Work

Carbide Inclusions in Delta-Phase Plutonium

Year: 2004

Type: article

Abstract: Inclusions in plutonium alloys are common and depend on the processing parameters and age of the material. Plutonium-bearing compounds frequently observed as inclusions include: hydrides, nitrides, oxides, and carbides. Optical metallography and electron probe microanalysis (EPMA) were used to characterize plutonium carbide (PuC) inclusions in delta-phase plutonium. The structural complexities of plutonium combined with its radioactivity, pyrophoric nature, and toxicity create a unique challenge to revealing and interpreting its microstructures. Samples of delta-phase Pu-239 were used in this study. Note that the delta phase is stabilized to room temperature by the addition of {approx}1 wt% gallium. After samples are cut, mounted in epoxy, ground, and polished, they are then electropolished at 40 V in an etchant of 10 vol.% nitric acid and 90 vol.% dimethylformamide and electroetched at 6 V in the same etchant. Optical micrographs were collected using an inverted metallograph equipped with a digital camera. Back-scattered electron images and elemental maps of the plutonium, carbon, and gallium content were collected using an EPMA equipped with wavelength dispersive spectrometers. After reviewing our data and consulting work done by Cramer and Bergin it was determined that the inclusions were acicular plutonium carbides and were formed during the casting process at the time the material was manufactured. It is believed that these inclusions would affect the high strain-rate properties. The response of plutonium alloys during implosion is critical to the performance and reliability of a nuclear weapon. We plan to further investigate these inclusions to gather information about orientation, composition, structure, and concentration. An x-ray diffractometer with a 10 {micro}m beam diameter will be used to gather information on the orientation and structure of individual inclusions. A field-emission scanning electron microscope (SEM) with a WDS will be used at low voltage to collect quantitative compositional data fromjust the inclusions. Finally, attempts will be made to fluoresce the inclusions using both light on a metallograph and electrons in a variable pressure SEM. Images will be collected using a digital camera and a cathodoluminescence detector respectively. The data from all four instruments will be compared to data collected from a PuC powder standard.

Source: Microscopy and Microanalysis

DOI: 10.1017/s1431927604880231