【作者】 秦秀娟；

【导师】 王文魁； 刘日平；

【作者基本信息】 燕山大学 ， 材料学， 2005， 博士

【摘要】 纳米ZnO以纳米材料和重要半导体氧化物两方面的完美结合吸引了广大的科研工作者,成为近年来研究的热点。本文在成功制备出纳米 ZnO 陶瓷粉体的基础上,对纳米 ZnO 粉体的素坯成型,常压烧结行为进行了系统的研究。同时,对纳米 ZnO高压下的晶粒演化进行了较为深入的探讨。在常压和高压下,成功的制备出了高密度 ZnO 纳米块体材料,并对其显微硬度,电性能和光吸收特性进行了研究。 采用均匀沉淀法制备纳米 ZnO 陶瓷粉体。运用干法成型方式系统讨论了致密化过程中素坯密度、烧结温度和时间对 ZnO 纳米烧结体的微观结构,密度和晶粒尺寸的影响,应用晶粒生长动力学唯象理论计算了纳米 ZnO 常压烧结晶粒生长的表观活化能、晶粒生长速率常数和晶粒生长的动力学指数。利用六面顶高压设备研究纳米ZnO 高压下的晶粒演化行为。 运用 X 射线衍射（XRD）, 场发射扫描电子显微镜（FEG）, 透射电镜（TEM, HRTEM）, 差示扫描量热分析（DSC）等手段对样品的组成,微观结构和形貌进行了分析和表征。采用显微硬度仪,MY-1 型三参数测试仪,双光束紫外可见分光光度计测定了 ZnO 纳米块体材料的硬度,电性能和光吸收特性。研究了微观结构对 ZnO纳米块体材料性能的影响。 制备的纳米 ZnO 陶瓷粉体纯度大于 99.5%,粒子形貌为球形或类球形、分散性良好,粒度分布均匀,平均粒径尺寸 20nm, 最大晶粒尺寸 35nm, 品质符合烧结要求D_最大<2D_平均。 获得了常压烧结制备 ZnO 纳米块体材料的优化条件:重复成型,700℃烧结 2h。烧结体相对密度 91.2%,晶粒尺寸 50-60nm。纳米 ZnO 常压烧结晶粒生长的动力学方程为: G⁶ =1.52×10¹²t exp（-6.4×10⁴/RT ） nm⁶·h^-1 冷高压调制下,纳米 ZnO 中存在着压致晶粒碎化现象。300℃、6GPa 制得了晶粒尺寸 40-50nm,相对密度大于 99%的 ZnO 纳米块体。计算出 300℃,压力分别为1-3GPa 和 4-6GPa 的激活体积为-5.82cm³/mol, 9.66cm³/mol。 常压烧结体的显微硬度随烧结温度的升高,呈现出先增大后减小的现象,硬度普遍较低。高压烧结体的硬度与理想致密 ZnO 的硬度很接近。高密度 ZnO 纳米烧结体具有非线性伏安特征,且相对密度越高,晶粒尺寸越小,其非线性特征越明显。更多还原

【Abstract】 In recent years, nanosized ZnO has been paid special attention because of its important semiconductive characteristic. In this paper, compaction and sintering of ZnO nanopowders under ambient and high pressure are investigated. Bulk samples of nanocrystalline ZnO with high density are successfully prepared. Microhardness, electrical properties and light absorption properties of the samples are also measured. ZnO nanopowders are prepared by the homogeneous precipitation method. The influences of density of the green disks, sintering temperature and time on microstructure, density and grain sizes during the process of densification are systematically discussed. The apparent activation energy for grain growth, the value of pre-exponential constant and the grain growth kinetic exponents are calculated using the phenomenological kinetic grain growth equation. Study on evolution of ZnO nanocrystalline grains is carried out on a cubic high-pressure apparatus. The structures, component and morphology of the samples are characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, and differential scanning calorimeter. Microhardness, electrical properties and light absorption are measured using durometer,MY-1 three-parameter durometer and UV-vis spectrophotometer respectively. Influence of microstructures on the properties of the bulk nano-materials ZnO is studied. The purity of ZnO nanopowders prepared is better than 99.5%. The morphologies of the particles tend to be rounded. Nanopowders exhibit good dispersion properties and narrower distribution in size. The average grain size is about 20nm and the largest of them is about 35nm, which agree to the requirement for sintering Dmax<2Daverage. Optimum method for preparing bulk nanosized ZnO is obtained. The sample sintered at 700℃ for 2 hours by repeat compaction process is 50 - 60nm in size and relative density 91.2%. Kinetic grain growth equation of nanosized ZnO sintered at ambient pressure is expressed as: G⁶ =1.52×10¹²t exp（-6.4×10⁴/RT） nm⁶·h^-1 Obvious pressure-induced grain refinement is observed during the compacting of nanosized ZnO under high pressure. The sample prepared at 300℃under the pressure of 6GPa is 40-50nm in size and relative density 99%. The activation volume at 300℃ from 1 to 3GPa and from 4 to 6GPa are calculated, which is about -5.82cm3/mol, 9.66cm3/mol, respectively. Microhardness of samples sintered at ambient pressure increases first and then decreases with increasing the sintering temperature. Microhardness of the sample sintered under high pressure is higher than that of the one prepared at ambient pressure. The bulk nanosized ZnO with high density has the non-linear current-voltage characteristics. The higher the relative density and the smaller the grain sizes, the better the non-linear current-voltage characteristics. UV-vis absorption spectra of nanosized ZnO all shift to the red at 200nm and shift to the blue at 400nm. The intensity is greater than that of the coarse crystalline ZnO and decreases with increasing grain sizes.更多还原