Oct., 1957
REACTION BETWEEN STRONTIUM HYDROXIDE AND SILICA
using the amount of cristobalite and quartz formed in each experiment (see Figs. 2 and 3) as a measure of the hydroxide ion concentration present a t 400°, the strengths of the various acids (at 400”) are found to decrease in the order sulfuric, phosphoric, hydrosulfate, hydrofluoric and dihydrogen phosphate. Thus only 0.61 g. of cristobalite was deposited-on the autoclave walls from M/40 potassium hydrogen sulfate solutions; while over 7.5 g. of cristobalite “was formed in sodium dihydrogen phosphate. No quartz was observed in either of these solutions, but traces of quartz were found in M/40 potassium sulfate with considerable quartz found in M / 4 0 potassium fluoride solutions. Finally, all of the silica was converted into quartz in M/40 disodium hydrogen phosphate solutions. In a previous paper on the growth of quartz in sodium fluoride solutions* we suggested that the mineralizing action of the fluoride ion was due to the formation of the fluosilicate ion by the reaction 2H20
+ Si02 + 6F- F? SiF6- + HOH
(1)
At that time a volumetric procedurezafor the determination of fluosilicate in the presence of fluoride based on the precipitation of potassium fluorosilicate in acid solution containing alcohol and saturated with potassium chloride was used. We have examined this procedure and have found that the fluosilicate ion is formed rapidly and nearly quantitatively when solujions containing sodium silicate and sodium fluoride are acidified The second step in this analysisz3is to reverse reaction 1 by digesting the precipitate of potassium fluosilicate. But this is essentially the conditions in the bombs, ie., any fluosilicate present in the bomb reactions would be decomposed a t the temperature of the run. Equilibrium studiesz4also have shown that the fluosilicate ion is most stable in acid solutions at low temperatures ; while preliminary studies in this Laboratory indicate that the rate of form(23) I. M. Kolthoff and V. A. Stenger, “Volumetric Analyses,” Interscience Publishers. Inc., New York, N. Y.,1947, p. 120. (24) J. G. Ryss, Zhur. Fir. Khim., 36, 654 (1951).
1437
PH.
Fig. 3.-Quartz (total) formed from silica glass in M/40 buffered solution at 400’: 0, hydroxide; 0, phosphate; A, fluoride; 0 , sulfate.
ation of the fluosilicate ion increases with increasing acidity. But these are just the conditions (M/40 HF) which prevent the devitrification of silica at 400’. The effect of the fluoride ion as a “mineralizing” agent therefore is not due to the formation of the fluosilicate ion, but like the anions of other weak acids, to its hydrolysis and the subsequent formation of hydroxide ion. Acknowledgments.-The authors wish to thank Dr. J. W. Edwards and the Monsanto Chemical Company, Dayton, Ohio, for making the X-ray analysis and Dr. Harry Knorr of the Kettering Foundation, Yellow Springs, Ohio, for the infrared analysis. We are indebted to Mr. Elwood Shaw of the Chemistry Department, Antioch College, and Dr. John White of the Geology Department, Antioch College, for their help with the optical measurements and for many valuable suggestions during the course of this work.
HYDROTHERMAL REACTIONS UNDER SUPERCRITICAL CONDITIONS. IV. THE REACTION BETWEEN STRONTIUM HYDROXIDE AND SILICA1 BY J. F. CORWIN, R. G. YALMAN, J. W. EDWARDS AND E. R. SHAW Contribution from the Department of Chemistry, Antioch College, Yellow Springs, Ohio Received J u l y 16, 1067
The hydrothermal reaction between dilute solutions of strontium hydroxide and silica glass was studied under carefully controlled experimental conditions at 400’, 340 atmospheres pressure, and in a time range from 0 to 192 hours. Through the devitrification of a controlled amount of silica glass rod, silica was added slowly to the solution during the reaction. Under these conditions strontium metasilicate was formed first, and on continued reaction the solid phase modified through a series of crystalline and amorphous materials to 8-cristobalite and finally to a-cristobalite. I n this respect the reaction closely resembles that of calcium hydroxide under the same conditions. (1) This research was supported in part by the United States Air Force through the Air Force Office of Scientific Research of the Air Research and Development Command, under contract No. A F 18(600)1490. Additional support was received from the U. S. Army Signal Corps (Contract No. DA 36-039 80-64605) through its Signal Corps Engineering Laboratories a t Fort Monmouth, New Jersey. Reproduction in whole or in part is permitted for any purpose of the United States Government. (2) Paper No. I, THISJOURNAL, 61, 939 (1957).
Introduction The investigation Of the reactio’ls Of the earth metal oxides with silica glass2 showed that calcium and strontium oxides have similar characteristics. The reaction was relatively rapid and showed signs of continuing devitrification of the glass even after equimolar quantities of silica had
J. I?. CORWIN, R. G. YALMAN, J. W. EDWARDS AND E. R. SHAW
1438
Vol. 61
vides a measure of the reaction at 400" shown in the final column of results. These results plotted against time are found in Fig. 1. 1.60-
TABLE I REACTIONS OF Sr(OH)z WITH SILICA 10 g. SiOz glass rod, pH 12.4, 0.025 N Sr(0H)Z
1.40 -
50% filling. 125 ml., 400'. 340 atm. ~ i i ate 4000, hr.
3 1 2 3 2 2 3 1 2 2 3
0 1 3 6 12 24 48 65 72 98 192
.
120w
;1.00 c
I 0'
No. of expt
24
4s
;2
Fig. 1.-Devitrification
96 li0 Time in hours.
144
s1;
I92
rate, Si02 g. vs. time in hours.
been removed from the source material. The reaction between Sr(OH)2and silica is so similar to that of Ca(OH)2 that further investigation seemed reasonable. Only a few papers dealing with hydrothermal reactions of strontium oxide with silica have been published. The most important of thesea was concerned with preparing a large number of strontium silicates by treating various molar ratios of SrO and silica gel with steam. The present work is concerned with the effect of dilute solutions, 0.025 N , on Si02 which is added to the solution during the reaction by the devitrification of clear silica glass rod. Experimental The equipment and methods used for reactions and for the analysis of the reaction products were identical to those already described.4 The only modification was that the analytical procedures described for CaO were modified in such a way that SrO could be determined. Sr(0H)Z conformed to C.P.A.C.S. Standards of purity.
Results and Discussion Since it was known3 that reactions between SrO and Si02 take place at as low as 124" no attempt was made to determine the initiation temperature of the reaction. Table I contains the data for the amount of reaction that takes place which was measured by the extent of devitrification (loss of weight) of a piece of silica glass of almost constant surface. As would be expected the reaction is accompanied by a drop in pH of the solution. The minimum pH 9 represents the hydrolysis of the strontium metasilicate dissolved in the water. The result marked zero hours shows the amount of loss incurred during the heating up period and this result subtracted from the total loss in weight pro(3) E. T. Carlson and L. s. Wells, J . Research N a t l . Bur. Standards. Sl,73 (1953). (4) Paper No. 11, THISJOURNAL,61, 941 (1957).
Final pH
12.0 9.8 9.3 9.1
8.8 9.1 9.1 9.0
8.7 9.1 8.8
Loss in wt. of rod, g.
0.0386 .I281 .1618 .1950 .2369 .3505 .3802
.4085 .4275 1.1220 1.7505
The reaction is rapid at first and then slows down and almost stops up to 65 hours. Then the rate picks up again and is relatively rapid up to 96 hours, and then slows down somewhat on continuing to 192 hours. Optical examination of the crystalline material formed during the reaction showed only SrSiOs and amorphous material up to 24 hours. At that point some new crystalline materials are observed, so these and longer runs were examined by X-ray methods. The results of this examination along with chemical analysis of the crystalline material are found in Table 11. TABLE I1 ANALYSIS OF CRYSTALLINE MATERIAL 10 g. SiOz glass rod, 0.025 N Sr(OH)2 50% filling, 125 ml., 400°, 340 atm. Time, hr.
SrO,
%
Bios,
%
H20,
%
X-Ray and optical examinationav b
4 . 5 SrO+SiOn(optical) 1.4 SrOt3iOz (optical), amorphous material . . SrO8iOz(S), 2SrO.Si0~24 .. (W), 3Sr0.2SiO~4H20 2 . 5 SrO.SiO2(S), other lines 46.7 50.8 G5 not identified, amorphous material . . SrO.SiOz(S), p-cristob.. 72 alite( W), amorphous material 3 . 8 70/30 mixture SrO.SiO 80.3 15.6 96 and p-cristobalite, tridymite( W), amorphous material . . 50/50 mixture SrO.SiOz .. 192 .. and intermediate pattern between a- and 6-cristobalite a (S) Strong, (W) Weak. b X-Ray analysis performed by Ralph L. Ferguson under the direction of Dr. J. W. Edwards, Monsanto Chemical Company, Dayton, Ohio.
0 12
62.8 58.7
32:7 39.9
..
..
Calculations from the percentages of SrO and Si02 show that by the time the reaction has reached 400' practically equi-molar quantities of SrO and
. l
NOTES
Oct., 1957 Si02 have combined to form the SrSi03 and by the time 12 hours had passed excess silica in the amorphous form had begun to appear. Because crystalline materials found in longer experiments are rather complex mixtures only a few more analyses were made, and those simply to show the trend toward larger amounts of silica present. Table 111 contains the chemical analysis of the solutions a t several time intervals.
1439
prevent further devitrification. Where the early coating was not tightly bound the reactions proceeded without difficulty. In this manner SrSiO resembles BaSi03 which adhered so tightly that reaction was stopped completely.2
Conclusions The reactions of a dilute solution of Sr(OH)2with silica resemble closely those of Ca(OH)2with the exception that the first insoluble silicates formed TABLE I11 have a tendency to adhere to the rod surface in the ANALYSISOF LIQUIDPHASE case of Sr(OH)z; while no such tendency was ob10 g. Si02 glass rod, 0.025 N Sr(0H)z served with Ca(OH)2. I n this respect the reactions 50% filling, 125 ml., 400°, 340 atm. of resemble those of Ba(OH)2 rather than Time at 400°,hr. SiOz, mg. SrO, mg. Ratio, SrO/SiOn Ca(OH)z. 0 3.0 46.6 15,58 After three hours a t 400" the reaction has pro4 34.0 2.89 0.085 ceeded beyond an equi-molar quantity of silica 12 51.5 3.25 .063 which would require the loss of 0.025 mole or 0.1522 48 57.5 1.71 .030 g. from the rod. Devitrification continues a t a 65 62.5 3.95 .Of33 slowly decreasing rate until 65 hours have passed, 96 44.0 1.48 .034 then a rapid increase in reaction occurs which corIt is evident from the results in Table I11 that responds with the appearance of a new crystalline although the reaction starts a t 124O, not much phase, @-cristobalite, among the solids present. strontium silicate (SrSi03) is built up in solution Unlike Ca(OH)2 the 0-cristobalite formed rapidly until several hours have passed, and then the ma- changes to a-cristobalite which is a lower energy terial in solution takes the form of a silica rich form of silica. This transformation is probably due complex rather than a simple silicate. This confirms to the higher pH of the solution.6 From a theoretical standpoint one would expect the results reported in the exploratory work2 published in THISJOURNAL. After 48 hours the mini- that because of the more basic character of Sr(OH)2 mum concentration of SrO is reached in solution, the reaction of this material should resemble more which corresponds with the slow rate of reaction, closely the reactions of the alkali metal hydroxides Fig. 1, after which the concentration of SrO in- with silica; however, the formation of the more increases in solution to 65 hours and then decreases to soluble silicates as intermediate materials in the reaction and the more acidic nature of the hydroa minimum again at 96 hours. One complicating condition that was observed lytic products of the strontium silicate, result in the during the course of these experiments was the formation of the more symmetrical and higher entendency of the insoluble strontium silicates t o ergy forms of quartz. adhere to the surface of the rod and in some cases (5) Paper No. I11 of this series, THIBJOURNAL, 61, 1432 (1957).
NOTES THE EXTRACTION OF ALUMINUM AND SILICON FROM MUSCOVITE MICA BY AQUEOUS SOLUTIONS B Y GEORGEL. GAINES,JR.AND
c. P. RuTKowsKI
General EEectric Research Laboratory, Scheneclady, N . Y . Received M a y 9, 1867
I n connection with studies on the ion-exchange properties of natural micas, we have been concerned about the possibility of attack on the .aluminosilicate framework of the mineral by aqueous solution. The importance of this type of phenomenon in connection with the ion-exchange behavior of clays has been emphasized before.' Bradley2 has also observed interesting surface effects with acid (1) N. T. Coleman and M. E. Harward, J. A m . Chsm. Soc., 76, 6045 (1953). (2) 'R.S; Bradloy, Trans. Faradau Soc., 36, 1361 (1039).
treated mica. We wish to report here some measurements of the extraction of aluminum and silicon from ground mica samples by several aqueous solutions. Experimental Carefully fractionated samples of ground Bengal Ruby muscovite mica of various particle sizes were used for this study. The origin, preparation and analytical data for these mica samples are given in the discussion of our ionexchange studies.a The surface areas of the samples used, as determined by adsorption of krypton at -196' in the conventional B.E.T. technique, were 0.70 m.2/g. for the 20-40 mesh fraction and 2.32 m.2/g. for the 100-200 mesh fraction. Solutions were prepared from reagent grade chemicals or commercial standard volumetric solutions, using distilled, deionized water. Extractions were performed by agitating 1-g. samples of the mica with 120-ml. portions of solution in a thermostat a t 25.0" for the desired length of time, then removing the supernatant liquid for analysis. Polyethylene containers were used throughout.
-
(3) G. L. Gainos, Jr., THIS JOURNAL, 61, 1408 (1957).
