Detection and quantification of residual Delta a-phase in Delta d-stabilized plutonium

• Published in: IOP conference series. Materials Science and Engineering 2010-01, Vol.9 (1), p.012020-012020
• Main Authors: Schwartz, Daniel S, Mitchell, J N, Pereyra, R A
• Format: Article
• Language: English
• Subjects: Alloying; Alloying elements; Alloys; Conferences; Differential scanning calorimetry; Gallium base alloys; Homogenizing; Plutonium; Transformations
• ISSN: 1757-899X
• DOI: 10.1088/1757-899X/9/1/012020

The temperature range of the Delta *d-phase field of plutonium can be expanded by alloying with Group IIIA elements. Ga is a particularly potent Delta *d-stabilizer and effectively stabilizes the Delta *d-phase to room temperature. Due to a strong propensity to wards s olute redistribution during cooling through the Delta *e-> Delta *d phase field, regions of the material often do not contain enough solute to stabilize the Delta *d-phase even after extensive homogenization annealing in the Delta *d-phase field. The result is a small, but persistent, fraction of Delta *a-phase in the material. A technique using differential scanning calorimetry to measure the enthalpy of transformation of the plutonium Delta *a-> Delta *b transformation is described which can detect and quantify Delta *a-phase in a Delta *d-phase matrix at levels as low as ~0.1 wt. %. Complications arise due to interference from the pressure-induced Delta *a-phase, and a peak separation method was developed to accurately measure the heat signal from each phase. A set of Delta *d-stabilized Pu-1.7 atomic % Ga alloys was examined using the technique and found to contain 0.32 plus or minus 0.06 weight % Delta *a-phase. The onset temperature of the Delta *a-> Delta *b transformation in these specimens was found to be 140.2 degree C, significantly higher than that for the transformation in pure plutonium, 126.2 degree C. This increase in onset temperature is a consequence of significant Ga content in the Delta *a-phase.