Measuring the adhesion of alumina coatings onto Fecralloy supports using a mechanical testing system

Tightening legislation for vehicles across the world has caused the use of monolith catalysts in automotive emission control to become ubiquitous. Control of the surface adhesion of the platinum group metal (PGM) coating onto the monolith block, to maximise catalytic performance for a minimum PGM loading, is therefore paramount. In this paper, an automatic film application is used for coating γ-alumina slurries onto Fecralloy®, an integral component of metallic monolith catalysts, to achieve the desired coating properties. A newly devised dual compression–tension technique using a mechanical testing system (MTS) is used for measuring the coating adhesion. This method involves compression of the coating with a probe at a fixed load, and then removing the probe together with the coating at right angles to the substrate surface at a speed of 10 mm/min. The MTS results are compared with those from conventional ultrasonic vibration tests. It is found that at 40 wt% solids concentration, the coatings of the finest particles (d0.9 of 12.14 μm) showed the best adhesion with an ultimate strength of 0.59 MPa and 85–90 mass% coating removal.