Systematic experimental comparison of particle filtration efficiency test methods for commercial respirators and face masks

Respirators, medical masks, and barrier face coverings all filter airborne particles using similar physical principles. However, they are tested for certification using a variety of standardized test methods, creating challenges for the comparison of differently certified products. We have performed systematic experiments to quantify and understand the differences between standardized test methods for N95 respirators (NIOSH TEB-APR-STP-0059 under US 42 CFR 84), medical face masks (ASTM F2299/F2100), and COVID-19-related barrier face coverings (ASTM F3502-21). Our experiments demonstrate the role of face velocity, particle properties (mean size, size variability, electric charge, density, and shape), measurement techniques, and environmental preconditioning. The measured filtration efficiency was most sensitive to changes in face velocity and particle charge. Relative to the NIOSH method, users of the ASTM F2299/F2100 method have commonly used non-neutralized (highly charged) aerosols as well as smaller face velocities, each of which may result in approximately 10% higher measured filtration efficiencies. In the NIOSH method, environmental conditioning at elevated humidity increased filtration efficiency in some commercial samples while decreasing it in others, indicating that measurement should be performed both with and without conditioning. More generally, our results provide an experimental basis for the comparison of respirators certified under various international methods, including FFP2, KN95, P2, Korea 1st Class, and DS2.

Влияние асимметрии расположения металлических масок на согласование нижнего электрода с высокочастотным генератором смещения при реактивно-ионном травлении массивных подложек

The effect of the degree of asymmetry in the arrangement of metal masks on the matching of the lower electrode with a high-frequency displacement generator during selective reactive-ion etching of massive substrates in plasma-forming gas mixtures based on freon-14 is studied theoretically and experimentally. Theoretically, the absence of the influence of the asymmetry of the mask location on the specific reactive power is shown. It is shown that at the edge of the substrate, especially with a mask, there is a sharp increase in the RF current density, which proves mainly the surface (end) nature of its flow. The influence of the mask location on the behavior of the electric charge density, which correlates with the distribution of the RF current density in the near-surface layer of the substrate, is established. No redistribution of the charge density of the chemically active plasma particles at the edge of the mask was detected. In accordance with the theoretical results obtained, it is experimentally shown that metal masks with a side length ratio of 36/0 mm reduce the power reflection coefficient within 5%.

Development of Taste Sensor to Detect Non-Charged Bitter Substances

A taste sensor with lipid/polymer membranes is one of the devices that can evaluate taste objectively. However, the conventional taste sensor cannot measure non-charged bitter substances, such as caffeine contained in coffee, because the taste sensor uses the potentiometric measurement based mainly on change in surface electric charge density of the membrane. In this study, we aimed at the detection of typical non-charged bitter substances such as caffeine, theophylline and theobromine included in beverages and pharmaceutical products. The developed sensor is designed to detect the change in the membrane potential by using a kind of allosteric mechanism of breaking an intramolecular hydrogen bond between the carboxy group and hydroxy group of aromatic carboxylic acid (i.e., hydroxy-, dihydroxy-, and trihydroxybenzoic acids) when non-charged bitter substances are bound to the hydroxy group. As a result of surface modification by immersing the sensor electrode in a modification solution in which 2,6-dihydroxybenzoic acid was dissolved, it was confirmed that the sensor response increased with the concentration of caffeine as well as allied substances. The threshold and increase tendency were consistent with those of human senses. The detection mechanism is discussed by taking into account intramolecular and intermolecular hydrogen bonds, which cause allostery. These findings suggest that it is possible to evaluate bitterness caused by non-charged bitter substances objectively by using the taste sensor with allosteric mechanism.

Staged Local Dissolution of Stainless Steel in Chloride Solutions

The paper defines galvanostatic polarization parameters (current density and test duration), to simulate self-dissolution conditions; the results are confirmed by potentiostatic tests. It is shown that under the conditions of self-dissolution simulation, increasing the solution concentration reduces the nucleation rate, while prolonging the pitting development time. Spectral analysis of chronopotentiograms reveals low-frequency potential fluctuations that characterize the nucleation and passivation of pits at the onset of pitting corrosion. The paper describes the basic regularities, observed in the alteration of surface electrochemistry by impedance spectroscopy; such alteration corresponds to the transition from the passive area to the pitting area. The researchers propose optimal electric equivalent circuits to reflect the surface conditions in early nucleation of pits. The paper also proposes an additional pitting resistance criterion, that is, cumulative electric-charge density.

Staged Local Dissolution of Stainless Steel in Chloride Solutions

The paper defines galvanostatic polarization parameters (current density and test duration) to simulate self-dissolution conditions; the results are confirmed by potentiostatic tests. It is shown that under the conditions of self-dissolution simulation, increasing the solution concentration reduces the nucleation rate, while prolonging the pitting development time. Spectral analysis of chronopotentiograpms reveals low-frequency potential fluctuations that characterize the nucleation and passivation of pits at the onset of pitting corrosion. The paper describes the basic regularities observed in the alteration of surface electrochemistry by impedance spectroscopy; such alteration corresponds to the transition from the passive area to the pitting area. The researchers propose optimal electric equivalent circuits to reflect the surface conditions in early nucleation of pits. The paper also proposes an additional pitting resistance criterion, that is, cumulative electric-charge density.

Electric Charge and Its Field as Deformed Space

The essence of electric charge has been a mystery. So far, no theory has been able to derive the attributes of electric charge, which are: bivalency, stability, quantization, equality of the absolute values of the bivalent charges, the electric field it creates and the radii of the bivalent charges. Our model of the electric charge and its field (this paper) enables us (in additional papers), for the first time, to derive simple equations for the radii and masses of the electron/positron muon/anti-muon and quarks/anti-quarks. These equations contain only the constants G, c, ℏ  and α (the fine structure constant). The calculated results based on these equations comply accurately with the experimental results. In this paper, which serves as a basis for the other papers, we define electric charge density, based on space density. This definition alone, without any phenomenology, yields the theory of Electrostatics. Electrostatics together with Lorentz Transformation is known to yield the entire Maxwell Electromagnetic theory.

Tribological Properties of Oxide Coatings Produced on EN AW-5251 Alloy using Different Distances between Electrodes

The subject of the presented work was the analysis of the influence of the distance between the electrodes using in the coating process on the tribological properties of oxide coatings. Oxide coatings were prepared on EN AW-5251 aluminum alloy samples. The samples surfaces were subjected to hard anodizing process in a multicomponent electrolyte based on sulfuric acid with an addition of organic acids. Anodizing was carried out with a constant electric charge density of 180 A·min/dm2. The distances between the electrodes for subsequent samples increased every 0.125 m up to 1 m. The tribological partner in a sliding couple with oxide layers was pin of PEEK/BG. Tribological tests were conducted on a T-17 tester in reciprocating motion, in technically dry friction conditions. Before and after tribological test, examination of the geometrical structure of counter-specimens’ surface was carried out using the Form Talysurf contact profilographometer, via a 3D method. The most satisfactory tribological parameters were obtained for the PEEK/BG association with the coating produced at a distance between the electrodes equal to 0.25 m.