【作者】 王建立；

【导师】 陈启元； 李旺兴；

【作者基本信息】 中南大学 ， 冶金物理化学， 2009， 博士

【摘要】 我国主要采用铝酸钠溶液晶种分解法制备超细氢氧化铝,生产中易存在产品粒度分布宽、颗粒形貌难以有效控制等问题。由于氢氧化铝分解温度低,在与有机高聚物加工过程中易分解,影响产品的使用性能,限制了其应用范围。为了解决超细氢氧化铝在生产和应用过程中存在的问题,为生产工艺优化和新产品开发提供理论指导,对其制备过程进行了系统研究,并开发了提高其热稳定性技术。论文利用激光粒度分析仪、扫描电子显微镜、表面电位仪、动态光散射粒度分析仪、浆体分散稳定性分析仪、电子束微区分析（EDS）等测试手段和分析方法,首次对铝酸钠溶液晶种分解制备超细氢氧化铝过程进行了系统研究,开发了氢氧化铝颗粒形貌控制及提高氢氧化铝阻燃剂热稳定性技术。主要结论和创新点如下:1)研究了分解温度、凝胶种子率、分解时间、铝酸钠溶液浓度等主要因素对铝酸钠溶液分解析出氢氧化铝过程中分解率、析出氢氧化铝粒度的影响。首次系统研究了凝胶晶种在分解过程中的作用,通过在线检测反应过程中体系的温度变化,结合铝酸钠溶液分解过程中分解液成分分析等,提出了凝胶晶种制备超细氢氧化铝的可能机理。2)根据分形理论,将粒度分布维数与超细氢氧化铝粒度分布的质量相关联,系统研究了温度、种子率等主要因素对铝酸钠溶液分解析出超细氢氧化铝粒度分布分维数的影响。发现从铝酸钠溶液中析出超细氢氧化铝的粒度分布具有分形特征,粒度分布宽度与其粒度分布分维数是对应的,粒度分布分维数可为颗粒粒度分布质量提供更为可靠的判据。3)系统研究了铝酸钠溶液中Na₂CO₃和Na₂SO₄杂质对铝酸钠溶液分解过程中分解率、析出氢氧化铝粒度分布的影响,对其影响机理进行了分析。Na₂CO₃和Na₂SO₄杂质的存在,降低了铝酸钠溶液的分解率,使分解析出氢氧化铝的粒度粗化,析出氢氧化铝晶体颗粒群的分维数随溶液中碳酸钠和硫酸钠杂质浓度的增加而不断增大。Na₂SO₄对分解率及超细氢氧化铝粒度分布的影响均大于Na₂CO₃。4)首次对铝酸钠溶液添加凝胶晶种分解制备超细氢氧化铝动力学进行了系统研究。通过研究分解温度、苛性碱浓度、种子率以及铝酸钠溶液浓度等对分解动力学的影响,得到了铝酸钠溶液添加凝胶晶种分解动力学方程。根据动态光散射粒度检测和扫描电镜结果,提出了种分制备超细氢氧化铝晶体生长机理。5)系统研究了电解质分散剂、高分子表面活性剂对超细氢氧化铝粉体的表面电性能、分散稳定性及水基浆体流变性的影响。电解质浓度及种类影响粉体的表面电位值,高价离子对粉体表面电位有较大的影响。添加少量的电解质类分散剂可以使粉体依靠静电排斥机制而分散。另外,浆体中加入适量的无机电解质和高分子表面活性剂可以改善浆体的流变行为,降低浆体表观粘度,并提出了添加剂对浆体流变性影响的作用机理。6)研究了超细氢氧化铝粉体颗粒形貌控制技术。通过在铝酸钠溶液分解过程中添加少量的多羟基或羧基类有机添加剂作为晶习改性剂,控制晶体的生长,制取了片状氢氧化铝;采用微乳液法,使氢氧化铝晶体在模板剂的作用下定向生长,制备出了球形的微米级氢氧化铝,并研究了有机添加剂对晶体生长过程的影响机理。7)紧密结合现有的氢氧化铝生产流程,开发了以单流反向加料、添加分散剂和有机改性剂为关键技术的高热稳定性氢氧化铝镁复合阻燃剂制备新工艺,解决了超细粉体的分散与团聚问题,提高了无机材料与有机高分子材料间的相容性,为改善超细氢氧化铝阻燃剂的使用性能提供了经济可行的技术。更多还原

【Abstract】 Super-fine aluminum hydroxide is mainly produced by seeded precipitation from sodium aluminate solution in China. There are many shortcomings in that the particle size of the products is too widely distributed and morphology of particles can not be controlled effectively during the production process of super-fine aluminum hydroxide. Aluminum hydroxide is easily decomposed when it is mixed with hot organic polymer materials. Its lower decomposition temperature limits its application performance and application field. In order to solve the problems presented in the production and application of super-fine aluminum hydroxide, preparation process of super-fine aluminum hydroxide was studied systematically and the technique for the improvement of its thermal stability was developed in this dissertation.Laser particles size analyzer, scanning electron microscopy(SEM), zeta potential analyzer, dynamic light scatter particle size analyzer, slurry dispersion stability analyzer, energy dispersive spectrometer(EDS) and other measure methods were utilized to study the precipitation process of super-fine aluminum hydroxide from sodium aluminate solutions with gel-seed, the technology for the control of particle morphology and for the enhancement of the decomposition temperature of super-fine aluminum hydroxide was developed. The main conclusions and innovations are as follows:1) The effects of the main factors such as precipitation temperature, gel-seed ratio, precipitation time and the concentration of the solution etc on the precipitation ratio and the particle size of the precipitated aluminum hydroxide from sodium aluminate solution were investigated. The action of gel-seeds in the precipitation process was studied for the first time, the possible mechanism for the precipitation of super-fine aluminum hydroxide from sodium aluminate solution with gel-seeds was proposed based on the temperature change and the analysis results of the liquors.2) According to fractal theory, the granularity distribution quality of super-fine aluminum hydroxide was associated with its fractal dimension of particle size distribution (PSD).The effects of the main process parameters, namely precipitation temperature, gel-seed amount, precipitation time and the concentration of the solution, on the PSD of super-fine aluminum hydroxide precipitated from sodium aluminate solution were investigated. It was found that the PSD of aluminum hydroxide precipitated from the liquor had the fractal characteristics of particle group, the results of PSD were in correspondent with its fractal dimension. So the fractal dimension of PSD can provide a credible criterion to the quality of the PSD.3) The influence of the impurities of sodium carbonate and sodium sulfate in sodium aluminate solution on the precipitation ratio and the PSD of super-fine aluminum hydroxide precipitation was studied, and their impact mechanism on PSD was analyzed. Both sodium carbonate and sodium sulfate in sodium aluminate solution could reduce the precipitation ratio and make the size of aluminum hydroxide precipitation coarser. The fractal dimension of PSD went up with the increase of the concentration of sodium carbonate or sodium sulfate. Sodium sulfate had greater effect on the precipitation ratio and PSD than sodium carbonate.4) Kinetics of super-fine aluminum hydroxide precipitation from sodium aluminate solution with gel-seed was studied. By studying the effects of precipitation temperature, the concentration of caustic soda, gel-seed ratio and the concentration of solution on the seeded precipitation kinetics, kinetic equation of super-fine aluminum hydroxide seeded precipitation from sodium aluminate solution was put forward. Based on the results of dynamics light scatter and SEM, the crystal growth mechanism of super-fine aluminum hydroxide from sodium aluminate solution with gel-seeds was obtained.5) The surfacial electrical property of super-fine aluminum hydroxide and the rheological behavior of its aqueous suspension were studied. It was found that both the content and the category of electrolytes affected the surfacial electrical property and surfacial potential. Highly charged ions had greater effect on the surface potential. The addition of small amount of electrolytes could make the super-fine powder disperse better by electrostatic repulsion. Proper amount of inorganic electrolytes and macromolecule surfactants in the slurry could improve its rheological behavior and reduce its viscosity. The mechanism how additives affected the rheology of the slurry was explored.6) The technology for the control of the morphology of super-fine aluminum hydroxide by seeded precipitation was developed. Super-fine aluminum hydroxide with plate shape was prepared via adding a small amount of organic additives with hydroxyl groups or carboxyl groups which acted as the crystal habit modifier agents for the control of the growth of aluminum hydroxide crystal. Spherical super-fine aluminum hydroxide was prepared with micro emulsion where aluminum hydroxide crystals could grow directionally under the mediating of organic templates. The action mechanism of organic additives on the crystal growth of aluminum hydroxide was also investigated.7) Combining with the current production process of aluminum hydroxide in China, a novel method to prepare aluminum magnesium hydroxide composite flame retardant with high thermal stability was developed with the key technologies such as adverse feeding with single flow, addition of dispersants and surface modifier additives. The difficulties namely dispersion and aggregation of super-fine powder were overcome, and the compatibility between inorganic material and organic polymer material was enhanced. The economical and feasible technology to improve the application performance of super-fine aluminum hydroxide flame retardant was provided.更多还原