Rheological investigation of coal-tar pitch during its transformation to mesophase

Low shear rheological behaviour of two-phase mesophase pitch

“…Thus for the systems presented here deformation is more likely at low mesophase contents with large drops and at high shear rates. The deformation of mesophase spheres into oblate spheroids in a coal tar pitch such as this one where the mesophase spheres are stabilised by the QI attached to the surfaces was demonstrated by Collett & Rand [11], but at much higher temperatures (around 400 °C) than the temperatures of measurement employed here.…”

“…During transformation to mesophase, the pitch materials show shear-thinning character, but at these temperatures they also behave as emulsions and the dispersed mesophase droplets can be deformed [11]. It has been shown that such two phase systems show non-Newtonian behaviour even at lower temperatures closer to softening [12] [3].…”

Rheological study of eucalyptus tar pitches

“…On the other hand, fossil pitches with a high degree of polymerization, mainly those having some mesophase content (nematic liquid crystals formed by the packing of large planar molecules22), usually display highly pseudoplastic behavior at low shear rates 23, 24. Collet and Rand25 suggested that coal tar pitches are initially Newtonian in character, but non‐Newtonian behavior appears when the average molar mass increases as a result of the polymerization process and volatilization of low molar mass species. The more accepted reason for this is that shearing can orient the larger and more planar molecules.…”

“…This behavior is characterized by a declining apparent viscosity at the time when the material is subjected to shearing at constant shear rate and temperature. Usually this effect is observed in the initial seconds or minutes after the spindle starts spinning and is attributed to the high degree of condensation and crosslinks among the molecules, which makes the material display an elastic component in the flow beyond the viscous one (viscoelastic behavior) 14, 25…”

Measurement of Vacuum Residue and Asphaltene Fluid Properties at Process Conditions

“…Allowing for empirical dependence on the thickness of the liquid film, δ, and the length of the liquid bridge, D, Aminu et al 10) proposed the following semi-empirical expression: (12) where k1, k2 and k3 were empirical constants. The total force on a liquid bridge for D ≥ b was (13) The coefficients were determined from a series of experiments with calibration oils of known viscosity (1-22 Pa s), giving best-fit values of k1 = 400.0, k2 = 0.752 and k3 = 0.677. Asprino 11) extended the range of the calibration to ca.…”