High Temperature Corrosion Of Metallic Materials Induced By Chloride Salts

Incineration has been adopted as an effective and hygienic method for disposal of the ever-increasing voluminous industrial and municipal solid waste in many countries. In most cases, the corrosion problems in incineration environment are rather severe due to the complex reactions between the combustion gases containing chlorine, sulfur or salt deposits of chlorides and sulfates, in these environments metallic materials usually undergo an aggressive corrosion and degrade completely before the end of the designed life. The researchers have attached importance to high-temperature chlorination corrosion which does with degradation of many incinerators for high Cl content in waste. These Chlorides include Cl2, HC1 and chloride salt deposits. Because a lot of chloride salts contained in waste generally have lower melting point and higher volatilization, incinerators have corroded by gases chlorides. However, the corrosion of materials caused by gases chloride salts has not been examined thoroughly up to date. In this paper, the high-temperature oxidation of several metal materials were investigated in the presence of gaseous ZnCl2,KCl and NaCl using homemade equipment for producing gases chlorides. The corrosion behaviors of several engineering alloys were investigated as well as beneath by KC1 deposits. Electron probe microanalysis (EPMA), scanning electron microscopy (SEM), optical microscopy (OM), energy dispersive spectroscopy (EDX), and X-ray diffraction (XRD) were used to analyze the corrosion products. It provides useful result and testing data for selecting material and protective coating under these conditions.Fe, Cr, Ni in gases ZnCl2-containing environments corroded at accelerated rate during short-term exposure( 6h). The corrosion rate usually increased markedly with increasing temperature or with increased ZnCl2 content. A layered and loose oxide scale had formed, and chlorine was always enriched at the scale/substrate interface. A mass loss was always present in the kinetic curves for the corrosion of Fe-Cr alloy at high temperature. A obviously accelerated corrosion was also observed in Fe-Cr alloy. However, the corrosion resistance of these materials would increase with an increasing Cr content though it is not highly effective. The Cr addition to the alloys showed poor corrosion resistance against such environments. The corrosion resistance of Al-containing materials was good in presence of minor amount of gaseous ZnCl2 due to the formation of protective Al2O3 oxide scales.Fe, Cr, Ni corroded at accelerated rate and formed non-protective scales in O2 with trace amount of KC1 vapor .The accelerated corrosion was attributed toan "active oxidation" process in which Cl2 was produced resulting from that KC1 vapor reacted with scale. The corrosion resistance of Fe-Cr alloy would be improved with increasing Cr content. Low melting point K2Cr2O7 was produced by KC1 reacted with scale. A certain extent the K2Cr2O7 damages the protection effect of Cr2O3. The corrosion resistance of Fe, Cr, Ni would be improved with decrease of O2 partial pressure.Fe, Cr and Ni all suffered from accelerated corrosion with increasing temperature or increasing NaCl concentration in O2 with trace amount of NaCll vapor. The excellent corrosion resistance hadn't been exhibit even Cr content was high in Fe-Cr alloy. An obviously mass loss was found in the kinetic curves of Ni-based alloy.The protective property of carbon-steels and low-alloy steels could hardly been provide, and sufficient corrosion resistance of heat-resistant steels and Ni-based alloy were also not found beneath KC1 deposits. Al-rich materials exhibited better corrosion-resistance compared to Cr-containing materials due to protective Al2O3 was formed in the process of an "active oxidation".