Rapoport-Samoilenko test for cathode carbon materials-II. Swelling with external pressure and effect of creep

The creep strain of an anthracitic commercial cathode material used for aluminium production has been measured on solid cylinder samples. Experimental results have been obtained using a Rapoport-Samoilenko-type apparatus for virgin material at room and high temperatures as well as for electrolyzed material under loading. When an external pressure is applied to the material, the reduction of sodium expansion is explained by the effect of compressive creep deformation related to the sodium penetration into the binder phase of carbon. The creep strain is much larger when sodium is absorbed under pressure compared with the creep strain when an external pressure is applied to the material after binder phase sodium saturation. A constitutive model for creep deformation in the binder phase of cathode carbon materials which is able to reproduce the relationship between the creep strain, external pressure and time during the Rapoport-Samoilenko-type test has been developed. The model has been extended to a three-dimensional stress-strain state. The calculations demonstrate that creep has to be considered in order to obtain realistic stress-strain results.