Lubrication Oxidation Behavior

The oxidation behavior was further investigated by DSC in air (7 bar pressure, 5 cmV min flow rate, heating rate j8= 10 K/min). The evaluations were carried out as described in chapter 4.7.2. The petroleum based oils supplied diagrams shown schematically in fig. 4-129. No significant differences were observed between virgin and reclaimed oils. In the diagrams of the synthetic lubricants, the first peak appears more slender and higher, the... 

Lubricants. Petroleum lubricants continue to be the mainstay for automotive, industrial, and process lubricants. Synthetic oils are used extensively in industry and for jet engines they, of course, are made from hydrocarbons. Since the viscosity index (a measure of the viscosity behavior of a lubricant with change in temperature) of lube oil fractions from different cmdes may vary from +140 to as low as —300, additional refining steps are needed. To improve the viscosity index (VI), lube oil fractions are subjected to solvent extraction, solvent dewaxing, solvent deasphalting, and hydrogenation. Furthermore, automotive lube oils typically contain about 12—14% additives. These additives maybe oxidation inhibitors to prevent formation of gum and varnish, corrosion inhibitors, or detergent dispersants, and viscosity index improvers. The United States consumption of lubricants is shown in Table 7. 

Polyethers. Acetal Resins. These stabilized polyoxymethy-lenes were introduced dramatically by DuPont and Celanese as engineering plastics to replace non-ferrous metals. Good mechanical strength, resilience, fatigue-resistance, lubricity, abrasion-resistance, heat distortion temperature, water and solvent-resistance can approach the behavior of metals on a volume basis, while processability, color possibilities, and corrosion-resistance are superior. Major weakness is sensitivity to thermal, oxidative, and ionic degradation. 

Lubricants are formulated products composed of a base stock, which is either a mineral or synthetic oil, and various specialty additives designed for specific performance needs. Additive levels in lubricants range from 1 to 25% depending on the application. Synthetic base stocks are oligomers of small molecules, synthesized to a defined molecular weight. Important performance indicators include viscosity index which measures the viscosity index behavior over a temperature range, oxidative stability, and pour point. The performance of synthetic and mineral oils (Morse, 1998 Shubkin, 1993) is summarized in Table 2.7. 

Xie et al. [49] investigated the tribological behaviors of different ILs as lubricants for tribo-pairs (low-temperature silicon oxide film/SijN ball, polysilicon Si film/ SijN ball, and silicon nitride (SijN ) film/SijN ball) by varying the applied load and the sliding velocity. The ILs lubricants showed the best lubricating properties for the three tribo-pairs at the intermediate load of 150 g. 

Chemical heterogeneity of a surface is an important property affecting adhesion, adsorption, wettability, biocompatibility, printability and lubrication behavior of a surface. It seriously affects gas and liquid adsorption capacity of a substrate and also the extent of a catalysis reaction. As an example, the partial oxidation of carbon black surfaces has an important, influence on their adsorptive behavior. In a chemically heterogeneous catalyst, the composition and the chemical (valence) state of the surface atoms or molecules are very important, and such a catalyst may only have the power to catalyze a specific chemical reaction if the heterogeneity of its surface structure can be controlled and reproduced during the synthesis. Thus in many instances, it is necessary to determine the chemical... 

Another factor which complicates the matching of theoretical deductions with observed behavior in the study of contact adhesion is the influence of surface films. The effect on friction of adsorbed gas films, metal oxide films and additive reaction films has been discussed in detail in Chapters 9 and 10. Since the major frictional mode is adhesive, it follows that the factors which influence lubricated friction in such instances ultimately resolve back to their influence on adhesion. The interactions among surface films, surface topography, contact and adhesion are discussed in detail in Section 12.6. 

Low resistance to oxidative degradation (Asadauskas et al., 1996, 1997, 2000) and poor low-temperature behavior (Erhan Asadauskas, 2000 Hagemann Roth-fus, 1988 Rhee, 1996) remain the major impediments to using soybean oil as a base stock in biobased lubricants. Soybean oil is the most widely available and least expen-... 

The large centrifugal compressors operate without oil lubrication in contact with air, and hence, no oil droplets are introduced into the air stream. The presence of small droplets of oil has a pronounced effect on the behavior of the oxidizing catalysts, and this must be borne in mind in attempting to use air produced by reciprocating or oil-lubricated compressors. 

PROPERTIES OF SPECIAL INTEREST Thermal stability. Oxidative stability. Wide serviceable temperature ( 70 to 260 °C) and minimal temperature effect. Good resistance to UV radiation. Good damping behavior. Excellent antifriction and lubricity, and good dielectric strength. 

Woydt et al. [225] evaluated the tribological behavior of SiC-TiC and SiC-TiB2 ceramic-matrix composites using a special high temperature tribometer. In an normal ambient environment these composites are able to form lubricious oxide reaction layers on the hard substrate the low friction coefficient of the couple SiC -TiC/SiC-TiC at room temperature with values of / = 0.2. and 0.3 was explained by the formation of self-lubricating layers of Ti02 and SiC O. The... 

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