纳米η-Al2O3双组元法合成Na-β″-Al2O3固体电解质

以纳米η-Al2 O3为原料,氧化镁(MgO)为稳定剂,采用双组元法制备Na-β″-Al2 O3固体电解质.通过Archimedes法,SEM和三点抗弯法研究试样的致密性、显微结构和力学性能;采用XRD和交流阻抗谱仪研究试样的β″-Al2 O3相含量和离子电导率.结果表明:双组元法有利于提高试样的结构均匀性;纳米η-Al2 O3比高纯α-Al2 O3更易于合成Na-β″-Al2 O3固体电解质;适量MgO的加入有利于提高试样中β″-Al2 O3相的含量和试样的致密性,减小试样的晶界电阻,提高试样的离子电导率;过多的Mg O掺杂量导致晶内气孔尺寸的长大,反而增大了试样的晶粒电阻,导致试样的离子电导率降低.当MgO的加入量为2％(质量分数)时,试样在300℃时的离子电导率最大,为0.0396 S·cm-1.     

Energetics of formation of lamellar porous microstructures in γ-Al2O3

The formation of a lamellar porous microstructure in -Al₂O₃ during the dehydration of boehmite (-AlOOH) has been studied as a function of the temperature and water vapour pressure conditions under which the dehydration was performed. The -Al₂O₃ samples were characterized by transmission electron microscopy and nitrogen adsorption. A marked dependence of the scale of the microstructure, and of the adsorption characteristics, on water vapour pressure was observed. This pressure dependence of scale and surface area has been discussed in terms of a model, similar to those derived for cellular growth of lamellar microstructures during eutectic and eutectoid reactions, in which the dehydration mechanism is diffusion controlled. The inter-lamellar spacing is determined by the energy available for the formation of a new surface, and an estimate of surface energy for -Al₂O₃ has been made. The partial pressure, , dependence observed has important implications for the possibility of tailoring pore structures.     

The mechanical and electrical properties of ZrO2-Naβ″-Al2O3 composites

ZrO₂-Na-Al₂O₃ composites were prepared by a conventional method using two different powder routes and different milling liquids. The retained tetragonal-phase ZrO₂ was 85 to 90% for composites with 2.4 to 15 vol% ZrO₂. The fracture toughness (K _lc) and strength increased with increasing ZrO₂ content. At 20 vol % ZrO₂,K _lc and bend strength were 4.35 M Pa m^1/2 and 390 MPa, respectively. Stress-induced transformation toughening is the predominant toughening mechanism. Dispersion toughening also contributes to the increase ofK _lc. Surface strengthening was found to be an effective strengthening method for low ZrO₂ levels. The critical tetragonal ZrO₂ grain size was found to increase from 0.86 to 1.02gmm as the ZrO₂ content increased from 2.5 to 15 vol %. A detailed study of the ionic conductivity of the 15 vol % ZrO₂ dispersed sample was conducted by an a.c. technique between –124° C and 300° C. The bulk and total conductivities were calculated via complex-plane analysis. The total (grain and grain-boundary) ionic specific resistivity was 9 cm at 300° C. The activation enthalpies of the bulk and total conductivity processes were 0.30 and 0.32 eV, respectively.     

TiO2掺杂对Na-β″-Al2O3性能的影响

以薄水铝石、氧化镁、碳酸钠为起始原料,采用传统的固相反应法并添加0．5％-2％的TiO2促进烧结,制备出高致密度的Na-β″-Al2O3电解质,并对不同TiO2添加量样品的相组成、微结构、力学性能以及电性能进行表征。结果表明,添加TiO2所得Na-β″-Al2O3材料的相纯度高于96％;未添加TiO2的烧结试样结构疏松...     

Preparation and characterization of ZnO-doped and Li2O-stabilized Na-β″-Al2O3 solid electrolyte via a solid-state reaction method

Journal of Materials Science: Materials in Electronics - In this paper, Na–β"–Al2O3 is prepared using a conventional solid-state method and cost-effective burying and...     

Influence of yttrium on microstructure and point defects in α-Al2O3 in relation to oxidation

Although the influence of yttrium on transport properties of alumina has been the object of many studies, the mechanisms by which this element acts have not yet been elucidated. The method of modification by yttrium of the microstructure of polycrystalline alumina and the nature of the point defects created by this doping element were studied. The results obtained are discussed in relation to alumina transport properties and especially in relation with the effect of yttrium on the oxidation mechanism of alumina former alloys, taking into account the doping amount.     

Density of adsorbed water in powder systems. 3. γ-Al2O3

The choice of dispersion medium is considered. Estimates are made of the density of water adsorbed on -Al₂O₃.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 48, No. 4, pp. 648–653, April, 1985.     

碳化硅与LAS(Li2O-Al2O3-SiO2)界面化学稳定性研究

借助最新最权威基本的热力学数据,按化学平衡理论,分析SiC和LAS(Li2O-Al2O3-SiO2)之间可能发生的化学反应,定量计算在SiC中不同C活度,不同温度下SiC和LAS间诸反应各气相产物的分压和分压总和,精确分析SiC和LAS界面的热力学稳定性,提供在一个大气压惰性气体环境下,SiC和LAS界面的热力学失稳判据,为SiC材料研究者提供可靠的参考资料.     

The effect of a Cr2O3-addition on the phase transformation and catalytic properties of γ-Al2O3 in treatment of lean-burn exhausts

The solid-state thermal behaviour of -Al₂O₃ doped with 10 mol% Cr (oxide) was studied with respect to phase-transition behaviour and the co-ordination of the dopant Cr cations. A series of transformations: -Al₂O₃ -Al₂O₃ -Al₂O₃ -Al₂O₃ was observed for Cr₂O₃-doped alumina samples between 500 °C and 1100 °C. Rapid grain growth occurred at temperatures close to 1100 °C. The electron spin resonance (ESR) spectra for the sample heat-treated at 500 °C corresponded to the resonance of -Cr³⁺ in an amorphous Cr oxide impregnated onto the - and -alumina support. The change of ESR spectrum indicated the existence of Cr³⁺, suggesting the formation of a solid solution with the same structures as -Al₂O₃ and/or -Al₂O₃ at 800–1000 °C. The evaluation of catalytic activities for model exhaust was performed under lean-burn (an excess of oxygen) condition of air/fuel ratio A/F = 18 and space velocity SV = 100 000 h^–1 . The modified Al₂O₃ catalyst heat-treated at 1000 °C in air showed removal conversion of 100% for hydrocarbon (C₃H₆), 92% for CO and 5% for NO at 550 °C. Present results suggest that Cr-modification to Al₂O₃ leads to catalytic improvement with good thermal durability.     

Observations on the formation of β-Al5FeSi phase in 319 type Al-Si alloys

In Al-Si alloys, the properties are influenced by the shape and distribution of the eutectic silicon particles in the matrix, as also by the iron intermetallics and copper phases that occur upon solidification. The -Al₅FeSi iron intermetallic phase, in particular, is known for its detrimental effect on the properties, and is controlled variously by the iron content and the melt/solidification conditions of the alloy. The formation of the iron intermetallics has been observed in commercial 319 alloy end-chilled castings, obtained from non-treated and treated melts, where the effects of cooling rate, strontium modification and grain refinement have been studied. The volume fraction of -phase formed was seen to increase with the decrease in cooling rate (i.e. with increasing distance from the chill) in the untreated alloy. Sympathetic (preferential) nucleation of the -iron needles was also observed, in which the branching of -needles from a parent needle resulted in the formation of large -needle entities that can cover distances of 1200 m across the matrix surface. The beneficial effect of modification, i.e. strontium addition to the melt, was manifested through its influence on the fragmentation and dissolution of the -needles. The strontium poisons the sites where sympathetic nucleation takes place. Dissolution was accelerated with increasing strontium content, the optimum level being 300 p.p.m. Grain refining, on the other hand, negated the beneficial effect of modification, in that the -needles underwent thickening and the sympathetic nucleation/branching also occurred. The modified alloy was found to possess the lowest volume fraction of -Al₅FeSi phase among the unmodified, modified, grainrefined, and modified/grain-refined alloys.     

Influence of kaolinite crystalline structure in the production of γ-Al2O3 by alkaline lixiviation

The main uses of γ-Al₂O₃ of high surface and thermal stability, as catalyst and catalyst support, has originated several production methods such as the selective dissolution of siliceous components of kaolinite thermally amorphised. A high crystallinity degree of the raw kaolinite thermally treated between 750 and 1100 °C allows to obtain γ-Al₂O₃, with the desired characteristics, whatever the alkali concentration used. The specific surface of γ-Al₂O₃ obtained seems to be related to the alkali concentration utilised. A further calcination at 1250 °C generated α-Al₂O₃ of high surface and crystallinity.     

Heteroepitaxial growth of the δ-Ta2O5 films on α-Al2O3 (0001)

Journal of Materials Science: Materials in Electronics - The heteroepitaxial δ-Ta2O5 films were deposited on α-Al2O3 (0001) by MOCVD. As the growth temperature increases from...     

Effects of MgO on properties of Li2O–Al2O3–SiO2 glass–ceramics for LTCC applications

Li₂O–Al₂O₃–SiO₂ (LAS) glass–ceramics for low temperature co-fired ceramics (LTCC) application were prepared by melting method, and the effects of MgO on the sinterability, microstructure, dielectric property, thermal expansion coefficient (CTE) and mechanical character of this glass–ceramics have been studied. The X-ray diffraction images represent that the main phase is β-spodumene solid solutions. And some ZrO₂ and CaMgSi₂O₆ phases in LAS glass–ceramics are detected. The LAS glass–ceramics without additive (MgO) sintered at 800° had the dielectric properties: dielectric constant (ε_r) of 5.3, dielectric loss (tanδ) of 2.97 × 10^?3 at 1 MHz, CTE value of 1.06 × 10^?6 K^?1, bulk density of 2.17 g/cm³, and flexural strength of 73 MPa. 5.5 wt% MgO-added LAS glass–ceramic achieves densification at 800° exhibited excellent properties: low dielectric constant and loss (ε_r = 7.1, tanδ = 2.02 × 10^?3 at 1 MHz), low CTE (2.89 × 10^?6 K^?1), bulk density = 2.65 g/cm³ as well as high flexural strength (145 MPa). The results indicate that the addition of MgO is helpful to improve the dielectric and mechanical properties. The formation of CaMgSi₂O₆ crystal phase with higher CTE leads to the increase of CTE value of LAS glass–ceramics due to the increasing MgO content, and the increase of CTE is favourable for matching with silicon (3.1 × 10^?6 K^?1). The prepared LAS glass–ceramics have the potential for LTCC application.     

The formation of NaMg2Al15O25 in an α-Al2O3 matrix and its effect on the mechanical properties of alumina

An in-situ sintering reaction was designed to produce lath-like \-alumina in an -alumina matrix in order to make alumina ceramics stronger and tougher. The reaction sequence to produce \-alumina (NaMg₂Al₁₅O₂₅) requires the formation of \-alumina (NaAl₁₁O₁₇) and spinel (MgAl₂O₄) at around 1100 dgC followed by a solid-state reaction of these two phases to give \-alumina at elevated temperatures; this reaction is complete at around 1600 °C. The in-situ sintering reaction produces near-theoretically dense alumina ceramics in which lath-like \-aluminas are homogeneously distributed. The bending strength and fracture toughness increase to 620 MPa and 5 MPam^1/2, respectively; these increases are thought to be due to the suppression of grain growth as well as the crack deflection and bridging associated with lath-like \-alumina.     

Complex impedance analysis of Sr(NO3)2 and Sr(NO3)2:γ-Al2O3 dispersed solid electrolyte systems

Complex impedance spectroscopic studies were carried out on Sr(NO₃)₂ and Sr(NO₃)₂:-Al₂O₃ dispersed solid electrolyte systems (DSES) in the temperature range 300 to 560° C and the frequency range 100 Hz to 1 MHz. Mole percentage of the dispersoid -Al₂O₃ was varied from 17.2 to 34.2. The d.c. conductivity estimated from the Cole-Cole plots was found to increase with the mole percentage of the dispersoid. Dissipation was found to vary in a manner similar to the variation of conductivity with temperature. A.c. conductivity was found to be frequency dependent in the extrinsic region, but frequency independent in the intrinsic region. The enhanced conductivity in DSES was attributed to the formation of a space-charge layer between the host material and the dispersoid.     

The relative stability ofβ andβ″-phases in Na2O-Al2O3 beta alumina

To reveal the relative stability of and -phases in beta alumina, effects of Na₂0 content and calcination and annealing history on the relative content of and -phases have been studied for compositions ranging from Na₂O-5Al₂O₃ to Na₂O-9.5Al₂O₃. The relative stability appears to be dependent on the calcination or annealing history, except holding time such as annealing or re-annealing time, but independent of the Na₂O content and the holding time. From these results it can be demonstrated that the relative stability of and -phases is sensitive to the heat treatment path, except the holding time. The two stage model on the /. polytypic transition in silicon carbide has been quoted to explain the heat treatment pathdependent characteristics.     

Selection of eutectic systems in AI2O3–Y2O3 ceramics

There are two eutectic reactions in the Al₂0₃–rich portion of the AI₂O₃-Y₂O₃ pseudo–binary system; one is the equilibrium A1₂0₃–YAG eutectic reaction at 1826%C, and the other is the metastable A1₂0₃–YAP eutectic reaction at 1702%C. Selection of the A1₂0₃–YAG and the A1₂0₃–YAP eutectics was examined in terms of cooling rate, nucleation temperature and maximum melt temperature. When the melt was cooled from 2100%C at any cooling rate, it always nucleated below the Al₂0₃–YAP eutectic temperature, therefore the Al₂0₃–YAP eutectic was selected. The Al₂0₃–YAG eutectic was selected when the melt was cooled from 1900%C at a cooling rate of less than 1 K s^-1. The selection of the two eutectic systems was determined by the nucleation temperature, although the maximum holding temperature of the melt and the cooling rate significantly affected the nucleation temperature. The structure of the melt, such as coordination of oxygen and chemical order when being heated to 2100%C may affect the nucleation behavior.