Advances in Nanoalumina Ceramic Particle Fabrication Using Sonofragmentation
TL;DR: In this article, the effects of various parameters such as ultrasonic frequency, feed concentration, sonication time, surfactant, and applied ultrasonic power on sonofragmentation were investigated.
Abstract: The present study is focused on fabrication of high-purity submicrometer alumina ceramic particles (predominantly in sub-100 nm range) from micrometer-sized feed (e.g., 70-80 mum) using sonofragmentation. The effects of various parameters such as ultrasonic frequency, feed concentration, sonication time, surfactant, and applied ultrasonic power on sonofragmentation were investigated. Sub-100 nm particle production by sonofragmentation was validated via three metrics, i.e., laser particle size analysis, high-resolution transmission electron microscopy, and turbidimetry. There is a significant change in color and shape of alumina ceramic particles as a result of sonofragmentation. Higher size reduction ratios are obtained at lower frequencies and at higher input power. Submicrometer particle generation increases as concentration of the feed particles increases, indicating that attrition by interparticle collision is a significant mechanism. The shape of the particles changes from angular to spherical as sonofragmentation time increases. Probe-type sonication produces fragmentation effects that are less uniform than those induced by tank-type ultrasonics. Surfactant plays a significant role in preventing agglomeration, especially as finer fragments are produced with prolonged sonication.
Citations
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TL;DR: While ultrasonic coal-wash is not entirely new in many countries, it has not yet been practiced in India, though it would appear that the relatively high-ash content of Indian coals would render th...
Abstract: While ultrasonic coal-wash is not entirely new in many countries, it has not yet been practiced in India, though it would appear that the relatively high-ash content of Indian coals would render th...
39 citations
TL;DR: In this article, the effectiveness of 20 kHz ultrasound to increase number density of fine bubbles within the mixing chamber of an effervescent atomizer by breaking up bubbles introduced in it by an aerator was investigated.
Abstract: Gas bubbles introduced into a liquid in the mixing chamber help to break up the liquid into fine droplets on being expanded to the ambient pressure. The passage of gas bubbles through the orifice of the nozzle requires that the size of the bubbles be much smaller than the diameter of the orifice. In the present work, the effectiveness of 20 kHz ultrasound to increase number density of fine bubbles within the mixing chamber of an effervescent atomizer by breaking up bubbles introduced in it by an aerator was investigated. Bubbles of initial size in the range of 5–10 mm were shown to get disintegrated into clusters of micron and sub-micron sized bubbles. A fine spray was produced in the presence of ultrasound at a gas-to-liquid mass flowrate ratio (GLR) of 0.063%. The half-cone angle of spray was in the range of 6–10°, which compares favorably with conventional atomizers. The experimental findings of bubble breakup were theoretically modeled by the Rayleigh–Plesset equation. The results of the model indicate that bubbles having initial radius less than 3 mm undergo growth and subsequent disintegration at 20 kHz for the given acoustic pressure of 0.3 MPa.
28 citations
TL;DR: This paper quantitatively investigates the fragmentation of ionic crystals during ultrasonic irradiation of slurries and proposes a mechanochemical extension of the Bell-Evans-Polanyi Principle or Hammond's Postulate: activation energies for solid fracture correlate with binding energies of solids.
Abstract: Mechanochemistry deals with the interface between the chemical and the mechanical worlds and explores the physical and chemical changes in materials caused by an input of mechanical energy. As such, the chemical and physical effects of ultrasound, i.e., sonochemistry, are forms of mechanochemistry. In this paper, the fragmentation of ionic crystals during ultrasonic irradiation of slurries has been quantitatively investigated: the rate of fragmentation depends strongly on the strength of the materials (as measured by Vickers hardness or by Young's modulus). This is a mechanochemical extension of the Bell–Evans–Polanyi Principle or Hammond's Postulate: activation energies for solid fracture correlate with binding energies of solids. Sonofragmentation is unaffected by slurry loading or liquid vapor pressure, but is suppressed by increasing liquid viscosity. The mechanism of the particle breakage is consistent with a direct interaction between the shockwaves created by the ultrasound (through acoustic cavitation) and the solid particles in the slurry. Fragmentation is proposed to occur from defects in the solids induced by compression–expansion, bending, or torsional distortions of the crystals.
23 citations
TL;DR: Halloysite-based polymethyl methacrylate and polystyrene (HNT-PS) nanocomposite coatings for glasses were synthesized by ultrasound assisted solution blending method as discussed by the authors.
20 citations
TL;DR: In this paper, a new computational method was developed to simulate a two-dimensional Eckart acoustic streaming field in an ultrasonic heptagonal chamber actuated by multiple acoustic transducers with different associated frequencies and acoustic incident pressures.
Abstract: A new computational method was developed to simulate a two-dimensional Eckart acoustic streaming field in an ultrasonic heptagonal chamber actuated by multiple acoustic transducers with different associated frequencies and acoustic incident pressures. Simulation was conducted using the superposition of multiple spatial gradients of the Reynolds stresses and the second mean sound pressures at different frequencies. The developed method extends beyond the capabilities of the conventional method that is restricted to uniform frequency and incident pressure. Various acoustic streaming patterns can be feasibly generated by tuning the frequency and incident pressure of each individual transducer. The implementation of multiple acoustic transducers offers flexibility to control acoustic flows in microfluidic devices for various applications. Furthermore, the developed simulation method for acoustic streaming fields provides an optimization tool for the frequency, incident pressure and location of each transducer.
18 citations
References
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TL;DR: Investigating the effect of sonication on the particle size and structure of a well-crystallized (KGa-1) kaolinite from Georgia showed that particle-size reduction can be controlled through different variables such as power of ultrasonic processor, amount of sample, and time of treatment.
221 citations
TL;DR: In this article, pressureless sintered alumina compacts with a submicrometer microstructure exhibit a hardness that approaches or even exceeds the level of advanced hot-pressed composites of Al{sub 2 O{sub 3} + 35 vol% TiC, whereas the strength of both ceramics is approximately the same.
Abstract: Pressureless sintered alumina compacts with a submicrometer microstructure exhibit a hardness that approaches or even exceeds the level of advanced hot-pressed composites of Al{sub 2}O{sub 3} + 35 vol% TiC, whereas the strength of both ceramics is approximately the same. The combination of reduced dislocation mobility (due to the small grain size), high density, and density homogeneity are the prerequisites for the surprisingly high hardness. Quasi-conventional powder processing is used to produce these outstanding alumina bodies.
200 citations
TL;DR: In this article, a review of the fracture properties of nanocomposites is presented, emphasizing the newly developed concept of material design for ceramics and several mechanisms proposed previously to explain these characteristics were reviewed.
177 citations
TL;DR: In this paper, a theory for ultrasonic fragmentation of agglomerate particles suspended in liquids is presented, and an expression for the fragmentation rate as a function of ultra-osnic power and agglerate size is derived.
134 citations
"Advances in Nanoalumina Ceramic Par..." refers background in this paper
...Ultrasonic fragmentation of alumina particles [8], [9] to produce a fine fraction of crystalline materials to produce particles in the 10-μm-size range, and of kaolinite [10] in the 1–2-μm-size range are examples of studies reported in literature....
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TL;DR: In this paper, the structure of as-synthesized samples (ZrO{sub 2}{center_dot}nH{sub2}O) and the formation mechanism of ZrO-sub 2} nanopowders are also discussed.
95 citations
"Advances in Nanoalumina Ceramic Par..." refers background in this paper
...nano-ZrO2 powders [14] are produced via sonochemical methods, which are simple and energy efficient....
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...Fragmentation by conventional attritional means such as grinding or milling is reported widely in literature, but contamination from the milling material, as well as energy efficiency, are definite drawbacks [2]–[6]; comminution by high-intensity ultrasound has also been studied [7]–[14], but to a lesser extent....
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