Ultrasonic processes Vacuum forming

Numerous atomization techniques have evolved for the production of metal/alloy powders or as a step in spray forming processes. Atomization of melts may be achieved by a variety of means such as aerodynamic, hydrodynamic, mechanical, ultrasonic, electrostatic, electromagnetic, or pressure effect, or a combination of some of these effects. Some of the atomization techniques have been extensively developed and applied to commercial productions, including (a) two-fluid atomization using gas, water, or oil (i.e., gas atomization, water atomization, oil atomization), (b) vacuum atomization, and (c) rotating electrode atomization. Two-fluid atomization... 

The HPLC pump draws the mobile phase from the reservoir via vacuum action. In the process, air dissolved in the mobile phase may withdraw from the liquid and form bubbles in the flow stream unless such air is removed from the liquid in advance. Air in the flow stream is undesirable because it can cause a wide variety of problems, such as poor pump performance or poor detector response. Removing air from the mobile phase, called degassing, in advance of the chromatography is a routine matter, however, and can be done in one of several ways 1) helium sparging, 2) ultrasonic agitation, 3) drawing a vacuum over the surface of the liquid, or 4) a combination of numbers 2 and 3. 

The metal reduction of the polycyclic system is usually carried out in an ether solvent and by an alkali metal at low temperature (—78 °C). When potassium metal is applied it is best to prepare a metal mirror. Sodium and lithium react, either directly in the form of a metal wire, or after treatment in an induction furnace. Cesium is prepared by thermolysis of cesium azide. It has recently been found that the application of an ultrasonic bath facilitates the reaction and avoids side reactions. The reaction can be carried out in a modified NMR tube or in an ESR cavity. Diamagnetic ions are prepared in extended NMR tubes to which the metal is extruded and sealed under vacuum. Reaction rates are difficult to compare as the electron-transfer process depends on various experimental conditions such as concentration, temperature, the presence of impurities, the solvent and the nature of the metal surface. It may take from minutes to days to form the first radical-anion the second step then follows and can sometimes be rather slow 10 13). 

Ultrasonic energy exists in a liquid as alternate rarefactions and compressions of the liquid. During rarefaction, small vacuum cavities are formed that collapse, or implode, during compression. This continuing rapid process, called cavitation, is responsible for the scrubbing effect that produces ultrasonic cleaning. 

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