【作者】 屈献永；

【导师】 张俊善；

【作者基本信息】 大连理工大学 ， 材料学， 2006， 硕士

【摘要】 使用后的核燃料—乏燃料的锂化还原技术是能够有效地减少乏燃料的体积和辐射性的一种新技术,便于其存储和管理。但是在乏燃料的处理过程中,结构材料受到熔融LiCl-Li₂O严重的腐蚀,从而阻碍了这种新技术的工业化的应用。本文采用浸没法模拟材料在乏燃料处理过程中的服役条件,利用X射线衍射（XRD）、金相、带能谱的扫描电镜（SEM/EDAX）、电子探针（EPMA）等手段研究了纯金属铁、40Cr、两种不锈钢、TiAl基金属间化合物、纯金属钛及纯钛渗氮后在熔融LiCl-Li₂O中的腐蚀行为,探讨了金属在熔盐中的腐蚀机制,为乏燃料锂化还原处理技术所需的结构材料的选材和防护金属涂层提供有益的研究结果和实验数据。 纯铁和40Cr在750℃下,熔融LiCl-10%Li₂O腐蚀后生成了相同的腐蚀产物LiFeO₂,二者的腐蚀减重均随时间的延长而增大,且40Cr的腐蚀失重略低于纯铁。奥氏体在熔融LiCl-10%Li₂O中的耐蚀性能优于铁素体,但是差别不大。 316L的腐蚀产物为Fe的含锂氧化物（LiFeO₂和LiFe₅O₈）和Cr的氧化物（Cr₂O₃和LiCrO₂）。1Cr17的腐蚀层分为三层,分别为LiFeO₂（外层）,LiFeO₂、LiCrO₂（中间层）,Cr₂O₃（内层）。1Cr17比316L在相同条件下腐蚀更为严重。这和两种不锈钢的成分和组织有关系。1Cr17为单一的铁素体组织,316L为单一的奥氏体组织:316L中的Ni和Mo元素的添入提高了其抗腐蚀性能。 Ti₃Al腐蚀后生成了双层腐蚀膜,外层为LiAlO₂和Al₂O₃,内层为Li₂TiO₃和TiO₂;TiAl-5Nb腐蚀后也生成了双层腐蚀膜,外层为LiAlO₂,内层为Li₂TiO₃和TiO₂。腐蚀初期的加速腐蚀归因于LiAlO₂的快速生长;而腐蚀后期较慢的腐蚀速率是由于Ti的氧化物（Li₂TiO₃和TiO₂）构成的内层具有较好的抗腐蚀性能。Nb的加入阻碍了Ti的向外扩散,对TiAl-5Nb的抗熔盐腐蚀起了一定的作用。 纯钛在熔盐中首先发生了Ti的氧化生成TiO₂,而后转化成Li₂TiO₃。形成的Li₂TiO₃由于致密、平整,阻碍了氧和O^2-向基体扩散,所以腐蚀速率在后期有所减慢。采用气体渗氮法在900℃对纯Ti进行了10h的表面渗氮处理,在纯钛表面制备了30～70μm致密、连续的Ti-N化合物（TiN和Ti₂N）渗层。在空气中650℃下,采用浸没法研究了渗氮层对纯钛在熔融LiCl-Li₂O中腐蚀行为的影响。结果表明,渗氮层改善了纯钛在熔融LiCl-Li₂O中的抗腐蚀性能,这归因于渗氮层有效阻碍了氧和O^2-向基体内部的扩散。更多还原

【Abstract】 A lithium reduction technique has been developed as an effective method for reducing the volume and radiation of the spent nuclear fuel, which can benefit to the disposal and management of the spent nuclear fuel. In this process, structural materials used in the technique undertake serious corrosion in molten LiCl-Li₂O, which delayed the application of the new technique. To date, there have been few studies on the corrosion behavior of materials in molten LiCl-Li₂O. In this paper, immersion experiments are used to simulate service environment of structural material in the lithium reduction process. X-ray Diffraction （XRD）, Optical Microscopy （OM）, Scanning Electron Microscopy with coupled with X-ray Microanalysis （SEM/EDAX）, and Electron Probe Microanalysis （EPMA） are used to investigate the corrosion behaviors of pure Fe, 40Cr, 316L, 1Cr17, Ti₃Al, TiAl-5Nb, pure Ti and nitrided Ti in molten LiCl-Li₂O. It primarily discusses the corrosion mechanism and provides useful results and testing data for selecting materials and protective coatings under these conditions.The corrosion products of pure Fe and 40Cr steel at 750℃ in molten LiCl-10wt%Li₂O both are LiFeO₂. The weight losses of the two materials both increase with the increasing of time, and the weight loss of 40Cr steel is slight lower than that of pure Fe. Under these experimental conditions, the corrosion resistance of austenite is better than that of ferrite, and the process of the corrosion in the melt is dominated by chemical corrosion.The two stainless steels are all corroded severely. The products of 316L are iron oxides （LiFeO₂ and LiFe₅O₈） and chromium oxides （Cr₂O₃ and LiCrO₂）. The products of 1Cr17 form three layers: LiFeO₂ （out layer）, LiFeO₂ and LiCrO₂ （middle layer）, Cr₂O₃ （inner layer）. The weight loss of 1Cr17 is higher than that of 316L because of the difference of composition and structure between the two stainless steels. The corrosion resistance of austenitic is better than ferrite; Ni and Mo can improve the resistance of corrosion.The products of Ti₃Al show a bilayered structure: the thicker outer layer is composed of aluminum oxides （LiAlO₂, Al₂O₃）, whereas the thinner inner layer is a compact titanium oxides （Li₂TiO₃, TiO₂） layer. The products of TiAl-5Nb also show a bilayered structure: the thicker outer layer is composed of grains of LiAlO₂, whereas the thinner inner layer is a compact titanium oxide-rich （Li₂TiO₃, TiO₂） layer. The fast corrosion at the beginning of corrosion is due to the fast growth of LiAlO₂, and the slower corrosion rate at the latter stageof corrosion is owing to the formation of protective inner layer of titanium oxides. Nb can improve the resistance of corrosion.Ti corrodes in the melt, forming layer of TiCh, which converted to I^TiCh. Because Li2TiC>3 is dense and continuous, which sets back the diffusion of O2" to the substrate, the corrosion rate becomes slow later. The bond strength of corrosion product and substrate being lower than that of product itself, the products separate from the substrate when the sample is carried out of the melt. The gas nitriding process has been used to treat pure titanium at a nitriding temperature of 900 °C for lOh. A dense and continuous nitrided layer 30⁷0/xm is obtained on pure titanium. Corrosion behavior of the nitrided layer has been investigated in molten LiCl-3%Li2O at 650°C under air. The nitrided layer effectively blocks the diffusion of O2’, which improves the corrosion resistance of pure titanium in molten更多还原