Photocatalytic degradation of organic dyes with H<Subscript>3</Subscript>PW<Subscript>12</Subscript>O<Subscript>40</Subscript>/TiO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript>

H₃PW₁₂O₄₀/TiO₂–SiO₂ was synthesized by impregnation method which significantly improved the catalytic activity under simulated natural light. The properties of the samples were characterized by Fourier transform infrared spectra (FTIR), X-ray powder diffraction pattern (XRD), Scanning electron micrographs (SEM), and Zeta potential. Degradation of methyl violet was used as a probe reaction to explore the influencing factors on the photodegradation reaction. The results show that the optimal conditions are as follows: initial concentration of methyl violet of 10 mg·L^?1, pH of 3.0, catalyst dosage of 2.9 g·L^?1, and light irradiation time of 2.5 h. Under these conditions, the degradation rate of methyl violet is 95.4 %. The reaction on photodegradation for methyl violet can be expressed as the first-order kinetic model, and the possible mechanism for the photocatalysis under simulated natural light is suggested. After used continuously for five times, the catalyst keeps the inherent photocatalytic activity for degradation of dyes. The photodegradation of methyl orange, methyl red, naphthol green B, and methylene blue was also tested, and the degradation rate of dyes can reach 81 %–100 %.     

In situ Formed α-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Nanocrystals Repaired the Preexisting Microcracks in Plasma-Sprayed Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Coating via Stress-Induced Phase Transformation

In the present study, the phase composition and generation mechanism of the nanocrystals located in the microcracks of plasma-sprayed Al₂O₃ coating were reevaluated. The Al₂O₃ coatings were investigated using transmission electron microscopy and x-ray diffraction. We supply the detailed explanations to support the new viewpoint that in situ formation of α-Al₂O₃ nanocrystals in the preexisting microcracks of the as-sprayed Al₂O₃ coating may be due to the stress-induced phase transformation. Owing to the partially coherent relationship, the phase interfaces between the α-Al₂O₃ nanocrystals with the preferred orientation and the γ-Al₂O₃ matrix may possess better bonding strength. The α-Al₂O₃ nanocrystals could repair the microcracks in the coating, which further strengthens grain boundaries. Grain boundary strengthening is beneficial to the coating fracture toughness enhancement.     

Phase and Microstructure Evolution and Toughening Mechanism of a Hierarchical Architectured Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–Y<Subscript>2</Subscript>O<Subscript>3</Subscript> Coating under High Temperature

In recent years, numerous techniques have been developed to mimic nacre-like hierarchical architectures in order to improve the damage tolerance of materials. We present herein a simple strategy to fabricate such a hierarchical architectured Al₂O₃–Y₂O₃ composite coating via atmospheric plasma spraying. The evolution of the phase and microstructure of the Al₂O₃–Y₂O₃ composite coating were characterized under conditions of high-temperature exposure in air at 800-1350 °C. The hardness and porosity of several typical coatings were determined. In situ formation of dense hierarchical architectured Al₂O₃–YAG composite coating with improved hardness was achieved after heat treatment at 1350 °C. Compared with Al₂O₃ coating, elevated toughness was found for the hierarchical architectured Al₂O₃–YAG composite coating, which can be ascribed to the distribution of YAG phase that contributed to crack termination and deflection, and microbridging. After thermal aging treatment at 1350 °C, the hierarchical architectured Al₂O₃–YAG composite coating was quite stable after 100 h of thermal exposure. Furthermore, the Al₂O₃–Y₂O₃ composite coating exhibited superior sintering resistance compared with the Al₂O₃ coating.     

The effect of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles on tribological and corrosion behavior of electroless Ni–B–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> composite coating

In this study, the Ni–B–Al₂O₃ composite was successfully coated on the surface of Ck45 steel by elecroless method. X-Ray diffraction analysis (XRD) and scanning electron microscopy (SEM) were utilized in order to investigate and identify the coating properties. Wear behavior of the coating was studied by the pinon- disk test. Corrosion behavior of the Ni–B and Ni–B–Al₂O₃ coatings was investigated by using Tafel polarization diagrams in the 3.5% NaCl solution at room temperature. The obtained data demonstrate that the addition of Al₂O₃ nanoparticles to the coating has resulted in improving the tribological behavior of the coating due to the presence of the composite nanoparticles. Also, the results of electrochemical testing show that corrosion resistance of the electroless Ni–B coating with Al₂O₃ nanoparticles has dramatically increased.     

Accelerated Hot Corrosion Studies of D-Gun-Sprayed Cr<Subscript>2</Subscript>O<Subscript>3</Subscript>–50% Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Coating on Boiler Steel and Fe-Based Superalloy

In the current investigation, Cr₂O₃–50% Al₂O₃ coating was deposited on ASTM-SA213-T-22 boiler steel and Fe-based superalloy Superfer 800H by D-gun spray process. The high-temperature corrosion performance of the coated as well as bare alloys was evaluated in Na₂SO₄–60%V₂O₅ molten salt, an aggressive environment at 900 °C under cyclic conditions. The kinetics of the corrosion were analyzed by the change in weight measurements which were taken after each cycle (i.e., 1-h heating in a tube furnace followed by 20-min cooling in ambient air) for a total period of 50 cycles. The X-ray diffraction and scanning electron microscopy/energy-dispersive X-ray analysis techniques were used for the analysis of corrosion products. During investigations, it was found that both the selected bare alloys have suffered intensive spallation in the form of removal of their oxide scales, which may be attributed to the formation of non-protective Fe₂O₃-dominated oxide scales, whereas the coated alloys have shown lesser weight gains along with better adhesiveness of the oxide scales with the substrate till the end of the experiment. The oxides of chromium and aluminum were the main phases revealed in the oxide scales of the coated specimens, which are reported to be protective against the hot corrosion.     

Electrochemical and interfacial properties of (PEO)<Subscript>10</Subscript>LiCF<Subscript>3</Subscript>SO<Subscript>3</Subscript>−Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanocomposite polymer electrolytes using ball milling

Electrochemical and interfacial properties of (PEO)₁₀LiCF₃SO₃−Al₂O₃ composite polymer electrolytes (CPEs) prepared by either ball milling or stirring are reported. Ball milling was introduced into a slurry preparative technique utilizing PEO, lithium salt and Al₂O₃ powder ranging from 5 to 15 wt.%. The ionic conductivity was increased by ball milling over a range of temperatures. In particular, a significant increase at low temperature below the melting point of crystalline PEO was observed. Interfacial stability between lithium electrode and CPE was significantly improved by the addition of alumina as well as by ball milling. The electrochemical stability window produced by (PEO)₁₀LiCF₃SO₃−Al₂O₃ ball milling was higher than that of stirring, which was about 4.4 V. Charge/discharge performance of Li/CPE/S cells with (PEO)₁₀LiCF₃SO₃−Al₂O₃-12 hr ball milling was superior to that of a pristine polymer electrolyte due to the low interface resistance and high ionic conductivity.     

Leakage currents in Ti−O/Ta<Subscript>2</Subscript>O<Subscript>5</Subscript> thin film deposited on Ta/Ti/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

The electrical characteristics of Ta/Ta₂O₅ films and Ta/Ti−O/Ta₂O₅ films deposited by RF reactive sputtering on Ta/Ti/Al₂O₃ substrates were investigated. Ta was used for the bottom and upper electrodes in order to simplify the fabrication process. Dielectric materials were annealed at 700°C for 60 sec under vacuum. XRD analysis showed that Ta was crystalline and Ta₂O₅ was amorphous in an as-deposited state, but amorphous Ta₂O₅ was transformed to a crystalline state by rapid thermal heat treatment. We compared lnJ-E², C−V, and C−F of both as-deposited and annealed dielectric thin films deposited on the Ta bottom electrode. From these results, we concluded that introducing a Ti−O buffer layer could reduce the leakage current. The conduction mechanisms of Ti−O/Ta₂O₅ could be interpreted appropriately by hopping conduction and space-charge-limited current.     

Densification Kinetics of CeO<Subscript>2</Subscript> Reinforced 8 Mol.% Y<Subscript>2</Subscript>O<Subscript>3</Subscript> Stabilized ZrO<Subscript>2</Subscript> Ceramics

The grain growth kinetics of 8YSZ ceramics processed using spark plasma sintering (SPS) has been investigated in the temperature ranging from 1100°C to 1500°C. The activation energy during SPS densification was obtained as 332 kJ/mol with grain boundary diffusion as a dominant mechanism. Further, the effect of CeO₂ on the densification kinetics of 8YSZ ceramic processed via SPS and conventional sintering (CS) has been delineated. The lower grain boundary mobility of CS-processed composites (an order of magnitude lower than SPS) is attributed to the solute drag and lattice distortion mechanism. However, no significant change in the grain boundary mobility was observed with CeO₂ addition (~?14.7–43.9?×?10^?18 m³/N/s for CS and 107.2–116.7?×?10^?18 m³/N/s for SPS) revealing that the defect concentration is nearly constant in 8YSZ. The study highlights the effect of sintering techniques (SPS and CS) and reinforcement (CeO₂) on engineering the desired microstructure of 8YSZ ceramic.     

Investigations on Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript>/Ti<Subscript>3</Subscript>O<Subscript>5</Subscript> Composite as an Anode Material for Lithium–Ion Batteries

The Ti₃O₅ powder with uniform morphology has been successfully obtained and used to synthesize Li₄Ti₅O₁₂/Ti₃O₅ composite material by ball milling for modifying Li₄Ti₅O₁₂-based, lithium–ion battery anodes. Moreover, according to the relative performance investigations, the synthesized Li₄Ti₅O₁₂/Ti₃O₅ composite shows better electrochemical properties than that of the Li₄Ti₅O₁₂. At a high rate (10 C), the capacity of the Li₄Ti₅O₁₂/Ti₃O₅ composite electrode is 139.8 mAhg^?1, whereas the value of Li₄Ti₅O₁₂ is 121.6 mAhg^?1, showing a capacity enhanced about 14.97%. After 100 cycles at 0.2 C, the discharge capacity of Li₄Ti₅O₁₂/Ti₃O₅ remains at 160 mAhg^?1 with a capacity loss of 2.6%. The results indicate that the Li₄Ti₅O₁₂/Ti₃O₅ composite electrode can be used as anode material with a relatively higher rate capability and excellent cycle performance in lithium–ion batteries.     

Hydrothermal conversion of Ti-containing minerals in system of Na<Subscript>2</Subscript>O–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript>–CaO–TiO<Subscript>2</Subscript>–H<Subscript>2</Subscript>O

Titanium has a great effect on the digestion of bauxite in the Bayer process because it reacts readily at high temperatures in alkaline sodium aluminate solution. Under this consideration, the hydrothermal conversion of Ti-containing minerals in the system of Na₂O–Al₂O₃–SiO₂–CaO–TiO₂–H₂O with increased temperatures was studied based on the thermodynamic analysis and systematic experiments. The results show that anatase converts to Al₄Ti₂SiO₁₂ at low temperatures (60–120 °C), which is similar to anatase in crystal structure. As the temperature continues to rise, Al₄Ti₂SiO₁₂ decomposes gradually and converts to Ca₃TiSi₂(Al₂Si_0.5Ti_0.5)O₁₄ at 200 °C. When the temperature reaches 260 °C, CaTiO₃ forms as the most stable titanate species for its hexagonal closest packing with O^2? and Ca²⁺. The findings enhance the understanding of titanate scaling in the Bayer process and clarify the mechanism of how additive lime improves the digestion of diaspore.     

Tribological Behavior of Plasma-Sprayed Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-20 wt.%TiO<Subscript>2</Subscript> Coating

Al₂O₃-20 wt.% TiO₂ ceramic coatings were deposited on the surface of Grade D steel by plasma spraying of commercially available powders. The phases and the microstructures of the coatings were investigated by x-ray diffraction and scanning electron microscopy, respectively. The Al₂O₃-20 wt.% TiO₂ composite coating exhibited a typical inter-lamellar structure consisting of the γ-Al₂O₃ and the Al₂TiO₅ phases. The dry sliding wear behavior of the coating was examined at 20 °C using a ball-on-disk wear tester. The plasma-sprayed coating showed a low wear rate (~4.5 × 10^?6 mm³ N^?1 m^?1), which was <2% of that of the matrix (~283.3 × 10^?6 mm³ N^?1 m^?1), under a load of 15 N. In addition, the tribological behavior of the plasma-sprayed coating was analyzed by examining the microstructure after the wear tests. It was found that delamination of the Al₂TiO₅ phase was the main cause of the wear during the sliding wear tests. A suitable model was used to simulate the wear mechanism of the coating.     

Production and Characterization of Metastable ZrO<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>Coatings Obtained by APS + Quench

Producing nanostructured materials through metastable phases is an interesting novel route in the field of ceramic materials. Due to their small grain size and uniform structure, these nanostructured bulk materials exhibit very interesting properties. Metastable coatings can be produced starting from microstructured powders through atmospheric plasma spray technique, followed by a quenching route. The initial powders are melted during the spraying and deposited over a substrate that is quenched with liquid nitrogen feeders, producing metastable coatings. The thermal-sprayed coatings have been characterized using x-ray diffraction, scanning electron microscopy, field emission scanning electron microscopy, and energy dispersive spectroscopy. The properties of such coatings have been also studied obtaining promising results.     

Synthesis and characterization of Ba<Subscript>0.5</Subscript>Sr<Subscript>0.5</Subscript>Co<Subscript>0.8</Subscript>Fe<Subscript>0.2</Subscript>O<Subscript>3−σ</Subscript>

Perovskite-type Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCFO) powders were synthesized using two methods, solid-state reaction (SSR) method and citrate-EDTA complexing method (CC-EDTA). Then the powders were pressed to green disks of 19 mm in diameter and sintered at 1140°C for 5 h. The shrinkage rate and relative density of the membranes prepared from the perovskite-type powders were determined and calculated, and the powders and derived membranes were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that the shrinkage rates of the two kinds of disks are nearly the same (about 10%). The disks prepared by the SSR method had a bigger grain size and lower relative density than those prepared by the CC-EDTA method. The conductivity of the membranes prepared by the SSR method was about 38 S/cm, higher than that of the membranes prepared by the CC-EDTA method, which was about 30 S/cm, at the same temperature of 600°C.     

<Superscript>57</Superscript>Fe Mössbauer spectroscopy of synthesized ɛ-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles

Magnetic nanoparticles have promising applications in many areas, for example optics, electronics, biology, medicine, etc. The primary goal of this study was to synthesize nanoparticles of magnetic ?-Fe₂O₃ embedded in amorphous SiO₂. The structure and properties of the final product have been found to depend strongly on the initial conditions of preparation. The Mössbauer spectroscopy analysis of the samples was complemented by the study of X-ray powder diffraction, magnetic measurements, and high-resolution transmission electron microscopy.     

Structure and Tribological Performance of Nanostructured ZrO<Subscript>2</Subscript>-3 mol% Y<Subscript>2</Subscript>O<Subscript>3</Subscript> Coatings Deposited by Air Plasma Spraying

In this study, nanostructured ZrO₂-3 mol% Y₂O₃ coatings were deposited by air plasma spray using reconstituted feedstock. The coating structures were characterized by x-ray diffractometer, micro-Raman spectrometer, field emission scanning electron microscope, and transmission electron microscope. It is revealed that the as-sprayed coating is mainly composed of columnar grains with diameters <100 nm and demonstrates the better toughness, higher microhardness, and lower porosity. It consists only of nontransformable tetragonal ZrO₂ phase. The tribological performance of the coating was examined with a ball-on-disk apparatus under dry sliding conditions. The results show that the friction coefficient of as-sprayed coating was approximately one-fifth of the conventional zirconia coating and wear rate was lower one order of magnitude than the conventional zirconia coating. The dominant wear mechanism is abrasive wear. The improved wear resistance can be attributed to the increased mechanical properties of as-sprayed coating.     

Synthesis of SnFe<Subscript>2</Subscript>O<Subscript>4</Subscript> Nanomaterials Via High Energy Ball Milling of SnO (Stannous) and α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> (Hematite) Solid Precursors

The synthesis of single phase tin-ferrite, SnFe₂O₄, from tin (II) oxide or stannous oxide (SnO), and hematite (α-Fe₂O₃) solid precursors was carried out via high energy ball milling (HEBM) under wet condition involving the addition of controlled amounts of acetone. The stoichiometric amounts of the precursor materials were ball milled continuously for up to 22 h in a Spex-8000D mill using a ball-to-powder ratio of 40:1, with hardened stainless steel balls in WC-lined jars. The time-dependent formation of the SnFe₂O₄ based on combined X-ray diffraction and room temperature Mössbauer spectroscopy (MS) measurements revealed reaction enhancements associated with particles size reduction. The 22 h milled material indicated that synthesized SnFe₂O₄ had a particle size of 10.91 nm, coercivity of 4.44 mT, magnetic saturation/remanent ratio (M _r/M _s) of 0.085, while its superparamagnetic behavior was confirmed based on the combined MS and vibrating sample magnetometer measurements.     

Functionally gradient (YSZ-20% Al<Subscript>2</Subscript>O<Subscript>3</Subscript>)−SUS422 composites

Functionally gradient materials (FGMs) were prepared by mixing 5 layers comprised of different ratios of (YSZ-20%Al₂O₃) and 422 stainless (SUS422) powders, followed by hot pressing for densification. Two design concepts were proposed: One as a FGM with a monotonic change of the CTE (coefficient of thermal expansion) for each layer, and is designated as the monotonic mode, and the other was a FGM with a change of CTE that is not monotonic for each layer, and is termed the non-monotonic mode. The FGM with a monotonic CTE mode cracked at the ceramic surface after it was removed from the hot pressing furnace. In contrast, the FGM with a non-monotonic CTE mode survived after hot pressing. Based on ABAQUS simulation results, a non-monotonic change in CTE resulted in a decrease of residual stress on the ceramic side but an increase inside the metal-rich layers of the FGMs. The induced change in the stress distribution inside the FGMs was compromised by the deformation of the metal-rich ingredient (SUS422) in the FGM. Thermal shock tests of FGMs were performed between 25°C and 600°C. The non-monotonic FGM endured up to 100 thermal cycles with only slight bending, and was free of delamination and cracking. The use of composition-adjusted layers to manipulate thermal expansion coefficients of each layer greatly changed the stress contour of the FGM. It is noted that a modified functional-gradient FGM can be fabricated with a hard ceramic surface on one side to resist high temperature, and a ductile metallic surface on the other side to provide toughness.     

Oxidation and Hot Corrosion Behavior of Plasma-Sprayed MCrAlY–Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> Coatings

The oxidation and hot corrosion behavior of two atmospheric plasma-sprayed NiCoCrAlY–Cr₂O₃ and CoNiCrAlY–Cr₂O₃ coatings, which are primarily designed for wear applications at high temperature, were investigated in this study. The two coatings were exposed to air and molten salt (75%Na₂SO₄–25%NaCl) environment at 800 °C under cyclic conditions. Oxidation and hot corrosion kinetic curves were obtained by thermogravimetric technique. X-ray diffraction analysis and scanning electron microscopy with energy-dispersive x-ray spectrometry were employed to characterize the coatings’ microstructure, surface oxides, and composition. The results showed that both coatings provided the necessary oxidation resistance with oxidation rates of about 1.03 × 10^?2 and 1.36 × 10^?2 mg/cm² h, respectively. The excellent oxidation behavior of these two coatings is attributed to formation of protective (Ni,Co)Cr₂O₄ spinel on the surface, while as-deposited Cr₂O₃ in the coatings also acted as a barrier to diffusion of oxidative and corrosive substances. The greater presence of Co in the CoNiCrAlY–Cr₂O₃ coating restrained internal diffusion of sulfur and slowed down the coating’s degradation. Thus, the CoNiCrAlY–Cr₂O₃ coating was found to be more protective than the NiCoCrAlY–Cr₂O₃ coating under hot corrosion condition.     

Hot Corrosion Behavior of YSZ and CaZrO<Subscript>3</Subscript>/YSZ Composite Thermal Barrier Coatings in Contact with 50V<Subscript>2</Subscript>O<Subscript>5</Subscript> + 50Na<Subscript>2</Subscript>SO<Subscript>4</Subscript> Salts

A novel thermal barrier coating system was formulated to resist hot corrosion environments. In this coating system, 5% CaZrO₃ was added to conventional yttria-stabilized zirconia (YSZ). The above composite coating system was compared with the standard YSZ system in the presence of a mixture of 50% Na₂SO₄ and 50% V₂O₅ at 950 °C. The results demonstrated that the lifetime of the CaZrO₃-added composite system in this highly hostile environment was longer compared with the standard YSZ system. This is due to the fact that the preferential reaction of NaVO₃ shifted from yttria to calcia, forming CaV₂O₄ instead of YVO₄. The preferential reactions are discussed in terms of free energy changes and acid–base theory of molten salts with ceramic oxides. Furthermore, calculations of lattice distortion also proved that the CaZrO₃-added composite system demonstrated less distortion, thus increasing the overall lifetime of the coating system.     

On the Al5083–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–TiO<Subscript>2</Subscript> Hybrid Surface Nanocomposite Produced by Friction Stir Processing

In this study Al5083–Al₂O₃–TiO₂ hybrid surface nanocomposite was successfully prepared by friction stir processing (FSP). The effects of different combination of rotational and travel speed of tool were investigated. The samples were characterized by optical and scanning electron microscopy (SEM), microhardness and undergone tensile and wear tests. Based on the maximum tensile strength and hardness value, optimum rotational speed of 710 rpm and travel speed of 20 mm/min was achieved. The microhardness and tensile strength of the as-received alloy and specimens having optimum surface nanocomposite were about 80 Hv, 285 MPa, 140 Hv and 375 MPa, respectively. Surface nanocomposites showed significantly lower friction coefficients and wear rates than those obtained for substrate. Based on scanning electron microscopy tests, abrasive wear as dominant wear mechanism was detected.