The aluminum complex soap greases made previously bad good high and low temperature shear properties and good oxidation stability at 210°F but at 250°F were deficient in the latter property. Efforts to correct this deficiency consisted of incorporating antioxidants which had proved effective at the higher temperature in other grease types. Federal Test Standard 791a Method 3453 (bomb oxidation) was used in evaluating these additives in several con¬centrations at 250°F.nThe antioxidants were generally less effective at 250°F in these aluminum base greases than they were in other greases at the same temperature. Two of the inhibitors, 2,4'-diisopropyl amino diphenyl ether and a proprietary mixture of complex organic amines, did impart superior resistance to oxidation at 2S0°F. The former, in a one percent concentration, limited the pressure drop to 25 psi in 400 hours and a 27 psi drop in 400 hours was recorded using the latter material in a 0.3 percent con¬centration. For each material this represented the least pressure drop for concentrations of 0.3, 0.6, 1.0. and 1.5 percent. This compares with a 55 psi pressure drop in 175 hours for the uninhibited grease at 250°F and an 18 psi drop in 400 hours for this grease at 210°F.nThe incorporation of several rust inhibitors reduced the effectiveness of the antioxidants in aluminum complex soap greases.nThis work shows that it will be difficult to find ' antioxidants for limiting the pressure drop of aluminum complex soap grease to 20 psi in 400 hours at 250°F.
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