In Situ Generated β‐Yb₂Si₂O₇ Containing Coatings for Steel Protection in Extreme Combustion Environments

Abstract

The rapid permeation and degradation of silazane‐based coatings by water vapor limit their application in combustion environments. Hence, this work reports on the reaction of the oligosilazane Durazane 1800 with an appropriate Yb‐complex by a molecular approach and its application as protective thin coatings (1.2 µm) for AISI 304 in comparison with the benchmark Durazane 2250 in combustion‐like environments. Fourier transform infrared‐ and nuclear magnetic resonance‐spectroscopy elucidate the reaction mechanism and the chemical structure of the resulting Yb‐modified silazanes, whereas elemental and X‐ray diffractometry analyses confirm the formation of crystalline β‐Yb2Si2O7 and SiO2 after pyrolysis at 1000 °C in air. Energy dispersive spectroscopy and X‐ray photoelectron spectroscopy profile analyses show the enhanced diffusion of Fe, Cr, and Mn from the substrate into the Yb50 coating, which is responsible for a better adhesion (23.7 MPa), scratch tolerance (38 N), and a decreased coefficient of thermal expansion‐mismatch to the substrate, resisting 9 thermal cycles between 1000 and 20 °C. Despite the low Yb‐silicate content (6.8 wt%), only minor damage is caused to the Yb50 coating after wet oxidation in moist flowing air (1000 °C for 15 h), whereas the Durazane 2250 coating spalled‐off. This is a clear indication of the potential of the Yb2Si2O7‐containing coatings to protect metals and ceramics in extreme combustion environments.

Joining and Coating of Plasma Electrolytic Oxidated Aluminum Using a Silica Preceramic Polymer

“…XRD analysis performed on the cured polymer treated at 1200 • C (Figure 3) confirms the amorphous structure of the obtained material: once heated at 1200 • C, the polymer appears colorless. Results in the literature, such as the study by [42], confirm that pyrolysis at this temperature leads to the formation of an amorphous phase.…”

“…XRD analysis performed on the cured polymer treated at 1200 °C (Figure 3) confirms the amorphous structure of the obtained material: once heated at 1200 °C, the polymer appears colorless. Results in the literature, such as the study by [42], confirm that pyrolysis at this temperature leads to the formation of an amorphous phase. Coated samples were obtained by manually depositing the polymer on the PEO side of the samples, followed by the curing process at 180 °C for 4 h. Figure 4a shows the top surface of the coating after curing; it is compact and shiny, except from some macro-cracks on the right side, probably due to an excessive thickness; the good quality of the coating is also confirmed via FESEM micrographs taken of the top surface (Figure 4b) and the cross sections (Figure 4c,d).…”