Corrosion Behavior of SiC Laminate Under Decomposed Sulfuric Acid at 850°C

In view of the possible application of SiC-based ceramic laminates as critical components of hydrogen generation plants based on sulfur-iodine or hybrid-sulfur thermochemical cycles, the effect of corrosion on this kind of ceramics has been investigated. For this purpose, the material was exposed for 1000 h at 850°C to the corrosive action of a gaseous atmosphere simulating the environment of a sulfur-based thermochemical hydrogen generation plant (a gaseous mixture containing several aggressive species: O2, H2O, SO2, SO3, and H2SO4, with relative concentrations representative of the inlet of an SO3 decomposer reactor). Specimens of multilayer SiC were prepared according to the following processing path: tape casting of a SiC-based slurry, building of the green multilayer by stacking 11 sheets, final de-binding and sintering treatments. The material microstructure and its flexural strength and modulus were studied before and after corrosion to investigate degradation phenomena. The microstructure was investigated by XRD, SEM-EDS, XPS, and density measurements. Flexural strength and modulus were measured by four-point bending test. The corrosive atmosphere displayed an oxidizing effect that resulted in the formation of silica, oxycarbides, and gaseous products of carbon oxidation. Nevertheless, the corrosion was hindered by the formation on the sample surface of a passivating silica layer. Bending strength and modulus were found unchanged or even improved after corrosion.