Dense, crack-free, uniform and well-adhered environmental barrier coatings (EBCs) are required to enhance the environmental durability of silicon (Si)-based ceramic matrix composites (CMCs) in high pressure, high gas velocity combustion atmospheres. This paper represents an assessment of different thermal spray techniques for the deposition of Yb 2 Si 2 O 7 EBCs. The Yb 2 Si 2 O 7 coatings were deposited by means of atmospheric plasma spraying (APS), high-velocity oxygen fuel spraying (HVOF), suspension plasma spraying (SPS), and very low-pressure plasma spraying (VLPPS), techniques. The initial feedstock, as well as the deposited coatings, were characterized and compared in terms of their phase composition. The as-sprayed amorphous content, microstructure, and porosity of the coatings were further analyzed. Based on this preliminary investigation, the HVOF process stood out from the other techniques as it enabled the production of vertical crack-free coatings with higher crystallinity in comparison with the APS and SPS techniques in atmospheric conditions. Nevertheless, VLPPS was found to be the preferred process for the deposition of Yb 2 Si 2 O 7 coatings with desired characteristics in a controlled atmosphere chamber.

No abstract

No abstract

At the focus of energy conversion efficiency and decreasing greenhouse gas emissions from power generation and energy-intensive industries, membrane technologies for H2 extraction and CO2 capture/utilization become pronouncedly important. In this context, the integration of mixed protonic-electronic conducting (MPEC) ceramic membranes in H2 extractors (as fuel) or H2/CO2 consumption (as raw materials for chemical production) would account for high environmental and economic impact. MPEC ceramic membranes may be therefore of interest for integrated gasification process, specifically in water gas shift reactors (T>600°C) and catalytic membrane reactors. Materials largely under focus are Lanthanum tungstates (LaWO), which exhibit appreciable protonic conductivity at intermediate temperatures, non-blocking grain boundaries, n-type electronic conductivity (under reducing atmosphere), good sinterability and stability in H2S, CO/CO2 and steam in comparison to zirconate-cerate solid solutions. All-ceramic (LaWOmem/LaWOsub;LaWOmem/MgOsub) and metal supported (LaWOmem/Crofersub) asymmetric membrane assemblies were developed by means of sequential tape casting and plasma sprayphysical vapor deposition (PS-PVD), respectively. The successful employment of these two complex methods for membrane manufacturing represents the core in further designing and pursuing strategies for integration of all-ceramic or ceramic-metallic assemblies in membrane modules/reactors. The present work therefore addresses fabrication aspects for achieving defect free LaWO membranes on porous ceramic and porous metallic substrates. Formation of LaWO cubic phase, gas tightness of the functional layers and stability of the structures could be achieved for all-ceramic and ceramic-metallic assemblies. This study encompasses furthermore insights on the fabrication parameters (e.g. plasma composition (for ceramic-metallic assemblies); sintering behaviour (for all-ceramic assemblies)) and understanding their correlation to reach desired material/membrane composition and functional properties.

No abstract