carbon materials, the anodes are followed by graphite electrodes for the production of electric arc furnace (EAF) steel with a market value of six billion €. Smaller markets are cathodes for the production of aluminum (1.4 billion €), fine‐grained graphite for multifold applications (0.7 billion €), furnace linings for blast furnace steel production (0.3 billion €), and carbon electrodes for the production of silicon (0.2 billion €). Other carbon materials like natural graphite, carbon fibers, and graphite for Li‐ion batteries play a minor role versus the conventional carbon products yet. Changes may happen in the near future driven by the need for the efficient storage and use of energy. The market for conventional carbon materials will continue to grow driven by the demand coming from the BRIC countries (Brazil, Russia, India, and China).
New forms of carbon, the carbon nanomaterials, created huge expectations but are currently not produced in an industrial scale with the exception of multiwall carbon nanotubes (MWCNTs). With the recent demonstration of the potential of graphene, a single graphite layer, in microelectronic circuits, we might see the beginning of a new market for carbon materials.
Figure 1.1 Carbon materials and their market value.
1.2 Traditional Carbon and Graphite Materials
Traditional carbon materials that are considered in this chapter are:
Graphite electrodes for melting of steel scrap.
Carbon electrodes for silicon production.
Cathodes for the aluminum electrolysis.
Furnace linings for blast furnaces.
Fine‐grained graphite for silicon production, machining, and others.
With the availability of stable electrical power networks, the electricity was used for heat generation and electrochemical industrial processes. Moisson demonstrated the first steel production with an EAF in 1891. The first EAF plant started its operation in 1906 (Remscheid, Germany). Simply baked carbon electrodes most probably with anthracite and carbon black as filler were used. The electrode diameter was small. In the 1920s more and more electrodes were used, which had been graphitized. The production of EAF steel grew to around 20 million t in 1950. After 1950 the production of EAF steel developed rapidly and exceeded 100 million t in the 1970s. The raw material in this time period was often pitch coke produced by chamber coking. Special coke grades, so‐called needle cokes, produced in the delayed coking process of crude oil refineries were developed later in 1960 and commercialized in 1970. This development represented a quantum leap in the quality of graphite electrodes. The most frequently used electrode became an electrode with 600 mm in diameter. As a consequence, there was substantial progress in the stability and efficiency of the melting process. The average consumption of graphite electrodes was reduced to below 4 kg/t steel. Further improvements in raw material quality, graphite electrode processing, furnace technology, and steelmaking process regulations reduced the graphite electrode consumption to about 2 kg/t steel in average (Figure 1.2). In particular the water spraying on top of the furnace roof was a genius idea to reduce significantly the graphite consumption due to oxidation. The lowest graphite consumption figure achieved so far was 0.74 kg/t with an electrode with a diameter of 800 mm on a direct current (DC) furnace.
Graphite electrodes are produced in mostly all continents. Traditional graphite electrode producers are GrafTech International, the SGL Group, and the Japanese producers Tokai, SDK, and Nippon Carbon. Later electrode producer followed in India and recently in China (Figure 1.3).
The production of EAF steel reached about 550 million t in 2020. Much stronger was the growth in blast furnace steel (Figure 1.4). This situation was created by the economic growth in China, which, as a young economy, is suffering the steel scrap required for EAF process. This will change over the times and the EAF process will pick up.
Figure 1.2 Development of the specific consumption of graphite electrodes.
Figure 1.3 Graphite electrode producers and their production capacity (2018). SGL: Since 2017 Showa Denko.
Figure 1.4 Blast furnace and EAF steel production.
Graphite electrodes are exposed to extreme conditions during the melting of steel. From a tip temperature of several thousand degrees centigrade, the temperature falls to about 1000 °C close to the roof of the furnace and to a few hundred degrees centigrade on top of the roof. Lengthwise and transversal temperature gradients create extensive thermal stresses. These high stresses initiate material cracks that can lead to severe material losses during the melting process (Figure 1.5).
Figure 1.5 Graphite electrode. (a) Graphite electrode with crack in the joint area. (b) Finite element simulation of temperature distribution.
The biggest disadvantage of these graphite losses is the expensive interruptions in the steel production chain. Thus the efforts of the graphite electrode producers focused on the minimization of these losses by the use of improved raw materials improved the process consistency, impacting the thermal compatibility between the connecting pin and the graphite electrode. These are only some approaches to minimize material losses and to enable a high efficiency of the scrap melting process. Although graphite electrodes have been produced since almost hundred years, the complete understanding was never accomplished.
Carbon electrode means a solely baked and not graphitized electrode composed of calcined anthracite and or synthetic graphite. These prebaked electrodes are an alternative to the Söderberg electrodes, a green paste that is baked and graphitized during its application in the EAF. Carbon electrodes reach diameters up to 1400 mm (Figure 1.6). They are mainly used for the production of metallic silicon and phosphorus. Notably the production of silicon doubled in between 1990 and 2010 (Figure 1.7). The strongest driver was the solar industry. The number of carbon electrode producers is rather small (Figure 1.8). The
