T H E SYSTEM Sa20-Si02-H20: ISOTHERMS AT 10' AND 31°C. C. L. BAKER Philadelphia Quartz C o m p a n y , Public Ledger B u i l d i n g , Philadelphia 6 , Pennsylvania AND
L. R . JC'E Philadelphia Quartz Company of California, Berkeley, California Received March 7, 1949 INTRODUCTION
A number of papers have been published, since Harman's (3) work in 1927, showing isotherms for the IYa20-Si02-H20 system from 14" to 25°C. The latest and perhaps the best of these is that by Lange (4). Data for isotherms a t 10°C. and 31°C. are presented here. The extrapolations show definitely the salts Na$iO,. 9H20, IYa2SiO3.6H20, Na2Si03.5H20,and IYa3HSi04.5H20. In addition a very short region of existence of Sa2Si03.8H20 is shown. The stable phases found have been described minutely by Baker, Woodward, and Pabst ( 2 ) . MATERIALS AND PROCEDURE
The materials and procedure used have been described by Baker and Jue (1). I n addition to the materials described by them, sodium hydroxide carefully freed from carbonate by precipitation with lime mas used as a source of sodium oxide in the more alkaline regions. Where the concentration of sodium oxide was high, the sodium hydroxide was recrystallized twice in the form of N a O H . H 2 0 and centrifuged inside a tight cellophane bag so as to prevent the absorption of carbon dioxide. For points on the curve more siliceous than the sodium metasilicate, small amounts of clarified commercial sodium silicate solutions were used. During the course of this work the microscope was used continuously to check the habit of the crystals in the solid phase. We were thus able to keep continuous check on the identity of the crystals present. As indicated in our previous paper we were careful to repeat analyses a t intervals of a t least 1 week until two and preferably more analyses indicated that the system had come to equilibrium. When we lvere fairly certain of equilibrium from supersaturation, two or more samples of undersaturated solution containing an excess of crystals were usually prepared to check the point from undersaturation. A period of from G t o 10 weeks was usually required to establish the true solubility, and even longer periods were necessary in the more siliceous regions. Analyses were usually made in duplicate. Particular care \vas taken to determine transition points accurately. Usually, metastable points beyond the transition point mere obtained in order to determine the intersection of the curves by interpolation. Then systems containing 299
300
C. L. BAKER A h D L. R . J U E
TABLE 1 The system I\’a20-Si02-H20 at 10°C. COMPOSITION OF SOLUTION STABLE SOLID PEASE
SiOs
Val0
per cent
S a O H . H 2 0 .. . , . . . . . . . . Pickering’s value. . . .
38.45 f 0.1 40.7
NaOH,H20. . . . . . . . . . . Xa3HSiO1.5H~0.. ... .
38.3 f 0 . 1
SasHSiOd ,5H20., . , , . . .
NaaHSiOl.5HzO iXa~SiOa.5H20.. , . . . . (transition point) Ka3SiOs.5Hz0., . . . . . . . Metastable. . . . . . . , . .
Metastable . . . .
.....
,
Na~SiO3.5H20 Na2Si03.6Hz0,. , . . . (transition point) NazSi03.6H20 Metastable . . . . . , . . . . Metastable . . . . . . . . . , Metastable, . . . . . iYazSiO~. 6Hz0 Xa2SiO3.9H20., (transition point)
.
Na2Si03.9H~O, . . . . , , . ,
~
1
COUPOSITIOS OF RESIDUE
Sal0
I
Si09
per cent
,
per cent
~
38.0 i 0.05 36.58 34.20 32.8 29.95 29.05 27.74 26.85 26.45
0 13 i 0 02 0 13 0 14 0.12 0.28 0.30 0.66 0.935 1.09
26.43 & 0.05
1.04 f 0.02
27.15 & 0.05 26.72 rt 0.05 25.92 i 0.05 25.22 24.65 24.28
1.04 f 0.02 1.06 f 0.04 1.02 f 0.02 1.04 1.06 1.07
24.65
0.05
1.05 f 0.02
24.82 f 0.05 24.72 24.05 23.52 22.78
1.06 f 0.02 1.05 1.01 1.05 1.03
23.46 zk 0.05
1.05 f 0.02
23.5 f 0.07 22.47 21.40 18.00
1.05 i 0.03 0.80 0.64 0.44
&
1
’ 37 07 f 0 07 ’
36 80 36 50 36.05 36.32 36.87 35.93 36.52 36.4
18 85
, 18 40
* 0 05
21 61 20.05 22.07 23.80 21.57 23.78 23.0
29.12 f 0.05 29.08 28.8 29.15 28.85 29.03
27.52 f 0.05 27.50 26.55 27.7 26.55 27.22
26.85 i 0.05 26,80 26.65 26.60 26.5
25.47 f 0.05 24.4 24.68 24.7 24.32
21.75 f 0.05 21.80 21.68 21.4
20.1 f 0.05 19.97 19.93 19.15
ISOTHERMS FOR THE SYSTEM
30 1
P;azO-SiOz-HzO
TABLE 1-Concluded
'
COMPOSITION OF SOLUTION
-
STABLE SOLID PHASE ~
i
-
COMPOSITION OF RESIDUE
NalO
SiOr
Na?O
5i02
per cent
per ccnl
per cenl
per cent
Ya2SiO3.9H2O.,. . , . . . . . , 16.32 14.77 i 13.25 7.88 5.32 ' 4.46 4.64 5.29 6.63 8.70 9.57 10.85 12.33 14.75 18.55
'
* 0.10 0.10
* 0.15
* 0.15 0.2
0.38 0.37 0.43 0.67 1.17 1.92 3.50 5.11 f 0.07 8.69 13.3 15.1 18.45 0.10 21.55 0.15 26.72 0.15 32.18 i~ 0 . 2
* + *
21.08 20.82 20.82 21.20 21.30
18.85 18.92 19.55 20.35 20.60
21.52 21.72 21.50 21.08
20.68 21.22 20.75 20.68
21.47 f 0 . 1 21.8 & 0 . 1 21.5 f 0.1
21.10 f 0.08 21.28 0.10 23.05 0.10
* *
I '
+
8
%slog
00
10
x
20 51Ot
30
FIG. 2. The isotherm at 31°C.
FIG.1. The isotherm a t 10°C.
both salts a t the transition point were very carefully prepared and studied until it was certain that the crystals were truly in equilibrium. DATA
The data obtained are given in table 1 and table 2 and shown in the corresponding figures 1 and 2 . Compositions are given in per cent by weight. The
302
C. L. BAKER A N D L. R . JUE
TABLE 2 The swstem NazO-SiO1-H~Oat SI'C. SOLUTION
RESIDUE SOLID PEASE
NatO per cent
Ka2Si03.9H20. . , . , . , , . , , , . . . . , . , . . .
21.65 21.65 21.57 21.70 21.72 21.72 21.75 21.78 21.41
SiOI
NaiO
SiOe
ccnt
pcr cant
per cenl
21.47 21.47
18.12 18.12 14.58 11.14 10.50 13.87 17.28 18.48 20.37
29.2 29.20 20.02 10.48 4.10 2.12 2.16 2.27 2.97
20.35
2.95
$6).
20.90 20.60 19.91 20.00
NazSi02~9Hz0 r\Ta&03.6HzO NazSi03 8 H 2 0
23.20
21.77
20.58
2.93
Ka2Si03.6Hz0 . , . , . , , . . , . , , . . , . , . . . .
26.92 26,87 26.95 26.92 26.90 27.05 26.82
25.90 25.53
20,32 21.50 21.68 22.40 22.53 23.15 24.32
2.93 2.72 2.78 2.73 2.63 2.59 2.81
22.95
2.63
22.76 22.97 23.18 23.42 24.16 24.60 24,73 25.91 26.54 25.67
2.68 2.57 2.50 2.33 2.40 2.31 2.31 2.23 2.27 2.28
26.72
2.28
26.72 26.98 27.21 27.98 28.10 29.20
2.14 2.13 1.82 1.20 1.00 0.73
25,70 23.51
NazSi03.6H20 XalSi03.5H20 . . . . . . . . . . . , . , , . . . . . Na2SiO3.5H20. , . . . , . . . , . . , . . . . . . . . .
29.23 29.05 29.25 29.10 29.00 29.05 29.10 29.21 29.05
27.44
27.81 27.66
Na2SiOs.5Hn0 iTalHSi04.5 H a NasHSi0,.5H20. . . .
, , ,
. , , . ., . .. .
36.35 36.08 36.41 36.01 36.10 36.31
22.64 22.33 23.00 22.35 21.68 22.10
ISOTHERMS FOR THE SYSTEM
Xa20SiO2-H20
TABLE 2-Concluded RESIDUE SOLW PEASE
NajHSi0i,5Hz0. . . .
,
,
. ....., ... ..,
NaiO
SiOn
per cent
per cent
36.27 36.13 36.52 35.90 36.20 36.61 36.90
NaOH.H20 51.25 51.41 52.17
1
303
SOLUTION
7:3
Si02
per cent
per cent
22.00 21.71
i ;:?::
22.13
35.41 35.72
0.43 0.41 0.39 0.34 0.37 0.37 0.37
21.85 21.42 0.07 0.07 0.08 0.00
~
1
1
38.88 40.10 40.60 40.85
0.30 0.26 0.00
temperature was controlled a t about 31°C. & 0.05" and at 10°C. =t0.2". I t is important to note how closely the extrapolated lines intersect at the composition of the solid phase. Similar nork published by other authors has frequently been equivocal. The crystals of ,Ua2Si03.9H20grown a t 10°C. changed their habit according t o xhether they mere grown in solutions more or less alkaline a t about the 3Sa20:2Si02 ratio. In the more alkaline range they appeared as flat plates, while they seemed equidimensional in the more siliceous range. The solubility of KaOH.H20 was found to be lower than that given by Pickering (5). Particularly noteworthy is the short region of stability of the ?;a2Si03.8Hz0 described by Baker et al. DISCUSSION
1I7ehave tried repeatedly but without success to duplicate the appearance of the hydrated disilicate indicated by Harman. We did not find evidence a t either 10°C. or 31OC. of the crystal Sa8HSi02.2H20found by Sprauer and by Leidenroth at 25%. and 20"C., respectively. Our isotherm a t 31°C. does not indicate the complexity found by Lange et a l . a t 25°C. I t is difficult to judge how much the temperature has affected the condition of the nonahydrate curve. His metastable hexahydrate curve could well be an extension of a hexahydrate curve corresponding to ours. CONCLUSIONS
Isotherms a t 10°C. and 31°C. for the system P\Ta20-Si02-H20have been presented. The following salts have been found as solid phases: Sa2SiOp.QH20, Sa2SiOa . 8 H z 0 , I\'a2Si03.6Hz0,Na2Si08.5H20, and Tu'a3HSi04.5H20.
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J. H. WILLS
REFEREXCES (1) BAKER,C. L., AND JVE,L . R . : J. Phys. Chem. 42, 165-9 (1938). (2) BAKER,C. L., WOODWARD, H . T., ASD PABST,A , : Am. Mineral. 18, 206-15 (1933). (3) HARYAN, R . W.: J . Phys. Chem. 31, 511-18 (1927). (4) LANGE,H . , AND VOX STACKELBERG, XI.:Z. anorg. Chem. 266, 273-84 (1948). (5) PICKERIKG, S. U . : J. Chem. SOC.63, 890 (1893).
X REVIEW OF T H E SYSTEM SaZO-Si02-HZO J. H. WILLS Philadelphia Quartz Company, Public Ledger Building, Philadelphia 6 , Pennsylvania Received March 7, 1949 ISTRODCCTION
When Harman ( 5 ) published his study on the stability of sodium silicate solutions in 1927 no other work was available save that on isolated solutions such as those mentioned by Erdenbrecher (4), from which crystals had been separated. There was no evidence that equilibrium had been reached and it was impossible to use such data for determining the composition of the crystals indirectly. Sprauer (8) has since published some results at 25°C. and Lange et al. (6) have done careful work at 14°C. and 25°C. Leidenroth ( 7 ) has published results at 20OC. which correlate well with the data of others. He also includes some data at 60°C. and 100°C. The preceding paper by Raker and Jue ( 2 ) reports isotherms at 10°C. and 31°C. DISCUSSION
The system is not an easy one to work out. I t frequently allows the determination of metastable curves. In the siliceous ranges crystallization may be very sloiv and many Tveeks may be required to reach equilibrium. In the same range viscosities are likely to be high and separation of the liquid phase is difficult. In the alkaline range, the crystals may change their habit without changing composition. Residual alkali is difficult to remove from the solid phase and may cause difficulty in analysis. All investigators have used some form of suction to remove samples. It is important t o recognize that this raises the question of evaporation losses when filtration is difficult. Baker and Jue (1, 2 ) did use a high-speed centrifuge on a sample enclosed against evaporation losses and contact ivith carbon dioxide where a thick magma or high viscosity was encountered. Of the group who have prepared solubility curves only Harman ( 5 ) and Baker and Jue have worked on the siliceous side of the metasilicate ratio. While Harman’s data on Sa2Si03.9H20appear to be satisfactory, no one else has been able to observe any indication of the hydrated disilicate. Unpublished work indicates that the so-called sodium tetrasilicate (9) is stable in this area of exceedingly
