| Dy2O3/MgO对304不锈钢高温氧化性能与K3合金钒腐蚀性能的影响 | |
| Alternative Title | Effect of Dy2O3 and MgO on high temperature oxidaton of type 304 stainless steel and on the Na2SO4-V2O5-induced hot corrosion of nickel-based K3 alloy |
| 宋篪 | |
| Subtype | 硕士 |
| Thesis Advisor | 曾潮流 |
| 2007-06-09 | |
| Degree Grantor | 中国科学院金属研究所 |
| Place of Conferral | 金属研究所 |
| Degree Discipline | 材料学 |
| Keyword | 304不锈钢 K3合金 高温氧化 钒腐蚀 电化学阻抗 |
| Abstract | MgO作为碱土金属氧化物，化学性质稳定，对热腐蚀，尤其是钒腐蚀（灰份腐蚀）有明显的抑制作用。稀土元素Dy及其氧化物可以明显提高合金的抗腐蚀性能。本文分别探讨了MgO和Dy2O3对304不锈钢氧化行为及对镍基K3合金K3的熔融Na2SO4-V2O5腐蚀行为的影响。 采用溶胶凝胶法在304不锈钢表面分别制备了MgO，Dy2O3，及 MgO+15% Dy2O3复合薄膜。采用热重法（TGA），并结合X-射线衍射仪（XRD），带有能谱的扫描电子显微镜（SEM/EDX）等分析测试手段，研究了氧化物薄膜对304不锈钢在900℃空气环境中的氧化行为的影响。结果表明：MgO和Dy2O3起到了活性元素的作用，明显的降低了合金的氧化速度。促进了保护性富Cr氧化膜的形成，并提高了氧化膜的粘附性。Dy2O3改善合金抗氧化性能的作用优于MgO。 电化学阻抗技术是研究腐蚀机制与腐蚀动力学过程的有效手段，并且通过测量可以获得反映腐蚀过程的许多信息。本文采用双电极体系，应用电化学阻抗技术对比研究了Dy2O3和MgO添加剂对镍基K3合金在800℃熔融0.4 Na2SO4-0.6V2O5（摩尔分数）中的腐蚀行为的影响。结果表明：在Na2SO4-V2O5环境中，合金遭受快速腐蚀，形成无保护性氧化膜，其腐蚀电化学阻抗谱呈Warburg阻抗特征，合金腐蚀受氧化剂扩散控制；想沉积盐中分别加入10和20wt%MgO或Dy2O3能显著抑制合金的腐蚀，但其作用机制不同。MgO能与V2O5反应形成高熔点的Mg3V2O8，但同时也能与Na2SO4反应形成低熔点的Na6Mg(SO4)4，这使得合金表面沉积盐难以清除，合金腐蚀仍受氧化剂扩散控制；而Dy2O3仅与V2O5反应形成高熔点DyVO4，使得参与灰份疏松，极易清除。同时，Dy2O3也促进了更具保护性的富Cr，Al氧化膜的形成，合金腐蚀电化学阻抗谱由双容抗弧组成。Dy2O3具有比MgO更好的缓蚀作用。 |
| Other Abstract | MgO as an alkaline earth oxide with high chemical stability can inhibit significantly got corrosion, especially vanadate-induced corrosion of alloys. It is shown that rare earth element Dy and its oxide can greatly improve the corrosion resistance of alloy. This paper presents comparative investigations of the effect of Dy2O3 and MgO on the air oxidation of type 304 stainless steel and on the Na2SO4-V2O5 induced hot corrosion of nickel based alloy K3. Sol-Gel method was employed to prepare MgO, Dy2O3 and MgO-15%Dy2O3 oxide films on 304 stainless steel, and the effect of the oxide films on the oxidation of the alloy at 900℃ in the air was examined by thermogravimetry (TGA), X-ray diffraction (XRD) and scanning electron microscopy equipped with an energy dispersive X-ray analyzer (SEM/EDX). Experimental results indicated that MgO and Dy2O3 films decreased greatly the oxidation rate of the alloy by promoting the formation of a Cr2O3-rich scale and improving the adhesion of the oxide scale, with a better effectiveness for the Dy2O3 film. Electrochemical impedance spectroscopy is a technique which has proved effective in understanding reaction mechanisms and kinetics, and by which more information for corrosion processes may bi obtained. In this paper, two-electrode system was established to study the effect of Dy2O3 and MgO additives on the hot corrosion behavior of nickel-based alloy K3 in molten 0.4Na2SO4-0.6V2O5 (in mole fracton) at 800℃. Experimental results indicated that K3 suffered from fast corrosion in Na2SO4-0.6V2O5 environment, forming a porous scale. Correspondingly, electrochemical impedance spectra for the corrosion of K3 exhibited the typical features of a diffusion-ontroled reaction. The addition of 10 and 20wt% Dy2O3 or MgO to Na2SO4-0.6V2O5 could decrease greatly the corrosion rate of K3, but with different inhibiting effect. MgO could react with V2O5 to form Mg3V2O8 with a high melting point. However, the formation of liquid Na6Mg(SO4)4 was also observed. The liquid phases can act as binders between the ash particles, and give rise to compaction of the salt deposits. The corrosion of the alloy was still controlled by the diffusion of oxidation through the salt layer. In contrast to MgO, Dy2O3 additive could just react with V2O5 to form refractory DyVO4, leading to the formation of a porous, friable deposit, which can be removed easily. Moreover, the Dy2O3 additive could promote the formation of a protective Cr and Al enriched oxide layer. As a result, electrochemical impedance spectra for the corrosion in the presence of Dy2O3 were composed of double capacitive loops. Conclusively, Dy2O3 exhibits better inhibiting effectiveness than MgO. |
| Pages | 64 |
| Language | 中文 |
| Document Type | 学位论文 |
| Identifier | http://ir.imr.ac.cn/handle/321006/17092 |
| Collection | 中国科学院金属研究所 |
| Recommended Citation GB/T 7714 | 宋篪. Dy2O3/MgO对304不锈钢高温氧化性能与K3合金钒腐蚀性能的影响[D]. 金属研究所. 中国科学院金属研究所,2007. |
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