Microgalvanic Corrosion of Mg–Ca and Mg–Al–Ca Alloys in NaCl and Na2SO4 Solutions

As a kind of potential biomedical material, Mg–Ca alloy has attracted much attention. However, the role of Ca-containing intermetallics in microgalvanic corrosion is still controversial. In 0.6 mol/L NaCl and Na₂SO₄ solutions, the microgalvanic corrosion behavior of the second phase and Mg matrix of Mg–Ca and Mg–Al–Ca alloys was examined. It was confirmed that the Mg₂Ca phase acts as a microanode in microgalvanic corrosion in both NaCl and Na₂SO₄ solutions, with the Mg matrix acting as the cathode and the Al₂Ca phase acting as the microcathode to accelerate corrosion of the adjacent Mg matrix. It was also found that Cl⁻ and SO₄²⁻ have different sensibilities to microgalvanic corrosion.     

Mechanism of H+ dissociation–induced O–O bond formation via intramolecular coupling of vicinal hydroxo ligands on low-valent Ru(III) centers

The understanding of O–O bond formation is of great importance for revealing the mechanism of water oxidation in photosynthesis and for developing efficient catalysts for water oxidation in artificial photosynthesis. The chemical oxidation of the Ru^II₂(OH)(OH₂) core with the vicinal OH and OH₂ ligands was spectroscopically and theoretically investigated to provide a mechanistic insight into the O–O bond formation in the core. We demonstrate O–O bond formation at the low-valent Ru^III₂(OH) core with the vicinal OH ligands to form the Ru^II₂(μ-OOH) core with a μ-OOH bridge. The O–O bond formation is induced by deprotonation of one of the OH ligands of Ru^III₂(OH)₂ via intramolecular coupling of the OH and deprotonated O⁻ ligands, conjugated with two-electron transfer from two Ru^III centers to their ligands. The intersystem crossing between singlet and triple states of Ru^II₂(μ-OOH) is easily switched by exchange of H⁺ between the μ-OOH bridge and the auxiliary backbone ligand.

Water oxidation to produce O₂ (Eq. 1) is an important biological reaction in photosynthesis. The geometric structure of the active site with a manganese-oxo core (Mn₄CaO₅) for water oxidation, so called oxygen-evolving complex (OEC), has been characterized by recently advanced X-ray crystallographic analysis (1–5). The elucidation of the water oxidation mechanism at OEC on the basis of their geometric structure is a high-interest topic in photosynthesis studies. On the other hand, water oxidation is also a crucial process to use water as an electron source for the solar fuel production in artificial photosynthesis technology that is participated as a future solar energy conversion system (6–8). There has been a great deal of interest in developing active catalysts to promote water oxidation to establish efficient artificial photosynthesis systems (9–13). The elucidation of the water oxidation mechanism provides a key clue of the guideline for developing active catalysts for water oxidation.2H2O→O2+ 4H++ 4e−.[1]In a water oxidation process to produce O₂ (Eq. 1), formation of an O–O bond from two molecules of water is necessary with removal of either consecutive or concerted four electrons and four protons from the water (14–16). Commonly, the O–O bond formation is assisted by catalysts (OEC in photosynthesis) with one or two molecules of water bound on them to decrease thermodynamic energy for formation of the intermediate species. Two main classes of the mechanism for the O–O bond formation on metal centers of the catalysts have been reported: water nucleophilic attack (WNA) on metal-oxo centers (Mⁿ = O) (17–22) and interaction of two Mⁿ = O centers (I2M) (23–29). In the WNA mechanism (17–20), a water molecule nucleophilically attacks onto the Mⁿ = O center to generate a Mⁿ⁻²-OOH hydroperoxide intermediate. Therefore, the high-valent Mⁿ = O center (e.g., Ru^{IV or V}) with electrophilic properties is required. In the I2M mechanism (23–27), the coupling of either two Mⁿ⁻¹-O· oxyl radicals (formally Mⁿ = O) or coupling of one Mⁿ⁻¹-O· oxyl radical with another unit (e.g., Mⁿ = O) of nonradical character affords a Mⁿ⁻¹-OO-Mⁿ⁻¹ peroxide intermediate. For this mechanism, the high-valent Mnⁿ = O centers are not necessarily attained, in contrast to the required high-valent Mⁿ = O center in the WNA mechanism. However, O–O bond formation via coupling of relatively low-valent Mⁿ = O units (e.g., Ru^III) has not been demonstrated so far.proximal,proximal-[Ru₂(tpy)₂(pyan)(OH)(OH₂)]³⁺ (Ru^II₂(OH) (OH₂)) (tpy = 2,2′;6′,2″-terpyridine and pyan = 5-phenyl-2,8-di(2-pyridyl)-1,9,10-anthyridine) with the vicinal OH and OH₂ ligands in the Ru^II₂ core was reported to work efficiently for electrocatalytic water oxidation in a homogenous solution (26). The O–O bond formation via intramolecular coupling between the Ru^V = O units, derived from the Ru^II₂ core with the vicinal OH and OH₂ ligands, was suggested for O₂ production. Recently, we reported that O₂ is produced via the intramolecular coupling between the Ru^IV = O and Ru^IV-OH units for the proximal,proximal-[Ru₂(cptpy)₂(pyan)(OH)(OH₂)]⁺ (Hcptpy = 4′-(4-carboxyphenyl)-2,2′;6′,2″-terpyridine) derivative with 4-carboxyphenyl linkers adsorbed on the TiO₂ surface (27). However, the direct spectroscopic evidence has not yet been provided for the O–O bond formation via intramolecular coupling between the Ru^{IV or V} = O units. Herein, we spectroscopically and theoretically investigate chemical oxidation of Ru^II₂(OH)(OH₂) by a Na₂S₂O₈ oxidant in an aqueous solution to provide a mechanistic insight into the O–O bond formation in the unique Ru₂ core. We demonstrate that the O–O bond formation via intramolecular coupling of vicinal OH ligands on Ru^III-OH units is induced by dissociation of one proton of two OH ligands in the core. This is an observation of the O–O bond formation at the low-valent Ru^III centers. The mechanism of the O–O bond formation is revealed to propose the important role of the central N atom (N_c) of the anthyridine moiety on the pyan backbone ligand as a neighboring proton acceptor site for concerted intramolecular electron/proton transfers.     

Thermodynamic Properties,Viscosity, and Structure of CaO–SiO2–MgO–Al2O3–TiO2–Based Slag

The effect of TiO₂ and the MgO/Al₂O₃ ratio on the viscosity, heat capacity, and enthalpy change of CaO–SiO₂–Al₂O₃–MgO–TiO₂ slag at constant heat input was studied. The variation of slag structure was analyzed by the calculation of activation energy and FTIR spectrum measurements. The results showed that the heat capacity and enthalpy change of the slag decreased with the increase of TiO₂ content. Under constant heat supply, the fluctuations in slag temperature were relatively apparent, and the temperature of slag increased as the TiO₂ content increased. The viscosity of slag decreased due to the increase in slag temperature. Increasing the MgO/Al₂O₃ ratio could decrease the temperature and viscosity of slag. The effect of increasing the MgO/Al₂O₃ ratio on the viscosity was more pronounced than the decreasing temperature caused by increasing the MgO/Al₂O₃ ratio. The apparent activation energy decreased with increasing TiO₂ content and MgO/Al₂O₃ ratio. The Ti–O bonds formed with TiO₂ addition, and the Ti–O bonds were weaker than Si–O bonds, which resulted in the decrease in heat capacity and viscosity of slag.     

Phase Relations in a NaFeO2-SnO2 (0–50 mol.% SnO2) System and the Crystal Structure and Conductivity of Na0.8Fe0.8Sn0.2O2

With the view of developing new materials for sodium and sodium-ion power sources, NaFeO₂-SnO₂ (0–50 mol.% SnO₂) powders were synthesized using a solid state method, and their phase composition and crystal structure were studied. A phase of the Na_0.8Fe_0.8Sn_0.2O₂ composition with a layered rhombohedral structure of the α-NaFeO₂ type was found when the tin dioxide content was 20 mol.%. The phase produced was of an O3 structural type. O3-type phases have sufficiently good performance when used as cathode materials in sodium-ion batteries and, moreover, often have a rather high sodium-cation conductivity. A two-dimensional migration map was built using Voronoi–Dirichlet partition and TOPOS software package. The sodium-ion conductivity of Na_0.8Fe_0.8Sn_0.2O₂ at room temperature was rated low (10⁻⁸ S × cm⁻¹ at 20 °C), which may be the result of channels too narrow for Na⁺ migration. The results obtained show that the application of the compound studied in this work as a solid electrolyte in sodium power sources is unlikely. It is the potential use of Na_0.8Fe_0.8Sn_0.2O₂ as the active material of cathodes in Na and Na-ion power sources that presents practical interest.     

Mechanical and Gamma Ray Absorption Behavior of PbO-WO3-Na2O-MgO-B2O3 Glasses in the Low Energy Range

The Makishima and Mackenzie model has been used to determine the mechanical properties of the PbO-WO₃-Na₂O-MgO-B₂O₃ glass system. The number of bonds per unit volume of the glasses (n_b) increases from 9.40 × 10²² to 10.09 × 10²² cm⁻³ as the PbO content increases from 30 to 50 mol%. The Poisson’s ratio (σ) for the examined glasses falls between 0.174 and 0.210. The value of the fractal bond connectivity (d) for the present glasses ranges from 3.08 to 3.59. Gamma photon and fast neutron shielding parameters were evaluated via Phy-X/PSD, while that of electrons were calculated via the ESTAR platform. Analysis of the parameters showed that both photon and electron attenuation ability improve with the PbO content. The fast neutron removal cross section of the glasses varies from 0.094–0.102 cm⁻¹ as PbO molar content reduced from 50–30 mol%. Further analysis of shielding parameters of the investigated glass system showed that they possess good potential to function in radiation protection applications.     

New Solid Solution and Phase Equilibria in the Subsolidus Area of the Three-Component CuO–V2O5–Ta2O5 Oxide System

The results of the study of the three-component system of CuO–V₂O₅–Ta₂O₅ oxides showed, inter alia, that in the air atmosphere in one of its cross-sections, i.e., in the CuV₂O₆–CuTa₂O₆ system, a new substitutional solid solution with the general formula CuTa_2−xV_xO₆ and homogeneity range for x > 0.0 and x ≤ 0.3 is formed. The influence of the degree of incorporation of V⁵⁺ ions into the CuTa₂O₆ crystal lattice in place of Ta⁵⁺ ions on the unit cell volume, thermal stability and IR spectra of the obtained solid solution was determined. Moreover, the value of the band gap energy of the CuTa_2−xV_xO₆ solid solution was estimated in the range of 0.0 < x ≤ 0.3, and on this basis, the new solid solution was classified as a semiconductor. On the basis of the research results, the studied system of CuO–V₂O₅–Ta₂O₅ oxides was also divided into 12 subsidiary subsystems.     

Effects of Vanadium on the Structural and Optical Properties of Borate Glasses Containing Er3+ and Silver Nanoparticles

The erbium-vanadium co-doped borate glasses, embedded with silver nanoparticles (Ag NPs), were prepared to improve their optical properties for potential optical fiber and glass laser application. The borate glasses with composition (59.5–x) B₂O₃–20Na₂O–20CaO–xV₂O₅–Er₂O₃–0.5AgCl (x = 0–2.5 mol%) were successfully prepared by conventional melt-quenching method. The structural properties of glass samples were investigated by XRD, TEM and by Fourier transform infrared (FTIR) spectroscopy while optical properties were carried out by UV–Vis spectroscopy by measuring optical absorption and the emission properties were investigated by photoluminescence spectroscopy. The XRD patterns confirmed the amorphous nature of the prepared glass samples whilst the FTIR confirmed the presence of VO₄, VO₅, BO₃ and BO₄ vibrations. UV–Vis–NIR absorption spectra reveal eight bands which were located at 450, 490, 519, 540, 660, 780, 980, and 1550 nm corresponding to transition of ⁴F_5/2, ⁴F_7/2, ²H_11/2, ⁴S_3/2, ⁴F_9/2, ⁴I_9/2, ⁴I_11/2, and ⁴I_13/2, respectively. The optical band gap (E_opt), Urbach energy and refractive index were observed to decrease, increase and increase, respectively, to the addition of vanadium. Under 800 nm excitation, three emission bands were observed at 516, 580 and 673 nm, which are represented by ²H_11/2–⁴I_15/2, ⁴S_3/2–⁴I_15/2 and ⁴F_15/2–⁴I_15/2, respectively. The excellent features of achieved results suggest that our findings may provide useful information toward the development of functional glasses.     

Experimental Investigation of Radiation Shielding Competence of Bi2O3-CaO-K2O-Na2O-P2O5 Glass Systems

The gamma-ray shielding features of Bi₂O₃-CaO-K₂O-Na₂O-P₂O₅ glass systems were experimentally reported. The mass attenuation coefficient (MAC) for the fabricated glasses was experimentally measured at seven energy values (between 0.0595 and 1.33 MeV). The compatibility between the practical and theoretical results shows the accuracy of the results obtained in the laboratory for determining the MAC of the prepared samples. The mass and linear attenuation coefficients (MACs) increase with the addition of Bi₂O₃ and A4 glass possesses the highest MAC and LAC. A downward trend in the linear attenuation coefficient (LAC) with increasing the energy from 0.0595 to 1.33 MeV is found. The highest LAC is found at 1.33 MeV (in the range of 0.092–0.143 cm⁻¹). The effective atomic number (Z_eff) follows the order B1 > A1 > A2 > A3 > A4. This order emphasizes that increasing the content of Bi₂O₃ has a positive effect on the photon shielding proficiencies owing to the higher density of Bi₂O₃ compared with Na₂O. The half value layer (HVL) is also determined and the HVL for the tested glasses is computed between 0.106 and 0.958 cm at 0.0595 MeV. The glass with 10 mol% of Bi₂O₃ has lower HVL than the glasses with 0, 2.5, 5, and 7.5 mol% of Bi₂O₃. So, the A4 glass needs a smaller thickness than the other glasses to shield the same radiation. As a result of the reported shielding parameters, inserting B₂O₃ provides lower values of these three parameters, which in turn leads to the development of superior photons shields.     

Fe–Doped TiO2–Carbonized Medium–Density Fiberboard for Photodegradation of Methylene Blue under Visible Light

Fe–doped titanium dioxide–carbonized medium–density fiberboard (Fe/TiO₂–cMDF) was evaluated for the photodegradation of methylene blue (MB) under a Blue (450 nm) light emitting diode (LED) module (6 W) and commercial LED (450 nm + 570 nm) bulbs (8 W, 12 W). Adsorption under daylight/dark conditions (three cycles each) and photodegradation (five cycles) were separately conducted. Photodegradation under Blue LED followed pseudo-second-order kinetics while photodegradation under commercial LED bulbs followed pseudo-first-order kinetics. Photodegradation rate constants were corrected by subtracting the adsorption rate constant except on the Blue LED experiment due to their difference in kinetics. For 8 W LED, the rate constants remained consistent at ~11.0 × 10⁻³/h. For 12 W LED, the rate constant for the first cycle was found to have the fastest photodegradation performance at 41.4 × 10⁻³/h. After the first cycle, the rate constants for the second to fifth cycle remained consistent at ~28.5 × 10⁻³/h. The energy supplied by Blue LED or commercial LEDs was sufficient for the bandgap energy requirement of Fe/TiO₂–cMDF at 2.60 eV. Consequently, Fe/TiO₂–cMDF was considered as a potential wood-based composite for the continuous treatment of dye wastewater under visible light.     

Amorphous–Crystalline Calcium Phosphate Coating Promotes In Vitro Growth of Tumor-Derived Jurkat T Cells Activated by Anti-CD2/CD3/CD28 Antibodies

A modern trend in traumatology, orthopedics, and implantology is the development of materials and coatings with an amorphous–crystalline structure that exhibits excellent biocopatibility. The structure and physico–chemical and biological properties of calcium phosphate (CaP) coatings deposited on Ti plates using the micro-arc oxidation (MAO) method under different voltages (200, 250, and 300 V) were studied. Amorphous, nanocrystalline, and microcrystalline statesof CaHPO₄ and β-Ca₂P₂O₇ were observed in the coatings using TEM and XRD. The increase in MAO voltage resulted in augmentation of the surface roughness R_a from 2.5 to 6.5 µm, mass from 10 to 25 mg, thickness from 50 to 105 µm, and Ca/P ratio from 0.3 to 0.6. The electrical potential (EP) of the CaP coatings changed from −456 to −535 mV, while the zeta potential (ZP) decreased from −53 to −40 mV following an increase in the values of the MAO voltage. Numerous correlations of physical and chemical indices of CaP coatings were estimated. A decrease in the ZP magnitudes of CaP coatings deposited at 200–250 V was strongly associated with elevated hTERT expression in tumor-derived Jurkat T cells preliminarily activated with anti-CD2/CD3/CD28 antibodies and then contacted in vitro with CaP-coated samples for 14 days. In turn, in vitro survival of CD4⁺ subsets was enhanced, with proinflammatory cytokine secretion of activated Jurkat T cells. Thus, the applied MAO voltage allowed the regulation of the physicochemical properties of amorphous–crystalline CaP-coatings on Ti substrates to a certain extent. This method may be used as a technological mechanism to trigger the behavior of cells through contact with micro-arc CaP coatings. The possible role of negative ZP and Ca²⁺ as effectors of the biological effects of amorphous–crystalline CaP coatings is discussed. Micro-arc CaP coatings should be carefully tested to determine their suitability for use in patients with chronic lymphoid malignancies.     

The Gd2−xMgxZr2O7−x/2 Solid Solution: Ionic Conductivity and Chemical Stability in the Melt of LiCl-Li2O

Materials with pyrochlore structure A₂B₂O₇ have attracted considerable attention owing to their various applications as catalysts, sensors, electrolytes, electrodes, and magnets due to the unique crystal structure and thermal stability. At the same time, the possibility of using such materials for electrochemical applications in salt melts has not been studied. This paper presents the new results of obtaining high-density Mg²⁺-doped ceramics based on Gd₂Zr₂O₇ with pyrochlore structure and comprehensive investigation of the electrical properties and chemical stability in a lithium chloride melt with additives of various concentrations of lithium oxide, performed for the first time. The solid solution of Gd_2−xMg_xZr₂O_7−x/2 (0 ≤ x ≤ 0.10) with the pyrochlore structure was obtained by mechanically milling stoichiometric mixtures of the corresponding oxides, followed by annealing at 1500 °C. The lattice parameter changed non-linearly as a result of different mechanisms of Mg²⁺ incorporation into the Gd₂Zr₂O₇ structure. At low dopant concentrations (x ≤ 0.03) some interstitial positions can be substituted by Mg²⁺, with further increasing Mg²⁺-content, the decrease in the lattice parameter occurred due to the substitution of host-ion sites with smaller dopant-ion. High-density ceramics 99% was prepared at T = 1500 °C. According to the results of the measurements of electrical conductivity as a function of oxygen partial pressure, all investigated samples were characterized by the dominant ionic type of conductivity over a wide range of pO₂ (1 × 10^–18 ≤ pO₂ ≤ 0.21 atm) and T < 800 °C. The sample with the composition of x = 0.03 had the highest oxygen-ion conductivity (10⁻³ S·cm⁻¹ at 600 °C). The investigation of chemical stability of ceramics in the melt of LiCl with 2.5 mas.% Li₂O showed that the sample did not react with the melt during the exposed time of one week at the temperature of 650 °C. This result makes it possible to use these materials as oxygen activity sensors in halide melts.     

The Effect of ZnO,MgO, TiO2, and Na2O Modifiers on the Physical,Optical, and Radiation Shielding Properties of a TeTaNb Glass System

Novel glass samples with the composition 75TeO₂–5Ta₂O₅–15Nb₂O₅–5x (where x = ZnO, MgO, TiO₂, or Na₂O) in mole percent were prepared. The physical, optical, and gamma radiation shielding properties of the glass samples were studied over a wide energy spectrum ranging between 0.015 and 20 MeV. The glasses’ UV–vis spectra were utilized to evaluate the optical energy gap and refractive index. Glass samples had a refractive index ranging from 2.2005 to 2.0967. The results showed that the sample doped with zinc oxide (ZnO) recorded the highest density (ρ_glass), molar polarizability (α_m), molar refraction (Rm), refractive index (n), and third-order nonlinear optical susceptibility (χ³) and the lowest optical energy gap (E_opt) among the samples under investigation. When comparing the current glass system with various standard glass shielding materials, the prepared glass system showed superior shielding performance at energies ranging between 40 and 85 keV. These findings indicate that the prepared glass systems can be used in diagnostic X-rays, especially in dental applications.     

Characterizing the Chemical Structure of Ti3C2Tx MXene by Angle-Resolved XPS Combined with Argon Ion Etching

Angle-resolved XPS combined with argon ion etching was used to characterize the surface functional groups and the chemical structure of Ti₃C₂T_x MXene. Survey scanning obtained on the sample surface showed that the sample mainly contains C, O, Ti and F elements, and a little Al element. Analyzing the angle-resolved narrow scanning of these elements indicated that a layer of C and O atoms was adsorbed on the top surface of the sample, and there were many O or F related Ti bonds except Ti–C bond. XPS results obtained after argon ion etching indicated staggered distribution between C–Ti–C bond and O–Ti–C, F–Ti bond. It is confirmed that Ti atoms and C atoms were at the center layer of Ti₃C₂T_x MXene, while O atoms and F atoms were located at both the upper and lower surface of Ti₃C₂ layer acting as surface functional groups. The surface functional groups on the Ti₃C₂ layer were determined to include O²⁻, OH⁻, F⁻ and O⁻–F⁻, among which F atoms could also desorb from Ti₃C₂T_x MXene easily. The schematic atomic structure of Ti₃C₂T_x MXene was derived from the analysis of XPS results, being consistent with theoretical chemical structure and other experimental reports. The results showed that angle-resolved XPS combing with argon ion etching is a good way to analysis 2D thin layer materials.     

Elastic Properties and Hardness of Mixed Alkaline Earth Silicate Oxynitride Glasses

The incorporation of nitrogen as a second anion species into oxide glasses offers unique opportunities for modifying glass properties via changes in glass polymerization and structure. In this work, the compositional dependence of elastic properties and the nanoindentation hardness of mixed alkaline-earth silicate oxynitride glasses containing a high amount of nitrogen (>15 at.%, c.a. 35 e/o) were investigated. Three series of silicon oxynitride glass compositions AE–Ca–Si–O–N glasses (where AE = Mg, Sr, and Ba) having varying amounts of modifiers were prepared using a new glass synthesis route, in which a precursor powder of metal hydrides was used. The obtained glasses contained high amounts of N (19 at.%, c.a. 43 e/o) and modifier cations (26 at.%, c.a. 39 e/o). Mg–Ca–Si–O–N glasses had high values of nanohardness (12–16 GPa), along with a reduced elastic modulus (130–153 GPa) and Young’s modulus (127–146 GPa), in comparison with the Sr–Ca- and Ba–Ca-bearing oxynitride glasses. Both the elastic modulus and the nanohardness of AE–Ca–Si–O–N glasses decreased with an increase in the atomic number of the AE element. These property changes followed a linear dependence on the effective cation field strength (ECFS) of the alkaline earth (AE) modifier, according to their valences and ionic radii. No mixed alkaline-earth effect was observed in the current investigation, indicating that the properties were more dictated by the nitrogen content.     

The Surface of Nanoparticle Silicon as Studied by Solid-State NMR

The surface structure and adjacent interior of commercially available silicon nanopowder (np-Si) was studied using multinuclear, solid-state NMR spectroscopy. The results are consistent with an overall picture in which the bulk of the np-Si interior consists of highly ordered (“crystalline”) silicon atoms, each bound tetrahedrally to four other silicon atoms. From a combination of ¹H, ²⁹Si and ²H magic-angle-spinning (MAS) NMR results and quantum mechanical ²⁹Si chemical shift calculations, silicon atoms on the surface of “as-received” np-Si were found to exist in a variety of chemical structures, with apparent populations in the order (a) (Si–O–)₃Si–H > (b) (Si–O–)₃SiOH > (c) (HO–)_nSi(Si)_m(–OSi)_4−m−n ≈ (d) (Si–O–)₂Si(H)OH > (e) (Si–O–)₂Si(–OH)₂ > (f) (Si–O–)₄Si, where Si stands for a surface silicon atom and Si represents another silicon atom that is attached to Si by either a Si–Si bond or a Si–O–Si linkage. The relative populations of each of these structures can be modified by chemical treatment, including with O₂ gas at elevated temperature. A deliberately oxidized sample displays an increased population of (Si–O–)₃Si–H, as well as (Si–O–)₃SiOH sites. Considerable heterogeneity of some surface structures was observed. A combination of ¹H and ²H MAS experiments provide evidence for a substantial population of silanol (Si–OH) moieties, some of which are not readily H-exchangeable, along with the dominant Si–H sites, on the surface of “as-received” np-Si; the silanol moieties are enhanced by deliberate oxidation. An extension of the DEPTH background suppression method is also demonstrated that permits measurement of the T₂ relaxation parameter simultaneously with background suppression.     

Structural,Thermal, and Vibrational Properties of N,N-Dimethylglycine–Chloranilic Acid—A New Co-Crystal Based on an Aliphatic Amino Acid

The new complex of N,N-Dimethylglycine (DMG) with chloranilic acid (CLA) was synthesized and examined for thermal, structural, and dynamical properties. The structure of the reaction product between DMG and CLA was investigated in a deuterated dimethyl sulfoxide (DMSO-d6) solution and in the solid state by Nuclear Magnetic Resonance (NMR) (Cross Polarization Magic Angle Spinning-CPMAS NMR). The formation of the 1:1 complex of CLA and DMG in the DMSO solution was also confirmed by diffusion measurement. X-ray single crystal diffraction results revealed that the N,N-dimethylglycine–chloranilic acid (DMG⁺–CLA⁻) complex crystallizes in the centrosymmetric triclinic P-1 space group. The X-ray diffraction and NMR spectroscopy show the presence of the protonated form of N,N-dimethylglycine and the deprotonated form of chloranilic acid molecules. The vibrational properties of the co-crystal were investigated by the use of neutron (INS), infrared (IR), and Raman (RS) spectroscopies, as well as the density functional theory (DFT) with periodic boundary conditions. From the band shape analysis of the N–CH₃ bending vibration, we can conclude that the CH₃ groups perform fast (τ_R ≈ 10⁻¹¹ to 10^‒13 s) reorientational motions down to a temperature of 140 K, with activation energy at ca. 6.7 kJ mol⁻¹. X-ray diffraction and IR investigations confirm the presence of a strong N⁺–H···O⁻ hydrogen bond in the studied co-crystal.     

Mechanism of and exquisite selectivity for O-O bond formation by the heme-dependent chlorite dismutase

Chlorite dismutase (Cld) is a heme b-dependent, O–O bond forming enzyme that transforms toxic chlorite (ClO₂⁻) into innocuous chloride and molecular oxygen. The mechanism and specificity of the reaction with chlorite and alternate oxidants were investigated. Chlorite is the sole source of dioxygen as determined by oxygen-18 labeling studies. Based on ion chromatography and mass spectrometry results, Cld is highly specific for the dismutation of chlorite to chloride and dioxygen with no other side products. Cld does not use chlorite as an oxidant for oxygen atom transfer and halogenation reactions (using cosubstrates guaiacol, thioanisole, and monochlorodimedone, respectively). When peracetic acid or H₂O₂ was used as an alternative oxidant, oxidation and oxygen atom transfer but not halogenation reactions occurred. Monitoring the reaction of Cld with peracetic acid by rapid-mixing UV-visible spectroscopy, the formation of the high valent compound I intermediate, [(Por^•+)Fe^IV = O], was observed [k₁ = (1.28 ± 0.04) × 10⁶ M⁻¹ s⁻¹]. Compound I readily decayed to form compound II in a manner that is independent of peracetic acid concentration (k₂ = 170 ± 20 s⁻¹). Both compound I and a compound II-associated tryptophanyl radical that resembles cytochrome c peroxidase (Ccp) compound I were observed by EPR under freeze-quench conditions. The data collectively suggest an O–O bond-forming mechanism involving generation of a compound I intermediate via oxygen atom transfer from chlorite, and subsequent recombination of the resulting hypochlorite and compound I.     

Influence of Bi2O3 on Mechanical Properties and Radiation-Shielding Performance of Lithium Zinc Bismuth Silicate Glass System Using Phys-X Software

We analyzed the mechanical properties and radiation-shielding performance of a lithium zinc bismuth silicate glass system. The composition of these glasses is 20ZnO-30Li₂O-(50-x)SiO₂-xBi₂O₃ (x varies between 10 and 40 mol%). The mechanical properties of the investigated glass system, such as Young’s modulus (E), bulk modulus (K), shear modulus (S), and longitudinal modulus (L), were determined using the Makishima–Mackenzie model. The elastic moduli gradually decreased with the addition of Bi₂O₃. E decreased from 46 to 31 GPa, K decreased from 27 to 14 GPa, S decreased from 19 to 14 GPa, and L decreased from 52 to 32 GPa as Bi₂O₃ was substituted for SiO₂. The mass attenuation coefficient (MAC) was investigated at energies between 0.284 and 1.33 MeV to understand the radiation-shielding performance of the glasses. The MAC value increased when SiO₂ was replaced by Bi₂O₃. We found that the effect of Bi₂O₃ on MAC values was noticeably stronger at energies of 0.284 and 0.347 MeV, while the effect of Bi₂O₃ on MAC values became weaker as energy increased. The linear attenuation coefficient (LAC) results demonstrated that if the samples were exposed to low-energy photons, the glass could prevent the penetration of photons, and thus, the glass samples were effective in radiation protection. The LAC values for the lowest- and highest-density samples changed from 0.998 to 1.976 cm⁻¹ (at 0.284 MeV) and from 0.286 to 0.424 cm⁻¹ (at 0.826 MeV). According to the radiation-shielding results, the thick, high-density glass sample has special and distinctive shielding properties.     

Performance Comparison of Lattice-Matched AlInN/GaN/AlGaN/GaN Double-Channel Metal–Oxide–Semiconductor High-Electron Mobility Transistors with Planar Channel and Multiple-Mesa-Fin-Channel Array

In this work, Al_0.83In_0.17N/GaN/Al_0.18Ga_0.82N/GaN epitaxial layers used for the fabrication of double-channel metal–oxide–semiconductor high-electron mobility transistors (MOSHEMTs) were grown on silicon substrates using a metalorganic chemical vapor deposition system (MOCVD). A sheet electron density of 1.11 × 10¹³ cm⁻² and an electron mobility of 1770 cm²/V-s were obtained. Using a vapor cooling condensation system to deposit high insulating 30-nm-thick Ga₂O₃ film as a gate oxide layer, double-hump transconductance behaviors with associated double-hump maximum extrinsic transconductances (g_mmax) of 89.8 and 100.1 mS/mm were obtained in the double-channel planar MOSHEMTs. However, the double-channel devices with multiple-mesa-fin-channel array with a g_mmax of 148.9 mS/mm exhibited single-hump transconductance behaviors owing to the better gate control capability. Moreover, the extrinsic unit gain cutoff frequency and maximum oscillation frequency of the devices with planar channel and multiple-mesa-fin-channel array were 5.7 GHz and 10.5 GHz, and 6.5 GHz and 12.6 GHz, respectively. Hooge’s coefficients of 7.50 × 10⁻⁵ and 6.25 × 10⁻⁶ were obtained for the devices with planar channel and multiple-mesa-fin-channel array operating at a frequency of 10 Hz, drain–source voltage of 1 V, and gate–source voltage of 5 V, respectively.     

Preparation and Performance of Ternesite–Ye’elimite Cement

Ternesite–ye’elimite (TCSA) cement is a new type of environmentally advantageous binder prepared by introducing ternesite, a reactive phase, into belite calcium sulfoaluminate cement clinker. This paper reports the laboratory production of TCSA cement by the addition of minor elements to achieve the coexistence of ternesite and ye’elimite. The influence of dopants on the mineralogical composition of clinkers and the clinkering conditions for the preparation of TCSA cement clinkers were investigated by X-ray powder diffraction and scanning electron microscopy. The mechanical properties and hydration products of the cement pastes were also studied. The results indicated that the addition of CaF₂, P₂O₅ and Na₂O can promote the coexistence of ternesite and ye’elimite, and that Na₂O is the most effective candidate. TCSA cement clinkers could be successfully prepared at 1150 °C for 30 min by doping 0.3% Na₂O. The TCSA cement clinkers exhibited shorter setting times than the BCSA cement clinkers. The later strength of TCSA cement showed a significant increase compared with BCSA cement. The effect of Na₂O was different on the strength development for TCSA and BCSA cement. The dissolution of ternesite could promote the formation of ettringite. The reactivity of belite was higher in TCSA cement due to the formation of strätlingite.