To deliver quantitative measurements, most analytical instruments require data comparison of the sample with a standard(s) of known composition. Standard Reference Materials (SRMs) are such samples, which are specially made for accurate calibration of analytical instruments. A category of SRMs is glasses that contain certain element(s) and/or isotope(s) with specific compositions for calibration and performance testing of microanalytical instruments (e.g., laser ablation – inductively coupled plasma mass spectrometry (LA-ICP-MS), and secondary ion mass spectrometry (SIMS)).
Traditionally, these SRMs are produced by melting oxides or powdered rocks; the mixture is then subject to rapid cooling so that it forms a glass. There are several problems with this approach. During the melting process, desired but volatile elements may be lost while furnace components, crucibles, and/or stirrers could potentially introduce unwanted contamination. In addition, during the heating or cooling process, instead of dispersing evenly throughout the glass, elements of interest may aggregate and form small metallic nuggets or crystals. Such inhomogeneity in the SRMs leads to inconsistencies in the calibration measurement. Poor repeatability impacts both the accuracy and precision in the sample results.
Having said that, the microanalytical community has a need for homogeneous solid standard reference materials, particularly for the platinum-group elements (PGE, i.e., Pt, Pd, Rh, Ir, Os, and Ru).
LLNL researchers have developed a method to manufacture solid standard reference materials (SRMs) that can be used as calibration standards for elemental and isotopic analyses. The novel method allows for the growth of compositionally controlled particles as starting materials, and the synthesis of SRMs with single or multi-component(s) through electrophoretic deposition (EPD). The SRMs are then thermally processed under controlled atmospheric and temperature conditions to produce a densified solid that can be either crystalline or amorphous. This manufacturing process can be tuned to produce either chemically and/or isotopically homogenous materials, or deliberate heterogeneity in prescribed patterns using different components and concentrations.
Image Caption: Example of a Standard Reference Material produced using EPD.
Current stage of technology development: TRL 3
LLNL has filed for patent protection on this invention.
U.S. Patent Application No. 2021/0032767 Additive manufacturing of microanalytical reference materials published 6/15/2020
- SRM homogeneity is achieved without melting and stirring.
- Because the size of the particles is extremely small, consolidation occurs in minutes rather than hours or days.
- Manufacturing process can be tuned to produce either chemically and/or isotopically homogenous materials.
- Deliberate heterogeneity in prescribed patterns using different components and concentrations is also possible.
- Potentially capable of making homogeneous standard reference materials, particularly for the PGE that would be used to calibrate microanalytical instruments such as LA-ICP-MS and SIMS).
LLNL’s invention is specifically for the production of standard references materials used in scientific instrument calibration and performance testing. Although the invention focuses on certain chemical compositions, it is anticipated that the manufacture of a broad range of SRMs (elements, stable and radioactive isotopes) would be useful to a wide variety of disciplines.
