Protection of silicon nitride ceramics against corrosion in acidic aqueous solutions by enforced internal passivation

Silicon nitride ceramics with Y2O3 and Al2O3 as sintering additives were corroded in 1 N sulphuric acid at 90degreesC. Any classical corrosion rate model cannot describe the overall kinetics of the corrosion process successfully. At longer corrosions times, a kinetic break occurs, after which slow linear corrosion kinetics prevail. The passivation is due to the formation of a defective silica sublayer in the corrosion zone. We show that it is possible to enforce this passivation long before it would occur naturally by a simple hot drying (150degreesC) procedure after a critical time. As consequence the total mass loss decreases by a factor of 2-3. (C) 2003 Elsevier Ltd and Techna S.r.l. All rights reserved.