Preparation electrodes for industrial applications in metal smelting is a multi-stage process. In the first stage of preparation, ground calcined cellulose fibers are mixed with a binder capable of being coked to form a carbon paste that has not been baked. This is then extruded to form pre-shaped electrodes. The carbon-paste electrodes can then be used as electrodes in the smelting processes of various metals such as aluminum. The electrodes used for this process must be strong, and have good conductivity. The smelting process of aluminum is energy-intensive and requires an electrode with high performance that can withstand higher temperatures. The electrodes must also be able to withstand the abrasion and corrosion caused by the molten metal.
In the past, coal pitch has been used to bind these carbon-paste electrodes. However, a number of investigations have shown that the polycyclic aromatic hydrocarbons in coal tar pitch are carcinogenic. Moreover, the vapors which escape in a gaseous state during the production and usage of such carbon-paste electrodes pose a health hazard to the industrial workers. As a result of this, many countries in western Europe have already introduced regulations that protect industrial workers from the hazardous binder vapors.
In order to minimize the potential hazards associated with the use of coal tar pitch, an alternative binder has been investigated. The purpose of this study was the investigation of the thermal and mechanical characteristics of an electrode-paste that contains petroleum coke as a binder. The results showed that carbon-paste containing petroleum coke, 68 wt% of solids, and a binder of 32 wt% of bitumens can be used for electrodes with high electrical conductivity while maintaining dimensional stability.
Carbon-paste can be used in the smelting aluminum in any electric furnace, including the Soederberg system or refractory linings in blast furnaces. Depending on their use, electrodes come in a variety of dimensions. For this reason it is important that the raw materials used to make these carbon-paste electrodes are analyzed for their dimensional behavior.
A method was developed to automate the measurement of the dimensional properties of raw materials when preparing Soderberg electrode paste. The method is built on the thermomechanical technique (TMA).
During TMA measurements, the samples are heated and cooled under constant pressure. The curves obtained allow for the determination of the dimensional behavior at different temperature levels. The measurements may be performed either in a controlled or an inert atmosphere.
The patented method for the preparation of the carbon-paste electrodes allows for the use of an inexpensive, convenient and easy-to-use device that can be used to hand press the conducting refractory powders from a variety of different sources. These include carbons, titanium oxides and bulk chemically modifying carbon powders. These materials have been compared to glassy carbon electrodes as well as known carbon-paste electrodes using voltammetric, chronoamperometric and stripping voltammetric tests.
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