Corrosion behavior of Si3N4-TiN composite in sulphuric acid

The corrosion behavior of a hot pressed Si-3-TiN elect roconductive composite, with Al2O3 and Y2O3 as sintering aids, was studied in 1.8 M H2SO4 aqueous solution at 70 and 90 degrees C up to 200 h in an open system. At 70 degrees C an outer corrosion zone with strong removal of the glassy grain boundary phase is developing on top of a zone of leaching. The outer zone exposes the formerly protected TiN-grains and results in an increasing level of Ti removal with time and overall nearly linear kinetics. At 90 degrees C the leaching of the network modifiers from the grain boundary phase dominates. A growing silica-rich residue inside the corrosion zone develops, while TiN exposure is developing very slowly: the overall kinetics is nearly parabolic. Thus simple extrapolation from lower to higher temperature behavior is not correct and at long times damage can even be lower at higher temperature. (c) 2004 Elsevier Ltd. All rights reserved.