PS-PVD Processing of Single-Phase Lanthanum Tungstate Layers for Hydrogen-Related Applications
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PS‑PVD Processing of Single‑Phase Lanthanum Tungstate Layers for Hydrogen‑Related Applications D. Marcano1 · M. E. Ivanova1 · G. Mauer1 · Y. J. Sohn1 · A. Schwedt2 · M. Bram1 · N. H. Menzler1 · R. Vaßen1
Received: 21 May 2019 / Revised: 27 August 2019 / Published online: 23 October 2019 © ASM International 2019
Abstract This work presents a systematic study of the lanthanum tungstate (LaWO) ceramic layers formation on porous metallic substrates as a function of the PS-PVD processing parameters including plasma characteristics, support type and temperature, as well as addition of O 2 during the spraying. Through precise control of the PS-PVD parameters, a set of processing conditions were found that led to He gas-tight purely cubic LaWO layers with negligible secondary phase precipitations. Being dependent on process conditioning, the formation and evolution of the cubic La6−xWO12−δ (x = 0.3-0.6) as the main phase of functional importance and of the undesired secondary phases (La2O3 and La6W2O15) was strongly affected by the cation and oxygen stoichiometries. The rapid cooling of the feedstock at particle impact on the substrate led to the formation of highly La-saturated compositions which exhibited significant lattice expansion in comparison with conventionally processed LaWO and is considered beneficial in terms of material performance. And indeed, the H2 permeation performance of the PS-PVD processed LaWO ceramic layers shown earlier by our group was 0.4 ml/min∙cm2 at 825 °C for 60 µm thickness of the functional layer, the highest value reported for this type of proton conducting ceramics, so far.
* G. Mauer g.mauer@fz‑juelich.de 1
Forschungszentrum Jülich GmbH, Institute of Energy and Climate Research, IEK‑1, Jülich, Germany
2
Gemeinschaftslabor für Elektronenmikroskopie RWTH, Aachen, Germany
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Vol:.(1234567890)
Keywords crofer®22APU supported ceramic coatings · electron backscatter diffraction (EBSD) · functional ceramic coatings · H2 separation · lanthanum tungstate · proton conducting ceramics · plasma spray-physical vapor deposition (PS-PVD)
Introduction Lanthanum tungstate ( La6−xWO12−δ, with x = 0.3-0.6, further referred to as LaWO) is a promising ceramic material for H2-related applications. The cubic polycrystalline LaWO phase is a predominant proton conductor at temperatures below 700 °C in humid atmospheres and a mixed protonelectronic conductor above this temperature in reducing atmospheres (Ref 1-3). Such properties, accompanied with significant thermo-chemical stability in a variety of gas conditions (including CO, CO2, H2, steam) (Ref 4-6), make it a promising candidate for applications at lower as well as at elevated temperatures. Target applications are as a solid electrolyte for proton conducting solid oxide cells (PC–SOCs) (Ref 7-9), as ceramic membranes for H2 separation from gas mixtures, in catalytic membrane reactors for CO2 utilization (e.g., CO2/H2O co-electrolysis to biofuels and other valuable chemicals) and in water gas shift process (WGS, C
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