THE SYSTEMS
NstlOSiOz-HzO
AND
NstlO-N~OrHz0
909
(6) KONDO,K.:Compt. rend. trav. lab. Carlsberg 16, No. 8 (1925). (7) NEUBERGER, A.: Biochem. J. 90,2085 (1936). (8) SCHMIDT, W.,KIRK,P. L., AND SCHMIDT, C. L. A.: J. Biol. Chem. 81,249 (1929). (9) SIMMS,H.S.: J. .4m. Chem. SOC.48, 1239 (1926). (10) SIMMS,H.S.:J. Phys. Chem. 32, 1121 (1929). (11) S@RENSEN, S. P. L.: Compt. rend. trav. lab. Carlsberg 12, 1 (1915-17). (12) S$RENSEN,S. P. L., LINDERSTR~M-LANG, K., A N D LUND,E.: J. Gen. Physiol, 8, 543 (1926).
EQUILIBRIA I N T H E SYSTEMS ll'a20-SiO2-HzO AND N%O-AlzOs-HzO AT 25°C. J. W. SPRAUER'
AND
D. W. PEARCE
Department of Chemistry, Purdue University, Lafayette, Indiana Received October 84, 1930
As a preliminary to a study of certain regions of the four-component system Na20-Si02-Al~Oa-H20 a t 25'C. some confirmatory work on the three-component systems Na20-A1208-H20 and N~O-SiOZ-HzO seemed advisable. The system Na20-A1208-H20 has been investigated by Goudriaan (3)and by Fricke and Jucaitis (2)a t 30°C. The present work on this system was carried only to the point necessary to confirm the results of the latter investigators, allowing for the 5" difference in temperature. The system Naz0-SiOz-H20 has been investigated by Harman (4). The results presented a t this time differ in several important respects from those reported by that investigator. MATERIALS
Three materials were used for the preparation of the solutions: AlzOa.3HzO, Xaz0.SiO2.9 HzO, and a solution (ca. 50 per cent) of sodium hydroxide. The alumina trihydrate was prepared by slow hydrolysis of C.P. sodium aluminate solutions, filtered off, rapidly washed with cold water on a suction filter, and dried in a steam chest. One such preparation gave 35.3 per cent loss on ignition (theoretical, 34.65 per cent H20) and contained less than 0.2 per cent sodium oxide. The hydrated sodium metasilicate was prepared by water recrystallization of the C.P. salt, was filtered with exclusion of carbon dioxide under a 1 This article is part of a thesis presented by J. W. Sprauer to the Graduate School of Purdue University in partial fulfillment of the requirements for the degree of Master of Science.
910
J. W. SPRAUER AND D. W. PEARCE
rubber hood fitted over the suction filter (the air being drawn through a soda-lime tube), washed with alcohol, and sucked dry. Analysis showed 21.65 per cent Na2O (theoretical, 21.81 per cent) and 21.7 per cent Si02 (theoretical, 21.13 per cent). The concentrated sodium hydroxide solution was made as nearly carbon dioxide-free as possible by dissolving C . P . pellets in an equal weight of water and decanting after long settling. One such solution contained 0.19 per cent sodium carbonate. I n a few instances more concentrated solutions were prepared by vacuum concentration on the steam plate and decantation after settling. PROCEDURE
Supersaturated solutions were stirred through mercury seals in glass equilibrium flasks contained in a thermostat. Solution samples were withdrawn a t bath temperature from a side arm on the flask through a fritted-glass plug filter by means of gentle suction and were transferred to stoppered weighing bottles; crystal samples with adhering mother liquor were drawn into sampling tubes and transferred to weighing bottles. I n some casea “residue” samples were rapidly centrifuged a t room temperature, and excess solution was decanted. The well-known procedure of determining composition of the solid phase by “residue” lines was not in all cases adequate in the study of the silicate system. The method of using a “tracer,” Le., a reference component present in small proportion only in the solution phase, was found reasonably satisfactory. Sodium iodide was employed for this purpose. I n three instances the solids were crystallized from a solution containing iodide; in all other cases the iodide was added about an hour before sampling. I n general, attainment of approximate equilibrium was judged by analytical checks of better than 1 per cent accuracy on samples taken a t an interval of about 1 week. Equilibrium was usually reached about 1 month after crystallization, although the aluminate solutions frequently required a longer time. The time required for spontaneous crystallization was decreased by seeding with the equilibrium solid when it was definitely known. ANALYTICAL METHODS
Si02 was determined (5) by double dehydration with hydrochloric acid, long ignition, and volatilization with hydrofluoric acid; Ka2O was determined (5) as sodium zinc uranyl acetate (it was previously ascertained that aluminum, in its maximum concentration encountered, did not interfere in the presence of an optimum concentration of hydrochloric acid); Ab08 was determined ( 5 ) with 8-hydroxyquinoline. Iodide wad deter-
THE SYSTEMS
NazO-SiOz-HzO
AND
Na20-A1203-H20
911
mined (6) by oxidation to iodate with chlorine, removal of excess chlorine by boiling, reduction to iodine with iodide, and titration with thiosulfate. RESULTS AXD DISCUSSION
The data obtained are presented in tables 1, 2, and 3. The data of table 1, dealing with the determination of solid phase composition by the “tracer” method, are not equilibrium values, as will be evident upon reference t o the method of preparation. TABLE 1 Composition of the solid phase in the system Ka20-Si02-H20 BOLUTION
BOLID PHASE
RESIDUE
CALCULATED MOLAR RATIO
NO.
SiOn
I
NalO
SiOe
I
per cent
per cent
per cent
per cent
per cent
per cent
27.2 33.0 27.2 33.2 37.1 26.4 27.9 41.0 35.4 26.1 20.7
1.55 0.34 1.62 0.36 0.38 2.07 1.01 0.34 1.60 2.29 2.39
0.266 0.310 0.431 0.410 0.488 0.300 0.366 0.248 0.210 0.366 0,390
31.4 34.9 31.8 35.2 37.0 30.9 32.8 43.9 41.4 28.1 24.4
11.3 12.1 10.8 11.5 12.1 11.9 14.2 13.5 17.1 16.3 16.8
0.146 0.131 0,238 0.197 0.256 0.167 0.155 0.136 0.112 0.178 0.149
Na#
15 16 17 18 19 20 21 22 23 24 25
__ __ __ __ __
-
Na#
: SiOn : HIO
3.1 3.4 3.3 3.3 2.9 2.94 2.96 3.1 2.7 0.98 1.08
: 2 : 11.6
: : : : : : :
: : :
2 2 2 2 2 2 2 2 1 1
: : : : : : : : : :
13.7 12.3 12.7 10.1 10.8 11.1 5.2 3.3 4.5 6.12
Notes: 15 and 16: residue from samples S o . 10 and 13; sodium iodide added and centrifuged. 17, 18, and 19: residue from samples KO.10, 13, and 14 a t room temperature for 2 weeks; sodium iodide added and centrifuged. 20 and 21: sodium iodide in supersaturated solution; crystallized by seeding a t 25°C.; analyses after 3 days. 22 and 23: spontaneously crystallized a t room temperature with occasional shaking for several weeks; sodium iodide added. 24: sodium iodide in supersaturated solution; spontaneously crystallized a t room temperature; analyses after 3 days. 25: residue from sample KO.5 a t room temperature for several weeks; sodium iodide added and centrifuged.
Assuming the iodide present only in the solution phase and uniformly distributed, one may calculate the solid phase composition reported in the last three columns of table 1. Such a calculation is subject t o cumulative error and is strongly dependent upon the iodide analyses. The proportion of water in the crystal, since it is determined by difference, is especially subject to error. However, the method is felt to be superior to the determination of composition by the intersection of “tie lines.”
912
I . W. SPRAUER AND I).
W.
PEARCE
We. 1. Photomicrographs. a, lower hydrate of 3NnS0.2Si0,,analysia No. 22; h, N&0.Si01.6H.0,aged crystale; c, frcshlypreeipitated Nax0.SiOz.6H00; d, spontaneously orystdliued 3Na10.ZSi01.11H,0,aged; e, seeded 3Na10.2Si0r-llHa0, analysis KO.9B before aecdinp- with Nn20.Si01.6H,0; f , Na,0.A1,0a.2.5H~0.
The assumption of uniform distribution of iodide is dependent upon the efficiency of mixing in the wses in which iodide was added after crystallization. If there were solution containing no iodide t,rapped within the
THE SYSTEMS
Naz0-Si02-H20
AND
Na20-A1203-H20
913
crystal, the Yap0 :Si02 and HzO :SiOz ratios of the calculated composition would be high, since the solution in all cases was relatively poor in silica. When iodide was added before crystallization, this would not be the case; therefore, such values should be given added weight. The distribution of iodide would be more nearly uniform in the case of large, well-formed crystals. The determination of the composition of 3IVa20.2SiO~.llH2O by the intersection of ‘‘tie lines” would have been impossible without greatly increasing the analytical accuracy and without growing larger, wellformed crystals by controlled seeding. However, the calculated composition by the “tracer” method is reasonably well represented by the formula given. Analyses No. 20 and 21 should be given added weight, both because iodide was added before crystallization and because the crystallization \$as effected by seeding. Photomicrographs of fairly characteristic crystals of 3Kaz0.2Si02.11Hz0 are shown in figure 1, d and e. This is the formula give by Rlorey (7) and mentioned in a footnote by Baker, Woodnard, and Pabst ( l ) , who reported crystallographic data on sodium metasilicate penta-, hexa-, octa-, and nona-hydrates. It presumably is the “crystalline sodium pyrosilicate hydrate” of Waddell (9). Analyses KO. 22 and 23 show evidence of lower hydrates of this salt. h photomicrograph of the No. 22 crystals is shown in figure 1, a. The crystals of S o . 23 were, unfortunately, not photographed, but were distinctly different from any of the others, being in the form of thick needles. The sodium metasilicate hexa- and nona-hydrates are well known. However, the characteristic habit of the hexahydrate observed in this study bore little resemblance to the triangular plates in the photographs by Tail (8), who summarizes the early work on this system, or to those of Baker, Woodward, and Pabst. The observed habit is well illustrated by figure 1, b. Analysis No. 24 shows evidence of a lower hydrate of metasilicate obtained in one attempt to crystallize 3 x a z 0 .2Si02.1 lHzO spontaneously. The crystals were of indistinguishable form. On the basis of only one analysis, identification with either the pentahydrate of Baker, Woodward, and Pabqt or the tetrahydrate of Vail would be unjustified. It is thought to be metastable a t 25”C., though the solution falls fairly close to the qolubility curve. The reproducibility of equilibrium data may be judged by the separate determinations of the invariant points of tables 2 and 3. The differences are a t least of the order of maximum estimated analytical error and presumably of the order of error in attainment of equilibria. The data obtained in this study and the results of Harman are compared graphically in figure 2. Our region of stability of sodium metasilicate hexahydrate cannot be metastable with respect to the nonahydrate, since
914
J. W. SPRAUER AND D. W. PEARCE
the seeding with nonahydrate of any solution in this region merely resulted in the dissolving of the seed. Harman did not experimentally establish Equilibria in the
TABLE 2 stem Na20-Si02-H20 at 86°C.
COMPOSITION OF SOLUTION NO.
SOLID PEASE
NalO par cent
per cent
1 2 3 4A 4B 5 6 7 8 9A 9B 10 11 12 13 14
9.65 8.69 17.8 21.06; 21.03’ 20.6 21.8 22.9 24.2 25.7; 25.9* 27.2 27.8 28.9 33.0 36.7
10.1 2.93 1.46 2.03* 1.98; 2.18 1.97 1.98 2.04 1.83* 1.87* 1.55 1.23 0.75 0.34 0.30
NatO, Si02.9H20 Ka20, SiO2. 9H20 Na20.Si02.9HzO S a 2 0 .SiO2.9H2O Na~O.Si02.6H~0 Xa20. Si02.9H20 NazO.Si02.6H~O N a 2 0 ,Si02.6H20(metastable) Na20.Si02.6H20(metastable) Na20.SiO2.6Hz0(metastable) N a z 0 . S i 0 2, 6 H 2 0 (metastable) N a 2 0 .SiO2.6H20 3 X a ~ 0 . 2 S i 0 ,l. l H 2 0 N a 2 0 .Si02.6H~O 3Na20.2SiO~.l l H 2 0 3 N a 2 0 .2Si02.llHzO 3Ka20.2Si02. llHzO 3 N a 2 0 .2SiO2. l l H 2 0 3Na20.2Si02.l l H 2 0 3Na20.2Si02.11H~0
* Determinations on separate equilibrium
+
+
+ +
preparations.
TABLE 3 Equilibria i n the system Naz0-AlzOrH20 at 36°C. BOLDTION SOLID P E A S 1
NO.
NalO
Alas
N d
AID:
~~
~~~
per cenl
per cenl
26
38.5
0.65
27 28 29
36.0 0.97 28.8 2.16 26.0 6.05 21.1 15.5 20.97 23.6t 20.1 23.4 18.6 9.7
30
31A 31B 32
er cent per cenl
35.0 29.0
9.80 11.14
25.2
29.5
t Three weeks in thermostat as compared t o about 7 weeks for 31B. Determinations on separate preparations. $ Reported by Fricke a n d Jucaitis (2) as 3 N a 2 0 . A l ~ 0 ~ . 6 H 2 0 . univariant points but obtained them by intersection of the solubility curves, whereas most conclusive in regard to the accuracy of the present
4C
30
t
9 R
20
IO
0
IO
20
7. s/02
FIG.2. The system Na20-Si02-Hp0 at 25°C.
-,
present work;
- - -, Harman
GO
50
40
6 .ial K
20
IO
0
present work at 25°C.; FIG.3. The system X a ~ O - A l ~ O r H ~ O-,. Jucaitis at 30°C. 915
- - -, Fricke and
916
J. W. SPRAUER AND D. W. PEARCE
work in this respect is the reproducibility of the univariant point NsnO. Si02 6HzO-SazO. Si02.9H~Oas indicated by analyses No. 4A and 4B,table 2. Harman's reported region of stability of N h O . SiO2. 6H20 might possibly be a metastable extension of our equilibrium curve. No attempt was made to follow the metastable curve. I n figure 3 the present data on the sodium aluminate system are compared with that of Fricke and Jucaitis (2). The crystalline habits of the two aluminates were identical with the photomicrographs which illustrate the paper of these investigators (cf. figure 1, f). No attempt was made to check the composition of the high-soda aluminate. Microscopic identification of the two spontaneously crystallized aluminates established the univariant point. SUMMARY
1. The system Saz0-SiO2-H20 has been investigated a t 25OC. from the ratio Sa2O:SiOz equal to 1:l up to 36 per cent Nan0 by weight. 2. The phase diagram shows, in several places, marked differences from that derived from the work of previous investigators. I n particular is the field of stability of NazO. SiOz.6H20 a t lower NsnO concentrations than reported by Harman. 3. Evidence for the compound 3Sazoa2Si02.(11?)HzO a t stable equilibrium is presented; lower hydrates may exist a t somewhat higher temperatures and concentrations. 4. Some data on the system Na20-Al2O3-H20 a t 25°C. are presented. We wish to acknowledge gratefully the valuable help given to us from time to time by Professor R. F. Newton of this laboratory. REFERENCES (1) BAKER,WOODWARD, AND PABST:Am. Mineral. 18, 2Q6 (1933). (2) FRICKEASD JUCAITIS: Z. anorg. allgem. Chem. 191, 129 (1930). Jucaitis: Z. anorg. allgem. Chem. 220, 257 (1934). (3) GOCDRIAAN: Proc. Acad. Sci. Amsterdam 23, 129 (1920); Rec. trav. chim. 41, 82 (1922). (4) HARMAN: J. Phys. Chem. 31, 511 (1927). (5) HILLEBRASDAND LUNDELL: Applied Inorganic Analysis, pp. 116, 522, 540. John Wiley and Sons, Inc., New York (1929). (6) KOLTHOFF A X D SANDELL: Teztbook of Quantitative Inorganic Analysis, p. 599. The hfacmillan Company, New York (1936). (7) MOREY:U.S.patent 1,948,730 (February 27, 1934). (8) VAIL:Soluble Silicates i n Industry, p. 58. Chemical Catalog Company, Inc., New York (1928). (9) WADDELL: U. S. patent 1,953,840 (April 3, 1934).
