Electric corrosion monitoring in ceramics:: Case study of a Si3N4-TiN particulate composite in sulphuric acid

As a model for active corrosion processes the corrosion behavior of a hot isostatic pressed Si3N4-TiN electroconductive composite was studied in 1.8 M H2SO4 aqueous solution at 70 and 90 degrees C up to 250h. The predominant mechanism is the dissolution of the grain boundary phase and the attack of TiN grains in a zone near the surface. Both corrosion process follows a linear kinetic. TiN removal turns the surface slowly into an insulator, which is easily followed by resistance measurements. It is a good monitor for the overall evolution of the corrosion process, which extends much deeper into the composite. The excellent resolution with time offers a new possibility to follow active corrosion processes in ceramic matrix composites in a non-destructive way.