R Nagarajan

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.

Erosion due to coal particles has a detrimental effect on economy of power plants. Alumina ceramic-lined pipelines and cyclones are in common use for fluid-laden coal transportation and separation. Several brittle erosion models are available for air-jet and slurry jet erosion in literature. From these, the most-cited erosion models were identified. An orthogonal fractional-factorial experimental matrix which includes all possible variables that contribute to brittle erosion was designed, conducted and validated. This paper gives a comparison between the most-cited literature model and a model developed on the basics of our experimental data. In general, slurry erosion models obtained experimentally were found to have better agreement with literature models when compared to air-jet erosion models. The reason for deviation of experimentally derived models from literature models is systematically studied and rationalized. © 2007 Elsevier B.V. All rights reserved.

Cavitation erosion is predominant in pipelines for liquid transportation, causing damage to pipe wall, impeller and their accessories. The present study is focused on development of cavitation -wear resistant nano-ceramic particle-reinforced polymer matrix material; and on study of its feasibility to be used as lining material in hydraulic transportation. The polymer/nano composite is fabricated using power ultrasound in all three process steps: synthesis of nano-dimensional particles of white fused alumina (WFA) from micron size particles, optimized blending and finally reinforcement into poly methyl methacrylate (PMMA) matrix. The effect of ultrasonic parameters on nanocomposite/ virgin polymers (like polyethylene and polypropylene) is studied by measuring mass loss of the materials and suspension turbidity during exposure time. At low frequency (20-60 kHz), cavitation intensity is predominant; this effect is utilized for fabricating sub-micron particles, and for performing accelerated cavitation erosion tests. At high frequency, acoustic streaming is predominant; this effect is utilized for blending and reinforcing of the nano ceramic particles into polymer matrix. The size and quantity of the particles generated by cavitation erosion was analyzed by Laser Particle Size Analyzer (20 nm-1400 micron range). The nano-composite coupons were analyzed before and after the ultrasonic erosion test using SEM. It is concluded that lowfrequency sonication is a viable option for cavitaton erosion testing of ceramic/polymer composites.

Cavitation erosion is predominant in pipelines for liquid transportation, causing damage to pipe wall, impeller and their accessories. The present study is focused on development of cavitation -wear resistant nano-ceramic particle-reinforced polymer matrix material; and on study of its feasibility to be used as lining material in hydraulic transportation. The polymer/nano composite is fabricated using power ultrasound in all three process steps: synthesis of nano-dimensional particles of white fused alumina (WFA) from micron size particles, optimized blending and finally reinforcement into poly methyl methacrylate (PMMA) matrix. The effect of ultrasonic parameters on nano-composite/ virgin polymers (like polyethylene and polypropylene) is studied by measuring mass loss of the materials and suspension turbidity during exposure time. At low frequency (20-60 kHz), cavitation intensity is predominant; this effect is utilized for fabricating sub-micron particles, and for performing accelerated cavitation erosion tests. At high frequency, acoustic streaming is predominant; this effect is utilized for blending and reinforcing of the nano ceramic particles into polymer matrix. The size and quantity of the particles generated by cavitation erosion was analyzed by Laser Particle Size Analyzer (20 nm-1400 micron range). The nano-composite coupons were analyzed before and after the ultrasonic erosion test using SEM. It is concluded that low-frequency sonication is a viable option for cavitaton erosion testing of ceramic/polymer composites.

This chapter describes the megasonic cleaning. Megasonic cleaning is a type of acoustic cleaning, related to ultrasonic cleaning. It is a gentler cleaning mechanism, less likely to cause damage, and is currently used extensively in wafer cleaning in semiconductor manufacturing. Similar to ultrasonic cleaning, megasonics utilizes a transducer, usually composed of piezoelectric crystals to create megasonic energy. The difference between ultrasonic cleaning and megasonic cleaning lies in the frequency that is used to generate the acoustic waves. Ultrasonic cleaning uses lower frequencies; it produces random cavitation. Megasonic cleaning uses higher frequencies at and above 1000 kHz; it produces controlled cavitation. An important distinction between the two methods is that the higher megasonic frequencies do not cause the violent cavitation effects found with ultrasonic frequencies. Megasonic cleaning is widely used for removing particles from wafer surfaces, as well as from critical component surfaces in other high-technology products, but its underlying mechanism is not clearly understood even by many of the practitioners. Unlike ultrasonics, which can function very effectively as a "physical" cleaner, with water and surfactant only, a megasonic cleaner typically relies upon strong chemistry to optimize cleaning. From an environmental point of view, this is not entirely desirable, but deploying megasonics very likely results in a reduction in chemical usage and in processing time, both highly desirable outcomes.

This chapter describes the megasonic cleaning. Megasonic cleaning is a type of acoustic cleaning, related to ultrasonic cleaning. It is a gentler cleaning mechanism, less likely to cause damage, and is currently used extensively in wafer cleaning in semiconductor manufacturing. Similar to ultrasonic cleaning, megasonics utilizes a transducer, usually composed of piezoelectric crystals to create megasonic energy. The difference between ultrasonic cleaning and megasonic cleaning lies in the frequency that is used to generate the acoustic waves. Ultrasonic cleaning uses lower frequencies; it produces random cavitation. Megasonic cleaning uses higher frequencies at and above 1000 kHz; it produces controlled cavitation. An important distinction between the two methods is that the higher megasonic frequencies do not cause the violent cavitation effects found with ultrasonic frequencies. Megasonic cleaning is widely used for removing particles from wafer surfaces, as well as from critical component surfaces in other high-technology products, but its underlying mechanism is not clearly understood even by many of the practitioners. Unlike ultrasonics, which can function very effectively as a "physical" cleaner, with water and surfactant only, a megasonic cleaner typically relies upon strong chemistry to optimize cleaning. From an environmental point of view, this is not entirely desirable, but deploying megasonics very likely results in a reduction in chemical usage and in processing time, both highly desirable outcomes. © 2011 Elsevier Inc. All rights reserved.