Filtration efficiency (FE), differential pressure (ΔP), quality factor (QF), and construction parameters were measured for 32 cloth materials (14 cotton, 1 wool, 9 synthetic, 4 synthetic blends, and 4 synthetic/cotton blends) used in cloth masks intended for protection from the SARS-CoV-2 virus (diameter 100 ± 10 nm). Seven polypropylene-based fiber filter materials were also measured including surgical masks and N95 respirators. Additional measurements were performed on both multilayered and mixed-material samples of natural, synthetic, or natural-synthetic blends to mimic cloth mask construction methods. Materials were microimaged and tested against size selected NaCl aerosol with particle mobility diameters between 50 and 825 nm. Three of the top five best performing samples were woven 100% cotton with high to moderate yarn counts, and the other two were woven synthetics of moderate yarn counts. In contrast to recently published studies, samples utilizing mixed materials did not exhibit a significant difference in the measured FE when compared to the product of the individual FE for the components. The FE and ΔP increased monotonically with the number of cloth layers for a lightweight flannel, suggesting that multilayered cloth masks may offer increased protection from nanometer-sized aerosol with a maximum FE dictated by breathability (i.e., ΔP).

A spectroscopic study was conducted on six simulant nuclear waste glasses using multi-nuclear NMR, Raman, and Mössbauer spectroscopies exploring the role of Si, Al, B, Na, and Fe in the glass network with the goal of understanding melt structure precursors to deleterious nepheline crystal formation. NMR showed two sites each for Al, Si, and Na in the samples which crystallized significant amounts of nepheline, and B speciation changed, typically resulting in more B(IV) after crystallization. Raman spectroscopy suggested some of the glass structure is composed of metaborate chains or rings, thus significant numbers of non-bridging oxygen and a separation of the borate from the aluminosilicate network. Mössbauer, combined with Fe redox chemical measurements, showed Fe playing a minor role in these glasses, mostly as Fe 3+ , but iron oxide spinel forms with nepheline in all cases. A model of the glass network and allocation of non-bridging oxygens (NBOs) was computed using experimental B(IV) fractions which predicted a large amount of NBO consistent with Raman spectra of metaborate features. local charge balance on the oxygens of alkaline-earth boro-aluminate crystals, where results from 11 B and 27 Al magic angle spinning (MAS)-NMR stressed the importance of three-coordinated oxygen O(III), where parentheses here and elsewhere denote nearest neighbor coordination, and indicated the importance of Al(V) and Al(VI) in all composition ranges [19]. In another example, Du and Stebbins [12] presented a modified Dell and Bray-type model [20] to include aluminum (i.e., alkali-alumino-borosilicate) and to describe boron speciation. Various tetrahedra compete for sodium, the modifier generally preferring Al, then B, then Si [21]. Tetrahedra building, on the other hand, is believed to start with Si then proceed to Al(IV), Fe(IV), and B(IV) (if present), as long as charged tetrahedron nearneighbor avoidance is maintained [12,22].Both boron and aluminum coordination are affected by modifier-cation field strength. In aluminoboro-silicates containing both Na and Ca, increasing the amount of Ca increases Al(V) [13], but has been said to increase B(IV) [23] or decrease it [13]. It has been shown in aluminoborates that higher-fieldstrength cations (e.g., Mg), can shift the normally encountered "chemical ordering" (i.e., Al and B tetrahedra avoidance due to Coulomb repulsion) seen in Na and Ca aluminoborates to the "statistical random mixing" of tetrahedra seen in Mg alumino-borate [24], and to an extent in Ca alumino-borosilicates [13]. Higher coordinated alumina units, Al(V) and Al(IV), can be charge compensated by 2 + cations (Ca, Mg) or 3 + cations (B, Al, La), and at the same time tend to "stabilize" B(IV) tetrahedra, acting as weakly positive ions themselves [19,24,25].Effects of differing Al/B ratios are explained by the local charge balance model [19], as B(III) is needed to stabilize units containing the charged Al(IV), so as more Al is added, the fraction of B(III) increases relative to B(IV) [23]. It has also been shown by ...