The system CaOAl2O3Fe2O3 with added fluoride flux

Effects of fluoride fluxes, especially CaSiF₆·2H₂O upon phase equilibria in the system CaOAl₂O₃Fe₂O₃ are described, presenting liquidus data, new phase field boundaries and invariant points and solid solution areas. The primary phase field for C_12?xA₇·CaF₂ is increased substantially in size, and liquidus or invariant temperatures are depressed by amounts ranging from 20 to 80°C.     

Effect of surface-modified Al2O3 on the thermomechanical properties of polybutylene succinate/Al2O3 composites

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.     

Fabrication and microstructure evolution of Al2O3/ZrBN-SiCN/Al2O3 high-temperature oxidation-resistant composite coating

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.     

Tricalcium silicate solid solutions in the sysyem CCaOAl2O3SiO2

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.     

Microstructure and microwave dielectric properties of Al2O3 added Li2ZnTi3O8 ceramics

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.     

Effect of the Al2O3/SiO2 mass ratio on the crystallization behavior of CaO-SiO2-MgO-Al2O3 slags using confocal laser scanning microscopy

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.     

Stable and metastable phase equilibria and reactions in the SiO2---αAl2O3 system

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.     

The impact of Al2O3 amount on the synthesis of CASH samples and their influence on the early stage hydration of calcium aluminate cement

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.     

Preparation of dense 0.9Al2O3−0.1TiO2 ceramics with highly improved microwave dielectric properties by a noncontaminated DCC method

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, ε_r =?12.17?±?0.02, Q ×?f =?25,637?±?749?GHz, τ_f =?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.     

Chemical zoning of calcium aluminoferrite formed during melt crystallization in CaO-SiO2-Al2O3-Fe2O3 pseudoquaternary system

In the CaO-SiO₂-Al₂O₃-Fe₂O₃ pseudoquaternary system, the solid solutions of Ca₂(Al_xFe_1−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 Ca_2.03[Al_1.27Fe_0.68Si_0.02]_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 Ca_12.03[Al_13.61Fe_0.37]_Σ13.98O₃₃, being free from the other foreign oxides (SiO₂ and P₂O₅).     

High solid loading,low viscosity photosensitive Al2O3 slurry for stereolithography based additive manufacturing

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.     

Fabrication of Al2O3@BaFe12O19 core-shell powder by a modified heterogeneous precipitation method

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.     

The influence of Na2O on the structure and properties of 3CaO.Al2O3

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.     

Sorption of gases by crystalline and molten 12CaO.7Al2O3

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.     

Improvement of Al3+ ion conductivity by F doping of (Al0.2Zr0.8)4/3.8NbP3O12 solid electrolyte for mixed potential NH3 sensors

New Al³⁺ ion conducting solid electrolytes (Al_0.2Zr_0.8)_4/3.8NbP₃O_12-xF_2x(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 (Al_0.2Zr_0.8)_4/3.8NbP₃O_12-xF_2x 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 (Al_0.2Zr_0.8)_4/3.8NbP₃O_12-xF_2x samples. Among the solids series, (Al_0.2Zr_0.8)_4/3.8NbP₃O_11.7F_0.6 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 (Al_0.2Zr_0.8)_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 (Al_0.2Zr_0.8)_4/3.8NbP₃O_11.7F_0.6 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 H_2.     

Influence of rare earth Tb4O7 addition on the densification,abrasion resistance and microstructure of alumina ceramics

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.     

The effect of solvent water content on the dielectric properties of Al2O3 films grown by atmospheric pressure mist-CVD

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.     

Effects of pore diameter and catalyst loading in hydroliquefaction of coal with CoO/MoO3/Al2O3 catalysts

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.     

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.     

Processing and physical properties of Al2O3/aluminum alloy composites

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.