Economical Methods for Recycling Thermal Barrier Coating Wastes from Military Aircraft Coating Operations

Thermal barrier coatings (TBCs) constitute some of the most important advanced materials utilized in military aircraft applications. The elevated operating temperatures, enhanced abilities to resist adverse environmental conditions, and increased fuel efficiencies of modern aircraft engines are all related to improvements in thermal barrier coatings. These improvements in TBC behavior and performance are the result of expansive development efforts focused on both coating material characteristics and coating application methods. Different material characteristics will yield coatings with distinct thermal conductivities, sintering behaviors, and interactions with environmental debris, while application methods can be varied to control features such as coating microstructure. Consequently, a myriad of TBC materials and coating methods have been developed and implemented to suite different aircraft requirements. Despite all the variation in current TBC materials, the raw materials from which the most prevalent coatings are produced are very limited. The two most common types of thermal barrier coating materials currently in use for military and commercial aviation applications are yttria-stabilized zirconia (YSZ) and gadolinium zirconate (Gd2Zr2O7). Both of these materials are entirely comprised of rare earth oxides (REOs) and zirconia, for which the raw material supply chains are exceedingly restricted. The vast majority of suppliers of REO and chemical-grade zirconia raw materials are located in China. This localized concentration of suppliers of these critical materials affords China immense influence over the means to produce thermal barrier coatings. Alleviating this reliance on non-domestic suppliers for the raw materials vital to TBC manufacturing would require either developing new TBCs which utilize different raw material components, or finding alternate sources of the necessary REO and zirconia raw materials. One approach to cultivating an alternate domestic source of raw materials for use in thermal barrier coating production is to implement a program for recycling used TBC wastes into new rare earth oxide and zirconia raw materials. Xylon Technical Ceramics has developed and patented a simple and effective method for recycling oxide materials that is especially suited for rare earth oxide- and zirconia-containing materials. This method has been demonstrated to be very effective for the processing of TBC waste materials into high purity REO and zirconia products. In this Phase II project, Xylon proposes to establish a recycling program for military TBC waste materials. TBC wastes will be collected from military aircraft engine coating operations, recycled into REO and zirconia raw materials, and then further processed into new TBC powders or ingots for reuse on military aircrafts. The execution of this proposed project would result in a secure domestic supply of TBC materials for military use.