Tribochemistry of Hard-Core Reverse Micelles

The hard-core reverse micelles considered in this chapter are composed of an amorphous Ca (Mg) carbonate (or borate) colloidal core surrounded by benzensulfonate, phenate or salicylate molecules strongly bonded to the colloidal 

The shape and size of micellar particles can be determined using transmission electron microscopy (TEM) and photo-correlation spectroscopy (PCS). The size distribution of the hard-core RMs measured by PCS was confirmed by TEM technique the hard-core RMs micelles of carbonate-sulfonate had mean particle sizes between 10 and 20 nm while the neutral sulfonate formed micelles with a diameter of 2 nm (Chinas-Castilio and Spikes, 2000). 

Following are described the physical properties of hard-core reverse micelles, the effect of changing the surfactant, the exchange solubilizates, and some specific aspects, e.g., technological relevance. To clarify this, the following five topics are considered  

The term hard-core RMs is used to describe dispersions containing an excess of colloidal carbonate over that required to neutralize the sulfonic acid. The excess is found in calcium carbonate trapped in a micellar structure. The total base number (TBN) of the additive so obtained is 368 mg KOH/g of oil. The crude additive consisted of 33 wt% CaC03 (Delfort et al., 1995 Giasson et al., 1992). Some typical results of the core particle with the overall diameter and the detergent layer thickness are shown in Table 3.6 (Marsh, 1987). 

Considering these results, the main difference between the antiwear action of the ZDDP soft-core RMs and the hard-core RMs is clear. In the case of ZDDP soft-core RMs, the anti wear film formation requires that chemical reactions occur between the additive and the metallic surfaces. In the case of hard-core RMs, the mineral material (CaC03) is directly introduced to the sliding contact and undergoes small physicochemical changes during the film build-up. Consequently no chemical reaction with the substrate surfaces is required. 

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