Until now, the only way to produce ceramic coatings was by using sintering techniques at temperatures over 1000ºC. Now, scientists from the University of Bayreuth in Germany have developed a new spraying method called Powder Aerosol Deposition (PAD) that works at room temperature. The researchers, led by Dr. Ralf Moos, present their findings in the journal of Advanced Materials.
The PAD method allows dense ceramic films to be applied to different materials, like steel, glass, plastic, or silicon. To begin, they use a carrier gas to convert a dry, ceramic powder to aerosol. The aerosol is then put into a vacuum chamber and is shot through a nozzle at 100 meters per second onto the material being coated. When the aerosol hits the material, it fractures, producing tiny fragments. These fragments have fresh surfaces that adhere to the material being coated. The thickness of the coating is between 1 and 100 micrometers.
"Thanks to their dense microstructure, the coatings already exhibit excellent mechanical properties even directly after the deposition. They are extraordinarily hard and have good chemical resistance," explains Dr. Jörg Exner, the first author of the study. Some of the properties of the coatings left something to be desired, especially the electrical conductivity.
When these aerosol particles fracture, it affects the conductivity and other properties. As Exner explains, “By a thermal post-treatment, or so-called tempering, these defects can be almost 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.”