喷雾合成中硝酸盐溶液液滴蒸发过程研究

Evaporation Process of Nitrate Solution Droplets in Spray Synthesis

摘要

喷雾合成法是一种在工业规模上生产多种金属氧化物材料的重要技术.该方法中,成本低、溶解性能好的硝酸盐水溶液应用广泛,有必要对过程中硝酸盐溶液的蒸发过程进行深入认识.本文对硝酸铝、硝酸钴两种硝酸盐浓溶液的蒸发过程开展了蒸发实验研究,并基于溶液液滴内部的传热传质过程建立起相应的数值模型,辅以基于热重和电子显微镜的化学反应和产物形貌分析.研究发现,受表面析出物影响,硝酸盐溶液的蒸发过程可划分为平方律阶段、冒泡阶段和收缩阶段.模拟结果表明,一旦溶液表面达到饱和浓度,少量生成物析出,就会使溶液液滴停止收缩,在表面形成一层球壳.产物形貌分析则揭示了这一球壳的两种形成机制:低熔点的硝酸铝在析出后熔融形成均匀薄层,进而产生出致密氧化铝层状壳结构；具有良好烧结性能的硝酸钴(氧化钴)在析出后表面形成难以扩散的大颗粒,迅速积聚后烧结固定成一层多孔介质球壳.该研究解释了金属硝酸盐蒸发过程中的关键物理过程,为喷雾合成模型建立和生产实践提供了指导.

Abstract

Spray synthesis is an important technique for producing metal oxide materials at an industrial scale. In this method, aqueous nitrate solutions are widely used due to their low cost and good solubility. Therefore, a deep understanding of the nitrate solution evaporation during this process is necessary. Experiments were conducted to study the evaporation of concentrated aluminum nitrate and cobalt nitrate solutions. A numerical model was developed based on the heat and mass transfer inside the solution droplets. To analyze chemical reactions and product morphology, thermogravimetric analysis and electron microscopy were employed. The results show that the evaporation process of nitrate solutions can be divided into three stages: a square-law stage, a bubbling stage, and a shrinkage stage. This division is influenced by surface precipitates. Simulations indicate that once the solution surface reaches saturation concentration, a small number of precipitates forms. This causes the droplet to stop shrinking and form a spherical shell on its surface. Morphology analysis reveals two formation mechanisms for this spherical shell. For aluminum nitrate with a low melting point, the precipitate melts and forms a uniform thin layer, which then develops into a dense alumina layered shell. For cobalt nitrate (or cobalt oxide) with good sintering properties, large particles form on the surface after precipitation, which accumulate rapidly and become fixed by sintering, forming a porous spherical shell. This study explains the key physical processes during metal nitrate evaporation, and provides guidance for the development of spray synthesis models and practical production.

关键词

喷雾合成 / 溶液液滴蒸发 / 烧结 / 质量传递

Key words

spray synthesis / solution droplet evaporation / sintering / mass transfer

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基金资助

国家自然科学基金资助项目(U24B2069)

华能集团总部科技项目基础能源与科技研究专项资助项目(HNKJ23-U23YYJC01)