Tham khảo tài liệu 'handbook of lubrication episode 1 part 11', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 246 CRC Handbook of Lubrication Table 8 SURFACE TENSION OF SEVERAL BASE OILS Liquid Surface tension dyn cm N m Water Mineral oils Esters Methylsilicone Fluorochloro compounds 72 X 10-3 30 35 X 10-3 30 35 x 10-3 20 22 x 10-3 15 18 x 10-3 spinning drop Relationships in this unit are expressed in the following equation. ơ K P1 - p d 3 ớ2 18 where P1 density of the heavy phase p2 density of the light phase d drop width 9 rotational speed and K constant characteristic of the test unit. With this unit interfacial tensions down to 10-4 to 10-5 dyn cm 10-7 to 10-8 N m can be measured. The detergents and dispersants in many automotive lubricants are so effective at reducing interfacial tension that used crankcase oils contaminanted with 10 to 15 water form a stable emulsion which defies separation by techniques which do not involve distillation. These general techniques can be used to suspend graphite in motor oil disperse calcium carbonate in over-based diesel lubes or prepare a 95 water invert emulsion. Both surface tension and interfacial tension are altered by additives and by lubricant degradation. THERMAL STABILITY Thermal stability is the resistance of the lubricant to either molecular breakdown or rearrangement at elevated temperatures in the absence of oxygen. Stability in an ordinary air environment oxidation stability is covered in the next section. One method of measuring thermal stability involves the isoteniscope a closed vessel with a manometer for measuring the rate of pressure increase at a specified heating rate. Thermal gravimetric and differential thermal analyses can also be used to evaluate thermal stability. Several thermal stability tests are described in Federal The test should allow for decomposition of a significant portion of the test sample and provide an analysis of the liquid and solid decomposition products as well as the gases Fluids such as mineral oils with a substantial percentage of C-C single
