Flexural strength of polygranular carbon and graphite materials after various heat treatments and their correlation with porosity

Abstract

Concerns the changes of flexural strength of fine grained extruded carbon and graphite materials caused by heat treatment between 1800 and 3000K. Measurements of flexural strength, bulk density and pore size distribution were performed at room temperature after heat treatment, whereas the thermal (reversible and irreversible) bulk expansion was measured in situ with a pushrod dilatometer up to 2700K. A correlation of all data points measured is discussed to explain the strength changed during heat treatment. A distinction is made between geometric effects, caused by isotropic bulk dilatation or shrinkage during heat treatment, and quality effects, consisting mainly of crystalline rearrangement processes. Special emphasis is given to 'sulphur-puffing and its influence on strength and porosity of the samples.