Microstructures and Functional Properties of Al2O3 and TiO2 Suspension Sprayed Coatings: An Overview

In the last years suspension/solution thermal spraying gained an increasing interest for the preparation of finely- or nano-structured sprayed ceramic coatings with promising properties for environmental and other applications. Alumina and titania belong to the materials intensively studied by this new technique of suspension spraying.
This contribution is structured in two parts. In the first a “state of art” of suspension-spraying of alumina and titanium oxide coatings and their properties is described. Focus is made on the electrical properties for Al₂O₃ deposits and photocatalytic performances of the TiO₂ coatings. The microstructures and properties are compared with coatings prepared by conventional spraying from powders. In the second part new experimental results for suspension-sprayed Al₂O₃ and TiO₂ coatings are given. The influence of working parameters (such as spraying conditions, suspension properties, injection mode of the liquid) on the characteristics of the deposits was investigated. In the case of Al₂O₃ focus was made to retain a high ratio of the initial a-phase, due to its improved properties, e.g. electrical, compared with transitional alumina oxides, usually found for coatings prepared from powders. For TiO₂ coatings, the working parameters were chosen in such a way to preserve the photocatalytic active phase, i.e. anatase. The results allow to affirm the potential of the suspension thermal spraying for advanced functional ceramic materials.