Design, Fabrication, and Characterization of New Materials Based on Zirconia Doped with Mixed Rare Earth Oxides: Review and First Experimental Results

Abstract

Monazite is one of the most valuable natural resources for rare earth oxides (REOs) used as dopants with high added value in ceramic materials for extreme environments applications. The complexity of the separation process in individual REOs, due to their similar electronic configuration and physical–chemical properties, is reflected in products with high price and high environmental footprint. During last years, there was an increasing interest for using different mixtures of REOs as dopants for high temperature ceramics, in particular for ZrO2-based thermal barrier coatings (TBCs) used in aeronautics and energy co-generation. The use of mixed REOs may increase the working temperature of the TBCs due to the formation of tetragonal and cubic solid solutions with higher melting temperatures, avoiding grain size coarsening due to interface segregation, enhancing its ionic conductivity and sinterability. The thermal stability of the coatings may be further improved by using rare earth zirconates with perovskite or pyrochlore structures having no phase transitions before melting. Within this research framework, firstly we present a review analysis about results reported in the literature so far about the use of ZrO2 ceramics doped with mixed REOs for high temperature applications. Then, preliminary results about TBCs fabricated by electron beam evaporation starting from mixed REOs simulating the real composition as occurring in monazite source minerals are reported. This novel recipe for ZrO2-based TBCs, if optimized, may lead to better materials with lower costs and lower environmental impact, as a result of the elimination of REOs extraction and separation in individual lanthanides. Preliminary results on the compositional, microstructure, morphological, and thermal properties of the tested materials are reported.

Nanostructured Cobalt Doped Barium Strontium Titanate Thin Films with Potential in CO2 Detection

“…The final suspension was introduced into a Teflon vessel of a sealed hydrothermal autoclave reactor (5 L, Berghof Products + Instruments GmbH, Berghof, Germany (Figure 1)) endowed with a cooling system. To control the reaction pressure, argon gas was purged inside the autoclave, according to working procedure described in [30]. The Teflon vessel was filled to 80% of its capacity.…”

Critical Raw Materials Saving by Protective Coatings under Extreme Conditions: A Review of Last Trends in Alloys and Coatings for Aerospace Engine Applications

“…Recently, some of the authors of this manuscript fabricated TBCs based on zirconia doped with 8 wt.% multicomponent REOs with the natural composition existing in monazite concentrates [ 13 ]. The powders prepared by a hydrothermal method were used to obtain by EB-PVD process multi-layered coatings consisting of YSZ, La 2 Zr 2 O 7 , and Gd 2 Zr 2 O 7 on Nimonic superalloy, using NiCrAlY bonding layer, as shown in Figure 15 .…”

“…This paper deals with the analysis of the alloys and coatings for the aerospace engine, aiming at providing future perspectives about CRMs saving and CO 2 reduction. Some results are also reported about an innovative thermal barrier coating (TBC) system obtained by doping zirconium oxide with mixed rare earth oxides (as yttrium oxide substitutes) occurring in the natural composition as extracted directly from monazite concentrate minerals through an efficient and green route [ 13 ]. This study, carried out by some of the authors of this manuscript in the frame of the EU ERA-MIN 2 project MONAMIX, New concepts for efficient extraction of mixed rare earths oxides from monazite concentrates and their potential use as dopant in high temperature coatings and sintered materials, is still in progress.…”

Phase Equilibrium in ZrO2-CeO2-Eu2O3 System at a Temperature of 1500 °C

“…There are various systems containing oxides of zirconium, cerium, and lanthanides, which are promising alternative materials for the development of heat-protective coatings and fuel cells [1][2][3][4][5][6][7]. Environmental pollution is a major concern due to the use of natural carbohydrates and their byproducts in industry and transport.…”

“…On the other hand, CeO2 is widely used as a surrogate material instead of PuO2 due to their similar physicochemical properties. Therefore, the nodes intended for plutonium ions in the pyrochlore structure will probably be replaced by cerium ions [1][2][3][4][5][6][7].…”