| 摘要: | 日益增長的對氣候變化的關注以及減少溫室氣體排放的需求，引發了人們對可再生能源的日益關注。其中，氫已經成為傳統化石燃料的有望替代品。然而，安全高效的氫氣儲存仍然是實現氫能經濟的主要問題。
有許多方法可以儲存氫氣，金屬氫化物配方目前被認為是最實際的方法，從結構穩定性、耐久性、能力和安全性等方面考慮。一種相對較新的儲存氫氣的方法是使用高熵合金（HEAs）。在這項工作中，對一種高熵合金Ti42Zr35Ta3Si5Co12.5Sn2.5進行了研究，以用於氫氣儲存。特別地，評估了HEA的製備過程以及結果顯微結構對氫氣儲存能力的影響。
本研究採用了三種不同的方法來製備Ti42Zr35Ta3Si5Co12.5Sn2.5，分別為激光熔化後的霧化過程（LM）、真空電弧熔化後的霧化過程，以及真空電弧熔煉鑄造。對於前兩種方法產生的粉末，使用篩分將這些粉末分離成不同的篩孔尺寸。對於鑄造HEA，對錠進行研磨以產生更細的顆粒。掃描電子顯微鏡（SEM）用於測量顆粒的形狀和尺寸，並表徵所製備的HEA的形態。電子探針微區分析儀（EPMA）顯示，霧化過程有助於消除霧化粉末中的任何偏析效應。 X射線衍射（XRD）顯示，不同粒徑的霧化HEA樣品將具有不同的晶化度。
篩選得到的第一種方法生產的Ti42Zr35Ta3Si5Co12.5Sn2.5粉末（樣品A至E）中，樣品A的粒度最細（小於53µm），且結晶度最低。樣品C的粒度在90-106µm之間，是這些霧化樣品中結晶度較高的。在此，僅對樣品A（小於53µm）和C（90-106µm）的氫儲存性能進行了研究，使用400℃下的Sievert型壓力組成等溫線（PCI）系統。樣品A的PCI結果顯示，在極低壓力（0.0001MPa）下有一個台地，最大氫含量為0.5wt%。當氫氣充入壓力升至2.7 MPa時，氫含量很慢地增加到1.6wt%。對於樣品C，在極低壓力下（0.0001 MPa）可以吸收0.6wt%的氫氣。第二台地壓力在4.4 MPa時可以吸收2.14wt%的氫。在氫吸收動力學方面，樣品A在極低壓力下的吸收速度較快。然而，樣品A和C的氫動力學相似。第二種方法生產的粉末吸收氫氣較少。
通過真空電弧熔煉產生的鑄造材料比霧化過程產生的材料結晶度更高。它在極低壓力範圍內的氫含量也最高。當壓力升至2.7 MPa時，它的氫含量與樣品A和C類似。
以上發現表明，這種Ti42Zr35Ta3Si5Co12.5Sn2.5高熵合金在極低壓力下能吸收氫。 2.7 MPa壓力下可以吸收1.6wt%的氫氣。所有這些都顯示了高熵合金非常獨特的氫吸收性能。在4.5 MPa時相對較高的2.14wt%氫含量也表明，這種高熵合金可以成為儲氫的候選材料。然而，為了充分利用這種高熵合金，需要盡量降低氫吸收溫度。
;Growing concern about climate change and the need to reduce greenhouse gas emissions have led to a growing interest in renewable energy. Among them, hydrogen has emerged as a promising substitute for traditional fossil fuels. Nevertheless, safe and efficient hydrogen storage remains a major issue for realizing a hydrogen economy.
There are many ways to store hydrogen, and the metal hydride formula is currently considered as the most practical method, in terms of structural stability, durability, capability and safety. A relatively new way to store hydrogen is the use of high entropy alloys (HEAs). In this work, a high entropy alloy Ti42Zr35Ta3Si5Co12.5Sn2.5 has been studied for its application in hydrogen storage. Particularly, the effects of fabrication process of HEA, and the resulting microstructure on the hydrogen storage capacity have been evaluated.
Three different processes to produce Ti42Zr35Ta3Si5Co12.5Sn2.5 have been employed here, namely, atomization process after laser melting (LM); atomization process after vacuum arc melting; and casting by vacuum arc melting. For the powder produced by the first two methods, sieving was used to separate these powders into different mesh sizes. For the cast HEA, the ingot was ground to produce finer particles. Scanning Electron Microscopy (SEM) was used to measure the particle shapes and sizes, and to characterise the morphology of the HEA so produced. It has been shown by Electron Probe Microanalyzer (EPMA) that the atomization process helped to eliminate any segregation effect in the atomized powders. X-ray Diffraction (XRD) showed that the atomized HEA samples with different particle sizes would have different crystallinity.
Among the sieved Ti42Zr35Ta3Si5Co12.5Sn2.5 powder produced by the first method (Samples A to E), Sample A had the finest sample size (smaller than 53µm), and it also had the lowest crystallinity. The Sample C, with a particle size between 90-106µm, was found to have the higher crystallinity among these atomized samples. Here, only the hydrogen storage properties Samples A (smaller than 53µm) and C (90-106µm) were studied using the Sievert type Pressure Composition Isotherm (PCI) system at 400℃. PCI result of the Sample A shows that there was a plateau at very low pressure (0.0001MPa), with the maximum hydrogen content of 0.5wt%. The hydrogen content increased very slowly to 1.6wt% of hydrogen, when the hydrogen charging pressure went up to 2.7 MPa. For Sample C, it could absorb 0.6wt% of hydrogen at very low pressure at 0.0001 MPa. A second plateau pressure could absorb 2.14wt% at 4.4 MPa. In terms of hydrogen absorption kinetic, it appears that Sample A had a faster absorption at very low pressure. However, both Samples A and C had the similar hydrogen kinetic. The powder produced by the second method absorbed less hydrogen.
The cast material produced by vacuum arc melting has the highest crystallinity than those produced by the atomization process. It also had the highest hydrogen content in the very low-pressure regime. As the pressure went up to 2.7 MPa, it had a hydrogen content similar to those of Samples A and C.
Above findings suggest the Ti42Zr35Ta3Si5Co12.5Sn2.5 HEA can absorb hydrogen at very low pressure. This HEA could absorb 1.6wt% hydrogen under a pressure of 2.7 MPa. All these show very unique hydrogen absorption properties of the HEA studied. The relatively high hydrogen content of 2.14wt% at 4.5 MPa also suggests that this HEA can be a suitable candidate for hydrogen storage. However, to make full use of this HEA, the hydrogen absorption temperature has to be lowered as much as possible. |
