Optimization of Alumina Ceramics Corrosion Resistance in Nitric Acid

The development of ceramic materials resistance in various aggressive media combined with required mechanical properties is of considerable importance for enabling the wider application of ceramics. The corrosion resistance of ceramic materials depends on their purity and microstructure, the kind of aggressive media used and the ambient temperature. Therefore, the corrosion resistance of alumina ceramics in aqueous HNO₃ solutions of concentrations of 0.50 mol dm^-3, 1.25 mol dm^-3 and 2.00 mol dm^-3 and different exposure times-up to 10 days-have been studied. The influence of temperature (25, 40 and 55 °C) was also monitored. The evaluation of Al₂O₃ ceramics corrosion resistance was based on the concentration measurements of eluted Al³⁺, Ca²⁺, Fe³⁺, Mg²⁺, Na⁺ and Si⁴⁺ ions obtained by inductively coupled plasma atomic emission spectrometry (ICP-AES), as well as density measurements of the investigated alumina ceramics. The response surface methodology (RSM) was used for the optimization of parameters within the experimental "sample-corrosive media" area. The exposure of alumina ceramics to aqueous HNO₃ solutions was conducted according to the Box-Behnken design. After the regression functions were defined, conditions to achieve the maximum corrosion resistance of the sintered ceramics were determined by optimization within the experimental area.