Corrosion Resistance in Supercritical Water

Supercritical fluid, especially supercritical water (SCW), that is above the thermodynamic critical point of water (374 C, 22.1 MPa), has attracted increasing attention in various applications, such as in supercritical water oxidation (SC WO), in supercritical water gasification (SCWG), and for the continuous synthesis of nanoparticles. The environment of reactors presents a big challenge for structural materials used in the components. Many kinds of materials including stainless steel, alloys, and ceramics have been studied for using in SCW atmosphere. However, the details of the corrosion mechanism of each ceramic in an SCW environment were not fully clarified. 

It has been reported that SigN corrodes in SCW by the following reactions [26, 27] 

In addition, due to Masahiro Nagae, on the basis of the composition of SiAlON, the crystalline corrosion products were identified as hydrates of the Si02-AI2O3 system, such as kaolinite (Al2Si205(0H)4). 

In our study, according to the results obtained now, we deem that the SiAlON ceramics should be basically corroded by a similar reaction with SijN in SCW. 

The aforementioned XRD results indicate that the main solid oxidation products are Al2SiOg for P-SiAlONs. Therefore, we propose the following oxidation reaction equations  

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R.J. Morin, Ceramics for Corrosion Resistance in Supercritical Water Environments, Thesis, University of Texas USA, (1993). 

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