NiFe2O4-10NiO基金属陶瓷惰性阳极表面致密层的动态腐蚀平衡与高电导的协同统一

It is difficult to realize large-scale industrilalization for aluminum electrolysis, if issues about how to realize the collaborative unity of dynamic corrosion balance (dynamic corrosion balance between the formation of dense layer in the interior of anode and the corrosion of dense layer on the surface of anode) and high electric conductivity of dense layer on the surface of cermet inert anodes are not solved properly. In this work, NiFe2O4-10NiO based cermet will be selected as the research object, and at the same time Yb of Yb2O3 doped will be chosen as the tracer element. In the perspective of grain boundary chemistry, the grain boundary composition variation of dense layer on the surface of anodes and the effect of electrolysis parameters on the corrosion behavor of grain boundary will be investigated through the micro-quantitative electron probe. Moreover, the relationship between the grain boundary composition of cermets and the corrosion evolution behavior of dense layer will be clarified, while the connection between the compositon of dense layer on the surface of anode and the elemental valence change, especially the connection between the grain boundary composition and electric conductivity will be illustrated, which can deduce the electric conductivity evolution law of dense layer. At last, the steady corrosion environment of anodes will be established so that the dynamic corrosion balance of dense layer on the surface of anode will be achieved, which can realize the collaborative unity between dynamic corrosion balance and high electric conductivity of dense layer on the surface of anodes, and a reference will be supplied for the ceramic design used in the electrolysis of high temperature molten salt electrolyte.

如何实现金属陶瓷惰性阳极表面致密层的动态腐蚀平衡(内部形成致密层和表面致密层腐蚀之间的动态平衡)与高电导的协同统一是阳极能否大规模工业化的难点。本课题选择NiFe2O4-10NiO基金属陶瓷为研究对象，以掺杂Yb2O3中的Yb为示踪元素，以晶界化学的角度通过电子探针微区定量分析考察阳极表面致密层晶界成分变化，掌握电解工艺参数对其晶界腐蚀行为的影响，获得金属陶瓷晶界成分与阳极致密层腐蚀演变行为之间的关系；研究致密外层成分与元素价态变化，特别是晶界成分与电导率变化之间的关系，阐明阳极致密层电导率演变规律；建立阳极稳态腐蚀环境，获得阳极表面致密层的动态腐蚀平衡，最终实现动态腐蚀平衡与高电导的协同统一，为应用于高温熔盐电解方面的陶瓷设计提供理论参考。

本课题选择NiFe2O4-10NiO基金属陶瓷为研究对象，以掺杂Yb2O3中的Yb为示踪元素，掌握电解工艺参数对其晶界腐蚀行为的影响，获得金属陶瓷晶界成分与阳极致密层腐蚀演变行为之间的关系；研究致密外层成分与元素价态变化，特别是晶界成分与电导率变化之间的关系，阐明阳极致密层电导率演变规律；建立阳极稳态腐蚀环境，获得阳极表面致密层的动态腐蚀平衡。得出如下结论：.1）热力学计算生成NiAl2O4和FeAl2O4反应的可能性都较大，阳极组元氧化物与AlF3的反应仍然具有发生反应的可能性并且Fe、Ni和Cu的各种氧化物与铝可能发生置换反应。. 2）NiFe2O4陶瓷、NiFe2O4-NiO陶瓷和NiFe2O4基金属陶瓷表层均形成了约200 um的致密层，且该层内的金属相均已消失，Fe/Ni原子比都非常接近于NiFe2O4陶瓷中的理论值2；致密层中均有少量的Al元素存在，且Al元素的含量从阳极表面向内呈递减趋势。. 3）不同金属相含量的NiFe2O4基金属陶瓷电解后阳极表面均形成了陶瓷致密层，但随着材料成分中金属相含量的增加致密层的孔洞有逐渐增多的趋势，表明金属相含量的增加并不利于NiFe2O4基金属陶瓷惰性阳极表面尖晶石陶瓷致密层的形成。.4）金属陶瓷阳极表面形成致密陶瓷层NiFe2O4-NiAl2O4-FeAl2O4，.5)电解过程中阳极表面致密层逐渐形成且其成分为NiFe2O4-NiAl2O4-FeAl2O4，晶界是氧化物主要的聚集地，而且各元素在晶界处存在元素含量变化的缓冲带，Al元素主要聚集在晶界处形成NiAl2O4和FeAl2O4。.6)首次引入Yb2O3作为NiFe2O4-10NiO基金属陶瓷晶界强化剂，提高了该材料晶界的耐蚀性能。晶界强化剂Yb2O3与NiFe2O4反应生成倾向于陶瓷晶界分布的YbFeO3相，同时消除了晶界气孔。陶瓷相晶界结构的强化有效抑制了电解过程金属相的流失和电解质熔体的渗透。.7）从不同组元的XRD和拉曼光谱中看到电解质中存在多种离子结构，可能产生Me-F、Me-O-F或是Me-Al-O-F的离子结构（Me对应Ni、Fe、Cu）。.8）高温拉曼光谱中也没有看到Me-F、Me-O-F等相应的离子结构，说明阳极组元Me-Al-O-F的离子结构。Fe、Ni、Cu也会部分取代铝氧氟离子中的Al，形成MexAlaOyFz(z+2y-