Graphite Electrode Thermal Expansion is the amount that a material expands at a certain temperature. This is a very important property for many refractory products, such graphite. It is crucial in the design and construction of high-performance equipment. The demand for graphite electrodes is expected to continue growing as the steel industry continues to be strong. However, there are other emerging industries such as electric cars and renewable energy that could drive this market's growth. Technological advancements and innovations of alternative carbon-based products could influence the demand even further.
The direction of the grains and their orientation within a given material determines how much thermal expansion a certain material will experience. Graphite is one example of a material that tends towards greater expansion perpendicularly than parallel to the grain. This is a result of the directional orientation of the carbon crystals within the pyrolytic graphite. Plotting a material's relative elongation versus a temperature is often used to determine its thermal expansion. The curves produced are called the coefficients of thermal expansion curve (CTE).
A CTE plot is usually plotted in a logarithmic format and includes the ranges of temperatures that have been tested. The mean of the curve can then be calculated to determine a linear correlation between the coefficients of thermal contraction and the temperature of the sample. The linear model obtained can be used for calculating the linear coefficients of thermal expansion in a new test.
Graphite is typically negative in CTE, measured on the A-axis. It has an absolute value of -1.35x10-6K-1 (according model A; 176K for model B). This is due the Lifshitz Effect, where a CTE of -1.35x10-6 K-1 is produced by vibrational modes that are out of plane.
For the C-axis it is a bit trickier. It is possible to use a similar approach to determine the negative CTE for a sample. However, it is not as straightforward due the non-uniformity in the lattice parameters along the c axis.
Despite these challenges, models A and B are capable of describing the thermal expansion of graphite reasonably well over a large temperature range. Both models can describe the positive thermal growth of a oriented graphite using very few fitting parameters. This is especially remarkable, given that a (T) values are usually obtained by numerical differentiation from experimental data. This process is prone to errors. Both models fit the a-T data well when compared by using khn2, Akaike, and Bayesian info criteria.
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