Standard Test Method for Air Oxidation of Carbon and Graphite in the Kinetic Regime

Importancia y uso:

5.1 This test method can be used to measure the rate of oxidation for various grades of manufactured carbon and graphite in standard conditions, and can be used for quality control purposes.

5.2 The following conditions are standardized in this test method: size and shape of the graphite specimens; their placement in the vertical furnace with upwards air flow; the method for continuous weight variation measurement using an analytical scale with under-the-scale port; the air flow rate, which must be high enough to ensure that oxidation is not oxygen-starved at the highest temperature used; the initial and final points on the weight loss curve used for calculation of oxidation rate.

5.3 This test method also provides kinetic parameters (apparent activation energy and logarithm of pre-exponential factor) for the oxidation reaction, and a standard oxidation temperature. The results characterize the effect of temperature on oxidation rates in air, and the oxidation resistance of machined carbon or graphite specimens with standard size and shape, in the kinetic, or chemically controlled, oxidation regime. This information is useful for discrimination between material grades with different impurity levels, grain size, pore structure, degree of graphitization, or antioxidation treatments, or a combination thereof.

5.4 Accurately determined kinetic parameters, like activation energy and logarithm of pre-exponential factor, can be used for prediction of oxidation rates in air as a function of temperature in conditions similar to those of this test method. However, extrapolation of such predictions outside the temperature range where Arrhenius plots are linear (outside the kinetic or chemically controlled regime of oxidation) should be made with extreme caution. In conditions where (1) oxidation rates become controlled by a mechanism other than chemical reactions (such as in-pore diffusion or boundary transport of the oxidant gas), or (2) the oxidant supply rate is not large enough to prevent oxidant starving conditions at high temperature, prediction of oxidation rates using kinetic parameters determined with this test method will produce overestimated results.

Subcomité:

D02.F0

Referida por:

C1793-15R24, C1783-15R24, C0781-20, D8289-20

Volúmen:

05.05

Número ICS:

71.060.10 (Chemical elements)

Palabras clave:

activation energy; air; carbon; graphite; kinetic regime; oxidation rate; pre-exponential factor; standard oxidation temperature; temperature;