The interaction of palladium with cobalt and erbium at 600°C

Article abstract of DOI:10.1016/S0925-8388(00)01373-6

The interaction of the components in the Er-Co-Pd system at 600°C was investigated over the composition range 0-50 at% of erbium by X-ray powder, metallography, electron probe microanalysis (EPMA), DTA and SEM. The isothermal section at 600°C was determin

Full text of DOI:10.1016/S0925-8388(00)01373-6

Journal of Alloys and Compounds 317–318 (2001) 475–477
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The interaction of palladium with cobalt and erbium at 6008C
*
J.I. Rousnyak , N.A. Tinikashvili, M.V. Raevskaya, A.V. Gribanov
Chemistry Department, Moscow State University, Leninskiye Gory, GSP-3, Moscow 119899, Russia
Abstract
The interaction of the components in the Er–Co–Pd system at 6008C was investigated over the composition range 0–50 at% of erbium
by X-ray powder, metallography, electron probe microanalysis (EPMA), DTA and SEM. The isothermal section at 6008C was determined
based on these results.
2001 Published by Elsevier Science B.V.
Keywords: Phase equilibria; Ternary section; Rare earth
1. Introduction
ErCo3, Er2Co7, ErCo5, Er2Co17. The ErCo5 decomposes
into Er2Co7 and Er2Co17 at 12408C [7] or 11508C [8].
The intermetallic compounds RE–Fe,Co,Ni (RE, rare
earth) are known to exhibit unique magnetic properties
(high saturation magnetization and Curie temperature). But
the practical use of such materials is limited due to their
high oxidizability and poor processibility. The addition of
noble metals (NM) could solve the problem and improve
their technological characteristics. Therefore, the study of
ternary alloys RE–Fe(Co,Ni)–NM is of great interest. This
report is devoted to the study of the phase equilibria in the
Er–Co–Pd system at 6008C.
There is no data on the physical–chemical interactions
of the elements in the Er–Co–Pd system in the literature.
The three limiting binary systems Er–Pd, Er–Co and
Co–Pd have been studied in detail [1–8]. Palladium and
cobalt form a continuous series of solid solution [1,2]. The
phase diagram of the Er–Pd system is characterized by a
wide range of palladium-based solid solution and by the
formation of the following intermetallic compounds
(IMC): ErPd3, ErPd2, Er2Pd3, Er3Pd4, Er4Pd5, ErPd,
Er3Pd2, Er5Pd2 [3–6]. The crystal structure of the IMC
ErPd2, Er2Pd3 and Er4Pd5 was not determined. At 565–
5488C, the equiatomic phase ErPd undergoes polymorphic
transformation CsCl(HT)→CrB(LT). Sacamoto et al. [5]
assumed that the regulated ErPd7 phase forms at 4508C.
The binary phase diagram Er–Co was investigated previ-
ously [7,8]. There are five intermediate phases in the
Co-rich (Co.50 at%) region in the Er–Co system: ErCo2,
2. Experimental details
The phase equilibria in the Er–Co–Pd system (Er,50
at%) have been determined by analyzing 70 samples
having a mass of 2 g. The starting materials were
palladium (purity: 99.9%), erbium (purity: 99.67%) and
cobalt (purity: 99.9%). The samples were pressed and
melted in an electric arc furnace in a purified argon
atmosphere with a nonconsumable tungsten electrode and a
water cooled copper hearth. Titanium was used as a getter
during melting. The alloys were remelted twice in order to
achieve complete fusion and homogeneity. After melting,
the alloys having mass losses of ,1.5% were sealed in
evacuated double-walled quartz ampoules containing
titanium chips as getters. Annealing was performed in a
resistance furnace at 6008C for 2500 h with a subsequent
quench in ice water.
Metallography, X-ray, electron probe microanalysis
(EPMA), scanning electron microscopy (SEM) and dif-
ferential thermal analysis (DTA) were used in the present
investigation. Microstructures were examined with a
Neophot 32 microscope at magnifications of 125–4003
and a Camebax microanalyzer (400–20003). Pd-rich
samples were etched in a Br21C2H5OH (1:4) solution;
Co-rich samples were etched by HNO31CH3COOH (1:2)
mixture. A HNO31C2H5OH (1:2) mixture was used for
etching Er-rich alloys.
*Corresponding author.
0925-8388/01/$ – see front matter
PII: S0925-8388(00)01373-6
2001 Published by Elsevier Science B.V.

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J.I. Rousnyak et al. / Journal of Alloys and Compounds 317–318 (2001) 475–477
3. Results and discussion
The results obtained enabled us to establish the iso-
thermal section at 6008C of the Er–Co–Pd phase diagram
over the composition range 0–50 at% of Er (Fig. 1). As
expected, the ternary phases are absent in above system.
We confirmed the existence of ErPd, Er3Pd4, Er2Pd3,
ErPd2, ErPd3, Er2Co17, Er2Co7, ErCo3 and ErCo2 binary
compounds (shown on the axes of the composition tri-
angle). The crystal structure of Er2Pd3 and ErPd2 inter-
metallides was not described previously. RE2Pd3 com-
pounds are known only for Y, Gd, Er, Dy, Ho, and their
crystal structure also were not determined. REPd2 com-
pounds exist in all RE–Pd systems, but the crystal
structure was only determined for EuPd2, ScPd2 (Laves
phases), LuPd2 (tetragonal, MoSi2 type) and SmPd2
(monoclinic, unknown prototype) [3]. Suitable monocryst-
als could not be obtained, so no crystal structure de-
terminations were performed. The phase corresponding to
the composition Er4Pd5 was not detected in the as-cast or
in the thermally treated (at 6008C) states (in agreement
with Ref. [4]). The ErPd7 ordered phase was supposed to
form at 723 K peritectoidly: a-Pd1ErPd3↔ErPd7 by
Sakamoto et al. [5]. We did not observe any ordering for
above composition. The crystal structure of the equiatomic
phase ErPd is bcc (CsCl type, a50.3453(5) nm), but is
orthorhombic (CrB type, a50.3661(9), b51.0540(8), c5
0.4507(5) nm) in the Er44Pd56 composition alloy. In the
palladium-rich alloys of the ternary system, the ErPd phase
was identified as CrB type also. So the increase of the
palladium content and addition of the third component
seem to intensify the bcc lattice destabilization and in-
Fig. 1. Isothermal cross-section of the Er–Co–Pd system at 6008C.
X-ray phase analysis was performed on powder samples
with a DRON-3.0 (Cu Ka monochromatizated radiation).
EPMA and SEM was carried out on a Camebax
Microbeam analyser using Kb, La and Lb lines for Co, Pd
and Er, respectively. Numerical evaluation of the results
was performed using standard computer programs.
High temperature VDTA-8M2 equipment (W–W/Re
thermocouples) was used for DTA experiments. Pure Fe,
Cu and Pt metals were used as calibration standards.
The alloys composition control was carried out by
control weighting, metallography, EPMA and spectropho-
tometry using SF-46 device.
crease
the
polymorphic
transformation
CsCl(HT)→CrB(LT) temperature.
Fig. 2. Microstructure of Er33Co57Pd10 (a) and Er14Co66Pd20 (b).

J.I. Rousnyak et al. / Journal of Alloys and Compounds 317–318 (2001) 475–477
477
Table 1
Data for the EPMA of some immiscible alloys of the Er–Co–Pd system
Alloy composition
(at%)
Composition of phases (at%)
Matrix
Phase
Inclusions
Co
Co
66
Er
14
Pd
20
Co
5.00
Er
Pd
Er
Pd
43.80
51.20
Er3Pd4
Co
Er2Pd3
Co
ErPd2
Co
99.93
0.00
0.00
59.8
0.07
40.20
69
84
11
11
20
5
99.96
99.97
0.00
0.00
0.04
0.03
3.10
3.27
64.20
0.00
0.00
40.40
42.90
59.60
57.10
Er2Pd3
Er3Pd4
Er3Pd4
Er2Co7
Er2Co17
Er2Co17
Er3Pd4
Co
55
25
20
5
0.00
42.20
57.80
78.20
84.60
19.80
13.10
2.00
2.30
81
95
14
85.10
98.30
12.70
0.00
2.20
1.70
0.00
43.00
9.60
57.00
3.00
2.5
2.5
87.40
Er2Co17
The isothermal section of the Er–Co–Pd system is
of immiscibility region. The DTA experiments confirm the
melting temperatures of the miscibility gap to be much
higher than 6008C, so melting the alloys by increasing the
temperature is impossible.
characterized by the formation of ternary solid solution
regions of different widths. All these regions are based on
the initial binary compounds of Er–Pd and Er–Co systems
and extend into the ternary system along the corresponding
constant Er concentration lines. The palladium solubility in
Er2Co17, Er2Co7 and ErCo3 phases does not exceed 2–3
at%, but reaches 8 at% in Laves phase ErCo2. An
homogeneity region of 22–25 at% Er (a50.4055(1)–
0.4051(1) nm) was defined for the ErPd3 phase (AuCu3
type), 5 at% of Co being dissolved. The other binary
phases of the Er–Pd system dissolve ,5 at% of Co. The
most extended region is the ternary solid solution based on
Co and Pd. The solid solubility of Er in Pd is 11 at% at the
temperature under investigation.
Acknowledgements
This work is supported by the Russian Foundation of
Basic Research (Grant No. 00-03-32651a).
References
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The distinctive feature of this state diagram is the
presence of a miscibility gap in the Co-rich region. The
alloys from this region have a very distinctive micro-
structure (Fig. 2). The composition of solidified immiscible
liquids correspond to one of the Co, Er2Co7, Er2Co17
phases on one side and one of the intermediate phases in
the Er–Pd system (Er2Pd3, Er3Pd4, ErPd2) on the other
side (Table 1). Using high pure metals, repeated remelting
and long-time annealing does not eliminate the existence