Microstructural and chemical stability of Y-ZrO2 reinforced β″-alumina in molten sodium sulfide and sulfur

The stability of -alumina reinforced with 10 vol% of tetragonal partially stabilized 3 mol% Y₂O₃-ZrO₂ (3Y-ZrO₂) and with 10 vol% of cubic 8 mol% Y₂O₃-ZrO₂ (8Y-ZrO₂) in molten sulfur or molten Na₂S₄ has been examined using scanning electron microscopy (SEM) X-ray diffraction (XRD) and electron probe microanalysis (EPMA) both before and after immersion at 350 °C. Tetragonal partially stabilized 3 mol % Y₂O₃-ZrO₂ was destabilized when reinforced into -alumina and immersed in molten Na₂S₄. Destabilization without incorporation into -alumina or using molten S as the immersion medium was minor. EPMA analyses indicated that the presence of -alumina enhanced zirconia destabilization in that -alumina can react with the molten corrodants to form corrosion products which are known corrosion agents for the leaching of Y₂O₃ from partially stabilized 3Y-ZrO₂. From XRD analyses, changing from partially stabilized 3Y-ZrO₂ to cubic 8Y-ZrO₂ in the composite increased resistance against phase destabilization. EPMA analyses revealed that the depletion was almost halted for cubic 8Y-ZrO₂ suggesting that the change in the zirconia phase used had reduced the chemical reactivity between Y₂O₃ and the corrodants. In order to avoid depletion destabilization of zirconia in -alumina, corrosion resistance can be increased by reducing chemical reactivity by using fully stabilizing zirconia. In addition, partially stabilized tetragonal zirconia may still be considered for use if a less reactive stabilizer such as CeO₂ is used.     

Using Selective Electron Beam Melting to Enhance the High-Temperature Strength and Creep Resistance of NiAl–28Cr–6Mo In Situ Composites

By increasing the density of interfaces in NiAl–CrMo in situ composites, the mechanical properties can be significantly improved compared to conventionally cast material. The refined microstructure is achieved by manufacturing through electron beam powder bed fusion (PBF-EB). By varying the process parameters, an equiaxed or columnar cell morphology can be obtained, exhibiting a plate-like or an interconnected network of the (Cr,Mo) reinforcement phase which is embedded in a NiAl matrix. The microstructure of the different cell morphologies is investigated in detail using scanning electron microscope, transmission electron microscopy, and atom probe tomography. For both morphologies, the mechanical properties at elevated temperatures are analyzed by compression and creep experiments parallel and perpendicular to the building direction. In comparison to cast NiAl and NiAl–(Cr, Mo), the yield strength of the PBF-EB fabricated specimens is significantly improved at temperatures up to 1,027 °C. While the columnar morphology exhibits the best improved mechanical properties at high temperatures, the equiaxial morphology shows nearly ideal isotropic mechanical behavior, which is a substantial advantage over directionally solidified material.     

The relative stability ofβ andβ″-phases in Na2O-Al2O3 beta alumina

To reveal the relative stability of and -phases in beta alumina, effects of Na₂0 content and calcination and annealing history on the relative content of and -phases have been studied for compositions ranging from Na₂O-5Al₂O₃ to Na₂O-9.5Al₂O₃. The relative stability appears to be dependent on the calcination or annealing history, except holding time such as annealing or re-annealing time, but independent of the Na₂O content and the holding time. From these results it can be demonstrated that the relative stability of and -phases is sensitive to the heat treatment path, except the holding time. The two stage model on the /. polytypic transition in silicon carbide has been quoted to explain the heat treatment pathdependent characteristics.     

Electromechanical Behavior of Al/Al2O3 Multilayers on Flexible Substrates: Insights from In Situ Film Stress and Resistance Measurements

A series of Al and Al/Al₂O₃ thin-film multilayer structures on flexible polymer substrates are fabricated with a unique deposition chamber combining magnetron sputtering (Al) and atomic layer deposition (ALD, Al₂O₃, nominal thickness 2.4–9.4 nm) without breaking vacuum and thoroughly characterized using transmission electron microscopy (TEM). The electromechanical behavior of the multilayers and Al reference films is investigated in tension with in situ X-ray diffraction (XRD) and four-point probe resistance measurements. All films exhibit excellent interfacial adhesion, with no delamination in the investigated strain range (12%). For the first time, an adhesion-promoting naturally forming amorphous interlayer is confirmed for thin films sputter deposited onto polymers under laboratory conditions. The evolution of Al film stresses and electrical resistance reveal changes in the deformation behavior as a function of oxide thickness. Strengthening of Al is observed with increasing oxide thickness. Significant embrittlement can be avoided for oxide layer thicknesses ≤2.4 nm.     

In Situ Investigation of Reversible Exsolution/Dissolution of CoFe Alloy Nanoparticles in a Co-Doped Sr2Fe1.5Mo0.5O6−δ Cathode for CO2 Electrolysis

Reversible exsolution and dissolution of metal nanoparticles in perovskite has been investigated as an efficient strategy to improve CO₂ electrolysis performance. However, fundamental understanding with regard to the reversible exsolution and dissolution of metal nanoparticles in perovskite is still scarce. Herein, in situ exsolution and dissolution of CoFe alloy nanoparticles in Co-doped Sr₂Fe_1.5Mo_0.5O_6–δ (SFMC) revealed by in situ X-ray diffraction, scanning transmission electron microscopy, environmental scanning electron microscopy, and density functional theory calculations are reported. Under a reducing atmosphere, facile exsolution of Co promotes reduction of the Fe cation to generate CoFe alloy nanoparticles in SFMC, accompanied by structure transformation from double perovskite to layered perovskite at 800 °C. Under an oxidizing atmosphere, spherical CoFe alloy nanoparticles are first oxidized to flat CoFeO_x nanosheets, and then dissolved into the bulk with structure evolution from layered perovskite back to double perovskite. Electrochemically, CO₂ electrolysis performance can be retrieved during 12 redox cycles due to the regenerative ability of the CoFe alloy nanoparticles. The anchoring of the CoFe alloy nanoparticles in SFMC perovskite via reduction shows enhanced CO₂ electrolysis performance and stability compared with the parent SFMC perovskite.     

Acrylic Resins as Rate-Controlling Membranes in Novel Formulation of a Nine-Day 17β-Estradiol Transdermal Delivery System: In Vitro and Release Modifier Effect Evaluation

The feasibility of transdermal controlled delivery system of 17 β-estradiol was investigated by conducting in vitro release studies. Several new 17 β-estradiol unilaminate adhesive devices capable of releasing 17 β-estradiol in a controlled fashion over a 24-h, 36-h, 96-h, 104-h, 168-h, and 216-h period have been developed using acrylic resins (Eudragits E100, RSPO, and RLPO) as adhesive and rate-controlling polymers. The in vitro release profiles of 17 β-estradiol from various TDS unilaminate devices were characterized in a new developed dissolution tester vessel (total volume 200 ml), using a new paddle. The release of drug from different formulations was measured by a sensitive high-performance liquid chromatographic (HPLC) method. The release of drug from all prepared adhesive devices seems to obey zero-order kinetics (r > 0.98). The effect of two different plasticizers (acetyltributyl citrate [ATBC] and triethyl citrate [TEC]) on the release patterns of 17 β-estradiol from TDS formulations was studied, and they were almost identical. The effect of two different release modifiers, propylene glycol (PG) and myristic acid (MA), on the release pattern of 17 β-estradiol from prepared unilaminate devices was evaluated. It was shown that the use of these release modifiers significantly increased the release of 17 β-estradiol from a TDS unilaminate patch. Furthermore, these data clearly demonstrated that the acrylic resins are suitable polymers for the preparation of 17 β-estradiol TDS adhesive devices.     

Superconducting Properties of In Situ Mg1.05(B1−xCx)2 Doped with Melanin (C16H2O3N2) via Ultrasonication in Ethanol

In this paper, we have reported melanin (C₁₆H₂O₃N₂) as a dopant of MgB₂ for the first time. Here, the effects of melanin doping to the microstructures and superconducting properties of bulk MgB₂ are thoroughly studied from XRD, SEM, TEM, magnetization, and resistivity data. We have analyzed the critical current density (J _c), irreversibility field (H _irr), flux pinning, resistivity, lattice parameters, grain sizes, critical temperatures (T _c), and other microstructures of all the samples. We have varied the doping percentage according to the nominal atomic ratio of Mg_1.05(B_1?x C _x )₂, x=0,0.02,0.06,0.08,0.1. The J _c of all the melanin-doped samples are improved as compared to that of the undoped sample in high-field region (above 6 Tesla) at low temperature. The 8 and 10 % doped samples give the best results. The 8 % doped sample registers an enhancement of J _c by a factor of 3.6 at 7 T and 5 K as compared to that of the undoped one. But, in the low-field region, melanin doping reduces J _c. The H _irr shows remarkable enhancement at low temperatures below 20 K. The best value of H _irr was found for the 8 % doped sample. However, H _irr reduces at high temperatures above 20 K in all the melanin-doped samples. The volume pinning strength of all the doped samples is enhanced over the entire field range. Further improvement in superconducting properties can be achieved by further reducing the size of the melanin particles, increasing density, and improving the homogeneity of doping.     

Dual Properties of Microwave Absorption and Thermal Protection in La0.5Sr0.5FeO3–Al2O3 Pseudobinary Composites

As multifunctional material for microwave absorption and thermal protection, the dielectric and thermophysical properties of equilibrium phases in LSF(La_0.5Sr_0.5FeO₃)–Al₂O₃ pseudobinary phase diagram are investigated herein. Four pseudobinary composites are obtained by sintering at 1400 °C for 10 h with different raw components (x wt% LSF-(100−x) wt% Al₂O₃, x = 20, 40, 60 and 80), labeled as LSFA20, LSFA40, LSFA60, and LSFA80, respectively. After sintering, the main equilibrium phase in LSFA20 and LSFA40 composites is SrAl₁₂O₁₉-based solid solution. For LSFA60 and LSFA80, however, LSF-based and SrAl₁₂O₁₉-based solid solutions are the main equilibrium phases. The increase of conductive LSF content results in the highest dielectric loss tangent and the best microwave absorbing property in LSFA80, in which the bandwidths for reflection loss less than −10 and −5 dB are about 2.37 and 7.7 GHz, respectively, when the thickness is only 1.5 mm. The thermophysical properties reveal that the thermal conductivity in LSF-Al₂O₃ pseudobinary composites shows weak temperature dependence because of the opposite contribution between phonons and electrons. It is lower than that of the traditional thermal barrier coating material of 8 wt% Y₂O₃-stabilized zirconia (8YSZ).     

Experimental Observation of 2 – Anion and its para → ortho Conversion in Solid para hydrogen Using High–Resolution ESR Spectroscopy

We present experimental observations and study of in solid parahydrogen. Since the parahydrogen molecule does not produce local magnetic fields, high–resolution ESR spectra of trapped radicals can be observed in the solid parahydrogen matrices. Using this high–resolution ESR spectroscopy, new quartet ESR signals were observed in –rays irradiated solid parahydrogen and assigned as In addition, para– was observed to convert into ortho– on the storage at 4.2 K. On the other hand, ortho–H ₂ molecule converts into para– at cryogenic temperatures. The difference in the conversion between the H ₂ molecule and the anion is explained by the parity conservation law of wavefunctions on exchanging the protons in homonuclear diatomic molecules such as the anion and H ₂ molecule.     

In situ fabrication of α-Al2O3 and Ni2Al3 reinforced aluminum matrix composites in an Al–Ni2O3 system

α-Al₂O₃ ceramic particles and Ni₂Al₃ intermetallic compound reinforced aluminum matrix composites were successfully fabricated via exothermic dispersion (XD) reaction in an Al–Ni₂O₃ system. Thermodynamic analysis indicated that the reaction between Al and Ni₂O₃ could occur spontaneously due to its negative Gibbs free energy. The reaction characteristic was discussed by using X-ray diffraction (XRD) method and differential scanning calorimetry (DSC) analysis. The results showed that the reactions of the Al–Ni₂O₃ system consisted of two steps as following: (1) the Al firstly reacted with Ni₂O₃ to form the stable α-Al₂O₃ particles and active Ni atoms; (2) the active Ni atoms further reacted with Al to form Ni₂Al₃. The values of activation energy of the two step reactions were around 457.3 and 282.4 kJ/mol, respectively. The scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS) revealed that the Ni₂Al₃ blocks were uniformly distributed throughout the matrix, while the α-Al₂O₃ particles were slightly segregated in the matrix. The strength of the composite is controlled by the strength of Ni₂Al₃ phase, and the tensile strength and the elongation rate of the composite with 30 vol.% reinforcement volume fraction are 210 MPa and 8%, respectively.     

In situ e.s.r. monitoring of the coordination and oxidation states of copper in Cu-ZSM-5 up to 500°C in flowing gas mixtures: 2. Interaction with CH4 and CO

A flow cell was used for the monitoring of the state of copper ions in Cu-ZSM-5 in situ at high temperatures by e.s.r. Reduction of the most reactive square-planar coordinated Cu²⁺ ions to Cu⁺ occurs at 500°C in methane flow. The reoxidation of cuprous to cupric ions at 500°C by NO or O₂ is very fast; and, at 500°C, in mixtures of CH₄ with excess oxygen, most of the copper in CuH-ZSM-5 retains the cupric state. The formation of weak adsorption complexes between isolated Cu²⁺ cations and CO molecules at 200°C leads to a measurable change in coordination. An activated formation of strong adsorption complexes, with charge transfer, takes place on treatment of the CuH-ZSM-5 by CO at 100–300°C. Subsequent heating in He flow removes all ligands at T > 400°C. At 500°C, in CO flow a slow reduction of Cu²⁺ takes place. Cooling of the CuH-ZSM-5 in a mixture [CO + NO] is accompanied by a change in Cu²⁺ coordination which is indicative of a mixed adsorption complex.     

In situ e.s.r. monitoring of the coordination and oxidation states of copper in Cu-ZSM-5 up to 500°C in flowing gas mixtures: 1. Interaction with He,O2, NO,NO2, and H2O

A flow cell was designed for the monitoring of the state of copper ions in Cu-ZSM-5 in situ at high temperatures by e.s.r. In thoroughly purified He or in vacuum there is no spontaneous reduction of the cupric ions up to 500°C. The formation of adsorption complexes between isolated Cu²⁺ cations and NO molecules at 20°C leads to a measurable change in coordination. Strong adsorption complexes of Cu²⁺ with NO₂ are formed on treatment of CuH-ZSM-5 by an [NO + O₂] mixture. Bonding of Cu²⁺ ions with such strong ligands as NO₂ or H₂O attenuates the spin-lattice interaction between Cu²⁺ and the zeolitic framework. The number of Cu²⁺ ions in CuH-ZSM-5 is quantified by the use of the e.s.r. signal of frozen, dilute water solutions of CuSO₄ as a reference. In the samples used in this work the e.s.r. signal is associated with all the copper introduced into ZSM-5 by ion-exchange.     

Fabrication of Shape-Controlled Au Nanoparticles in a TiO2-Containing Mesoporous Template Using UV Irradiation and Their Shape-Dependent Photocatalysis简

A SiO_2-TiO_2 template with ordered tubular mesochannels has been prepared by the sol—gel method.Au nanorods are deposited in the tubular mesochannels of the SiO_2—TiO_2 template,and the shape of Au is changed from nanorods to nanospheres by ultraviolet irradiation during thermal deposition.The photocatalytic activity of mesoporous SiO_2—TiO_2 with/without Au nanorods/nanospheres is evaluated.Deposition of Au in the mesoporous SiO_2—TiO_2 template enhances the photocatalysis of TiO_2.Interestingly,the sample containing Au nanorods exhibits higher photocatalytic activity than that with Au nanospheres.Photocatalysis by exciting surface plasmon resonance is not detected in the composite samples regardless of the shape of the deposited Au nanoparticles.     

Atomic?Scale Layer?by?Layer Deposition of FeSiAl@ZnO@Al2O3 Hybrid with Threshold Anti?Corrosion and Ultra?High Microwave Absorption Properties in Low?Frequency Bands

Developing highly efficient magnetic microwave absorbers (MAs) is crucial, and yet challenging for anti-corrosion properties in extremely humid and salt-induced...     

Revealing the Anisotropy in MgB<Subscript>2</Subscript> Superconductor and Investigation of Critical Current near Critical Temperature by Using Hall Probe Susceptibility Technique

We report the results of an investigation on critical current measurements in bulk MgB₂ superconductor by using Hall probe ac susceptibility. The temperature versus ac susceptibility has been measured as a function of external ac magnetic field with no dc part and magnitude in the range 240–1200 A/m by using the Hall probe method. The real part of the Hall probe susceptibility showed two-step transitions near critical temperature. We attributed this behavior to the anisotropic nature of the MgB₂ compound. Close to the critical temperature the estimated anisotropy parameter is γ≈2.5, a value that is in fair agreement to the ones reported in the literature for polycrystalline and single crystals MgB₂. We have also analyzed the susceptibility data within the framework of a critical state model (using the real part of the susceptibility) and an anisotropic nature of MgB₂ compound. The inter-grain critical current is found to be 4×10⁶ A/m² at 39.59 K by using the critical state model. The temperature dependence of the critical current density was found to be in the form of J _c (T)∝(1−T/T _c ) ^β , where β was calculated as 2.30 by using critical state model, respectively. Scanning electron microscopy was used for grain size estimation.     

Ultrahigh Mass Accuracy in Isotope-Selective Collision-Induced Dissociation Using Correlated Sweep Excitation and Sustained Off-Resonance Irradiation: A Fourier Transform Ion Cyclotron Resonance Mass Spectrometry Case Study on the [M + 2H](2+) Ion of Bradykinin

Using electrospray ionization with a 9.4 T Fourier transform mass spectrometer, fragment ion spectra were acquired for a single isotopomer of doubly protonated bradykinin (molecular mass, 1059.6 Da). Correlated sweep excitation methods were applied to mass-select the single isotopomer (m/z = 530.8). Sustained off-resonance irradiation was used to activate and fragment the ions. The accuracy (in terms of m/z) in detection of the fragment ions was on average 1.2 ppm, making the assignments unambiguous. The methods employed would be generally applicable to ions in the mass range of approximately 50 Da to 50 kDa.     

Electronic Absorption Spectra of GaCl<Subscript>3</Subscript> and Ga<Subscript>2</Subscript>O<Subscript>3</Subscript> Solutions in Chloride—Fluoride Melts

Electronic absorption spectra of GaCl₃ and Ga₂O₃ solutions in molten alkali metal chlorides and in NaCl-KCl-NaF and LiF-NaF melts were measured by reflection-absorption spectroscopy. The spectral data showed that the main structural units in the solutions are complexes GaHlg ₄ ^? (Hlg = Cl, F) with T _d symmetry and GaOHlg ₃ ^2? with C_3v symmetry, respectively. Molecular oxygen occurring in molten systems as an admixture causes exchange decomposition with formation in all the melts of molecular complexes of chlorine, Cl₂Cl^?, with C_∝v symmetry.