Electro-catalytic degradation properties of Ti/SnO_2–Sb electrodes doped with different rare earths

Ti/SnO_2–Sb electrode has a good effect on the removal of organic pollutants. But its short service life limits its large-scale application in industry. Electro-catalytic degradation performances and service life of the electrode can be significantly improved by doping rare earth(RE) ions into the oxide coating of Ti/SnO_2–Sb electrode. Ti/SnO_2–Sb electrodes doped with different RE elements(Ce, Dy, La, and Eu) were prepared by the thermal decomposition method at 550 °C. Electro-catalytic degradation performances of electrodes doped with different RE elements were evaluated by linear sweep voltammetry(LSV) and Tafel curves. During the electrolysis,the conversion of p-nitrophenol was performed with these electrodes as anodes under galvanostatic control. The structures and morphologies of the surface coating of the electrodes were characterized by scanning electron microscope(SEM). The results demonstrate that the electro-catalytic degradation performances of Ti/SnO_2–Sb electrodes are improved to different levels by doping different RE ions. Improved Ti/SnO_2–Sb electrodes by the introduction of different RE have higher oxygen evolution potential, better electro-catalysis ability, better coverage,and longer electrode life.     

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 %.     

Characterisation of acidic properties of the surface of SiO<Subscript>2</Subscript>–SnO<Subscript>2</Subscript> obtained by sol-gel method in anhydrous conditions

A series of SiO₂–SnO₂ samples of the Sn/Si molar fractions of 0.05, 0.1, 0.25, 0.5 and 1.0 were synthesised by the sol-gel method in anhydrous conditions. The SiO₂–SnO₂ samples were characterised by XRD, low-temperature nitrogen adsorption, SEM, 29Si MAS NMR and TPD, using pyridine and acetonitrile as probes. It has been proved that incorporation of small or even insignificant amount of tin in the structure of SiO₂ gel lattice considerably increased the number and power of acidic centres accessible to the probe molecules in the samples synthesised by the sol-gel method in anhydrous conditions. The increase in the number and power of acidic centres can substantially improve the catalytic properties of the SiO₂–SnO₂ system.     

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.     

Impact of supporting electrolytes on the stability of TiO<Subscript>2</Subscript>–Ti counter electrode during H<Subscript>2</Subscript>O<Subscript>2</Subscript> electrogeneration

This work focuses on the role of common supporting electrolytes (SEs) in the electro-chemical inertness of Ti-based materials employed for the anodic (direct) oxidation coupled with H₂O₂ electro-generation at the graphite cathode for the concurrent decomposition of organic contaminants. SEs are added to boost up the ionic conductivity of solution but a question always remains on the effect of SEs on the stability of anode materials. The use of ClO ₄ ^? is encouraged in the electro-Fenton process as it does not form complexes with Fe²⁺/Fe³⁺; however, it is found that ClO ₄ ^? corroded the TiO₂ coated Ti (TiO₂–Ti) anode very fast (>60 min) and, Ti⁴⁺ ions formed a yellow color complex (λ_max = 380 nm) with H₂O₂. The influence of Cl^–, NO ₃ ^? and SO ₄ ^2? was insignificant on the stability of TiO₂–Ti. The cell current efficiency of H₂O₂ formation dropped sharply with in the case of TiO₂–Ti anode. The TiO₂–Ti corrosion also reduced the mass transfer co-efficient of DO transport from bulk to the cathode surface because of Ti⁴⁺ adsorption on graphite.     

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.     

Spark Plasma Sintering of α/β Si<Subscript>3</Subscript>N<Subscript>4</Subscript> Ceramics with MgO-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and MgO-Y<Subscript>2</Subscript>O<Subscript>3</Subscript> as Sintering Additives

In the present work, the α/β Si₃N₄ ceramics were fabricated by spark plasma sintering (SPS) at 1400-1500 °C for 6 min with 3wt.%MgO + 5wt.%Al₂O₃ and 3wt.%MgO + 5wt.%Y₂O₃ as sintering additives. The results showed that the phase composition, microstructure and mechanical properties of α/β Si₃N₄ ceramics were highly dependent on the type of sintering additive. The incomplete phase transformation from α to β occurred in the presence of an oxynitride (Mg-Al(Y)-Si-O-N) liquid phase. Compared with MgO-Al₂O₃, MgO-Y₂O₃ can significantly improve the β conversion rate of as-sintered α/β Si₃N₄ ceramics. And the as-sintered ceramics using MgO + Al₂O₃ as sintering additives had higher mechanical properties.     

Reaction between Ti–6Al–4V and Y<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript> based face shell for investment casting

The pH value and viscosity of Y₂O₃–SiO₂ (Y–Si) slurry made by Y₂O₃ powders and silica sol for the face coat of Ti–6Al–4V investment casting were measured. The thermal behavior of the shell made by the Y–Si face coat system was investigated by differential scanning calorimeter (DSC), thermal gravimetric (TG) analysis combined with mass spectrometry (MS), and the phase transformations were determined by X-ray diffraction (XRD). Hot strength, residual strength, linear expansion coefficient, and wearing resistance performance of the shell were also tested. The microstructure and elements distribution of the interaction layer were studied by scanning electron microscope (SEM) and energy-dispersive spectrometer (EDS), respectively. The microhardness tester was applied for the microhardness. The results showed that the slurry was stable for at least 60 h. A very small amount of YZrO₃ was formed below 1050 °C and Y₂SiO₅ was formed around 1450 °C. The shell made by Y–Si system had good mechanical property which could reduce cracks during the procedure of dewaxing and inclusions during pouring. Some Al volatilized from the melt, permeated the surface of the face coat shell, and formed the black reaction layer, which blocked the permeation of O so that O penetration was limited to 5 μm. The depth of Si penetration was about 60 μm. The hard layer was also around 60 μm.     

Bridge polysilsesquioxane xerogels with a bifunctional surface layer of the ≡Si(CH<Subscript>2</Subscript>)<Subscript>3</Subscript>NH<Subscript>2</Subscript>/≡Si(CH<Subscript>2</Subscript>)<Subscript>3</Subscript>SH composition

Xerogels with a bifunctional surface layer of the ≡Si(CH₂)₃NH₂/≡Si(CH₂)₃SH composition are synthesized by hydrolytic co-polycondensation of bis(triethoxy)silane (C₂H₅O)₃Si(CH₂)₂Si(OC₂H₅)₃ and two trifunctional silanes, namely, 3-aminopropyltriethoxysilane and 3-mercaptopropyltrimethoxysilane. Using IR, ¹H MAS NMR, and ¹³C CP/MAS NMR spectroscopic techniques, it is shown that in addition to complexing groups, the surface layer also contains water, silanol groups that are involved in the hydrogen bond formation and also residual ethoxysilyl groups. According to ²⁹SiCP/MAS NMR spectroscopic data, the degree of polycondensation of synthesized xerogels exceeds 80%. It is found that the use of 1,2-bis(triethoxysilyl)ethane as the structuring agent in place of tetraethoxysilane allows one to synthesize bifunctional xerogels with the highly developed biporous structure (S _sp = 607–680 m²/g, V _c = 1.38–1.47 cm³/g, d = 2.9–3.1 and 18.3 nm). Changing the ratio structuring-silane/functionalizing-silane-mixture from 2: 1 to 4: 1 in the reaction system has virtually no effect on the porous structure parameters of final xerogels.     

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.     

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.     

Embrittlement and conditions of the optimization of magnetic properties in the amorphous alloy Co<Subscript>69</Subscript>Fe<Subscript>3.7</Subscript>Cr<Subscript>3.8</Subscript>Si<Subscript>12.5</Subscript>B<Subscript>11</Subscript> in the absence of a viscous–brittle transition

The influence of the holding time upon annealing on the temperature of the viscous–brittle transition (temperature of embrittlement) T_f in a cobalt-based amorphous alloy of the composition Co₆₉Fe_3.7Cr_3.8Si_12.5B₁₁ with a very low saturation magnetostriction λ_s (<10^–7) has been studied. It has been established that the dependence of the embrittlement temperature T_f on the of time of holding t_a can be described by an Arrhenius equation and that the embrittlement at the annealing temperatures above and below 300°C is described by different kinetic parameters. In the alloy under study, irrespective of the holding time, embrittlement occurs in a very narrow range of annealing temperatures, which does not exceed 5 K. Based on the experimental data on the evolution of the hysteresis magnetic properties upon the isochronous annealings and upon the isothermal holding, the regime of heat treatment that ensures a very high (about 50000) magnitude of the permeability µ₅ (H = 5 mOe, f = 1 kHz) without the transition of the alloy into a brittle state has been determined.     

The effect of heat treatment on properties of Ni–P–SiO<Subscript>2</Subscript> nano-composite coating

In this study, the surface morphology of Ni–P–SiO₂ composite coating was investigated by field emission scanning electron microscopy (FESEM). The amount of SiO₂ in the coating was examined by energy dispersive analysis of X-ray (EDX) and the Corrosion behavior of coating was evaluated by electrochemical impedance spectroscopy (EIS) and polarization techniques, showing the corrosion resistance of Ni–P–SiO₂ diminished after heat treatment. The results showed that in the coating with 12.5 g/L SiO₂, the coating hardness enhanced from 453VH to 980 VH before and after heat treatment. Furthermore, the wear behavior of the coating was analyzed before and after heat treatment.     

Oxidation Behavior of HVAF-Sprayed NiCoCrAlY Coating in H<Subscript>2</Subscript>–H<Subscript>2</Subscript>O Environment

Isothermal oxidation behavior of an HVAF-sprayed NiCoCrAlY coating on AISI 304L was studied in an Ar–10 %H₂–20 %H₂O environment at 600 °C. Techniques such as BIB/SEM, EDS, and XRD were used to comprehensively characterize the coating and the coating/substrate interface to investigate the oxidation mechanisms. Results were also compared with those obtained from an uncoated AISI 304L substrate. The alumina-forming NiCoCrAlY coating was found to exhibit superior oxidation behavior due to the formation of a slow-growing and protective Al₂O₃ scale, while the chromia-forming bare 304L substrate lost its protective capability due to the formation of a duplex [Fe₃O₄ on (Fe,Cr)₃O₄ spinel oxide] corrosion product layer.     

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.     

Acoustic Emission Investigation of Rolling/Sliding Contact Fatigue Failure of NiCr–Cr<Subscript>3</Subscript>C<Subscript>2</Subscript> Coating

NiCr–Cr₃C₂ coating was fabricated using supersonic plasma spraying technology. Subsequently, rolling/sliding contact fatigue (R/SCF) testing was carried out, using acoustic emission (AE) technology to monitor the failure process. The results showed that R/SCF consists of three failure modes, namely abrasion, spalling, and delamination. Abrasion is the main failure mode, but delamination is the most severe. The AE monitoring results indicated that the R/SCF failure process is composed of normal contact, crack initiation, crack propagation, and material removal stages. The frequency of each stage was analyzed by fast Fourier transform, revealing a peak frequency for each stage mainly distributed from 200 to 250 kHz.     

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.     

Transport properties of solid solutions of <Emphasis Type="Italic">х</Emphasis>KYF<Subscript>4</Subscript>–(1–<Emphasis Type="Italic">х</Emphasis>)PbF<Subscript>2</Subscript> system

In the system (1–x)PbF_2–x YF_3–x KF, solid solutions of aliovalent substitution with fluorite structure at 0.47 < x < 0.69 are formed, in which the fluorine ions are found to be in three structurally nonequivalent positions that differ in the local environment and mobility. There are immobile, locally mobile, and highly mobile anions. The conductivity of the synthesized polycrystalline samples is ensured by highly mobile interstitial fluoride ions, whose concentration and hence electrical conductivity increase on heating. The contribution of the surface conductivity of crystallites is not detected. The electronic component is two orders of magnitude lower than the ionic one.     

Effect of the atmosphere of low-temperature annealing on the structure and electrophysical properties of nonstoichiometric YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7 − δ</Subscript> ceramics

The fine structure and electrophysical properties of nonstoichiometric YBa₂Cu₃O_{7 − δ} ceramics and the effect of low-temperature annealing (t ⩾ 200°C) in various atmospheres on these parameters have been studied. It has been shown that, during annealing in a vacuum, the decomposition is quite sluggish; structures typical of initial stages of decomposition are observed. The decomposition in an inert-gas atmosphere occurs more actively, and structures typical of stages of deep decomposition are realized. It has been found that, during low-temperature annealing, the structure and properties are affected by two factors; these are the decomposition into phases differing in the oxygen content, and water absorption, leading to the transformation with the formation of a pseudo-cubic lattice. The annealing atmosphere substantially affects the kinetics of both processes.     

The influence of SiO<Subscript>2</Subscript> and Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles on corrosion resistance enhancement of Ni–P on magnesium

In this study, the influence of adding SiO₂ and Al₂O₃ to Ni–P coated on magnesium substrate and the related corrosion resistance behavior were evaluated. The surface morphology of Ni–P–SiO₂–Al₂O₃ composite coating was investigated by field emission scanning electron microscopy (FESEM). The amount of Al₂O₃ and SiO₂ in the coating was measured by energy dispersive analysis of X-ray (EDX) and the corrosion behavior of coating was monitored by electrochemical impedance spectroscopy (EIS) and polarization techniques, showing the corrosion resistance of Ni–P–SiO₂–Al₂O₃ increases compare to Ni–P–SiO₂ and Ni–P–Al₂O₃. Furthermore, the microhardness of the coating was examined and the final hardness of Ni–P–SiO₂–Al₂O₃ reached 461 VH.