NiFe2O4/Nano-TiN陶瓷基惰性阳极微结构分形特征及热应力研究

NiFe2O4-based inert anodes can help to decrease the emission of greenhouse gas, fluorocarbons and asphalt fumes and alleviate the present environmental load. However, high brittleness and unsatisfactory thermal shock resistance are still the obstacles, limiting the practical application of NiFe2O4-based composite anodes. Thus, basic research about morphology characteristics of structure after thermal shock, temperature distribution characters and evolution mechanism of thermal stress at the micro-scale level needs to be carried out necessarily. After studying on the sintering behavior of preparing NiFe2O4/Nano-TiN based ceramic anodes, the synthesis mechanism of the ceramic composite anodes will be revealed. Through the fractal characterization of microstructure after thermal shock and fractal dimensional calculation of cracks and fracture surface with Box-counting method, the quantitative relationship between the fractal dimension and thermal shock critical temperature difference, statistical residual strength of the composite anode will be established. Through simulation of heat transfer behavior for NiFe2O4/Nano-TiN based anode structure with extended finite element, the temperature field cloud chart of anode structure will be obtained. Besides, through modeling study on the structure thermal stress, establishing model of the mechanical structure, calculation of thermal stress and deformation, characteristics of thermal stress and strain distribution will be clarified. This will provide theoretical basis and technical support for manufacturing large-sized NiFe2O4 ceramic anodes with better thermal shock resistance, which will contribute to sustainable development of aluminum electrolysis industry.

NiFe2O4陶瓷基惰性阳极有助于减少温室气体、碳氟化合物和沥青烟气的排放，减轻当前环境负荷。但其脆性高、抗热震性差等问题限制了它的实际应用。因此，从微观尺度出发，针对该材料热冲击后结构的形貌特征、阳极高温服役环境下温度场分布特征和热应力演变机制开展研究十分必要。本项目对合成NiFe2O4/Nano-TiN陶瓷基惰性阳极的烧结行为进行研究，揭示阳极材料的合成机制。利用分形法对阳极微结构进行刻画，采用盒计维数法计算阳极裂纹及断口形貌的分形维数，建立分形维数与热冲击临界温差和剩余强度间的定量关系。通过扩展有限元模拟NiFe2O4/Nano-TiN阳极结构的传热行为，建立温度分布云图。对阳极结构热应力进行模拟，建立力学结构模型，计算阳极结构的热应力和热变形，阐明阳极热应力场和应变分布特征，为实现大尺寸、抗热震NiFe2O4陶瓷基惰性阳极的制备提供理论依据和技术支持，助力于铝电解工业的可持续发展。

本研究采用固相烧结法制备了NiFe2O4/Nano-TiN阳极材料，对烧结过程和热冲击后的微结构进行了系统研究，确定了合成机制，明确了热冲击微结构的分形维数，建立了阳极结构温度分布云图，阐明了阳极热应力场分布特征。.空气气氛条件下所制样品以沿晶断裂为主，氩气和氮气气氛下所制样品断裂模式包括：沿晶断裂和穿晶断裂。添加TiN可以加速晶粒生长，提高试样密度，降低试样气孔率。适当提高烧结温度和延长烧结时间可促进晶粒生长，改善材料结构和性能。优化工艺参数后，发现1300℃下烧结4h所制样品的平均抗弯强度为80.2MPa，960℃时的电导率可达9.80 S·cm-1。添加TiN后，体系初期烧结机制从晶界扩散转变为体积扩散，表观烧结活化能出现了降低。.等温烧结过程中，晶粒生长指数均随温度升高而减小。添加1.0wt%TiN后，平均晶粒生长动力学指数从2.607增加到3.088。晶粒生长主要是依赖晶界扩散和体积扩散生长机制，晶粒生长活化能随烧结温度上升而整体呈下降趋势。.水淬热冲击实验结果表明，随着试样表面裂纹的产生，其弯曲强度迅速衰减。利用盒计维数法计算了陶瓷材料表面裂纹分形维数，发现当水淬温度超过一定温度后，陶瓷表面裂纹分形维数增大，强度迅速衰减，裂纹分形维数增大会降低材料热冲击后剩余强度。.基于经典抗热冲击临界温差模型，建立了裂纹分形维数与热冲击临界温差之间的关系。结果表明，临界温差分形模型与经典模型的比值，只与材料中初始裂纹分形维数等几何特征相关，与材料性能参数无关。基于脆性固体统计强度分形理论，建立了热冲击后统计剩余强度分形模型，给出了热冲击前后材料的强度衰减比。结果表明，强度衰减比与裂纹数量及裂纹分形维数相关。.利用ABAQUS传热分析模块，针对未浸入电解质中的阳极上部结构进行了分析，根据模型传热分布云图可知，温度呈梯度分布。通过数值模拟，理想结构模型(不含初始裂纹和孔洞)在受到较极端热冲击载荷后，在其接触高温的端部产生集中应力现象。.本研究可为实现大尺寸、抗热震NiFe2O4陶瓷基惰性阳极的制备提供一定的理论依据和技术支持。