Dispersion Of Alumina Particles Research Articles

Thermal Stability of Nanocrystalline Ag–Cu–Al Alloy Films with Densely Dispersed Alumina Particles Prepared via Reactive Sputtering Using Ar–O2 Mixed Gas

Thermal Stability of Nanocrystalline Ag–Cu–Al Alloy Films with Densely Dispersed Alumina Particles Prepared via Reactive Sputtering Using Ar–O2 Mixed Gas

Nanocrystalline Ag–Cu–Al Alloy thin films with densely dispersed alumina particles prepared using reactive sputtering method with Ar–O2 mixed gas

As a first step to challenge the fabrication of highly O2-permeable Ag membranes, thin films of nanocrystalline Ag–Cu–Al alloys with densely dispersed Al2O3 particles were successfully prepared via reactive sputtering using Ar–O2 mixed gas. The effect of O2 partial pressure on the thin film structure during sputtering was investigated. A critical O2 partial pressure was required to obtain a nanocrystalline structure via simultaneous internal oxidation during sputtering. The critical condition was correlated with the flux ratio of O2 to Al impinging on the Ag film surface and the stoichiometric ratio of O to Al in Al2O3.

High-Speed Alumina Stereolithography

The additive manufacturing of ceramics offers a reliable and repeatable method for fabricating parts with complex geometries. To compete with conventional ceramic forming methods, the time and cost associated with material and process optimization for ceramic stereolithography should be improved. Computational analysis methods can be utilized to reduce the number of experimental steps required for material and process optimization. This work used the discrete element method and ray tracing analyses to predict suitable material parameters and processing conditions for ceramic stereolithography. The discrete element method was used to create alumina particle dispersion models to predict suitable paste compositions, and ray tracing was used to predict suitable laser power and scan speed to achieve a sufficient curing depth for stereolithography processing. The predicted conditions of paste composition and processing parameters were comparable to experimental values, reducing the number of experimental iterations required for process optimization. Furthermore, suitable processing parameters for high-speed fabrication by stereolithography was predicted, achieving a processing speed much faster than previously reported ceramic stereolithography. The reduction in process optimization timeline, and the increase in fabrication speed, could increase the appeal of ceramic stereolithography to industry.

Understanding the electrosteric dispersion of α-alumina particles using a sulfonated tannin of natural origin

This work explores the stabilization effect of a sulfonated tannin (black wattle extract) on water-suspended α-alumina particles. Results showed that first additions lead to particle agglomeration. A minimum of 0.5 wt% tannin (relative to the alumina content) is required to cover the whole particle surface. Suspensions regain stability at ca. 1.0 wt% tannin (ca.1 mg tannin/m2 alumina surface area), due to a high negative ζ-potential (−60 mV, pH = 8.0). Both ζ-potential and particle hydrodynamic diameter are then close to those in electrostatically dispersed alumina particles. Changes in ionic strength cause changes in ζ-potential and hydrodynamic diameter but hardly affect the tannin adsorption. The electrosteric stabilization results from the repulsion provided by the ~15 nm thick adsorbed tannin layer (steric effect) and the enveloping electric double layer, which remains sensitive to the suspension ionic strength (electrostatic effect). Changes in hydrodynamic diameter can be used to infer the electric double layer thickness.

Comparison of acidic and basic ionic liquids effects on dispersion of alumina particles in Pebax composite membranes for CO2/N2 separation: Experimental study and molecular simulation

In this study, two types of acidic and basic ionic liquids (ILs) were used to modify the γ-Al2O3 particles. Different amounts of modified particles were added to the poly (ether-block-amide) (Pebax) polymeric matrix, and various composite membranes were prepared. FTIR (Fourier transform infrared), SEM (scanning electron microscopy), XRD (X-ray diffraction), DSC (differential scanning calorimetry), tensile and gas permeation analyses, as well as molecular simulations, were used to study the effect of ILs on the structure of membranes and their performances. The results indicated that ILs prevented well the sedimentation and agglomeration of particles through the electrostatic and steric forces. The electrostatic forces were more effective than steric forces. In addition to improving membrane separation performance and overcoming the trade-off limit, the modification of γ-Al2O3 particles has improved membranes mechanical strength. The comparison of ILs performances showed that the acidic IL had a better effect on the particle dispersion than the basic one. The CO2 permeability and CO2/N2 selectivity in the membrane containing 10 wt% acidic IL-modified particles increased about 47% and 124%, respectively, compared to the pure Pebax membrane. The molecular simulation confirmed the experimental results and showed that the employed ILs had different effects on the diffusivity and solubility coefficients of CO2 molecules in the membranes. Based on simulation results, the acidic IL improved the solubility coefficient by 95%, and the basic IL enhanced the diffusivity coefficient by 71%.

Microstructural and mechanical properties of Al2O3 reinforced Al7010 matrix composites, fabricated by stir casting

The microstructural and mechanical properties of alumina reinforced Al7010 matrix composites, fabricated by stir casting, were investigated by varying size and volume fractions of alumina particles. The optical microscope, micro Vickers hardness tester, tensile tester, and impact testers were used to evaluate the microstructure and mechanical properties of produced alumina reinforced Al7010 matrix composites. Results show that the alumina reinforced Al7010 matrix composites, incorporating lower volume fractions of alumina particles, exhibited much better morphological and mechanical properties than composites with higher volume fractions. The composite with 14% alumina particles of size 15 µm exhibited uniform dispersion of alumina particles in the Al7010 matrix with superior interfacial bonding and negligible agglomeration of alumina particles and excellent morphological properties. On the other hand, the composite, having 21% alumina particles of size 1 µm demonstrated very poor morphological properties and intensive agglomeration of alumina particles. Similarly, the maximum values of Rm (349 MPa) and ƐT (3.41%) were also offered by composite, incorporating 14% Al2O3 particles of size 15 µm attributed to the uniform dispersion and negligible agglomeration of alumina particles throughout the matrix. The composite with 21% alumina particles of size 1 µm offered the minimum values of Rm (172 MPa) and ƐT (1.69%) due to the presence of intensive agglomeration of alumina particles. The superior impact toughness (11.4 J) and the overall optimum combination of morphological and mechanical properties were offered by the composite with 14% alumina particles of size 15 µm.

Effect of fluorosurfactant on alumina membrane for oil and water separation

In this study, the surfactant sodium perfluorooctanoate with alumina composite was synthesized via a sol–gel method. The effects of perfluorooctanoic (PFO) acid as an anionic surfactant on the morphological structures, amorphous crystalline, and the functional elements using field emission scanning microscope (FESEM), X-ray diffraction (XRD), energy dispersive X-ray (EDX) and Fourier transform infrared (FTIR) were evaluated after grafting on kaolin-based hollow fibre membrane through a dip-coating process. The post-heat treatment on the coated surface was investigated. The performance was examined for oil rejection and contact angle test. The results reveal intercalation of PFO on the alumina in the form of film-like top layer, and the oil rejection was attained at 98% and water flux of 21.62 L/m2.h was also obtained after heat treatment. The heat treatment significantly did not alter the surface structure, while the fluorine atoms in the PFO decreased with an increase in temperature from 40 °C to 60 °C. The PFO largely influence the oleophobicity of the membrane. Thus, post thermal treatment of the coated surface influences the properties and performance of the membrane. Fluorosurfactant plays a significant role in simultaneously acting as interfacial surface material and improving the dispersion of alumina particles on the alumina composite membrane.

Effect of dispersed particles on TiAl alloys fracture behavior

γTiAl based alloys are very attractive for structural applications at high temperatures. The addition to the selected alloy of dispersed alumina particles increases the yield strength and the elastic modulus of γTiAl alloys but affects their fracture behavior by favoring the propagation of brittle fracture. The analysis of the fracture surface revealed that the addition to oxide particle, during component production by means of investment casting, favors brittle fracture propagation by intensifying stresses and by increasing the quantity of shrinkage cavities inside the casting.

High strength alumina tapes prepared by gel-tape casting method

In the current work, high strength alumina (Al2O3) thin tapes were prepared by a novel gel-tape casting method. The water-based slurries were gelled by the polymerization of the epoxy monomers. Low viscosity slurries consisting of nanometer-sized alumina particles were prepared with a solid loading reaching 42 vol%. Sodium and ammonium polyacrylate dispersants were used for alumina particle dispersion and stabilization. The individual Al2O3 tapes reached a relative density of over 99.5% and a grain size between 1.1 and 1.3 μm after pressureless sintering at 1450 °C. The biaxial strength of sintered samples was measured in the ball-on-three-balls setup and the values of characteristic Weibull strength up to 1400 MPa were obtained for as-sintered tapes with a thickness of about 190 μm. The effect of sodium and ammonium-based polyacrylate dispersants on tape processing and properties of the Al2O3 tapes were investigated and explained.

Continuous manufacturing of 3D patterned hybrid film via a roll-to-roll process with UV curing

A strategy for continuous fabrication of a microscale 3D-patterned hybrid composite film composed of alumina and acrylate resin was developed using roll-to-roll production. Conventional thermal curing was replaced with a UV curing procedure to facilitate rapid and economical processing. A seamless engraved soft urethane mold was first produced using a patterned metal roll. Subsequently, alumina and acrylate resin were cured on the engraved mold via UV irradiation to produce patterned hybrid films. The dispersion of alumina particles in acylate resin was enhanced by utilizing amine acrylate. Photopolymerization was measured using Fourier-transform infrared spectroscopy. The morphology of the soft engraved mold and the patterned hybrid film was investigated using scanning electron microscopy.

Fabrication and characterization of SiC whiskers toughened Al2O3 paste for stereolithography 3D printing applications

To prevent the agglomeration of silicon carbide whiskers (SiCw) in photosensitive ceramic paste, a butanone-ethanol azeotropic solvent is employed to facilitate the dispersion of alumina particles, SiC whiskers and UV resins. Moreover, SiCw/Al2O3 ceramic pastes, with 5–15 vol % SiCw, are prepared by using ball milling, stirring and distillation processes. The mixture of butanone-ethanol solvent and resins can be effectively separated at 70 °C without weakening the polymerization of UV resin. Moreover, an empirical equation is established to evaluate the relationship between SiCw content, aspect ratio and viscosity of resulting ceramic paste. The 15 vol % SiCw/Al2O3 composite ceramic, with SiCw aspect ratio of 50, renders higher resistance to liquid flow and results in a high viscosity of 30,000 mPa s at the shear rate of 30 s−1. Furthermore, a modified equation is established to predicate the curing depth of ceramic pastes with different amounts of SiCw, where 15 vol % SiCw/Al2O3 composite results in higher light scattering properties, leading to lowest Cd of ∼0.061 mm. Finally, the complex-shaped SiCw/Al2O3 ceramic component, prepared by SL 3D printing technology, debinding and sintering processes, exhibited a superior fracture toughness of 7.1 ± 1.20 MPa m1/2 and a higher hardness of 17.6 ± 0.78 GPa.

Effect of Alumina Contents on the Physicomechanical Properties of Alumina (Al2O3) Reinforced Polyester Composites

Polyester-based composites filled with various contents of alumina (Al2O3) (i.e., 0, 1, 5, and 10 vol%) have been fabricated in this study. Physical and mechanical properties of the composites have also been analysed. The analysis results showed that the experimental density of the polyester/alumina composites was smaller than the theoretical density, which could be attributed to the formation of voids during preparation of the composites. Meanwhile, the tensile strength, stiffness, and hardness of the composites increased with increasing alumina content, while the strain-at-break of the composites decreased. It was observed that the composites containing 5 vol% of alumina had the best tensile strength, stiffness, and hardness. The uniform distribution and dispersion of alumina particles were likely responsible for the improvement of the mechanical properties. In other hand, small decrease in tensile strength, stiffness, and hardness of composite was found in the composites with 10 vol% of alumina. The formation of agglomerates and voids was believed to be the main factor for the decrease of the both properties.

CFD Modeling of Alumina Diffusion and Distribution in Aluminum Smelting Cells

With the increase in line current and decrease in bath volume of aluminum smelting cells, alumina distribution is critical to cell performance. A VOF-DPM model with four flat anodes was developed to simulate the distribution, and can track both the gas–bath interface and dispersed alumina particles. The results show that alumina is more likely to accumulate in the anode gaps, and from there travels to side channels. More than 20 min are needed for the fed alumina to reach the concentration equilibrium; the alumina gradient in the transversal direction of the model exceeds that in the longitudinal direction.

Quantifying Alumina Nanoparticle Dispersion in Hybrid Carbon Fiber Composites Using Photoluminescent Spectroscopy.

Composites modified with nanoparticles are of interest to many researchers due to the large surface-area-to-volume ratio of nano-scale fillers. One challenge with nanoscale materials that has received significant attention is the dispersion of nanoparticles in a matrix material. A random distribution of particles often ensures good material properties, especially as it relates to the thermal and mechanical performance of composites. Typical methods to quantify particle dispersion in a matrix material include optical, scanning electron, and transmission electron microscopy. These utilize images and a variety of analysis methods to describe particle dispersion. This work describes how photoluminescent spectroscopy can serve as an additional technique capable of quickly and comprehensively quantifying particle dispersion of photoluminescent particles in a hybrid composite. High resolution 2D photoluminescent maps were conducted on the front and back surfaces of a hybrid carbon fiber reinforced polymer containing varying contents of alumina nanoparticles. The photoluminescent maps were analyzed for the intensity of the alumina R1 fluorescence peak, and therefore yielded alumina particle dispersion based on changes in intensity from the embedded nanoparticles. A method for quantifying particle sedimentation is also proposed that compares the photoluminescent data of the front and back surfaces of each hybrid composite and assigns a single numerical value to the degree of sedimentation in each specimen. The methods described in this work have the potential to aid in the manufacturing processes of hybrid composites by providing on-site quality control options, capable of quickly and noninvasively providing feedback on nanoparticle dispersion and sedimentation.

Corrosion and Tribocorrosion Behavior of Ti-Alumina Composites

This work focuses in the corrosion and wear properties of titanium reinforced with 1% wt. alumina particles, produced by a combination of colloidal techniques and powder metallurgy. The alumina particles were added to control the grain growth of titanium during sintering, and simultaneously to increase hardness and wear resistance. Colloidal techniques permitted a homogeneous dispersion of alumina particles on the surface of fine Ti particles by the formulation of stable aqueous suspensions that were further processed by spray-dry to obtain spherical granules with improved compressibility. Ti-alumina samples were produced by uniaxial pressing of granules and vacuum sintering leading to materials with homogeneous microstructure, a reduction of grain size higher than 50 % with respect to pure titanium, and a sensible increase in hardness. But the addition of ceramic particles can also have an influence on the corrosion behavior that is one of the most interesting properties of titanium alloys, and on wear resistance, that is one of the drawbacks of Ti. Moreover, the study of simultaneous action of wear and corrosion (tribocorrosion) is an area of highest interest in applications like biomedical or automotive. The corrosion behavior was evaluated by Electrochemical Impedance Spectroscopy (EIS) and Potentiodynamic Polarization (PP) in NaCl at two concentrations (0.9 % and 3.5 %) and temperatures (37 oC, and room temperature). Tribocorrosion tests were performed using a reciprocating ball-on-plate tribometer where a 10 mm diameter alumina ball was used as counter material, and 10 N normal load was applied during 30 min in the same concentrations and temperatures of NaCl as in the static corrosion tests. The results showed a clear improvement of wear resistance on the composite without reducing the corrosion behavior in both conditions.

Ultrasound induced colloidal particles oscillation in liquid at elevated temperatures

Ultrasound attenuation spectroscopy provides a unique means for studying various properties of complex fluids such as aggregative stability, particle size, longitudinal rheology, zeta potential, etc. Additionally, ultrasound emerges as an important tool for microfluidics. These features of ultrasound attenuation spectroscopy are dependent upon a theory that describes colloidal particle motion in an ultrasound field. Here we verify experimentally the validity of this well-known theory at elevated temperatures. We measured the attenuation frequency spectra for a stable dispersion of alumina particles (300nm) at different temperatures from 25°C to 50°C. Temperature variation affects water viscosity, which is a key parameter in said theory. We have demonstrated that the theory accounts for such dependence accurately, because critical hydrodynamic relaxation frequency shifts as the theory predicts, and particle size calculated from the measured attenuation spectra remains constant over the complete temperature range.

Mechanical Characteristics of Hot Forged Al6061-Al<sub>2</sub>O<sub>3</sub> Composite

Commercially available Al6061 alloy added with 5wt% of alumina particles was developed by liquid metallurgy route. Cast aluminum alloy and composite were hot forged. Microstructure, hardness and strength behavior of forged alloy and composite were investigated. Optical micrograph examination confirms the homogeneity in the dispersion of alumina particles. Addition of alumina particles increased the hardness and tensile strength by 21% and 18% respectively.

Hybrid Processing of AZ91 Magnesium Alloy/Nano-Al<sub>2</sub>O<sub>3</sub> Composites

In the present work mechanical and wear behaviour of AZ91 magnesium alloy based composites, reinforced with nanoAl2O3 particles is studied. The composites with different amount of alumina particles are fabricated by a hybrid processing approach. The hybrid processing involved alumina particles dispersion in molten AZ91 alloy by mechanical stirring assisted with ultrasonic processing. Dry sliding wear tests are performed using a pin on disc apparatus against hardened steel at loads ranging from 4.9 N to 14.7 N. The microstructural investigation revealed that, a refined microstructure is obtained because of the heterogeneous nucleation induced by ultrasonic processing and nanoAl2O3 dispersion. Hardness, yield strength and maximum compressive stress of the nanocomposites are found to be superior to that of the matrix alloy. The resistance against wear is increased due to incorporation of reinforced nanoAl2O3particles. The wear rate of nanocomposite is decreased with increasing the amount of the reinforcement. The identified wear mechanisms are abrasion and oxidation.

Three‐Dimensional Stereolithography of Alumina Photonic Crystals for Terahertz Wave Localization

Using stereolithography as an additive manufacturing (AM) process, photonic crystals, with a diamond‐like structure composed of alumina microlattices, were fabricated and their electromagnetic band gap profiles, in terahertz frequency ranges, were investigated. Acrylic resins with dispersed alumina particles were fabricated by stereolithography with micrometer‐order accuracy. After dewaxing and sintering processes, alumina lattices were obtained with high relative densities that reflected the terahertz waves, through Bragg diffraction, perfectly in all directions. Twinned crystal structures with mirror symmetric diamond lattices were designed to introduce defect interfaces. Double‐cavity defects consisting of unit cells hollowed from the diamond lattices formed the coupled resonation modes.

Dispersion Caused by Carbon Dioxide During Secondary Alumina Dissolution: A Lab-Scale Research

Secondary alumina is the byproduct of dry scrubbing in aluminum smelting. Secondary alumina has superior dissolution characteristics to primary alumina. Secondary alumina dissolves in pieces in molten cryolite, which results in larger contact area and better diffusion kinetics. In this work, the dissolution phenomenon of primary alumina, secondary alumina, and primary alumina doped with sodium carbonate or calcium carbonate (mass ratio = 10:1, 20:1) was observed and compared to estimate carbon-induced dispersion in industrial secondary alumina. Temperature fluctuations during sample dissolution were measured to evaluate the benefits of preheating on alumina dissolution. It was found that carbon mixed in secondary alumina significantly influences the dispersion of alumina particles at the moment of feeding, and thermodynamic analysis also shows that the combustion heat from carbon facilitates dispersion.