本文選題：原位X射線衍射　切入點：錳氧化物Sr_7Mn_4MO_(15)　出處：《南京大學(xué)》2017年碩士論文　論文類型：學(xué)位論文

【摘要】：X射線衍射技術(shù)是材料科學(xué)研究中重要的一種手段,廣泛地應(yīng)用于材料的結(jié)構(gòu)表征。由于原位的測量過程可以提供更多更全面的信息,原位X射線衍射可以更準(zhǔn)確地獲得材料結(jié)構(gòu)對外加環(huán)境的響應(yīng)過程,為材料的應(yīng)用奠定更加可靠的研究基礎(chǔ),因此廣泛應(yīng)用于材料結(jié)構(gòu)表征中。論文研究了具有4層RP結(jié)構(gòu)(n=4)錳氧化物和SiC兩種功能陶瓷材料的高溫結(jié)構(gòu)演變與相關(guān)的相變過程,取得了一些創(chuàng)新性結(jié)果:1、從錳氧化物Sr7MnO15高溫下原位結(jié)構(gòu)變化解釋了相應(yīng)的熱敏特性。結(jié)果表明,Sr7Mn4O15陶瓷結(jié)構(gòu)單元(晶胞)晶格參數(shù)隨溫度升高線性增大;在Sr7Mn4O15單胞內(nèi)部,共面的八面體單元發(fā)生橫向膨脹,而共點的八面體單元則是在軸線上發(fā)生拉伸,而Sr原子的位置也隨著溫度的升高產(chǎn)生一個有序性的調(diào)整。高溫下輸運測量表明該陶瓷材料電阻值(lnR)與溫度(1000/T)出現(xiàn)一個非常完美的線性變化過程,并擬合得到一個非常大的熱敏因子B=13050K;第一性原理計算結(jié)果顯示Sr7Mn4O15陶瓷其帶隙結(jié)構(gòu)隨溫度的升高從1.141eV降低到0.349eV;內(nèi)耗相關(guān)的實驗充分證明Sr7Mn4O15陶瓷材料結(jié)構(gòu)具有高度穩(wěn)定性。2、獲得Al2O3-Y2O3助劑作用下SiC陶瓷高溫液相燒結(jié)機制。研究表明:Al2O3-Y2O3在制備SiC過程中起助劑的作用。論文通過原位XRD研究,系統(tǒng)的討論了整個陶瓷燒結(jié)過程中的相變過程。在1400℃以下原料并不發(fā)生反應(yīng),Al2O3-Y2O3體系主要生成Y4Al2O9(YAM)和YAlO3(YAP)作為燒結(jié)助劑,該過程發(fā)生在1500℃以上,但并未反應(yīng)生成Y3Al5O105(YAG)。當(dāng)燒結(jié)助劑含量足夠多的時候,SiC液相燒結(jié)過程也將更加明顯,SiC顆粒之間將出現(xiàn)明顯的熔合重結(jié)晶過程,并伴隨著Si02高溫相的結(jié)晶析出。SEM的形貌研究則給出了實驗組中最優(yōu)的助劑含量體系,即10wt%(3#試樣)�；谙嚓P(guān)物相和形貌的研究,我們討論了 Al2O3-Y2O3助劑作用下SiC陶瓷高溫液相燒結(jié)的機理。主要包括兩個階段:階段一,在1500℃以上,助劑體系發(fā)生化合反應(yīng),并且進入液相促進SiC顆粒的重排列;階段二,SiC燒結(jié)的核心階段發(fā)生在1600℃以上,在這個階段,SiC顆粒之間發(fā)生熔合重結(jié)晶過程,并伴隨這SiC特征峰擇優(yōu)趨向的發(fā)生和SiO2結(jié)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，

本文編號：1618005