29th October 2020

Aerosol Process Offers New Possibilities for Ceramic Coatings

Researchers at the University of Bayreuth, in Bayreuth, Germany, are working on a new spraying method for powdered ceramics. Powder Aerosol Deposition (PAD), they say, enables production of ceramic coatings at room temperature, without the need for a curing stage in the process. Previously, ceramic coatings production has only been possible by means of sintering techniques, which require temperatures of more than 1,000 degrees C.
 
Engineering scientists under the direction of professor Ralf Moos are working on the development of the technology.
 
According to the University, with PAD, dense ceramic films can be applied to different types of substrates, such as steel, glass, silicon or plastic. To achieve this, a dry ceramic powder is first converted into an aerosol—a mixture of gas and solid particles—with the aid of a carrier gas. The aerosol is then transported into a vacuum chamber and accelerated to several 100 meters per second through a nozzle, and directed onto the material to be coated. On impact, the tiny ceramic particles fracture and the resulting fragments—only a few nanometers in size—form tightly adhering, dense coatings with a thickness of between 1 and 100 micrometers.
 
"Thanks to their dense microstructure, the coatings already exhibit excellent mechanical properties even directly after the deposition,” says Jörg Exner, the first author of the study, who is involved with the research work on PAD at the University. “They are extraordinarily hard and have good chemical resistance.”
 
The researchers note, however, that some properties such as electrical conductivity need further development, because the impact of the ceramic particles on the materials causes structural defects in the resulting fragments. This not only affects electrical conductivity, but also other functional properties.
 
However, Exner says, "By a thermal post-treatment, or so-called tempering, these defects can be almost completely eliminated. We have been able to show that the required temperatures are generally much lower than for conventional sintering. The avoidance of these extremely high temperatures is what makes PAD so attractive. It therefore remains true: This technology offers very high industrial potential, especially where high-quality ceramic coatings are required.”
 
Scientific understanding of the ceramic film structures and of their functional properties, the researchers add, will contribute significantly to the goal of integrating high-quality coated components into complex systems in a sustainable way. New technologies in fields such as energy storage and conversion, or for the purpose of environmental monitoring, stand to benefit considerably from PAD applications.
 
https://doi.org/10.1002/adma.201908104