Impregnation of Electrodes and Other Carbon/Graphite Articles

W.M. Zadorsky

1. Introduction

In manufacture of carbon/graphite articles like electrodes, crucibles, components of chemical processing equipment etc., repeated impregnation with tar, pitch and other viscous liquids is carried out.

The pores in the pieces to be impregnated, however, are always filled with air. The air may block penetration of impregnant into some of such pore cavities. Even though the impregnation step may be repeated, the impregnation will remain incomplete and the quality of final product unsatisfactory. With articles like Soderberg electrodes, this may lead to breakdown during a heat, resulting in severe losses.

Furthermore, many of the impregnants used are hazardous. It is therefore desirable to carry out the impregnation step not more than once for considerations of production rate, product quality, labor safety and environmental protection alike.

The project is aimed at developing a rapid, effective, environmentally friendly and low-cost method to ensure perfect impregnation of carbon/graphite articles with organic impregnants.

2. Project Description
2.1. Process Development

The method requires only minor additions to the existing equipment. It relies on a simple three-step treatment of the carbonaceous material directly before impregnation. The pretreatment removes all air trapped in the open pores and involves the following steps carried out in quick succession:

heating the charge,
introducing a specific non-reactive gas, and
desorption of the gas.

It activates every open pore and results in their quick and complete filling during the impregnating step.

2.2. Materials and Equipment

The non-reactive gas characteristics and the timing are unique to each carbon/impregnant system. This necessitates their tailoring to the system at hand. The gas will invariably be selected among those inexpensive and readily available ones.

2.3. Process and Product Characteristics

Laboratory and industrial-scale experiments with articles over 1 m in diameter like graphite electrodes revealed that the method may cut down the number of impregnation steps to unity. The impregnation step as such was effected very rapidly and resulted in complete filling of the pores. This increased production rate, enhanced product quality and reduced exposure time and emissions of pollutants.

3. Novelty

The method is believed to be patentable because it has not been disclosed and no analog to it has been found in the literature.

4. Marketing

The market for electrodes and other carbon/graphite articles is ever expanding. This is due to the proportion of steel produced in electric arc furnaces increasing steadily throughout the world. Another important consumer of electrodes is aluminum industry with its rapidly growing outputs.

The cost of equipment adaptation to the new process is negligible as is the running cost for the new appliances.

At the customer's side, the gain will come directly from reduced prices and also indirectly from improved service properties and extended life of product.

5. Applications

Electrodes, heat exchangers, crucibles, heat insulators, heat exchangers, fittings and valves, absorbers, rectification columns, electrolytic tanks, anti-friction materials and other products of carbonization are among possible applications.

Contact:
Prof.William Zadorsky
PEF&PCPC

Information supplied by the Author October 1999.  Page last updated: July 03, 2005