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Synthesis and characterization of Yb and Er based monosilicate powders and durability of plasma sprayed Yb2SiO5coatings on C/C–SiC composites

Authors
Journal
Materials Science and Engineering B
0921-5107
Publisher
Elsevier
Publication Date
Volume
177
Issue
2
Identifiers
DOI: 10.1016/j.mseb.2011.12.004
Keywords
  • Solid-State Fabrication
  • Yb/Er-Monoslicate
  • Microstructure
  • Thermal Analysis
  • Coating
  • Thermal Cycling
Disciplines
  • Earth Science
  • Ecology
  • Geography

Abstract

Abstract Rare-earth silicates such as Yb 2SiO 5 and Er 2SiO 5 are promising environmental barrier coating materials for ceramic matrix composites. In this work, Yb 2SiO 5 and Er 2SiO 5 ceramic powders have been synthesized by solid-state reaction using Yb 2O 3, Er 2O 3 and SiO 2 as starting materials. The fabricated powders were subjected to spray drying treatment for subsequent synthesis of coatings by plasma spraying. The spray drying resulted in well-dispersed and spherical powder particles with good flowability. Analytical techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetry and differential scanning calorimetry (TGA/DSC) and dilatometry were applied to study the microstructural and thermal characteristics of the powders. Ultra-high purity monosilicate powders formed as a result of heating treatments at 1400 °C in a box furnace for 20 h. TG/DSC revealed the genesis temperatures of the silicate formation (low temperature polymorphs) and also showed that the solid-state reactions to form Yb and Er based monosilicates proceeded without any weight-loss in the tested temperature range. The values of coefficients of thermal expansion (CTE) of the fabricated compounds are found to be 7.1 ppm/°C for Yb 2SiO 5 and 7.5 ppm/°C for Er 2SiO 5 by dilatometric measurements. Besides these studies, coating formation by plasma spraying of spray-dried Yb 2SiO 5 powders on the ceramic matrix composite specimen such as C/C–SiC has also been evaluated. Well-adhered and uniformed coatings result on composite specimens whose durability is tested by thermal cycling from ∼400 °C to 1500 °C in a gas burner rig.

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