THESYSTEMNa,0-Si02-H20
Dec., 1950
tube was kept a t a.temperature of 875". The hydrogen thus purified was absorbed into ordinary degassed titanium contained in a heated silica tube L. After absorption and cooling, the resulting hydride was evacuated briefly a t 200-300 ', following which pure tydrogen was obtained as needed by heating t o above 500 Helium.-This gas was used for volume calibration and was dried over Drierite and purified by passage through a tube containing zirconium powder heated to 875 Apparatus.-The dissociation measurements were made by observing the equilibrium pressure of hydrogen over a sample at a given temperature. The hydrogen content was determined by calculation from the pressure and known volume of the system. Changes in the volume of the sample due to the presence of hydrogen were found t o have a negligible effect and were ignored. The equipment used is shown in Fig. 4. A weighed sample of pure titanium was placed in a 347-alloy stainless steel crucible which had previously been subjected to a blank run. The crucible was placed in the silica tube B in furnace F and degassed in high vacuum overnight at room temperature. The temperature was raised to 1000" over 17 hr. and a pressure of 0.1 p maintained. A known volume of hydrogen at known pressure was admitted to the isolated sample from storage vessel E, the furnace allowed t o cool overnight to 400" and then slowly a t 25". After evacuation the volume of the measuring portion of the system was determined by admitting a known volume of helium from H and observing the pressure a t C. The system was evacuated through V, then heated to the temperature of the desired isotherm. Known volumes of hydrogen were added or removed from the sample tube B via the double gas buret D. Equilibrium pressures were measured by manometer C and recorded by a Brown Instrument Co. pressure gage G. The Hoskins FA 120 furnace F was controlled to 0.5" by a rdection-galvanometer and phototube relay system connected to thermocouple TI. The other thermocouple, Te (chromelalumel), was frequently calibrated us. a Bureau of Standards Pt-Pt, 10% Rh thermocouple and was used for measurement of temperature t o 0.5 Equilibrium pressures were usually attained in a matter of minutes and could be maintained without change over a period of days. In general 45 min. was allowed after a constant pressure was noted. Diffusion losses were negligible and within experimental error over a period of weeks, as evidenced by constancy and reproducibility of readings. Contamination of the sample by mercury vapor was prevented by keeping the U-tubes adjoining the gas buret and each manometer immersed in Dry Iceacetone.
.
".
.
[CONTRIBUTION FROM
THE
5,769
Stoichiometric hydride TiH2 was prepared in the above equipment, by cooling slowly to room temperature, and also in a large vacuum furnace consisting of a welded 347alloy, stainless steel retort within a Hevi-Duty 1200' muffle furnace. Crucibles of the same alloy were broke: in by trial runs. Titanium was degassed below 450 for 8-48 hr. t o avoid fixation of adsorbed gases, then a t 1000° for several hours in high vacuum. Hydrogen purified by passage through red hot Ti-Zr mixture was admitted and the furnace cooled over a period of 12-24 hr. A titanium getter layer was used to protect the sample from traces of oxygen and nitrogen which were always detected by slight discoloration of the getter. Hydrogen pressure was atmospheric throughout the absorption process.
Ac6owledgment.-The work reported herein was sponsored by the NEPA Project. The authors wish to express their appreciation for this support and for many helpful discussions with Drs. V. P. Calkins, W. K. Anderson and J. W. Johnson, of the NEPA Group. Suggestions by Drs. A. E. Finholt, M. D. Banus and Mr. R. W. Bragdon, of this company, contributed materially to the solution of experimental difficulties. Dr. H. T. Evans, of M. I. T., carried out the X-ray studies and the interpretation thereof. Summary Stoichiometric titanium hydride was prepared and its density determined. The dissociation pressure was measured for the Ti-H system over the range 500-800', 50-800 mm. and an hysteresis noted in the 600' isotherm. X-Ray diffraction patterns were observed for several compositions in the range TiHo.86 to TiH2 and two evanescent lines were found in the pattern of the stoichiometric hydride. A nearly linear relation of density to composition was found in this system from Ti to TiHz. Titanium containing small quantities of interstitial hydrogen was found to react rapidly with pure hydrogen a t room temperature and atmospheric pressure. BEVERLY, MASS.
RECEIVED MAY13, 1950
CHEMICAL LABORATORY OF THE PHILADELPHIA QUARTZ COMPANY ]
The System Na,O-SiO,-H,O at 50, 70 and 90°* BY C. L. BAKER,L. R. JUE The only available information on phase stability in the system NaaOSiOgHtO from 50 to 100' is the solubility curve for sodium metasilicate hydrates' and some data on phases separating at 60 and 100' determined by Leidenroth.2 Leidenroth reported a compound 3NazO. 2SiO2.6HnO which is certainly the 3Naz0.2SiOr
*
Presented before the Division of Phyaical and Inorganic Chemistry of the American Chemical Sodety 116th Meeting, Atlantic City, N. J., September, 1949. (1) C. L. Baker and L. R. J u s J . ?hyr. Chm., U , 166 (1988). (2) P; Lddemroth, "Eh Bdtmg e m Kenntnis der Natrlar 9111tata," XuMrat.tion, Y a r t h Lmther Unirerdtr. B;.tkwimrksr. J.ww, 1w.
AND
J. H. WILLS
5Hz0 or NasHSi0~2HzOfound a t lower temperatures.8 His data a t 60' indicate that he obtained NasHSiOclH20 as well as the other hydrates. A t 100' his data usually approach the NasHSiO,. lHzO composition rather than that of the dihydrate. Jordis' reported Na&iOz.1.5Hz0 formed at 100'. Fairly complete isotherms at 50 and 70" are here reported. An incomplete system showing the more alkaline silicates a t 90' is included. The new compounds found are aNazSiO~.6H10, (8) J. E.Wills, 1.Phyr. Chmn.,U,804 (19ILo). (4) P.Jodi., C k n . Br., Ih 988 (191U.
5370
C.L. BAKER,I,. R. J W E A r m J. H. Wn.1.s
Vol. 72
No isothermally invariant point was obtained for NaOH-NatHSiOcHZO. Such an invariant point probably lies within the range between 50 57.0 and 57.5% Na,O. The solubility curve is considered accurate to about f0.15% NazO and 0.05% SiOz. A t one time there was 40 thought to be some indication of the existence of an orthosilicate, but in every case the materials secured €4 were finally proven'to be 0: 30 NasHSiOcHSO and NaOH. It was noticed that when 5 a portion of the solution in equilibrium with NatHSiO,. 2HI0 at 90" was removed 20 and allowed to cool a t room temperature, crystals of NeHSiOc2H90 continued to separate and appeared to be quite stable even a t room 10 temperature and underwent transition to the pentabydrate only in rare cases. This observation of stability corroborates findings of 0 Harman and Leidenroth. 10 20 30 40 50 Working in the neighborhood sa,%. of the invariant point heFig. 1.-The system Na,O-SiorHIO at SOo. akaline salts only. weight per cent. tween NarHSi0~2H,@Nar basis: @, points of isothermal invariance; 13, themtical rompmition; 0. &-SiOs one could easily pas3 mental equilibrium points; 0. wet residue determinations; --,field boundaries. from a suspension Containing NaHSi04.2H,0 to one N&HSi04.1Hz0 and an unidentified salt which containing N&iOa. However, the slow rate of may be N&iOvlHtO. solution of NafiiOa apparently impeded change in the opposite direction. The accuracy of the The Isotherm at 90' data on the NaHSiOv2HtO curve is considered A t 90 f 0.3' only the metasilicate and more as *0.2y0 NarO and *0.1% SO,. alkaline salts have been studied (Table I, Fig. 1). At this temperature the crystalline compound, anhydrous NaSiOt, has a long stable range. The fact that this salt is stable a t 90" in contact with solutions containing considerably less Si02 and N a O than any of the solutions in equilibrium with other salts a t 70" probably explains the " difficulty experienced with solutions at that temperature as due to contamination with anhydrous N&iOs. Sample crystals prepared a t 100' (Illust. 1) had refractive indices 1.513, 1.520, 1.528. corresponding to crystals fomied .. ~, I from an anhydrous melt. By very careful operation. according to the methods detailed in the section on analytical methods.the solubility of NaOH was found to be 57.5 * 0.1% NatO. If data given by Pickerin@ are interpolated, a figure of 60% NazO is found. His methods are open to question. (0 8. u. Pkkriu, 1. C h . s%,
u m (11191).
L
Illust. l.-Anhydmus N&Ch
g m m at 100.. 140 X.
THESYSTEM Na&SiOa-HIO
Dec., 1950
The curve for NazSiO3 was approached from supersaturation. Satisfactory results could not be obtained by preparing an undersaturated solution and depending upon the NazSiO3 crystals to dissolve until equilibrium was reached. The accuracy of this portion of the curve is thought to be 0.3% NaaO and * 0.3% SiOz. Since approach from supersaturation took several weeks, there is some likelihood that a slow reaction with the silver containers later observed in very alkaline solutions, and described in the section on analytical procedures, may have depressed the alkali content so rapidly as to make impossible the true determination of the NaaiO3 solubility near its invariant point with NasHSi04.2H20. The latter curve was more readily f
TABLE Ib THESYSTEM Na20-SiO2-H20 Composition of soh. b NasO Sios
Composition of residue NasO Si&
AT
90"
Stable solid phase
NazSiO3 NazSiOs NaSiOa NazSiOa NazSiOa NazSiOs NarSiOa NazSiOa Na2SiOI NazSiO, Na2SiOs and NasHSiO4.2H20 41.30 1.34 46.60 27.72 N~HSi04.2H20 39.88 1.65 46.60 27.70 NaaHSiO4.2H20 39.85 1.64 46.60 28.96 NaaHSiOd *2H20 38.60 1.80 46.60 28.65 NaaHSi04.2H20 38.45 1.95 46.75 28.95 Na3HSi0, ~2H20 37.60 2.47 46.15 27.85 NasHSi04.2H20 37.30 2.70 46.05 27.65 KaaHSiO, .2H20 36.95 2.87 46.15 28.65 NasHSi04.2H20 35.80 4.33 45.90 30.65 NarHSi04.2H~O 35.30 4.52 44.80 30.18 Na8HSi04.2H20 35.10 5.02 46.60 31.65 NaaHSi04.2HzO 34.60 6.95 46.25 30.30 Na3HSi04.2Hz0 34.60 7.45 46.10 28.70 KaaHSi04.2H20 NaaHSiOa.2H20 and 40.0 1.50 NasHSiO,.H20 57.00 0.18 54.10 17.80 iYa3HSi04.H~O 55.25 .20 53.15 19.75 NaaHSiO4.HzO 55.50 .20 53.70 16.55 NaaHSi04.H~0 48.80 .26 50.80 22.30 NaaHSiO4 .HzO 46.75 .49 50.50 25.62 NasHSi04.Hz0 45.20 .44 49.70 23.52 NaaHSi04.HzO 44.10 .48 49.15 22.40 NasHSiO,.H~O 42.65 .62 48.15 21.95 NasHSi04*Hz0 40.85 .93 47.80 21.55 NasHSiOc.HzO 40.10 1.13 48.35 25.70 NasHSi04.Hz0 40.00 1.54 49.80 28.25 Na,HSiO,.HzO Cryst. NaOH soly. 67.5 Na20' Numerical values Vdue by Pickering 60% NmO. in the tables are all per cent. by weight. 34.47 5.76 46.90 33.70 2.56 48.90 32.20 0.85 47.30 30.83 0.44 43.50 28.10 0.80 42.30 27.60 1.10 45.80 25.74 2.39 46.75 23.50 12.40 37.60 23.30 10.80 39.12 24.28 23.70 41.30 35.0 5.50
36.10 40.60 37.92 29.40 29.95 36.80 40.10 30.68 31.90 39.45
established, and the invariant point suggested is .considered accurate only to *0.3% Na2O and f0.3% SiOz. The actual determinations are given in Table I, Since for theoretical reasons6it is not possible for the tangent to a saturation curve to pass through the composition of the saturating solid, the curve is drawn slightly above the most alkaline point on the NazSiOs curve. In developing the siliceous portion of the Na&i03 curve, solutions of high viscosity were encountered, and the points are probably accurate only to 0.4Yo Na2O and 0.15% SiOr. The Schreinemakers' residue lines for NazSiOs converge a t a-point on the graph corresponding to a composition about 1% higher in Na2O than the theoretical point. It may be that crystals of NazSiOa tend to include or adsorb an excess of Na20. The Isotherm at 70' The isotherm a t 70' has been worked out more completely (Table I1 (a) and (b), Fig. 2). Solubility of NaOH a t 70' was found to be 56.45 f 0.05%, which is not far from the 56.75% obtained by interpolating the curve of Piekering? but is definitely lower than the 56.97% found by Morey and Burlewd in a solution saturated with NaZCOs. TABLE I1 (a) THESYSTEM NazO-Si02-H20 Compn. of soh. NarO Si02
0.32 1.16 2.41 5.71 8.08 9.20 11.84 12.54 12.66 13.41 13.73 14.00 16.34 16.97 17.69 18.68 20.44 20.10 22.5
0.80 3.59 5.00 11.40 16.57 19.33 24.06 25.64 25.98 26.93 29.86 28.63 33.66 35.30 36.34 38.m 41.40 42.15 47.0
22.02 24.11 23.00 22.80 22.08 25.6
42.59 39.95 40.65 40.38 41.16 40.4
AT
70"
Stable solid phase
3Na20.13Si02.1lHsO 3P\'asO.13sio2.11H20 3Na20.13SiO2.1lHlO 3Na10.13SiO~.llH~O 3NatO-13Si02.llH~O 3Na20.13Si02.1lHlO 3Na20.13Si02.11H~O 3Na~0.13Si02.1lHlO 3Na20.13SiO2.1lH2O 3Na~O.13SiO2.11H20 3Na20.13Si02.11HtO 3iYa20.13Si02.1lH2O 3Naz0.13Si02.1lH2O 3NazO.13Si02.1lH2O 3Na~O.l3SiO~.llH20 3Na20.13Si02.11H20 3Na20.13SiO2.11H~O 3Na20.13Si02.11H20 3Na~O.13Si02.11H~O f Ka&i20s NazSiz06 NazSizOb Na2Si~Os Na2SizOs NarSi~Ob Na2Si01
(6) E. D. Williamson and 0. W. Morey, THISJOURNAL, 40, 66 (1918). (7) F. A. H. Schreinernakers,2. physik. Chcm., 11, 76 (1898). (8) G. W. Morey and 3. S. Burlew, Am. J . Sci., [VI, XXXV-A, 212 (1088).
C'. 1.. R A K E R , T., R . TABLE I1 (a) (Continued) Compn. of sob. NatO Si02
25.5 24.97
40.0 34 66
25.34 23.98 23.90 23.93 24.14 23.63 23.59 23.28 23.16 22.98 23.69 22.69 22.28 23.16 23.45 23.56 23.95 22.94 25.02 25.68 28.19 29.36 30.11 35.86 38.75 25.0 23.74 23.27 21.22 20.61 18.99 19.50 18.21 18.45 18.76 20.19 22.03 23.45 23.75 28 80 30.5
34.15 27.11 25.66 25 01 25 00 24 38 20 50 12 , 5 0 11 68 ti 81 9 24 8 84 8 93 7 87 6.38 5 60 5.04 3 98 2.45 1 47 1.os 0 TI 0 4; u.30 0.26 34.8 34,28 33.47 31.08 24.48 22.72 18.55 14.80 12.54 11.21 7 3.5 6.45 6.10 6.00 6.28 6.70
TABLE I1 (b) THESYSTEM NasO-SiOs- -H20AT 70" Composition of soln. NESO Siol
27.80 26.58 26.40 27.00 27.85 28.96 s.47 W.7Q
Composition of residue,
NarO
StoI
29.70 25.85 24.50 21.97 21.55
28.75 29.05
28.75 28.25 27.70 27.70 28.05
a2.12
2Q.26 a9.37
88.60
29.08 29.08
28.22
28,aS 20'18
%,12 28.02 27 an
JUE AND J.
H.WILI,S
:10.6 30 .35 29.81 29.70 29.55 29.45 29 51 30.00 :io :;5 ;io. 89 k10.9 1 33.18 34.65 35.42 36.05 31 , tj7 31 . a ;
24.8 2B. 65 21.20 20.30 17.75 15.74 12.45 %98 7.35 i1.05 5.35
:15,0
8 , li
34.90 36. 08 36.80 rj7.00 37,60 38.92 39. Y2 40.7 43 . 50 39.30 41.90 45.50 46.60 4%.00 48.85 49.60 55.10 56.45 56.75 56.97
ITol. 72
36.25 30.72 *'3 6 . ;io 34, 35 34.80 35.35 35.88 36 38
23.85 23,70 23.55 21.88 21.50 21.75 21.85 22.72
36.18 36.42 36. fi8 37.15 36.67 35.36 35.09
21.65 21.90 22.85 21.90 21 * 12 20.52 19.87
2.52 1.72 1.33 1.57 1.18 1.03 0.76 0.6
45.45 45.25 46. 15
27.30 26.3 27.52
45.60 44.70 46.50
25.50 22.57 26.68
.58
46.50 48.60 47.80 49.90 49.90 50.75 51.30 50.85 52.80
26.65 25.75 20.68 24.70 24.75 25.40 26.90 22.45 23.90
3.94
3.67 3.62 3.84 3.48 3 '30
.79 .44 .25 .19 .1
.27 .08 .I5
Xa3HSiO4.5H20 XaaHSi04.5H20 SaaHSi04.5H20 NaaHSi04.5H20 NaaHSi04.5H20 Na*HSi04.5Hp0 KaaHSi0,.5H20 NaaHSi04.5H20 NaaHSi046HzO NaaHSi046 H 2 0 NarHSi04.5H20 Sa3HSiO*.5H20 S a~HSiO4.5H~O Na3HSi04.5H20 Ka3HSi046HtO r\'a,HSiO4.5H20 PiasHSi04.5Hz0 NaaHSi04.2HzO NaaHSi04'2H20 NaaHSi04.2€120 NapHSi04.2H20 SasHSi04.2H20 Na,HSi04.2H20 NaaHSiOc e2H20 ITaPHSi04.2H20 Ka3HSiO4.H2O NaoHSiOc.HzO NarHSiOh.HeO NaaHSiOI.H20 NaaHSiOl.HzO NasHSiOc HzO KaaHSiOc.HzO XaaHSiO4.H20 NaaHSi04.H20 ?u'asHSi0,.H20 XaOH Pickering Sa20 HtO Morey & Burlew (NaOH NavCOa)
+
The invariant point between NaSHSiO*.H20NasHSiOc2HaO is also in some doubt, but is probably accurate to 0.2% NazO and 0.02% SiOz. Solutions of original composition close to the invariant point invariably shifted to lower alkalinity dong either one curve or the other. This also may be an effect of reaction with the silver flasks, as explained in the section on procedure. The invariant point NasHSiO4-2H@-NaaHSiOa. 5H20 gave considerable dif6culty. Any solution prepared with a NazO concentration less than 34.8% invariably led to the crystallization of NaaHSiO&H*O. It is therefore thought that the value of 35.0% NazO is accurate to about *0.2% NapO and the Si% value to &0,02%. The invariant point NaHSi0~5H@-NazSiOr 5H20 was obtained by the extrapolated intersection of twocurves meeting a t a small angle, and is thedore believed to be accurate only to about 0.3% NIlro and 0.6% Si@. The accurpcy of ea& of the deteminations far
THESYSTEM Na20-Si02-H20
Dec., 1950
5373
! 50
40
f
30
20
10
0 10
20
30
40 50 60 70 Si@, %. Fig. 2.-The system Na20-Si02-HzO a t 70", weight per cent. basis: @, points of isothermal invariance; 0 , theoretical composition; 0, experimental equilibrium points; +, wet residue determinations; - , field boundaries.
-
Na2O and for Si02 on the NaaHSiO, hydrate TABLE I11 curves is thought to be =t0.03~0/0. For the Naz- ANHYDROUShlETASILICATE, DATAUSED TO DETERMlNE SiOg5HaO the accuracy is about *0.1570 NazO THE COMPOSITION AT 70" and *0.1570 SiOz. Composition of soln. Composition of complex NalO SiOr NazO SiOa An anhydrous NazSiOa made by sintering soda 25.66 1.47 30.36 9.84 ash and quartz sand was used to determine an 23.08 6.61 36.70 26.01 anhydrous sodium metasilicate curve. Since 24.14 13.22 29.6 20.4 the refractive indices of anhydrous melt crystals, Wet residue of the sintered product, and of the residues in %5,07 15.27 36.92 30.96 reaction flasks a t 70 and 100' are the same, it is 22.95 5.43 34.65 23.22 believed that the same solid phase was present. 24 51 20.07 31.09 27.56 The curve extends from the disilicate almost to the NazO ordinate, and this salt is more stable than I t was also noted that in the most alkaline any of the others just mentioned. The solubility regions the reaction with the silver flasks mencurve is in nearly the same position as a t 90' tioned earlier occurred, and an appreciable and does not correspond to what one would quantity of the silver compound was found in expect from comparison with the retrograde soluresidue after long periods of reaction. bility of the a-sodium metasilicate shown by theEquilibrium was established from above and Baker and Jue.l Analyses by the Hill-Riccig below saturation a t the siliceous end, method and the Schreinemakers wet residue where the viscosityexcept was so great that approach method (Table 111, Fig. 2) indicate that this is an from supersaturation was exceedingly slow. The anhydrous product, although the extrapolations accuracy of this anhydrous metasilicate curve is are long and not as precise as in some of the considered to be *0.04% Na20 and *0.0370 other work. The crystals are exceedingly small, SiOt. Illustration 2 shows a mass of crystals of usually rectangles about 1 p in width, and come the sintered product in solution. Crystals grown out slowly from supersaturated solutions. a t 100' in a metasilicate ratio solution are more needle-like, as shown in Illust. 1. (9) A. E. Hill and J. E.Ricci, THIS JOURNAL, 68, 4305 (1931).
C. L. BAKER,I,. R. Jr JEAND J. H.WnLs
5374
-..
-
----.-
C-_--r----.----
Illurt. ?.--SarSiOl at 70' from sintered seed. 1.111
VOl. 72
-
-r_
x
An interesting discovery in this system is that of a second form of NarSiOafjH~Owhich has been termed the high temperature or alpha form (Illust. 3). The wet residue extrapolations make the composition rather certain (Table IV, Fig. 2). An X-ray diffraction pattern obtained by courtesy of G. W. Morey of the Geophysical Laboratories, Carnegie Institution of Washington, shown in Illust. 4 is different from that of other known hydrates. TABLE IV a-%I)ICM
blErASll.lCATE
I)alenhllsa Conll>,,.01 so111. SS.0
21).Rli 2i.m
SXh 24.lifi 2.5. i n i
k ~ E X A l l \ ' l ~ R A l ' E .D A T A USED
compn. 01 W C I
Sio,
2.-, . 37
2:I.!M 22.83 22.31 32.1 8.9
19.6!l 2n.m
lX.51
19.2x
24.41
28.21 27.62 23.9s 23.61
211.22
2 7 , ox 27.:11 24.5 24.3
Ns,O
1.02 1.m 0.95
19.0:1
4.82
Plc%wdand washed residues Mole vrtio Si& HsO
1.W 1.00 1.00
lCIitlllP
Sa,
24.40 24.il 24.:3x
33.76
TO
TIIE C"MPI)SInON
6.13 5.75 5.97
25.w 23. X i
Illust. 3R.--Bs;,2Si0.,-n1110 grolvll at 500, 90 x Remarks
Washed \Vashed Pressed
This stable hexahydrate varies in both refractive indices and melting point from that described by previous workers, Baker, et Sprauer, ci af.," and Erdenhrecher.I' All three reproduced photographs of the hexahydrate. The form obtained here is more nearly that shown
by Sprauer, but he does not give any other properties by which identity may be established. The melting point has not been determined hut it is The highest and lowest thought to be about SO'. indices are about 1.488 and 1.49P compared to
1.465, 1.473, 1.485.Io
nlolilt.
This salt is more stable than any of the other salts during most of its range. Its curve, however, has not been as carefully established as those of the other solutions excepting that of the disilicate. Certain solutions approached close to the limit from supersaturation, hut they gener-
(1040). (121 A. H. Brdcnbrcchcr. 2. o m ( . (1922).
(13) C ~ ~ N mKdeatly II 1nr.c and nli lorm-d for comdtte opfic.1 ex.mln.Uoa were aotoblaiacd. but C. W. More7 i n a personal eammunicPtion remrtcd the- value, aod mid the1 he did 001 rceov nix the salt.
(10) C L.Bat=. H. T.W d r u d and A. Pabst, Anurirm Uirn-
18, rn ( m a ) . (Ill J. W. Spnorr *ad D. W. Pum.J . Phw. Ckn.. 44, WB
dIrmt. C h m . .
114. 339
.
Dec., 1950
5375
THESYSTEM Na20-SiOz-H10
the sintered metasilicate, which may then recrystallize slowly to the hexahydrate. Other examoles o f snch inhibited crvstallization are to bc fo;iid in the work of KracekI4;' and of Hill and Wills."b Some experiments from undersaturation were carried rnit with anhydrous sodium disilicate crystals obtained from an anhydrous melt. As far as could be observed. i t was not possible to obtain growth from supersaturation but it,is very dillicult to work in this region .of high VIScosity. After long reaction one washed residue did appear to have a slightly altertd index, but the crystals as shown in Illust. 5 did not appear ti) have changed. IVe do not feel capable of judging the accuracy of this curve. The soluhilitv of Na&Os does not fit a smooth curve nmdr up froin the data of Mercy" and of Tuttle and Friednidn,'6 a l l d this fact may indicate a shift in phase.
1
1
i
Illusl. 4.-X-R:iy
diffraction pattern of oNarSiOa.GHt0 formed at i o 3
ally crystallized to a solid from which liquid samples could not be removed, before equilibrium could be determined. The points determined are thought accurate to *O.ly0 Na,O and *O.l'% SiO2. In the alkaline section a drift with time was found which is attributed t o the reaction with the silver flask. This new form of hexahydrate appeared not to form spontaneously but only after seeding with
Illast. 5.--S;~2SitOsCI.YSLBIS originally from ii melt b u t aftcr long itnmersion in solution fp:wtixIly crosscd nicvl prisms. 193 X).
In the most siliceous portion of the sodium tetrasilicate" region, a year or more may be required for equilibrium from supersaturation. (14) (n) F. C. (b) A.
A m . J . Sri.,
VI.
XXXV-A. 143 (1838):
E. Hill and J. H.Wills, Tiiii J o u r ~ r l60, , 1047 (1838).
(IS) I. G. Vail, "5olublc Silicnfci in Inclu%lry."A.C.S. Monos. 46. (Chemic4 Catdog Co.). Rciobold Publ. Curp.. N. Y.,1028. p. 110. (18) 0. F. T11111e and 1. 1. I:cicdni:&n T R l S JouIY*L, TO, 818 (1948). (17) \V. 1'. W e p t and I. I I . \\rills, U. S. Reiruue. 23.013 (1848).
5376
Approach is much more rapid in the middle por- the water content tion, where one or two weeks was sufficient in directly, since the some cases. From undersaturation one or two equilibrium content weeks also seemed to be required, the time de- as shown by conpending on the position of the initial solution. stant weight deterThe accuracy of points on this solubility curve is minations at any considered to be +0.040/, NazOand *0.04% SiOr. one temperature apThe composition was studied by various peared to change methods. Table V shows results for the wet gradually over the residue extrapolation and for tracer ion experi- rangefrom62t0100° ments using NaCI. It is very difficult t o obtain and quite rapidly a t satisfactory extrapolations because the crystals about 100'. From are very fine, 1to 15 pin length by 0.2 t o 5 p wide, then on equilibrium and hold the viscous liquid strongly. Further- was reached only more, it is difficult to keep the solutions warm gradually up to and thus maintain the viscosity near the original about 150°, but a t figure. The best approximation to the com- 2;0° equilibrium was in an hour. position appears to he 3 N a z 0 ~ 1 3 S i ~ ~ l l H 2reached 0. Most wet residue studies for sodium tetrasilicate The dried salt takes resulted in such long cxtrapolations that little up water rapidly weight could be placed on the results. The inert even over sulfuric tracer (NaCI) results, Table V, are all a little acid in a large desichigh in water content. It is difficult to obtain cator. Illustration Tr gives TABLEV an idea of the apSODIUM TETRASILICATE. DATAUSEDTO DETERMINE THE pearance of these COMPOSl7ION crystals. I n some LiWOl wet *Clid"C cases they tend to Sih N8.0 SioI NmO form n structure 25.50 5.13 12.41 7.87 similar to a chestnut fi.02 32.70 24.24 7.98 burr. Illustration 5 33.74 R.24 24.12 9.89 shows an X-ray dif3R.98 13.00 28.20 13.87 fraction pattern of 13.20 39.81 29.07 14.07 this sodium tetra13.95 3R.W 13.31 28.57 silicate. 17.08 42.03 17.31 35.57 For a long time it COMPOSITION BY NaC1 TRACER EXTRAPOL. hl~riion was thought that a NlrO Sih H10 simple formula such 16.04 G5.78 18.18 as Na*04SiOyiH*O 16.53 65.68 17.78 would be correct. 15.90 64.69 19.40 A damp specimrn dried over partially dehydrated material did appear t o reach this degree of hydration, hut the weight of evidcncc for the complcx form was finally convincing and the name has i : been retained brcause of usage, sim!a plicity and the unlikelihood that a t r u e tetrasilicate will he found. (It has heen mggrsted that this compound may be considered as an isopolyacid salt havinr: a camAike strucIllust. 6.-3NarO.l3SiOrllH@ grown at 70'. 140 X. tu&.) .I
r
Vol. 52
C. L. BAKER.L. R. Jus AND J. H. WILLS
~
a,
.
r - a
THESYSTEMNazOSiOz-HzO
Bec., 1950
The Isotherm at 50' At 50' the two forms of NazSi08.6HzO were found, but not the NasHSiOa.lHz0. At this temperature, too, appeared the supposed NazSiOs-lHSO. Otherwise the same salts are present as at 70" (Table VI, Fig. 3). TABLE VI THESYSTEM Naz0-SiO2-Hz0 AT 50" Composition of soh. SiOs
NalO
0.5 5.2 8.6 14.2 17.8 19.4 19.7 19.8 21.3 17.9 19.3 18.4 18.7 16.2 14.7 12.5
1.5 11.2 18.5 30.8 37.9 39.2 36.8 35.2 36.5 5.0 30.4 26.4 25.0 20.2
13.5
4.8 4.6 3.3 2.9 2.7 3.1 3.9 4.4
15.3 8.1
13.6 15.3 18.4 21.8 23.0 25.1 25.6 20.2
35.3
19.2 16.8
30.6 22.0
16.2 14.7 15.0 15.2 16.7 18.3 21.9 24.0
19.6 15.3 15.1 10.4 8.4 6.7 4.3 3.4
26.2 37.0 24.2 23.4 24.25 23.81 23.3 23.6
2.5 0.5 39.4 38.4 37.34 34.44 30.6 30.3
23.10 22.42
30.30 26.92
Composition of residue NarO SiOn
24.3
21.21 20.28 19.98 19.80 19.96 20.02 20.28 20.61 20.88 21.03
24.10 19.55 16.90 15.57 13.25 12.45 10.72 10.00 9.96 9.94
26.37 26.54 26.88 26.87 26.91 26.90 26.78 26.89 26.75
26.30 25.52 25.70 25.78 25.52 25.67 25.53 25.52 25.49
21.01 21.30 21.68 21.82 23.01 23.25 24.93 26.31 26.45
10.15 8.68 8.16 7.82 6.47 6.17 5.65 5.90 6.03
29.0 29.05 28.80 28.83 29.03 29.08 28.95 29.08
27.34 27.47 27.05 27.00 27.24 27.28 27.00 27.75
26.45 27.20 30.10 33.00 36.87 36.90 37.32 37.0
5.98 3.82 1.51 1.10 1.15 1.11 1.15 1.15
36.00 36.20 36.30 36.30 36.80 36.63 36.45
22.87 22.47 22.28 22.00 21.57 21.62 21.63
37.38 37.62 37.97 38.83 39.07 39.80 39.90 40.30 41.50 41.75 42.00
0.75 .80 .64 .55 .59 .50 .50 .42 .26 .26 .26
45.60 45.10 45.40 45.00 45.35 45.30 46.60 46.00 46.15 45.90
25.90 26.00 25.25 22.57 26.57 26.35 26.85 24.67 25.62 23.10
42.40 43.70 45.00
.26 .20 .00
20.0
22.7
22.5
23.7
19.6
26.32 25.75
5377
26.37 26.17
@-NazSiOa*6HsO
'
,6-Na2Siq.6Hz0 @-Na2Si08 .6H20 B-NazSiOa .6Hz0 p-NanSiOa.6Hz0 j3-NazSiOa.6H~O @-NazSiOa*6HzO @-Na&iOa*6HzO @-Na&O8.6HzO @-NazSiO1.6H~0 NazSiOa.5HzO pNa~Si0~.6H~0 NasSiO&H20 NazSiOa.5HzO NazSiOa.5HzO NazSiQ.5H~0 NazSiOa.BHz0 NazSiO:.5HzO NazSiOa.5HzO NazSiOs.5Hz0 NasHSiO4.5HzO NazSiOa.5HzO NaaHSi04.5H20 NaaHSiO4.5HzO NaaHSi04.5HzO NarHSi04.5Hz0 NasHSi04.5Hz0 NaaHSiOd .5Hz0 NaaHSi046Hz0 NasHSi04.2H~O hTaaHSi0d.5Hz0 ISaaHSiO4.2HzO NaaHSi04.2HzO NarHSi04.2Hz0 NasHSi04.2H~O NalHSi04.2H~O NaaHSiO4.2H20 NaaHSiO4.2HzO NaaHSi04.2HzO NaaHSi04.2Hz0 h'a3HSiO4.2H20 NaOH.HZ0 NaaHSi04.2HzO NaOH.H20 NaOH.HzO NaOH .H20
+
+
+
+
As before, the work may be divided into two sections. The curves for the metastable more readily crystallizable alkalies were determined first. The solubility of NaOHSH20 was found to be 45.00 * 0.0570 NazO. This may be compared to 45.7% as obtained by P i ~ k e r i n g . ~The transformation from this sodium hydroxide hydrate to NaaHSi04-2HzO was not determined exactly, because the two curves are quite parallel to each other. The invariant point is taken a t about 42.0 * 0.3% NazO and 0.26 * 0.02% SiOz. Attempts to establish isothermally invariant points using mixtures of the two solid phases were unsuccessful, either because of the slowness with which equilibrium was attained in the viscous
3378
C . L. BAKER, I,. li. J U E
AND
J.
H.I\ ILL^
Vel. 73
50
40
,
80
' /
.c) ox
4
' /
2
/
20
10
0 -1-0 50 60 70 Sios,%. Fig. 3.-The system NazO-SiOTHzO a t 50 ', weight per cent. basis: @, points of isothermal invariance; a,theoretical composition; 0, experimental equilibrium points; -0, wet residue determinations; X , composition of washed and dried solid phase; - -, field boundaries 10
"0
30
solution or because of reaction of the alkali with the silver flask. The invariant point between Na3HSi04.5H20 and NagHSiOg2H20 was obtained by extrapolation. Transformation invariably occurs a t about 37.0 * 0.1% NaeO and 1.15 =t0.03% Si02. Conditions for transformation of NasHSiOh. 5HzO to NapSiOn,3H& were established quite accurately. The metasilicate has a considerably shorter curve than a t io", and soon reaches the point of transformation to PIKazSi03.liH20, a salt with a very prominent curve. The invariant point between the penta- and the hexahydrate of NazSiOa was established definitely by the crossing of the two curves. Equilibrium a t the siliceous end of the /3 NazSiOS. GHeO curve was difficult to obtain and required a t least four months. The accuracy of points on these solubility curves in the inore alkaline range is thought to he about +0.05% NazO and =!=0.05% SiOo. A metastable curve for ailhydrous sodiuni metasilicate was obtained from undersaturation, the sintered product being used as starting material. It is in about the same position and has about the same accuracy as at SO", but the ,? XazSi03.6Hz0 interferes. A curve for the unidentified salt was found toward the close of the work and could not be
studied carefully. The refractive indices, roughly about 1.49, 1.50 and 1.51, serve to distinguish it from other phases. The photographs show aggregates of small crystals grown from supersaturation (Illust. 8). One stock was grown a t 65" from a i9% solution of NazSiOs.5Hz0, seeded with a small amount of solution which contained crn'a&i034HzO crystals, but which had been prepared from supersaturation over a period of six months by seeding a solution of Na3HSi0~5H20with sintered NaZSiO, crystals. Another batch of crystals was formed from melted NazSi03.9Hz0 a t 70' over a two-year period. The seed used was thought, according to its indices, to be aNazSi03.6Hz0. The mother liquor of both batches was metastable to the crNazSiO3.6HnO curve, but the solid phase appeared to consist mainly of the unidentified salt. I n this region, a similar batch of crystals underwent transition to cuNazSiO3.6HzO when seeded after reaching the new curve. The stock of crystals obtained was used to obtain the alkaline section of the curve €or the unidentified salt from undersaturation. The siliceous end had been obtained earlier and is considered highly questionable. Change of any kind seemed to be so slow as to defy interpretation. As crystals remained present it could only be assumed that some kind of equilibrium was established.
Dec., 1950
THE
Since growth from supersaturation was obtained only in solutions near the metasilicate ratio line, wet residue extrapolations were of little help. Several attempts to wash and dry the solid phase for analysis were made. and the hydration was found to vary from 1.3 to 4.6. I t is thought that some aNarSiOa.6Hz0 was probably present in the solid portions of these metastable mixtures, and that the saturating solid phase may be either a low temperature form or iiNa2SiOr,or a NarSiOa.lHIO. The indices and the habit of the crystals both suggest some hydration. The curve is stable in both the more siliceous and the more alkaline ranges, and if time had permitted when ample seed stock was available, solutions prepared from undersaturation should have given useful wet residue extrapolations. It is thought that the transformation points at which aNazSiO&HzO becomes stable are fairly well known by interpolation. There is no indication as to whether or not the curve would intersect any of the more alkaline curves other than that of NaOH.HzO. The probable intersection with a disilicate curve is not considered accurate. The curve for aNazSiOa.GHzO, although this is still the most stable alkaline salt, is not as prominent as at 70'. Its accuracy is also at least Na20 and -0.1% SOz. The about *O.l% small rate of growth of the alpha form is shown by an experiment in which a solution at about 13% Si02 on the @Na&iOa.GHtO curve was prepared, containing beta crystals. Its composition remained constant for a t least one month, and heta crystals still remained in part four months later. In the course of five more months, the composition gradually shifted t o the more stable curve. One solution of initial composition 28.8% Na20 and 6.3% SiOz fell to the Na3HSi0,.3Hz0 curve, followed that curve t o the intersection with the NazSi0~.~5HzO curve, and then followed down that curve to 24.3% Nap0 and Ci.O';b SO?. This shift required 367 days; even a year later at 6.59 days it had not reached the stable phase, and at 799 days the analysis was Zl.S7, Nap0 and 4.7y0 SiOl. Examination of the course showed that it took nearly a year for all of the NarSiOr5HsO to transform to the stable Xa&i03. 6Hz0. A solubility curve for anhydrous sodium disilicate obtained from a furnace melt is given. Its X-ray diffraction pattern corresponds to the alpha form discussed hy Rracek.'* Solubility of this salt is extremely high, nud solutions arc viscous and ditlicult to handle. 13quilihrium is established only slowly antl we have not bcen able to determinr any growth from supersatnriltion. The accuracy of the position or this rnrvr cannot he estimated. The cnrvc for sodium tetrasilicate appears in (181 F. C. Knerk. T A ~JS o u n ~ r t .Sl, 2883 (1030).
6379
SYSTEM
aooroximatelv the same A ;&ition as & 70'. It is not certain whether or not these crystals arecongruently soluble. When dissolved in water, the ratio of NatO to SiO, in the liquid phase usually approximated that of the solid phase. Where considerable growth from supersaturation occurred, wet residue experiu ments indicated the same composition found a t 70". IVashed and dried residues marked X on Fig. 3 also appear to indicate the same formula, although only the most thoroughly washed example shows a composition identical with that proposed. The accuracv of the position of chis curve llluat. s.-(:~) saZsioz.~is thought to be about H ~ Ofornled at a", 70 x. *0.04% Nap0 and (h) \Vith crossed nicol prisms *O.O.IC/;, SiOz. show that the particles are It is very evident that there are still many interesting unsolved points in the knowledge of phase relations of the systems N a z M i O r H s O from 0 to 100". This paper and previous ones may SCNC to point out these questious and mdkc easier the work of later investigators.
Materials and Procedure Stanhrtl methds of analysis were used. NazO was rlrtrmiincd hy voluinrtric titration with standard 0.2 N IICI, the traces of CO? hy nbsorption aiirl weighing on Ascnritr in thp usiiitl train, iuid SO? gravimetricnlly by prrcipit:ition with HCI. The residue of Si02 from such rrletirely pure soluble silicates docs not require donhle precipitation and FlJp* trcatmcnt if care is t;ikcn to dry the initial precipitate thoroughly on a steam-lxith. \\'hrre H . 0 wxs determinrd as a cheek on the other analyses, ignitrd loss was found by thc following tcchniqur. The sample was alloawl to filler into a hcrl of anhytlrou~sand in a weighed mullite or platiiiiim cmcihlc. Vrry viscous samplcr were wctted down with a little watrr to facilitate distribution through thc sand. \Vhcu dried slowly antl ignited, the sand inhibits puffing or intiini(~scrtiwanid aitls i i i liberating COz. Onr workins w i t h :tI!aliw sohitiom is soon aware of thc d;mgrr of roiiti),iiiii:,tii)ii of his S ~ S ~ C . I I Ihy C dmrl>tion of Co.. l l w r f l ~ of t t l i i < ;uldcrl c i m i l ~ o ~ ~ c018r i tthc rqtdil,riiiiii w c w + is tmwrtitiu. In11 t i n t s t 1. coiisitkwtl. 111 wry ;tILaliuc solutions tlic 4,ibility uf SnrCO, is w r y low. Init io, g c n c ~ i lit inrrcwrs w i t h dilution. As SiO, roiicciitriitiuti iiiewiiscs, C Q tcwk tu kdl. 111 this work wv wrd t w o a ~ ~ p r m t d ~ tllat c s , tlcsrril~CtlI,y liakvc atid l u ~ . i .' (... ~ ~;tvoiclisg ~ eont;iinin:ttimi. : ~ i i t lthat t t w l in our lrcond seetiou of ;illowing for its preserice it) detrrmining the rrsults. (IO) C I,.
nskcr wid I,. I
