Corrosion penetration monitoring of advanced ceramics in hot aqueous fluids

Abstract

Advanced ceramics are considered as components in energy related systems, because they are known to be strong, wear and corrosion resistant in many environments, even at temperatures well exceeding 1000 °C. However, the presence of additives or impurities in important ceramics, for example those based on Silicon Nitride (Si3N4) or Al2O3 makes them vulnerable to the corrosion by hot aqueous fluids. The temperatures in this type of corrosion range from several tens of centigrade to hydrothermal conditions above 100 °C. The corrosion processes in such media depend on both pH and temperature and include often partial leaching of the ceramics, which cannot be monitored easily by classical gravimetric or electrochemical methods. Successful corrosion penetration depth monitoring by polarized reflected light optical microscopy (color changes), Micro Raman Spectroscopy (luminescence changes) and SEM (porosity changes) will be outlined. The corrosion process and its kinetics are monitored best by microanalysis of cross sections, Raman spectroscopy and eluate chemistry changes in addition to mass changes. Direct cross-calibrations between corrosion penetration and mechanical strength is only possible for severe corrosion. The methods outlined should be applicable to any ceramics corrosion process with partial leaching by fluids, melts or slags

Effect of Al dopant on the hydrothermal oxidation behavior of Ti3SiC2 powders

“…The observed up-shift of the D band indicates that the bond-angle disorder of carbon is decreased with temperatures and treatment time. 1 Little carbon is produced after hydrothermal treatment of Ti 3 SiC 2 at 500 • C for 24 h (Fig. 6); however, amounts of carbon present for Ti 3 Si 0.9 Al 0.1 C 2 at the similar conditions.…”

“…5). After hydrothermal oxidation, the Raman spectra clearly show strong bands of the graphite band (G) and the disordered/nanocrystalline carbon band (D), [1][2][3][4][5] which give evidence of carbon formation. The amounts of asformed carbon, however, remarkably decrease with treating time (Fig.…”

“…At the first stage, Ti 3 Si 0.9 Al 0.1 C 2 reacts with H 2 O to produce TiO 2 , SiO 2 , Al 2 SiO 5 and carbon. For an exact balance with a complete transformation to the oxides the corresponding reactions are Ti 3 Si 0.9 Al 0.1 C 2 + 7.95H 2 O = 3TiO 2 + 0.85SiO 2 + 0.05Al 2 SiO 5 + 2C + 7.95H 2 (1) and Ti 3 Si 0.9 Al 0.1 C 2 + 7.95H 2 O = 3TiO 2 + 0.85SiO 2 + 0.05Al 2 SiO 5 + C + CH 4 + 5.95H 2 (2) Afterwards the formed carbon is consumed through reacting with water (Fig. 5(e) and (f)).…”

“…But this is not really true under hydrothermal conditions. 1 Attack of aggressive aqueous media can deteriorate ceramics even at 150 • C. 1 Under supercritical conditions, water is a corrosion medium and dangerous to advanced ceramics, because it can dissolve formed oxides during hydrothermal oxidation. Since advanced ceramics have been attracting great attention in energy related systems, where high-temperature and highpressure water is usually involved, the hydrothermal oxidation behavior of silicon carbide, 2-7 silicon nitride [8][9][10] and alumina 11 has been investigated.…”

Microbial corrosion of silicon nitride ceramics by sulphuric acid producing bacteria Acidithiobacillus ferrooxidans

“…Concerning the latter applications, numerous works have revealed that sintered silicon nitride is susceptible to corrosion by acids, bases, saline solutions and hydrothermal treatments. [3][4][5][6][7][8][9][10][11][12] Only a few studies report corrosive attacks of the silicon nitride grains. [3][4][5]13 The common feature is the attack of the GBP 1,3,4,6,11,12,14,15 with an extent depending on various parameters such as pH, temperature, composition and concentration of acids or bases in the corrosive medium.…”