【作者】 苏兴华；

【导师】 李建功；

【作者基本信息】 兰州大学 ， 材料物理与化学， 2010， 博士

【摘要】 Al2O3和MgAl2O4纳米陶瓷具有广阔的应用前景,因此制备α-Al2O3和MgAl2O4纳米颗粒粉体具有重要的意义。我们先是采用了一种新方法—化学沉淀一隔离相辅助煅烧技术,利用廉价的原料制备出了MgAl2O4和片状α-Al2O3纳米颗粒粉体。探讨了作为隔离相的无机盐对于氧化铝前驱体的相变、形貌、尺寸和团聚状况的影响。后来又分别采用了均匀沉淀法、醇盐水解法来制备单分散的氧化铝前驱体。研究了制备条件对氧化铝前驱体颗粒的形貌、尺寸和团聚状况的影响。随后,我们对所制备的氧化铝前驱体进行热处理,研究了其相变及所得产物的形貌变化。研究结果表明,以无机盐MgSO4作为隔离相,煅烧MgSO4和α-Al(OH)3混合粉末时,可以在相对低的温度800℃下,制备得到MgAl2O4纳米颗粒粉体。在煅烧混合粉末的过程中,MgSO4不仅仅是隔离相,而且是反应物。MgSO4在混合粉末中的含量影响着MgAl2O4纳米颗粒的尺寸及团聚状况。当混合粉末中的Mg/Al原子比为20时,所制备的MgAl2O4纳米颗粒尺寸分布窄、团聚轻,平均颗粒尺寸为12 nm。当Mg/Al原子比为5时,所得到的MgAl2O4纳米颗粒尺寸分布宽、团聚严重,平均颗粒尺寸为22 nm。通过烧结实验发现,所制备出的MgAl2O4纳米颗粒具有很好的烧结活性。以无机盐K2SO4作为隔离相,煅烧K2SO4和α-Al(OH)3混合粉末时,可以在相对低的温度900℃下,制备出分散性良好的片状α-Al2O3纳米颗粒粉体。K2SO4对混合粉末中α-Al(OH)3的相变有极大的影响。这是因为,在煅烧混合粉末的过程中,过渡相γ-Al2O3和K2SO4发生了固相反应生成K3Al(SO4)3。随后,由于K3Al(SO4)3分解生成了α-Al2O3晶粒,这些α-Al2O3晶粒为未参与固相反应的γ-Al2O3提供了低能形核点,降低了α-Al2O3的相变激活能,从而降低了α-Al2O3的生成温度。K2SO4在α-Al(OH)3和K2SO4混合粉末中的含量对最终产物α-Al2O3的形貌没有影响。当混合粉末中的K／Al原子比为12时,所制备的片状α-Al2O3颗粒的直径为0.5-1.5μm,厚度为50-150 nm。片状α-Al2O3颗粒的晶体惯习面为{0001}面。在α-Al(OH)3和K2SO4混合粉末中添加α-Al2O3晶种后,所得片状α-Al2O3颗粒的直径减小到300-600 nm,厚度减小到30-60 nm。通过均匀沉淀法制备了单分散、球形的非晶态Al(OH)3纳米颗粒。调节溶液中Al3+的浓度,可以控制Al(OH)3纳米颗粒的尺寸。当Al3+浓度从10 mmol／L减小到0.5 mmol／L时,平均颗粒尺寸从350 nm减小到60 nm。当Al3+浓度为0.21mol／L时,所制备的Al(OH)3粉体的平均颗粒尺寸约为10 nm,但是颗粒团聚严重。均匀沉淀法所制备的Al(OH)3颗粒粉体的相变顺序为：非晶态Al(OH)3→γ-Al2O3→α-Al2O3。在1200℃的温度下煅烧Al(OH)3纳米颗粒,可以得到近单分散的α-Al2O3纳米颗粒粉体。以异丙醇铝为前驱体,在乙腈和水体系中利用醇盐水解法制备了单分散、球形的非晶态Al2O3纳米颗粒。调节溶液中水与异丙醇铝的比例,可以适当控制所得产物的颗粒尺寸。当水与异丙醇铝的摩尔比从10减小到5时,粉体的平均颗粒尺寸从857 nm减小到783 nm。当水与异丙醇铝的摩尔比为1时,最终的产物为无规规形貌的颗粒团聚体。所制备的非晶态Al2O3颗粒粉体的相变顺序为：非晶态Al2O3→γ-Al2O3→α-Al2O3。在1200℃煅烧2 h后,非晶态Al2O3转变为α-Al2O3。所得α-Al2O3颗粒接近单分散,但为多孔结构。更多还原

【Abstract】 Since Al2O3 and MgAl2O4 nanoceramic have extensively potential applications, it is of great signification to prepare nanosizedα-Al2O3 and MgAl2O4 powders. At first, using the cheap raw materials, theα-Al2O3 platelets and MgAl2O4 nanoparticles were prepared by a new method, namely the chemical precipitation-isolating phase assistant calcination technique. The influence of inorganic salt serving as isolating phase on the phase transformation of the alumina precursors, particle morphology, size and agglomeration degree was investigated. Then, the monodispersed alumina precursors were prepared by the homogenious precipitation method and hydrolysis of aluminum alkoxide, respectively. The influence of preparation conditions on the morphology of alumina precursors, particle size and agglomeration degree was studied. The phase transformation and morphology change of alumina precursors during the calcination were investigated.It is found that the MgAl2O4 nanoparticles can be prepared at a relatively low temperature of 800℃by calcining the mixture of MgSO4 andα-Al(OH)3. The inorganic salt MgSO4 acts not only as an isolating phase, but also a reactant in this process. The content of MgSO4 in the powder mixture has an influence on the particle size and agglomeration degree. As the Mg/Al atomic ratio is 20, the obtained MgAl2O4 nanoparticles have an average particle size of 12 nm, a narrow size distribution, and weak agglomeration. However, as the Mg/Al atomic ratio reduces to 5, the obtained MgAl2O4 nanoparticles have an average particle size of 22 nm, a broad size distribution, and severe agglomeration. Furthermore, these MgAl2O4 nanoparticles with particle size of 12 nm show excellent sinterability.Using the inorganic salt K2SO4 as an isolating phase, the dispersedα-Al2O3 platelets can be prepared at a relatively low temperature of 900℃by calcining the powder mixture of K2SO4 andα-Al(OH)3. The K2SO4 has a large influence on the phase transformation ofα-Al(OH)3. In calcination of K2SO4 andα-Al(OH)3 powder mixture, K3Al(SO4)3 forms in situ by solid reaction ofγ-Al2O3 and K2SO4. The decomposition of K3Al(SO4)3 can produceα-Al2O3 crystallite, which acts as a heterogeneous nucleation site and thus accelerates theγ-Al2O3 toα-Al2O3 transformation. The content of K2SO4 in the powder mixture has no influence on the particle morphology. As the K/Al atomic ratio is 12, the obtainedα-Al2O3 platelets have a diameter of 0.5-1.5μm and a thickness of 50-150 nm. The habit plane of obtainedα-Al2O3 platelets is {0001}. By addingα-Al2O3 seeds into the powder mixture, the diameter of obtainedα-Al2O3 platelets reduces to 300-600 nm, and thickness reduces to 30-60 nm.The monodispersed, spherical, and amorphous Al(OH)3 nanoparticles are prepared by the homogenious precipitation method. The particle size can be controlled by changing the concentration of Al3+. As the concentration of Al3+ reduces from 10 mmol/L to 0.5 mmol/L, the average particle size reduces from 350 nm to 60 nm. When the concentration of Al3+ increases to 0.21 mol/L, the average particle size reduces to 10 nm. However, the obtained Al(OH)3 nanoparticles have a severe agglomeration. The phase transformation sequence of Al(OH)3 nanoparticles obtained by homogenious precipitation is amorphous→γ-Al2O3→α-Al2O3. The near monodispersedα-Al2O3 nanoparticles can be prepared by calcining these Al(OH)3 nanoparticles at 1200℃for 2 h.The monodispersed, spherical, and amorphous Al2O3 particles are prepared by hydrolysis of Al(O-i-Pr)3 in acetonitrile-water system. The particle size can be controlled by changing the H2O/Al(O-i-Pr)3 molar ratio. As the H2O/Al(O-i-Pr)3 molar ratio reduces from 10 to 5, the average particle size of obtained amorphous Al2O3 particles reduces from 857 nm to 783 nm. However, as the H2O/Al(O-i-Pr)3 molar ratio reduces to 1, the obtained Al2O3 particles have no regular morphology. The phase transformation sequence of these Al2O3 particles is amorphous→γ-Al2O3→α-Al2O3. The monodispersedα-Al2O3 particles obtained by heating these amorphous Al2O3 particles at 1200℃for 2 h have porous structure.更多还原