NOTES
174
parent) of the particles as well as their geometry, except when they are spherical, and so it will be higher than the 0.6 given here for zero conductivity. Nevertheless these very limited measurements a t least shorn the correct order of magnitude and indicate that it will be useful to carry out careful experiments using spherical particles. Calculation of zeta potentials from such measurements may provide useful checks on double layer theory. HYDROTHERMAL REACTIONS IN THE Naz0-Ge02-H20 SYSTEM. 11. INFRSRED STUDIES OF GERMAKIUM DIOXIDE' B Y ELWOOD R . S H A w , JAMES F. CORWIN AND HARRY V. K N O R R ~ Contribution from the Department of Chemistry, Antioch College, Yellow Springs. Ohio Receieed July 31, 1069
During the investigation of the hydrothermal reactions of germanium dioxide3 variations which depended on the conditions of the reaction were noted in the indices of refraction and infrared patterns of inversion products which according to X-ray analyses consisted of the hexagonal form. Studies of these products have indicated that the reaction GeOz (amorphous, *V = 1.607) --t GeOz (hexagonal, No = 1.697, NE = 1.724) proceeds through intermediate states which contain varying amounts of difficultly removed water and/or quantities of a finely divided low index form. The fibrous variety of these intermediates has been described previously as a "chalcedony-like variety of germania."4 The crystal structure of germanium dioxide from aqueous solution with or without subsequent ignition was found by Goldschmidt5 to be trigonal. Crystals formed by heating the tetragonal form of germanium dioxide a t 1100" for two hours and also by heating fused germanium dioxide for four hours a t 1080" were studied by Laubengayer and Mortons and found to belong to the hexagonal system. Comparisons of X-ray patterns of the hydrolyzed oxide with those of the above preparations by fusion also were made and only one crystalline form was indicated. The presence of heat stable HzGe6011 was ruled out by Brauer and Renner7 on the basis t.hat on ignition the X-ray pattern of the hexagonal form was the same throughout and no fixed water content was found. The infrared pattern for the hexagonal form of germanium dioxide has been reported in the literature with principal bands in the 2 to 15 p region reported a t 10.34, 11.31and 13.90p.*
1-01. 64 I500
1000
WAVELENGTH
900
803
700
imcrrenii
Fig. 1.-Infrared patterns of germanium dioxide: (1) freshly fused glass; ( 2 ) commercial sample of glass after standing 1 year; (3) glass heated in water for 1 day at 90100"; (4) commercial sample, 99.99% pure, A. D. Mackay Co.; ( 5 ) hydrothermal preparation from glass, 200" for 3 hours; (6) hydrothermal preparation from glass, 400' for 3 days.
Recently, the spectra of the three forms of germanium dioxide have been reported with bands at: amorphous 11.17 p ; hexagonal 10.38 p , 11.30~;tetragonal 13.89 p.9 Experimental All samples were examined from 2 to 15 p with a PerkinElmer Model 21 infrared spectrophotometer equipped with a sodium chloride prism. The samples were ground alone to the desired particle size either in an agate mortar or in a Rig-L-Bug Amalgamatorlo following which samples in the order of 3 mg. were then reground in the amalgamator for about two minutes with one gram of reagent grade potassium chloride. The mixed samples were pressed into a transparent plate at 40,000 p.5.i. in a vacuum press. Germanium dioxide samples were obtained commercially or prepared hydrothermally as described earlier.3 Water introduced into the sample during grinding with potassium chloride and indicated by weak but sharp bands a t 2.95 and 6.10 p was removed for water determination experiments by drying the pressed plate in a desiccator. Otherwise these bands were not objectionable since the band height was relatively constant in the humidity controlled analysis room. All samples were predried a t 110' prior to any type of water determination.
Results and Discussion The spectra for germanium dioxide are shown in Fig. 1 and the band locations shown in Table I. Bands due to absorbed water which could be removed by drying the pellet a t 110' were not included. The precision of determining the location of the broad bands and their reproduction depended on the symmetry of the band a t its maximum. In all cases, with a properly prepared sample, it was between 0.02-0.05 p. The sharp band a t 10.43 p did not vary over =kO.Ol p regardless of the preparation and appeared whenever a small quantity of the soluble form was present in a form other than in a solid solution. The devitrification of amorphous GeOz proceeds slowly in air (pattern 2), much more rapidly in hot water (pattern 3) and very rapidly under hydrothermal conditions (pattern 5). After short runs of the latter two methods, the birefringent product exhibits variable indices of refraction
( 1 ) This research was suprmrted by tiit 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)14BO. Reproduction in whole or in part is perniitted for any purpose of the United States Government. (2) Kett.ering Foundation, Yellow Springs, Ohio. (3) E. R. Shaw, J. F. Corwin and J. W. Edwards, J. A m . Chem. Sac., 80,1536 (1958). (4) J. W. White, E. R. Shaw and J. F. Corwin, A m . Mineralogist. 43, 580 (1958). ( 8 ) L D'Or, RI. Haccuria and R. Nlachirous, Compt. rend. conwr. antern. chzm. znd. 27e Congr., B r u s s e l ~1964, , Ind. chim. belue, 80, 150 ( 5 ) V . Goldechmidt, NaturwissensRaften, 14, 295 (1926). ( 6 ) A. W. Laubengayer and D. 6 . Morton, J. A m . Chem. SOC., (1955). 54, 2303 (1932). (9) E. R. Lippincott. A. V. Valkenburg, C . E. Weir and E. N. (7) G. Braucr and H. Kenner. Z . anorg. allgem. Chem., 2T8, 108 Bunting, J. Research Null Bur. Standards, 61, 61 (1958). (1955). (IO) Cresoent Dcntal RIanufacturing Co., Chicago, Illinois.
NOTES
Jan., 1960
175
TABLE I INFRARED BANDSIN Pattern and sample
Amorphous 1. Freshly fused 2. Devitrified in air Hexagonal Hydrolysis in water a t 90-100" Dried a t 110' 3. Dried a t 400" Dried a t 1050' Hydrolysis, HC1 Ka4Ge9020 4. Commercial -4.D. Mackay Co. Commercial Eagle Picher Co. 5 . Hydrothermal 200" for 3 hr.
+
THE
SPECTRA OF GERMANIUM DIOXIDE
Indices of refraction
NO
NE
Bands ( p ) "
1.607 b
b
1.66-1.67 1.67-1.69 I .68-1.69
1.67-1.69 1.68-1.70 1.69-1.70
1.63-1.64
1.64-1.65
11,25b, s 11.40b, s
10.44W
2 . 9 5 ~6 . l w 6 . 5 ~7 . 0 ~7 . 6 ~10.22s 10.9sh 11.35b,s 6 . 5 ~6 . 9 ~7 . 5 ~10.43s 1 l . l s h 11.35b, s 6 . 5 ~6 . 9 ~7 . 5 ~10.43 11.05sh 11.35b; s 10.42s
11.44b, s
1.64-1. 66c
6 . 5 ~7 . 0 ~7 . 6 ~10.43s
11.25sh 11.47b, s
1.64-1.66~
6 . 5 ~7 . 0 ~7 . 6 ~10.42s 1l.Osh
1.697
1.724
10.44s
11.45b, s 11.45b, s
Tetragonal 6. Hydrothermal 400' for 3 days 1.9 2.1 12.9b, s 13.9b,S a sh-shoulder; s-strong; w-weak; b-broad. * Surface layer is hexagonal with same indices as hydrolysed variety. Very fine pou-der, treatment uncertain, probably hydrolysed from GeC14.
which rise as the reaction proceeds, as does the broad band of the spectra, until the characteristic rhombohedrons of the hexagonal form appear. The rhombohedrons have the appearance of forming only after solution and redeposition from solution, while the lower index material described above appears to be the result of an in situ type inversion. The cubical habit of the hexagonal form prepared hydrothermally is of interest since it displays diagonal extinction in contrast to that observed for the same habit by Laubengayer and Morton.6 The difference in indices of refraction of the products of the two preparations has been previously pointed 0ut.3'4 It is presumable that under hydrothermal conditions mater penetrates the amorphous structure and aids in the formation of centers where inversion takes place. The resulting crystallites are small and variably oriented so that under crossed nicols a rotating black cross is observed in the clear birefringent crystals rather than complete extinction. As shown by the loss of 0.9% weight and non-appearance of the weak broad bands near 3 and 6 p after drying the sample a t 400" absorbed water detectable by infrared methods has been removed. Ignition a t 1000" caused a total loss of weight of 1.3% but the indices were raised to only between 1.68-1.70 and the broad band of the spectra was not moved perceptibly from 11.35 p. The presence of other crystalline forms has been disproven by X-ray and the presence of a low index compound with water has been ruled out.' The extremely small and randomly oriented crystallites of the "hydrolysed form" could contribute to the low index of refraction of this form, whether prepared from the enneagermanate, tetrachloride or inverted from the amorphous form. The presence of the amorphous form as a minor part of a mixture does not appreciably affect the infrared
pattern of the hexagonal form other than in the possible formation of a shoulder on the broad band and also the presence of a small amount would not be detected by X-ray analysis. As only the products of the incomplete inversions to single crystals exhibit, in addition to the low index of refraction, an anomalous location of the broad band a t 11.35 p , it is presumable that the band location is varied by the presence of small centers of incompletely inverted glass. Thus, it is evident that to be reproducible, the infrared patterns of inorganic compounds prepared by inversion must be based on well crystallized samples.
THE COMPOSITIOK AND ENTHALPY O F DISSOCIATED WATER YAPOR BY P. J. FRIELA N D R. C. GOETZ Geiieial Electric Company, Missile and Space Vehicle Departmelit, Philadelphia 4* Pennsylvania Received J u l y 88, 1969
We have calculated the enthalpy arid composition of dissociated water vapor to 5000°K. for total pressures between 0.001 and 10 atmospheres assuming the gas mixture to be in chemical equilibrium. In this temperature range the following reactions occur
+
Hz0 = '/zH2 OH HzO = '/202 Hz '/zHz = H 1/20* = 0
+
(1)
(2) (3) (4)
The equilibrium constants for reactions 1 to 4 are
