Industrial Carbon and Graphite Materials. Группа авторов
target="_blank" rel="nofollow" href="#ulink_0fb838b6-481f-5bf7-8c5a-464ac51c8eb8">Figure 1.10 Cathode production by grade.
Figure 1.11 Cathode producers and their capacity. SGL: Since 2018 COBEX.
Figure 1.12 Increase in cell amperage over the last 70 years.
Carbon and graphite bricks are used to construct the hearth of a blast furnace and basic oxygen furnace (BOF) for the production of iron and steel. Carbon and graphite materials are first choice in a chemically aggressive environment at high temperatures (Figure 1.13). The demand for blast furnace steel was consistently growing on a global basis, but the regional developments are different (Figure 1.4). The growth flattened in the 1970s in the Western economies including Japan. The growth happened from there on in Asia, first went to South Korea, then to China, and later to India. The production capacities for furnace linings are located in Germany and Japan, as well as in China and Russia (Figure 1.14).
Figure 1.13 Test assembling of a blast furnace lining.
Figure 1.14 Hot metal production in blast furnaces.
Figure 1.15 Blast furnace diameter.
Over the last 20 years, the increasing BOF steel production was achieved with fewer furnaces. The furnace size also referred to as the diameter of the heart increased from a few meters up to 15 m (Figure 1.15). Today a single blast furnace produces about four million t of liquid iron annually. The lifetime of the lining reaches typically 12–15 years, but in few cases 20 years have been demonstrated with a production of 60 million t iron during such a campaign. It is evident that the steel companies are very conservative in changing lining concepts or the grades of the lining material. Challenge is the chemical erosion caused by the interaction between the liquid iron and the carbon material. One improvement in the recent past was the introduction of so‐called microporous linings with mainly pores below 1 μm in diameter. The right selection of anthracite can significantly elongate the lifetime of the furnace cycle. Hence, best chemical resistance and mechanical wear resistance are the goals for development.
So far we have considered coarse‐grained carbon and graphite materials. Specialty graphite is a polygranular material with very fine grain sizes. To achieve a high isotropy, not only the raw material is carefully selected among isotropic cokes, but also the process of forming by isostatic pressure application supports the isotropy. This graphite material is known as iso‐graphite. Its main application is the production of silicon single crystals (Figure 1.16) for the semiconductor industry and the production of polysilicon for the solar industry (Figure 1.17). Other applications are electrical discharge machining, casting of non‐iron metals, and many other applications.
Figure 1.16 Silicon single crystal production.
Figure 1.17 Demand for fine‐grained graphite.
The main production capacities are located in Japan (Figure 1.18). China entered this market recently and strives to become a serious competitor in this field.
Figure 1.18 Fine‐grained graphite producer.
The mechanical strength is the key quality parameter for iso‐graphite. Fundamentally the strength of graphite increases with decreasing grain size. This led to a decrease in grain size during the last decades to nowadays few microns and mechanical strength of up to 100 MPa. The future challenging task is the process technology and automation to produce bigger block sizes at high process yield.
It was shown that traditional carbon and graphite materials have a long‐lasting history. During this history they have improved their quality and reliability. Their consumption in their respective application was reduced. Despite this long history there is still room for improvement and open questions for basic research. The industrial perspectives for these materials are prosperous. The most probably ongoing growth in the BRIC countries will provide a constant grown in the demand for graphite electrodes, cathodes, and furnace linings. Iso‐graphite will benefit from the global expansion of clean solar energy.
1.3 Modern Application of Carbon Materials
Carbon fibers are thin (diameter = 7 μm), light (real density = 1.8 g/cm3), strong (strength up to >6 GPa), and stiff (Young’s modulus up to 900 GPa) (Figure 1.19). These fibers exceed any other fiber material in its specific properties and come close to the theoretically predicted properties of pure graphite. The properties depend on the temperature weakly only. Only the presence of oxygen limits the application at elevated temperatures. Carbon fibers can be made from different fiber precursors. These fiber precursors can be polyacrylonitrile (PAN), pitch, or rayon. During the history of the carbon fiber development, PAN‐based carbon fiber won the race. Reasons had been the relatively easy processing and the wideness of achievable mechanical properties. Mesophase pitch‐based carbon fibers are only competitive in applications with extreme stiffness. Embedded in a polymer matrix (carbon fiber reinforced polymer [CFRP]) or a carbon matrix (carbon fiber reinforced carbon [CFRC]), superior material properties are the outcome. These spectacular properties were soon recognized for military application,