1 Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China 2 School of Materials Science and Engineering, University of Science and Technology of China, Hefei 230026, China 3 State Key Laboratory of Coal-Based Low Carbon Energy, ENN Science and Technology Development Co., Ltd. Langfang 065001, China 4 Jiangsu Toland Alloy Co., Danyang 212352, China
Cite this article:
Meiqiong OU,Yang LIU,Xiangdong ZHA,Yingche MA,Leming CHENG,Kui LIU. CORROSION BEHAVIOR OF A NEW NICKEL BASE ALLOY IN SUPERCRITICAL WATERCONTAINING DIVERSE IONS. Acta Metall Sin, 2016, 52(12): 1557-1564.
The productivity of municipal sewage sludge is difficult to treat by traditional methods. Supercritical water oxidation (SCWO) is an attractive municipal sewage sludge treatment technology. However, the process of SCWO must be carried out in a reactor which will resist not only high temperature (above 374.15 ℃) and high pressure (above 22.1 MPa) conditions but also a corrosive environment. Thus, the material used in the equipment is referred to be a key factor that restricts the application of the SCWO technology. Many materials have been selected for corrosion test under corrosive environments with SCWO, including austenitic stainless steel, nickel base alloys, titanium alloys and zirconium alloys. At present, in order to treat rich phosphorous sewage sludge, a new corrosion resistant nickel base alloy X-1# alloy has been developed to apply to the reactor of SCWO process. X-1# alloy has excellent corrosion-resistance and oxidation-resistance properties in supercritical water containing PO43-, Cl- and SO42-. The corrosion behaviors of X-1# alloy exposed to 550 ℃, 23 MPa supercritical water containing PO43-, Cl- and SO42- were investigated in this research. The exposed time was 72, 159, 248, 429 and 537 h. Morphologies, microstructures and chemical composition of oxide films in X-1# alloy and deposit sediment in reaction were studied using grazing incidence XRD, XPS and SEM equipped with EDS. The XRD, EDS and XPS analysis of X-1# alloy was performed to identify the composition of oxide layers, which were identified as NiCr2O4, Cr2O3, NiO, Ni3(PO4)2, CrPO4 and Na3PO4. In addition, it was founded that continuous and uniform oxide films were formed in supercritical water. The oxide film was a duplex-layer structure, the loose outer layer was NiO, Ni(OH)2 and phosphates, including Ni3(PO4)2, CrPO4 and Na3PO4, while the compact inner layer consisted of NiCr2O4 and Cr2O3. X-1# alloy showed a high corrosion rate in the initial stage and the corrosion rate decreased obviously after exposed to 248 h, the reason of which was that the compact inner layer of oxide films had good stability and benefited to the corrosion behavior of X-1# alloy. In order to explain the corrosion behavior of X-1# alloy, the oxide films growth mechanical, metal ions and oxygen ions dissolution mechanism and phosphates precipitation mechanism will be discussed in this research.
