Recognition on systems RbF-GaF3 and CsF-GaF3

Article abstract of DOI:10.1016/S0040-6031(00)00596-7

The systems RbF-GaF₃ and CsF-GaF₃ were re-investigated by DTA and XRD method. In the system RbF-GaF₃, with eutectic E₁ at 750°C in the location of 8.5 mol% GaF₃ and E₂ at 749°C in the location of 43.0 mol% GaF₃, three compounds Rb₃GaF₆, RbGaF₄ and RbF·2GaF₃ were identified and indexed by XRD. The indexed result of α-Rb₃GaF₆ could not be successfully obtained, β-Rb₃GaF₆ is tetragonal, a = 6.324±0.004, c = 8.860±0.003 A?. RbGaF₄ is orthorhombic, a = 9.821 ± 0.006, b = 9.517 ± 0.005, c = 8.060 ± 0.006 A?; RbF·2GaF₃ is also orthorhombic, a = 9.459 ± 0.005, b = 9.336 ± 0.005, c = 7.685 ± 0.005 A?. In the system CsF-GaF₃, with eutectic E₁ at 66<4ri>C in the location of 7.5 mol% GaF₃ and E₂ at 675°C in the position of 44.0 mol% GaF₃, two compounds were confirmed. α-Cs₃GaF₆ is orthorhombic with a = 10.62 ± 0.02, b = 9.959 ± 0.006 and c = 5.607 ± 0.005 A?; β-Cs₃GaF₆ is also orthorhombic, a = 10.356 ± 0.003, b = 8.280 ± 0.003, c = 7.621 ± 0.005 A?; γ-Cs₃GaF₆ is tetragonal, a = 6.833 ± 0.003, c = 9.869 ± 0.002 A?; CsGaF₄ is orthorhombic, a = 8.571 ± 0.007, b = 7.575 ± 0.007 and c = 6.981 ± 0.006 A?. (C) 2000 Elsevier Science B.V.

Full text of DOI:10.1016/S0040-6031(00)00596-7

Thermochimica Acta 363 (2000) 55±59
Recognition on systems RbF±GaF3 and CsF±GaF3
Rong Chen*, Qiyun Zhang
Department of Chemistry, Peking University, Beijing 100871, PR China
Received 6 April 2000; accepted 3 July 2000
Abstract
The systems RbF±GaF3 and CsF±GaF3 were re-investigated by DTA and XRD method. In the system RbF±GaF3, with
eutectic E1 at 7508C in the location of 8.5 mol% GaF3 and E2 at 7498C in the location of 43.0 mol% GaF3, three compounds
Rb3GaF6, RbGaF4 and RbFÁ2GaF3 were identi®ed and indexed by XRD. The indexed result of a-Rb3GaF6 could not be
Ê
successfully obtained, b-Rb3GaF6 is tetragonal, a ˆ 6:324 Æ 0:004, c ˆ 8:860 Æ 0:003 A. RbGaF4 is orthorhombic,
Ê
a ˆ 9:821 Æ 0:006, b ˆ 9:517 Æ 0:005, c ˆ 8:060 Æ 0:006 A; RbFÁ2GaF3 is also orthorhombic, a ˆ 9:459 Æ 0:005,
Ê
b ˆ 9:336 Æ 0:005, c ˆ 7:685 Æ 0:005 A. In the system CsF±GaF3, with eutectic E1 at 6648C in the location of 7.5 mol%
GaF3 and E2 at 6758C in the position of 44.0 mol% GaF3, two compounds were con®rmed. a-Cs3GaF6 is orthorhombic with
Ê
a ˆ 10:62 Æ 0:02, b ˆ 9:959 Æ 0:006 and c ˆ 5:607 Æ 0:005 A; b-Cs3GaF6 is also orthorhombic, a ˆ 10:356 Æ 0:003,
Ê
Ê
b ˆ 8:280 Æ 0:003, c ˆ 7:621 Æ 0:005 A; g-Cs3GaF6 is tetragonal, a ˆ 6:833 Æ 0:003, c ˆ 9:869 Æ 0:002 A; CsGaF4 is
Ê
orthorhombic, a ˆ 8:571 Æ 0:007, b ˆ 7:575 Æ 0:007 and c ˆ 6:981 Æ 0:006 A. # 2000 Elsevier Science B.V. All rights
reserved.
Keywords: RbF; CsF; GaF3; Phase diagram; Aluminum brazing
1. Introduction
2. Experimental
The systems RbF±GaF3 and CsF±GaF3 have been
investigated by Chassaing [1]. Minimal eutectic were
located at 43 mol% at 5488C and 45 mol% at 5008C of
GaF3 in respective systems were determined. A sys-
tem of type similar to that of RbF±AlF3 and CsF±AlF3
[2,3], along with their lower temperature of eutectics
suggested at these compositions as a ¯ux used in
Nocolok method [4] for brazing aluminum and its
alloys. But we could not repeat the reported tempera-
tures of Chassaing. So we decided to re-study these
two systems.
2.1. Preparation of GaF3
A certain amount of Ga metal with purity >
99.99% was reacted with excessive hydro¯uoric
acid in a polyvinyl beaker protected with N2
¯ow. The beaker was heated on a water-bath. H2O2
was gradually dropped into the blend under contin-
uous stirring. As the reaction was completed the
product was vaporized until dry on the water-
bath. The white crystal hydrate GaF3ÁxH2O was
obtained. The GaF3ÁxH2O was put into a platinum
crucible which was heated at 2008C for 2 h under
HF-¯ow protection. The white mass obtained was
con®rmed as anhydrous GaF3 by X-ray diffraction
analysis.
* Corresponding author. Fax: ‡86-10-6275-1496.
E-mail address: chenr@rose.nsfc.gov.cn (R. Chen).
0040-6031/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 0 4 0 - 6 0 3 1 ( 0 0 ) 0 0 5 9 6 - 7

56
R. Chen, Q. Zhang / Thermochimica Acta 363 (2000) 55±59
2.2. Preparation of the samples
Samples were prepared from GaF3 which was
placed in a platinum crucible blending with a HF
solution of RbF or CsF with known concentration
and content. Twenty-three samples of RbF±GaF3
and 18 samples of CsF±GaF3 mixtures were prepared
in this way and gradually heated until dry at 2008C,
then annealed for 48 h at a higher temperature such
that no melting of any phase could occur. During the
annealing process, grinding and mixing of the samples
were repeatedly carried out in order to obtain homo-
geneous and equilibrium samples.
2.3. Differential thermal analysis
The high-temperature DTA equipment used (of the
CR-G type, Beijing Optical Instruments, Inc.) was
employed and calibrated using standard substances
with known melting points. Both heating and cooling
curves were calibrated. Al2O3 was used as a reference.
The heating rate was 15 min. Temperatures were
determined by the heating curve, and the cooling
curve also was used to correct the liquidus tempera-
ture. Experiments were conducted in dry air (relative
humidity <30%) in the static state. The error in
measuring temperature was Æ 38C.
Fig. 1. Phase diagram of system RbF±GaF3.
reacts with RbF to form eutectic E1 at 7508C in
the location of 8.5 mol% GaF3.
2. RbGaF4 peritectic melts at 7768C and reacts with
Rb3GaF6 to form E2 at 7498C and in the location
of 43.0 mol% GaF3.
3. The existence of RbFÁ2GaF3 is identi®ed by X-ray
diffraction powder analysis. Its formation tem-
perature was at least over 9008C has not been
determined yet.
2.4. X-ray powder diffraction analysis
All these compounds were identi®ed and indexed
by X-ray diffraction analysis. The diffraction data of
a-Rb3GaF6 coincided with JCDPS(22±1275). Due to
the data too complicated, the indexed result could not
be successfully obtained. XRD data of b-Rb3GaF6
listed in Table 2 was indexed as tetragonal, the cell
parameters being: a ˆ 6:324 Æ 0:004, c ˆ 8:860 Æ
The intermediate compounds in the system were
determined by X-ray diffractometry (XRD, Model
Dmax 2400, Rigaku Co., Tokyo, Japan) under CuKa
radiation, with a nickel ®lter and l ˆ 1:5409.
3. Results and discussion
Ê
0:003 A. XRD data of RbGaF4 are presented in
Table 3. The compound is orthorhombic, with
3.1. System RbF±GaF3
Phase diagram of the system RbF±GaF3, based on
DTA data is shown in Fig. 1. The invariant data is
presented in Table 1.
Fig. 1 reveals three intermediate compounds formed
in the system RbF±GaF3:
Table 1
Invariant points of the system RbF±GaF3
Invariant point
Temperature (8C)
GaF3 (mol%)
E1
750
749
776
860
8.5
43.0
50.0
25.0
E2
P
1. Rb3GaF6 congruently melts at 8608C and trans-
forms from a to b form at 3888C. The compound
m.p. (Rb3GaF6)

R. Chen, Q. Zhang / Thermochimica Acta 363 (2000) 55±59
57
Table 2
a ˆ 9:821 Æ 0:006, b ˆ 9:517 Æ 0:005, c ˆ 8:060Æ
a
Indexed data of b-Rb3GaF6
Ê
0:006 A. Compound RbFÁ2GaF3 was also indexed
(data listed in Table 4) as orthorhombic too, with
a ˆ 9:459 Æ 0:005, b ˆ 9:336 Æ 0:005, c ˆ 7:685Æ
Observed
Ê
d (A)
Calculated
Ê
d (A)
I/I0
h
k
l
Ê
0:005 A.
5.151
5.151
3.162
3.151
2.576
2.236
2.215
1.816
1.574
1.414
1.412
1.403
1.188
3
1
2
1
2
2
0
2
2
4
3
1
3
0
0
1
0
2
0
0
2
2
3
1
1
1
0
2
2
0
4
4
4
0
2
6
6
3.151
2.572
2.239
2.218
1.812
1.575
1.414
100
9
13
20
17
8
Table 4
a
Indexed data of RbFÁ2GaF3
Observed
Ê
d (A)
Calculated
Ê
d (A)
I/I0
h
k
l
5
5.961
4.679
3.318
5.980
5.941
4.667
3.326
3.324
2.986
2.985
2.966
2.957
2.919
2.829
2.612
2.513
2.418
2.360
2.342
2.233
2.130
2.030
2.021
1.967
1.922
1.920
1.892
1.840
1.836
1.826
1.823
1.694
1.691
1.663
1.623
1.622
1.555
1.478
1.466
1.461
1.460
1.420
1.407
8
1
0
0
1
2
3
2
0
1
3
1
3
2
0
3
1
0
3
2
2
4
0
3
5
2
5
2
3
2
4
2
4
2
6
2
2
0
6
4
6
0
1
2
1
2
1
0
2
3
0
2
2
2
3
1
3
4
3
2
4
1
0
3
0
4
0
3
4
5
3
2
4
4
1
6
0
2
0
2
3
1
1
0
2
0
0
2
2
0
1
2
0
2
2
2
2
1
1
3
1
2
4
2
0
2
1
3
1
1
2
4
1
3
0
0
5
5
2
4
0
1.403
1.187
5
3
3
5
a
Ê
Tetragonal cell: a ˆ 6:324 Æ 0:004; c ˆ 8:860 Æ 0:003 A.
2.966
12
2.928
2.816
2.623
2.523
2.412
2.351
15
34
23
23
10
15
Table 3
Indexed data of RbGaF4
a
Observed
Ê
d (A)
Calculated
Ê
d (A)
I/I0
h
k
l
4.197
4.073
3.735
3.418
3.276
2.919
2.316
4.192
4.092
3.735
3.424
3.276
2.938
3.313
2.279
2.276
2.274
2.194
2.106
2.097
2.029
2.008
2.006
1.767
1.708
1.489
1.460
1.458
1.297
1.299
1.265
1.149
13
15
9
2
0
1
2
3
1
1
4
3
1
3
4
4
3
1
1
5
4
5
1
2
4
2
4
6
0
2
0
2
0
2
4
1
3
2
3
2
0
1
3
4
0
4
4
6
2
2
0
6
0
1
1
2
0
0
2
0
1
0
3
1
1
2
3
3
2
2
0
1
2
5
5
6
2
5
2.231
2.132
2.026
5
7
4
54
23
43
17
1.971
1.922
3
100
1.890
1.840
3
3
2.271
2.197
2.102
9
24
12
1.823
3
2.026
16
1.692
1.665
8
2.004
1.765
1.705
1.489
1.460
14
6
12
18
8
1.621
1.552
1.478
5
4
28
11
1.297
7
1.461
15
1.265
1.149
8
5
1.420
1.406
3
6
aOrthorhombic cell: a ˆ 9:821 Æ 0:006; b ˆ 9:517 Æ 0:005;
aOrthorhombic cell: a ˆ 9:459 Æ 0:005; b ˆ 9:336 Æ 0:005;
Ê
Ê
c ˆ 8:060 Æ 0:006 A.
c ˆ 7:685 Æ 0:005 A.

58
R. Chen, Q. Zhang / Thermochimica Acta 363 (2000) 55±59
a-Cs3GaF6 was indexed as orthorhombic with
and
a ˆ 10:62 Æ 0:02,
b ˆ 9:959 Æ 0:006,
Ê
c ˆ 5:607 Æ 0:005 A; b-Cs3GaF6 is also orthorhom-
bic with a ˆ 10:356 Æ 0:003, b ˆ 8:280 Æ 0:003,
Ê
c ˆ 7:621 Æ 0:005 A; g-Cs3GaF6 is tetragonal with
Ê
a ˆ 6:833 Æ 0:003,
c ˆ 9:869 Æ 0:002 A.
The
indexed results of these compounds are listed in
Tables 6±8.
CsGaF4 was indexed (see Table 9) by X-ray dif-
fraction as orthorhombic with a ˆ 8:571 Æ 0:007,
Ê
b ˆ 7:575 Æ 0:007 and c ˆ 6:981 Æ 0:006 A.
Except for two compounds Rb3GaF6 (Cs3GaF6) and
RbGaF4 (CsGaF4) being only commonly recognized,
these re-investigated phase diagrams are quite differ-
ent from that reported in Chassaing's research. The
compounds Rb2GaF5 and Rb2Ga5F17 in system
RbF±GaF3, Cs5Ga3F14 and CsGa2F7 in the system
CsF±GaF3 reported by Chassaing, could not con®rm
their existence in this research. Another compound
RbFÁ2GaF3 was indexed in our research but no infor-
Fig. 2. Phase diagram for the system CsF±GaF3.
3.2. System CsF±GaF3
The phase diagram of the CsF±GaF3 system, based
on the results of DTA is displayed in Fig. 2. Invariant
points can be seen in Table 5.
Fig. 2 reveals two intermediate compounds formed
in the system.
Table 6
a
Indexed data of a-Cs3GaF6
Observed
Ê
d (A)
Calculated
Ê
d (A)
I/I0
h
k
l
4.993
4.985
4.960
4.436
3.720
3.601
3.336
3.323
2.712
2.696
2.612
2.427
2.421
2.342
2.331
1.931
1.912
1.652
1.641
1.481
1.480
1.479
1.391
1.335
1.333
36
0
1
1
0
2
3
0
1
0
1
1
3
4
4
4
3
3
1
1
6
3
1
2
7
2
0
1
2
1
1
3
0
1
1
4
3
2
1
0
4
0
6
4
1
3
0
7
0
0
1
1
1
1
0
0
2
2
2
0
0
0
1
2
1
3
0
3
2
3
4
1
2
1. Cs3GaF6 congruently melts at 8128C and trans-
forms from a to b and g form at 3548C and 6348C,
respectively. Cs3GaF6 reacts with CsF to form
eutectic E1 at 6648C in the location of 7.5 mol%
GaF3.
2. Peritectic reaction of CsGaF4 takes place at
7258C. The compound reacts with Cs3GaF6 to
form eutectic E2 at 6758C and in the position of
44.0 mol% GaF3.
4.447
3.743
3.594
43
35
34
3.312
84
2.700
2.608
2.428
27
21
21
2.342
33
A technique of quenching in liquid N2 ¯ow was
used to keep the structure for determining the sample
by X-ray diffractometry.
1.930
1.911
1.653
1.641
21
29
18
100
Table 5
Invariant points of the system CsF±GaF3
1.479
1.392
16
16
Invariant point
Temperature (8C)
GaF3 (mol%)
E1
664
675
725
812
7.5
42.0
44.0
25.0
E2
1.333
15
P
m.p. (Cs3GaF6)
aOrthorhombic cell: a ˆ 10:62 Æ 0:02; b ˆ 9:959 Æ 0:006;
Ê
c ˆ 5:607 Æ 0:005 A.

R. Chen, Q. Zhang / Thermochimica Acta 363 (2000) 55±59
59
Table 7
Table 8
a
a
Indexed data of b-Cs3GaF6
Indexed data of g-Cs3GaF6
Observed
Ê
d (A)
Calculated
Ê
d (A)
I/I0
h
k
l
Observed
Ê
d (A)
Calculated
Ê
d (A)
I/I0
h
k
l
5.157
3.639
3.581
3.466
5.180
3.644
3.575
3.463
3.451
3.410
3.288
3.145
3.066
2.704
2.597
2.590
2.453
2.446
2.434
2.324
2.154
1.922
1.905
1.902
1.857
1.852
1.827
1.819
1.818
1.816
1.799
1.776
1.771
1.730
1.729
1.726
1.649
1.640
1.636
1.636
1.478
1.471
1.358
1.247
26
6
2
0
1
0
3
1
1
3
2
1
0
4
4
3
2
2
3
2
0
4
0
5
1
5
0
4
5
5
4
0
3
6
6
2
3
1
7
6
0
1
0
2
0
1
0
2
1
0
0
2
3
0
0
1
3
3
3
4
0
2
1
2
1
0
4
0
2
1
1
2
4
0
1
2
1
5
0
2
6
1
0
1
2
2
0
1
2
1
2
2
1
0
1
2
0
1
0
0
4
2
4
0
4
2
2
3
1
2
3
4
1
0
1
4
4
0
0
2
1
6
3.288
3.054
2.966
2.919
2.740
2.321
1.920
1.898
3.287
3.070
2.966
2.930
2.724
2.321
1.924
1.897
1.600
1.599
1.518
47
11
15
12
7
0
2
1
2
1
1
2
1
1
3
4
0
1
0
1
1
0
1
0
0
3
2
3
0
3
1
3
4
4
5
6
1
1
9
4
3.411
3.300
3.140
3.083
2.693
2.595
6
100
15
5
10
100
12
11
4
1.599
1.520
6
6
a
Ê
Tetragonal cell: a ˆ 6:833 Æ 0:003; c ˆ 9:869 Æ 0:002 A.
2.442
4
2.328
2.151
1.922
18
5
Table 9
Indexed data of CsGaF4
a
26
Observed
Ê
d (A)
Calculated
Ê
d (A)
I/I0
h
k
l
1.902
1.856
18
4
3.645
3.336
3.306
2.829
2.704
2.527
2.328
1.907
1.646
1.461
3.647
3.330
3.290
3.837
2.704
2.526
2.328
1.908
1.646
1.461
1.460
26
15
100
23
22
20
27
25
8
2
0
2
2
2
0
0
3
4
3
1
0
2
1
2
0
3
0
2
2
1
5
1
1
1
0
2
0
3
2
2
4
1
1.826
1.817
4
4
1.799
1.780
1.770
1.730
1.730
4
4
4
3
5
16
1.649
1.638
6
4
aOrthorhombic cell: a ˆ 8:571 Æ 0:007; b ˆ 7:575 Æ 0:007;
Ê
c ˆ 6:981 Æ 0:006 A.
1.478
1.473
1.358
1.246
4
7
Acknowledgements
4
16
aOrthorhombic cell: a ˆ 10:356 Æ 0:003; b ˆ 8:280 Æ 0:003;
The authors wish to acknowledge the support from
Beijing Science Fund.
Ê
c ˆ 7:621 Æ 0:005 A.
mation was indicated in the Chassaing's report. The
difference in our study is that the original material
GaF3 was prepared from supper-pure metal gallium
and the samples used for DTA analysis were prepared
by total solution synthesis. This, we believe, may be
the best way for preparing the real homogeneous and
equilibrium samples.
References
[1] J. Chassaing, Rev. Chim. Miner. 5 (6) (1968) 1115.
[2] R. Chen, Q. Zhang, Thermochimica Acta 297 (1997) 125.
[3] R. Chen, J. Cao, Q. Zhang, Thermochimica Acta 303 (1997)
145.
[4] S. Takahashi, Heat Treating 10 (10) (1988) 20.