In the late 1940s and 1950s, ultrasonic transducers applied to cleaning systems were mainly piezoeletctric elements with natural quartz. However, these transducers proved very weak and unable to tolerate the high power needed to achieve acceptable cleaning results.
In the 1960s, therefore, producers turned to magnetostriction technique with iron-nickel components with different shapes and braze-welding. Ferrous materials, of course, were less effective than piezoelectric quartz; on the other hand, it was possible to increase power due to their higher resistance. Because ferrous materials cannot extend and restrict as quickly as quartz, the main problem of magnetostriction lied in its low working frequency; this led to loud noise, often above legal standards, which required insulation and sound-deadening treatments on external panels. Moreover, some of the power was lost as it turned into heat due to the Joule effect. Finally the magnetism induced, on ferrous pieces before they were cleaned undermined the removal of fine metallic powder on their surface.
PZT elements proved to be extremely efficient for the cleaning of metals and other materials:
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Very high resonance frequencies.
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Elevated efficiency in case of high-temperature cleaning liquids.
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High mechanic resistance to extension and reduction, with no molecular frictions and, consequently, no heat generation.
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Possibility of producing disks, rings, plates and tubes of different shape and size.
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Very easy to apply on walls or on the tank bottom.
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No induction of magnetism on pieces to clean.
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In conclusion, if compared to magnetostrictive materials, PZT elements offer an equivalent, if not superior, mechanic resistance; if compared to natural quartz, they present the same piezoelectric electrostrictive effect , this is the reason why they were immediately adopted by manufacturers in the ultrasonic cleaning field.
During the 1980s ceramic industry, thanks to sintering and polarization processes succeeded in producing new piezoelectric elements made of particular materials (lead titanate and barium zirconate).