Centrifuge adhesion test to evaluate icephobic coatings

Ice accumulation is a human safety risk and a cause of important material damages in maritime, ground and air transportation, on ground and maritime energy exploitation and in telecommunication and electric networks. Many ice protection systems have been developed to prevent ice formation, but they are expensive to use due to their energy consumption. Passive systems, such as icephobic coatings applied on exposed surfaces, appear to be an interesting solution to prevent ice accumulation by reducing its adherence; but coating icephobicity is difficult to quantify. To measure icephobicity, the Anti-icing Material International Laboratory (AMIL) developed the Centrifuge Adhesion Test (CAT) in 2006. The test involves icing the extremity of small beams under freezing drizzle in a climatic chamber. Following icing, the beams are balanced in a centrifuge and rotated at an accelerating speed until the ice detaches and the corresponding rotation speed is measured. The adhesion shear stress is calculated from the centrifugal force evaluated at the detachment rotation speed, and the ice contact surface. The results are then reported as an Adhesion Reduction Factor (ARF) which is the ratio of the adhesion shear stress of the beams with a candidate coating with respect to uncoated beams. The higher the ARF, the more icephobic the coating; values below one indicate an increase in adhesion. For coatings with high icephobicity, the CAT apparatus sensitivity proved to be insufficient to evaluate the ARF. To remedy this, in 2009, AMIL modified the CAT apparatus to increase its sensitivity. The new CAT, called CAT-NG, can measure ARF in a range of 0.6 to 1 000 inexpensively and timely. To ensure reliable ARF factor with confidence level of 95%, the beam area exposed to icing is polished after 5 tests, or every month, to reduce the ice erosion effect on aluminum surface. Also, the ice specimen mass should be 5.5 g ± 5% with a length of 34 mm ± 5%. For glaze ice tested at -10°C on 6061-T6 aluminum with AMIL Standard Surface roughness of 0.7 μm, the detachment speed is 7 800 RPM ± 7% when the beam is rotated at speeds increasing linearly at rate of 300 RPM/s corresponding to a shear stress of 0.51 MPa ± 7%