It has been reported that there is a dispersed phase in vacuum residua consisting of spherical particles in the 5-10 nm size range. These vacuum residua behave as Newtonian fluids at 93 degrees C (366 K). We suggest that temperature dependent theological studies are useful for studying temperature dependent phase behavior in such vacuum residua, because the Peclet number is so small. As discussed by Russel, the appearance of non-Newtonian behavior in such normally stable dispersions is caused by a change in structure. In this work we investigate the response of Ratawi vacuum residue to applied stresses in the 25-400 degrees C temperature range. Our experimental data can be understood in terms of the well-studied theology of hard-sphere dispersions. In particular we infer that two phase transitions occur as the temperature is changed from 93 degrees C. We infer that a liquid to solid transition begins as the temperature is reduced below 65 degrees C. This transition is analogous to the order-disorder transition for hard sphere dispersions initially. We also infer that a flocculation of the dispersed phase occurs above 150 degrees C. This change in structure is analogous to a flocculation of polymerically stabilized hard spheres that occurs when the layer of polymer becomes too thin to prevent van der Waals forces from dominating the repulsive forces generated by the polymer layer on the particles. We suggest the physicochemical nature of the liquid to solid phase transition that begins below 65 degrees C is important for an understanding the rigidity, and the shrinking tendency of asphalt binders, while the physical flocculation that occurs at higher temperatures is important for an understanding upgrading chemistry during refining.