两种陶瓷材料高温结构的原位X射线衍射研究

发布时间：2018-03-16 03:00

  本文选题：原位X射线衍射　切入点：锰氧化物Sr_7Mn_4MO_(15)　出处：《南京大学》2017年硕士论文　论文类型：学位论文

【摘要】：X射线衍射技术是材料科学研究中重要的一种手段,广泛地应用于材料的结构表征。由于原位的测量过程可以提供更多更全面的信息,原位X射线衍射可以更准确地获得材料结构对外加环境的响应过程,为材料的应用奠定更加可靠的研究基础,因此广泛应用于材料结构表征中。论文研究了具有4层RP结构(n=4)锰氧化物和SiC两种功能陶瓷材料的高温结构演变与相关的相变过程,取得了一些创新性结果:1、从锰氧化物Sr7MnO15高温下原位结构变化解释了相应的热敏特性。结果表明,Sr7Mn4O15陶瓷结构单元(晶胞)晶格参数随温度升高线性增大;在Sr7Mn4O15单胞内部,共面的八面体单元发生横向膨胀,而共点的八面体单元则是在轴线上发生拉伸,而Sr原子的位置也随着温度的升高产生一个有序性的调整。高温下输运测量表明该陶瓷材料电阻值(lnR)与温度(1000/T)出现一个非常完美的线性变化过程,并拟合得到一个非常大的热敏因子B=13050K;第一性原理计算结果显示Sr7Mn4O15陶瓷其带隙结构随温度的升高从1.141eV降低到0.349eV;内耗相关的实验充分证明Sr7Mn4O15陶瓷材料结构具有高度稳定性。2、获得Al2O3-Y2O3助剂作用下SiC陶瓷高温液相烧结机制。研究表明:Al2O3-Y2O3在制备SiC过程中起助剂的作用。论文通过原位XRD研究,系统的讨论了整个陶瓷烧结过程中的相变过程。在1400℃以下原料并不发生反应,Al2O3-Y2O3体系主要生成Y4Al2O9(YAM)和YAlO3(YAP)作为烧结助剂,该过程发生在1500℃以上,但并未反应生成Y3Al5O105(YAG)。当烧结助剂含量足够多的时候,SiC液相烧结过程也将更加明显,SiC颗粒之间将出现明显的熔合重结晶过程,并伴随着Si02高温相的结晶析出。SEM的形貌研究则给出了实验组中最优的助剂含量体系,即10wt%(3#试样)。基于相关物相和形貌的研究,我们讨论了 Al2O3-Y2O3助剂作用下SiC陶瓷高温液相烧结的机理。主要包括两个阶段:阶段一,在1500℃以上,助剂体系发生化合反应,并且进入液相促进SiC颗粒的重排列;阶段二,SiC烧结的核心阶段发生在1600℃以上,在这个阶段,SiC颗粒之间发生熔合重结晶过程,并伴随这SiC特征峰择优趋向的发生和SiO2结晶析出。
[Abstract]:X-ray diffraction (XRD) is an important method in material science. It is widely used to characterize the structure of materials. Because the in-situ measurement process can provide more and more comprehensive information, In situ X-ray diffraction can obtain the response process of the material structure to the external environment more accurately and lay a more reliable research foundation for the application of the material. Therefore, it is widely used in structural characterization of materials. In this paper, the evolution of high temperature structure and the related phase transition processes of two functional ceramics with four layers of RP structure, manganese oxide and SiC, have been studied in this paper. Some innovative results have been obtained: 1, which explain the corresponding thermosensitive properties from the in-situ structural changes of manganese oxide Sr7MnO15 at high temperature. The results show that the lattice parameters of Sr7Mn4O15 ceramic structural units increase linearly with the increase of temperature, and the lattice parameters increase linearly in the Sr7Mn4O15 cells. The coplanar octahedron element expands laterally, while the co-point octahedral element is stretched on the axis. And the position of Sr atoms is adjusted with the increase of temperature. The transport measurement at high temperature shows that the resistance of the ceramic material has a very perfect linear variation process with the temperature of 1000 / T. The results of first-principle calculation show that the band gap structure of Sr7Mn4O15 ceramics decreases from 1.141eV to 0.349eV with the increase of temperature, and the experiments related to internal friction fully prove that the structure of Sr7Mn4O15 ceramics is highly stable. The mechanism of high temperature liquid phase sintering of SiC ceramics under the action of Al2O3-Y2O3 promoter was obtained qualitatively. The results show that Al 2O 3-Y 2O 3 acts as promoter in the preparation of SiC. The phase transformation process in the whole sintering process of ceramics is systematically discussed. The system of Al _ 2O _ 3-Y _ 2O _ 3 does not react under 1400 鈩，

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