【作者】 胡立杰；

【导师】 闵光辉； 朱艳秋；

【作者基本信息】 山东大学 ， 材料加工工程， 2013， 博士

【摘要】 LaB6是稀土类六硼化物,属于立方晶系CsCl型,具有高熔点(熔点为2715℃)、高导电率和高的化学稳定性,在各种现代技术器件组元中有着广泛的应用前景。纳米LaB6材料,在紫外和近红外透光率几乎为零的情况下,对可见光仍有很高的透光率,具备新一代窗用隔热材料所需的性能。PMMA作为一种透明性最好的聚合物材料之一,广泛的应用于光学、车窗、洁具和建筑等领域,尤其可作为优异的光学材料。因此对LaB6及其PMMA基复合材料的研究,将丰富LaB6的光学性能研究,极大地促进硼化物功能陶瓷材料在隔热、透光等领域的应用。本文以LaCl3·7H2O和NaBH4为原材料,通过高温固相反应和低温固相反应两种方法制备了纳米LaB6粉末,利用表面改法对制备的纳米LaB6粉末进行了改性处理,对改性效果好的纳米粉末利用静置法和离心法对纳米颗粒进行了粒度的分选,最后将不同粒度和不同含量的LaB6颗粒分散在MMA单体中,通过MMA单体的本体聚合法制备了纳米LaB6粉末/PMMA基复合材料。研究结果表明,高温固相反应和低温固相反应虽然都能制备出纳米LaB6粉末,但反应机制有所不同,低温固相反应是依靠添加剂Mg与环境中的水或氧气反应而释放出大量的热来维持反应的进行。高温固相反应中,温度直接决定了产物的物相、颗粒的大小和形貌。低温固相反应合成的纳米颗粒的晶粒尺寸比较小,基本上在10-15nm之间,形状为类球形。而高温固相反应在900℃下保温2h可得到平均晶粒尺寸为18.2nm、形状为方形的纳米粒子。随着温度的升高,粒子的尺寸变大,颗粒之间的界面不再规则。不同的表面活性剂对LaB6进行表面改性的机理不同,使用CTAB在pH为11的水溶液中进行改性是利用了电荷理论,经过改性后的LaB6纳米颗粒可以很好的分散于CTAB的水溶液中。而使用OA对LaB6改性则是通过OA的羧基与LaB6表面的活性羟基发生化学键合而接枝到纳米颗粒表面,60℃的弱碱性环境更有助于化学键合作用。而MMA单体对LaB6的改性则是利用了MMA单体在LaB6质点上发生的乳液聚合反应而接枝到纳米颗粒表面,单体MMA的量和乳化剂SDS的浓度对产物的结构和形貌影响较大。适度的MMA和SDS才能得到分散较好的LaB6纳米颗粒。在使用静置法分层对纳米颗粒进行分选时,发现以水作为溶剂时分选出的纳米颗粒尺度不均一。但在使用了PVP水溶液时,成功地分选出几个不同粒度级别的纳米颗粒,分别为30nm、40nm、60nm、80nm、100nm和150nm,并且每个级别的颗粒的粒度比较均匀。而使用离心法分离出来的颗粒含量较少,而且每个级别颗粒的尺度分布不集中。在研究纳米颗粒的尺寸和含量对复合材料的光学性能的影响时,发现用PVP水溶液分选的纳米颗粒在复合材料中分散的比较均匀,而且相应的复合材料的透光率随着纳米颗粒含量的增加而降低,同时随着纳米颗粒尺寸的增大而降低。通过对光学数据进行计算分析得到满足实际需要的工艺参数,本研究选择加入粒径为30nm、质量分数为0.01wt%的LaB6粒子制备的PMMA基复合材料,作为一种理想的隔热而又不影响可见光透过的先进窗用节能环保材料。更多还原

【Abstract】 Lanthanum hexaboride (LaB6) was an excellent thermionic electron emitter material characterized by excellent thermal stability. Nanosized LaB6powder was reported to have excellent selective light absorption and scattering recently. PMMA was widely used as lens, windows and wind screens due to high transparency and light weight. It was advantageous to incorporate LaB6nanoparticles into PMMA, to produce a nanocomposite with additional properties brought by the filler nanoparticles, however, the dispersion of inorganic nanosized particles in organic polymer matrix was a key problem.In this paper, nanosized LaB6powder was prepared through high temperature solid state reaction and low temperature solid state reaction as well, surface modification was used in order to improve the dispersion of LaB6nanoparticle in PMMA matrix. Then, LaB6nanopaticles was separated to several levels with different size. Then polymerization was used to prepare the LaB6/PMMA composites.It was found that the mechanism between high temperature solid state reaction and low temperature solid state reaction was different, as Mg addition was indispensable in low temperature solid state reaction, to provide much more energy through reacting with vapor and oxygen. The product synthesized from low temperature solid reactions had smaller grain size and round-shaped morphology. However, the one from high temperature solid reactions showed good cubic shape particle with higher crystllinity. The temperature was very important in high temperature solid state reaction, as proper temperature could lead to products with good crystallization. The best technology for high temperature solid state reaction was the raw materials named LaCl3and NaBH4with a molar ratio of1:12heated to900℃rapidly for2h.CTAB, OA, and MMA was used to modify LaB6nanomaterials. CTAB, working as a cationic surface active agent, helped LaB6to get a well dispersion in deonized water with pH of11. Alkaline environment was a better choice as it favored CTAB to absorb onto the surface of nanoparticles. Modification with OA was realized through reaction between its’ carboxy group and hydroxyl group from the surface of the LaB6, and the alkaline environment proceeded the cooperation between chemical bonds, however,60℃was the best temperature for this reaction as higher teperature could cause secondary reaction to prevent the absorbing of OH group. MMA, was used to grafted to the surface of LaB6nanoparticles through emulsion reaction. SDS had significant effect than CTAB as emulsifiers, meanthile, the concentration of SDS and the volume of MMA monomer were very important to the reaction, proper amounts of SDS and MMA could get well dispersed LaB6, the extreme values would get poor dispersion of LaB6.Compared to deionized water, PVP aqueous solution was a better choice for nanoparticles to be separated to particles with various sizes. The final average size of LaB6particle was30nm,40nm,60nm,80nm,100nm and150nm. Finally, the particle with different size was used to prepare LaB6/PMMA composites. LaB6particles dispersed well in the PMMA matrix, and the particle size and LaB6weight ratio of PMMA matrix affected the composites’optical properties. The transmittance of the composite was decreased with the weight ratio of LaB6increased, and with the size of nanoparticles increased as well. After calculation on Tvis, Tsol, and the ratio between them, PMMA containing0.01wt%of nanoparticles with size of30nm was found to meet the need of reality. It could absorb much infrared light and let most of visible light in.更多还原