Aluminum and silicon co-deposition by the chemical vapor deposition in fluidized bed reactor technique as a precursor of protective coatings of mullite

Ceramic coatings are excellent candidates to protect metallic structures that operate at high temperature. Regarding these ceramic coatings, mullite is a good option, since it presents very good mechanical properties, great corrosion resistance, high thermal resistance and high durability. The chemical vapor deposition by fluidized bed reactor (CVD-FBR) is an interesting technique to create thin and adherent protective films on metallic surfaces. Furthermore, this method is cheap and easy to apply. The first step to obtain mullite coatings would be the co-deposition of aluminum and silicon coatings by CVD-FBR. Thermodynamic calculations were made before the experiments to study the system and optimize the working conditions. These depositions take place in a fluidized bed reactor and the base material used is a commercial AISI-304 stainless. This technique is based upon reaction among aluminum chloride (AlCl3 (g)) and silicon chloride (SiCl4 (g)). The optimization of the deposition conditions (deposition temperature, time, fluxes, etc.) is discussed. The analysis of the results is carried out by X-ray diffraction (XRD), optical microscopy (OM), scanning electron microscopy (SEM) and energy dispersion spectroscopy (EDS). In addition, further oxidation of these precursor coatings is made in order to obtain the definitive system of a protective ceramic layer. Oxidation of the coated samples is made at different temperatures and times to obtain the best mullite structure.