Mechanics of Metals with Phase Changes
- Brigham Young Univ., Provo, UT (United States)
New experimental data is presented on some exotic metals that exhibit phase changes at cryogenic temperatures. The types of phase changes that were detected in the specific heat data range from martensitic (diffusion less) transitions to superconducting transitions. In addition, the charge density wave (CDW) state in uranium metal was detected in the specific heat. Specific-heat measurements were made in zero-magnetic field using an apparatus capable of obtaining temperatures as low as 0.4 K. Calibration performed on this apparatus, using a single-crystal copper sample, show its accuracy to be 0.50%, while the resolution was better than 0.1%. Our measurements demonstrate that similar high precision and accurate specific-heat measurements can be obtained on milligram-scale samples. In Chapters 2 and 3, specific-heat measurements are presented for the B2 (CsCl structure) alloy AuZn and for α-uranium (orthorhombic symmetry). The AuZn alloy exhibits a continuous transition at 64.75 K and an entropy of transition of (ΔStr) 2.02 J K-1 mol-1. Calculation of the Debye temperature, by extrapolating of the high temperature phase elastic constants to T = 0 K yields a value of 207 K (±2 K), in favorable agreement with the calorimetric value of 219 K (±0.50 K), despite the intervening martensitic transition. Reported results for single-crystal α-U show a low-temperature limiting θD of 256 K (±0.50 K) and four low-temperature anomalies: a superconducting transition below 1 K, an electronic transition at 22 K, and two anomalies at 38 K and at 42 K indicative of the CDW state. In order to continue the study of the actinide series of elements, a program was initiated to first purify and then grow single crystals of plutonium. Accordingly, the focus of Chapters 4 through 6 will be a description of plutonium sample preparation. In this program plutonium metal was purified via zone refining, using a levitated molten zone to minimize the introduction of impurities. Several impurities were reduced to levels below that of instrument detection limits. Results indicate that six sequential zone refining passes are required to obtain metal with 130 ppm total impurities (excluding N, O, F, Cl, and Br). Small single crystals with a volume of 1 mm3 were grown of δ-plutonium by a strain-anneal technique. The values obtained for the critical strain in the strain-anneal experiments are in favorable agreement with values obtained by other researches using loading methods other than biaxial loading.
- Research Organization:
- Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
- Sponsoring Organization:
- USDOE Office of Nuclear Energy, Science and Technology (NE)
- DOE Contract Number:
- W-7405-ENG-36
- OSTI ID:
- 776183
- Report Number(s):
- LA-13788-T; TRN: AH200112%%416
- Resource Relation:
- Other Information: TH: Thesis (Ph.D.); Submitted to Brigham Young Univ., Dept. of Chemistry and Biochemistry, Provo, UT (US); PBD: 1 Jan 2001
- Country of Publication:
- United States
- Language:
- English
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