A look on the role of ultrasound: from theories to practice

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The first experiments on the use of ultrasound in electroplating led to some disappointment. But the subsequent theoretical studies confirmed the correctness of the basic principles of ultrasonic methods. Now, it is obvious that ultrasonic irradiation promotes electrolytic deposition, removing bubbles, which tends to accumulate on the coated metal surface by cleaning and possibly even by releasing the formed grains of deposited metal. All these effects play an important role, apparently due to cavitation. It can be assumed that ultrasound will find widespread use in the manufacture of electroplating, especially in the nickel plating of various products, as experiments with nickel have been particularly promising.

Less successful was the application of ultrasound in coagulation (clotting) and deposition of dust aerosols. During ultrasound interest rise in the United States plenty of units equipped with rotary sirens were built, intended for the deposition of dust. Experiments have shown that under the action of ultrasound tiny dispersed particles are collected in separate groups (the opposite effect to the one achieved in the preparation of emulsions). Today, however, none of these units is not valid. However, recent studies carried out in Japan, indicate that the ultrasonic deposition of dust is quite viable. Another very interesting and promising area of application of ultrasound – the implementation of liquids dispersion. In particular, numerous experiments investigated the possibility of using ultrasound atomisation of fuel in the oil burners, working at a low speed combustion. With the rapid combustion fuel leaves the nozzle under high pressure and gets sprayed, turning into small droplets. Therefore, combustion takes place quietly and evenly. When the combustion speed is less than 2.4 L/hr (typically occurs in domestic boilers for heating and some industrial furnaces), any dispersion medium is formed. To explain this phenomenon a range of ultrasound studies was initiated by governmental bodies and commercial enterprises, such as Hilsonic, a prominent manufacturer of ultrasonic cleaner appliances in the UK.

Along with the numerous applications of ultrasound that don’t represent particularly interesting cases from a technical point of view (e.g., plugging bottles of fizzy drinks, where the main task is to completely remove all the air from the bottle), there are aspects playing a very important role in the research. First of all, the effect of sonication on chemical reactions should be noted. This is where all the various effects associated with ultrasound irradiation can be explained by introducing the concept of sonolysis water, ie splitting of water molecules by ultrasound into hydrogen and hydroxyl free radicals.

Many complex chemical processes are a sequence of simple reactions such as oxidation, reduction, hydrolysis, polymerisation, depolymerisation reactions and molecular rearrangement. The effect of ultrasound on them have been studied in details. According to one theory, the origin and evolution of life on Earth is partially based on ultrasound. Under the influence of sound waves rattling the world’s oceans as a result of sonolysis, water on its surface and the polymerisation reaction took place, which led to the formation of the first giant organic molecules.