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1.
Effects of fluoride fluxes, especially CaSiF6·2H2O upon phase equilibria in the system CaOAl2O3Fe2O3 are described, presenting liquidus data, new phase field boundaries and invariant points and solid solution areas. The primary phase field for C12?xA7·CaF2 is increased substantially in size, and liquidus or invariant temperatures are depressed by amounts ranging from 20 to 80°C. 相似文献
2.
This study investigates the effect of the incorporation of alumina particles on the thermomechanical properties of polybutylene succinate (PBS)/Al2O3 composites. The alumina surface was modified with the carboxylic groups of maleic acid through simple acid-base and in situ polymerization reactions. Scanning electron microscope (SEM) results revealed the introduction of maleic acid treated alumina significantly affect the morphology of the PBS/Al2O3 composites as compared to the neat PBS. The thermal conductivity of the composite (0.411?W?m?1 K?1) was more than twice that of neat PBS. The composite containing polymerization-modified alumina showed a 50% increase in storage modulus compared with that of neat PBS. In addition, universal testing machine (UTM) and differential scanning calorimetry (DSC) measurements indicated an increase in the tensile strength and degree of crystallinity after the incorporation of modified alumina in the PBS/Al2O3 composite. 相似文献
3.
Xiaohui Zhao Shuai Yan Hongmin Wang Hongchuan Jiang Wanli Zhang 《Ceramics International》2019,45(1):247-251
The oxidation-resistance of thin film sensors, particularly at high temperatures, is critical for the lifetime and performance of the sensor. The preparation and oxidation-resistance of an Al2O3/ZrBN-SiCN/Al2O3 composite film with a sandwich-structure was performed using reactive magnetron sputtering. The microstructure evolution of the composite film is examined herein using X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) analysis. Oxygen diffusion was significantly inhibited by the formation of crystalline Al2SiO5 and Zr-B-C amorphous phase inside the composite film. The Pt-13%Rh/Pt thin film thermocouple (TFTC) with the Al2O3/ZrBN-SiCN/Al2O3 composite film as a protective layer was fabricated and calibrated. Both the stability and lifetime of the TFTC was significantly enhanced for temperatures up to 1000?℃. The test error of the TFTC was reduced by half, compared with that of the TFTC with the Al2O3 protective layer, indicating an excellent oxidation-resistant performance of the composite film. 相似文献
4.
G. Roed 《Cement and Concrete Research》1978,8(3):325-331
The solid solutions formed by simultaneous incorporation of CaO and Al2O3 into Ca3SiO5 have been investigated. By chemical methods the solubility of Al2O3 in Ca3SiO5 was determined to 0.64% (wt) and the amount of CaO accompanying each mole of Al2O3 in the solid solution reaction was found to be constant 4.5. These findings were confirmed by reflected light microscopy. 相似文献
5.
Recently, the rapid development of advanced communication systems increasingly strongly demands high-performance microwave dielectric ceramics in microwave circuits. Among them, Li2ZnTi3O8 ceramics have been one of the most widely investigated species, due to its high quality factor, moderate firing conditions and low cost. However, the dielectric constants of the already reported Li2ZnTi3O8 ceramics are fixed in a narrow range, limiting their wider applications. To adjust the dielectric constant of the Li2ZnTi3O8 based ceramics, in this work Li2ZnTi3O8 ceramics added with different amounts of Al2O3 (0–8?wt%) were prepared by conventional solid-state reaction. The microstructure and microwave dielectric properties of the samples were investigated. Due to the addition of Al2O3, the sintering temperature of the ceramics would be increased somewhat. Some Al3+ ions could substitute for Ti4+ ions in Li2ZnTi3O8, and the added Al2O3 would react with ZnO to produce a ZnAl2O4 phase accompanying with the formation of TiO2 phase, which would inhibit the growth of Li2ZnTi3O8 grains. The dielectric constant of the finally obtained ceramics would be reduced from 26.2 to 17.9, although the quality factors of the obtained ceramics would decrease somewhat and the temperature coefficient of resonant frequency would deviate further from zero. 相似文献
6.
The crystallization behavior of a CaO-SiO2-MgO-Al2O3 slag system with varying Al2O3/SiO2 mass ratios from 0.03 to 1.10 has been investigated using a confocal laser scanning microscopy (CLSM). The resulting continuous cooling transformation (CCT) and time-temperature-transformation (TTT) curves showed that the initial crystallization temperature increased and the incubation time for crystallization slightly decreased with increasing Al2O3/SiO2 ratio. The crystal growth rate first increased and then decreased with decreasing isothermal temperature. X-ray diffraction (XRD) analysis suggested that Ca2MgSi2O7 or Ca3MgSi2O8 precipitated as the primary phase at lower Al2O3/SiO2 ratios, while the Ca2Al2SiO7 phase was preferred at higher Al2O3/SiO2 ratios. The observed crystalline phases correlated well with the expected thermodynamic predictions from FactSage. In addition, structural analysis using 27Al magic angle spinning nuclear magnetic resonance (27Al MAS-NMR) microscopy of the as-quenched slags indicated the presence of a higher ratio of tetrahedral [AlO4]5-structural units with increasing Al2O3/SiO2 ratio, which enhanced the polymerization of tetrahedral [AlO4]5- and [SiO4]4- structural units to form Ca2Al2SiO7. 相似文献
7.
Joseph A. Pask 《Ceramics International》1983,9(4):107-113
Procedures in the preparation of specimens in this system are critical due to the difficulty of nucleating αAl2O3 when the silicate liquid is not saturated with Al2O3 even though it may be supersaturated relative to crystalline αAl2O3, and the ease with which mullite growing from an alumino-silicate melt during cooling accomodates an excess of Al2O3. Metastable phase compositions and microstructures occur commonly. As a result, misinterpretations of experimental data have occurred in published reports. Stable and metastable phase equioibria diagrams in the αAl2O3---SiO2 system are presented. 相似文献
8.
Kestutis Baltakys Anatolijus Eisinas Jolanta Doneliene Tadas Dambrauskas Gabriele Sarapajevaite 《Ceramics International》2019,45(2):2881-2886
In this work the impact of Al2O3 amount on the synthesis (200?°C; 4–8?h) of calcium aluminium silicate hydrates (CSAH) samples and their influence on the early stage hydration of calcium aluminate cement (CAC) was examined. It was found that the amount of Al2O3 plays an important role in the formation of calcium aluminate hydrates (CAH) because in the mixtures with 2.7% Al2O3 only calcium silicate hydrates (CSH) intercalated with Al3+ ions were formed. While in the mixtures with a higher amount of Al2O3 (5.3–15.4%), calcium aluminate hydrate – C3AH6, is formed under all experimental conditions. It is worth noting that the largest quantity of mentioned compound was obtained after 4?h of hydrothermal treatment, in the mixtures with 15.4% of Al2O3. It was proved that synthesized C3AH6 remain stable up to 300?°C and at higher temperature (945?°C) recrystallized to mayenite (Ca12Al14O33), which reacted with the rest part of CaO and amorphous structure compound, resulting in the formation of gehlenite (Ca2Al2SiO7). Moreover, the synthesized C3AH6 addition induced the early stage of CAC hydration. Besides, in the samples with an addition, the induction period was effectively shortened: in a case of pure CAC (G70) paste, hydration takes about 6–6.5?h, while with addition – only 2–2.5?h. The synthesized and calcinated compounds was characterized by using XRD and STA analysis. 相似文献
9.
Jia-Min Wu Shan-Shan Liu Meng-Yue Liu Ying Chen An-Nan Chen Meng Li Rong-Zhen Liu Yu-Sheng Shi Chen-Hui Li 《Ceramics International》2018,44(18):22205-22211
In this paper, dense 0.9Al2O3 ??0.1TiO2 ceramics with highly improved microwave dielectric properties were prepared by a noncontaminated direct coagulation casting (DCC) method. The suspension was destabilized and coagulated by consumption of the dispersant without introducing impurity ions. The effect of dispersant content, pH value and solid loading on the rheological properties of 0.9Al2O3 ??0.1TiO2 suspension was investigated. It was found that 0.9Al2O3 ??0.1TiO2 suspension with a high solid loading of 50?vol% and low viscosity of 0.7?Pa?s could be prepared by adding 0.5?wt% TMAOH at the pH in the range of 10–12. The suspension was coagulated by adding 2?vol% GDA when it was treated at 60 ~ 80?°C for 40 ~ 60?min. Compared with dry pressing method, more homogeneous and denser microstructure could be obtained in 0.9A12O3 ??0.1TiO2 ceramics prepared by DCC via dispersant reaction which were sintered at 1550?°C for 3?h and annealed at 1100?°C for 5?h. The Al2TiO5 second phase in 0.9A12O3 ??0.1TiO2 ceramics prepared by DCC via dispersant reaction could be eliminated more easily by annealing treatment. After annealing treatment, only Al2O3 and TiO2 phases could be detected. Therefore, higher density and much better microwave dielectric properties with ρ?=? 3.81?±?0.02?g/cm3, εr =?12.17?±?0.02, Q ×?f =?25,637?±?749?GHz, τf =?13.12?±?1.62?ppm/°C were obtained by DCC via dispersant reaction, and the Q ×?f value almost improved by 25%. Without introducing impurity ions, it provides a new insight into preparing complex shaped function ceramics with high properties. 相似文献
10.
In the CaO-SiO2-Al2O3-Fe2O3 pseudoquaternary system, the solid solutions of Ca2(AlxFe1−x)2O5, with x<0.7 (ferrite), Ca2SiO4 (belite), Ca3Al2O6 (C3A) and Ca12Al14O33 (C12A7), were crystallized out of a complete melt during cooling at 8.3 °C/min. Upon cooling to 1370 °C, both the crystals of ferrite with x=0.41 and belite would start to nucleate from the melt. During further cooling, the x value of the precipitating ferrite would progressively increase and eventually approach 0.7. At ambient temperature, the ferrite crystals had a zonal structure, the x value of which successively increased from the cores toward the rims. The value of 0.45 was confirmed for the cores by EPMA. The chemical formula of the rims was determined to be Ca2.03[Al1.27Fe0.68Si0.02]Σ1.97O5 (x=0.65). As the crystallization of ferrite and belite proceeded, the coexisting melt would become progressively enriched in the aluminate components. After the termination of the ferrite crystallization, the C3A and belite would immediately crystallize out of the melt, followed by the nucleation of C12A7. The C12A7 accommodated about 2.1 mass% Fe2O3 in the chemical formula Ca12.03[Al13.61Fe0.37]Σ13.98O33, being free from the other foreign oxides (SiO2 and P2O5). 相似文献
11.
Keqiang Zhang Chen Xie Gang Wang Rujie He Guojiao Ding Min Wang Dawei Dai Daining Fang 《Ceramics International》2019,45(1):203-208
Photosensitive Al2O3-resin slurries with high solid loading, low viscosity used for stereolithography based additive manufacturing were prepared in this paper. The dispersion behavior and rheological behavior of the Al2O3-resin slurries were studied by rheology observation and sedimentation tests. The dispersant type, concentration and solid loading had significant effects on the rheological behavior and stability of the photosensitive Al2O3-resin slurries. A long term stability and homogeneity slurry was obtained when the dispersant and concentration were KOS110 and 5?wt%, respectively. The Al2O3 slurry prepared with a high solid loading up to 60?vol%, low viscosity of 15.4?Pa?s at 200?s?1 was chosen for stereolithography based additive manufacturing. 相似文献
12.
Xiaoyan Yang Mengni Ge Jianfeng Zhang Baoping Jia Fan Bu 《Ceramics International》2019,45(3):3269-3275
Core-shell structural composites are promising to quench the desire for low-cost, lightweight and multifunctional magnetic materials, but the fabrication of highly pure shell nanoparticles with a desired morphology on a heterogeneous nuclear is still a big challenge. This study gives a successful illustration by in-situ synthesizing BaFe12O19 nanoparticles as a shell on Al2O3 core powders using BaCl2 and FeCl3 as precursors, instead of commonly used Ba(NO3)2 and Fe(NO3)3, by a modified heterogeneous precipitation process followed by calcination for crystallization. After calcination of the precipitants from the raw precursor mixture of BaCl2:FeCl3 for 1:10 at 800?°C, and for 1:8.5 at 900?°C, respectively, pure BaFe12O19 formed on pristine Al2O3, mostly with a hexagonal plane, about 100–200?nm in basal diameter and 20–100?nm in thickness. The highest saturation magnetization and coercivity of the coated Al2O3 @?BaFe12O19 powders was 23.3?emu/g and 5149?Oe, quite higher than that of the direct-mixed Al2O3-BaFe12O19 composite powder, and BaFe12O19-containing composites reported in literature, which could be attributed to the hexagonal shape of BaFe12O19 and uniform shell dispersion on Al2O3 core. The formation mechanism for the Al2O3@BaFe12O19 powders was discussed in detail. 相似文献
13.
A.I. Boikova A.I. Domansky V.A. Paramonova G.P. Stavitskaja V.M. Nikushchenko 《Cement and Concrete Research》1977,7(5):483-492
Four crystal forms of solid solutions of Na2O in 3CaO.Al2O3 have been synthesized. Chemical, crystal-optical, X-ray diffraction and IR-spectroscopic investigations have been made.The hydration activity at the early and later stages has been studied. It is shown that the hydration process can be divided into three stages. The analysis of the kinetic curves permitted the conclusion that the retardation of the hydration process is controlled by diffusion of the liquid phase through the product layer. 相似文献
14.
《Cement and Concrete Research》1985,15(3):442-452
In order to explain the role of gases in the stabilization of the structure of 12CaO.7Al2O3 a mass-spectrometric study was carried out in vacuum of 10−9 atm and in the temperature range of 900° – 1346°C, using polycrystalline samples obtained from the crystallization of melts soaked at 1500°C. It has been demonstrated by thermodynamic analysis of partial pressures of H2O, CO2, CO and O2 measured over the samples that the gases CO2, CO and O2 were sorbed by the specimens in molten state and were encapsulated during its crystallization, while the water vapours further penetrated into the zeolitic structure of the crystals at the time of their cooling. High values of isosteric heat of desorption of gases CO2, CO, and O2, such as 70–80 K-cal/mole, show that the desorption of these gases takes place due to the breakdown of the crystal lattice, while the removal of water with isosteric heat of desorption of about 11 K-cal/mole occurs as a result of its escape through the ‘windows’ in the cellular structure of the crystal. Based on these experimental results a structural model of the melt formed from 12CaO.7Al2O3 crystals has been developed. 相似文献
15.
Ling Wang Ce Gao Lei Dai Huizhu Zhou Yuehua Li Wei Meng Zhangxing He R.V. Kumar 《Ceramics International》2018,44(8):8983-8991
New Al3+ ion conducting solid electrolytes (Al0.2Zr0.8)4/3.8NbP3O12-xF2x(0?≤x?≤?0.4) with Nasicon-structure are successfully prepared by solid state reaction method. The influences of the doped F- content on the properties of the (Al0.2Zr0.8)4/3.8NbP3O12-xF2x samples are investigated using X-ray powder diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). The results show that F- doping can effectively improve the sinterability and the total conductivity of the (Al0.2Zr0.8)4/3.8NbP3O12-xF2x samples. Among the solids series, (Al0.2Zr0.8)4/3.8NbP3O11.7F0.6 shows the highest conductivity of 1.53?×?10?3 S?cm?1at 500?°C, which is approximately 7.9 times higher than that of the undoped (Al0.2Zr0.8)4/3.8NbP3O12. The ion transference number of the samples is higher than 0.99 at 300–700?°C. On the basis of the promising properties, a mixed-potential type NH3 sensor based on (Al0.2Zr0.8)4/3.8NbP3O11.7F0.6 electrolyte and In2O3 sensing electrode has been developed. The sensing performance of the sensor is evaluated. The mixed-potential type sensor can work at relatively low temperatures of 200–350?°C and an excellent sensitivity of 99.71?mV/decade at 250?°C is obtained. The sensor also displays excellent stability and reproducibility, accompanied by low cross-sensitivities to CO2, CH4 and H2. 相似文献
16.
This study aimed to improve the purity and performance of alumina ceramics used as ball milling media. High-alumina ceramics (>?96?wt% Al2O3), with high densification and excellent abrasion resistance, were fabricated by the cold isostatic pressing method. The effects of adding the rare earth Tb4O7 on the densification, abrasion resistance, crystalline phase, micro-morphology and grain size of the ceramics were studied. The experiment results showed that the densification and abrasion resistance of the samples increased with Tb4O7 addition. The sample with 0.8?wt% Tb4O7 sintered at 1625?°C exhibited the best performance, with a linear shrinkage, relative density and abrasion rate of 22.28%, 95.70% and 0.103‰, respectively. The abrasion resistance improved by 27.5% compared with the sample without Tb4O7. X-ray diffraction analysis indicated that the primary phases of the samples were corundum, spinel, CaAl12O19 and α-quartz, and a small quantity of Tb3Al5O12 was generated when more than 0.4?wt% Tb4O7 was added. Furthermore, some Mg2+ and Ca2+ ions in the liquid phases dissolved into Tb3Al5O12 crystalline grains during the sintering process, which enhanced the grain boundary cohesion of the materials. Scanning electron microscopy indicated that the existence of Tb3Al5O12 at grain boundaries reduced the average size of the corundum grains. This helped transform inter-granular fractures into trans-granular fractures, thereby improving the abrasion resistance of the ceramic materials. 相似文献
17.
Aluminum oxide (Al2O3) dielectric layers were grown by a mist-chemical vapor deposition (mist-CVD) process at 300 °C, using solvent mixtures containing acetone and water. As the acetone to water ratio was varied from 9:1 to 7:3, the leakage current of Al2O3 at an electric field of 7 MV/cm2 decreased from 9.0 × 10?7 to 4.4 × 10?10 A/cm2, and the dielectric constant increased from 6.03 to 6.85 with improved hysteresis during capacitance-voltage measurements. Consequently, the most robust Al2O3 films were obtained at an acetone to water ratio of 7:3, with a dielectric constant (κ) close to the ideal value 7.0, and a breakdown field of approximately 9 MV/cm. Thin film transistors (TFTs) incorporating In-Sn-Zn-O (ITZO) as the semiconductor were fabricated with the Al2O3 (7:3) dielectric onto p++-Si substrates. The devices exhibit high electrical performance, with a high field effect mobility of 42.7 cm2V?1s?1, and a small subthreshold swing (S.S.) value of 0.44 V/decade. 相似文献
18.
The effect of catalyst pore size has been studied for the hydroliquefaction of a West Virginia coal in the presence of Co/Mo/Al2O3 catalyst. The alumina supports used for catalyst preparation had relatively sharp, unimodal pore size distribution with average pore diameters in the range of 100 Å to almost 1000 Å. Loading of MoO3 and CoO on the Al2O3 supports was in the constant weight ratio of 5:1, but the absolute loading was in direct proportion to the surface area of the support. Two series of catalyst were studied: “High loading”, with 9.7 × 10?4 g MoO3/m2 Al2O3, and “low loading”, with 4.5 × 10?4 g MoO3/m2 Al2O3; both loadings were less than the amount necessary for monolayer distribution of MoO3 on Al2O3. The weight of catalyst charged in each autoclave run was varied so that the same weight of MoO3 and CoO was present for each experiment.The principal results were: (1) Al2O3 alone is not catalytic, even in large amount; (2) conversion of coal increases as catalyst pore diameter increases; from 100 Å to at least 500 Å; (3) the increased conversion with increasing pore size is manifested mainly as increased yield of asphaltenes at 400°C, so the ratio of oil to oil-plus-asphaltenes decreases as pore diameter increases; and (4) catalysts with “low loading” of MoO3 and CoO on the Al2O3 surface give higher liquefactions than their counterparts with “high loading”. Most of the results are consistent with an expected low diffusion rate of large, coal-derived molecules through the catalyst pore system. The higher liquefaction with “low loading” of the Al2O3 surface might result from slow desorption of large product molecules (asphaltenes) exhibiting multiple-site adsorption to Mo neighbors on the surface. 相似文献
19.
B. Fernández J.M. AlmanzaJ.L. Rodríguez D.A. CortesJ.C. Escobedo E.J. Gutiérrez 《Ceramics International》2011,37(8):2973-2979
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. 相似文献
20.
Porous aluminum oxide (Al2O3) preforms were formed by sintering in air at 1200 °C for 2 h. A356, 6061, and 1050 aluminum alloys were infiltrated into the preforms by squeeze casting in order to fabricate Al2O3/A356, Al2O3/6061, and Al2O3/1050 composites, respectively, with different volumes of aluminum alloy content. The content of aluminum alloy in the composites was 10–40% by volume. The resistivity of Al2O3/A356, Al2O3/6061, and Al2O3/1050 composites decreased dramatically from 6.41 × 1012 to 9.77 × 10−4, 7.28 × 10−4, and 6.24 × 10−4 Ω m, respectively, the four-points bending strength increased from 397 to 443, 435.1, 407.2 MPa, respectively, and the deviations were smaller than 2%. From SEM microstructural analysis and TEM bright field images, the pore volume fraction and the relative density of the composites were the most important factors that affected the physical and mechanical properties. The ceramic phase and alloy phase in Al2O3/aluminum alloy composites were found to be homogenized and uniformly distributed using electrical and mechanical properties analysis, microstructure analysis, and image analysis. 相似文献