Ultrasonic compression

Tab. 5.26 Optimum conditions for ultrasonic compression moulding of thermosets and thermoplastics.

Figure 1. Ultrasonic compression and shear waves generated by the application of a sinusoidal force F(t) to the material.

Marshall, T., Challis, R.E., Holmes, A.K., Tebbutt, J.S. 2002. Modeling ultrasonic compression wave absorption during the seeded crystallization of copper (II) sulphate pentahydrate from aqueous solution. IEEE Trans. Ultrasonics, Ferroelectrics and Frequency Control 49, 1583-1591. 

Barium carbonate also reacts with titania to form barium titanate [12047-27-7] BaTiO, a ferroelectric material with a very high dielectric constant (see Ferroelectrics). Barium titanate is best manufactured as a single-phase composition by a soHd-state sintering technique. The asymmetrical perovskite stmcture of the titanate develops a potential difference when compressed in specific crystallographic directions, and vice versa. This material is most widely used for its strong piezoelectric characteristics in transducers for ultrasonic technical appHcations such as the emulsification of Hquids, mixing of powders and paints, and homogenization of milk, or in sonar devices (see Piezoelectrics Ultrasonics). 

In the case of x-cut quartz there is excellent agreement between second-order constants determined in the shock-compression studies and ultrasonic... 

The piezoelectric constant studies are perhaps the most unique of the shock studies in the elastic range. The various investigations on quartz and lithium niobate represent perhaps the most detailed investigation ever conducted on shock-compressed matter. The direct measurement of the piezoelectric polarization at large strain has resulted in perhaps the most precise determinations of the linear constants for quartz and lithium niobate by any technique. The direct nature of the shock measurements is in sharp contrast to the ultrasonic studies in which the piezoelectric constants are determined indirectly as changes in wavespeed for various electrical boundary conditions. 

The bubble formed in stable cavitation contains gas (and very small amount of vapor) at ultrasonic intensity in the range of 1-3 W/cm2. Stable cavitation involves formation of smaller bubbles with non linear oscillations over many acoustic cycles. The typical bubble dynamics profile for the case of stable cavitation has been shown in Fig. 2.3. The phenomenon of growth of bubbles in stable cavitation is due to rectified diffusion [4] where, influx of gas during the rarefaction is higher than the flux of gas going out during compression. The temperature and pressure generated in this type of cavitation is lower as compared to transient cavitation and can be estimated as ... 

Sekar, J. and Naidu, P.R. Ultrasonic speeds and isentropic compressibilities of 1,2-dichlorobenzene + methyl ethyl ketone + 1-alkanols at 303.15 K, J. Chem. Eng. Data, 41(1) 170-172, 1996. 

The ultrasonic irradiation of a solution induces acoustic cavitation, a transient process that promotes chemical activity. Acoustic cavitation is generated by the growth of preexisting nuclei during the alternating expansion and compression cycles of ultrasonic waves. For example, in aqueous liquid, temperatures as high as 4300 K and pressures over 1000 atm are estimated to exist within... 

Yue, G. Q., Nikoonahad, M and Ash, E. A. (1982). Subsurface acoustic microscopy using pulse compression techniques. IEEE 1982 Ultrasonics Symposium, pp. 935-8. IEEE, New York. [70]... 

The top-down approach involves size reduction by the application of three main types of force — compression, impact and shear. In the case of colloids, the small entities produced are subsequently kinetically stabilized against coalescence with the assistance of ingredients such as emulsifiers and stabilizers (Dickinson, 2003a). In this approach the ultimate particle size is dependent on factors such as the number of passes through the device (microfluidization), the time of emulsification (ultrasonics), the energy dissipation rate (homogenization pressure or shear-rate), the type and pore size of any membranes, the concentrations of emulsifiers and stabilizers, the dispersed phase volume fraction, the charge on the particles, and so on. To date, the top-down approach is the one that has been mainly involved in commercial scale production of nanomaterials. For example, the approach has been used to produce submicron liposomes for the delivery of ferrous sulfate, ascorbic acid, and other poorly absorbed hydrophilic compounds (Vuillemard, 1991 ... 

---