Corrosion of Polycrystalline Wool by Na₂CO₃ Vapor

Abstract

The corrosion behavior of six types of polycrystalline wool blanket samples, which were composed of alumina and silica, and exposed to Na 2 CO 3 vapor at 1350°C for 24 h, was investigated. The corrosion in sample A100 (Al 2 O 3 : 99.6 mass%) by alkaline vapor was suppressed remarkably as the corundum phase changed to the ¢-alumina (Na 2 O•11Al 2 O 3 ) phase only at the surface of the fiber, and the surface layer functioned as a protective layer against corrosion. The corundum phase in sample A95 (Al 2 O 3 : 94.9 mass%) changed slightly to ¢-alumina due to the formation of the carnegieite phase via the decomposition of mullite phase corroded by alkaline vapor. The corrosion in samples A80 (Al 2 O 3 : 80.280.8 mass%) and A72 (Al 2 O 3 : 72.273.2 mass%) by alkaline vapor was more intense than that in samples A100 and A95 because of the high silica content. Alkaline vapor remained near the reaction surface and reacted locally with fibers in a narrow region because the area of the amorphous phase in the high-density samples (A80-H and A72-H) was wider than that in the low-density samples (A80-L and A72-L), and the permeability of the vapor was low in the high-density samples. The carnegieite phase, which was present in the temperature range of 1000 1300°C, disappeared and the amorphous phase was simultaneously formed during alkaline vapor exposure at 1350°C for 8 h in the corrosion process of A72-H.