Published: Jan 2009
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IN THIS CHAPTER WE DESCRIBE ANALYTICAL AND spectroscopic techniques and physical and chemical tests that are used to establish structural/compositional identity and physical and chemical properties of the additives, base stocks, and finished lubricants. Tribological (mechanical) tests are also included and so are the performance requirements of the finished lubricants and their in-service condition monitoring. The chapter also contains discussion pertaining to the new lubricant approval process and a list of ASTM and other standardized tests that are commonly used to assess lubricant quality. Lubricant additives are either supplied individually or as a performance package for the user to blend in the base fluid of his or her choice to make a finished lubricant. The former is the case for nonautomotive lubricants and the latter is the case for automotive lubricants. In either case, the finished lubricant must meet the performance requirements established by a variety of technical organizations, OEMs, and the end-users. At high concentrations, the additive molecules exist as association structures, called micelles, due to intermolecular association via their polar ends. Upon dilution, deaggregation occurs and the additive molecules attain a more active form. Because the additives are reactive chemicals, they can interact with one another, when in a package, either synergistically or antagonistically . The formulators challenge is to deliver the intended performance by minimizing the antagonistic effects and maximizing the synergistic effects through careful balancing. For automotive use, the viscosity modifier and the performance package are usually sold separately  and for the applications needing a viscosity modifier, it is blended in the base fluid along with the performance package to obtain the finished lubricant. Typically, the lubricant additive suppliers develop general-purpose performance packages, which when blended in widely available base stocks in a predetermined amount meet industry specifications. Additive suppliers may fine tune their packages for an individual company's use in its base stocks. Table 4.33 shows the classes of additives that are used to formulate engine lubricants and Table 4.34 contains the classes of additives that are used to formulate nonengine lubricants. Formulation examples were provided in previous chapters dealing with the various fluid types.