7808 20 23699 25 Tcp 30 Txp 30 Tbb 360

Figure 4

It should be noted in these microoxidation tests that as the temperature increases the evaporation loss also increases. This evaporation is due primarily to the increased vapor pressure of the unreacted material and to a much lesser degree to the primary oxidation product. For the case of zero deposit build up on a high temperature operating bearing, it is desirable to have evaporation dominate the oxidation and condensation reactions.

In this microoxidation evaluation, some typical commercial SF-CC and SF-CD lubricants showed an oxidation amounting to 30 percent in a 30 minute test at 225°C. Based on kinetic models developed (16), the time required to get any amount of degradation can be estimated based on the assumption that primary oxidation is first-order and the rate determining reaction. These estimated times are shown on Table 4. These data suggest that excessive sludge formation should be a problem with only small increases in current engine temperature with a recirculating liquid system. Assuming the same activation energy for the phosphate esters, they will survive oxidation in the bearing system at much higher temperatures. The

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