Graphite electrode for electrothermic reduction furnaces, electrode column, and method of producing graphite electrodes

Abstract

A graphite electrode for an electrothermic reduction furnace is formed from anode grade coke and graphitized at a graphitization temperature below 2700° C. The resulting electrode is particularly suited for carbothermal reduction of alumina. It has an iron content of about 0.05% by weight, a specific electrical resistivity of above 5 μOhm·m, and a thermal conductivity of less than 150 W/m·K. The graphite electrode is manufactured by first mixing calcined anode coke with a coal-tar pitch binder, and a green electrode is formed from the mixture at a temperature close to the softening point of the pitch binder. The green electrode is then baked to carbonize the pitch binder to solid coke. The resultant carbonized electrode, after further optional processing is then graphitized at a temperature below 2700° C. for a time sufficient to cause the carbon atoms in the carbonized electrode to organize into the crystalline structure of graphite.

Description

CROSS-REFERENCE TO RELATED APPLICATION [0001] This application claims the benefit under 35 U.S.C. § 119 (e), of copending U.S. Provisional Application No. 60 / 570,984, filed May 12, 2004.BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present invention relates to graphite electrodes for electrothermic reduction furnaces, in particular for the production of aluminum, titanium, silicon, ferroalloys, phosphorous. The invention also pertains to a method of producing such graphite electrodes. [0004] 2. Description of the Related Art [0005] For a century the aluminum industry has relied on the Hall-Heroult process for aluminum smelting. In comparison with processes used to produce competing materials, such as steel and plastics, the process is energy-intensive and costly. Hence, alternative aluminum production processes have been sought. [0006] One such alternative is the process referred to as direct carbothermic reduction of alumina. As described in U.S. Pat. No. ...

AI Technical Summary

Benefits of technology

[0016] It is accordingly an object of the invention to provide a graphite electrode for electrothermic reduction furnaces, in particular for the production of aluminum, titanium, silicon, ferroalloys, and phosphorous, as well as a production method for such electrodes and electrode columns, which overcome the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which provide for graphite electrodes that do not contaminate the melt with iron, which can be used in melt furnace atmospheres that are rich in CO, and which are economical to produce.

Problems solved by technology

In comparison with processes used to produce competing materials, such as steel and plastics, the process is energy-intensive and costly.

Unless recovered, these volatile species represent a loss in the yield of aluminum.

To achieve electrical resistivities below 10 μOhm m, such graphite electrodes are produced using well-ordered needle cokes and they are graphitized at temperatures above 3000° C. The use of costly needle coke and the high electricity costs for graphitization bar such electrodes from being used in low-power electric furnaces that are used for producing non-steel materials.

Hence, the increased iron content can contaminate the melt and cause high electrode erosion in melt furnace atmospheres that are rich in CO, such as in the case of carbothermic reduction of alumina.