Anisotropic Thermal Expansion of Single Crystals of Thallium, Yttrium, Beryllium, and Zinc at Low Temperatures

Abstract

The anisotropic thermal expansion of the hexagonal elements, thallium, yttrium, beryllium, and zinc, has been measured. The temperature range for the thallium, yttrium, and zinc measurements was 4.2−273.2°K, while for beryllium the range was 77−273.2°K. Dimensional changes were detected by an interferometric technique, and the movement of the interference fringes was detected with a photomultiplier tube. From the measured values of ΔL/L0 the coefficients of thermal expansion and the c/a ratios of the metals were calculated as a function of temperature. A review of previous measurements of the thermal expansion of these metals is also included.

Solid-Solid Transitions in Titanium and Zirconium at High Pressures

“…The axial ratios also increase with temperature for Ti, 17 Zr, 17 and probably Hf and TI. 21 The phase diagram for thallium up to 50 kbar is now well established due to the work of Jayaraman et at. 10 ; Piermarini and Weir 22 have verified that the structure of the high-pressure polymorph is fee.…”

Beryllium and Beryllium Alloys and Composities

“…Natural beryllium contains 100% of the 9 Be isotope. The principal isotopes and respective half-life are 6 Be, 0.4 s; Be, 53 d; 8 Be, 10 À16 s; 9 Be, stable; 10 Be, 2.5 Â 10 6 y. Beryllium can serve as a neutron source through either the (a,n) or (n,2n) reactions.…”

“…Natural beryllium contains 100% of the 9 Be isotope. The principal isotopes and respective half-life are 6 Be, 0.4 s; Be, 53 d; 8 Be, 10 À16 s; 9 Be, stable; 10 Be, 2.5 Â 10 6 y. Beryllium can serve as a neutron source through either the (a,n) or (n,2n) reactions. Beryllium has a low (9 Â 10 À30 m 2 ) absorption cross-section and a high (6 Â 10 À28 m 2 ) scatter cross-section for thermal neutrons making it useful as a moderator and reflector in nuclear reactors.…”

Literature Survey: Physical Properties of Lithium and Beryllium at Low Temperatures.

“…23 Also listed in the appendix are the mean thermal expansion values for single crystalline beryllium measured by Meyerhoff and Smith. 24 The expansion coefficients in the different crystallographic directions differ .from the mean values onfy by about 20 percent.…”