【作者】 张伟；

【导师】 王宝和；

【作者基本信息】 大连理工大学 ， 化学工程， 2004， 硕士

【摘要】 本论文简要介绍了纳米氧化镁粉体材料制备技术的研究进展、纳米氧化镁粒子形成机理以及在溶液以及干燥过程中的防团聚理论、热分解动力学理论和晶粒生长动力学的唯象理论。在试验基础上，分析了各工艺条件对纳米氧化镁的影响规律，并采用正交试验表进行了试验，找到了纳米氧化镁制备过程中影响晶粒直径以及产品收率的关键因素，以及较好的工艺条件。本文通过X-射线衍射、透射电镜、红外光谱、热重和差热分析等手段，对纳米材料不同溶剂置换干燥法、热分解过程机理、纳米氧化镁晶粒生长动力学进行了研究。 纳米氢氧化镁的煅烧是一个晶型转化和热分解反应的过程。它是由Mg（OH）₂多晶转化为MgO多晶，中间经过一个非晶过程。当干燥时间为3小时，200℃至350℃之间是一个过渡过程，350℃以后，晶型比较完好。煅烧温度越高，粒径越大。 若以晶粒直径为控制指标，结合单因素试验结果，较佳的合成纳米氧化镁工艺条件为：反应温度95℃，反应时间3小时，反应物浓度2.1mol／dm³，反应配比为5：1再用50ml乙醇浸泡0.5h，干燥温度100℃，干燥3小时，煅烧温度400℃，煅烧3小时。 正交试验结果表明，反应物浓度对晶粒直径影响最大，反应温度、反应时间与配比对晶粒直径的影响较小。而反应温度对氧化镁收率的影响最大，反应时间次之，反应配比与反应物浓度对氧化镁收率的影响较小。 不同溶剂置换干燥的研究表明，不同的溶剂置换方法和干燥方法都会影响纳米氧化镁晶粒直径的大小，其中五种溶剂置换方法所得到的纳米氧化镁的晶粒直径的大小顺序是：水洗、醇洗、水+NN二甲基乙酰胺洗涤、正丁醇共沸蒸馏和醇洗共沸蒸馏；三种干燥方法得到的纳米氧化镁的晶粒直径大小的顺序是：直接煅烧，烘箱干燥和微波干燥。团聚程度随溶剂置换方法变化，团聚程度最大的为水洗所得样品，最小的为醇洗共沸蒸馏与水洗+正丁醇共沸蒸馏所得的产品，水+N，N二甲基乙酰胺洗涤、醇洗所得的产品团聚程度没有显著的差别。 在纳米粉体的干燥试验中笔者发现，纳米氢氧化镁的湿物料干燥曲线与高斯方程拟合得很好。在湿物料湿基含水量在70％左右，大约干燥3小时以后，纳米氢氧化镁可以干燥到恒重。纳米氢氧化镁的干燥速率曲线可近似分为恒速干燥阶段和降速干燥阶段。 在热分解机理的研究中，采用Coats-Redfern与Doyle法联合推断氢氧化镁的热分解反应机理，确定其分解机理符合Avrami Erofeev n=1.5法则，即氢氧化镁的分解是一个边成核边生长的过程。计算得到分解活化能为126.6kJ／mol，指前因子为8.5×10⁸。 在晶粒生长动力学的研究中发现，煅烧时间越长、温度越高，纳米氧化镁晶粒增长越大。利用晶粒生长的唯象理论，借助方程Gⁿ=Atexp（-E／RT）确定了晶粒生长动力学指 摘要数为2.56 x10“帅4.h一’，活化能108.skJ/mol，动力学指数n为4。本实验的活化能E和n明显小于文献的报道，进一步说明纳米氧化镁的活性远远高于常规粒子的活性。更多还原

【Abstract】 The properties and application of nanometer magnesia have been briefly reviewed in this paper. Both the progress in the research and the synthesis of nanometer magnesia has been remarked, and the basic theory of nanometer powder has been discussed. According to conclusion of the mono-factor experiments, the multifactor orthogonal experiments have been applied in order to analyze systematically. The optimum processing conditions and the key factor in preparation of nanometer magnesia are achieved. TG/DTA/DTG, XRD, TEM and FI-IR techniques were used to characterize the samples. Drying methods, kinetics is studied. The main contents and results are as follows:The decompounded-experiments of nanometer magnesium hydroxide demonstrate that the transformation of crystalloid happens in the temperature range from about 250 C to 350 C; magnesium hydroxide absolutely decompounds at 400 C; the higher the calculations temperature is, the bigger the diameter of nanometer magnesia is.To determine influence of technical conditions on Product diameter, the influences of concentrations , molar ratio, reaction temperature and time on average size were investigated by means of multifactor orthogonal experiments. The results of experiments indicated that product diameter was mostly influenced by concentration of reactants, reaction temperature, followed by molar ratio of reactant and reaction time. According to conclusion of the monofactor experiments and multifactor orthogonal experiments, The optimum processing conditions in preparation of nanometer magnesia: C(MgCl2-6H20)=2.1mol/L , n(CO(NH2)2):n(MgCl2’6H20)=5:l, reaction temperature 95癈 and reaction time 3h.Under these conditions MgO nano-Particles with average crystalline diameter of 4nm were obtained.The result of drying experiment indicates that agglomeration degree of nanoscale magnesium oxide particles is relevant with solvent-replacement method. As for the same drying method, agglomeration degree mitigated by the following order: water-washing, water+N,N-dimethyl acetamide washing, alcohol-washing, water-washing + butyl alcohol azeotropic distillation and alcohol-washing + butyl alcohol azeotropic distillation.the diameter of MgO crystalline is affected on drying method. As for the same drying method, the diameter of MgO crystalline mitigated by the following order: water-washing, alcohol-washing,water+N-N-dmiethyl acetamide washing, water-washing + butyl alcohol azeotropic distillation and alcohol-washing + butyl alcohol azeotropic distillation.The TG and DTA techniques were used to research the decomposition kinetics of Mg(OH)2.The decomposition mechanism and kinetics equation were investigated according to Coats-Redfern and Doyle methods, the activation energy was about 126.6kJ/mol, and the equation can be depict as follow:By means of the kinetic theory, the dynamics equation of nanometer MgO grain growth is obtained, the activation energy was about 108.8kJ/moL and the equation can be depict as follow:更多还原