For a long time, ceramic coatings could only be produced by sintering at temperatures above 1000 degrees Celsius. However, a new coating method, Powder Aerosol Deposition (PAD), enables their fabrication at normal room temperature. This makes it highly attractive for industrial applications. Under the supervision of Prof. Dr.-Ing. Ralf Moos, engineering scientists at the University of Bayreuth are working on the continuous development of this technology. In the journal Advanced Materials, they have demonstrated its advantages and shown how to optimize the functional properties of ceramic films for high-tech applications.
PAD allows high-density ceramic thin films to be applied to a wide variety of materials such as steel, glass, silicon and even plastics. To achieve this, dry ceramic powder is first converted into an aerosol using a mixture of carrier gas, gas and solid particles. The aerosol is then transported into a vacuum chamber, accelerated through a nozzle to speeds of several hundred meters per second, and sprayed directly onto the material to be coated. The impact shatters the ceramic particles. The resulting fragments are only a few nanometers in size and feature fresh, reactive surfaces. They form tightly bonded, high-density coatings with a thickness ranging from 1 to 100 micrometers. “Thanks to the fine microstructure of the coating, it exhibits excellent mechanical properties immediately after deposition. It is extremely hard and offers outstanding chemical resistance.” Jörg Exner, the lead author of this study, is a driving force behind PAD research. Nevertheless, some functional properties of the coatings, especially electrical conductivity, have proven insufficient without additional processing steps. Their new study now enables the engineering scientists in Bayreuth to report effective optimization approaches. The crystal structure plays a decisive role in this context. The intense impact of ceramic particles on the substrate induces structural defects in the final fragments. This affects not only electrical conductivity but also other functional properties. “These defects can be almost completely eliminated by thermal post-treatment, also known as tempering. We have shown that the temperatures required are generally much lower than those for conventional sintering. It is the possibility of avoiding these extreme high temperatures that makes PAD so appealing. This technology therefore retains high industrial potential, particularly where high-quality ceramic coatings are required,” Exner summarizes. The type of ceramic material used depends on the intended technical application: dielectric ceramic coatings are suitable for capacitors, electrically conductive functional ceramics for sensors, and yttria-stabilized zirconia for high-temperature fuel cells. Even lithium-ion batteries can be manufactured using this method. The scientific understanding of ceramic film structures and their functional properties gained at the University of Bayreuth will greatly support the goal of integrating high-quality coated components into complex systems in a sustainable manner. New technologies in areas such as energy storage and conversion, or for environmental monitoring, will therefore benefit significantly from the application of Powder Aerosol Deposition.