Effect of La modification on the stability of coating alumina layer on FeCrAl alloy substrate

• Newly developed La modification method of Al2O3 resulted in better slurry for coat.
• Alumina coat showed stable morphology and high surface area at up to 1200 °C.
• An interlayer grown on FeCrAl alloy can effectively bond into alumina topcoat layer.

In this work, better washcoating technology on a FeCrAl alloy support was studied, and the improving factors towards optimal coating were attained with regard to alumina primer. Surface La-modification of alumina stabilized the metastable phase of Al2O3 by inhibition of α-transformation leading to the maintenance of high surface area at temperatures of up to 1200 °C. Newly developed two step modification in 2 mol% La-modified Al2O3 resulted in better slurry with regard to surface charge as colloid dispersion and rheological properties under stress vs. shear rate condition. Surface La2O3 was able to control zeta potential to high pH region so that alkaline solution was applied to metallic substrate. The layer from a suspension coat process using the present alumina was morphologically stable without strong cracks, and maintained the surface area of 70 m2/g, even when it was subjected to high temperatures of up to 1200 °C. The surface area of the dried slurry becomes lower than that of the coated layer after heat treatment in the case of 1 mol% La-modified Al2O3, while in 2 mol% La-modified Al2O3 this negative influence was not found. The present coat layer effectively reacts with alumina interlayer grown on FeCrAl alloy edge by oxygen bulk diffusion and bonded into porous topcoat layer without heavy phase transformation. Surface La-modification of alumina induced better composite structure of both porous coat layer and strong bonding with alloy substrate.