Ultrasonic atomization
Ultrasonic atomization is a process in which a liquid, in contact with a surface vibrating at ultrasonic frequencies, forms standing capillary waves that lead to the ejection of fine droplets. As the amplitude of these waves increases, the wave crests can reach a critical height where the cohesive forces of the liquid are overcome by the surface tension, leading to the ejection of small droplets from the wave tips.
Mechanism and principles
[edit]The formation of droplets during ultrasonic atomization remains complex and not fully understood, though several theories attempt to explain it. One leading theory, the capillary wave hypothesis by Lang.,[1] suggests that droplets form at the peaks of capillary waves on the liquid surface. Lang developed a formula that relates droplet size to capillary wavelength. The average diameter estimation was obtained using a constant that was later adjusted by Yasuda[2] to better predict smaller droplet sizes in the micrometer range. This prediction aligns well with observations from laser diffraction, though other methods have detected finer droplets that Lang's model does not account for. An alternative theory, proposed by Sollner,[3] is the cavitation hypothesis. This theory links droplet formation to cavitation—when bubbles in the liquid rapidly form and collapse, creating shockwaves that break apart the liquid surface into droplets. Sollner's findings suggest cavitation is essential for dispersing liquids and shares similarities with emulsion formation. A combined theory was later proposed by Bograslavski and Eknadiosyants,[4] suggesting that both mechanisms work together: shockwaves from cavitation enhance the breaking of capillary wave crests, leading to droplet formation. However, this combined theory faces some scepticism, as cavitation requires high power at MHz frequencies, which some researchers argue may be too high to support this mechanism effectively in practice.[5]
History
[edit]The phenomenon of ultrasonic atomization was first reported by Wood and Loomis in 1927.[6] They observed that a fine mist was produced from the liquid surface when a liquid layer was subjected to high-frequency sound waves. Wood and Loomis's work hinted at a variety of applications for ultrasonics, many of which became realities in later decades, with the development in the scope of ultrasound generation (piezoelectricity), transfer (sonotrode materials), and control (horn analyzers).
Atomization of aqueous solutions
[edit]First commercial application of ultrasonic atomization effect was nebulizers. Ultrasonic nebulizers made their first appearance in 1949, initially designed as humidifiers. Medical professionals quickly recognized their potential for delivering therapeutic aerosols suitable for inhalation,[7] leading to the incorporation of medications into the nebulization process.[8] Ultrasonic nebulizers have been utilized for various respiratory diseases, including asthma and cystic fibrosis. Their ability to deliver medications directly to the lungs has made them a valuable tool in managing these conditions[9]
Aqueous solutions containing metal derivatives
[edit]In the late 20th century, scientists exploring nanoparticle synthesis via spray pyrolysis began to testsee ultrasonic atomization as a promising technique for precursor droplet formation such as noble metal based salts solutions. Known as ultrasonic spray pyrolysis (USP), this technique allowed for finer control over particle size as it strongly depends on the frequency, making it particularly suited for nanomaterials used in electronic devices, solar cells, and batteries. By the 1980s and 1990s, ultrasonic atomization was gaining ground as researchers demonstrated its utility in producing complex oxides and other materials essential for energy storage like lithium-ion batteries.[10] By the early 2000s, this method was integral to industries seeking uniform coatings and nanoparticle films, demonstrating the impact of ultrasonic atomization on industrial manufacturing.[11]
Liquid metals
[edit]
In 1965, Pohlman and Stamm[12] published a book, which marked a contribution to the field of ultrasonic atomization by identifying and describing the parameters influencing the process such as viscosity, capillary wavelength, surface tension and amplitude. One of the key chapters in the book, titled "5.1 Vernebelung geschmolzener Metalle," detailed the first experiments on the high temperature ultrasonic atomization in which molten metals were used. They discussed its potential technical applications as well as limitations stating that the transition from successful laboratory experiments to a usable technical plant has not yet been found due to issues with conciliation wettability and sonotrode durability. They were able to atomize lead at 350 °C and showcased the damage to the sonotrode induced by cavitation. In 1967, Lierke and Grießhammer published their work in which they were able to ultrasonically atomize metal with melting points up to 700 °C[13]
Ultrasonic atomization is increasingly being applied to liquid metals to produce high-quality spherical powders used in advanced applications such as additive manufacturing. The process enables effective fragmentation of molten metals into fine droplets using high-frequency ultrasonic vibrations. Its benefits include excellent particle sphericity, narrow size distribution, and minimal contamination. The method is suitable for various metals, including aluminum, titanium, nickel-based superalloys, and even high-melting-point materials.
A significant advancement in industrial implementation of this method was achieved by the Polish company 3D Lab, which developed and commercialized a compact ultrasonic atomization system under the brand name ATO. The company filed its first patent on ultrasonic atomization in 2017[14] and has since introduced systems capable of processing metals with melting points exceeding 3000 °C from various feedstocks (wire, rod, or scrap).[15]
Key patents for this technology include:
- JP 7228274B2, "Ultrasonic atomization apparatus and method", published 2022
- KR 10-2539861, "Method and system for ultrasonic metal atomization", published 2023
- CN 113993642B, "Ultrasonic metal powder production system", published 2023
- US 12,090,554B2, "Apparatus and process for ultrasonic atomization of metals", published 2024
For a detailed overview of this topic, see the main article on Ultrasonic metal atomization.[16][17]
See also
[edit]References
[edit]- ^ Lang, Robert J. (1962-01-01). "Ultrasonic Atomization of Liquids". The Journal of the Acoustical Society of America. 34 (1): 6–8. Bibcode:1962ASAJ...34....6L. doi:10.1121/1.1909020. ISSN 0001-4966.
- ^ Yasuda, Keiji; Bando, Yoshiyuki; Yamaguchi, Soyoko; Nakamura, Masaaki; Oda, Akiyoshi; Kawase, Yasuhito (January 2005). "Analysis of concentration characteristics in ultrasonic atomization by droplet diameter distribution". Ultrasonics Sonochemistry. 12 (1–2): 37–41. Bibcode:2005UltS...12...37Y. doi:10.1016/j.ultsonch.2004.05.008. PMID 15474950.
- ^ Söllner, Karl (1936). "The mechanism of the formation of fogs by ultrasonic waves". Trans. Faraday Soc. 32: 1532–1536. doi:10.1039/TF9363201532. ISSN 0014-7672.
- ^ Eknadiosyants, O.K. (January 1969). "Role of cavitation in the process of liquid atomization in an ultrasonic fountain". Ultrasonics. 7 (1): 78. doi:10.1016/0041-624X(69)90560-5.
- ^ Nii, Susumu (2016), "Ultrasonic Atomization", Handbook of Ultrasonics and Sonochemistry, Singapore: Springer Singapore, pp. 239–257, doi:10.1007/978-981-287-278-4_7, ISBN 978-981-287-277-7, retrieved 2024-11-08
- ^ Wood, R.W.; Loomis, Alfred L. (September 1927). "XXXVIII. The physical and biological effects of high-frequency sound-waves of great intensity". The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science. 4 (22): 417–436. doi:10.1080/14786440908564348. ISSN 1941-5982.
- ^ Ari, Arzu (2014-05-12). "Jet, Ultrasonic, and Mesh Nebulizers: An Evaluation of Nebulizers for Better Clinical Outcomes". Eurasian Journal of Pulmonology. 16 (1): 1–7. doi:10.5152/ejp.2014.00087.
- ^ Yeo, Leslie Y; Friend, James R; McIntosh, Michelle P; Meeusen, Els NT; Morton, David AV (June 2010). "Ultrasonic nebulization platforms for pulmonary drug delivery". Expert Opinion on Drug Delivery. 7 (6): 663–679. doi:10.1517/17425247.2010.485608. ISSN 1742-5247. PMID 20459360.
- ^ Dessanges, Jean-François (March 2001). "A History of Nebulization". Journal of Aerosol Medicine. 14 (1): 65–71. doi:10.1089/08942680152007918. ISSN 0894-2684. PMID 11495487.
- ^ Nii, Susumu (2016), "Ultrasonic Atomization", Handbook of Ultrasonics and Sonochemistry, Singapore: Springer, pp. 239–257, doi:10.1007/978-981-287-278-4_7, ISBN 978-981-287-278-4, retrieved 2024-11-03
- ^ Ramisetty, Kiran. A.; Pandit, Aniruddha. B.; Gogate, Parag. R. (January 2013). "Investigations into ultrasound induced atomization". Ultrasonics Sonochemistry. 20 (1): 254–264. Bibcode:2013UltS...20..254R. doi:10.1016/j.ultsonch.2012.05.001. PMID 22672979.
- ^ a b Pohlman, Reimar; Stamm, Klaus (1965). Untersuchung zum Mechanismus der Ultraschallvernebelung an Flüssigkeitsoberflächen im Hinblick auf technische Anwendungen. doi:10.1007/978-3-663-07399-4. ISBN 978-3-663-06486-2.
- ^ Lierke, E.G.; Grießhammer, G. (October 1967). "The formation of metal powders by ultrasonic atomization of molten metals". Ultrasonics. 5 (4): 224–228. doi:10.1016/0041-624X(67)90066-2.
- ^ "Patent application by 3D Lab (2017)". PatBase.
{{cite web}}: CS1 maint: url-status (link) - ^ "ATO Ultrasonic Metal Atomizers Official Website". Retrieved 2025-04-10.
- ^ Kowalski, J.; Nowak, P. (2023). "The Role of Ultrasonics in Metal Powder Production" (PDF). Advanced Materials Research. 45 (3): 112–126.
- ^ "ATO ultrasonic metal atomization technology". Retrieved 2025-04-10.