Nanoindentation responses near single grain boundaries in oxide ceramics

Local mechanical responses near single grain boundaries (GBs) of 9.8 mol% Y₂O₃-stabilized ZrO₂ bicrystals, SrTiO₃ bicrystal, and Al₂O₃ polycrystal were investigated by nanoindentation at room temperature to reveal single GB contributions to the mechanical properties. Contrary to the concept of the Hall–Petch strengthening, the hardness showed negligible variations among grain interiors, GB vicinities, and just on GBs in the samples. Importantly, the hardness may be underestimated owing to GB grooving in thermally etched samples. Despite the negligible change in intrinsic hardness, the transmission electron microscopy observation of the ZrO₂ specimen under impressions revealed dislocation pileups at GBs. These results suggest that single GBs of oxide ceramics prevented dislocation movement but with limited strengthening contributions. This should correspond to the macroscopic Hall–Petch behaviors in oxide ceramics, where the Hall–Petch coefficients normalized by friction stress are significantly smaller than those in metals.     

Influence of inversion level on the optical absorption spectra of Ti-doped transparent MgGa2O4 ceramics

Ti-doped (0.08, 0.30, and 1.00 atomic% [at.%]) transparent MgGa₂O₄ ceramics (possessing a high inversion level; i up to 0.8) were fabricated by pulsed electric current sintering, at 950°C, under vacuum for 30–90 min. Optical transmission, emission, and electron paramagnetic resonance spectra were recorded. The maximal transmission level was ∼70% (820 nm), for a thickness of ∼1 mm, which, while not very high, permitted the observation of the optical absorption bands location and profile. Interpretation of the fluorescence spectra suggests that some Ti⁴⁺ cations (mostly hexacoordinated) were accommodated by the host despite the scarcity of oxygen in the atmosphere during the sintering process. The Ti³⁺ cations substitute native ions located in tetrahedral sites, distorting the original T_d symmetry toward a D_2d symmetry. Comparing the Ti-doped MgGa₂O₄ (high inversion) and MgAl₂O₄ (low inversion) spinels, spectral characteristics revealed that a significant increase in the inversion level drives Ti³⁺ cations from octahedral toward tetrahedral sites. This is reflected in the optical absorption spectra by the disappearance of the band at ∼20 000 cm⁻¹ (detectable in MgAl₂O₄) in MgGa₂O₄; the two d–d bands, of MgA₂O₄, in MgGa₂O₄ are reduced to a single one, located at 11 800 cm⁻¹. These results, for MgGa₂O₄, strongly support a similar assignment—of the strong band at 12 800 cm⁻¹, in Ti-doped MgAl₂O₄—to a tetracoordinated Ti³⁺. Thus, while in MgAl₂O₄, Ti³⁺ appears in both octahedral and tetrahedral coordination and in MgGa₂O₄ only the latter state is stable. In both spinels, Ti dopant speciates into Ti³⁺ and Ti⁴⁺ cations.     

Synthesis and characterization of ferrimagnetic glass‐ceramic frit from waste

The large amount of generated waste determines the importance of their valorization. Red mud is the residue of the Bayer process, which stored cumulative value raises 2.7 Bt. This paper describes an easy way to produce a ferrimagnetic glass‐ceramic frit, using bauxite residue, fly ash and glass cullet as raw materials. The synthesized frit consists of faceted and dendritic agglomerated crystals of magnetite and titanomagnetite embedded in a glass matrix, which exhibits a saturation magnetization (M_S) of 6.3 emu/g, a remanent magnetization (M_R) of 2.7 emu/g and a coercive field (H_C) of 347 Oe. Furthermore, it presents Vickers hardness value of H_V = 5.55 ± 0.16 GPa and fracture toughness value of K_IC = 1.64 ± 0.34 MPa·m^1/2.     

Synthesis of Fe:ZnSe nanopowders via the co-precipitation method for processing transparent ceramics

Fe:ZnSe nanopowders were synthesized via the co-precipitation method for fabricating transparent ceramics. Fe_xZn_1−xSe (0.00 ≤ x ≤ 0.06) powders that were calcined at 400°C yielded a single-phased cubic ZnSe, but when the calcination temperature was raised to 500-600°C, ZnO phase was created. Introduction of pressure could avoid appearance of ZnO. XRD Scherrer analysis revealed a monotonic increase in lattice parameter with increasing Fe²⁺ content. The average powder particle size increased with calcination temperature from several nanometers at 80°C to hundreds of nanometers at 600°C. Attempts to pressurelessly sinter ZnSe powders resulted in the partial decomposition of ZnSe, thus spark plasma sintering was employed to sinter Fe_0.01Zn_0.99Se transparent ceramics with pure ZnSe phase composition, which could be well sintered at 950°C for 30 minutes under an applied pressure of 60 MPa. SEM observations of the polished and thermally etched microstructure of the ceramic revealed a dense microstructure with average grain size of approximately 35 μm, and a few micropores were observed at the grain boundaries. The transparent ceramic exhibited good transmittance in the mid-far infrared range, with the highest transmittance 57% at 12 μm. This paper confirmed the scheme of synthesis of Fe:ZnSe nanopowders by liquid-phase co-precipitation method for sintering transparent ceramics.     

Effect of dilute concentrations of Sm on the temperature‐dependent electrical and dielectric properties of ZnO

Compounds of undoped and samarium (Sm) doped ZnO have been prepared by standard solid‐state reaction method. X‐ray diffraction (XRD), Williamson‐Hall (W‐H) analysis, Transmission Electron Microscopy (TEM), temperature‐dependent electrical and dielectric studies have been done to characterize these materials. Inclusion of Sm as dopant in hexagonal wurtzite ZnO changes the lattice parameters to a small extent with some Sm aggregation at higher concentration. Also, the mean particle sizes of ZnO:Sm compounds showed an inter‐correlation with the Scherrer method, W‐H analysis as well as with TEM results. The electrical resistivity depicts an exponential decay and metal‐semiconductor transition (MST) at ~300 K for the pristine sample whereas there is large decrement in the resistivity with Sm doping. The analysis of σ_ac of ZnO suggests that the power law is obeyed and indicated an increase in the ac conductivity with Sm content. The mechanism behind this type of conductivity is elucidated by small polaron tunneling (SPT) model of conductivity. The dependence of ln dc on the temperature inverse shows that the traps of electrons are thermally activated such that low and high temperature activation energies confirm the presence of vacancies and interstitials of both O and Zn ions. Thus, a high value of dielectric constant makes these materials suitable for high frequency and charge storage device applications.     

Amorphous carbon nanotubes incorporated MgO-graphite composite with enhanced properties for steel making furnaces

Conventional MgO-graphite composite used in steel ladles suffer drawbacks like limited lifetime due to slag corrosion and inherent tendency of rapid oxidation of carbon. Carbon content of MgO-graphite refractories was varied by replacing graphite partly by amorphous carbon nanotubes to decrease the total carbon content keeping the surface area of carbon the same or larger. The structural and compositional characterizations were performed by X-ray diffraction and energy dispersive analysis of X-rays. The Fourier transformed infrared and Raman spectroscopies were used to find bonding information and distinctive carbon phases. Distribution of amorphous carbon nanotubes within MgO matrix and its nature of attachment were studied by field emission scanning electron microscopy and transmission electron microscopy respectively. The cumulative volume of the large pores decreased significantly by incorporation of amorphous carbon nanotubes. Cup test using the composite material with actual molten slag indicated significantly less penetration of slag in the nanocarbon based nanocomposite.     

Yttrium -barium oxide as a robust photocatalyst for photocatalytic degradation of organic dyes under visible light

Based on the structure related to the high-temperature superconductor yttrium-barium-copper oxide, two novel high-efficiency visible light photocatalysts were created in this study. The yttrium-barium oxide (YBO) semiconductors Y₂Ba₃O₆ (YB3O) and Y₂Ba₄O₇ (YB4O) were prepared by a copper-free solid-phase sintering method. They were applied for the effective treatment of dye-containing wastewater by photocatalysis under visible light irradiation. The degradation efficiency of methylene blue (MB) reached more than 95% within 10 min. Stable visible light degradation of methyl orange (MO) was achieved in the presence of YB3O and YB4O. The electron spin resonance technique and active substance capture technique confirmed the presence of superoxide radicals (·O₂^?), hydroxyl radicals (·OH) and holes (h_VB⁺) under visible light illumination. UV–Vis diffuse reflectance spectroscopy analysis showed that the direct optical band gaps of YB3O and YB4O were 2.550 eV and 2.583 eV, respectively, which resulted in their high visible absorption at 486.27 nm and 480.06 nm. After five cycles, the recoveries of YB3O and YB4O reached 67.15% and 72.98%. Therefore, YB3O and YB4O are considered as powerful semiconductor catalysts for the photocatalytic degradation of organic dyes in wastewater.     

Zirconia-based alumina compound aerogels with enhanced mesopore structure

In this study, zirconia-based alumina compound aerogels with enhanced thermal stability were synthesized using a sol-gel process, followed by ambient-pressure drying (APD). Phase-separation control during alcogel synthesis was a critical aspect of APD because of the different sol-gel reaction rates of two-component aerogels. In the present study, we effectively addressed this issue by controlling the sol-gel reaction parameters to obtain a zirconia-based alumina aerogel with atomically bonded Zr–O–Al. This atomic bonding played an important role in maintaining the pore structure of the zirconia aerogels during APD. The compound aerogels inhibited pore structure collapse and increased the specific surface area. In addition, their thermal stability was better than that of pure zirconia aerogels. The textural and physical properties also improved due to the formation of a compound with alumina. Considering these results and the enhanced pore structure of these compound aerogels, they are potentially useful for high-temperature thermal insulation.     

Enhanced activity of iron oxide dispersed on bentonite for the catalytic degradation of organic dye under visible light

Natural clay-supported iron oxide was prepared by deposition method, and dried at 120 °C. It was found that under visible light in the presence of H₂O₂, this catalyst was highly active for degradation of cationic (malachite and fuchsin basic) and anionic dyes (orange II and X3B) in water at pH 6.5, as compared with bare iron oxide or the clay-supported iron oxide sintered at 350 °C. The excellent performance of the catalyst is correlated with its high sorption capacity toward both types of dyes, thus resulting in enhanced dye degradation via a photosensitization pathway. The catalyst was characterized by XRD, nitrogen adsorption, infrared, and UV–visible spectroscopy.     

Photocatalytic degradation of Basic Blue 41 dye under visible light over SrTiO3/Ag3PO4 hetero-nanostructures

In an attempt to develop nanostructured photocatalysts with high performance, SrTiO₃/Ag₃PO₄ hetero-nanostructures were successfully fabricated. The formed binary heterojunctions were composed of SrTiO₃ nanotubes prepared using liquid-phase deposition, and Ag₃PO₄ nanoparticles prepared using a sol–gel method. Synthesis details, including morphology, structure, and optical properties of the prepared photocatalysts, were characterized and comparatively discussed. The results showed that at an optimal ratio of SrTiO₃ to Ag₃PO₄ (20–80), the photocatalytic degradation of Basic Blue 41 under 80-min visible light irradiation is the maximum amount of 99%, which is about 4.4 and 1.5 times higher than that of pristine SrTiO₃ nanorods and Ag₃PO₄ nanoparticles, respectively. It can be due to the synergistic effect of two materials that provide high light absorption and charge carriers’ separation. Finally, a detailed possible mechanism for enhancing the photocatalytic activity of the SrTiO₃/Ag₃PO₄ hetero-nanostructures was proposed.     

Impact of carbon monoxide on PEFC catalyst carbon support degradation under current-cycled operating conditions

It is well known that, even at ppm levels, the presence of CO in a PEFC anode feed stream has a significant impact on the MEA performance. Numerous work on short-term CO impact on PEFC performance under steady-state current demands has been carried out. However, to the best of our knowledge, the impact of long-term (i.e., >600 h) CO contamination on intrinsic Pt and C support aging (Pt oxidation/dissolution/ripening, C oxidation, …) under current-cycled operating conditions has never been explored. In this paper, on the basis of a combined theoretical and experimental approach, we investigate the long-term CO effect on PEFC performance and degradation. Firstly, on the basis of our previously published PEFC materials degradation models, we suggest that anodic CO poisoning could be used to mitigate the cathodic carbon catalyst-support corrosion phenomena and thus to enhance the MEA durability. Secondly, endurance experiments are performed on single fuel cells with current-cycled protocols representative of transport applications. The impact of CO on electrochemical transient response shows a reasonable agreement with simulated behaviors, and it is experimentally demonstrated that the impact of CO on the cell potential degradation rate is strongly dependent on the current-cycle mode.     

Effective photopolymerization of C60 films under simultaneous deposition and UV light irradiation: Spectroscopy and morphology study

An effective method for uniform photopolymerization of C₆₀ films using simultaneous deposition and irradiation with ultraviolet (UV) light is described. The photopolymerization process was monitored as a function of irradiation time using Raman and infrared (IR) spectroscopy. New features appeared in the Raman (near the pentagonal pinch A_g(2) mode) and IR spectra (400-1500 cm⁻¹) after more than 20 h of UV irradiation testifying to the transformation of pristine C₆₀ to polymerized C₆₀ phases. Band shape analysis of the vibrational data revealed: (i) the degree of photopolymerization to be ∼90% after 20 h of irradiation, and (ii) the presence of orthorhombic, tetragonal, and rhombohedral phases in the photopolymerized films. Electron microscopy and diffraction studies revealed the amorphous nature of the photopolymerized films which comprised of crystals with a linear dimension of ∼40-60 nm. No evidence for cracks in the surface of the polymerized film was found. The proposed route for photopolymerization provides an opportunity to prepare extended polymeric C₆₀ films suitable for technological applications.     

Electrophoretic co-deposition of Mn1.5Co1.5O4, Fe2O3 and CuO: Unravelling the effect of simultaneous addition of Cu and Fe on the microstructural,thermo-mechanical and corrosion properties of in-situ modified spinel coatings for solid oxide cell interconnects

A systematic microstructural, thermo-mechanical and electrical characterization of simultaneous Fe–Cu doped Mn–Co spinel coatings processed by electrophoretic co-deposition on Crofer 22 APU is here reported and discussed. An innovative approach for the simultaneous electrophoretic deposition of three spinel precursors is designed, conceived and optimised, with the aim of outlining time- and energy-saving spinel modification routes. The effect of different levels of Cu and Fe co-doping is observed on the stability of the modified Mn–Co spinel phase, the coefficient of thermal expansion (CTE), the corrosion resistance and on the densification behaviour of the obtained coatings. Cu determines an increase of CTE, while Fe has the opposite behavior. The synergic effect of the simultaneous Fe and Cu co-doping results in an improved densification and the stabilization of the MnCo₂O₄ cubic phase. The most interesting results in terms of corrosion resistance are obtained for the Mn_1.28Co_1.28Fe_0.15Cu_0.29O₄ spinel.     

Nature as a blueprint for polymer material concepts: Protein fiber-reinforced composites as holdfasts of mussels

Today’ demands for novel high-performance polymeric materials with precisely adjusted task-specific mechanics, durability and reliability require new concepts. This review introduces the byssus of blue mussels as a conceptual example of a natural functional proteinaceous material with gradual mechanical properties. The structure–function relationship of the involved proteins, as well as their arrangement and interplay are described in detail to gain insights into how nature deals with mechanical polymer gradients. The mussel byssus can serve as a blueprint which already led to bioinspired approaches for novel applications.     

Fe3O4-intercalated reduced graphene oxide nanocomposites with enhanced microwave absorption properties

Fe₃O₄-intercalated reduced graphene oxide (Fe₃O₄-rGO) nanocomposites were synthesized by an in situ reduction process. The results of XRD and XPS analyses suggested the successful formation of a Fe₃O₄ crystal phase within the rGO sheets. The SEM and TEM images demonstrated that Fe₃O₄ was flaky and was inserted stably within the rGO layers to form a typical sandwich-like structure. The hysteresis loops revealed the superparamagnetic behavior of the Fe₃O₄-rGO nanocomposites at room temperature. The electromagnetic parameters revealed that Fe₃O₄-rGO nanocomposites exhibited multiple dielectric relaxation and magnetic resonance. The reflection loss revealed that the maximum loss was −49.53 dB at 6.32 GHz for a thickness of 3.4 mm while the highest effective absorption bandwidth was 2.96 GHz.     

A review of the features and analyses of the solid electrolyte interphase in Li-ion batteries

The solid electrolyte interphase (SEI) is a protecting layer formed on the negative electrode of Li-ion batteries as a result of electrolyte decomposition, mainly during the first cycle. Battery performance, irreversible charge “loss”, rate capability, cyclability, exfoliation of graphite and safety are highly dependent on the quality of the SEI. Therefore, understanding the actual nature and composition of SEI is of prime interest. If the chemistry of the SEI formation and the manner in which each component affects battery performance are understood, SEI could be tuned to improve battery performance. In this paper key points related to the nature, formation, and features of the SEI formed on carbon negative electrodes are discussed. SEI has been analyzed by various analytical techniques amongst which FTIR and XPS are most widely used. FTIR and XPS data of SEI and its components as published by many research groups are compiled in tables for getting a global picture of what is known about the SEI. This article shall serve as a handy reference as well as a starting point for research related to SEI.     

Conducting polymer coated carbon surfaces and biosensor applications

This review article focuses on several approaches in the characterization and modification of carbon surfaces with electrocoated thin films which has been realized by recent progress in experimental methods. Electropolymerization and electrocopolymerization of π-conjugated polymers (pyrrole, carbazole, N-vinylcarbazole and aniline) onto carbon surfaces are reviewed with 348 references. Particular emphasis is placed on the recent nanoscale surface characterization techniques applied to the resulting electrocoated polymers onto carbon fibers (i.e., scanning electron microscopy (SEM), cyclic voltammetry (CV), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), focused ion beam-secondary ion mass spectroscopy (FIB-SIMS), Fourier transformed infrared spectroscopy (reflectance-FTIR), and Raman spectroscopic measurements).     

Effect of process water chemistry and particulate mineralogy on model oilsands separation using a warm slurry extraction process simulation

Variability in ore composition and process parameters is known to affect bitumen recovery from natural oilsands. In this work, we extend our earlier investigations with model oilsands systems (MOS) to determine the effects of calcium, magnesium and bicarbonate ion concentrations in the process water and their interactions with ‘active’ solids such as: kaolinite, montmorillonite and ultra-fine silica. Our results demonstrate that solids mineralogy and decreasing particle size produce negative outcomes on bitumen recovery related to concomitant effects on bitumen droplet size during flotation. In some cases, certain process water chemistries were found to restore recovery, but clay concentration was the key factor.Naturally acidic oilsands are known to give poor bitumen recoveries. An MOS prepared with connate water at pH 2 responded in the same way. Comparison with a typical oilsands showed no significant differences in middlings pH and the large, negative effect on bitumen recovery was not reversed by higher caustic loading during separation. This result may be caused by irreversible co-flocculation of bitumen and mineral particles during preparation of the MOS and may reflect similar behavior in comparable natural samples.     

Organic-inorganic nanocomposite polymer electrolyte membranes for fuel cell applications

Organic-inorganic nanocomposite polymer electrolyte membrane (PEM) contains nano-sized inorganic building blocks in organic polymer by molecular level of hybridization. This architecture has opened the possibility to combine in a single solid both the attractive properties of a mechanically and thermally stable inorganic backbone and the specific chemical reactivity, dielectric, ductility, flexibility, and processability of the organic polymer. The state-of-the-art of polymer electrolyte membrane fuel cell technology is based on perfluoro sulfonic acid membranes, which have some key issues and shortcomings such as: water management, CO poisoning, hydrogen reformate and fuel crossover. Organic-inorganic nanocomposite PEM show excellent potential for solving these problems and have attracted a lot of attention during the last ten years. Disparate characteristics (e.g., solubility and thermal stability) of the two components, provide potential barriers towards convenient membrane preparation strategies, but recent research demonstrates relatively simple processes for developing highly efficient nanocomposite PEMs. Objectives for the development of organic-inorganic nanocomposite PEM reported in the literature include several modifications: (1) improving the self-humidification of the membrane; (2) reducing the electro-osmotic drag and fuel crossover; (3) improving the mechanical and thermal strengths without deteriorating proton conductivity; (4) enhancing the proton conductivity by introducing solid inorganic proton conductors; and (5) achieving slow drying PEMs with high water retention capability. Research carried out during the last decade on this topic can be divided into four categories: (i) doping inorganic proton conductors in PEMs; (ii) nanocomposites by sol-gel method; (iii) covalently bonded inorganic segments with organic polymer chains; and (iv) acid-base PEM nanocomposites. The purpose here is to summarize the state-of-the-art in the development of organic-inorganic nanocomposite PEMs for fuel cell applications.