Popocatepetl Ash Infiltration in Lanthanum-Gadolinium Zirconate Ceramics

Abstract

Currently, the most widely used material for thermal barrier coatings (TBC) in aeronautical industry is zirconia stabilized with 6- 8% of yttria (7YSZ). However, 7YSZ transforms from tetragonal to monoclic at temperatures above 1200°C causing phase destabilization [2]. This transformation can also be accelerated by the presence of silica compounds as in molten volcanic ashes (VAs) [3]. These deposits of molten silica infiltrate throughout the coating porosity and solidify during cooling producing residual stresses that eventually generate TBC failure [4]. Rare earth zirconates (REZs) have been considered as a promising material due to phase stabilization at high temperatures, these crystalize in a typical pyrochlore structure. Compared to 7YSZ, REZs are ceramic materials that have many advantages for TBC applications: no phase transformation from room temperature to their melting temperature, considerably high sintering resistance, a very low thermal conductivity, and a lower oxygen ion diffusivity [2]. Among these REZs, gadolinium zirconate (GZO) and lanthanum zirconate (LZO) have received great attention due to their stability at temperatures above 1500°C. When LZO and GZO interact with Si-based melts, they exhibit the formation of reaction products such as apatites (Ap). The formation of Ap is considered as a mechanism against infiltration of Si-based melts because they can act as a sealing layer along the interphase preventing the infiltration mechanism [5]. The objective of this work is to analyze the behavior of ash infiltration Popocatepetl VA (Mexico) with LZO, GZO and LZGO solid solutions ((La1-xGdx)2Zr2O7) by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS).