Developing Compositional Control During Additive Manufacturing of Surrogate Debris Reference Materials and Microanalytical Standards

Project Overview

Building on the success of our previous feasibility study (FS-18-004), this project aimed to further develop advanced electrophoretic deposition (EPD) for the fabrication of high-fidelity microanalytical standard-reference materials (SRMs) and realistic surrogate debris-reference materials (SDRMs) needed to evaluate and exercise analytical techniques for post-detonation nuclear forensics, a key component of nuclear-threat reduction. Ideal SDRMs would be highly reproducible and robust glassy, solid objects between tens of mg and a few g in size, with bulk composition reflecting the environment of interest and trace amounts of actinides, fission, and activation products in realistic proportions. Glassy microanalytical SRMs are needed more broadly for spatially-resolved analytical techniques due to the limited availability of suitable standards. Our approach was to incorporate trace analytes into silica nanoparticles and to consolidate them along with other feedstock particles, including desired matrix elements, into ~130 mg pieces via EPD, followed by thermal densification. The goals were 1) to optimize each stage of the process to include a wide array of trace elements and study their distribution, 2) to establish facilities for additive manufacturing (AM) of radioactive materials in LLNL radiochemistry laboratories, and 3) to prepare prototype SDRMs that are reproducible from piece to piece and contain realistic actinide- and fission-product ratios.

The synthesis of analyte-doped silica feedstock particles via the Stöber method was optimized targeting a 500 ± 100 nm diameter and spherical morphology, which was influenced by pH and analyte concentration when in excess of ~30 ppm. Sixty-four elements ranging from Li to Pu were tested for incorporation into particles, resulting in high analyte yields for all except for less than 50% Se, Mo, and Pd incorporation and 0% for Re. The incorporation of nearly all fission elements exhibited less than 20% variation across five replicate reactions. Commercial Fe2O3, Al2O3, and MgO nanoparticles, as well as synthesized tricalcium phosphate (TCP), were silica coated for multi-material EPD of mixed-matrix silicate materials. The distribution of major elements in multi-feedstock sintered EPD samples appeared homogenous down to the ~100 µm length scale, but segregation patterns were observed at the 5-10 µm scale. A 3D printed disposable EPD cell, designed to minimize cross contamination, yielded deposition of 70-80% of suspended particles for silica and 60-70% for mixed matrix samples. Sintering is necessary to form robust materials but can displace volatile analytes; heating in a reducing atmosphere improved retention and homogeneity of most elements. Fresh fission products were prepared and doped into feedstock silica particles, with and without stable trace-element carriers, along with Pu. Fabrication of two sets of four samples with reproducible isotope ratios of actinide and fission analytes from piece to piece (within experimental uncertainty) could be achieved within 48 hours of receiving the irradiated target. Many relevant analyte ratios could be controlled, but the limited uptake of Mo into feedstock particles and loss of some volatile analytes during sintering still represent current limitations of the methods. However, we expect these challenges can be mitigated with adjustments to the process, and the versatility of these methods offers advantages for preparation of customized SRMs. This work established AM capabilities for radioactive materials and demonstrated the use of EPD to make reproducible, robust SDRMs.

Mission Impact

The SDRM production methods developed will enable evaluation of the full forensic analytical processes in post-detonation nuclear-forensics exercises, including dissolution of surrogate debris. They will also enable further validation of cutting-edge microanalytical techniques currently being researched and developed for application to nuclear forensics. This work helps advance nonproliferation, counterterrorism, counterproliferation, and emergency-response capabilities across the entire threat spectrum.

Publications, Presentations, and Patents

Sio, C.K. et al. 2020. "Additive Manufacturing of Platinum Group Element (PGE) Standard Reference Materials with a Silica Matrix." Rapid Communications in Mass Spectrometry, 34: e8627 (2020); doi: 10.1002/rcm.8627, LLNL-JRNL-785024.

Sio, Kin I. et al. "Additive Manufacturing of Microanalytical Reference Materials." U.S. Patent application 16/902,076 filed June 15, 2020 and published February 4, 2021.

Sio, C.K. et al. 2020. "Additive Manufacturing of PGE Standards with a Silica Matrix." Presentation, Goldschmidt Conference, Virtual June 2020. LLNL-PRES-811418.

Parsons-Davis, T. et al. 2020. "Additive Manufacturing of Surrogate Debris Reference Materials and Microanalytical Standards." Presentation, Physical and Life Sciences External Review Committee, Virtual. April 2021. LLNL-VIDEO-822899.

Parsons-Davis, T. et al. 2021. "Additive Manufacturing of Surrogate Debris Reference Materials and Microanalytical Standards." Fall 2021 ACS National Meeting and Exposition, Virtual. August 2021.LLNL-PRES-826178.

Parsons-Davis, T. et al. 2022. "Additive Manufacturing of Surrogate Debris Reference Materials and Microanalytical Standards." Presentation, Twelfth International Conference on Methods and Applications of Radioanalytical Chemistry (MARC XII), Kona, HI. April 2022. LLNL-PRES-833410.

Shusterman, J. et al. "Additive Manufacturing of Actinide- and Fission Product-Doped Silica for Production of Surrogate Debris Reference Materials." Presentation, Twelfth International Conference on Methods and Applications of Radioanalytical Chemistry (MARC XII), Kona, HI. April 2022. LLNL-PRES-833405.