes, and carbon nanofibers.
12. The method of claim 1 , wherein the carbon comprises carbon nanotubes, carbon nanofibers, or a combination thereof, in which the nanotubes, nanofibers, or both also comprise nanoparticles of one or more metal attached to or encapsulated within the nanotubes or nanofibers.
13. The method of claim 1 , wherein the electron beam is rastered across the precursor mixture during step (a), step (b) or both steps (a) and (b).
14. The method of claim 1 , wherein the metal comprises copper and the carbon material comprises graphite or carbon black.
15. The method of claim 1 , wherein the metal comprises copper and the carbon material comprises graphite.
16. The method of claim 1 , wherein the carbon comprises about 1 to about 10 percent by weight (wt %) based on the total weight of the precursor mixture.