Ultrasound radiation

The ultrasound radiated from a horn tip, however, is not a plane wave. The acoustic pressure amplitude is more accurately calculated by Eq. (1.21) along the symmetry axis [1, 89]. 

Ohayon E, Gedanken A (2010) The application of ultrasound radiation to the synthesis of nanocrystalline metal oxide in anon-aqueous solvent. Ultrason Sonochem 17(1) 173-178... 

Fig. 8.10 Residual styrene concentration in PS extruded at 225°C. The open symbols refer to experiments without ultrasound, while the filled ones refer to experiments where ultrasound radiation was applied. The parameter is the absolute pressure in the chamber. Triangles 150 mmHg squares 50 mmHg, and circles 12 mmHg. [Reprinted by permission from A. Tukachinsky, Z. Tadmor, and Y. Talmon, Ultrasound-enhanced Devolatilization in Polymer Melt, AIChE J., 39, 359 (1993).]...

Ultrasound radiation produces free radicals in the solvent which can alter the chemical composition of analytes and hence the analytical results. 

We are all aware of the use of ultrasound radiation in medicine, where it is being used mostly for diagnosis. More recently, however, focused ultrasound radiation is being used to burn cancer cells. Less is known regarding its application in chem-... 

Sonochemistry is the research area in which molecules undergo chemical reaction due to the application of powerful ultrasound radiation (20 KHz-10 MHz) [4]. The physical phenomenon responsible for the sonochemical process is acoustic cavitation. Let us first address the question of how 20 kHz radiation can rupture chemical bonds (the question is also related to 1 MHz radiation), and try to explain the role of a few parameters in determining the yield of a sonochemical reaction, and then describe the unique products obtained when ultrasound radiation is used in materials science. 

Metallic nanopartides were deposited on ceramic and polymeric partides using ultrasound radiation. A few papers report also on the deposition of nanomaterials produced sonochemically on flat surfaces. Our attention will be devoted to spheres. In a typical reaction, commerdally available spheres of ceramic materials or polymers were introduced into a sonication bath and sonicated with the precursor of the metallic nanopartides. In the first report Ramesh et al. [43] employed the Sto-ber method [44] for the preparation of 250 nm silica spheres. These spheres were introduced into a sonication bath containing a decalin solution of Ni(CO)4. The as-deposited amorphous clusters transform to polyciystalline, nanophasic, fee nickel on heating in an inert atmosphere of argon at a temperature of 400 °C. Nitrogen adsorption measurements showed that the amorphous nickel with a high surface area undergoes a loss in surface area on crystallization. 

The use of ultrasound radiation for polymerizing various monomers was reviewed in [la]. Here we will discuss how ultrasound waves have been used successfully been to embed ultrafine metallic partides in a polymeric matrix. The first report was by Wizel and coworkers [57]. They used ultrasound radiation to prepare a composite material made of polymethylacrylate and amorphous iron nanopartides. 

In a similar work, ultrasound radiation was used to prepare EU2O3 doped in zir-conia and yttrium-stabilized zirconium (YSZ) nanoparticles [83]. Europium oxide was also coated sonochemically on the surface of submicron spherical zirconia and YSZ, which were fabricated by wet chemical methods. Time decay measurements of the doped and coated materials were conducted using a pulsed laser source. Lifetimes < 1.1 ms radiative lifetime of the Eu+ ions were detected for the doped and coated as-prepared materials. When the doped and coated samples were an-... 

In(OH)3 nanopowder was prepared via the sonication of an aqueous solution of InCl3 at room temperature and at 0 °C. At these temperatures, nonsonicated hydrolysis does not occur. The role of the ultrasound radiation and the mechanism of the reaction are discussed. The proposed mechanism is based on the sonohydrolysis of In (III) ions in the outer ring, and the liquid shell, of the collapsing bubble. The product, In(OH)3, was obtained as needle-shaped particles. 

The Sonochemical Synthesis of Mesoporous Materials and the Insertion of Nanopartides into the Mesopores by Ultrasound Radiation... 

Rana [117] has recently demonstrated that ultrasound radiation can be employed for the formation of vesicular mesoporous silica. The dimension of the vesicles ranged from 50-500 nm. If the synthesis is compared with a previous work on the synthesis of MSP silica vesicles [118], the advantages of the sonochemical synthesis are as follows (1) It employs the commonly used CTAB as a surfactant, instead of Gemini surfactant, C H2 +iNH(CH2)2NH2 (2) the sonochemical reaction takes 1 h as compared with 48 h (3) the reaction is conducted at 25-35 °C instead of 100 °C and (4) a higher surface area is obtained, 940, as compared with 280-520 m g k The special role of the bubbles in the formation of the vesicle is also explained. 

In addition to the above reported synthesis of ferrites our search has revealed that aluminates [119], nickelates [120], and manganates [121], have also been prepared by the sonochemical method. Nanosized nickel aluminate spinel particles have been synthesized [119] with the aid of ultrasound radiation by a precursor approach. Sonicating an aqueous solution of nickel nitrate, aluminum nitrate, and urea yields a precursor which, on heating at 950 °C for 14 h yields nanosized N1A1204 particles with a size of ca. 13 nm and with a surface area of about 108 m g-i. 

Cobalt hydroxide with an interlayer spacing of 7.53 A and needle-like morphology has been synthesized with the aid of ultrasound radiation [124]. Characterization methods indicate the formation of a-cobalt hydroxide. Thermal decomposition of the hydroxide at 300 °C under air or argon yields nanometer-sized oxide particles of C03O4 (ca. 9 nm) and CoO (ca. 6 nm), respectively. 

We will conclude this survey of the synthesis of nanomaterials by sonochemical methods by mentioning that the most important material of the last decade, carbon nanotubes, were also synthesized by ultrasound radiation [144]. The carbon nanotube is produced by applying ultrasound to liquid chlorobenzene with ZnCl2 partides and to o-dichlorobenzene with ZnCh and Zn particles. It is considered that the polymer and the disordered carbon, which are formed by cavitational collapse in homogeneous liquid, are annealed by the inter-particle collision induced by the turbulent flow and shockwaves. 

Abramov, O.V. and Astashkin, Yu.S. On peculiarities of ultrasound radiation in melts under cavitation conditions. In Better Metallurgical Processes through Novel Physical Methods. Metallurgia, Moscow, 1974, pp. 155-160 (in Russian). 

Photooxidation rates of propan-2-ol in aqueous Ti02 suspensions are reported to be increased by ultrasound radiation, an observation which has been rationalised in terms of mass transport of the substrate and activation of the solid catalyst. The value of the newly described photochemical rearrangement of 2-phenylthio-l,3-cyclohexanediols such as (69) to deoxysugars (70) which are in equilibrium with the closed form (71) has been illustrated by its application to the synthesis of (+)-m-rose oxide (72), and the same authors have also described the regioselective photorearrangement of 2-phenylthio-3-aminocyclohexanols (73) to deoxyazasugars (74) this has proved to be useful in the synthesis of various piperidines (75), amino-sulfones, -sulfoxides and -acids. Hydroxy(alkoxy)methyl radicals have been generated by photo-induced electron transfer. ... 

The introduction of an atom other than carbon to either dienes or dienophiles will result in the hetero-Diels-Alder reaction. Owing to the nature (steric effect, electronic effect, etc.) of substituents on dienes and dienophiles, the Diels-Alder reaction might occur through a synchronous concerted, an asynchronous concerted, or a stepwise reaction mechanism. The stepwise and asynchronous concerted Diels-Alder reactions proceed via diradical intermediates, whereas the synchronous concerted mechanisms does not. It should be pointed out that most of the Diels-Alder reactions are concerted as a result, both the rate constants and the stereoselectivities of Diels-Alder reaction are only moderately sensitive to the changes in the nature of organic sol vents. However, it has been clearly shown that the applications of water to the reaction system can greatly accelerate such reactions. Other modifications on this reactions include the application of high pressure, Lewis acid, and ultrasound radiation.More information about this reaction can be easily attained from reviews and relevant books. 

MBH adduct 825, obtained from A-Boc-a-amino aldehydes in the presence of DABCO upon ultrasound radiation at room temperature, has been treated with 2,2-dimethoxypropane in the presence of a catalytic amount of cam-phorsulfonic acid to successfully furnish the corresponding oxazolidine 826 in... 

Kumar, R.V., Koltypin, Y, Cohen, Y.S., Cohen, Y, Aurbach, D., Palchik, O., Felner, I., Gedanken, A. Preparation of amorphous magnetic nemoparticles embedded in polyvinyl alcohol using ultrasound radiation. J. Mater. Chem. 10, 1125-1130 (2(XX))... 

Yosioka, K. Kawasima, Y. Particle separation with ultrasound radiation force. Acustica 1955, 5, 167. 

Hydrostatic piezoelectric effect is applied in the sensors for the dynamic hydrostatic pressure measurement and for the ultrasound radiation and sensing in underwater sonars. 

The possibility of using sound energy in chemistry was established more than 70 years ago. By definition, sonochemistry is the application of powerful ultrasound radiation (10 kHz to 20 kHz) to cause chemical changes to molecules. The physical phenomenon behind this process is acoustic cavitation. Typical processes that occur in sonochemistry are the creation, growth and collapse of a bubble. A typical laboratory setup for sonochemical reactions is shown in Fig. 8.17. More details of sonochemistry and the theory behind it can be found elsewhere. - ... 

Recently, Chen and Du designed a novel polymer vesicle that respond to both physical [ultrasound] and chemical [pH] stimuli based on a PEO-b-P[DEA-stat-TMA] block copolymer, [PEO— poly[ethylene oxide] DEA—2-[diethylamino]ethyl methacrylate TMA—[2-tetrahydrofuranyloxy]ethyl methacrylate] [180], These dually responsive vesicles exhibiting retarded release profile and controllable release rate when subjected to ultrasound radiation or varying pH. 

The technique involves evaluating reflection (echo) and transmission characteristics of an ultrasound radiation, when crossing layers of different density, which present different acoustic impedance. Illumination intensity of different zones using echography is proportional to the density of the crossed structures, thus, the technique detects the presence... 

Physical methods employ such techniques as heat, cold, immobilization, exercise, ultrasound, radiation, electroshock, and acupuncture. These are important modalities of treatment but are gross methods which do not deal directly with the specific biochemistry of a disease. 

---