MSU, East Lansing, USA
Michigan State University, East Lansing, USA
FRIB, East Lansing, Michigan, USA
(MSU), East Lansing, USA
The phonon peak in the thermal conductivity kpp of high purity niobium is an unknown function of heat treatment temperature Th and RRR, amongst other variables. The relationship between Th and kpp of large grain niobium is investigated using two sets of four specimens. The specimens of Set 1 were randomly cut from four ingot discs with different RRR. These specimens were subjected to different heat treatments. Specimens of Set 2 were cut from the same grain of an ingot disc, with the heat flow direction of each specimen along the same crystal orientation. Each of these specimens was subjected to one heat treatment, at a temperature ranging between 600 C and 1200 C, while maintaining a constant temperature for an interval of 2 hours for each specimen. Results from the specimens of Set 1 show that there is no change in kpp after heating at 140 C for 48 hours. Set 1 specimens also show that for a given heat treatment protocol, the maximum in kpp shows a monotonic dependence on RRR. Results from the specimens of Set 2 suggest that the phonon conduction response to heat treatments for 2 hours shows no increase for Th < 600 C and plateaus at Th > 1000 C.
