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1.
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. 相似文献
2.
E. Potgieter M. A. Res I. Sigalas H. Schönberger J. Bednarik 《Journal of Materials Science》1987,22(2):752-756
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. 相似文献
3.
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. 相似文献
4.
《Materials Letters》2005,59(2-3):355-360
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 m1/2. 相似文献
5.
Hao QI Gao-shao CAO Jian XIE Xin-bing ZHAO 《Frontiers of Materials Science in China》2008,2(3):291-294
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. 相似文献
6.
A. Hayashi M. Nakai H. Morimoto T. Minami M. Tatsumisago 《Journal of Materials Science》2004,39(16-17):5361-5364
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. 相似文献
7.
G. Sh. Shekhtman E. I. Volegova E. I. Burmakin B. D. Antonov 《Inorganic Materials》2010,46(5):534-539
Rb2 − 2x
Al2 − 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 Rb2 − 2x
Al2 − 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. 相似文献
8.
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). 相似文献
9.
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). 相似文献
10.
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. 相似文献
11.
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. 相似文献
12.
Zhichao Miao Zhenbin Li Cong Suo Jinping Zhao Weijiang Si Jin Zhou Shuping Zhuo 《Advanced Powder Technology》2018,29(12):3569-3576
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. 相似文献
13.
Electrical properties of Li2O-La2O3-SiO2 electrode glasses after Ta2O5 doping and Ta implantation 总被引:1,自引:0,他引:1
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. 相似文献
14.
《Materials Research Bulletin》2006,41(4):825-833
We have synthesised the new protonated layered perovskite H2La2/3Ta2O7 which is related to the Ruddlesden–Popper family. This compound is obtained by ionic exchange starting from Li2La2/3Ta2O7 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 La1/3TaO3. 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. 相似文献
15.
《Materials Letters》2004,58(27-28):3474-3476
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. 相似文献
16.
Yan Yang Qingqin Liang dinghong Li Yuan Zhuang Yunhua He Bo Bai Xun Wang 《Nano Research》2011,4(9):882-890
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.
相似文献
17.
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 SBET of 228 and 85 m2 g−1, respectively. When calcined at 1100 °C, the alumina monolith presents a single θ-Al2O3 phase with SBET of 80 m2 g−1. The 1300 °C calcined sample takes on the single α-Al2O3 phase with SBET 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. 相似文献
18.
Monodispersed hexagonal Al2−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. Al2−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. 相似文献
19.
《Advanced Powder Technology》2022,33(1):103377
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 (SBET = 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 (SBET = 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. 相似文献
20.
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. 相似文献