No abstract

No abstract

No abstract

The mechanism of overbasing of additives used in lubricating oils is studied. Overbased calcium sulphonates, the most widely used, are examined. Although the geometrical and physical nature of colloidal carbonate particles has been well studied, little is known about the fundamental aspects and mechanism of the overbasing process. In this paper, assessment of the physical and/or chemical nature of the reaction is made from equations related to the chemical engineering model of the shrinking spherical particle. The results show that the overbasing process is under diffusion control, and the chemical reaction is not determining.

Dilute solutions of a styrene-hydrogenated butadiene copolymer, a viscosity index improver, were studied by static and dynamic light-scattering techniques. In n-hexane ( a model solvent for paraffinic oils) and a mineral base oil, aggregation is observed below 30°C. In cyclohexane ( a model solvent for napthenic oils) only isolated polymers are present in the whole temperature range.Kinematic viscometric measurements from 20 to 6OoC in the mineral oil show a continuous increase of the intrinsic viscosity together with a decrease of kH, the Huggins coefficient, from 2.5 to 0.5. At shear rates between 5000 and 40000 s-', a large shear thinning is observed a t room temperature for the polymer in the mineral base oil. This effect progressively disappears as the temperature increases and the suspension becomes Newtonian near 100°C. All results can be interpreted in terms of micelle formation. 0 1994