Increasing Al2O3 Concentration Research Articles

Correlation of rare earth coordination and spectral properties in Er3+ doped Na2O–Al2O3–SiO2 glasses with different Al2O3 concentrations by molecular dynamics simulations

The molecular structure of Er2O3 doped Na2O–Al2O3–SiO2 glasses with varying Na2O/Al2O3 ratios is explored via molecular dynamics (MD) simulations using the so-called inherent structure sampling method, which allows the calculation of a large number of local structures of low concentration, as needed to determine the surrounding of low concentration dopants. General structural parameters, including radial distribution functions, coordination numbers and interatomic distances of all network forming and network modifying ions are reported. However, in this work, special attention is devoted to the effect of Al2O3 concentration on the local surrounding of the doped Er3+ ions. It is shown that the Er atoms coordinate 5–6 oxygen ions in their first coordination sphere in the investigated glasses. The Er–O coordination number increases monotonically with increasing Al2O3 concentration and decreasing Na2O/Al2O3 ratio. It is found that the Er atoms are preferably connected to non-bridging oxygen atoms (NBO) in all glasses, even in the peraluminous composition. Additionally, the MD simulation results are compared to the glasses spectral properties that were already investigated in detail by Tanabe and Hanada. The increasing Er-NBO coordination number derived by MD simulations could be correlated with the increased peak splitting of the Er3+ absorption peaks reported by Tanabe and Hanada. Furthermore, a correlation between the Judd-Ofelt parameters published by Tanabe and Hanada and the Er3+ coordination in the glass structure is discussed. It is shown that the Er–O coordination increases with increasing Ω2 parameter as the Al2O3 concentration increases in the glass composition. A correlation of the average overall Er–O coordination number with the symmetry of the local Er site is proposed.

Two-step growth of alumina nanoparticle decorated graphene oxide surfaces: Effect on photocatalytic activity

As water pollution is increasing due to industrialization, there is a high demand for easy-processing photocatalytic materials to clean wastewater. Here, the improvement in the photocatalytic dye degradation effect of graphene oxide (GO) surfaces, made of ultra-sonication assisted modified Hummer's method, is demonstrated with increasing alumina (Al2O3) concentration in the range of 4–30 wt. %. Scanning electron microscopy and x-ray diffraction results suggest a gradual increment in crystalline Al2O3 nanoparticles (NPs) by reducing GO, in good agreement with the first-principles calculations. Moreover, x-ray photoelectron spectroscopy reveals the appearance of oxygenated functional groups with increasing Al2O3 concentration, leading to the formation of defect-rich GO as demonstrated by Raman spectroscopy. Ultraviolet-visible spectroscopy further reflects a maximum reduction in the optical bandgap from 1.88 to 1.56 eV up to a concentration of 15 wt. % Al2O3. Interestingly, the methylene blue degradation efficiency of GO under ultraviolet irradiation is also found to be improved from 45% to 64% with 15 wt. % Al2O3, whereas the formation of Al2O3 NPs in the range of 100–300 nm with 30 wt. % Al2O3 is found to be detrimental for photocatalytic activity.

Investigation of Raman spectra and ionic conductivity of composites based on NaClO4 and KClO4 salts obtained by mechanoactivation

The work is aimed at studying the effect of mechanical activation on the structure and electrical conductivity of the NaClO4 – and KClO4 – basedcomposites. Based on the result of the analysis of the DSC curves of the (1–x) NaClO4 – x Al2O3 and (1–x) KClO4 – x Al2O3 composites measured while heating and cooling the samples, it was established that the enthalpy of phase transitions in them decreased with an increase in the concentration of the nanosized dopant. A complication of all active vibrational contours corresponding to internal vibrations of the molecular anion in the composites with increasing Al2O3 concentration and a shift of the band of the fully symmetric stretching vibration v1 (A) to a low-frequency region was revealed by Raman spectroscopy. Based on electrochemical impedance spectroscopy data, it was determined that for the 0.4NaClO4 – 0.6Al2O3 system subjected to mechanoactivation, the values of specific ionic conductivity increased by two orders of magnitude as compared to that of pure NaClO4, while for the 0.4KClO4 – 0.6Al2O3 system, the values of specific ionic conductivity increased by three orders of magnitude as compared to the initial salt at T = 320 °C.

Homogeneous solid-solution formation in Fe2O3–Al2O3 system observed by TEM, XAFS, and Mössbauer spectroscopy

We have characterized the mechanically alloyed (Fe2O3)1-x(Al2O3)x solid solution with corundum-type structure by means of TEM, EXAFS, and Mössbauer spectroscopy emphasizing the homogeneity of cation distribution and the variation of magnetic property with the composition. HR-TEM revealed that the typical crystallite size of the solid solution is 10–20 nm and the observed lattice spacing is consistent with that evaluated from Vegard's law. EXAFS measurements showed that the radial distribution at Fe–Fe distance decreases monotonously with aluminum substitution, while Fe–O is not largely altered. Mössbauer spectroscopy showed a gradual change in spectra from sextet peaks at x = 0 into doublet with increasing Al2O3 concentration up to x = 0.67, indicating that spin interaction is diluted by the homogeneous substitution of aluminum ions over the wide compositional range keeping corundum-type structure.

Improving Thermal Conductivity of Injection Molded Polycarbonate/Boron Nitride Composites by Incorporating Spherical Alumina Particles: The Influence of Alumina Particle Size.

In this work, the influences of alumina (Al2O3) particle size and loading concentration on the properties of injection molded polycarbonate (PC)/boron nitride (BN)/Al2O3 composites were systematically studied. Results indicated that both in-plane and through-plane thermal conductivity of the ternary composites were significantly improved with the addition of spherical Al2O3 particles. In addition, the thermal conductivity of polymer composites increased significantly with increasing Al2O3 concentration and particle size, which were related to the following factors: (1) the presence of spherical Al2O3 particles altered the orientation state of flaky BN fillers that were in close proximity to Al2O3 particles (as confirmed by SEM observations and XRD analysis), which was believed crucial to improving the through-plane thermal conductivity of injection molded samples; (2) the presence of Al2O3 particles increased the filler packing density by bridging the uniformly distributed BN fillers within PC substrate, thereby leading to a significant enhancement of thermal conductivity. The in-plane and through-plane thermal conductivity of PC/50 μm-Al2O3 40 wt%/BN 20 wt% composites reached as high as 2.95 and 1.78 W/mK, which were 1183% and 710% higher than those of pure PC, respectively. The prepared polymer composites exhibited reasonable mechanical performance, and excellent electrical insulation properties and processability, which showed potential applications in advanced engineering fields that require both thermal conduction and electrical insulation properties.

Thermal and Physico-Mechanical Properties of Irradiated Aluminum Oxide Filled Ethylene Propylene Diene Monomer Rubber Composites

Composites from ethylene propylene diene monomer (EPDM) rubber filled with different concentrations 20, 40, and 60 parts per hundred rubber (phr) of aluminum oxide (Al2O3) were prepared. The samples were vulcanized by gamma irradiation at doses (50,100, 150, and 200) kGy. The effects of irradiation doses and Al2O3 contents on the mechanical prorerties (particularly tensile strength, elongation at break % and hardness), physical properties (volume fraction and crosslinking density), thermal properties was studied by thermogravimetric analysis (TGA) and fire resistance was tested using Limiting Oxygen Index (LOI) and rate of burning methods of EPDM and its composites were studied. The results indicated that the improvement of mechanical as well as, physical properties occurred by increasing the concentration of Al2O3 (except the tensile strength values, where the highest values were obtained at concentration 20 phr Al2O3 in the composite irradiated at 100 kGy). The thermal stability and fire retardancy properties of the prepared composites were improved by increasing Al2O3 concentration. Generally, the addition of Al2O3 and gamma irradiation has improved composite’s performance. This is suitable for preparing products of rubber serving in dynamic conditions, with longer expected service life

Viscosity and Structural Investigation of High-Concentration Al2O3 and MgO Slag System for FeO Reduction in Electric Arc Furnace Processing

In the present study, the viscosity of the CaO–SiO2–FeO–Al2O3–MgO slag system was measured for the recovery of FeO in the electric arc furnace (EAF) process using Al dross. Considering the MgO-saturated operational condition of the EAF, the viscosity was measured in the MgO-saturated composition at 1823 K with varying FeO and Al2O3 concentrations. An increase in the slag viscosity with decreasing temperature was observed. The activation energy was evaluated, and the change in the thermodynamically equilibrated phase was considered. The changes in the aluminate structure with varying FeO and Al2O3 concentrations were investigated by Fourier-transform infrared spectroscopy, which revealed an increase in the [AlO4] tetrahedral structure with increasing Al2O3 concentration. Depolymerization of the aluminate structure was observed at higher FeO concentrations. The Raman spectra showed the polymerization of the silicate network structure at higher Al2O3 concentrations. By associations between the silicate and aluminate structures, a more highly polymerized slag structure was achieved in the present system by increasing the Al2O3 concentration.

Electrical Conductivities of Solid and Liquid Cryolite Systems

The electrical conductivities of the NaF–AlF3 cryolite systems with a cryolite ratio 2.4–3.0 containing 3.0–7.0 wt % CaF2, 1.2–2.0 wt % MgF2 and 0–8.0 wt % Al2O3 in the temperature range 700–1050°C are studied by impedance spectroscopy. The addition of CaF2 or MgF2 to molten sodium cryolite decreases the electrical conductivity. However, below the liquidus temperature in the two-phase solid–liquid region the electrical conductivity increases with the fluoride salt concentration. The electrical conductivities of the cryolite systems decrease with increasing Al2O3 concentration over the entire temperature range.

Optical properties of PVC/Al2O3 nanocomposite films

In this work, polyvinyl chloride (PVC) polymer films doped with 0, 2, 4, and 6 wt% Al2O3 nanoparticles with average size of 10 nm were prepared by solution casting route. Al2O3 nanoparticles are found to possess rhombohedral crystal structure, and PVC is partly crystallized as confirmed with XRD analysis. SEM images showed that Al2O3 nanoparticles are well distributed in the PVC film surface. The direct optical energy gap (Eopt) decreased from 5.05 to 3.60 eV and Urbach energy (EU) increased with increasing Al2O3 concentration. The typical excitation energy for electronic transitions (E0), the dispersion energy (Ed), refractive index, dipole strength (f), average oscillator wavelength (λ0), oscillator strength parameter (S0), optical conductivity, and both static and high-frequency dielectric constants are found to increase with increasing Al2O3 content. The third-order nonlinear optical susceptibility (χ(3)) and the nonlinear refractive index (n2) were estimated. Also, the ratio of free carriers to effective mass (N/m*) increased from 2.69 × 1057 to 170.91 × 1057 m−3 kg−1 with increasing Al2O3 nanoparticles percentage. Finally, the group velocity dispersion (GVD), dispersion coefficient for material dispersion (D), and third-order dispersion (TOD) are found to increase upon increasing Al2O3 filler ratio.

Microstructure and luminescence of erbiumdoped Na2O/K2O/CaO/CaF2/Al2O3/SiO2 nano glass-ceramics

Oxyfluoride glasses with the mol% compositions (63-x) SiO2, x Al2O3, 12.3 CaO, 5.3 K2O, 9.0 Na2O and 10.4 CaF2 with x = (10, 8, 6) were doped with an Er3+-concentration of 1·1020 cm−3. The glasses were thermally treated at temperatures in the range from 550 to 620 °C. This led to the crystallization of cubic CaF2 with extremely broadened XRD-lines caused by mean crystallite sizes ranging from 14 to 38 nm. An interface controlled crystallization mechanism is proposed. Phase separation was observed in the as casted glasses by electron microscopy. Droplet like particles occur with a size of ca. 360 nm after heat treatment. These particles are composed by small crystallites with sizes of around 50 nm. Increasing Al2O3 concentration increases the tendency to liquid/liquid phase separation and decreases the crystallization temperature. Doping with Er3+ triggers CaF2 nanocrystallization by decreasing the crystallization temperature.

Effect of Al2O3 on the fluoride volatilization during melting and ion release in water of mold flux

In this study, in view of the hazard associated with the volatilization of fluoride during the melting and ion release in the secondary cooling water from traditional mold flux, the mold flux with a higher Al2O3 content was investigated. The volatilization of fluoride during slag melting was monitored by thermogravimetric analysis. The results showed that the tendency to form volatile substances decreased with increasing Al2O3 concentration. The leaching and dissolution behaviors of the traditional and high Al2O3 content mold fluxes resulting by change in pH and F− concentration were investigated. The leach tests of molten mold flux showed that pH was controlled by the ion exchange processes and varied from 4.0 to 9.5. The F− released from the traditional mold flux was up to 35.4mg·L−1. Similarly, the F− concentrations and the pH ranges decreased sharply in the beginning and then slightly increased with increasing Al2O3 content from 4mass% to 34mass%. The ion release ability and pH range were decreased by adjusting the Al2O3 content in the mold flux. The formation of volatile fluoride was effectively inhibited when the Al2O3 content was controlled in the mass range ~16–34% in the experimental mold fluxes, and the F− concentrations remained within the range ~4–10mg·L−1. Moreover, the pH varied from 6.5 to 7.5 during the water leaching, thus the harm caused by fluoride volatilization and ion release was significantly inhibited.

Viscosity and viscosity estimation model of fully liquid slags in TiO2–Al2O3–CaO–SiO2 and TiO2–Al2O3–CaO–SiO2–MgO systems with high TiO2 concentration and low mass ratio of CaO to SiO2

The present paper focuses on the viscosity of high titanium containing slags in the process of titanomagnetite smelting by taking the TiO2–Al2O3–CaO–SiO2 quaternary system with TiO2 in the range from 23 to 43%, Al2O3 in the range from 3 to 12% and basicity (mass ratio of CaO/SiO2) in the range from 0·3 to 0·7 as the object. Experimental determinations of the viscosity were carried out in the temperature range from 1573 to 1873 K using the rotation cylinder method. The effects of TiO2, Al2O3, basicity and temperature on viscosity were studied. The experimental results indicated that the viscosity decreased with increasing TiO2 concentration and basicity, and increased with increasing Al2O3 concentration. Based on the experimental data of the TiO2–Al2O3–CaO–SiO2 quaternary system, a new viscosity model was proposed by modifying the Urbain model. The new model was applied successfully to predict the viscosity of TiO2–Al2O3–CaO–SiO2 and TiO2–Al2O3–CaO–SiO2–MgO systems in the fully liquid condition with high TiO2 concentration and low basicity over a wide range of composition and temperature using one set of model parameters.

Enhancement in ammonia sensitivity with fast response by doping Al2O3 in polyaniline

ABSTRACTAl2O3 mixed polyaniline composite with different dopant concentrations have been synthesized successfully by chemical oxidation method. X‐ray diffraction, Fourier transform infrared spectroscopy, and UV–visible spectroscopy confirm the synthesis of the polyaniline and Al2O3 mixed polyaniline composite. Scanning electron microscopy shows the weak crystalline quality of the samples. The samples are found sensitive to ammonia gas. The sensing properties have been studied at different temperatures i.e. 25°C, 50°C, and 100°C by varying the ammonia concentration over a range of 100–1500 ppm. The sensitivity increases with increasing Al2O3 concentration, increasing ammonia concentration, and also with increasing the sensing temperature. Sensitivity of these samples to ammonia gas is good with fast response. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1941–1948, 2013

Silico-ferrite of Calcium and Aluminum (SFCA) Iron Ore Sinter Bonding Phases: New Insights into Their Formation During Heating and Cooling

The formation of silico-ferrite of calcium and aluminum (SFCA) and SFCA-I iron ore sinter phases during heating and cooling of synthetic iron ore sinter mixtures in the range 298 K to 1623 K (25 °C to 1350 °C) and at oxygen partial pressure of 5 × 10−3 atm has been characterized using in situ synchrotron X-ray diffraction. SFCA and SFCA-I are the key bonding phases in iron ore sinter, and an improved understanding of their formation mechanisms may lead to improved efficiency of industrial sintering processes. During heating, SFCA-I formation at 1327 K to 1392 K (1054 °C to 1119 °C) (depending on composition) was associated with the reaction of Fe2O3, 2CaO·Fe2O3, and SiO2. SFCA formation (1380 K to 1437 K [1107 °C to 1164 °C]) was associated with the reaction of CaO·Fe2O3, SiO2, and a phase with average composition 49.60, 9.09, 0.14, 7.93, and 32.15 wt pct Fe, Ca, Si, Al, and O, respectively. Increasing Al2O3 concentration in the starting sinter mixture increased the temperature range over which SFCA-I was stable before the formation of SFCA, and it stabilized SFCA to a higher temperature before it melted to form a Fe3O4 + melt phase assemblage (1486 K to 1581 K [1213 °C to 1308 °C]). During cooling, the first phase to crystallize from the melt (1452 K to 1561 K [1179 °C to 1288 °C]) was an Fe-rich phase, similar in composition to SFCA-I, and it had an average composition 58.88, 6.89, 0.82, 3.00, and 31.68 wt pct Fe, Ca, Si, Al, and O, respectively. At lower temperatures (1418 K to 1543 K [1145 °C to 1270 °C]), this phase reacted with melt to form SFCA. Increasing Al2O3 increased the temperature at which crystallization of the Fe-rich phase occurred, increased the temperature at which crystallization of SFCA occurred, and suppressed the formation of Fe2O3 (1358 K to 1418 K [1085 °C to 1145 °C]) to lower temperatures.

Preparation and characterisation of electrodeposited Ni-Cr/Al<SUB align="right">2O<SUB align="right">3 nanocomposite coatings from a trivalent chromium-based bath

Ni-Cr/Al2O3 composite coatings were co-deposited on mild steel substrates by co-electrodeposition of Ni-Cr alloys and Al2O3 nanopowders from a trivalent chromium plating bath. Variations of Cr and Al2O3 nanoparticles in nanocomposite coatings as a function of Al2O3 concentration in electrolyte, cathode current density, stirring rate and temperature of plating bath was investigated. It was found that these parameters strongly affect the weight percentage of Cr and Al2O3 nanoparticles in the coatings. Microstructural characterisation of the coatings was performed by x-ray diffraction (XRD), scanning electron microscopy and energy-dispersive x-ray analysis (EDX). The corrosion behaviour of the nanocomposite coatings was evaluated by charting the Tafel curves of the solution of H2SO4 (5%) at room temperature. The results showed that the amount of Al2O3 nanoparticles in the coating increases with increasing Al2O3 concentration in electrolyte. This also enhances the co-deposition of Ni and Cr. It was also found that the presence of Al2O3 nanoparticles leads to an increase in hardness and corrosion resistance of the coatings. The distribution of Al2O3 nano-particles across the coatings was uniform even in those cases which resulted from baths of higher concentrations of Al2O3.

Phase equilibria studies in alumina-containing high zinc fayalite slags with CaO/SiO2 = 0.55 Part 2

Abstract The phase equilibria and liquidus temperatures in the ZnO„FeO“Al2O3-CaO-SiO2 system have been determined experimentally in equilibrium with metallic iron. Specifically, the effect of Al2O3 concentrations in high zinc fayalite slags is identified and the results are presented in a form of pseudo- ternary sections ZnO„FeO“(Al2O3 + CaO + SiO2) with CaO/SiO2 = 0.55 and (CaO + SiO2)/Al2O3 = 5.0 and 3.5. It was found that in the presence of Al2O3 the spinel phase is formed, and the spinel primary phase field expands and the wustite and melilite primary phase fields are reduced in size with increasing Al2O3 concentration. The implications of the findings to industrial practice are discussed.

Photoluminescence Characterization of Al-Doped ZnO Films Deposited by Using DC Magnetron Sputtering

We investigated the structural and the optical properties of Al-doped ZnO (AZO) lms deposited by DC magnetron sputtering without substrate heating as a function of the Al2O3 content. The resistivity of the AZO lms decreased from 2.6 10 2 cm to 1.9 10 3 cm and the optical band gap energy increased from 3.34 eV to 3.38 eV when the Al2O3 content in the AZO targets was increased from 0 wt% to 3.0 wt%. The AZO lms showed a highly c-axis preferred orientation which was enhanced with increasing Al2O3 concentration. In order to investigate the e ects of the crystallinity and the defect number on the emitting properties of the AZO lms, we estimated photoluminescence excitation (PLE) spectra were estimated by using photoluminescence (PL) measurements. The PLE spectra of the AZO lms revealed a near-band-edge (NBE) emission at 3.43 eV (UV region) and a deep-level emission centered at around 2.64 eV (blue-green region). The NBE intensity tended to increase markedly with increasing Al2O3 addition in the AZO targets. The doping e ciency of Al3+ ions is important to determine the correlation between the electrical and the structural properties.

Mechanism of Alumina‐Enhanced Sintering of Fine Zirconia Powder: Influence of Alumina Concentration on the Initial Stage Sintering

The isothermal shrinkage behavior of 2.9 mol% Y2O3‐doped ZrO2 powders with 0–1 mass% Al2O3 was investigated to clarify the effect of Al2O3 concentration on the initial sintering stage. The shrinkage of the powder compact was measured at constant temperatures in the range of 950°–1050°C. The Al2O3 addition increased the densification rate with increasing temperature. The values of apparent activation energy (nQ) and apparent frequency‐factor term (β0n), where n is the order depending on the diffusion mechanism, were estimated at the initial sintering stage by applying a sintering‐rate equation to the isothermal shrinkage data. The diffusion mechanism changed from grain‐boundary diffusion (GBD) to volume diffusion (VD) by Al2O3 addition and both nQ and β0n increased with increasing Al2O3 concentration. The kinetic analysis of the sintering mechanism suggested that the increase of densification rate by Al2O3 addition largely depends on the increase of β0n, that is, the increases of n with GBD→VD change and β0 with an increase in Al2O3 content, although the nQ also increases with Al2O3 addition. This enhanced sintering mechanism is reasonably interpreted by the segregated dissolution of Al2O3 at ZrO2 grain boundaries.

Effect of Al2O3 concentration on zirconolite (Ca(Zr,Hf)Ti2O7) crystallization in (TiO2,ZrO2,HfO2)-rich SiO2–Al2O3–CaO–Na2O glasses

Glass-ceramic matrices containing zirconolite (nominally Ca(Zr,Hf)Ti2O7) crystals in their bulk that would incorporate high proportions of minor actinides (Np, Am, Cm) or plutonium could be envisaged for their immobilization. Zirconolite-based glass-ceramics can be prepared by controlled crystallization of zirconolite in glasses belonging to SiO2–Al2O3–CaO–Na2O–TiO2–ZrO2–HfO2 system. In this study, neodymium was used as trivalent actinides surrogate. Increasing Al2O3 concentration in glass composition had a strong effect on the nucleation rate I z of zirconolite crystals in the bulk, on the amount of neodymium incorporated in zirconolite phase and on the crystal growth rate of silicate phases (titanite + anorthite) from glass surface. These results could be explained by the existence of competition—in favor of aluminum—between Al3+ and (Ti4+, Zr4+, Hf4+) ions for their association with charge compensators cations to facilitate their incorporation in the glassy network. Differential thermal analysis (DTA) was used to study exothermal effects associated with bulk and surface crystallization. 27Al magic angle spinning nuclear magnetic resonance (MAS NMR) spectra showed that aluminum enters glasses network predominantly in 4-fold coordination. Neodymium optical absorption and fluorescence spectroscopies showed that the Al2O3 concentration changes performed in this study had not significant effect on Nd3+ ions environment in glasses.

Phase relations in the Al2O3-MoO3 and Al-MoO3 systems, investigated by X-ray powder diffraction, FTIR, and DTA techniques

This study focuses on the phase transformation induced during mixing fixed quantities of MoO3 and Al2O3 or aluminum powder (2, 3, 4, 5, 10, 20, 40, 50%). Different solid solutions were identified by x-ray powder diffraction, FTIR, and DTA. In the Al2O3 concentration range 2–20%, the only phase present besides MoO3 is Al2(MoO4)3. The concentration of this latter phase increases with increasing Al2O3 concentration, while the concentration of MoO3 decreases at the same time. For high concentrations of Al2O3 (more than 20%), MoO3 disappears completely, and Al2(MoO4)3 becomes the dominant phase. When MoO3 is mixed with various concentrations of aluminum powder, three kinds of samples were obtained. For aluminum concentration less than 4%, no other phase than MoO3 is present. For the concentration of aluminum in the range 4–20%, a new phase of Al2(MoO4)3 is observed. This phase increases while MoO3 decreases with increasing aluminum loading. At high concentrations of aluminum (more than 20%), the MoO3 disappears completely, and a new phase M0.975Al0.025O2 is present besides the Al2(MoO4)3 already formed.