Spreading of lithium on a stainless steel surface at room temperature

Lithium conditioned plasma facing surfaces have lowered recycling and enhanced plasma performance on many fusion devices and liquid lithium plasma facing components are under consideration for future machines. A key factor in the performance of liquid lithium components is the wetting by lithium of its container. We have observed the surface spreading of lithium from a mm-scale particle to adjacent stainless steel surfaces using a scanning Auger microprobe that has elemental discrimination. The spreading of lithium occurred at room temperature (when lithium is a solid) from one location at a speed of 0.62 μm/day under ultrahigh vacuum conditions. Separate experiments using temperature programmed desorption (TPD) investigated bonding energetics between monolayer-scale films of lithium and stainless steel. While multilayer lithium desorption from stainless steel begins to occur just above 500 K (E_des = 1.54 eV), sub-monolayer Li desorption occurred in a TPD peak at 942 K (E_des = 2.52 eV) indicating more energetically favorable lithium-stainless steel bonding (in the absence of an oxidation layer) than lithium-lithium bonding.