Powder Metallurgy Fabrication of Molybdenum Accelerator Target Disks

Abstract

Powder metallurgy approaches for the fabrication of accelerator target disks are being examined to support the development of Mo-99 production by NorthStar Medical Technologies, LLC. An advantage of powder metallurgy is that very little material is wasted and at present, dense, quality parts are routinely produced from molybdenum powder. The proposed targets, however, are thin wafers, 29 mm in diameter with a thickness of 0.5 mm, with very stringent dimensional tolerances. Although tooling can be machined to very high tolerance levels, the operations of powder feed, pressing and sintering involve complicated mechanisms, each of which affects green density and shrinkage, and therefore the dimensions and shape of the final product. Combinations of powder morphology, lubricants and pressing technique have been explored to produce target disks with minimal variations in thickness and little or no distortion. In addition, sintering conditions that produce densities for optimum target dissolvability are being determined.

Optimization of the dissolution of molybdenum disks. FY-16 results

“…12×1mm Disks of Recycled Mo Material A small batch of recycled Mo material as MoO 3 obtained using a precipitation method developed at Argonne [5], and ammonium heptamolybdate (AHM) derived by solvent extraction [6], was sent to ORNL. At ORNL this material was reduced to Mo metal using a two-stage process [7], producing 121 mm sintered Mo disks for Argonne dissolution studies. Characteristics and dissolution rates of the sintered Mo disks are listed in Table 2.…”

Crystallization of Ammonium Heptamolybdate for Reduction to Mo Metal

“…It is important to produce the AHM product with consistent particle size and morphology before its thermal treatment and reduction to Mo metal in a furnace. AHM particles that are too small (< 50 µm) result in Mo metal powder that is much too fine to properly fabricate into targets with optimum properties [2,3].…”

Dissolution of Additively Manufactured Mo Disks and Structures for Accelerator Based Production of Mo-99

“…The press-and-sinter approach for production of Mo targets has been successfully tested and demonstrated [1][2][3]. The main advantage of this process is that it uses readily available technology and tools that have been tuned for production of various metal and metal oxide targets.…”