Some Aspects of the Tribological Behavior of Materials in Sodium

摘要

The influence of boundary lubricating films formed by reaction of metallic surfaces with oxygen-containing sodium is discussed. In general, pre-existing surface metallic oxides are reduced in high-temperature low-oxygen sodium, and tribological behavior is accordingly poor. Chromium-containing alloys, however, can react more readily with oxygen-containing sodium to form sodium chromite, NaCrO sub 2 , on the alloy surfaces. Such an oxide could plausibly account for significantly improved tribological behavior at higher oxygen levels. Sodium chromite is only marginally stable at typical reactor outlet conditions and frictional behavior of typical chromium-containing alloys has therefore been studied as a function of rig cold trap temperature for exposure temperatures ranging from 650 to 500 exp 0 C in order to define the effective tribological boundary. The behavior of aluminized surfaces has also been studied and results from sliding and fretting wear tests are discussed in the context of the role of a lubricating oxide, believed to be sodium aluminate (formed by reaction of aluminum and oxygen-containing sodium) which is considerably more stable than sodium chromite at reactor outlet temperatures. (ERA citation 06:007741)