纳米晶镁铝水滑石的制备及其热分解机理

Preparation and Thermal Decomposition Mechanism of Nanocrystalline Mg,Al-hydrotalcite

研究了无机阻燃剂镁铝水滑石纳米晶的制备及其热分解机理.采用常压下,一步反应的液相法制备镁铝水滑石试样,用XRD和TEM测试试样的相组成和形貌,针状镁铝水滑石纳米晶体的长度约80nm.依据DSC和DTA-TG测试结果,发现镁铝水滑石纳米晶的热分解由两个阶段组成:第一个吸热峰出现在220℃左右,第二个吸热峰出现在380℃左右.研究了反应时间对所得镁铝水滑石试样的热分解性能的影响,发现延长反应时间,镁铝水滑石试样的第一次、第二次热分解的起始温度升高,第一次热分解的失重值增大,最后剩余氧化物的量增大,从而增强镁铝水滑石阻燃剂的阻燃性能.根据不同升温速率下获得的DSC测试数据,应用Achar微分法、atava-estk积分法和Ozawa积分法对镁铝水滑石纳米晶热分解的第二个阶段进行了动力学计算和分析,确定该段的热分解机理函数积分式为(1-α)-1-1.

The preparation and the thermal decomposition mechanism of nanocrystalline Mg, Al-hydrotalcite were studied. The phase composition and the microstructures of the samples were tested by XRD and TEM. The highly pure acicular nanocrystalline Mg, Al-hydrotalcite was synthesized by the one-step liquid reaction method at atmospheric pressure. Based on the DSC, DTA and TG test results, the thermal properties of the nanocrystalline Mg, Al-hydrotalcite were investigated, and two thermal decomposition process stages were recognized. In its first decomposition stage, the crystal water is released. In its second decomposition stage, the hydroxyl (OH-) octahedral structure is destroyed, with the hydroxyl (OH-) released as the gas of H2O and CO32- anion released as the gas of CO2, and MgO and Al2O3 are formed. Moreover, it is also found that the longer the reaction time, the higher the beginning decomposition temperature and the more the amount of the residual oxides (MgO and Al2O3). Besides, the non-isothermal chemical reaction kinetic theory was employed here, and the Satava-Sestak integral method, Achar differential method and Ozawa integral method were used. After the calculation and comparison, the thermal decomposition mechanical function of the acicular nanocrystalline Mg, Al-hydrotalcite in its second thermal decomposition is confirmed as the functional form of (1 - alpha)(-1) - 1.