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 μm) 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. © 2008 IEEE.

Ramamurthy Nagarajan

Department Of Chemical Engineering

Agglomeration

Alumina

Ceramic materials

Concentration (process)

High resolution electron microscopy

High resolution transmission electron microscopy

Microscopic examination

ORE TREATMENT

Sonication

Surface active agents

Thickness measurement

Ultrasonics

LASER PARTICLE SIZE ANALYSIS

NANOCERAMIC PARTICLES

SONOFRAGMENTATION

TURBIDIMETRY

Ultrasonic

Particle size analysis

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Advances in Nanoalumina Ceramic Particle Fabrication Using Sonofragmentation

IEEE Transactions on Nanotechnology

Coal is the one of the world's most abundant fossil fuel resources. It is not a clean fuel, as it contains ash and sulfur. SOx as a pollutant are a real threat to both the ecosystem and to human health. There are numerous de-sulfurization methods to control SO2 emissions. Nowadays, online flue gas de-sulfurization is being used as one such method to remove sulfur from coal during combustion. The biggest disadvantage associated with this method is formation of by-products (FGD gypsum). A way for effective usage of FGD gypsum has not yet been found. This will lead to acute and chronic effects to humans as well as plants. Power ultrasound can be used for the beneficiation of coal by the removal of sulfur from coal prior to coal combustion. The main effects of ultrasound in liquid medium are acoustic cavitation and acoustic streaming. The process of formation, growth and implosion of bubbles is called cavitation. Bulk fluid motion due to sound energy absorption is known as acoustic streaming. In addition, coupling of an acoustic field to water produces OH radicals, H 2O2, O2, ozone and HO2 that are strong oxidizing agents. Oxidation that occurs due to ultrasound is called Advanced Oxidation Process (AOP). It converts sulfur from coal to water-soluble sulphates. Conventional chemical-based soaking and stirring methods are compared here to ultrasonic methods of de-sulfurization. The main advantages of ultrasonic de-sulfurization over conventional methods, the mechanism involved in ultrasonic de-sulfurization and the difference between aqueous-based and solvent-based (2 N HNO3, 3-volume percentage H2O 2) de-sulfurization are investigated experimentally. © 2010 Elsevier B.V.

Fulltext

Ultrasonics Sonochemistry

Ultrasonic coal-wash for de-sulfurization

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. © 2011 Elsevier B.V.

Chemical Engineering and Processing: Process Intensification

Effect of ultrasound on bubble breakup within the mixing chamber of an effervescent atomizer

The present work investigates utilization of ultrasound in reagent-based coal de-ashing and de-sulfurization. The coal under study was received from Girald mine, Rajasthan, India. Three different ultrasonic frequencies (25kHz, Dual (58/192kHz) and 430kHz) and three reagents (HCl, HNO3 and H2O2) were used. The study employed a Taguchi fractional-factorial L27 DOE. Experimental data were used to derive an empirical model for the prediction of total sulfur removal. The model incorporates cavitational intensity, reagent concentration, sonication time, coal particle size and coal concentration as key parameters. Effects of above factors on reagent-based ultrasonic coal-desulfurization are presented here. An optimum set of process parameters are identified and validated. Larger-scale trial with high-ash and high-sulfur coals is strongly recommended. © 2011 Elsevier B.V.

Feasibility of using ultrasound-assisted process for sulfur and ash removal from coal

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 them particularly suitable for such a washing procedure. In this study, state-of-the-art ultrasonic equipment, spanning the frequency range from highly cavitational (&lt;100 kHz), to mostly acoustic-streaming dominated (&gt;100 kHz), were used. The coal to be studied was received from Giral mine, Rajasthan, India. Four stages for ultrasound assisted coal particle breakage have been proposed and characterized with SEM images of sonicated coal. Sono-treatment, followed by the decanting process, has been found to remove detached ash effectively. Decanted coal samples were analyzed by SEM/EDX to determine the mechanism of ash removal by sonication. The present investigation also encompasses aqueous-based ultrasonic coal desulfurization. Ultrasound in aqueous medium produces OH, H2O 2, HO2, O2, and ozone, which are strong oxidizing agents. The oxidation occurring in the presence of ultrasound is called "advanced oxidation process", and this converts the sulfur present in the coal to water-soluble sulfates, thereby enhancing sulfur removal. Larger-scale trials with high-ash and sulfur coals are strongly recommended. © 2011 American Chemical Society.

Industrial and Engineering Chemistry Research

Investigation of high-frequency, high-intensity ultrasonics for size reduction and washing of coal in aqueous medium

Magnetic resonance imaging of acoustic streaming: Absorption coefficient and acoustic field shape estimation

The Journal of Physical Chemistry B

Effect of Surfactants on Inertial Cavitation Activity in a Pulsed Acoustic Field

Journal	IEEE Transactions on Nanotechnology
ISSN	1536125X
Open Access	No