Single and multi-component REDS systems for TEBC application: Synthesis and study of high temperature interaction with CMAS

Multi-component rare earth disilicates RE2Si2O7 (REDS) are considered as promising materials to be used as thermal environmental barrier coatings (TEBCs) to protect ceramic matrix composites (CMCs) against environmental degradation. The combination of multiple cations in a single phase is expected to decrease the overall thermal conductivity of the material. In addition, they can also increase the phase stability at high temperatures, toughness, inertness to water vapor attack, and stability against molten deposits (CMAS) attack. In this work, single and multi-component rare earth disilicates have been successfully synthesized using a novel and quick synthesis method through solid-state reaction. The main goal of this study is to understand the thermochemical interactions of single cation (Y, Yb, Er, Ho, Lu, and Sc) disilicates and multiple cation disilicates e.g. (Y,Yb)2Si2O7, (Y,Yb,Er)2Si2O7, (Y,Yb,Er,Ho)2Si2O7 with CMAS at 1350 and 1400°C for 1h. Results have shown that the synthesized powders exhibit formation of a single monoclinic phase (β or γ types) both in single and multi-component disilicate systems. The CMAS interaction resulted in formation of REDS reprecipitates (Yb, Lu, Sc), apatite (Er, Ho, Y), and diopside (Sc) as reactive crystallization products. Finally, the multiple cation effect on the formation of the reaction products will be discussed

Rare-earth disilicate systems for T/EBC application: Synthesis and high temperature interaction with CMAS

Thermal and environmental barrier coatings (TEBCs) that are intended to be used on top of ceramic matrix composites (CMCs) require complex properties such as high temperature phase stability, toughness, inertness to water vapor attack, and protection against silica deposit (CMAS) attack. Multi component rare earth disilicates RE2Si2O7 (REDS) such as mixtures of Y, Yb, Er, Ho, Lu, and Sc have been identified as promising TEBC materials due to their high-temperature phase stability, low thermal conductivity, and coefficients of thermal expansion similar to SiC-CMCs (4.5x10-6). A novel synthesis method using high-energy milling and solid-state reaction has been successfully developed for producing multi-component REDS powders rapidly. The current work also focuses on understanding the thermochemical reactions between single-component Y, Yb, Er, Ho, Lu, and Sc disilicates as well as multi-component REDS with different CMAS sources at 1350 and 1400 °C for 1h using REDS+CMAS powder mixtures (), respectively. Results showed the successful synthesis of monoclinic RE disilicatephases (β and γ types). Structural and chemical analysis confirmed the formation of REDS (Yb, Lu, Sc) reprecipitates, reactive crystallization products as apatite (Er), and intrinsic crystallization products such as diopside. Additionally, Y and Ho thermochemical reactions will be discussed

Reaction Products from High Temperature Treatments of (LaxGd1x)2Zr2O7 System and Volcanic Ash Powder Mixtures

Rare-earth zirconate (REZ) pyrochlores, specifically (La,Gd)2Zr2O7, are promising alternatives to substitute 7YSZ in thermal barrier coatings (TBC) due to their increased phase stability and resistance to calcium-magnesium-aluminosilicate (CMAS)-based damage at high temperatures. This work analyses the reaction products of isothermal treatments at 1250°C of (LaxGd1−x)2Zr2O7 powder mixtures in reaction with natural volcanic ashes (VAs) with different chemical compositions (Popocatepetl, Colima, and Eyjafjallajökull). The chemical composition in the (LaxGd1−x)2Zr2O7 system showed a strong influence on the formation of reprecipitation products (Zr,Gd,La oxides), reactive crystallization products (La-Gd apatites, lanthanum silicates, zirconolite, and garnets), and intrinsic crystallization products (hematite-like structures). The formation of garnets, which enhances the mitigation effect against molten VAs/Si deposit damage, was observed more promptly on (La0.5Gd0.5)2Zr2O7 promoted by high contents of Fe, Ca, Ti, and Mg on VAs. Thus, the (La0.5Gd0.5)2Zr2O7 system stands as a possible candidate to overcome today’s threats for the integrity of current TBCs

Evaluation of the reactivity of dense lanthanum‑gadolinium zirconate ceramics with Colima volcanic ashes

The effects of ingestion of airborne particles from pyroclastic events of active volcanoes by aircraft turbines and their subsequent reaction with thermal barrier coatings have attracted the attention of the scientific community in recent years. The reaction products of infiltration experiments of lanthanum‑gadolinium zirconate (LGZO) ceramics with molten ashes from the active Colima volcano at 1250 °C for 10 h are presented and discussed as a function of the Gd3+ content. Five ceramic compositions, varying the Gd3+ content in solid solution were synthesized by the chemical coprecipitation and calcination method of pressed powders. These compositions include pure lanthanum and gadolinium zirconates, LZO, and GZO, respectively. Penetration depth and identification, and in some cases quantification of the reaction products between the molten ash and LGZO ceramics were performed by scanning electron microscopy, chemical composition with energy dispersive X-ray spectroscopy, grazing incident X-ray diffraction as well as micro-Raman spectroscopy. The LZO ceramic exhibited the greatest infiltration resistance with an infiltration depth of approximately 23 μm from the surface. The phase characteristics of the reaction layers were dependent on the gadolinium content. LZO, LGZO25, and LGZO50 (x = 0, 0.25, and 0.5) showed the presence of apatite as well as monoclinic and tetragonal zirconia, while LGZO75 and GZO (x = 0.75 and 1), additionally showed the presence of cubic zirconia and anorthite. As the Gd3+ content increases in the LGZO solid solutions, the wavenumber value corresponding to the stretching vibrational mode of the silicon tetrahedra in apatite shifts from 862 to 877 cm−1, which is associated with a decrease in Sisingle bondO bond lengths. These findings indicate that the amount and kind of rare earth cations dissolved in the melt plays an important role in the precipitation of the reaction products

Popocatepetl Ash Infiltration in Lanthanum-Gadolinium Zirconate Ceramics

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)

NEOTROPICAL ALIEN MAMMALS: a data set of occurrence and abundance of alien mammals in the Neotropics

Biological invasion is one of the main threats to native biodiversity. For a species to become invasive, it must be voluntarily or involuntarily introduced by humans into a nonnative habitat. Mammals were among first taxa to be introduced worldwide for game, meat, and labor, yet the number of species introduced in the Neotropics remains unknown. In this data set, we make available occurrence and abundance data on mammal species that (1) transposed a geographical barrier and (2) were voluntarily or involuntarily introduced by humans into the Neotropics. Our data set is composed of 73,738 historical and current georeferenced records on alien mammal species of which around 96% correspond to occurrence data on 77 species belonging to eight orders and 26 families. Data cover 26 continental countries in the Neotropics, ranging from Mexico and its frontier regions (southern Florida and coastal-central Florida in the southeast United States) to Argentina, Paraguay, Chile, and Uruguay, and the 13 countries of Caribbean islands. Our data set also includes neotropical species (e.g., Callithrix sp., Myocastor coypus, Nasua nasua) considered alien in particular areas of Neotropics. The most numerous species in terms of records are from Bos sp. (n = 37,782), Sus scrofa (n = 6,730), and Canis familiaris (n = 10,084); 17 species were represented by only one record (e.g., Syncerus caffer, Cervus timorensis, Cervus unicolor, Canis latrans). Primates have the highest number of species in the data set (n = 20 species), partly because of uncertainties regarding taxonomic identification of the genera Callithrix, which includes the species Callithrix aurita, Callithrix flaviceps, Callithrix geoffroyi, Callithrix jacchus, Callithrix kuhlii, Callithrix penicillata, and their hybrids. This unique data set will be a valuable source of information on invasion risk assessments, biodiversity redistribution and conservation-related research. There are no copyright restrictions. Please cite this data paper when using the data in publications. We also request that researchers and teachers inform us on how they are using the data