The isothermal section of the phase diagram of the La-Ni-Cu ternary system at 673 K

Article abstract of DOI:10.1016/j.jallcom.2004.05.076

The isothermal section of the phase diagram of the ternary system La-Ni-Cu has been investigated by X-ray diffraction, differential thermal analysis, optical microscopy and electron microscopy techniques. It consists of 13 single-phase regions, 23 two-phase regions and 11 three-phase regions. At 673 K, the maximum solid solubility of Cu in La₂Ni₃, La ₂Ni₃, La₂Ni₃, LaNi is and LaNi is about 2, 2, 3, 3 and 5 at.% Cu, respectively. The solid solubility of Cu in La₇Ni₃ and Ni in LaCu₆ is too small to observe. Cu and Ni can replace each other in LaNi₅ and LaCu₅, the LaNi₅ and LaCu₅ form a continuous solid solution. The maximum solid solubility of Ni in LaCu₂ and LaCu is about 15 and 4at.% Ni, respectively. A new ternary compound La₁₀Cu ₈₅Ni₅ has been observed in the La-Ni-Cu ternary system.

Full text of DOI:10.1016/j.jallcom.2004.05.076

Journal of Alloys and Compounds 386 (2005) 174–176
The isothermal section of the phase diagram of the La–Ni–Cu
ternary system at 673 K
Jingqi Liu∗, Fengquan Ma, Yinghong Zhuang, Fangwei Jiao, Jialing Yan
Key Laboratory of Nonferrous Metal Materials and New Processing Technology, Guangxi University,
Ministry of Education, Nanning, Guangxi 530004, PR China
Received 19 April 2004; received in revised form 26 May 2004; accepted 26 May 2004
Abstract
The isothermal section of the phase diagram of the ternary system La–Ni–Cu has been investigated by X-ray diffraction, differential
thermal analysis, optical microscopy and electron microscopy techniques. It consists of 13 single-phase regions, 23 two-phase regions and 11
three-phase regions. At 673 K, the maximum solid solubility of Cu in La2Ni7, LaNi3, La7Ni16, La2Ni3 and LaNi is about 2, 2, 3, 3 and 5 at.%
Cu, respectively. The solid solubility of Cu in La7Ni3 and Ni in LaCu6 is too small to observe. Cu and Ni can replace each other in LaNi5 and
LaCu5, the LaNi5 and LaCu5 form a continuous solid solution. The maximum solid solubility of Ni in LaCu2 and LaCu is about 15 and 4at.%
Ni, respectively. A new ternary compound La10Cu85Ni5 has been observed in the La–Ni–Cu ternary system.
© 2004 Elsevier B.V. All rights reserved.
Keywords: Phase diagram; La–Ni–Cu ternary system; X-ray diffraction; Compound La10Cu85Ni5
1. Introduction
2. Experimental
The lanthanum–nickel alloys are well established as
hydrogen-storage alloys due to their excellent performance.
The substitution of a small amount of Cu for Ni in LaNi5
alloys can change the property and hydrogen storage ability
of LaNi5 alloys and decreases the cost of LaNi5 alloys and
increases the stability of LaNi5. The phase diagrams and
thermodynamics are an important basis for the study of
the phase transformation of the materials and the materials
performance. Up to the present, the isothermal section of
the La–Ni–Cu ternary system phase diagram has not been
reported. In this paper, we studied the isothermal section of
the La–Ni–Cu ternary system at 673 K.
The phase diagrams of the binary La–Ni, Ni–Cu, and
La–Cu systems were reported in refs. [1–3], respectively.
At 673 K, there are eight intermetallic compounds in the
La–Ni system, namely La3Ni, La7Ni3, LaNi, La2Ni3, LaNi2,
LaNi3, La2Ni7 and LaNi5. There is no intermetallic com-
pounds in the Ni–Cu system. There are four intermetallic
compounds in the La–Cu system, namely LaCu, LaCu2,
LaCu5 and LaCu6.
In this work, the purities of lanthanum, nickel, and copper
were 99.8, 99.99, and 99.9%, respectively. One hundred and
fifty-two alloy buttons have been produced. Each sample was
prepared with a total weight of 3 g. These alloy buttons were
prepared in an argon atmosphere in a vacuum arc furnace or
in a high-frequency induction furnace. Each arc-cast button
had been melted two times and turned around after melting
for better homogeneity.
After melting, the sample buttons were sealed in evac-
uated quartz tubes for homogenization heat treatment. The
homogenization temperatures of the binary and ternary sam-
ples were chosen according to the phase diagrams of the
La–Ni, Ni–Cu, and La–Cu systems and the results of differ-
ential thermal analysis (DTA) of some ternary alloys. The
La-rich alloys containing more than 50 at.% La were ho-
mogenized at 693 K for 400 h. The Cu-rich alloys containing
more than 85 at.% Cu were homogenized at 873 K for 300 h.
The others sample buttons were homogenized at 773 K for
300 h. Subsequently, they all were cooled at a rate of 9 K/h to
673 K and kept at this temperature for 400 h, then quenched
into liquid nitrogen.
X-ray powder diffraction analysis was mainly used in the
present investigation. EPMA and DTA were carried out to
check the results of X-ray diffraction analysis when needed.
∗
Corresponding author.
E-mail address: zhuang@gxu.edn.cn (J. Liu).
0925-8388/$ – see front matter © 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jallcom.2004.05.076

J. Liu et al. / Journal of Alloys and Compounds 386 (2005) 174–176
175
Samples for X-ray diffraction analysis were powdered and
analyzed on a Rigaku D/Max 2500 V diffractometer with
Cu K␣ radiation and graphite monochromator operated at
40 kV, 250 mA (20◦ ≤ 2θ ≤ 60◦). The Materials Data soft-
ware Jade 5.0 [6] and Powder Diffraction File (PDF release
2001) were used for phase analysis. By all these means, the
phase relationships in the La–Ni–Cu ternary system were
determined.
3. Results and discussion
3.1. Binary system
3.1.1. La–Ni system
According to Pan and Nash [1], eight kinds of La–Ni
compounds, La3Ni, La7Ni3, LaNi, La2Ni3, LaNi2, LaNi3,
La2Ni7 and LaNi5, have been observed in the La–Ni binary
system. But, according to refs. [4,8], La3Ni does not exist,
and LaNi2 is rather La7Ni16. In our work, our result obtained
agrees with ref. [4].
Fig. 1. The isothermal section of the phase diagram of the La–Ni–Cu
ternary system at 673 K.
solution. The result obtained agrees with [7]. The solid
solubility of other compounds is too small to be ob-
served.
3.1.2. Cu–Ni system
The Cu–Ni binary system was reported in ref. [2], there
is no compounds in this system. Cu and Ni can replace each
other; they form a continuous solid solution phase (Cu·Ni).
3.4. Isothermal section
By comparing and analyzing the X-ray diffraction pat-
terns of 152 samples, combined with metallography, DTA
and EPMA, and identifying the phases presented in each
sample, the 673 K isothermal section of the phase diagram
of the La–Ni–Cu ternary system was determined (shown in
Fig. 1). The isothermal section consists of 13 single-phase
regions, 23 two-phase regions and 11 three-phases re-
gions. Details of the three-phase regions are given in
Fig. 1.
3.1.3. La–Cu system
In ref. [5], six compounds, LaCu, LaCu2, LaCu4, LaCu5,
LaCu6 and LaCu13, were reported. LaCu13 is a high temper-
ature phase. Under our present experimental conditions, we
did not find the LaCu4 and LaCu13 at 673 K in the isother-
mal section of the phase diagram of the La–Ni–Cu ternary
system, and the result obtained agrees with Chakrabarti and
Laughlin [3].
The 13 single-phase regions are: A (La10Cu85Ni5), B
(La), C (Cu·Ni), D (LaCu5·LaNi5), E (La2Ni7), F (LaNi3),
G (La7Ni16), H (La2Ni3), I (LaNi), J (La7Ni3), K (LaCu),
L (LaCu2) and M (LaCu6).
3.2. Ternary compound
Up to present, we have not found any reports about a
ternary compound in the La–Ni–Cu system. But, a new
ternary compound in the La–Ni–Cu ternary system was ob-
served in our present experiment. By tentative analysis, its
molecular formula is about La10Cu85Ni5. Its crystal struc-
tural is face centered cubic. Its space group is Fm3c; its lat-
tice constant a is equal to 1.158 nm. The details of the new
phase will be studied in another article.
The 23 two-phase regions are: C + D, D + E, E + F, F
+ G, G + H, H + I, I + J, J + B, B + K, K + L, L + D,
D + M, M + C, C + A, A + M, A + D, L + E, L + F, L
+ G, L + H, L + I, K + I and K + J.
The 11 three-phase regions are: 1: B + J + K, 2: K + J
+ I, 3: L + K + I, 4: L + I + H, 5: L + H + G, 6: L + G
+ F, 7: L + F + E, 8: L + E + D, 9: A + M + D, 10: A
+ M + C and 11: A + C + D.
3.3. Solid solubility
At 673 K, the maximum solid solubility of Ni in LaCu
and LaCu2 is about 4, 15 at.%, respectively. The maxi-
mum solubility of Cu in La2Ni7, LaNi3, La7Ni16, La2Ni3
and LaNi is about 2, 2, 3, 3 and 5 at.% Cu, respec-
tively. Cu and Ni can replace each other in LaNi5 and
LaCu5, LaNi5 and LaCu5 form a single-phase region
LaNi5−xCux (0 ≤ x ≤ 5), they are a continuous solid
Acknowledgements
This work was jointly supported by the National Nat-
ural Science Foundation of China (authorized number:
50001002) and the Natural Science Foundation of Guangxi.
(Matching Items).

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J. Liu et al. / Journal of Alloys and Compounds 386 (2005) 174–176
[3] D.J. Chakrabarti, D.E. Laughlin, Binary Alloy Phase Diagrams, ASM
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