| Chlorine containing environments are widely encountered in energy conversion,chemical and metallurgical industries,e.g.in coal fired boilers,waste incinerators and polymer decomposition mills.The most severe corrosion problems in biomass-fired systems are expected to occur due to the presence of considerable amounts of alkali chlorides,HCl(g)and Cl-rich deposits in the flue gas originated from the combustion of biomass and waste fuels.At present,in addition to a thorough study of the chlorination of some pure metals,most of the understanding of chlorination corrosion is due to the corrosion behavior of current service materials.The porous Ni-Cr-Fe and Ni-Cr-Si materials were prepared by reactive element powder synthesis method,which used the principle of partial diffusion in solid phase sintering in this paper.The high-temperature chlorination corrosion of the materials was investigated in the presence of chlorine-containing environments using homemade equipment for producing chlorine.The corrosion behaviors of the materials were investigated as well as beneath by KCl deposits.Scanning electron microscopy(SEM),energy dispersive spectroscopy(EDX)and X-ray diffraction(XRD)were used to analyze the corrosion products.It provided two new types of chlorine-resistant corrosive porous material strengthened the basic research on the mechanism of chlorinating corrosion,and enriched the chlorinated-corrosion data.KCl caused accelerated corrosion,but the porous Ni-Cr-Fe and Ni-Cr-Si materials covered with KCl maintain good thermal corrosion resistance at 800 ?.The samples showed good resistance to chlorinated corrosion in chlorine-containing environments at 500?,pre-oxidation increased the resistance to high temperature chlorination corrosion of the samples,and the porous Ni-Cr-Si materials have higher resistance to high temperature chlorination corrosion than the porous Ni-Cr-Fe materials.The Ni-based porous material covered with KCI showed parabolic mass increase at 800?.After being exposed for 40 hours,the samples had similar corrosion morphology,characterized by a two-layered oxide with a total thickness of approximately 10?m,depending on the selective oxidation of the elements.For the porous Ni-Cr-Fe materials,the outward growing oxide layer is mainly composed of a spinel oxide containing iron,chromium and nickel(NiFe2O4 and NiCr2O4),the oxide layer has many holes and peels away from the substrate;the inward growing part is suggested to be Cr2O3.For the Ni-Cr-Si materials,the outward growing oxide layer is mainly composed of NiO and a spinel oxide containing chromium and nickel(NiCr2O4);the inward growing part is suggested to be Cr2O3.The erosion of Cl to materials is mainly divided into three processes:the initial reaction between Cl and the metal matrix;the volatilization of metal chlorides;the reoxidation of chlorides.Cl reacts with the samples directly to generate the corresponding chloride.The metal chloride volatilized at high temperatures diffused out through the deposit to areas with higher partial pressures of O2 where they may react with O2.Due to the lower partial pressure of p(O2)necessary for the conversion of one chloride to corresponding oxide,the chloride will be converted near the metal surface.Then,the corrosion morphology is characterized by a layered corrosion interface on the sample surface.After being exposed in chlorine-containing environments at 500 ? for 30 days,the porous Ni-Cr-Fe material had a weight gain of 25.2%,and the surface corrosion products were mainly NiCl2,Cr2O3,and(Cr,Fe)2O3.The weight gain of the pre-oxidized porous Ni-Cr-Fe material was 19.1%,and the surface corrosion products were mainly NiCl2,CrCl3,Cr2O3,and(Cr,Fe)2O3.The porous Ni-Cr-Si material had a weight gain of 7.4%,and the pre-oxidized had a weight gain of 6.7%.The porous Ni-Cr-Si materials pre-oxidized or not were basically consistent in corrosion products to be NiCl2,CrCl3 and Cr2O3. |
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