本文選題：Y-Fe系儲氫合金 + YFe_2相��； 參考：《北京有色金屬研究總院》2016年碩士論文

【摘要】：本文以YFe_2和YFe_3合金為研究對象,采用XRD、SEM/EPMA、PCT等測試分析方法,研究了A、B側(cè)的元素替代對該體系合金結(jié)構(gòu)及儲氫性能的影響規(guī)律,以期開發(fā)出一種低成本、高性能的非鎳基稀土系新型儲氫材料。首先,研究了YFe_2合金的結(jié)構(gòu)及儲氫性能。鑄態(tài)合金為多相結(jié)構(gòu),除主相YFe_2之外,還存在一定量的YFe_3相和Y的氧化物相。第一性原理計(jì)算表明,YFe_2相和YFe_3相的自由能十分接近,成分的不均勻和能量起伏,極易導(dǎo)致兩相間的轉(zhuǎn)變。熱處理提高了YFe_2相的含量,合金初始最大吸氫量可達(dá)1.998 wt.%,但經(jīng)吸放氫循環(huán)后,YFe_2相易發(fā)生歧化反應(yīng),導(dǎo)致合金吸放氫容量下降。A側(cè)Ce對Y的適量替代改善了Y_(1-x)Cex Fe_2合金(x=0,0.15,0.25)的吸放氫動(dòng)力學(xué)性能和循環(huán)性穩(wěn)定性,隨著Ce替代量的增多,合金中YFe_3相含量升高,其穩(wěn)定吸氫容量增大。當(dāng)Ce的替代量為x=0.25時(shí),合金中YFe_3相含量最多,經(jīng)7次吸放氫循環(huán)后,具有最高的穩(wěn)定吸氫容量,且合金吸氫動(dòng)力學(xué)性能好,容量衰減最低,具有最好的循環(huán)穩(wěn)定性,但當(dāng)x增至0.5時(shí),YFe_3相減少,合金的吸放氫循環(huán)穩(wěn)定性降低。在以上基礎(chǔ)上,進(jìn)一步研究了YFe_3合金的結(jié)構(gòu)及吸放氫特性。其鑄態(tài)合金亦為多相結(jié)構(gòu),除主相YFe_3相外,還含有較多的Y6Fe_(23)相。經(jīng)過量添加Y(2 wt.%),并在1100℃退火熱處理72小時(shí)后,有效提高了合金中的YFe_3相含量,達(dá)到75.8 wt.%,降低了合金中YFe_2相含量,提高了合金吸氫循環(huán)穩(wěn)定性,其穩(wěn)定吸氫容量可達(dá)1.433wt.%,但合金吸氫坪臺壓偏低。為改善YFe_3合金吸氫坪臺特性,對YFe_3合金進(jìn)行B側(cè)元素替代研究;研究發(fā)現(xiàn),YFe_3-xMx(M=Mn,Al)合金吸氫容量隨著Mn、Al元素替代量的增加而逐漸減小,吸氫坪臺傾斜加劇。對YFe_3合金A側(cè)元素進(jìn)行元素替代(La、Ce等)。研究發(fā)現(xiàn),La并不能有效替代YFe_3合金中的Y元素,且La以氧化物形式存在,隨著La含量的增多,合金吸氫容量及動(dòng)力學(xué)性能逐漸下降,合金吸氫坪臺更加傾斜。在Y_(1-x)Cex Fe_3合金(x=0,0.15,0.25和0.5)中,適量的Ce替代,可以有效提高合金的吸氫坪臺壓力,當(dāng)Ce替代量為x=0.15和0.25時(shí),合金坪臺特性較好。但隨著合金中Ce替代量的增加,合金中YFe_2相含量逐漸增多,合金吸放氫循環(huán)穩(wěn)定性降低。同時(shí),Mg元素的少量(x"f0.15)替代并未改善Y_(0.85-x)Mg_xCe_(0.15)Fe_3合金的吸氫坪臺特性。綜合對比發(fā)現(xiàn),YFe_3相穩(wěn)定性優(yōu)于YFe_2相,且合金吸氫量高,適量的Ce替代可以改善YFe_3合金的吸氫坪臺特性,但Ce的替代量x應(yīng)低于0.25。
[Abstract]:In this paper, the effects of element substitution on the structure and hydrogen storage properties of YFe_2 and YFe_3 alloys were studied by means of XRDX SEM / EPMA-PCT and other methods, in order to develop a low cost. High performance non-nickel-based rare earth is a new hydrogen storage material. Firstly, the structure and hydrogen storage properties of YFe_2 alloy were studied. The as-cast alloy has a multiphase structure, in addition to the main phase YFe_2, there are a certain amount of YFe_3 phase and Y oxide phase. The first principle calculation shows that the free energy of YFe2 phase and YFe_3 phase are very close, and the inhomogeneity and energy fluctuation of the composition can easily lead to the transition between the two phases. Heat treatment increases the content of YFe_2 phase, and the initial maximum hydrogen absorption capacity of the alloy can reach 1.998 wt. however, after the cycle of hydrogen absorption and desorption, the phase of YFe2 is easily disproportionated. The hydrogen absorption and desorption kinetic properties and cyclic stability of Y_(1-x)Cex Fe_2 alloy were improved due to the decrease of hydrogen absorption and desorption capacity. The content of YFe_3 phase increased and the stable hydrogen absorption capacity increased with the increase of ce substitution. When the substitution amount of ce is x0. 25, the content of YFe_3 phase in the alloy is the highest. After 7 cycles of hydrogen absorption and desorption, the alloy has the highest stable hydrogen absorption capacity, and its hydrogen absorption kinetic property is good, the capacity attenuation is the lowest, and the alloy has the best cycle stability. However, when x increases to 0.5, the phase of YFe3 decreases and the cycle stability of hydrogen absorption and desorption decreases. On the basis of above, the structure and hydrogen absorption and desorption properties of YFe_3 alloy were further studied. The as-cast alloy also has a multiphase structure. In addition to the main phase YFe_3 phase, it also contains more Y _ 6Fe _ 2O _ 3) phases. After annealing at 1100 鈩，

本文編號：1950728