This paper presents a comprehensive electromagnetic transient model for a switched reluctance motor to enable its simultaneous integration into an electromagnetic transient (EMT) type solver with surrounding drive components. In this regard, a circuit-based representation of the machine is developed and used. The proposed model seamlessly integrates a nonlinear permeance network. The machine’s electromagnetic model is automatically constructed using a mesh-based approach, enabling local studies within the machine while accounting for the complete drive system. The airgap is modeled with variable permeances, enabling transient studies without remeshing or reconnecting nodes during runtime. Comparison with the finite element-based model confirms the accuracy of the proposed model and demonstrates its lower computational time. The proposed model is used to simulate transient scenarios of the entire switched reluctance drive system under faulty conditions.
The reduction of tetravalent manganese (Mn-(IV)) to trivalent manganese (Mn-(III)) by HEPES Good's buffer is often used to modify the reactivity of δ-MnO2 and to distinguish between the Mn-(III) and Mn-(IV) oxidants in redox reactions. However, the structure of HEPES-reacted δ-MnO2 has remained elusive, hindering a detailed understanding of interfacial electron transfer between adsorbed species and structural Mn. Here, we characterized the structure of δ-MnO2 reacted with HEPES at pH 6 and 8 under low and high NaCl ionic strength, using chemical analysis, high-energy X-ray diffraction, pair distribution function (PDF), extended X-ray absorption fine structure (EXAFS) spectroscopy, and high-resolution transmission electron microscopy (HRTEM) coupled with selected area electron diffraction (SAED). The average Mn oxidation state (AMOS) decreases from 3.92-3.87 to 3.71-3.59 after HEPES addition, depending on pH and ionic strength. HEPES-reacted δ-MnO2 has a distinctly different structure at low and high ionic strength. At low ionic strength, the δ-MnO2 HE crystallites are 3-6 nm across, and the MnO2 layers have approximately 23% vacant sites capped with mainly Mn-(III) and some Mn-(II). At high ionic strength and pH 8, δ-MnO2 HE contains large crystals, several hundred nanometers across, made up of crystallographically oriented nanodomains. Most SAED patterns show streaks along the [100]* direction, indicating a high degree of disorder in the close packing of the anionic sheets, in the Na position within the interlayer, and in the Mn-(IV)-Mn-(III) distribution within the layer. Some nanodiffraction patterns show distinct superstructure reflections along the streaks with A* = 3a*, as seen in well-crystallized triclinic birnessite, and A* = 6a*. High-ionic-strength δ-MnO2 HE has no interlayer Mn-(III), and the Na-(I) ions, along with the layer Mn-(III) and Mn-(IV) cations, are semiordered at the short- to medium-range scales and essentially disordered over longer distances. Identifying the two distinct structures of HEPES-reacted δ-MnO2 clarifies structural ambiguities reported in the literature and provides a solid foundation for exploring its redox reactivity and electrochemical performance.
Iron-titanium (Fe-Ti) charge transfer is mentioned in numerous articles as the source of the coloration of many natural minerals and some manufactured materials, but no global review of this phenomenon has been provided so far. Iron and titanium are ubiquitous in nature and are often found in the same material as Fe2+ and Fe3+, and Ti4+ (more rarely Ti3+). When Fe and Ti ions are in close geometric proximity in an oxide or (alumino)silicate structure, charge transfer can occur between the two ions, even though their concentration might be below 100 ppm. This results in a variety of absorption features that contribute to the color of minerals. A debate remains on the exact nature of Fe/Ti electronic transition, i.e., Fe2+ + Ti4+ -> Fe3+ + Ti3+ or the reverse, but solving this issue is not within the scope of the present work. Ascertaining a metal-metal charge transfer is often not straightforward. This review compiles existing knowledge on Fe-Ti charge transfer in both crystalline and amorphous materials and identifies several key characteristics in more than 40 different materials. A charge transfer is associated with broad, intense, optical absorption bands that decrease in intensity at elevated temperatures. It is also strongly pleochroic in non-isotropic materials. Until now, Fe-Ti charge transfer transitions have been primarily described in the 2.25 to 3.1 eV range, corresponding to yellow to orange to brown colors, with notable exceptions such as blue sapphire or kyanite, and green andalusite. This review suggests that Fe-Ti charge transfer can occur across the entire visible spectrum, and the position of the absorption band correlates with the Fe-Ti interatomic distance. This correlation highlights the presence of multiple crystallographic sites for both Fe and Ti in many oxides, leading to multiple Fe-Ti bands within these materials (e.g., sapphire, ilmenite, pseudobrookite). Finally, the use of metal-metal distances is suggested to differentiate this heteronuclear Fe-Ti charge transfer from the common homonuclear charge transfer Fe2+-Fe3+.
Organic electrode-active materials (OAMs) represent an alternative to (transition-) metalbased materials used in conventional battery cells. Reversibly oxidizable p-type OAMs allow realizing full-organic battery cells operating in an anion-rocking chair mechanism. In the search for p-type materials with a low redox potential so-called super-electron-donors (SEDs) are a promising class of molecules. Herein, we implement a bi(benzimidazole) (BBI)-based SED into three polymers, PBBI, a conjugated homopolymer, PSBBI as a styrene-based side chain polymer, and X-PSBBI as its crosslinked counterpart. Their properties as potential OAMs in lithium-organic half cells were investigated, and PBBI was found to be electrochemically inactive. The sidechain polymers showed reversible cycling behavior in binder-free powder electrodes in LiBF4-based electrolytes, even though the accessible capacity quickly faded. As possible degradation mechanism we propose decomposition via a dicarbene species as a plausible, reactive key species. This study showcases bi(benzimidazole)s as redox-active groups in OAMs with low redox potential and provides insight into challenges associated with obtaining a reversibly cycling behavior in battery electrodes.
Sand-clay mixtures are often employed as typical reconstituted soils for geotechnical experiments in the laboratory. Sample preparation is an important factor that influences the mechanical behavior of reconstituted clayey soils. It is necessary to use an adapted sample preparation procedure to ensure an optimized sample homogeneity for sand-clay mixtures. There are various methods of soil sample preparation documented in the literature; however, the effect of sample preparation on soil-structure interface shear behavior and soil physical properties has not been well investigated so far. The objective of this paper is to characterize how sample preparation affects the shear behavior of the sand-clay mixture-structure interface and the related physical properties. Sand-clay mixture specimens with clay fractions of 13.75 %, 27.5 %, 41.25 %, and 55 % are prepared by the slurry method and the dry tamping method for the tests. Direct shear tests were carried out on the sand-clay mixture-concrete interface through a device in the laboratory. The physical parameters of the sand-clay mixture samples were measured after the sample preparation and shear tests. A comparison of these results provides an understanding of the role of sample preparation on the sand-clay mixture-concrete interface shear response and physical properties of the samples.
