【作者】 张鹏宇；

【导师】 刘家臣；

【作者基本信息】 天津大学 ， 材料学， 2010， 博士

【摘要】 在一定条件下,晶体沿着线性链方向生长的陶瓷材料被称为一维陶瓷材料。一维材料在其他维度方向上生长受限,因此表现出不同于传统材料的特殊性能。其中一维莫来石陶瓷由于其优异的热震性、抗蠕变性,以及高温下室温强度衰减小的特性,已经应用于晶须补强、涂层技术、过滤膜、高温催化反应器等方面。熔盐法是一种湿法化学合成方法,其优势在于合成的粉体无团聚、工艺简单;与其他液相法相比,其合成出的一维晶体质量更高。本文中,对采用熔盐法合成一维莫来石陶瓷进行了研究。对前驱体的研究表明,采用化学活性高、溶解能力强的前驱体,有助于获得独立分散的一维莫来石晶体。以Al₂（SO₄）₃、无定形SiO₂、Na₂SO₄为原料,其配比Al/Si/Na为2/1/8（原子比）时,在1000℃保温3h条件下,HF酸洗后最终产物全部为一维莫来石晶体。XRD、EDS、HR-TEM结果表明所得的莫来石晶体为富Al组成,光致发光性能反映出富Al组成产生的氧空位缺陷。对温度制度的研究表明,快速升温有助于莫来石相的生成;合成温度过高,莫来石晶体会在1100℃左右发生分解形成NaAlSiO₄。对莫来石晶体生长机理的研究表明。熔盐法合成过程中,当液相中不断生成的莫来石超过其过饱和度时,莫来石开始成核。在液固生长界面处,莫来石单体的沉淀是可逆的,因此生长能够按照其能量最低的原则不断进行调整,从而最大限度的保证其在c轴方向的自由生长。莫来石晶体在界面处的生长位置是由二维平台提供的,这个过程所需克服的能量壁垒大,当二维平台耗尽时,晶体即停止生长。莫来石晶体在熔盐法中的生长属于LS生长机理。通过对B₂O₃外加剂的研究,发现莫来石晶体尺寸的减小,当B₂O₃/SiO₂达到0.04（摩尔比）时形成了纳米级别莫来石晶体,其归因于B₂O₃的加入有助于成核速率加快。通过对莫来石晶种的研究,发现晶种的加入能够在一定程度上提高熔盐法制备莫来石晶体的产率,莫来石晶体的尺寸减小、尺寸更加均匀,这是由于晶种的加入能够为莫来石晶体提供生长位点,提高了莫来石晶体初期形核速率。更多还原

【Abstract】 The specific crystals which grow along the linear chain are classified to one-dimension structured ceramic materials, which can exhibit special properties owing to the growth restriction in other directions. Owing to its great thermal shock resistance, creep resistance and stable room-temperature ?exural strength at high temperature, mullite has been applied in whisker technology, coating technology, filter membrane, high-temperature catalytic reactor, and so on. The molten salts synthesis （MSS） belong to a wet chemical method. In MSS, the resultant production without aggregation can be easily obtained, and has a higher quality when compared with other liquid phase methods. In this paper, the prepariton of one-dimension structured mullite by MSS was investigated.The investigation shows that high chemical activity and strong dissolve ability precursors were helpful to obtain isolated mullite crystal. The mullite was obtained when the sample with Al₂（SO₄）₃, amorphous-SiO₂, Na₂SO₄ （Al/Si/Na=2/1/8, atoms ratio） was heated at 1000℃for 3h after HF etching. XRD, EDS, and HR-TEM results show the Al-rich compostion in mullite, and photoluminescence results show the oxygen vacancies defects presence. The investigation on temperature schedule shows that rapid heating was helpful to form mullite, and mullite was transformed to NaAlSiO₄ at about 1100℃.The investigation on growth mechanism shows that supersaturation led to the mullite crystal nucleus formation in MSS. At the growth interface, the decomposition of mullite monomers was reversible, so the growth was revised continuously as energy minimum and along the c-axis. The new two-dimensional islands provided nucleations, which reqired large supersaturation because the nucleation barrier is high. The mullite crystal growth in MSS can be explained by liqiud-solid mechanism.With the B₂O₃ addition, the size of mullite crystal decreased. The mullite nanowires were obtained at B₂O₃/SiO₂ = 0.04. The phenomenon can be abscribed to the nucleation rate increase when B₂O₃ was added in MSS. With the mullite seeds addition, it was found that the yield of mullite was promoted and the the size of mullite crystal decreased. At the same time, the size distribution was narrower with higher seeds addition.更多还原