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.     

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.     

Mössbauer study of the process of the room-temperature aging of the alloy Cu<Subscript>79</Subscript>Ni<Subscript>14</Subscript>Fe<Subscript>7</Subscript>

Mössbauer spectroscopy was used to investigate the initial stage of the phase separation in the quasi-binary system Cu₇₉Ni₁₄Fe₇ and the subsequent transformation of the alloy structures as a result of prolonged aging at room temperature. For describing the Mössbauer spectra of ferromagnetic particles, which appear upon the spinodal decomposition in a paramagnetic matrix, a model was proposed and approved, which uses particle-size distribution in the approximation of the generalized Lifshitz-Slezov-Wagner (LSW) model and of the linear decrease of the hyperfine field at the ⁵⁷Fe nuclei in the near-surface layers of spherical particles.     

Effect of the decomposition of the supersaturated β solid solution in melt-quenched Ni<Subscript>65</Subscript>Al<Subscript>35</Subscript> and Ni<Subscript>56</Subscript>Al<Subscript>34</Subscript>Co<Subscript>10</Subscript> alloys on the reversibility of the martensitic transformation

Melt-quenched Ni₆₅Al₃₅ and Ni₅₆Co₁₀Al₃₄ (at %) alloys are studied by electrical resistance measurement and electron microscopy. The effects of the isothermal holding time in the supersaturated β solid solution field and the heating rate during thermal cycling on the restoration of the reversibility of the martensitic transformation are investigated. After short-term aging in the B2 austenite field followed by long-term aging in the L1₀ martensite field, the melt-quenched Ni₆₅Al₃₅ and Ni₅₆Co₁₀Al₃₄ alloys retain their high thermal stability of the reversibility of the martensitic transformation.     

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 %.     

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.     

Air Oxidation of a Ni<Subscript>53</Subscript>Nb<Subscript>20</Subscript>Ti<Subscript>10</Subscript>Zr<Subscript>8</Subscript>Co<Subscript>6</Subscript>Cu<Subscript>3</Subscript> Glassy Alloy at 400–550 °C

Air-oxidation behavior of a Ni₅₃Nb₂₀Ti₁₀Zr₈Co₆Cu₃ amorphous ribbon was studied at 400–550 °C. The oxidation kinetics of the amorphous alloy followed a two-stage parabolic rate law with its oxidation rates steadily increasing with temperature. The steady-state oxidation rate constants of the alloy were faster than those of pure Ni. Triplex scales formed on the glassy alloy, containing an outer layer of NiO. The scales formed in the intermediate layer consisted of Nb₂O₅, NiO, and uncorroded α-Ni, while an additional Nb₂Zr₆O₁₇ phase was also detected in the inner layer. The formation of multilayered scales is responsible for the faster oxidation for the Ni6-AR.     

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.     

Phase Equilibria in the Sb<Subscript>2</Subscript>Te<Subscript>3</Subscript>–InSb System

The phase diagram of the (Sb₂Te₃)_100?x –InSb _x system was determined based on x-ray diffraction (XRD) analysis, differential thermal analysis (DTA), and microhardness and density measurements. An intermediate compound with composition Sb₂Te₃·2InSb was formed as a result of syntectic reaction, melting incongruently at 553 °C. This compound has tetragonal lattice with unit cell parameters of a = 4.3937 Å, b = 4.2035 Å, c = 3.5433 Å, α = 93.354°, and β = γ = 90°. Sb₂Te₃·(2 + δ)InSb (?1 ≤ δ ≤ +1) and (Sb₂Te₃)_100?x (InSb) _x (90 ≤ x ≤ 100) solid solutions exist in the investigated system, based on the intermediate compound Sb₂Te₃·2InSb and on InSb, respectively. Also, two invariant equilibria exist in the system, with eutectic point coordinates at compositions of x = 60 and x ≈ 85 mol% InSb and eutectic temperatures of T _E = 541 and T _E ≈ 501 °C, respectively.     

Experimental investigation of in-situ transformations of the <Emphasis Type="Italic">M</Emphasis><Subscript>7</Subscript>C<Subscript>3</Subscript> carbide in the cast Fe–Cr–Ni alloy

The microstructure and the phase composition of a heat-resistant Fe–Cr–Ni alloy (0. 45C–25Cr–35Ni) has been investigated in the cast state and after annealing at 1150°C for 2–100 h. After a 2-h high-temperature annealing, the fragmentation of the crystal structure of the eutectic M ₇C₃ carbides into domains of ~500 nm in size with a partial transition into M ₂₃C₆ carbides is observed. After a 100-h holding, the complete transition of the hexagonal M ₇C₃ carbides into M ₂₃C₆ with a face-centered cubic structure occurs. The carbide transition M ₇C₃ →M ₂₃ can be considered to be an in situ transformation.     

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.     

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.     

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.     

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.     

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.     

Effect of doping and substitution on the low-temperature decomposition of oxygen-nonstoichiometric Ba<Subscript>2</Subscript>YCu<Subscript>3</Subscript>O<Subscript>7 − δ</Subscript>

Effects of doping (with Ce and Pr) and substitution of Sr, Nd, Eu, and Ni for Ba and Cu on the lowtemperature (T = 200–300°C) decomposition of oxygen-nonstoichiometric Ba₂YCu₃O_{7 ? δ} have been studied. Both the doping and partial substitution for any of the principal components was found to increase the stability of the 123 compounds with respect to the decomposition into oxygen-depleted and oxygen-rich phases. Both doping and substitution to a level of ～2% lead to a narrowing of the immisibility dome and a decrease in the critical temperature. In the first place, the decomposition is suppressed in the bulk of grains. To increase the stability of near-boundary regions of grains, a high degree (～20 at %) of substitution is necessary.     

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.     

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.     

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.     

Dependence of Protein Adsorption on Wetting Behavior of UHMWPE–HA–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–CNT Hybrid Biocomposites

Ultrahigh-molecular-weight polyethylene (UHMWPE) is used as an articulating surface in total hip and knee joint replacement. In order to enhance long-term durability/wear resistance properties, UHMWPE-based polymer–ceramic hybrid composites are being developed. Surface properties such as wettability and protein adsorption alter with reinforcement or with change in surface chemistry. From this perspective, the wettability and protein adsorption behavior of compression-molded UHMWPE–hydroxyapatite (HA)–aluminum oxide (Al₂O₃)–carbon nanotube (CNT) composites were analyzed in conjunction with surface roughness. The combined effect of Al₂O₃ and CNT shows enhancement of the contact angle by ~37° compared with the surface of the UHMWPE matrix reinforced with HA. In reference to unreinforced UHMWPE, protein adsorption density also increased by ~230% for 2 wt.%HA–5 wt.%Al₂O₃–2 wt.%CNT addition to UHMWPE. An important conclusion is that the polar and dispersion components of the surface free energy play a significant role in wetting and protein adsorption than do the total free energy or chemistry of the surface. The results of this study have major implications for the biocompatibility of these newly developed biocomposites.