Jamie L. Weaver

NIST SRM 610 and 612 (Trace Elements in Glass) are routinely used for microanalytical measurements but were designed to be bulk‐scale reference materials. This study investigates an approach to quantify the differences between values for elements obtained using the bulk techniques ICP‐OES, INAA and CNPGAA, and values obtained using the predominant microanalytical technique LA‐ICP‐MS. The results from bulk techniques and LA‐ICP‐MS were also compared with currently accepted mass fractions reported in the Certificates of Analysis (CoA) and the literature. The element suite measured was based on the needs of the forensic and geological microanalysis communities, and included B, Ce, Hf, K, La, Li, Ti and Zr. These additional elements are either not included or do not have uncertainty values in the CoAs for NIST SRMs 610 and 612 but are available as community consensus values, which include uncertainties. The measurement results were processed using Monte Carlo (MC) uncertainty analysis for each technique to provide a comprehensive calculation of expanded uncertainties for use in future research. Measurements of mass fractions of the same element both within and between fragments in the LA‐ICP‐MS data were observed to be correlated due to the use of only one calibration material, which was Float Glass Standard (FGS) 2, as that reference material is not directly traceable to NIST SRMs 610 and 612, and is predominantly used in the forensic community. The MC treatment was expected to cause increases in the overall uncertainty values compared with traditional Guide to the Expression of Uncertainty in Measurement (GUM) treatment for all measurements, which was the case for LA‐ICP‐MS measurements of all elements in NIST SRM 610 and NIST SRM 612 (except for Mn in NIST SRM 610). However, for bulk measurements of Ce, Li and Rb in NIST SRM 610, and bulk measurements of Li, Mn, Ti and Zr for NIST SRM 612, the uncertainty decreased due to MC more precisely determining the uncertainty contribution compared with a more conservative approximation from GUM. All results were compared by using E _n scores to assess the relative agreement between bulk‐ and micro‐scale measurements, CoA values and to community consensus values. The findings point out the limitations of the current forensic glass reference materials for high precision microanalytical measurements, especially due to the relatively high uncertainty values associated with Float Glass Standard (FGS) 2. This situation underscores the need for new reference materials specifically designed for homogeneity at the micro‐scale for trace element measurement.

A suite of natural, synthetic, and mixed synthetic-natural woven fabrics, along with nonwoven filtration layers from a surgical mask and an N95 respirator, was examined using visible light microscopy, scanning electron microscopy, and micro-X-ray computed tomography (µXCT) to determine the fiber diameter distribution, fabric thickness, and the volume of solid space of the fabrics. Nonwoven materials exhibit a positively skewed distribution of fiber diameters with a mean value of ≈3 μm, whereas woven fabrics exhibit a normal distribution of diameters with mean values roughly five times larger (>15 μm). The mean thickness of the N95 filtration material is 1093 μm and is greater than that of the woven fabrics that span from 420 to 650 μm. A new procedure for measuring the thickness of flannel fabrics is proposed that accounts for raised fibers. µXCT allowed for a quantitative nondestructive approach to measure fabric porosity as well as the surface area/volume. Cotton flannel showed the largest mean isotropy of any fabric, though fiber order within the weave is poorly represented in the surface electron images. Surface fabric isotropy and surface area/volume ratios are proposed as useful microstructural quantities to consider for future particle filtration modeling efforts of woven materials.

Boron (B) alloying transforms the magnetoelectric antiferromagnet Cr₂O₃ into a multifunctional single‐phase material which enables electric field driven π/2 rotation of the Néel vector. Nonvolatile, voltage‐controlled Néel vector rotation is a much‐desired material property in the context of antiferromagnetic spintronics enabling ultralow power, ultrafast, nonvolatile memory, and logic device applications. Néel vector rotation is detected with the help of heavy metal (Pt) Hall‐bars in proximity of pulsed laser deposited B:Cr₂O₃ films. To facilitate operation of B:Cr₂O₃‐based devices in CMOS (complementary metal‐oxide semiconductor) environments, the Néel temperature, T_N, of the functional film must be tunable to values significantly above room temperature. Cold neutron depth profiling and X‐ray photoemission spectroscopy depth profiling reveal thermally activated B‐accumulation at the B:Cr₂O₃/ vacuum interface in thin films deposited on Al₂O₃ substrates. The B‐enrichment is attributed to surface segregation. Magnetotransport data confirm B‐accumulation at the interface within a layer of ≈50 nm thick where the device properties reside. Here T_N enhances from 334 K prior to annealing, to 477 K after annealing for several hours. Scaling analysis determines T_N as a function of the annealing temperature. Stability of post‐annealing device properties is evident from reproducible Néel vector rotation at 370 K performed over the course of weeks.

The complex distribution of particle charge states resulting from neutralization processes by radioactive or soft X-ray charge neutralizers is a well-documented problem in aerosol science. Here, we demonstrate that non-idealities in the collection efficiency of an impactor allows for the transmission of an unexpected population of multiply charged particles by a differential mobility analyzer that can bias optical measurements. The extinction cross sections (C_ext) of ammonium sulfate particles were quantified using cavity ring-down spectroscopy and particle counting. Particles were selected by electrical mobility (i.e., a metric of particle size) using a differential mobility analyzer (DMA) or electrical mobility and mass selected by a tandem DMA and aerosol particle mass analyzer (APM), respectively, to elucidate multiple charging artifacts. Measured C_ext exhibited statistically significant differences at particle sizes near the impactor cut point implying that these multiply charged particles should not be present and could not be confirmed by parallel size distribution measurements. Additionally, comparison of C_ext with Mie theory demonstrates that misclassification of the multiply charged particles can give rise to numerically accurate results. To understand these observations, the collection efficiency (CE) of four impactors from similar electrostatic classifiers was investigated. From these measurements, it was determined that the nominal and actual diameters of the impactors differed by -0.5% (457 μm versus (455 ± 1) μm, respectively (uncertainty is 1σ standard deviation)) but the average Stk₅₀ (the Stokes number at the cut-point, D₅₀) values differed by ≈ 23% (0.23 versus 0.18 ± 0.01, respectively). The measured CE as a function of √Stk (a metric of particle aerodynamic size) exhibits a long tail towards higher √Stk values, allowing for transmission of the larger and multiply charged particles observed in the optical measurements. These measurements highlight the utility of using orthogonal, spectroscopic methods to quantify the presence of multiply charged particles. Graphical Abstract

Archaeological glasses with prolonged exposure to biogeochemical processes in the environment can be used to understand glass alteration, which is important for the safe disposal of vitrified nuclear waste. Samples of mafic and felsic glasses with different chemistries, formed from melting amphibolitic and granitoid rocks, were obtained from Broborg, a Swedish Iron Age hillfort. Glasses were excavated from the top of the hillfort wall and from the wall interior. A detailed microscopic, spectroscopic, and diffraction study of surficial textures and chemistries were conducted on these glasses. Felsic glass chemistry was uniform, with a smooth surface showing limited chemical alteration (<150 nm), irrespective of the position in the wall. Mafic glass was heterogeneous, with pyroxene, spinel, feldspar, and quartz crystals in the glassy matrix. Mafic glass surfaces in contact with topsoil were rougher than those within the wall and had carbon-rich material consistent with microbial colonization. Limited evidence for chemical or physical alteration of mafic glass was found; the thin melt film that coated all exposed surfaces remained intact, despite exposure to hydraulically unsaturated conditions, topsoil, and associated microbiome for over 1,500 years. This supports the assumption that aluminosilicate nuclear waste glasses will have a high chemical durability in near-surface disposal facilities.

There is wide industrial interest in developing robust models of long‐term (>100 years) glass durability. Archeological glass analogs, glasses of similar composition, and alteration conditions to those being tested for durability can be used to evaluate and inform such models. Two such analog glasses from a 1500‐year‐old vitrified hillfort near Uppsala, Sweden have previously been identified as potential analogs for low concentration Fe‐bearing aluminosilicate nuclear waste glasses. However, open questions remain regarding the melting environment from which these historic glasses were formed and the effect of these conditions on their chemical durability. A key factor to answering the previous melting and durability questions is the redox state of Fe in the starting and final materials. Past work has shown that the melting conditions of a glass‐forming melt may influence the redox ratio value (Fe ⁺³ /∑Fe), a measure of a glass's redox state, and both melting conditions and the redox ratio may influence the glass alteration behavior. Synthetic analogs of the hillfort glasses have been produced using either fully oxidized or reduced Fe precursors to address this question. In this study, the melting behavior, glass transition temperature, oxidation state, network structure, and chemical durability of these synthesized glass analogs is presented. Resulting data suggests that the degree of network connectivity as impacted by the oxidation state of iron impacted the behavior of the glass‐forming melt but in this case does not affect the chemical durability of the final glass. Glasses with a lower degree of melt connectivity were found to have a lower viscosity, resulting in a lower glass transition temperature and softening temperature, as well as in a lower temperature of foam onset and temperature of foam maximum. This lower degree of network connectivity most likely played a more significant role in accelerating the conversion of batch chemicals into glass than the presence of water vapor in the furnace's atmosphere. Future work will focus on using the results from this work with outcomes from other aspects of this project to evaluate long‐term glass alteration models.

Atomic layer deposited (ALD) amorphous aluminium oxide and titanium oxide coatings have been investigated for use in reducing the rate of silicate glass alteration. Mass spectrometric analysis of leachate from elevated temperature aqueous immersion alteration experiments showed a marked decrease in the concentration of released Na and Si from the glass when the vitrified material was ALD coated as compared to uncoated glass. This decrease is consistent with the proposed protective effect of the ALD coating. Additionally, visual observations indicate formation of significant amounts of amorphous, secondary phase sediment for immersed, uncoated glass. This sediment was not present in the solution of the ALD coated and altered glass samples. However, the ALD coating did delaminate after protracted immersion, a likely limiting factor of the efficacy of ALD coatings. This limitation may be mitigated through a proposed refinement of the ALD coating procedure.

Li distribution within micron-scale battery electrode materials is quantified with neutron depth profiling (NDP). This method allows the determination of intra- and inter-electrode parameters such as lithiation efficiency, electrode morphology change, and Li transport. In this work, a Sn electrode was lithiated at a constant potential and in situ Li movement was monitored and quantified. This contrasts to traditional methods where Li diffusion is inferred based on the passed electrochemical charge. Diffusion constants obtained through Fick's 1st and 2nd laws using this direct detection method, ranging from 1 × 10⁻¹² cm² s⁻¹ to 10 × 10⁻¹² cm² s⁻¹, are in good agreement with each other and reduce the range from the literature reported values for this system by over an order of magnitude. A significant difference between the electrochemical charge passed and Li incorporated into the Sn electrode as measured by NDP was detected. This indicates that NDP can be used to separate lithiation current from other parasitic currents. Advantages, challenges, improvements, and opportunities for using NDP to investigate many battery-related phenomena are presented.