文章信息/Info

Title:

Material Design of Mg-Ni-RE (La,Nd,Ce,Y)-H System Based on Thermodynamics and Kinetics Calculation

作者:

 羅群1; 周國治1; 陳雙林1; 李謙1;  2;  張捷宇 1

 (1. 上海大學，省部共建高品質特殊鋼冶金與制備國家重點實驗室
(2. 上海大學，材料基因組工程研究院

Author(s):

LUO Qun 1;  CHOU Kuochih 1;  CHEN Shuanglin 1;  LI Qian 1;  2;  ZHANG Jieyue 1

 (1. State Key Laboratory of Advanced Special Steels, Shanghai University
(2. Institute of Genomic Material, Shanghai University

關鍵詞:

稀土-鎂基合金; Mg-Ni-RE (La; Nd; Ce; Y)-H; 熱力學; 動力學; 材料設計

DOI:

10.7502/j.issn.1674-3962.2016.01.07

文獻標志碼:

A

摘要:

稀土因性質活潑被以單質或者中間合金的方式添加到鎂基儲氫合金中形成稀土－鎂基體系儲氫合金，該合金由于具有優良的儲氫性能而備受關注。但是目前缺少多元系稀土－鎂基合金相圖的指導，難免在設計材料配方時出現盲區，繼而陷入“炒菜”式的摸索之中，缺乏針對性。儲氫材料的吸放氫反應動力學研究，目前絕大多數的實驗反復測定恒溫條件下的反應分數與時間的關系上，很少研究各種因數，諸如溫度、氣相分壓、顆粒大小等對反應速率的影響，更談不上顆粒分布、變溫變速等對反應速率的影響。基于熱力學和動力學計算，研究了Mg-Ni-RE(La, Nd, Ce, Y)-H多元系，通過引入氫組元對比說明清楚相關儲氫合金與金屬氫化物的熱力學穩定性的差別，利用CALPHAD技術預報多元系的壓力-組成-溫度（PCT）曲線，結合原位高溫XRD和高分辨透射電鏡(HR-TEM)結果，闡釋了儲氫合金吸放氫的熱力學機制。同時，通過研究恒溫和變溫條件下氫化還原反應動力學模型，將吸放氫反應分數表達為溫度、壓力、顆粒大小、顆粒形貌等因素的函數，不但簡化了計算，而且還便于從理論上對各種物理量進行討論。引進了一個“特征時間”的新概念，它將在儲氫材料的研究中發揮重要的作用。

Abstract:

Rare earth (RE) elements have been added into Mg-based hydrogen storage alloys to form Mg-based RE-Mg hydrogen storage alloys due to their active properties. These alloys have attracted extensive attention owning to their good hydrogen storage performance. However, because of the lack of the guidance by phase diagrams in the RE-Mg system, the material design is aimlessly and would fall into a “cooking” exploration. For the study of hydriding and dehydriding kinetics, the current experimental measurement mainly repeated on determining the relationship between reaction fraction and time at isothermal condition. Few research focused on the effect of temperature, pressure, particle size… on the reaction rate, much less the particle size distribution, heating rate and other factors. This work investigates the Mg-Ni-RE(La,Nd,Ce,Y)-H quarternary system based on the thermodynamic and kinetic calculations. The calculation based on thermodynamic database reveals the thermodynamic stability of hydrogen storage alloys and hydrides. The Pressure-Composition-Temperature (PCT) curves are predicted through CALPHAD method. The thermodynamic calculation and experimental results of in situ X-ray diffraction (XRD) and high resolution transmission electron microscopy (HR-TEM) indicate the thermodynamic mechanism of hydriding and dehydriding. Meanwhile, the isothermal and non-isothermal hydriding/dehydriding kinetics are investigated and the reacted fraction is expressed as a function of temperature, pressure, particle size, particle morphology etc. This method not only simplifies the calculation, but also makes the physical quantities easy to discuss theoretically. A new concept “characteristic time” is introduced, which will act an important role in the research of hydrogen storage materials.