【作者】 杨水兰；

【导师】 贺拥军； 周安宁；

【作者基本信息】 西安科技大学 ， 材料学， 2010， 硕士

【摘要】 本文通过简单的沉淀法对CdCO₃形貌进行控制,以制备均匀的单分散超细CdCO₃颗粒;对CdCO₃颗粒进行表面改性,使CdCO₃颗粒获得良好的润湿性;改性CdCO₃颗粒作为稳定剂,以石蜡或苯乙烯为油相,制备水包油Pickering乳液;将Pickering乳液固化,对暴露部分的CdCO₃进行硫化反应,由此制备分区域复合的CdS/CdCO₃复合材料。本论文制备的CdS/CdCO₃复合材料可通过气氛保护高温锻烧得到CdS/ CdO复合材料,CdS和CdO都是重要的半导体材料,为进一步研究CdS/ CdO复合材料性能做好基础工作。先以CdCl₂和Na₂CO₃为原料,采用直接沉淀法制备了多种形貌的CdCO₃颗粒。不同的表面活性剂在反应中均能对CdCO₃颗粒起到良好的分散作用,加入CTAB制备的CdCO₃颗粒最均匀,基本为方形结构。反应中不加入任何表面活性剂或晶形控制剂,当CdCl₂和Na₂CO₃溶液浓度皆为2 mmol/L、4 mmol/L时,CdCO₃颗粒都为双晶结构,前者聚片结构特征明显;当CdCl₂溶液浓度为2 mmol/L,Na₂CO₃溶液过量时,制备的CdCO₃颗粒为花生状双晶;溶液浓度增大,CdCO₃为分散、均匀的方形颗粒,浓度继续增大,颗粒不均匀,有团聚。采用均匀沉淀法,以尿素和CdCl₂为原料制备了多种形貌的CdCO₃颗粒。反应前对尿素溶液高温陈化,有利于制备单分散的颗粒。在水浴中以搅拌方式进行反应,尿素过量,CdCl₂溶液浓度为3 mmol/L,制备的CdCO₃颗粒为粒径约1.5μm均匀的方形;CdCl₂溶液增大,颗粒层状结构明显,为棱角不明显的类球形;当CdCl₂溶液增大至0.05 mol/L时,CdCO₃颗粒为球形双晶结构。将反应置于超声波中进行,制备的CdCO₃颗粒层状结构明显,当慢滴尿素溶液时,制备了双晶结构的CdCO₃颗粒。以A-151为改性剂对CdCO₃颗粒进行表面改性,采用液滴量高法测量改性CdCO₃的润湿接触角。红外光谱分析说明硅醇单体在CdCO₃颗粒表面自身发生了缩聚,形成了硅烷膜覆盖在CdCO₃颗粒表面,使之获得良好的润湿性。CdCO₃颗粒的润湿接触角随A-151用量的增加而增大,但当A-151与CdCO₃质量比大于1.26时,接触角增加不明显。改性CdCO₃颗粒作为Pickering乳液的稳定剂,稳定性受颗粒润湿程度、油相、油水比等多种因素的影响,接触角为79°的CdCO₃颗粒嵌入苯乙烯乳液液滴中,制备了稳定的Pickering乳液。苯乙烯聚合后得到CdCO₃/PS复合球,对暴露在复合球外的CdCO₃进行硫化反应,制备了分区域复合的CdS/CdCO₃单颗粒复合材料,CdS层的厚度随反应时间而不断增加,但由于生成的CdS会阻碍硫化反应的进行,CdS层最终仍为半圆壳状。更多还原

【Abstract】 Uniform monodispersed CdCO₃ fine particles were prepared through simply precipitation method. Good wettability of CdCO₃ was obtained by surface modification using coupling agent. Using modified CdCO₃ particles as stabilizer, paraffin or styrene as oil phase, a oil-in-water （W/O） Pickering emulsion was prepared. Sulfuration reaction was carried out on exposed CdCO₃ particles in cured Picking emulsion, then CdS/CdCO₃ sub-region complex were prepared. CdS/CdO composite can be prepared by using the obtained CdS/CdCO₃ through high temperature calcination under nitrogen atmosphere. CdS and CdO both are important semiconductor materials, thus this study provide basic information for further investigation of the performances of CdS/CdO composites.Firstly, using Na₂CO₃ and CdCl₂ as reagents, a serious of CdCO₃ particles with various morphologies were prepared through direct precipitation method. Good dispersion CdCO₃ can be reached by using different surfactants in the reaction. When cetyltrimethylammonium bromide （CTAB） was added, the prepared CdCO₃ particles were the most uniform with basically cubic shape. Also there can be no surfactants or crystal control agent during the reaction. When the concentration of CdCl₂ and Na₂CO₃ were 2 mmol/L and 4 mmol/L respectivly, polysynthetic twinning CdCO₃ particles were get. While, with excess Na₂CO₃ in 2 mmol/L CdCl₂, peanut-like-twinning of CdCO₃ was obtained. With the increase of concentration of the reagents, uniformly dispersed cubic CdCO₃ was obtained. But further increased reagents concentration led to ununiform particle size and aggregation.Then, Using urea and CdCl₂ as reagents, another serious of CdCO₃ particles with various morphology were preparaed through homogeneous precipitation method. High temperature aging of urea before reaction was beneficial to synthesize monodispersed particles. In water bath, stirred 3 mmol/L CdCl₂ with excess urea produced cubic CdCO₃ particles with approximately 1.5μm diameter. Increasing the concentration of CdCl₂ resulted in near spherical CdCO₃ particle with layered structure. When the concentration rose up to 0.05 mol/L, the obtained CdCO₃ existed in spherical-twinning. Whereas reaction system under ultrasonic produced obviously layered structure of CdCO₃. And twinning CdCO₃ was synthesized by slowly adding urea in drops into the ultrasonic reaction system.Furthermore, CdCO₃ particles were surface modified by A-151. The wetting contact angle of the modified CdCO₃ was measured by using height-width method. The results of FTIR analysis indicated that silanol monomers had already polymerized on the surface of CdCO₃ particles and formed a thin film around, therefore, gave good wettability to the CdCO₃ particles. The wetting contact angle of the modified CdCO₃ increased with the content of A-151. But it did not increase obviously when the weight ratio of A-151 to CdCO₃ exceeded 1.26.The stability of the Pickering emulsion stabilized by modified CdCO₃ particles affected by the degree of wetting of the particle, oil phase, and oil to water ratio. CdCO₃ particles with 79o contact angle embedded in styrene emulsion droplets to prepare stable Pickering emulsion. CdCO₃/PS composite sphere were prepared through polymerization of styrene. Sulfuration reaction was carried out on exposed CdCO₃ particles on the obtained CdCO₃/PS composite surface. Then sub-region complex of monodispersed CdS/CdCO₃ was gained. The thickness of CdS layer increased with reaction time. For the hindrance of CdS to further sulfuration, the CdS layer finally stabilized in semicircle shell.更多还原