Temperature Dependence of the Thermal Coefficient of Linear Expansion

The thermal coefficient of linear expansion (TCLE) of grade MPG-7 structural fine-grained graphite manufactured using the method of pressing into a “dead” matrix is experimentally determined for the first time in the temperature range 1650‒2350 К. A method with which the sample temperature diagnostics is carried out outside the TCLE measurement range is implemented. The experiments were carried out in a steady thermal mode on samples cut out in directions parallel and perpendicular to the graphite pressing direction. It is pointed out that a sample cut in the direction perpendicular to that of pressing features TCLE values higher than those in the sample cut out in the direction parallel to that of pressing. This points to the fact that grade MPG-7 graphite has a TCLE anisotropy. The temperature dependences of grade MPG-7 graphite TCLE are compared with the data given in the literature for conventional grade MPG-6 graphite manufactured using the piercing pressing method through a die carrier. An analysis of the TCLE values of grades MPG-6 and MPG-7 graphite has shown that they are within the limits of relative expanded measurement uncertainty equal to around 17%. The TCLE measurement results for fine-grain graphite of conventional MPG-6 and MPG-7 grade were used for comparison with the data for fine-grained isotropic isostatic graphite of modern grades GIP-4 and DE-24 in the temperature range 1300‒2300 К. In manufacturing graphite of GIP-4 and DE-24 grades, a method of volumetric isostatic pressure was implemented. The specific feature of this graphite is that it does not have a TCLE anisotropy. A comparison of the obtained results from measurements of TCLE of fine-grained graphites of all considered grades has shown that isotropic isostatic graphites of grades DE-24 and GIP-4 have lower TCLE values in comparison with fine-grain graphites of grades MPG-6 and MPG-7. A conclusion has been drawn that it is inexpedient to use anisotropic graphite of grades MPG-6 and MPG-7 for manufacturing thermal power equipment.