Increasing Al2O3 Content Research Articles

Dielectric Properties of CaCu<sub>3</sub>Ti<sub>4</sub>O<sub>12</sub>/Al<sub>2</sub>O<sub>3</sub> Composites

In this work, (1-x)CaCu3Ti4O12/xAl2O3 (x = 0, 0.01, 0.03, 0.05 and 0.1) composite samples were prepared by the conventional solid-state reaction method. The dielectric properties of the samples were investigated at frequency range of 20 – 106 Hz. X-ray diffractogram results show that the samples with Al2O3 sintered at 1040 °C/10 h are mixed phase and consist of CaCu3Ti4O12, CuAl2O4, TiO2 and Al2O3. The average grain size of the samples increased greatly for x = 0.01, then abruptly depressed for x ≥ 0.03. Al2O3-added (x = 0.01) has been shown to increase the dielectric permittivity (ε’) up to ~5000 over frequency range of 102 – 105 Hz, while retaining the dielectric loss (tan δ ~ 0.15) at 1 kHz. With further increase of Al2O3 content, the ε’ and tan δ values of the samples are decreased monotonically in all frequency ranges. The improvement of dielectric properties in the composite sample was attributed to the enhanced grain boundary resistance.

温度1573 Kおよび酸素分圧10<sup>−6</sup>~10<sup>−2</sup> atmにおけるFeO<sub>x</sub>-CaO-SiO<sub>2</sub>-Al<sub>2</sub>O<sub>3</sub>系のFeO<sub>x</sub>側液相線

The performance of iron ore sinter in a blast furnace such as strength and reducibility is strongly affected by the amount and the chemical composition of liquid phase in sinter during the sintering process. Thus, it is necessary to control the production of liquid phase during the sintering process. Iron ore sintering process consists of rapid heating of pulverized raw materials, partial reduction reaction of iron ores as well as liquid phase production, which are caused by combustion of cokes and suction of flaming gas. The heating time of raw materials is too short that the chemical reactions within the sinter never reach the thermodynamic equilibriums. Nevertheless, controlling the melt production could be attempted based on the thermodynamic data such as the phase diagrams. In this study, liquidus lines coexisting with iron oxides and/or 2CaO·SiO2 in the FeOx-CaO-SiO2 system have been measured at 1573 K in the range of oxygen partial pressures between 10–6 atm and 10–2 atm. In addition, the effect of Al2O3 content on the liquidus has also been investigated as Al2O3 is a major gangue component affecting the quality of sinter. It has been found that the homogenous liquid region extends over a wide range of CaO/SiO2 (C/S) ratio between 0.6 and 2 or even more for all the measurement oxygen partial pressures. It has also been found that the FeOx content in liquid phase at C/S=1.0 in equilibrium with solid FeOx is almost constant to be 40-45 mass% irrespective of oxygen partial pressures. However, the FeOx content decreases with an increase in Al2O3 content, indicating that the homogenous liquid region in the FeOx-rich side becomes narrower. As a consequence, it is considered that the amount of slag melt produced in sinter during the sintering process becomes smaller with increasing Al2O3 content.

Influence of Al2O3, CaO/SiO2, and B2O3 on Viscous Behavior of High Alumina and Medium Titania Blast Furnace Slag

The effect of Al2O3, CaO/SiO2, and B2O3 on the viscosity of high alumina and medium titania blast furnace slag was analyzed. An increase in CaO/SiO2 ratio from 1.14 to 1.44 resulted in higher slag viscosity and break point temperature. They also increased with increasing Al2O3 content but decreased with adding B2O3 and Al2O3 simultaneously at a fixed CaO/SiO2 ratio of 1.14, which suggested that the effect of B2O3 on viscosity and break point temperature is predominant compared to Al2O3. Apparent activation energies of CaO–SiO2–MgO–Al2O3–TiO2–B2O3 slag were found to be between 74 and 169 kJ/mol.

Effect of Al2O3 content on the mechanical and interdiffusional properties of ion-exchanged Na-aluminosilicate glasses

The effect of the variation in the Al2O3 content on select physical properties of pristine and ion-exchanged glasses in the systems: (75−x)SiO2mol%-25Na2O-xAl2O3 and (75−x)SiO2-15Na2O-10CaO-xAl2O3, are reported. The surface compressive stress, surface hardness and K+/Na+ exchange ratio increase, while the depth of the interdiffusion distance decreases, with increasing Al2O3 content. These trends are shown to be consistent with the compositional variation of the glass transition temperature and the molar volume, and their atomistic and thermodynamic bases are discussed.

Effect of Al2O3 Nanofiller on ion conductivity, transmittance, and glass transition temperature of PEI:LiTFSI:PC:EC polymer electrolytes

In the present study, ion conductivity, optical properties, and glass transition temperatures are characterized for polymer electrolytes composed of poly(ethyleneimine) (PEI), lithium bis(trifluoromethane)sulfonylimide (LiTFSI) salt, propylene carbonate (PC), and ethylene carbonate (EC). It was doped with nanoceramic particles in different ratio (0–15 wt.%) to see the effect of ceramic particles. The salt concentration was fixed as 1.04 mol.kg−1. Although valuable improvement in ion conductivity could not be achieved due to nano-Al2O3 fillers, ion conductivity results are placed between 10−2 and 10−4 S/cm. Differential scanning calorimetry (DSC) measurements and optical measurements of all electrolytes were performed between −80 and 140 °C, in the wavelength range between 400 and 700 nm for sample with 80 μm thickness, respectively. The results showed that transmittance of electrolytes decreased monotonically for increasing Al2O3 contents. In particular, its transmittance value at 550 nm where human sight is at its greatest sensitivity went from 100% without nanoparticles to 50% for 15 wt% of Al2O3.

Transition of Blast Furnace Slag from Silicate-Based to Aluminate-Based: Structure Evolution by Molecular Dynamics Simulation and Raman Spectroscopy

To determine the effect of Al2O3 content and Al2O3/SiO2 mass ratio on the structure of molten aluminosilicate systems, CaO-SiO2-Al2O3-MgO-TiO2 systems were investigated by conducting molecular dynamics (MD) simulation and Raman spectroscopy. The capabilities of different elements to attract O on the basis of bond length are ranked as follows: Si > Al > Ca. The CNSi-O (approximately 4) and the average CNAl-O (approximately 4.09) demonstrate that the [AlO4] tetrahedron is not as stable as the [SiO4] tetrahedron and that some highly coordinated Al units exist in the slags. Non-bridging oxygen prefers to be coordinated with Si, and Al tends to be localized in polymerized environments as a network intermediate phase. In addition, Ca2+ is more energetically active than Mg2+ as the charge compensation ion. MD results and Raman analysis show that an increase in Al2O3 content complicates the structure at a fixed CaO/SiO2 ratio. In addition, the viscosity of the sample may increase with increasing Al2O3 content but is also influenced by polymerization strength. The substitution of Al2O3 for SiO2 simplifies the structure of the slag at a fixed CaO concentration when Al2O3/SiO2 is less than 0.92, as indicated by the (Q4 + Q3)/(Q2 + Q1) ratio of Al and the structure complexity. The results of MD and Raman analysis agree with those of viscosity measurement.

Lamellar-interpenetrated Al−Si−Mg/Al2O3−ZrO2 composites prepared by freeze casting and pressureless infiltration

Using freeze casting and pressureless infiltration methods, we prepared lamellar Al−Si−Mg/Al2O3−ZrO2 composites with initial ceramic loading of 30vol% and different Al2O3:ZrO2 weight ratios (Al2O3:ZrO2=1:9, 3:7, 5:5, 7:3 and 9:1). The resultant composites inherited the lamellar structure of the Al2O3−ZrO2 scaffolds, and the thickness of both metal and ceramic layers showed a trend of first increase and then decrease with increasing Al2O3 content. During pressureless infiltration, multiple chemical reactions took place between ZrO2 and the Al−12Si−10Mg alloy and the main reaction products were (Al1−m, Sim)3Zr, Al2O3 and ZrSi2 phases. The degree of the reaction depended on the ZrO2 content in the ceramic composition. In general, the compressive strength of the composites decreased with increasing Al2O3 content, but three-point bending strength showed a first decrease and then increase. When Al2O3:ZrO2=1:9, the compressive and bending strength of the composites reached about 997±60MPa and 426±10MPa, respectively. A simple model was proposed to illustrate the fracture mode and toughening mechanism of the composites.

Structural and mechanical properties of zinc aluminoborate glasses with different content of aluminum oxide

The glass samples were prepared according to the following formula: (35 − x) ZnO, 55B2O3, 10Li2O, x Al2O3, where (x = 0.5; 1; 1.5; 2; 2.5; 3; 3.5; 4 mol%) by melt quenching method. Structural parameters such as density, molar volume, cation–anion bond length, and packing density were studied and were correlated to the structural changes. It is found that the density decreases and the molar volume increases with increasing Al2O3 content. FT-IR spectra were measured to investigate the glass structure of these samples and to confirm the formation of non bridging Al–O–B bond with the addition of Al2O3 content. The FT-IR spectra were deconvoluted using curves of Gaussian shape at approximately the same frequencies. The fraction of fourfold coordinated boron atom (N4) was calculated from the deconvoluted data. The longitudinal and transverse ultrasonic wave velocities were measured using the pulse-echo technique. The longitudinal L, shear S, Young’s E and bulk B module were calculated from the measured velocity and density values of the prepared samples and were correlated with the structural changes and all reflects that addition of Al2O3 to present glasses results in de-polymerization of the glass network and formation of non-bridging oxygen (NBOs).

Thermoluminescence features of alumina‐mixed borophosphate glasses with Tb3+ ions for dosimetric applications

AbstractAmorphous barium borophosphate materials doped with small quantity of terbium ions and with the addition of some amounts of alumina were prepared. Thermoluminescence (TL) characteristics of these glasses were investigated after irradiating them with different doses of γ‐rays (in the range 0.5‐8.0 kGy). The TL emission exhibited a dosimetric peak at about 210°C. The TL output under this glow peak is observed to increase with the γ‐ray dose. For any fixed γ‐ray dose, the TL output is increased with increase in Al2O3 content up to 3.0 mol%, and beyond this concentration, quenching of TL is visualized. The dose response of TL output of these glasses exhibited linear behavior in the dose range 0.5‐4.0 kGy. The mechanisms responsible for TL emission and the variation of TL output with the concentration of Al2O3 are quantitatively discussed in terms of structural defects induced during γ‐ray irradiation. Finally, it is concluded that these glasses are potential materials for dosimetry applications in the dose range 0.5‐4.0 kGy.

Influence of Al2O3 on the structure and the physical properties of low-temperature ceramic vitrified bond

The SiO2-B2O3-Al2O3-CaO vitrified bonds with low sintering temperatures and high strength are widely used in the manufacture of diamond abrasive tools. The effects of Al2O3 on the microstructure, crystallization, phase-separated and mechanical properties were comprehensively investigated by DSC, FTIR, XRD, SEM and EDS in this paper. The results showed that the addition of Al2O3 promoted the accumulation and enhanced the binding of structure, inhibited crystallization and phase-separated. Performance analysis showed that the thermal expansion coefficients decreased with increasing Al2O3 content, the minimum value was 6.8074×10−6°C−1. When the content of Al2O3 was 5wt%, the vitrified bond had the best mechanical properties, the maximum bending strength reached 113MPa and effectively improved the wettability between vitrified bond and diamond grains.

Influence of alumina on photoluminescence and thermoluminescence characteristics of Gd3+ doped barium borophosphate glasses

Gd3+ doped barium borophosphate glasses mixed with varying concentration of Al2O3 are synthesized. Photoluminescence, thermoluminescence and other spectroscopic studies viz., IR and EPR spectral studies, have been carried out. IR spectral studies of these glasses indicated that there is a gradual increase in the degree of depolymerization of the glass network with increase in the concentration of Al2O3 upto 3.0mol%. The EPR spectral studies revealed the lowest concentration of Gd3+ ion clusters in the glass mixed with 3.0mol% of Al2O3. The photoluminescence emission spectra exhibited strong ultraviolet blue emission at 311 under excitation at 273nm due to 6P7/2→8S7/2 transition of Gd3+ ions. The intensity of this band is found to be enhanced four times when the glass mixed with 3.0mol% of Al2O3 with respect to that of alumina free glass. The enrichment of this emission is attributed to the declustering of Gd3+ ions by Al3+ ions. Thermoluminescence (TL) characteristics of these glasses have also been investigated after irradiating them with different doses of γ-rays (in the range 0–8.0kGy). The TL emission exhibited a dosimetric peak at about 200°C. The TL output under this glow peak is observed to increase with increase of γ-ray dose. For any fixed γ-ray dose, the TL output is increased with increasing Al2O3 content up to 3.0mol% and beyond this concentration quenching of TL is observed. The mechanisms responsible for TL emission and the variation in TL output with the concentration of Al2O3 are quantitatively discussed in terms of electron and hole centers developed due to interaction of γ-rays with the glass network. The dose response of these glass samples exhibited linear behavior in the dose range 0–8.0kGy.

A Study of the Heat Transfer Behavior of Mold Fluxes with Different Amounts of Al2O3

The element Al in molten aluminum containing steel reacts with the liquid mold flux and thus be transferred into the mold flux during the continuous casting process. Additionally, the increase in alumina in a mold flux changes its performance significantly. Thus, in this paper, the heat transfer properties of mold fluxes with the Al2O3 content ranging from 7 to 40 wt. % were studied with the Infrared Emitter Technique (IET). Results found that heat flux at the final steady state decreased from 423 kW·m−2 to 372 kW·m−2 with the increase in Al2O3 content from 7% to 30%, but it increased to 383 kW·m−2 when the Al2O3 content was further increased to 40%. Both crystalline layer thickness and crystalline fraction first increased, then decreased with the further addition of A2O3 content. Moreover, it indicated that the heat transfer process inside the mold was dominated by both a crystallization of mold flux and the resulting interfacial thermal resistance. Further, the Rint increased from 9.2 × 10−4 m2·kW−1 to 11.0 × 10−4 m2·kW−1 and then to 16.0 × 10−4 m2·kW−1 when the addition of Al2O3 content increased from 7% to 20% and then to 30%, respectively; however, it decreased to 13.6 × 10−4 m2·kW−1 when the Al2O3 content reached 40%.

Study on Viscosity of the La2O3-SiO2-Al2O3 Slag System

The viscosities and free-running temperatures of slag in a La2O3-SiO2-Al2O3 slag system were measured using an internal rotating cylinder method. For different La2O3 mass contents (45, 50, and 55 pct) in the La2O3-SiO2-Al2O3 ternary slag, the slag viscosity and free-running temperature decreased with a decrease in SiO2 content and an increase in Al2O3 content, and decreased with an increase in La2O3 content. Minor components B2O3, FeO, and MnO could decrease the viscosity and free-running temperature of La2O3-SiO2-Al2O3 ternary slag, especially FeO, and a small amount of FeO and B2O3 had an additive effect on slag viscosity and free-running temperature reduction.

Density measurements of gasified coal and synthesized slag melts for next-generation IGCC

The densities of re-melted coal slag melts were measured in air using Archimedean double-bob method in the temperature range from 1350 to 1600°C. The main components of gasified coal slags are SiO2, Al2O3, CaO, MgO, FeO and Fe2O3. Slags consisting of the main components with systematic composition variations were synthesized and evaluated for comparison. The experimental results of chelate titration analysis revealed that the percentages of Fe3+ in coal and synthesized slag samples were 47–56% and 68–80% of total Fe, respectively. The density decreased linearly with increasing temperature for all melt samples. The density of gasified and synthesized coal slag melts was found to decrease with increasing Al2O3 and SiO2 contents and to increase with increasing Fe2O3 and FeO contents. The molar volume and the coefficient of volume expansion, which were calculated from measured density values, increased monotonically with increasing Al2O3 content for CaOAl2O3SiO2 (CAS) synthesized samples with 40mol% SiO2. The molar volume for CaOFeOFe2O3SiO2 (CFS) synthesized samples with 60mol% SiO2 increased with Fe2O3 addition and exhibited discontinuous change at ∼7.5mol% Fe2O3. The coefficient of volume expansion in the same CFS series decreased with increasing Fe2O3 content showing a minimum value at ∼7mol% Fe2O3 and increased in higher Fe2O3 content. A composition parameter calculated from chemical composition was proposed to predict the density of coal slag melts. The relationship between measured density and the composition parameter was analyzed.

Enhanced ionic conduction of CdI2[sbnd]Ag2CrO4 and Al2O3 composite solid electrolytes

A series of Al2O3 doped CdI2Ag2CrO4 composite solid electrolytes was prepared and studied by various techniques. XRD pattern and DTA curve show the presence of AgI component formed due to an ion exchange reaction by following the Pearson’s acid base theory. The peaks of XRD and DTA curve became broad after the composite formation. SEM images clarified the presence of multiphase composite. A.C. impedance spectroscopy shows the single semicircle at lower frequency attributed to dominant nature of grain boundary over the grain. The Arrhenius plots of the conductance show a sharp jump at 150 °C due to β → α phase transition and it decreases with increase of Al2O3 content due to partial amorphization of the salt. The conductivity of the composite increases with increase of dispersoid (Al2O3) and displayed maximum value (σ = 2.49 × 10−5 S cm−1 at 30 °C) for x = 0.3. The value of dielectric constant was increased by increasing temperature owing to increase in mobility and activity of charge carriers, while it shows the decreasing order with respect to frequency.

Transition of Blast Furnace Slag from Silicates-Based to Aluminates-Based: Viscosity

The effect of Al2O3 and the Al2O3/SiO2(A/S) ratio on the viscosity of the CaO-SiO2-Al2O3-MgO-TiO2 slag system was studied in the present work. At a fixed CaO/SiO2(C/S) ratio of 1.20, 9 mass pct MgO, and 1 mass pct TiO2, the viscosity increases with an increase in Al2O3 content at a range of 16 to 24 mass pct due to the polymerization of the aluminosilicate structures, while it decreases when the Al2O3 is higher than 24 mass pct, which means that Al2O3 acts as a network modifier at higher content. Increasing A/S from 0.47 to 0.92 causes a slight decrease in viscosity of the slags and has an opposite effect when A/S is more than 0.92. The free running temperature increases with the Al2O3 content and appears to show a peak at an A/S ratio of 0.92. The change of the apparent activation energy is in accordance with the change of viscosity. When Al2O3 content is more than 24 mass pct with low SiO2, CaO content ranges from 35 to 45 mass pct, and the slag transform from silicates-based to aluminates-based can still get a good operation region. Four different viscosity models were employed to predict the viscosity and RIBOUD’s model was found to be the best in predicting the viscosity by comparing the estimated viscosity with the measured viscosity.

Sound velocities of aluminum‐bearing stishovite in the mantle transition zone

AbstractThe elasticity of Al‐bearing stishovite with 1.0, 3.3, and 4.5 wt % Al2O3 was investigated in the multianvil apparatus at high pressures and temperatures up to 21 GPa and 1700 K, by ultrasonic interferometry in conjunction with in situ X‐ray techniques. The moduli KS and G are found to decrease with increasing Al2O3 content, while their pressure and temperature derivatives do not change in a significant manner for 1.0 and 3.3 wt % Al2O3. The temperature derivatives for 4.5 wt % Al2O3, however, are larger, which may result from a change in the Al substitution mechanism at high Al2O3 content. It is shown that acoustic velocities of any mid‐ocean ridge basalt are lower by −0.4% than those calculated from pure stishovite data. Velocity perturbations up to −3.4% (VP) and −4.2% (VS) in subducted slabs are explained by the combination of the thermal equilibration (ΔT ~ 600 K) of the slab and Al enrichment in stishovite.

Preparation and properties of high-strength molybdenum alloy sheets doped with Al2O3 particles

The pure molybdenum sheet and the Al2O3-doped molybdenum alloy sheets were prepared by the hydrothermal method and a subsequent powder metallurgy process. The effects of Al2O3 particles addition on the recrystallization temperature, microstructures and properties of the Mo sheets were investigated as the focus. The Al2O3-doped Mo sheets have greater strength than the pure Mo sheet, and the 0.50 wt% Al2O3-doped Mo sheet has the best performance. For the unannealed specimens, the strength increases with the increase in Al2O3 content. Compared with that of pure Mo sheet, the strength of 0.50 wt% Al2O3-doped Mo sheet increases by 72 %, 54 %, 73 % and 76 %, respectively, when annealed at 1000, 1100, 1200 and 1300 °C, which is a very obvious reinforcement effect. When lower than 1100 °C, the elongation of the pure Mo sheet is the best. However, when the annealing temperature is equal to or greater than 1100 °C, the 0.50 wt% Al2O3-doped Mo sheet obtains the best elongation. Moreover, the Al2O3 addition can greatly improve the recrystallization temperature of molybdenum sheets; for example, the recrystallization temperature of the 0.50 wt% Al2O3-doped Mo sheet increases by 200 °C at least than that of the pure Mo sheet. Lastly, the strengthening mechanism was discussed.

Desulphurisation ability of blast furnace slag containing high Al2O3 and 5 mass% TiO2 at 1773 K

The sulphide capacities (CS) of CaO–SiO2–Al2O3–MgO–TiO2 blast furnace slags were experimentally measured at 1773 K, and the percentages of free oxygen ions (O2−) and bridge oxygen (O0) of molten slag were calculated using molecular dynamics at 1773 K. The measured and calculated results were closely correlated with the change in CaO/SiO2, MgO, and Al2O3 contents in the slag. The results show that CS increases with increasing CaO/SiO2 and MgO contents in the slag, but decreases with increasing Al2O3 content. The effects of O2− and O0 on CS were analysed using multiple linear regression, and results show that sulphide increases with the increase in the mass percentage of free oxygen and decreases with the increase in the mass percentage of bridge oxygen.

Phase transformations on the surface of YAG composite ceramics under the action of directed laser treatment

The laser treatment of composite ceramics based on Y3Al5O12 with Y2Ti2O7, Al2Y4O9, and Al2O3 additives is accompanied by the melting of the surface layer and formation of tracks. In the volume of tracks, the partial dissociation of Y3Al5O12, Y2Ti2O7, and Al2Y4O9, and the formation of new phases such as YAlO3 of orthorhombic and hexagonal modifications along with the appearance of additional content of Y3Al5O12 and Al2O3 are observed. The content of all these phases depends on the irradiation mode and the phase composition of the ceramics. With increase in the corundum content in ceramic specimens, in the tracks, the Al2O3 content increases, and the Y3Al5O12 content decreases. In the volume of tracks, Y3Al5O12 crystallites are textured. The size of YAG crystallites and their crystallographic texturing depend on the irradiation mode and Y3Al5O12/Al2O3 phase ratio. On the surface of tracks, a layer enriched in YAlO3 forms. Thus, as a result of laser treatment, on the surface of the ceramics, a two-layer coating with a radically new phase composition and specific texture of Y3Al5O12 crystallites forms.