镁基合金的吸放氢动力学模型与机理研究
发布时间：2019-05-18 21:10
【摘要】：具有良好吸放氢动力学性能的储氢材料一直是广大研究者探索的热点。镁基合金因其丰富的资源,较高的吸放氢容量而备受关注。但纯镁仍存在一系列问题,比如动力学性能较差、活化困难、放氢温度高等缺点,限制了其实际应用。稀土-镁系储氢合金具有储放氢条件温和、平台压适中、原料储量丰富等优点,在能源储存和利用方面显示出良好的应用前景。本文针对合金吸放氢过程中的扩散控速与界面控速两种控制机制提出了一系列易于应用的动力学模型公式,包括反应时间与反应分数、最优氢化温度与对应的最小特征时间等关系式。采用粉末烧结法与氢化燃烧合成法两种工艺制备镁基储氢合金,并用推导模型系统研究了合金的吸放氢动力学性能。另外,本文还归纳了部分文献中的动力学实验数据,利用推导的模型研究了文献中镁系合金的吸放氢动力学,并进一步验证了模型的正确性。通过对富镁储氢合金的相关动力学数据进行模型分析,发现Nd的添加对改善镁基储氢合金吸氢动力学性能较为显著,在提升吸氢量的同时,能将活化能降低至79.29 k J/mol H_2,最优反应温度(696 K)、4 MPaH_2条件下吸氢完成所需的特征反应时间(83 s)最少。Mg_(95)Ni_5与少量Zr_(0.7)Ti_(0.3)Mn_2形成的富镁储氢合金吸氢活化能为109.85 k J/mol H_2,所需特征时间仅为49 s,比纯镁有大幅度降低,主要受界面控速为主,模型拟合相关系数平方值R~2高达0.99045。经过对Mg_2Ni基三种储氢合金吸放氢动力学实验数据的拟合分析可得出:三种合金均受扩散控速。其中,采用球磨制备的Mg_2Ni合金拟合度R~2最高(0.98186),活化能为110.326 kJ/mol H_2,在4MPaH_2下最优温度707 K所需特征时间仅为109 s,整体效果最佳。放氢动力学结果显示:在不同磁场下制备的三种合金中,4MPaH_2下的合金放氢速率最快,623 K时仅需约160 s就能够将氢全部释放出来,远远快于前两者。三种合金的模型拟合度较高,R~2均大于0.95,2MPaH_2下得到的合金活化能最低,为161.371 kJ/mol H_2。La-Mg系复合储氢材料动力学拟合结果显示:Ni的加入对La-Mg系复合储氢材料的吸氢动力学改善效果最佳,在573 K及2 MPa H_2条件下,达到3.87 wt.%的最大吸氢量所需时间仅为250 s,并且在80s内就能达到最大吸氢量的90%。模型拟合分析后发现:不同压力条件下的动力学数据都可用扩散控速模型进行拟合,R~2均大于0.98,La_2Mg_(17)-Ni的吸氢活化能为39.492 kJ/mol H_2,最优氢化温度下的特征反应时间可达到222 s,综合性能最优。通过对实验制备的储氢合金以及文献中的吸放氢动力学数据进行模型拟合分析,得到了不同体系合金的吸放氢动力学机理和表观活化能等信息,验证了推导模型的正确性。对于吸氢过程,还可求出体系的最优反应温度和最少特征反应时间,模型的建立为储氢合金的吸放氢以及类似气固反应的理论研究提供了新的思路和方法。
[Abstract]:Hydrogen storage materials with good kinetic properties of hydrogen absorption and desorption have always been the focus of exploration by researchers. Magnesium-based alloys have attracted much attention because of their rich resources and high hydrogen absorption and desorption capacity. However, there are still a series of problems in pure magnesium, such as poor kinetic performance, difficult activation, high hydrogen release temperature and so on, which limit its practical application. Rare earth-magnesium hydrogen storage alloys have the advantages of mild hydrogen storage and desorption conditions, moderate platform pressure and rich raw material reserves, so they have a good application prospect in energy storage and utilization. In this paper, a series of kinetic model formulas, including reaction time and reaction fraction, are proposed for the control mechanism of diffusion control rate and interface speed control in the process of hydrogen absorption and desorption of alloys. The relationship between the optimal hydrogenation temperature and the corresponding minimum characteristic time. Magnesium-based hydrogen storage alloys were prepared by powder sintering process and hydrogenation combustion synthesis process, and the kinetic properties of hydrogen absorption and desorption of the alloys were studied systematically by using the derived model. In addition, the kinetic experimental data in some literatures are summarized, and the hydrogen absorption and desorption kinetics of magnesium alloys in the literature is studied by using the derived model, and the correctness of the model is further verified. Through the model analysis of the related kinetic data of magnesium-rich hydrogen storage alloy, it is found that the addition of Nd can improve the hydrogen absorption kinetics of magnesium-based hydrogen storage alloy significantly, and at the same time, it can increase the hydrogen absorption capacity of magnesium-based hydrogen storage alloy. The activation energy can be reduced to 79.29 k J/mol H 鈮，
本文编号：2480338
[Abstract]:Hydrogen storage materials with good kinetic properties of hydrogen absorption and desorption have always been the focus of exploration by researchers. Magnesium-based alloys have attracted much attention because of their rich resources and high hydrogen absorption and desorption capacity. However, there are still a series of problems in pure magnesium, such as poor kinetic performance, difficult activation, high hydrogen release temperature and so on, which limit its practical application. Rare earth-magnesium hydrogen storage alloys have the advantages of mild hydrogen storage and desorption conditions, moderate platform pressure and rich raw material reserves, so they have a good application prospect in energy storage and utilization. In this paper, a series of kinetic model formulas, including reaction time and reaction fraction, are proposed for the control mechanism of diffusion control rate and interface speed control in the process of hydrogen absorption and desorption of alloys. The relationship between the optimal hydrogenation temperature and the corresponding minimum characteristic time. Magnesium-based hydrogen storage alloys were prepared by powder sintering process and hydrogenation combustion synthesis process, and the kinetic properties of hydrogen absorption and desorption of the alloys were studied systematically by using the derived model. In addition, the kinetic experimental data in some literatures are summarized, and the hydrogen absorption and desorption kinetics of magnesium alloys in the literature is studied by using the derived model, and the correctness of the model is further verified. Through the model analysis of the related kinetic data of magnesium-rich hydrogen storage alloy, it is found that the addition of Nd can improve the hydrogen absorption kinetics of magnesium-based hydrogen storage alloy significantly, and at the same time, it can increase the hydrogen absorption capacity of magnesium-based hydrogen storage alloy. The activation energy can be reduced to 79.29 k J/mol H 鈮，
本文编号：2480338
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