Effect of Preparation Technique on Microstructure and Hydrogen Storage Properties of LaNi3.8Al1.0Mn0.2 Alloys

doi:10.1016/j.jmst.2016.11.005

Abstract

Abstract:

LaNi_3.8Al_1.0Mn_0.2 alloy was prepared by vacuum induction melting and melt-spinning. The effects of different preparation techniques of the as-cast, cast then annealed, as-spun and spun then annealed alloys on the microstructure and hydrogen storage properties were investigated. The results indicated that the non-CaCu₅ phases in the alloy became tinier and more dispersive after annealing or melt-spinning compared to those of the as-cast one. But in the spun then annealed alloy, the non-CaCu₅ phases disappeared and only a single-phase with CaCu₅ type structure was found. For all the alloys, the cell volume was increased in an order of as-cast < spun then annealed < cast then annealed < as-spun, and the change of plateau pressure showed the opposite trend with that of the cell volume. The plateau could be flattened after melt-spinning or annealing, and the spun then annealed alloy showed the minimum plateau slope. The absorption kinetics of the alloy was promoted after melt-spinning or annealing. It is suggested that the change in cell volume and compositional homogeneity resulting from different preparation techniques contribute to the difference of the hydrogen storage properties of the investigated alloys.

Key words: Annealing, Melt-spinning, Metal hydride, Hydrogen absorption

Han X.B.,Qian Y.,Liu W.,Chen D.M.,Yang K.. Effect of Preparation Technique on Microstructure and Hydrogen Storage Properties of LaNi_3.8Al_1.0Mn_0.2 Alloys[J]. J. Mater. Sci. Technol., 2016, 32(12): 1332-1338.

Figures/Tables 13

Fig. 1. Cross-section of the LaNi3.8Al1.0Mn0.2 alloys prepared by different techniques: (a) as-cast; (b) cast then annealed at 1223 K; (c) as-spun; (d) spun then annealed at 1223 K.

Fig. 2. Phase distribution of the LaNi3.8Al1.0Mn0.2 alloys prepared by different techniques: (a) as-cast; (b) cast then annealed at 1223 K; (c) as-spun; (d) spun then annealed at 1223 K.

Fig. 3. Phase composition of the LaNi3.8Al1.0Mn0.2 alloys prepared by different techniques: (a) as-cast; (b) cast then annealed at 1223 K; (c) as-spun; (d) spun then annealed at 1223 K.

Fig. 4. XRD patterns of the LaNi3.8Al1.0Mn0.2 alloys prepared by different techniques.

Table 1. Constituents of different phase of the LaNi3.8Al1.0Mn0.2 alloys prepared by different techniques

Alloy	Spot	Element content (at.%) ------------------				Formulate	Phase
Alloy	Spot	La	Ni	Al	Mn	Formulate	Phase
As-cast	A1	17.18	62.02	17.79	3.01	La(Ni_3.771Al_1.024Mn_0.205)_0.964	LaNi₅
	B1	34.33	49.56	13.69	2.42	LaNi_1.444Al_0.399Mn_0.070	LaNi₂
	C1	25.3	49.33	24.2	1.17	LaNi_1.950Al_0.957Mn_0.046	LaNi₃
	D1	0.09	51.55	38.79	9.57	La_0.002NiAl_0.752Mn_0.186	AlNi
Cast then annealed at 1223 K	A2	17.42	61.54	17.6	3.44	La(Ni_3.712Al_1.078Mn_0.209)_0.954	LaNi₅
	B2	47.42	48.03	4.23	0.32	LaNi_1.013Al_0.089Mn_0.007	LaNi
	C2	25.51	49.44	24.15	0.89	LaNi_1.938Al_0.947Mn_0.035	LaNi₃
	D2	0.22	51.15	39.33	9.3	La_0.004NiAl_0.769Mn_0.182	AlNi
As-spun	A3	17.27	61.45	17.81	3.46	La(Ni_3.714Al_1.077Mn_0.209)_0.948	LaNi₅
	B3	43.88	50.52	4.95	0.66	LaNi_1.151Al_0.113Mn_0.015	LaNi
	C3	25.65	50.88	22.25	1.22	LaNi_1.984Al_0.867Mn_0.048	LaNi₃
	D3	8.65	53.05	31.02	7.27	La_0.163NiAl_0.585Mn_0.137	AlNi
Spun then annealed at 1223 K	A4	16.84	64.17	16.07	2.92	La(Ni_3.858Al_0.966Mn_0.176)_0.988	LaNi₅

Table 2. Lattice parameters and cell volumes of the LaNi3.8Al1.0Mn0.2 alloys prepared by different techniques

Alloy	a (nm)	c (nm)	c/a	V (nm³)	e
As-cast	0.50829	0.40652	0.79978	0.090958	0.1796%
Cast then annealed at 1223 K	0.50992	0.40872	0.80154	0.092035	0.0070%
As-spun	0.51049	0.40806	0.79934	0.092095	0.0578%
Spun then annealed at 1223 K	0.51012	0.40800	0.79981	0.091947	0.0044%

Table 3. Change of B/A and (Al + Mn)/Ni ratio in the matrix of the LaNi3.8Al1.0Mn0.2 alloys prepared by different techniques

Alloy	Formulate	(Al + Mn)/Ni	B/A
As-cast	La(Ni_3.771Al_1.024Mn_0.205)_0.964	0.326	4.82
Cast then annealed at 1223 K	La(Ni_3.712Al_1.078Mn_0.209)_0.954	0.347	4.77
As-spun	La(Ni_3.714Al_1.077Mn_0.209)_0.948	0.346	4.74
Spun then annealed at 1223 K	La(Ni_3.858Al_0.966Mn_0.176)_0.988	0.296	4.94

Fig. 5. PCT curves of the LaNi3.8Al1.0Mn0.2 alloys prepared by different techniques at 433 K.

Table 4. PCT curve characteristics at 433 K of the LaNi3.8Al1.0Mn0.2 alloys prepared by different techniques

Alloy	P (kPa) --------------------		S_f
Alloy	Absorption	Desorption	S_f
As-cast	75.32	62.50	0.62
Cast then annealed at 1223 K	37.77	35.88	0.43
As-spun	36.39	33.04	0.50
Spun then annealed at 1223 K	41.85	39.49	0.19

Fig. 6. Correlation between the equilibrium pressure (Pa and Pd) at 433 K and unit cell volume of the LaNi3.8Al1.0Mn0.2 alloys prepared by different techniques.

Fig. 7. Correlation between the slope factor Sf and lattice strain of the LaNi3.8Al1.0Mn0.2 alloys prepared by different techniques.

Fig. 8. Hydrogen absorption kinetic curves of the LaNi3.8Al1.0Mn0.2 alloys prepared by different techniques.

Fig. 9. Hydrogen absorption kinetic curves of the LaNi3.8Al1.0Mn0.2 alloys prepared by different techniques together with fitting curves of diffusion and surface penetration control modes, (a) as-cast; (b) cast then annealed at 1223 K; (c) as-spun; (d) spun then annealed.

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