Suspension and solution plasma spraying of finely structured layers: potential application to SOFCs

Abstract

Suspension direct current plasma spraying allows achieving finely structured coatings whose thickness is between few tens and few hundreds of micrometres. Drops (200–300 µm in diameter) or liquid jets are mechanically injected in the plasma jet. With radial injection they are rapidly (a few µs) fragmented into droplets (a few µm in diameter). The latter are vaporized (in a few µs) and the solid particles contained in suspension droplets are accelerated and melted by the plasma jet. As in conventional plasma spraying (CPS), much smaller splats (with diameters between 0.2 and 3 µm and thicknesses between 30 and 200 nm) are arranged in layers up to form the coating. The low inertia of particles requires spray distances between 40 and 60 mm which induces plasma heat fluxes up to 22 MW m−2 participating in coating densification. Even more than in CPS, the plasma jet fluctuations, particularly for plasmas containing di-atomic gases, perturb drops penetration and fragmentation. It has been chosen to illustrate difficulties and possibilities of this new method, through the spraying of the three layers of an element of solid oxide fuel cells. Indeed, it requires a dense stabilized zirconia electrolyte, if possible thin (15–20 µm) with two porous electrodes: cathode made of perovskite prone to decomposing upon spraying and anode made of two materials (nickel and zirconia) with very different melting points. These components were obtained by spraying ethanol suspensions, with, first, LaMnO3 perovskite particles doped with 10 mol% of MnO2 and 3 µm in mean diameter sprayed with pure argon to limit their decomposition and achieve porous coatings, second, Yttria (13 wt%) stabilized zirconia (YSZ) with two different particle size distributions and morphologies for which plasma compositions were adapted, producing in both cases 15 µm thick and fully dense coatings, third, porous Raneigh nickel by co-spraying the YSZ suspension and solution of nickel nitrate.

Pressure-Based Liquid Feed System for Suspension Plasma Spray Coatings

“…Recently, a suspension plasma spray (SPS) process has been developed for the deposition of nanostructured coatings ( Ref 4,[8][9][10][11][12][13][14][15][16]. In SPS, the ultrafine or nanosized particles are dispersed in a liquid medium such as water or ethanol to form a suspension that is injected into the plasma torch.…”

Microstructure of Suspension Plasma Spray and Air Plasma Spray Al2O3-ZrO2 Composite Coatings

“…Recently, a suspension plasma spray (SPS) process has been developed for the deposition of various types of coatings ( Ref 2,4,[8][9][10][11][12][13][14][15]. In SPS, the ultrafine or nanosized particles are dispersed in a solvent such as water or ethanol to form a suspension and then the suspension is injected into the plasma torch.…”

Electrochemical Performance of Plasma Sprayed Metal Supported Planar Solid Oxide Fuel Cells

“…Moreover the latest developments in plasma spraying techniques, in particular for atmospheric plasma spraying (APS) with the introduction of suspension plasma spraying (SPS) and plasma spray -thin film (PS-TF) for low pressure plasma spraying (LPPS), bring unprecedented improvements in terms of possibilities to produce coatings with low thickness (from few to tenths of microns) and/or coatings with very low porosity and almost gas tight; characteristics which were not available a few years ago and are of key importance to produce high performance SOFCs. 18,22,23 Detailed electrochemical analysis is however required to evaluate the limitations of these techniques and to adapt the new processes to the specific needs of metal supported SOFCs.The objective of this work was to evaluate the electrochemical performance of metal-supported planar cells produced by plasma spraying. The anode in this study was deposited by APS while the electrolyte was deposited by PS-TF based on a recently developed LPPS hybrid technology.…”