Preparation and thermophysical properties of LaMgAl11O19–Yb3Al5O12 ceramic composites

LaMgAl₁₁O₁₉–Yb₃Al₅O₁₂ ceramic composites were prepared by pressureless sintering process at 1700 °C for 10 h in air. The microstructure and thermophysical properties of the composites were characterized by X-ray diffraction, scanning electron microscopy, high-temperature dilatometer and laser flash diffusivity measurements. LaMgAl₁₁O₁₉–Yb₃Al₅O₁₂ ceramic composites are composed of magnetoplumbite and garnet structures. LaMgAl₁₁O₁₉–Yb₃Al₅O₁₂ ceramic composites exhibit typical linear increase in thermal expansion with the increase of temperature. The measured thermal diffusivity gradually decreases with increasing temperature. Thermal conductivity of LaMgAl₁₁O₁₉–Yb₃Al₅O₁₂ ceramic composites is in the range of 2.6–3.9 W·m⁻¹·K⁻¹ from room temperature to 1200 °C.     

Preparation, characterization and dielectric properties of CaCu3Ti4O12 ceramics

CaCu₃Ti₄O₁₂ nano-sized powders were successfully prepared by sol-gel technique and calcination at 600-900 °C. The thermal decomposition process, phase structures and morphology of synthesized powders were characterized by IR, DSC-TG, XRD, TEM, respectively. It was found that the main weight-loss and decomposition of precursors occurred below 450 °C and the complex perovskite phase appeared when the calcination temperature was higher than 700 °C. Using above synthesized powders as starting materials, CCTO-based ceramics with excellent dielectric properties (?₂₅ = 5.9 × 10⁴, tan δ = 0.06 at 1.0 kHz) were prepared by sintering at 1125 °C. According to the results, a conduction mechanism was proposed to explain the origin of giant dielectric constant in CCTO system.     

Carbothermal synthesis, spectral and magnetic characterization and Li-cyclability of the Mo-cluster compounds, LiYMo3O8 and Mn2Mo3O8

The molybdenum cluster compounds, LiYMo₃O₈ and Mn₂Mo₃O₈ are prepared by the carbothermal reduction method and characterized by various techniques. The FT-IR at ambient temperature (RT), and Raman spectra at various temperatures (78-450 K) are reported for the first time and results are interpreted. Magnetic studies on Mn₂Mo₃O₈ in the temperature range, 10-350 K confirm that it is ferrimagnetic, with T_C = 39 K. Magnetic hysteresis and magnetization data at various fields and temperatures are presented. The Li-cyclability is investigated by galvanostatic cycling in the voltage range, 0.005-3.0 V vs. Li at 30 mA/g (0.08 C). LiYMo₃O₈ shows a total first-discharge capacity of 305 ±5 mAh/g whereas the first-charge capacity is only 180 mAh/g at RT. However, both values increased systematically with an increase in the cycle number and yielded a reversible capacity of 385 ±5 mAh/g at the end of 120th cycle. At 50 °C, the reversible capacity is 418 ±5 mAh/g at the 60th cycle. The coulombic efficiency ranges from 94% to 98%. The Li-cyclability behavior of Mn₂Mo₃O₈ is entirely different from that of LiYMo₃O₈. The total first-discharge and charge capacities are 710 ± 5 and 565 ±5 mAh/g, but drastic capacity-fading occurs during cycling. The reversible capacity at the end of 50th cycle is only 205 ±5 mAh/g. Plausible reaction mechanisms are proposed and discussed based on the galavanostatic cycling, cyclic voltammetry, ex situ XRD, ex situ TEM and impedance spectral data.     

Synthesis and luminescence properties of nitrided lanthanum magnesium hexaluminate LaMgAl11O19 phosphors

Nitrided LaMgAl₁₁O₁₉ phosphors were prepared by a two-step method involving synthesis at 1550 °C for 4 h, trituration, and firing at 1650 °C for 5 h under a nitrogen atmosphere. Nitrogen was doped into LaMgAl₁₁O₁₉ and bonded with aluminium atoms. The nitrided LaMgAl₁₁O₁₉ phosphors showed plate-like morphology with a rough surface and exhibited strong blue emission at 442 nm and 450 nm, which may be attributed to the energy transition between defect levels. A weak emission band at 590 nm was ascribed to the transition between the V_Al acceptor and the valence band, which was excited at 254 nm.     

Influence of H4SiW12O40 loading on hydrocracking activity of non-sulfide Ni-H4SiW12O40/SiO2 catalysts

The effect of H₄SiW₁₂O₄₀ loading on the catalytic performance of the reduced Ni-H₄SiW₁₂O₄₀/SiO₂ catalysts for hydrocracking of n-decane with or without the presence of thiophene and pyridine is studied. The catalysts were characterized by BET, XRD, Raman, XPS, H₂-TPR, H₂-TPD, NH₃-TPD and FT-IR of pyridine adsorption. It was found that addition of H₄SiW₁₂O₄₀ to the system increases the catalytic activity and the promoting effect is a function of the H₄SiW₁₂O₄₀ loading. The best result was obtained on 5%Ni-50%H₄SiW₁₂O₄₀/SiO₂ catalyst which shows the highest activity for hydrocracking of n-decane and excellent tolerance to the sulfur and nitrogen compounds in the feedstock. The results showed that a suitable amount of H₄SiW₁₂O₄₀ loading on the 5%Ni/SiO₂ catalyst increases the amount of both hydrogen adsorbed and Brønsted acid and Lewis acid sites on the catalyst. The high catalytic performance of the catalyst can be related to the nature of H₄SiW₁₂O₄₀ and the proper balance between metal and acid functions.     

The catalytic performance in oxidative coupling of methane and the surface basicity of La2O3, Nd2O3, ZrO2 and Nb2O5

The catalytic performance in oxidative coupling of methane (OCM) of unmodified pure La₂O₃, Nd₂O₃, ZrO₂ and Nb₂O₅ has been investigated under various conditions. The results confirmed that the activity of La₂O₃ and Nd₂O₃ was always much higher than that of the remaining two. The surface basicity/base strength distribution of pure La₂O₃, Nd₂O₃, ZrO₂ and Nb₂O₅ was measured using a test reaction of transformation of 2-butanol and a temperature-programmed desorption of CO₂. Both methods showed that La₂O₃ and Nd₂O₃ had high basicity and contained medium and strong basic sites (lanthanum oxide more and neodymium oxide somewhat less). ZrO₂ had only negligible amount of weak basic sites and Nb₂O₅ was rather acidic. The confrontation of the basicity and catalytic performance indicated that in the case of investigated oxides, the basicity (especially strong basic sites) could be a decisive factor in determination of the catalytic activity in OCM. Only in the case of ZrO₂ it was observed a moderate catalytic performance in spite of negligible basicity. The influence of a gas atmosphere used in the calcination of oxides (flowing oxygen, helium and nitrogen) on their basicity and catalytic activity in OCM had been also investigated. Contrary to earlier observations with MgO, no effect of calcination atmosphere on the catalytic performance of investigated oxides in OCM and on their basicity was observed.     

Preparation of columbite MgNb2O6 and ZnNb2O6 ceramics by reaction-sintering

Columbite MgNb₂O₆ (MN) and ZnNb₂O₆ (ZN) ceramics produced by the reaction-sintering process were investigated. Secondary phases Mg_0.652Nb_0.598O_2.25 and Mg_0.66Nb_11.33O₂₉ were found in MgNb₂O₆ pellets. After 1250 °C sintering for 2 h, a density 4.85 g/cm³ (97.1% of the theoretical value) was obtained in MgNb₂O₆ pellets. In ZnNb₂O₆ pellets, no secondary phase formed. The maximum density 5.55 g/cm³ (98.7% of the theoretical value) occurs at 1200 and 1180 °C sintering for 2 and 4 h, respectively.     

Corrosion mechanisms of Al2O3/MgAl2O4 by V2O5, NiO, Fe2O3 and vanadium slag

The effects of V₂O₅, NiO, Fe₂O₃ and vanadium slag on the corrosion of Al₂O₃ and MgAl₂O₄ have been investigated. The specimens of Al₂O₃ and MgAl₂O₄ with the respective oxides above mentioned were heated at 10 °C/min from room temperature up to three different temperatures: 1400, 1450 and 1500 °C. The corrosion mechanisms of each system were followed by XRD and SEM analyses. The results obtained showed that Al₂O₃ was less affected by the studied oxides than MgAl₂O₄. Alumina was only attacked by NiO forming NiAl₂O₄ spinel, while the MgAl₂O₄ spinel was attacked by V₂O₅ forming MgV₂O₆. It was also observed that Fe₂O₃ and Mg, Ni, V and Fe present in the vanadium slag diffused into Al₂O₃. On the other hand, the Fe₂O₃ and Ca, S, Si, Na, Mg, V and Fe diffused into the MgAl₂O₄ structure. Finally, the results obtained were compared with those predicted by the FactSage software.     

The preparation and characterization of Li4Ti5O12/carbon nano-tubes for lithium ion battery

Li₄Ti₅O₁₂/carbon nano-tubes (CNTs) composite was prepared by sol-gel method while Ti(OC₄H₉)₄, LiCH₃COO·2H₂O and the n-heptane containing CNTs were used as raw materials. The characters of Li₄Ti₅O₁₂/CNTs composite were determined by XRD, SEM, and TG methods. Its electrochemical properties were measured by charge-discharge cycling and impedance tests. It was found that the prepared Li₄Ti₅O₁₂/CNTs presented an excellent rate capability and capacity retention. At the charge-discharge rate of 5C and 10C, its discharge capacities were 145 and 135 mAh g⁻¹, respectively. After 500 cycles at 5C, the discharge capacity retained as 142 mAh g⁻¹. It even could be cycled at the rate of 20C. The excellent electrochemical performance of Li₄Ti₅O₁₂/CNTs electrode could be attributed to the improvement of electronic conductivity by adding conducting CNTs and the nano-size of Li₄Ti₅O₁₂ particles in the Li₄Ti₅O₁₂/CNTs composite.     

XANES study of polyaniline-V2O5 and sulfonated polyaniline-V2O5 nanocomposites

In this work, two materials for secondary lithium battery cathodes formed by polyaniline-V₂O₅ and sulfonated polyaniline-V₂O₅, which have a higher charge capacity than the V₂O₅ xerogel, were synthesized. X-ray absorption and Fourier transform infrared spectroscopies were employed to analyze the short-range interactions in these materials. Based on these experiments, it was possible to observe significant differences in the symmetry of the VO₅ units, and this was attributed to the intimate contact between V₂O₅ and the polymers, and to some flexibility of the VO₅ square pyramids due to the low range order of the nanocomposites.     

Mechanochemical synthesis of MgTa2O6 ceramic

MgTa₂O₆ powders were prepared by mechanochemical synthesis from MgO and Ta₂O₅ in a planetary ball mill in air atmosphere using steel vial and steel balls. High-energy ball milling gave nearly single-phase MgTa₂O₆ after 8 h of milling time. Annealing of high-energy milled powder at various temperatures (700–1200 °C) indicated that high-energy milling speed up the formation and crystallization of MgTa₂O₆ from the amorphous mixture. The powder derived from 8 h of mechanical activation gave a particle size of around 28 nm. Although at low-annealing temperatures the grain size was almost the same as-milled powder, the grain size increased with annealing temperature reaching to around 1–2 μm after annealing at 1200 °C for 8 h.     

Preparation and characterization of negative thermal expansion Sc2W3O12/Cu core-shell composite

A composite of Sc₂W₃O₁₂/Cu where Sc₂W₃O₁₂, the core, is coated by the Cu shell was synthesized using simple electroless plating method. As-prepared Sc₂W₃O₁₂/Cu composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and thermomechanical analyzer (TMA) techniques. The study results show that the Pd-Sn activator was successfully formed on the surface of Sc₂W₃O₁₂ after the sensitization and activation. In the electroless plating process, Cu nanocrystals formed firstly, and then grew together to form a continuous coating. Sc₂W₃O₁₂/Cu core-shell composites exhibit a negative linear coefficient of thermal expansion CTE = −4.47 × 10⁻⁶ °C⁻¹ from room temperature to 200 °C.     

Anhydrous proton conductivity of KHSO4–H3PW12O40 composites and the correlation with hydrogen bonding distance under ambient pressure

Anhydrous proton conductive KHSO₄–H₃PW₁₂O₄₀ (KHS–WPA) composites were successfully synthesized using mechanochemical treatment. 95KHS·5WPA (mol%) composite, for example, showed very high anhydrous proton conductivity of 1.3 × 10⁻² to 2.4 × 10⁻³ S cm⁻¹ in a temperature range from 160 °C to 80 °C under ambient pressure. Chemical interactions via ion-exchange and hydrogen bond between KHS and WPA were confirmed from structural studies. Furthermore, the anhydrous proton conductivity of the KHS–WPA composites was well correlated with their estimated hydrogen bonding distance, indicating that reduction of the hydrogen bonding distance in the KHS–WPA composites is significant in the proton hopping to achieve anhydrous high proton conductivity.     

Ordered CoFe2O4 nanowire arrays with preferred crystal orientation and magnetic anisotropy

CoFe₂O₄ nanowire arrays were fabricated by electrodeposition of Fe²⁺ and Co²⁺ into anodic aluminum oxide (AAO) templates and further oxidization. The phase structure of the nanowires is cubic spinel-type, and the XRD result exhibits perfect preferred crystallite orientation along the nanowire axes. Compared with CoFe₂O₄ nanowire arrays synthesized by other methods, the magnetic hysteresis loops demonstrate that the arrays of nanowires exhibit uniaxial magnetic anisotropy with easy magnetization direction along the nanowire axes owing to the large shape anisotropy. This approach provides a facile technology to fabricate oxide nanowires with uniaxial magnetic anisotropy.     

Effects of the starting materials and mechanochemical activation on the properties of solid-state reacted Li4Ti5O12 for lithium ion batteries

Li₄Ti₅O₁₂ was synthesized by a solid-state reaction between Li₂CO₃ and TiO₂ for applications in lithium ion batteries. The effects of the TiO₂ phase and mechanochemical activation on the Li₄Ti₅O₁₂ particles as well as the corresponding electrochemical properties were investigated. Rutile TiO₂ was more desirable in acquiring high purity Li₄Ti₅O₁₂ than anatase due to the anatase to rutile phase transformation, which was found to be more rigid in the solid-state reaction than the intact rutile phase. Mechanochemical activation of the starting materials was effective in decreasing the reaction temperature and particle size as well as increasing the Li₄Ti₅O₁₂ content. The specific capacity depended significantly on the Li₄Ti₅O₁₂ content, whereas the rate capability improved with decreasing particle size due to the enhanced contact area and reduced diffusion path. Overall, a 200 nm-sized Li₄Ti₅O₁₂ powder with a specific capacity of 165 mAh/g could be synthesized by optimizing the milling method and starting materials.     

Electrochemical performance of Li4Mn5O12 nano-crystallites prepared by spray-drying-assisted solid state reactions

Nanosized Li₄Mn₅O₁₂ has been synthesized by a spray-drying-assisted solid state method. The effect of spray drying and drying temperature on the microstructure and electrochemical performance of the final products has been investigated. The microstructure of the products has been characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The electrochemical performance of the products has been studied by galvanostatic cycling, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). It has been found that the products prepared with a spray-drying pretreatment of the precursor exhibit a smaller grain size and a narrower size distribution than that prepared without the pretreatment. Among the three samples with a precursor pretreatment, that pretreated at 250 °C shows the best electrochemical performance due to the smallest grain size of below 50 nm and the narrowest size distribution.     

The viscosity reduction of nano-keggin-K3PMo12O40 in catalytic aquathermolysis of heavy oil

Nano-keggin-K₃PMo₁₂O₄₀ was synthesized, characterized by FT-IR, XRD and TEM, and then used in catalytic aquathermolysis of extra-heavy oil for the first time. The results evidently showed a viscosity reduction by 92.3% for the extra-heavy oil Zhen 411 at 280 °C, and by 80% and 90% in viscosity reduction for the extra-heavy oil G540 at 200 °C and 280 °C, with 9.25% and 11.69% in conversions of heavy to light content, respectively. To evaluate the performance, the structure and group composition of the heavy oil before and after the reaction were tested and analyzed by TLC-FID, FT-IR, GC-FID, ¹H NMR, EL and GC-MS. It was found that changes in oxygen-containing groups mainly happen during the catalytic aquathermolysis.     

Microstructure and mechanical properties of Al2O3/Er3Al5O12 eutectic rods grown by the laser-heated floating zone method

Eutectic rods of Al₂O₃-Er₃Al₅O₁₂ were grown by directional solidification using the laser-heated floating zone method at rates in the range 25-1500 mm/h. Their microstructure and mechanical properties (hardness, toughness and strength) were investigated as a function of the growth rate. A homogeneous and interpenetrated microstructure was found in most cases, and interphase spacing decreased with growth rate following the Hunt-Jackson law. Hardness increased slightly as the interphase spacing decreased while toughness was low and independent of the microstructure. The rods presented very high bending strength as a result of the homogeneous microstructure, and their strength increased rapidly as the interphase spacing decreased, reaching a maximum of 2.7 GPa for the rods grown at 750 mm/h. The bending strength remained constant up to 1300 K and decreased above this temperature. The relationship between the microstructure and the mechanical properties was established from the analysis of the microstructure and of the fracture mechanisms.     

A crucial role of O2 and O2 on mayenite structure for biomass tar steam reforming over Ni/Ca12Al14O33

Newly synthesized nickel calcium aluminum catalysts (Ni/Ca₁₂Al₁₄O₃₃) were tested in a fixed bed reactor for biomass tar steam reforming, toluene as tar destruction model compound. Four catalysts (Ni/Ca₁₂Al₁₄O₃₃) were prepared with Ni loading amount from 1, 3, 5 to 7 wt%, even 1% loading catalyst also showed excellent performance. Catalysts aged experiments in the absence (60 h on stream) and presence of H₂S were characterized by BET, X-ray diffraction (XRD), and Raman spectra. It was observed that Ni/Ca₁₂Al₁₄O₃₃ showed excellent sustainability against coke formation due to the “free oxygen” in the catalysts. It also exhibited higher H₂S-poisoning resistance property compared to the commercial catalysts Ni/Al₂O₃ (5%) and Ni/CaO_0.5/MgO_0.5. Raman spectra revealed that “free oxygen O₂⁻ and O₂²⁻” in the structure of the catalysts could be substituted by sulfur then protected Ni poisoning on some degree, but reactivation experiments by O₂ flowing showed that the sulfide Ni/Ca₁₂Al₁₄O₃₃ was difficult to completely restore, incorporation of sulfur in the structure only partly regain by O₂. The kinetic model proposes, as generally accepted, a first-order reaction for toluene with activation energy of 82.06 kJ mol⁻¹ was coincident with the literature data. The Ni/Ca₁₂Al₁₄O₃₃ catalyst was effective and relative cheap, which may be lead to reduction in the cost of hot gas cleaning process.     

Preparation of micro-dot electrodes of LiCoO2 and Li4Ti5O12 for lithium micro-batteries

Fabrications of micro-dot electrodes of LiCoO₂ and Li₄Ti₅O₁₂ on Au substrates were demonstrated using a sol-gel process combined with a micro-injection technology. A typical size of prepared dots was about 100 μm in diameter, and the dot population on the substrate was 2400 dots cm⁻². The prepared LiCoO₂ and Li₄Ti₅O₁₂ micro-dot electrodes were characterized with scanning electron microscopy, X-ray diffraction, micro-Raman spectroscopy, and cyclic voltammetry. The prepared LiCoO₂ and Li₄Ti₅O₁₂ micro-dot electrodes were evaluated in an organic electrolyte as cathode and anode for lithium micro-battery, respectively. The LiCoO₂ micro-dot electrode exhibited reversible electrochemical behavior in a potential range from 3.8 to 4.2 V versus Li/Li⁺, and the Li₄Ti₅O₁₂ micro-dot electrode showed sharp redox peaks at 1.5 V.