Optimization of Alumina Ceramics Corrosion Resistance in Nitric Acid

Abstract

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.

Statistical Optimisation of Chemical Stability of Hybrid Microwave-Sintered Alumina Ceramics in Nitric Acid

“…The calculated average grain size of 2.1 µm, determined by the line intercept method [41,42], is in accordance with findings in the literature [43][44][45][46]. The average grain size of the same alumina ceramics sintered in a high-temperature electric kiln (conventional sintering) at the same temperature was greater, i.e., 7.6 µm [24]. The grain size decreases in hybrid microwave sintering compared to conventional sintering due to the shorter sintering time.…”

“…The Vickers hardness (HV1), the ratio of c/a, and the Vickers indentation fracture toughness (K IC ) values are listed in Table 4. In comparison to the hardness and indentation fracture toughness of the same alumina ceramics sintered in an electric kiln, which amount to 1762 ± 77 and 5.44 ± 0.93 MPa m 1/2 (Casellas), respectively, the values for the ceramic samples sintered in a hybrid microwave oven are higher (Table 4) [24].…”

“…This approach does not include interactions between the independent parameters of the process. However, the use of the response surface methodology (RSM) approach, which is a multidimensional system, allows us to examine and optimise the interactions between the factors of the process by implementing a statistical technique, as shown in our previous paper [24].…”

Kinetics investigation of alumina ceramics corrosion in nitric acid

“…Density of sintered samples was determined using the Archimedes method (Mettler Toledo GmbH, Switzerland, density kit MS-DNY-43) according to the ASTM C373-88. The measured bulk density was 3.864 ± 0.018 g cm −3 , while the total porosity was 3.1 ± 0.5% [15].…”

“…Properties of sintered alumina samples may be found at our previous manuscript [15]. Density of sintered samples was determined using the Archimedes method (Mettler Toledo GmbH, Switzerland, density kit MS-DNY-43) according to the ASTM C373-88.…”