Zirconium Copper — a New Material for Use at Low Temperatures?

Cryogenic instruments usually require components with high thermal conductivity. Pure (non alloyed) copper offers very high conductivity, but is soft and not thus always suitable structurally. High conductivity beryllium copper (BeCu) alloys are a common choice when copper is unsuitable since they offer a good compromise between hardness and thermal conductivity. These alloys contain a small (<1%) amount of beryllium (along with a few percent of nickel or cobalt), with strength being obtained by precipitation hardening. An alternative precipitation hardened copper alloy is C15000 zirconium copper (ZrCu), which contains < 0.2% zirconium with the remainder being copper. This material does not seem to be generally used in cryogenic systems, though hardness and strength are comparable to BeCu. Moreover, the lower impurity content suggests that the thermal conductivity should be higher than for BeCu. I present residual resistivity measurements suggesting that ZrCu does indeed possess considerably higher conductivity than BeCu (19 Wm 1K 1 at 1 K compared to approximately 2 Wm 1K 1), and should therefore be a very useful material. A method is given for extrapolating the low temperature thermal conductivity values to temperatures up to 300 K; good agreement is seen with room temperature data-sheet values. This extrapolation method is shown to also be applicable to BeCu and thus presumably other dilute copper alloys, and is used to give recommended values for coin silver and various BeCu alloy types, including C17510 and C17200. To appear in the proceedings of the 24th International Conference on Low Temperature Physics, Orlando, Florida, USA, 10-17th August 2005. ©American Institute of Physics, Suite 1N01, 2 Huntingdon Quadrangle, Melville, NY, USA