Resistance of white sapphire and hot-pressed alumina to collision with liquid drops

Fused alumina has been reported to be one of the most promising materials for resistance to erosion due to high-speed collision with liquid drops. In this paper, data are presented that show the resistance of 0.318-cm (0.125-in.)-thick plates of white sapphire and hot-pressed alumina to impingement damage by 0.2-cm-diam waterdrops and mercury drops. The type of damage done to these high-strength ceramics as a result of collision with a mercury drop at high velocity was found to be qualitatively the same as that produced on low-strength plastics as a result of collision with a waterdrop at relatively low velocity. In collision with mercury drops, the velocity at which damage was first observed was 3.514×10⁴ cm/sec (1,153 ft/sec) for white sapphire and 4.276×10⁴ cm/sec (1,403 ft/sec) for hot-pressed alumina; the difference in the velocities found for the two ceramics is not considered to be significant. The velocity required to damage these ceramic materials on collision with a waterdrop was not reached experimentally. A theoretical extrapolation suggests that plates of these ceramics of the indicated thickness can be expected to survive collision with a 0.2-cm waterdrop without damage up to a velocity of 33.7×10⁴ cm/sec (11,100 ft/sec). For air at 0 °C, this is equivalent to a Mach Number of 10.