【作者】 姜晓辉；

【导师】 马峻峰；

【作者基本信息】 中国海洋大学 ， 材料物理与化学， 2008， 硕士

【摘要】 纳米材料由于其介观效应等而表现出不同于常规材料独特的物理化学性质,因而对纳米材料的合成和性质研究已成为材料科学、物理学以及化学学科的前沿。钨酸盐和钼酸盐是无机材料中的两个重要家族,在光学、微波、闪烁体、传感器,催化等方面具有广泛的用途。钨酸盐和钼酸盐的合成方法很多,主要有柠檬酸法、固相法,溶胶凝胶法等。然而,这些方法都存在一定的局限性:合成过程复杂,需要较高的反应温度或者较长的保温时间、所得颗粒尺寸较大,形貌不规则等;而熔盐法和水热法具有合成温度低,工艺简单,粉体大小均匀,形貌可以控制等优点。本论文首次采用熔盐法和水热法在低温下成功合成了钨酸盐和钼酸盐纳米材料,并对各种影响因素进行了讨论,确定了各纳米材料合成所需的最佳条件,并对其生长机理和发光机理进行了探讨。1.以钨酸钠(Na2WO4·2H2O)和硝酸锌(Zn(NO3)2·6H2O)为原料制备前驱体,以硝酸锂为反应介质(熔点为253℃),采用低温熔盐法制得了具有良好结晶性能的棒状ZnWO4纳米晶粉体。并利用X-射线衍射技术(XRD)、透射电子显微镜(TEM)和室温荧光光谱(PL)等分析技术对制备样品的矿相组成、结晶形貌和发光性能进行了表征。研究结果表明:在合成过程中,通过调节反应介质与前躯体的比例和保温时间,而不需要任何模板、表面活性剂、有机溶剂和高温处理作为辅助,就可以成功得合成棒状的ZnWO4纳米晶;同时研究也表明,越小的颗粒具有更好的发光强度。2.以钨酸钠(Na2WO4·2H2O)和氯化锶(SrCl2·6H2O)为原料制备前驱体,以硝酸锂为反应介质(熔点为253℃),采用低温熔盐法制得了具有良好结晶性能的SrWO4纳米晶粉体;利用XRD、SEM、TEM对粉体矿相组成和结晶形貌进行了表征。实验结果表明:常温下得到的SrWO4粉体是微米级颗粒,而在熔盐体系下可以得到SrWO4纳米晶。熔盐存在条件下,保温时间和反应介质与前驱体的比例对SrWO4纳米晶的结晶性能和结晶形貌有重要的影响,并做了详细的探讨,提出了溶解再结晶的过程。3.以硝酸镉(Cd(NO3)2·4H2O)和钼酸钠(Na2MoO4·2H2O)为原料,分别采用常规方法和反相微乳法制备前躯体,然后在水热条件下90oC保温20h制备了CdMoO4微晶,并采用XRD、TEM、SEM、PL等分析测试手段对制得的CdMoO4粉体进行了表征。实验结果表明:用常规方法制备前驱体,然后水热条件得到产物为微米级尺度;而用反相微乳法制备前驱体,同样水热条件下可以得到形貌均一,分散性好的CdMoO4纳米晶。另外,纳米颗粒具有更高的发光强度,并且荧光峰的半峰宽也比较大,这与纳米颗粒的小尺寸效应是有关的。4.以钼酸钠(Na2MoO4·2H2O)和Cd(NO3)2·4H2O为原料,利用微乳液法制备前驱体;以硝酸锂为反应介质(熔点为253℃),采用低温熔盐法制得了具有不同形貌、结晶性能良好的CdMoO4微晶颗粒。分别用XRD、TEM、SEM、PL等分析测试手段对制得的CdMoO4样品进行了表征。实验结果表明:反应介质与前驱体比例一定的条件下,延长保温时间对CdMoO4结晶形貌有较大的影响;而在保温时间不变的条件下,增加盐的比例,对CdMoO4结晶形貌没有较大的影响。更多还原

【Abstract】 Nanoparticles and nanocluster materials are a new class of advanced materials exhibiting unique chemical and physical properties compared to those bulk materials. Tungstates and molybdates are two important families of inorganic materials which have high potential applications in various fields, such as in photoluminescence, microwave applications, optical fibers, scintillator materials, humidity sensors, magnetic properties, and catalysis. Tungstates and molybdates have been prepared by different routs, such as Czochralski method, solid state reaction, heating of RO film with WO3 vapor, sol-gel reaction. However, these methods have some disadvantages, e.g. high temperature and prolonged reaction time being needed, larger particles in size and irregular in morphology, and inhomogeneous chemical composition. On the contrary, molten salt method and hydrothermal method are of simple instrumentations, low temperature, short holding time and available to a large scale production. Therefore, in this thesis, we have prepared tungstates and molybdates powders by a molten salt method and hydrothermal method.1. Na2WO4 and Zn(NO3)2 were used as the starting materials, and ZnWO4 nanoparticles were successfully synthesized by a molten salt method with LiNO3 salt. The powders obtained were characterized by using X-ray diffractometer (XRD), a transmission electron microscope (TEM) and photoluminescence spectra (PL), respectively. The morphology and dimension of the ZnWO4 nanorods were affected by such conditions as calcining time and the weight ratio of the salt to ZnWO4 precursor. The improved PL properties of the ZnWO4 nanorods can be obtained with the decease to nanometer scale in particle size.2. SrWO4 nano-particles with a scheelite structure were successfully prepared by a molten salt method, Na2WO4 and SrCl2 as the starting materials. SrWO4 nano-particles were characterized by XRD, SEM, TEM and PL, respectively. The results showed that we could get SrWO4 powders by a direct precipitation in the room temperature, which were larger and inhomogeneous. However, SrWO4 nano-particles could be obtained by a molten salt method at a low temperature. The particle size, morphology, and crystallinity of SrWO4 nanoparticles are strongly relied on such experimental parameters as holding time and weight ratio of LiNO3 salt to SrWO4 precursor. The formation and development of SrWO4 crystallites should be based on a dissolution-recrystallization process. The improved PL properties of SrWO4 crystallites strongly relied on their particle size and crystallinity. The better crystallinity, the higher PL emission peak is.3. CdMoO4 nano-particles were successfully synthesized by a hydrothermal process at a low temperature, and the powders were characterized in detail by XRD, SEM, TEM and PL, respectively. CdMoO4 particles could be obtained under the hydrothermal condition from micrometer to nanometer sizes by varying their precursors. The PL spectra results showed that the optical properties of CdMoO4 crystallites obviously relied on their particle sizes. The improved PL properties of CdMoO4 crystallites can be obtained by decreasing the particle size to a nanometer scale.4. CdMoO4 precursor was synthesized by a microemulsion method with Na2MoO4 and Cd(NO3)2 as the starting materials, and CdMoO4 nano-particles were successfully synthesized by a molten salt method. The powders were characterized in detail by XRD, SEM, TEM and PL, respectively. The results showed that with a proper weight ratio of the salt, prolonging the holding time can affect the CdMoO4 crystallinity and particle size a lot. However, with a definite holding time, changing the weight ratios of the salt has little influence on the CdMoO4 crystalinity and particle size. The improved PL properties of CdMoO4 crystallites strongly relied on their particle size and crystallinity. The better crystallinity, the higher PL emission peak is.更多还原