单分散纳米氢氧化镁晶须形成机制研究

发布时间：2018-03-02 09:10

  本文关键词： MOS前驱物 水热法 单分散纳米氢氧化镁晶须 形成机制　出处：《沈阳理工大学》2015年硕士论文　论文类型：学位论文

【摘要】：纳米氢氧化镁晶须是一种新型绿色功能材料,具有表面能低、机械性能优良、弹性模量较高等特性。用作复合材料添加剂不仅可以提高材料的力学性能,还能有效提高材料的阻燃、抑烟性能。目前,对于纳米氢氧化镁晶须的制备研究多处于实验室阶段,对于其形成机制的研究尚未见文献报道。本课题主要采用水热合成法来制备单分散纳米级氢氧化镁晶须,并对其形成机制进行探讨。本文以菱镁矿制备出的亚微米级碱式硫酸镁晶须(Mg SO4·5Mg(OH)2·3H2O简称MOS)为原料,Na OH为沉淀剂,采用水热法制备单分散纳米氢氧化镁晶须。采用单因素实验法,探讨MOS初始料浆浓度、Na OH/MOS摩尔比、水热反应温度、反应时间、搅拌转速、助剂种类及添加量、MOS性能等因素对制备产物性能的影响。利用SEM、XRD、EDS、FT-IR、TG-DSC等先进的测试手段对制备产物的微观形貌、物相组成、元素含量、表面基团、热稳定性进行了测试分析;应用统计学规律,以晶须总数≥100为统计总数,单根晶须占晶须总数的百分比称为单根晶须含量,以此来表征纳米氢氧化镁晶须的分散性。通过对各影响因素的不断优化设计,得出最佳制备参数为:MOS前驱物平均直径≤200nm、MOS前驱物平均长径比100、MOS初始料浆浓度0.03mol/kg、反应温度180℃、反应时间4h、Na OH/MOS摩尔比4.5:1、搅拌转速100r/min、添加剂种类为硬脂酸钠、硬脂酸钠/MOS质量比2%。最佳制备条件下产物平均直径85nm,平均长度14μm,平均长径比100,晶须直径D在80~95nm范围占统计晶须总数的57%,晶须长度L在10~15μm范围占统计晶须总数的66%,长径比L/D在100~180范围占统计晶须总数的70%;合成产物为纳米Mg(OH)2晶须且纯度较高;晶须的热分解温度范围为318~490℃,在380~420℃之间热分解速率最快。在最佳实验条件下,通过过程取样,取出不同时刻的反应液,测得溶液中OH-和SO42-的浓度,根据结晶动力学原理,利用MATLAB软件和Runge-Kutta数值算实验数据进行处理,得出结晶动力学方程:以OH-浓度为基准:22300.179()()dcc c c c dt￥- = - -以SO42-浓度为基准:22300.154()()dcc c c c dt￥=--最终确定晶须形成的动力学模型为MA-2,结晶过程受多核表面反应控制。根据氢氧化镁晶须的结晶动力学模型,结合实验结果与相关理论进行综合分析并得出结论:本实验条件下纳米氢氧化镁晶须形成过程既包括以MOS为模板的模板机制,又包含液固机制下的螺旋位错生长方式。
[Abstract]:Nanocrystalline magnesium hydroxide whisker is a new green functional material with low surface energy, excellent mechanical properties and high elastic modulus. At present, the preparation of nano-magnesium hydroxide whiskers is in the laboratory stage. The mechanism of its formation has not been reported in literature. In this paper, monodisperse nano-sized magnesium hydroxide whiskers were prepared by hydrothermal synthesis. The formation mechanism was discussed. In this paper, the monodisperse nano-magnesium hydroxide whiskers were prepared by hydrothermal method, using mg SO4 路5MgOH2 路3H2O as precipitant and magnesium sulfate whisker prepared from magnesite as raw material. The initial slurry concentration of MOS, Na OH/MOS molar ratio, hydrothermal reaction temperature, reaction time and stirring speed were studied. The influence of the kinds of additives and the addition amount of MOS on the properties of the prepared products was studied. The microstructure, phase composition, elemental content, surface group and thermal stability of the prepared products were tested and analyzed by means of advanced testing methods, such as SEMXRDX EDST-IRT TG-DSC. According to the statistical law, taking the total number of whiskers 鈮，

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