真空冷冻干燥法制备纳米碳酸钙粉体实验研究

发布时间：2018-11-10 21:25

【摘要】：近几年来,随着纳米科技的迅速发展,纳米材料的应用受到各个领域的广泛关注,纳米碳酸钙作为一种优质填料和白色颜料,由于具有成本低、性能优、无毒无味等特点,广泛应用在橡胶、塑料、造纸、涂料、油墨、医药、化妆品等众多行业。目前制备纳米碳酸钙的方法主要有：复分解法、碳化法、乳液法、凝胶法、非冷冻法。真空冷冻干燥法制备的纳米粉体具有微粒形状规则、粒径小而均匀、粒度分布窄、化学成分纯、粒子间无硬团聚、分散性好等特点,因而受到关注。所以本文不仅选用真空冷冻干燥方法制备纳米碳酸钙而且利用自行开发的真空冷冻干燥显微镜成功的观测、记录了溶液冻结蒸发的全过程,并且对溶液冻结蒸发的过程进行了分析和研究。本文利用碳酸氢钙溶液为制备纳米碳酸钙的前驱体溶液,在同样的条件下分别采用直接冷冻干燥方法和真空蒸发冻结方法制备粉体,通过X射线检测和透射电镜检测发现所制备的粉体为多晶体,存在两种晶体类型,粉体很纯净不含其它的杂质,粉体疏松多孔,采用上述两种方法都能得到粒径在50纳米左右的碳酸钙,用两种方法得到的粉体从形貌到成份都没有太大的区别,但是利用真空蒸发冻结方法就会节约很多的能源,这对以后对利用真空冷冻干燥方法制备纳米碳酸钙有很大的指导意义。本文还设计实验探索如何防止溶液在真空蒸发冻结过程中的爆沸(除去温度和压力因素)。以纯水为例通过实验可以得出结论：纯水中的溶解气体对自冻结过中的第一次爆沸有很大的影响,把经过脱气处理的水中放入瓷片会很有效的防止第二次爆沸时液体的飞溅。本文完成了对真空冷冻干燥显微镜的开发工作,并对其结构、工作原理和能够在实际工作中的应用进行了详尽的描述。利用冻干显微镜实现了对冻于过程的显微观测,并对其温度和压强的纪录,分析了液体冻结的结晶状态,通过控制系统对导热块的升温和降温掌握了溶液真空蒸发和真空冷冻干燥的微观特点,验证了在冷冻干燥过程中溶液的偏析,首次利用冻干显微镜直接观测法测定了碳酸氢钙溶液的共晶点和共熔点温度。首次在显微结构上研究了碳酸氢钙溶液的冻结过程,对以后利用真空冷冻方制备成分均匀,颗粒尺寸理想的粉体有着重要的影响。
[Abstract]:In recent years, with the rapid development of nanotechnology, the application of nano-materials has received extensive attention in various fields. As a kind of high-quality filler and white pigment, nano-calcium carbonate has the characteristics of low cost, excellent performance, non-toxic and tasteless, etc. Widely used in rubber, plastics, paper, paint, ink, medicine, cosmetics and many other industries. At present, the main methods of preparing nanometer calcium carbonate are: double decomposition, carbonation, emulsion, gel, non-freezing. The nano-powder prepared by vacuum freeze-drying method has the characteristics of regular particle shape, small and uniform particle size, narrow particle size distribution, pure chemical composition, no hard agglomeration between particles, good dispersion and so on. So this paper not only uses vacuum freeze drying method to prepare nanometer calcium carbonate, but also records the whole process of solution freezing evaporation by using vacuum freeze drying microscope developed by ourselves. The process of solution freezing evaporation is analyzed and studied. In this paper, calcium bicarbonate solution was used as the precursor solution to prepare nanometer calcium carbonate. Under the same conditions, the direct freeze-drying method and the vacuum evaporation freezing method were used to prepare the powders, respectively. X-ray and transmission electron microscopy showed that the prepared powder was polycrystalline, and there were two crystal types. The powder was pure and free of other impurities. The powder was porous and porous. Calcium carbonate with a particle size of about 50 nanometers can be obtained by either of the two methods. There is no great difference between the morphology and composition of the powders obtained by the two methods, but the vacuum evaporation freezing method will save a lot of energy. It is of great significance for the preparation of nano calcium carbonate by vacuum freeze drying. Experiments are also designed to explore how to prevent the solution from boiling during vacuum evaporation freezing (removing temperature and pressure factors). Taking pure water as an example, it can be concluded that the dissolved gas in pure water has a great influence on the first explosion and boiling in the self-freezing process. Putting the water treated by degassing into the porcelain chip will effectively prevent the spatter of the liquid during the second explosion. In this paper, the development of vacuum freeze-drying microscope is completed, and its structure, working principle and practical application are described in detail. The microscopic observation of freezing process was realized by using freeze-dried microscope, and the crystallization state of liquid freezing was analyzed by recording the temperature and pressure. The microcosmic characteristics of solution vacuum evaporation and vacuum freeze drying are grasped by the control system for the heating and cooling of the heat conduction block, and the segregation of the solution in the process of freeze-drying is verified. The eutectic point and eutectic point temperature of calcium bicarbonate solution were measured by the direct observation of freeze-dried microscope for the first time. The freezing process of calcium bicarbonate solution was studied for the first time in microstructure, which has an important effect on the preparation of powders with uniform composition and ideal particle size by using the vacuum freezing formula.
【学位授予单位】：东北大学
【学位级别】：硕士
【学位授予年份】：2010
【分类号】：TB383.1

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