稀土掺杂方镁石-尖晶石耐火材料晶界相重构机理及高温行为

Magnesia-spinel composite refractory is widely used in metallurgy, building materials and other high temperature process industry. However, the problems of such as low high-temperature strength and poor performance of slag erosion resistance have existed for a long time. This is because of the thermal mismatch grain boundary in the materials and the relatively low melting point of grain boundary phase. The basis to solve this problem is the reconstruction of the grain boundary phase. The previous study of our project team indicated that different kinds of rare earth oxides introduced have obviously different effects on the composition of grain boundary phase and properties due to the different ionic radius and reactivity. The construction of grain boundary phase with low expansion coefficient and high melting point are expected to effectively solve the prominent problems of poorer high-temperature performance. In this project, the reconstruction law of rare earth oxides with different features on the composition and structure of grain boundary phase in the materials will be the further studied. The control mechanism of the formation of rare earth doped grain boundary phase and the occurrence state of rare earth ions in the grain boundary to the microstructures of the materials will be clarified. The correlations among the “grain boundary phase, microstructure and high-temperature properties” in the rare earth doped magnesia-spinel composite refractory will be established. The new method of reconstructing grain boundary phase through rare earth doping put forward in this project will provide theoretical basis for the design and control theories of refractory microstructure. This is beneficial to achieve basic refractory with high performance.

冶金、建材等高温过程工业广泛应用的方镁石-尖晶石耐火材料因材料内部晶界热失配及晶界相的熔点相对较低，导致高温强度和抗熔渣侵蚀性差的问题长期存在，对材料的晶界相进行重构是有效解决问题的基础。项目组前期工作发现，引入不同种类的稀土氧化物因离子半径和反应活性等不同，对材料的晶界相组成及性能的影响差别很大。重构低膨胀系数、高熔点晶界相可望有效解决此类材料高温性能较差的突出问题。项目拟深入研究不同性状的稀土氧化物对材料晶界相组成与结构的重构规律，阐明稀土掺杂晶界相形成及稀土离子在晶界相中赋存状态对材料显微结构的调控机理，建立稀土掺杂方镁石-尖晶石耐火材料中“晶界相、微结构与高温性能”的关联。项目提出稀土掺杂重构晶界相的新方法将为耐火材料微结构设计与调控提供理论依据，以实现碱性耐火材料的高性能化。

方镁石-尖晶石耐火材料因抵抗碱蒸气、氧化-还原气氛变化的能力强，是碱性耐火材料无铬化的首选材料。但方镁石-尖晶石耐火材料高温热态强度低、抗高温熔渣侵蚀性能较差等问题限制了其在相关高温领域的推广应用。本项目基于方镁石-尖晶石耐火材料晶界相结构特征，引入半径、反应活性不同的稀土离子，调控晶界相组成，重构低膨胀系数、高熔点晶界相，解决方镁石-尖晶石耐火材料高温性能差的问题。不同特性稀土氧化物在方镁石-尖晶石耐火材料中的掺杂，原位形成了结构、形貌、性质不同的系列高熔点晶界相（晶界互锁的YAG相、板片状LMA相或稀土硅酸盐相），经过重构的稀土掺杂晶界相及赋存特征对材料显微结构的形成与致密化过程具有重要的调控作用。稀土掺杂晶界相的原位形成，改善了主晶相界面结合，提高了材料的断裂韧性和抗热损伤能力，弹性模量提高30%以上，1400℃断裂能提高1.10~3.03倍，高温压缩蠕变率降低至0.08%以下；在调节孔隙结构的同时，稀土掺杂晶界相对尖晶石晶粒构成了原位包裹，调控了材料与熔渣的润湿性，显著提高了材料抗高温熔渣、碱蒸气等介质侵蚀的能力。项目在摸清了稀土掺杂晶界相形成及稀土离子赋存状态对材料显微结构与高温性能调控规律的基础上，建立了稀土掺杂方镁石-尖晶石耐火材料中“晶界相、显微结构、高温性能”的关联。项目研究成果对于方镁石-尖晶石质耐火材料及相关材料体系的显微结构设计与高温性能优化，以及拓展我国稀土矿产资源利用，具有重要的理论参考价值。