Method for making metal-nanostructured carbon composites
A method for making covetic metal-nanostructured carbon composites or compositions is described herein. This method is advantageous, in that it provides substantially oxygen-free covetic materials and allows precise control of the composition of the covetic material to be produced. The method comprises introducing carbon into a molten metal in a heated reactor under low oxygen partial pressure, while passing an electric current through the molten metal. The reactor is heated at a temperature sufficient to form a network of nanostructured carbon within a matrix of the metal. After heating the covetic material is recovered from the reactor.
1. A process for preparing a covetic metal-carbon composite material comprising the steps of:
(a) introducing carbon into a molten metal in a heated reactor under an atmosphere comprising a partial pressure of oxygen of not more than about 0.1 Torr, while passing an electric current through the molten metal at a current density of about 10 to about 100 amperes per square centimeter by a pair of electrodes contacting the molten metal and in circuit with an electrical power source; wherein the molten metal fills the reactor to a level such that an exposed surface of the metal is located about one third to one half of the distance from an internal height in the reactor; the carbon is introduced at or below the exposed surface of the molten metal with mixing to distribute carbon within the molten metal; and the reactor is heated at a temperature above the melting point of the metal sufficient to form a network of nanostructured carbon within a matrix of the metal; and
(b) recovering the resulting covetic metal-carbon composite material from the reactor.
2. The process of claim 1 , wherein the metal comprises at least one metal selected from the group consisting of copper, aluminum, silver, gold, platinum, iron, lead, zinc, silicon, tin, and nickel.
3. The process of claim 1 , wherein the metal comprises copper; and the reactor is heated at a temperature of at least about 1150° C.
4. The process of claim 1 , wherein the metal comprises aluminum; and the reactor is heated at a temperature of at least about 700° C.
5. The process of claim 1 , wherein the carbon is a particulate carbon material.
6. The process of claim 1 , wherein the carbon comprises graphite.
7. The process of claim 1 , wherein the reactor is composed of graphite or a ceramic material.
8. The process of claim 1 , wherein the partial pressure of oxygen is in a range of about 0.001 Torr to about 0.1 Torr.
9. The process of claim 1 , wherein the carbon is introduced into the reactor through a feed tube that passes through a shield that extends over at least 50% of the area of the exposed surface of the molten metal.
10. The process of claim 1 , wherein the mixing is non-vortexing mixing.
11. The process of claim 1 , wherein the total amount of carbon introduced into the metal comprises about 0.1 to about 10 percent by weight based on the total weight of the metal and carbon in the reactor.
12. A covetic metal-carbon composite material produced by the process of claim 1 .