Transformation of Na2O-HfO2-B2O3 glass into a material having interconnected pores

Substitution of SiO₂ in the ternary sodium borosilicate system with HfO₂ was found to produce glasses, which after heat treatment decomposed into immiscible microphases, one of which was water soluble. The structure of the leached material after heat treatment was either glassy (mainly in the presence of Al₂O₃) or crystalline. Crystalline forms found during X-ray diffraction analysis of heat treated and leached material (melted in Pt/Rh crucibles) were monoclinic HfO₂. Monoclinic HfO₂ was also found in heat treated, leached and then fired materials melted in Pt/Rh or Al₂O₃ crucibles, in the latter an additional 9Al₂O₃ · 2B₂O₃ phase was detected. The higher solubility of HfO₂ in a Na₂O-B₂O₃ matrix than that of ZrO₂ (30 wt% against 15 wt%) resulting in clear glasses is of interest. The specific surface areas of the leached materials ranged between 41.3 and 290 m²g^–1, while the mean radii of interconnected pores were calculated to be 1.2 and 15.2nm. A firing temperature between 1450 and 1500° C is estimated from void volume and bulk density measurements.     

Al2O3-Ta2O5-rich glass-ceramic with interconnected pores and its sintering

Substitution of SiO₂ in the ternary sodium borosilicate system with Al₂O₃ plus Ta₂O₅ was found to produce glass which decomposed into microphases and/or crystallized after heat treatment. At least one of the phases present was water soluble. The structure of the material was glassy with the presence of a small crystalline content. Crystalline forms found during powder X-ray diffraction analysis of heat treated, leached and then sintered materials were orthorhombic NaTaO₃ plus AIBO₃, orthorhombic NaTaO₃ and orthorhombic Na₂O · 4Ta₂O₅ plus rhombic 9AI₂O₃ · 2B₂O₃, respectively. The specific surface areas of the leached materials ranged between 96 and 304 m²g^–1, while the mean pore radii of interconnected pores were calculated to be between 2.0 and 8.4 nm. A sintering rate of between 1520 and 1580° C for 5 min were estimated from void volume and bulk density measurements.     

Transformation of Na2O-CeO2-B2O3 glass into a material with interconnected pores

Substitution of SiO₂ with CeO₂ in the ternary sodium borosilicate system was found to produce phase-separable glasses. Heat treatment of these glasses resulted in separation into two different phases. The one phase enriched in sodium borate was then leached out leaving a CeO₂-rich framework. The structure of the leached material was crystalline (Pt/Rh crucible melt) which changed to a rather net-like appearance if Al₂O₃ resulting from erosion of alumina crucibles was added. B₂O₃ remained partially in the insoluble CeO₂-skeleton. X-ray diffraction analysis of leached material proved the presence of crystalline cubic CeO₂ and cerium borate (metaborate of the aragonite type) in Pt/Rh crucible melts, whereas cubic CeO₂, 2Al₂O₃ · B₂O₃ and traces of sodium borate were detected in Al₂O₃ containing melts. The specific surface areas of the leached materials ranged between 25 and 120m²g^–1 while the main radii of interconnected pores were calculated to be between 0.5 and 17nm. A sintering temperature of about 1500° C was estimated from void volume and bulk density measurements.     

Microstructure of sol–gel synthesized Al2O3–ZrO2(Y2O3) nano-composites studied by transmission electron microscopy

The Al₂O₃–ZrO₂(Y₂O₃) composite powder was synthesized through a sol–gel process using aluminum sec-butoxide and zirconium butoxide as precursors. The as-received powders in an amorphous phase were crystallized with c-ZrO₂ at around 980 °C. As the calcination temperature increased, the c-ZrO₂ crystalline phase was transformed to t-ZrO₂ at about 1200 °C. However, the Al₂O₃ phase in the Al₂O₃–ZrO₂(Y₂O₃) composite powders still existed in an amorphous phase up to 1050 °C. In the sintered body using the calcined powders at 400 °C, the Al₂O₃ phase was crystallized in an α-phase at 1200 °C during the sintering for 2 h. Using the sol–gel Al₂O₃–ZrO₂(Y₂O₃) powder, a typical nano-composite having a nano-crystalline phase (less than 20 nm) can be successfully obtained by a pressureless-sintering process even at 1200 °C for 2 h.Using the sol–gel Al₂O₃–ZrO₂(Y₂O₃) powder, a typical nano-composite having a nano-crystalline phase (less than 20 nm) can be successfully obtained by a pressureless-sintering process even at 1200 °C for 2 h. The values of relative density and Vickers hardness were comparatively high value with about 96.2% and 1100 Hv, respectively, even though it was made at low temperature. In the composite sintered at 1400 °C, the hardness value was saturated with 1570 Hv and the values of fracture toughness were almost same with about 6 MPa m^1/2.     

Enhanced cycle stability of spinel LiMn2O4 by a melting impregnation method

Spinel LiMn₂O₄ particles were successfully coated with CuO, MgO, ZnO, Al₂O₃ and CeO₂ by a melting impregnation method. Except for the CeO₂-coated sample, all the others exhibit better cycling stability than bare LiMn₂O₄ at room temperature and at 55°C. Among these samples, the ZnO-coated sample shows the best cycling stability. A capacity of 100 mA·h·g⁻¹ still remained after 100 cycles at 55°C while the bare LiMn₂O₄ retains a capacity of only 80 mA·h·g⁻¹ after the same number of cycles. The improvement in the cycling stability is attributed to the suppressed Mn dissolution caused by HF.     

Mechanochemical synthesis of SnO-B2O3 glassy anode materials for rechargeable lithium batteries

The xSnO·(100 ? x)B₂O₃ (0 ≦ x ≦ 80) glasses were successfully prepared by a mechanical milling technique. The glass with 40 mol% SnO showed the maximum glass transition temperature of 347°C. The SnO-B₂O₃ milled glasses consisted of both BO₃ and BO₄ units, and the fraction of BO₄ units was maximized at the composition of 50 mol% SnO. The electrochemical properties of the milled glasses were examined using a simple three electrodes cell with a conventional liquid electrolyte. The glasses with high SnO content exhibited high charge capacities more than 1100 mAh g^?1 and discharge capacities more than 700 mAh g^?1 at the first cycle. The SnO-B₂O₃ milled glasses proved to work as anode materials for rechargeable lithium batteries.     

Rubidium ion conducting Rb2 ? 2xAl2 ? xAxO4 (A = Nb, Ta) solid electrolytes

Rb_{2 − 2x} Al_{2 − x} A _x O₄ (A = Nb, Ta) solid solutions have been synthesized, and their conductivity has been measured as a function of temperature and composition. The highest rubidium ion conductivity in the Rb_{2 − 2x} Al_{2 − x} A _x O₄ solid solutions is 3.16 × 10⁻³ S/cm at 300°C and ∼ 2 × 10⁻² S/cm at 700°C. The high rubidium ion conductivity of the synthesized solid electrolytes is mainly due to the formation of rubidium vacancies when Nb⁵⁺ or Ta⁵⁺ substitutes for Al³⁺ and to the specific features of the crystal structure of RbAlO₂.     

Formation and properties of SnO–MgO–P<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses

A new glass system SnO–MgO–P₂O₅ with low viscosity has been developed by a melt-quenching method. Formation, thermal properties, and chemical durability of these glasses have been investigated. For a constant P₂O₅ concentration, the glass formation ability is enhanced with the increasing Sn/(Sn + Mg) ratio. The glasses exhibit low glass transition temperature (T _g = 270–400 °C), low dilatometric softening temperature (T _DS = 290–420 °C), and high thermal expansion coefficient (CTE = 110–160 × 10⁻⁷ K⁻¹). With the increasing Sn/(Sn + Mg) ratio, T _g and T _DS decrease, and CTE increases. When Sn/(Sn + Mg) ratio is varied, the relationship between chemical durability and thermal properties of the present glasses is not consistent with what expected in general cases. It is noted that the glasses with 32–32.5 mol% P₂O₅ exhibit excellent chemical durability and tunable T _g, T _DS, and CTE (by varying Sn/(Sn + Mg) ratio).     

Low temperature synthesis of glassy solids of the system Al2O3-P2O5-SiO2

Glassy solids of the system Al₂O₃-P₂O₅-SiO₂, which have not been obtainable because of the devitrification of glass during the cooling process after melting, were obtained by the gel method. After the gels of the system Al₂O₃-P₂O₅-SiO₂ were prepared from AlCl₃·6H₂O, H₃PO₄ and Si(OC₂H₅)₄, they were heat treated up to 800° C to obtain glassy solids. In SiO₂ concentrations ranging from 75 to 82 mol % in batch compositions, non-porous transparent solids were obtained, while in SiO₂ concentrations above 87 mol %, porous transparent solids were obtained. Tridymite was precipitated because of the crystallization of glassy solids during heat treatment above 800° C. It depended upon the microstructure of the gels whether non-porous glassy solids were obtained or not. The thermal expansion coefficients of the glassy solids were greatly dependent upon the concentration of P₂O₅, ranging from 1.7×10⁻⁶ to 4.2×10⁻⁶ (1/° C).     

Glass formation region and electrical conductivity in the system B2O3-Li2O-Li3PO4

Glass formation region was determined for the B₂O₃-Li₂O-Li₃PO₄ system. Under the present experimental conditions, binary lithium borate glasses could be formed containing a maximum of 27 mol% Li₂O. However, this could be increased to 36 mol% in the ternary system. Electrical conductivity was measured at temperatures ranging from room temperature to 350°C. The temperature dependence of the electrical conductivity of these glasses follows Arrhenius equation. The conductivity increased with increasingly alkali content. Maximum conductivity of the order of 10⁻⁴ ohm⁻¹ cm⁻¹ was obtained with the glass containing about 36 mol% Li₂O at 250°C. Activation energy for conduction also varied with total Li₂O content.     

Deformation behaviour and microstructure of a 20% Al2O3 reinforced 6061 Al composite

Deformation and microstructural behaviours of a 20% (volume percent) particle reinforced 6061 Al matrix composite have been studied by torsion from 25 to 540°C with strain rates of 0.1, 1 and 5 s⁻¹. The logarithmic stress versus reciprocal temperature relationship exhibits two slopes indicating different deformation mechanisms. The 20% Al₂O₃/6061 Al composite shows a greater hardening behaviour than those of the 10% Al₂O₃/6061 Al composite and of the monolithic alloy. Above 250°C, TEM investigations reveal much smaller subgrain size and higher volume of non-cellular substructures, as well as dynamic recrystallization nuclei in the 20% Al₂O₃/6061 Al composite in comparison to those of the 10% Al₂O₃/6061 Al composite and matrix alloy the same test condition. The torsion fracture surface was studied and compared to the three point bending failure specimens.     

One-pot synthesis of Al2O3 modified mesoporous ZrO2 with excellent thermal stability and controllable crystalline phase

In this paper, a series of Al₂O₃ modified mesoporous ZrO₂ (M-ZrAl) materials are designed and achieved through a one-pot EISA strategy. As proved by different characterizations, the introduced Al₂O₃ species exist as highly dispersed states, and the crystalline phase (t-ZrO₂ and m-ZrO₂) of M-ZrAl material could be accurately controlled through adjusting the content of Al₂O₃ species. Moreover, the M-ZrAl-10 material exhibits excellent textural properties (specific surface area (56?m²·g^?1), pore size (8.2?nm) and pore volume (0.13?cm³·g^?1)) even treated at 800?°C. The obtained materials are employed as support for MoO₃/M-ZrAl solid acid catalyst, and the relationship between catalytic performance (Friedel-Crafts alkylation, acetalization and esterification) and crystalline structure of support is specially explored. The result shows that the support with t-ZrO₂ phase is beneficial for the formation of acid sites and enhancement of catalytic performance for the MoO₃/M-ZrAl solid acid catalyst.     

Electrical properties of Li2O-La2O3-SiO2 electrode glasses after Ta2O5 doping and Ta implantation

Electrical conductivities, , of the Li₂O-La₂O₃-SiO₂ glasses were investigated as functions of Ta₂O₅ doping and Ta ion-implantation. A linear relationship between logarithm and the inverse of the sample temperature, T, was found in 2 to 4 mol% Ta₂O5 doped Li₂O-La₂O₃-SiO₂ glasses. The conductivity increases as Ta₂O₅ content increases at sample temperatures above 100°C. Fluences of 50 keV Ta ions per cm² from 5 × 10¹⁶ to 2 × 10¹⁷ were implanted into 0% and 2% Ta₂O₅ containing Li₂O-La₂O₃-SiO₂ glass samples. The activation energy of the conductivity was deduced from the relation between log and 1/T. It was found in implanted samples that the conductivity increased, but the activation energy and T _k–100 decreased, where T _k–100 is the sample temperature when the conductivity reaches 100 × 10^–1 S/cm. However, the Ta₂O₅ containing implanted samples show higher conductivities, lower activation energies and lower T _k–100. X-ray photoelectron spectroscopy (XPS) was used to study the structural modification introduced by implantation. Bridging oxygen (BO) and non-bridging oxygen (NBO), were observed in all samples. The changes in relative concentrations of BO and NBO before and after implantation clearly indicate the structure modification which results in the increase of the conductivity. It was clearly demonstrated in this study that both doping Ta₂O₅ and implanting Ta ions enhance the conductivity of Li₂O-La₂O₃-SiO₂ electrode glasses.     

Structural and thermal studies of H2La2/3Ta2O7, a protonated layered perovskite

We have synthesised the new protonated layered perovskite H₂La_2/3Ta₂O₇ which is related to the Ruddlesden–Popper family. This compound is obtained by ionic exchange starting from Li₂La_2/3Ta₂O₇ maintained in dilute HNO₃ at 60 °C. Thermal X-ray diffraction and DTA/TGA revealed interesting dehydration properties with formation of a layered anhydrous phase leading at higher temperature (1550 °C) to La_1/3TaO₃. This latter compound exhibits the original lanthanum ordering expected similarly to that of the Li form, while at 900 °C a metastable form, presenting a disordered La distribution, is observed.     

Coprecipitation method for the preparation of nanocrystalline ferroelectric CaBi2Ta2O9

A simple coprecipitation technique had been successfully applied for the preparation of pure ultrafine single-phase CaBi₂Ta₂O₉ (CBT). Ammonium hydroxide and ammonium oxalate were used to precipitate Ca²⁺, Bi³⁺ and Ta⁵⁺ cations simultaneously. No pyrochlore phase was found while heating powder at 800 °C and pure CaBi₂Ta₂O₉ phase was found to be formed by XRD. Particle size and morphology was studied by transmission electron microscopy (TEM). The room temperature dielectric constant at 1 kHz is 100. The ferroelectric hysteresis loop parameters of these samples were also studied.     

NiaSi2O5（OH）4 Multi-Walled Nanotubes with Tunable Magnetic Properties and Their Application as Anode Materials for Lithium Batteries

Highly crystalline and thermally stable pure multi-walled Ni₃Si₂O₅(OH)₄ nanotubes with a layered structure have been synthesized in water at a relatively low temperature of 200–210 °C using a facile and simple method. The nickel ions between the layers could be reduced in situ to form size-tunable Ni nanocrystals, which endowed these nanotubes with tunable magnetic properties. Additionally, when used as the anode material in a lithium ion battery, the layered structure of the Ni₃Si₂O₅(OH)₄ nanotubes provided favorable transport kinetics for lithium ions and the discharge capacity reached 226.7 mA·h·g⁻¹ after 21 cycles at a rate of 20 mA·g⁻¹. Furthermore, after the nanotubes were calcined (600 °C, 4 h) or reduced (180 °C, 10 h), the corresponding discharge capacities increased to 277.2 mA·h·g⁻¹ and 308.5 mA·h·g⁻¹, respectively.      

Macroporous alumina monoliths prepared by filling polymer foams with alumina hydrosols

Macroporous alumina monoliths have been prepared for the first time by filling polystyrene foam templates with alumina hydrosols which were prepared from pseudo-boehmite. Polystyrene foam templates were obtained by polymerization in highly concentrated water-in-oil (W/O) emulsions. The organic templates were subsequently removed by calcination. The effects of filling times of the alumina hydrosols, calcination temperature, and CTAB surfactant addition in the hydrosols on the properties of the monolith have been investigated. TG, FT-IR, SEM, TEM, N₂ adsorption–desorption, and XRD techniques were used for characterization. The so prepared monoliths are the replicas of the polystyrene foams and are characterized with hierarchically porous structure. The macropores are interconnected and the macropore walls contain many meso and/or micropores. The hierarchically macro-meso-microporous structure can be controlled and tailored by adjusting the preparation conditions stated above and by addition of surfactant, and the organic components can be eliminated by high temperature calcination. When the calcination temperatures are 600 °C and 900 °C, the γ-Al₂O₃ phases are obtained, with S_BET of 228 and 85 m² g⁻¹, respectively. When calcined at 1100 °C, the alumina monolith presents a single θ-Al₂O₃ phase with S_BET of 80 m² g⁻¹. The 1300 °C calcined sample takes on the single α-Al₂O₃ phase with S_BET of 5 m² g⁻¹ and compressive strength of 3.1 MPa. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Synthesis of hexagonal Al2−x Cr x O3 nanodisks by a thermal decomposition of mesoporous Cr4+:Al2O3 powders

Monodispersed hexagonal Al_2−x Cr _x O₃ nanodisks are synthesized through a reactive doping of Cr⁶⁺ cations in a hydrogenated mesoporous AlO(OH)·αH₂O powder followed by annealing at 1,200 °C in air. The reaction was carried out by a drop wise addition of an aqueous Cr⁶⁺ solution (0.5–1.0 M) to AlO(OH)·αH₂O, at room temperature. Al_2−x Cr _x O₃ nanostructure formation was controlled by the nucleation and growth from the intermediate amorphous mesoporous Cr⁴⁺:Al₂O₃ composites in the temperature range 400–1,000 °C. The nanodisks of ∼50 nm diameter and thickness of ∼16 nm is observed in the sample with x of 0.2 and similar nanodisks with a low dimension is observed at a higher value of x of 1.6 (after 2 h of heating at 1,200 °C). The Cr³⁺ ↔ Al³⁺ substitution, x ≤ 1.2, inhibits grain growth in small crystallites. The crystallites in x = 0.2 composition have 43 nm diameter while it is 15 nm in those with x = 1.2 composition.     

Hierarchical laminated Al2O3 in-situ integrated with high-dispersed Co3O4 for improved toluene catalytic combustion

Hierarchical structure and surface properties of selective support afford some special effects on the catalytic activity, which could be tuned to achieve improved performance. Herein, using a combination of hydrothermal coprecipitation and thermal processing, we integrated highly-distributed Co₃O₄ spinel nanospecies on laminated hierarchically structured Al₂O₃ which could be used as a highly efficient VOCs treatment catalyst. Impressively, compared to Co-free Al₂O₃ counterpart (S_BET = 188.2 m²·g^?1), these obtained Co₃O₄ spinel functionalized catalysts are endowed with adjustable Co loading, optimized Co activity state, and obviously improved hierarchically structural properties (S_BET = 274.7 m²·g^?1). The microporous and mesoporous structures both existed in the obtained Al₂O₃, which is beneficial to the heterogeneous catalytic reaction process. The results reveal that the proper Co loading in the hierarchically structured Al₂O₃ could enable the rational modulation of catalytic activity in the combustion of toluene and exceeds the commercial 5 wt% Pd/C catalyst in the light of total catalytic oxidation ability. This developed heterogeneous Co₃O₄ compositing hierarchically structured Al₂O₃ provides a significant potential value for practical VOCs treatment.     

Optical properties of the Al2O3/SiO2 and Al2O3/HfO2/SiO2 antireflective coatings

Investigations of bilayer and trilayer Al₂O₃/SiO₂ and Al₂O₃/HfO₂/SiO₂ antireflective coatings are presented in this paper. The oxide films were deposited on a heated quartz glass by e-gun evaporation in a vacuum of 5 × 10^?3 [Pa] in the presence of oxygen. Depositions were performed at three different temperatures of the substrates: 100 °C, 200 °C and 300 °C. The coatings were deposited onto optical quartz glass (Corning HPFS). The thickness and deposition rate were controlled with Inficon XTC/2 thickness measuring system. Deposition rate was equal to 0.6 nm/s for Al₂O₃, 0.6 nm ? 0.8 nm/s for HfO₂ and 0.6 nm/s for SiO₂. Simulations leading to optimization of the thin film thickness and the experimental results of optical measurements, which were carried out during and after the deposition process, have been presented. The optical thickness values, obtained from the measurements performed during the deposition process were as follows: 78 nm/78 nm for Al₂O₃/SiO₂ and 78 nm/156 nm/78 nm for Al₂O₃/HfO₂/SiO₂. The results were then checked by ellipsometric technique. Reflectance of the films depended on the substrate temperature during the deposition process. Starting from 240 nm to the beginning of visible region, the average reflectance of the trilayer system was below 1 % and for the bilayer, minima of the reflectance were equal to 1.6 %, 1.15 % and 0.8 % for deposition temperatures of 100 °C, 200 °C and 300 °C, respectively.