添加剂对SAZ系陶瓷晶化行为、微观形态和性能的影响

【作者】 刘荣；

【导师】 梁叔全；

【作者基本信息】 中南大学 ， 材料物理与化学， 2011， 硕士

【摘要】 Si-Al-Zr-O系复相陶瓷由于其独特的高温性能,忆成为新型陶瓷材料的研究热点。本实验采用一种新的工艺,即高温熔胶-凝胶工艺和原位受控晶化技术。通过调整基础非晶的化学成分,在较低的温度(1650～1700℃)下制得了Si-Al-Zr-O系高温熔胶,通过强制冷却得到凝胶,然后经过不同热处理温度获得纳米复相氧化锆莫来石陶瓷。本文借助DSC、XRD、SEM、TEM、EDS、Raman(?)口IR等现代分析测试技术探讨了添加剂MgO、CaO和Ti02对Si-Al-Zr-O非晶晶化行为的影响。根据分析结果,拟定了Si-Al-Zr-O系非晶的二步热处理程序获得了结构均匀致密,性能较好的Si-Al-Zr-O超微细晶复相陶瓷。并初步探讨了该类非晶添加对烧结法制备Si-Al-Zr-O复相陶瓷的影响。具体来讲,得到如下几点结论：1.非晶在受热过程中,Zr首先以t-ZrO2析出,Al首先形成了Al-Si尖晶石相。温度进一步升高,Al-Si尖晶石相先增强随后消失,同时mullite形成；当温度升高至1100-1150℃,出现了m-ZrO2的拉曼特征峰,表明有一部分t-ZrO2发生相变转化为单斜相m-ZrO2, t-ZrO2和mullite成为主晶相,而过剩的非晶二氧化硅就转化为了方石英。SAZ系非晶在析晶过程中主要存在两个反应：在930-1050℃温度区间内进行的析晶反应析出t-Zr02；在1100-1200℃温度区间内进行的析晶反应析出莫来石和方石英。2.添加剂CaO、MgO对材料物相、显微结构和力学性能产生明显影响。经940℃预处理1200℃晶化后,单一MgO掺杂试样中,除了mullite、t-ZrO2、m-ZrO2物相外,还有少量Mg2Si04和Si02相生成。而在MgO和CaO复合掺杂(用相同含量的CaO取代MgO)的试样中, mullite, ZrO2仍为主晶相,但Mg2SiO4消失,堇青石相(2MgO·2Al2O3·5SiO2)出现。随着CaO含量增加(1-3wt%),MgO含量的减少,方石英相析出增多,m-Zr02含量有所增加,没有检测到含Ca物相。单一MgO掺杂试样由类似球状的<100nm的粒子组成,与之相比,MgO和CaO复合掺杂有利于晶粒异性生长。随着CaO含量增加,晶粒的长宽比增大。这表明CaO添加剂在晶粒异性生长中起了重要作用。这是因为CaO促进了方石英相的析出,为微区富Al创造了条件。与单一MgO掺杂相比,MgO和CaO复合掺杂试样的力学性能得到了提高。随着CaO含量的增加,试样断裂韧性先明显升高,当CaO>2wt%时,断裂韧性增大缓慢。这可能与晶粒的异性生长有关。3.添加Ti02没有改变主物相的析出顺序,且降低了t-Zr02和莫来石的形成温度,促进了主晶相的析出和晶粒的生长。结合XRD、IR、Raman和TEM分析可知,当Ti02含量不超过5 wt%时,Ti4+主要固溶于t-Zr02中,少量进入mullite晶格,当Ti02含量超过5 wt%时,过量的Ti02参与了新相的形成,生成了ZrTiO4杂相。同时可得到,随着Ti02含量的增加,方石英含量减少,堇青石相析出。材料的断裂韧性随着Ti02含量的增加,先增加后减小,而维氏硬度呈增长的趋势。4.随着掺入非晶的增加,主晶相SiO2消失,同时ZrSiO4(?)目明显增加,说明随着非晶相的添加,促进Zr02与Si02反应生成ZrSiO4或者促进Si02固溶于Zr02中。非晶的添加越多,晶化越完全；基体相主要为莫来石相和硅酸锆相,而氧化锆做为最主要的析出物。非晶含量百分比在0-10 wt%范围内真实密度增长最快；气孔率在非晶含量添加量为0-8 wt%之间有一个较明显的增长趋势,之后随着非晶含量的增加,保持着较平稳的变化；收缩率在非晶含量为0-10wt%下降的最为明显,在10 wt%之后下降速度放缓。硬度在非晶含量为0-20wt%增长的趋势最为明显,之后增长趋势变缓；在非晶含量为0-20 wt%时,断裂韧性随着非晶含量的增长有一个较大幅度的增长。综合各种检测手段,当非晶含量添加为20 wt%既可以达到较好的性能的同时也可以最大程度简化实验程序。更多还原

【Abstract】 The SAZ composite ceramics, which have unique high temperature property, have been one of the hottest issues in the research of novel ceramic materials. In the present study, a new method, high temperature sol-gel and in-situ controlled crystallization, was used to prepare SAZ composite ceramics with ultra fine grains. First, the homogeneous sol was obtained at 1650-1700℃and additions. Second, gel was attained by controlling cooling processing. Finally, the ceramics samples were obtained by a two-step heat treatment.The effects of MgO, CaO, and TiO2 additions on the crystallization behaviors of Si-Al-Zr-O system amorphous bulk were investigated by DSC, XRD, SEM, TEM, EDS, Raman and IR techniques. According to the results, the homogeneous and dense Si-Al-Zr-O composite ceramics with ultra fine grains were prepared by the the two-step heat treatment schedule. In the paper, the effection of the armorphous on the structure and properties of SAZ ceramics prepared by sintering method were also studied. Several important conclusions can be summarized as follows:1. During the heating process of the amorphous, Zr4+ firstly precipitates in form of t-ZrO2, Al3+ firstly formes Al-Si spinel phase. As further increase in temperature, Al-Si spinel phase firstly increases then disappeares; when the temperature rises to 1100～1150℃, Raman peaks of m-ZrO2 appears, while the cristobalite is formed, the main phase are t-ZrO2 and mullite; a part of t-ZrO2 phase transforms into m-ZrO2, while the surplus amorphous silica formes cristobalite phase. The main two reactions during crystallization process of SAZ amorphous are:during 930-1050℃crystallization reaction t-ZrO2 precipitates; during 1100-1200℃crystallization reaction mullite and cristobalite phases precipitate.2. The phases, microstructure and mechanical properties of samples were effectively affected by CaO and MgO additions. For the only MgO-doped sample, the main crystalline phases were identified as t-ZrO2 and mullite with a small amount of cristobalite (SiO2), forsterite (Mg2Si04) and m-ZrO2. When 1wt% CaO replaced the same content of MgO, the main crystalline phases did not change, but Mg2Si04 disappeared and cordierite (2MgO·2Al2O3·5SiO2) existed. Meanwhile, the content of cristobalite was increased obviously and mullite was decreased due to the formation of cordierite. With the increase of CaO content (1-3wt%), more cristobalite formed, less cordierite precipitated, and no new phase for CaO additives occured. The only MgO-doped specimen has homogenous structure with fine, equiaxed grains of< 100nm, but the anisotropic growth of mullites occurred in CaO, MgO-doped samples. As CaO doping concentration increased, the aspect ratio of mullite grains was increased, which implied that the addition CaO played a major role in the anisotropic growth of mullite. The possible reason for this is that CaO additions promote cristobalite forming which results in the formation of the Al-rich zone. Compared with the only MgO-doped sample, the doping of CaO and MgO exhibited a strong increasing in the KIC of the doped samples. It is most likely related to the anisotropic growth of grains.3. The amount of TiO2 additives (1 wt%-7 wt%) decreases the formation temperature of t-ZrO2 and mullite, promotes the growth of mullite and ZrO2 grains, while has little effect on the orders of precipitation. The results show that when the addition of TiO2 is less than 5 wt%, most of Ti4+dissolves in the t-ZrO2, a small amount of Ti4+are soubled into mullite grain; and When TiO2 additives are more than 5 wt%, the excessive Ti4+ formates a new phase, ZrTiO4. Meanwhile, With TiO2 additives increase, a small amount of cordierite phase is formed, while cristobalite phase decreases. The hardness increases with the content of TiO2, while the fracture toughness presentes a slightly increase firstly and then the fracture toughness decreases with the TiO2 addition higher than 3 wt%.4. With the increasing incorporation of amorphous, the main phase of SiO2 disappears, while ZrSiO4 phase increases significantly, which indicates adding the amorphous promotes the reaction between ZrO2 and SiO2 or promotes ZrO2 solute into SiO2. By adding more amorphous, crystallization process becomes more complete; the matrix phases are mainly mullite and zirconium silicate phase, while zirconia is the most important precipitation. The density grows fastest when the percentage of amorphous content is 0 wt%-10 Wt%; porosity shows a obvious growth trend when the amorphous content is 0 wt%-8 wt%, with the increase of amorphous content, porsity maintains the relatively stable change; shrinkage decline is most apparent when amorphous content is the 0 wt%-10 wt%. Hardness growth trend is most apparent when the amorphous content is 0 wt%-20 wt%.The fracture toughness presentes a relatively large increase with the amorphous content growth. Combination of all those tests, when the amorphous content was 20 wt% better propersity and simpler procedure can be achieved at the same time.更多还原