轻质负膨胀纳米球的制备及性能研究

发布时间：2018-03-29 15:43

本文选题：负热膨胀　切入点：钨酸锆　出处：《上海交通大学》2015年硕士论文

【摘要】：近年来,钨酸锆作为负热膨胀系数大、负热膨胀温度范围大、且具有各向同性等优点的负热膨胀材料,在航空航天、精密仪器等对材料的热稳定性要求极高的领域获得了广泛的关注与应用。然而,钨酸锆晶须和不规则的颗粒作为增强相制备复合材料可能影响材料的机械性能,同时钨酸锆较大的密度制约了其在追求轻量化的航空航天等领域的应用。而纳米材料,尤其是空心结构纳米材料,由于其自身的特殊性能,可以显著降低复合材料的热膨胀系数,并有效降低复合材料密度。因此如何制备纳米尺寸、低密度、并具有几何均匀性的钨酸锆空心球,是本文研究的重点。本文探讨了钨酸锆空心微纳米结构的液相合成、表征、反应机理以及其负热膨胀性能,通过选择适当的制备方法、对液相合成中溶液酸碱性的控制、选择合适的前驱体反应物与表面添加剂等,制备了三种不同的钨酸锆结构,包括一维纳米棒包覆空心球结构、零维纳米空心球与零维纳米实心球,分析了反应机理,并对后续热处理过程的结晶动力学进行了分析。1.一维纳米钨酸锆包覆空心球结构的制备利用水热反应制备了单分散胶体碳微球作为模板,采用模板法-溶胶凝胶法相结合,制备了钨酸锆纳米棒包覆的空心球壳结构,并对其进行了系统的表征与负膨胀性能测试。产物具有较高的结晶度与纯度,制备过程简单、清洁,所得钨酸锆空心球密度为2.8g/cm3,较理论值降低约45%;具有良好的负热膨胀性能,在室温-200°C温度区间的平均热膨胀系数为-11.4×10-6K-1,较理论值有所降低,这是由于溶胶-凝胶法制备得到纳米棒,提高了负热膨胀性能。2.零维钨酸锆纳米球的制备通过对水热合成反应过程、影响因素与反应机理的研究,实验采用了在水热条件下改变矿化剂盐酸与金属的摩尔比,控制了水热合成过程,观测到了依赖于反应反应酸碱度的形貌演化过程,并利用这一方法分别制备得到纳米级别钨酸锆空心球与实心球,产率高、尺寸小、分布较为均匀,并具有良好的负热膨胀性能。同时分析了不同条件下,得到不同形貌的水热合成机理,分别为溶解-再结晶机制与原位转化机制。实验所得钨酸锆空心球密度为3.6g/cm3,较理论值降低约29.1%;具有良好的负热膨胀性能,在室温-200°C温度区间的平均热膨胀系数为-9.15×10-6K-1。3.钨酸锆前驱体结晶动力学的研究钨酸锆在烧结过程中的结晶动力学不仅受到固相转变过程中外部因素的影响,也受到反应前驱体形貌与尺寸的制约。利用KJMA方程对不同形貌前驱体的结晶过程进行分析,对于实心纳米球,740°C时反应级数为0.54,反应活化能为489 kJ/mol遵循D3扩散机制。空心纳米球,反应级数为0.96,在900°C时为一级反应,由于尺寸较小且表面存在细微结构,因此反应活化能仅为63 kJ/mol。晶须的热处理温度为610°C,所需时间最长为2h,该温度下的反应级数为0.62,D1扩散模型,活化能353kJ/mol。
[Abstract]:In recent years, zirconium tungstate as negative thermal expansion coefficient, negative thermal expansion temperature range, and has a negative thermal expansion material isotropy, in aerospace, precision instruments and other materials on the thermal stability of high demand areas get extensive attention and application. However, zirconium tungstate whiskers and irregular preparation of composite particles as may affect the mechanical properties of reinforced materials is made, and the density of zirconium tungstate greatly restricted its application in pursuit of lightweight aerospace and other fields. And nano materials, especially the hollow structure of nano material, because of its special properties, can significantly reduce the thermal expansion coefficient of the composites. And effectively reduce the density of the composites. So how to prepare nano size, low density, and has a hollow spherical zirconium tungstate geometric uniformity, is the focus of this paper. This paper discusses the zirconium tungstate hollow The micro nano structure of liquid phase synthesis, characterization, reaction mechanism and the expansion properties of negative heat, by choosing proper preparation methods, the pH of the solution phase control in the synthesis of liquid, suitable precursor reactants and surface additives, three kinds of zirconium tungstate structure were prepared, including nanorods coated hollow spherical structure, zero dimensional nano hollow spheres with zero dimension nano solid ball, the reaction mechanism was analyzed and the crystallization kinetics of the subsequent heat treatment of.1. one-dimensional nano zirconium tungstate coated hollow spherical structure was prepared by hydrothermal reaction to prepare monodisperse colloidal carbon spheres as template by template method sol gel method, spherical shell coated zirconium tungstate nanorods were prepared, and the characterization of the system with negative expansion performance test. The crystallinity and purity of the product is high, the preparation process. Simple, clean, the zirconium tungstate hollow ball density is 2.8g/cm3, lower than the theoretical value of about 45%; with negative thermal expansion performance good, the average heat ambient temperature -200 C temperature range expansion coefficient is -11.4 * 10-6K-1, lower than the theoretical value, this is because the sol-gel prepared nanorods, improved negative thermal expansion properties of zero dimensional.2. zirconium tungstate nanospheres were prepared by hydrothermal synthesis reaction process, reaction mechanism and influence factors of the experiment, by changing the molar ratio of hydrochloric acid and metal mineralization agent under hydrothermal conditions, controlled hydrothermal synthesis process, observed the morphology dependent reaction pH the process of evolution, and using this method respectively to prepare nano level zirconium tungstate hollow spheres and solid spheres, high yield, small size, uniform distribution, and has a negative thermal expansion performance good. At the same time is analyzed under different conditions, By hydrothermal synthesis mechanism of different morphologies, respectively, recrystallization mechanism and transformation mechanism of in situ dissolution. The zirconium tungstate hollow ball density is 3.6g/cm3, lower than the theoretical value of about 29.1%; with negative thermal expansion performance good, the average thermal expansion coefficient at room temperature of -200 DEG C temperature range for the crystallization kinetics of -9.15 * 10-6K-1.3. zirconium tungstate precursor crystallization kinetics of zirconium tungstate in the sintering process is not only influenced by external factors in the process of solid phase transition, is constrained by the precursor morphology and size were analyzed. The crystallization process of different morphology of the precursor using the KJMA equation for the solid nanoparticles, 740 C reaction order 0.54, the activation energy of the reaction follows the D3 diffusion mechanism is 489. KJ/mol hollow nanospheres, the reaction order is 0.96, in 900 ~ C is a first-order reaction, due to the small size and surface fine structure, therefore The activation energy of reaction is only 63 kJ/mol., the heat treatment temperature of whisker is 610 degree C, the longest time is 2h, the reaction order at this temperature is 0.62, D1 diffusion model and activation energy 353kJ/mol..

【学位授予单位】：上海交通大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB383.1;TQ134.12

【相似文献】