Structural factors determining the change in young's modulus of polycrystalline carbon materials in heat treatment
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The structural factors determining the change in Young's modulus of polycrystalline carbon materials based on fired coke (type ARV) and unfired coke (type MPG) in relation to treatment temperature t in the 1000–3200°C range were investigated. The microstructure of the specimens was characterized by the density and coefficient of coherence, which was determined from the ratio of the electrical conductivity of the material to the electrical conductivity of its porosity-free volumes. The degree of perfection of the layers of specimens with a graphitic structure was determined from the magnetic resistance. It was established that the change in Young's modulus in this range of treatment temperatures is determined by the change in Young's modulus of the porosity-free volumes E0 ∼ c44 and in the coefficient of coherence. The value of E0 decreases sharply with an increase in t from 1000 to ∼1800°C and after ∼2400°C it is practically independent of the degree of perfection of the graphite-like layers. The coefficient of coherence increases in density with an increase in t from 1000 to ∼2000°C and decreases as the result of appearance of disk-shaped cracks in a change in t from 2400 to 3200°C. The physical reasons for the rules found were analyzed.
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