Viscoelastic indentation on iodine-treated coal tar pitch Original Research Article

The viscoelastic behavior of iodine-treated coal tar pitch is examined by the use of a Vickers indenter as an efficient micro probe. The charge-transfer complexes formed by the iodine treatment of a coal tar pitch significantly alter the rheological behavior. Five different iodine-treated pitches are prescribed at 100°C by controlling the soaking time in saturated iodine vapor. Two different types of time-dependent indentation tests, tests for a constant rate of indentation penetration and creep tests with a constant indentation load, are conducted. The softening and the creeping are progressively and significantly suppressed by increasing the soaking time. The effects of iodine treatment on these rheological behaviors are quantitatively discussed and related to the molecular/ionic structures in terms of the stress relaxation modulus E(t), instantaneous creep compliance D(0), steady-state creep compliance Ds, creep compliance function D(t), retardation time spectrum L(τ), steady-state shear viscosity ηs, etc.