DOE OSTI2014
There are various processes and techniques by which one can achieve well polished (highly reflective) and smooth, flat (low roughness) surfaces on a wide variety of materials. Historically, precision lapping processes were first applied to optical materials for the production of lenses for telescopes and microscopes. These processes have been developed by a multitude of technicians over the centuries and reported in countless publications. These same grinding, lapping and polishing processes have been of great importance in the fabrication and structural characterization of countless optical materials and engineering structures, e.g. optics, Si wafers, precision machined surfaces, engineered devices, low-friction surfaces, mechanical systems, metallographic examination of microstructures, to name but a few. The development of lapping and polishing processes and techniques as applied to extremely hazardous and highly (chemically) reactive materials, such as metallic plutonium (Pu), has been limited. This is due in part due to the sensitive nature of the work as applied to nuclear applications, and limited access and need to work with these materials. For the limited information regarding polishing and lapping of Pu materials that has been documented, there has been virtually no quantitative assessment of qualities such as surface roughness and flatness on the nanometer scale. In this report we use the word “lapping” to refer to the traversing of a specimen surface across an abrasive surface in a controlled manner in order to achieve smooth/flat surfaces. We differentiate lapping from polishing, in that we define polishing as traversing of a sample surface across a non-abrasive surface that contains loose abrasive particles, e.g. diamond paste on nylon nap, in order to achieve a highly reflective surface. In this report, we will detail a simple and repeatable lapping process as applied to alpha-phase metallic Pu. We will provide quantitative measurements of the surface roughness and flatness. We will demonstrate the ability to achieve sub-10 nm surface roughness and to lap millimeter-size areas to a flatness of approximately 1.0 µm. Additionally, we will assess the current limitations and discuss any artifacts that arise as a result of our polishing processes applied to metallic Pu materials.