NOTES
Dee., 1958
1593
NOTES THE EXCHANGE OF F18 BETWEEN METALLIC FLUORIDES AND SILICON TETRAFLUORIDE’ BY THEODORE A. GENS,~ JOHN A. WETHINGTON, JR., AND
*-e-. SiF4 ALONE LlF
> *-*-
600
-D-e-.o-e-e-.-a
.--e-*-*.
A. R. BROSI
HEATING RATE- 5O/rnin.
1
Departments of Chemical Engineering and Chemistry University of Florida, and Chemistry Division, Oak Ridge National Laboratory, Oak Ridge, Tennessec Received January 86, 1968
I n a survey of exchange reactions between 300 gaseous and solid fluorine-containing materials, the systems silicon tetrafluoride-alkali fluorides 100 200 300 400 500 were studied. Even though SiF4 possesses one T , ‘C. of the strongest chemical bondslait is known to enter Fig. 1.-Pressure of SiFd when heated with several alkali into reactions of the type fluorides. 2MF
+ SiFc
MzSiFs
I
where MF denotes many metallic fluoride^.^^^ Alkali fluorides containing FIB were prepared by the reaction F’g(p, pn)F18. The appropriate salt was bombarded in the ORNL 86-inch cyclotron, carrier was added, and the salt was recrystallized from water. The exchange reaction was studied by circulating SiF, in a closed system over the alkali halide and through a counter. The salt was heated at the rate of 5’/minute. Calculations of the fraction exchanged from the observed counting rates were made as described in a previous paper.6 The silicon tetrafluoride pressure was measured with a mercury manometer as the reactor was heated.
Results The pressure-temperature data for SiF4 alone and for SiFd in the presence of alkali fluorides are shown in Fig. 1. The increase in pressure for the SiF4 alone was caused by the temperature rise in the reaction chamber; consequently this curve may be regarded as a blank. Comparison of these data with the data obtained from the systems KF, RbF, CsFSiF4 showed that fluorosilicates were formed in each case. Spectrographic analyses of the solid products showed large amounts of silicon. The pressure-temperature data obtained with the system LiF-SiF4 showed no evidence for appreciable compound formation. Spectrographic analysis for silicon confirmed this result. Figure 2 shows the fraction exchanged as the temperature of the salt was increased. Despite the fact that no stable fluorosilicate was found, the exchange results with LiF were similar to the exchange results obtained with KF, R b F and CsF (1) This research waa performed a t the Oak Ridge National Laboratory which is operated by Union Carbide Nuclear Company for the Atomio Energy Commission. The Chemistry Branch of the Office of Naval Research contributed to the work through its contract with the University of Florida. This publication may be reproduced i n part or in whole for the benefit of the United States Government. (2) Oak Ridge Institute of Nuclear LPtudies Fellow, 1955-1957. (3) L. Pauling. “Nature of the Chemical Bond,” Cornel1 University Press, Ithaca, N. Y.,1945, p. 53. (4) G. Hantke, Z . angew. Chem., 39, 1065 (1926). ( 5 ) R. Caillot, Ann. Chim., 20, 367 ( 1 9 4 5 ) . (6) T. A. Gena, J. A. Wethington, Jr., A. R. Brosi and E. R. Van Artsdalen, J . A m . Chem. Soe., 19, 1001 (1957). Complete details can be found in the Ph.D. thesis of T. A. Gena, University of Florida, August, 1957. T o be microfilmed.
0.3
1
I HEATING RATE
I
I
I
I
- 5°Jrnin.
r, o c . Fig. 2.-The exchange of FlSbetween SiFl and several alkali fluorides as a function of temperature.
when fluorosilicates were found. Exchange calculations were not made with any of the alkali fluorides a t temperatures above which the pressure changes indicated fluorosilicate formation. Conclusions Large amounts of radioactivity were introduced into the SiF4in all cases before measurable amounts of SiF4were lost by formation of fluorosilicate. Silicon tetrafluoride, containing F1* in high specific activity, can be prepared rapidly a t moderate temperatures by passage over LiF which has been bombarded with protons. Rapid methods for preparing labeled fluorine compounds are needed because of the short half-life of FIB.
A MOVING BOUNDARY METHOD FOR THE DETERMINATION OF TRANSPORT NUMBERS IN PURE FUSED SALTS BY FREDERICK R. DUKEAND JAMESP. COOK Institute for Atomic Research and Department of Chemistry Iowa Slate College, Ames, Iowa. Work was performed i n the Ames Labdratory of the U. S. Atomic Energy Commission. Received April 19, 1968
Previous work in this Laboratory has described various methods for the determination of transport
NOTES
1594
numbers in fused salts, including the “bubble cell,”’ radioactive tracer2 and modified Hittorf methods.a The present paper describes a method based upon the visual observation of the boundary between the salt under investigation and a following indicator salt. The chief advantage of the method lies in the removal of the requirement for a reversible metal electrode.
Experimental The apparatus consisted of a U tube, one leg of which contained a Pyrex ca illary six cm. long with an internal radius of 0.5 mm. &he lower end of the capillary was joined to a larger tube (10 mm. i.d.) containing a Pyrex ultrafine disk with a pore size of 0.9 to 1.4 p . The volume between the disk and the capillary is kept to a minimum. The other leg of the capillary was an extension of the 10 mm. tubing. At the top, both arms of the U tube were enlarged to 20 mm. i.d. to contain the electrodes and to make changes in head during a run negligible. The apparatus was placed in a vertical tube furnace containing a window. Lead chloride, prepared by recrystallizing analytical grade salt, was used to fill the large-diameter leg of the cell and finally, when molten, was forced through the disk and to the top of the capillary by the application of a vacuum to the leg of the apparatus containing the capillary. Only a small volume of molten lead chloride passed through the disk, since the apparatus was designed with a small volume between the disk and the top of the capillary. The time required for filling the cell was about four hours. The zinc chloride, prepared by direct union of zinc metal with chlorine gas, was used to fill the upper portion of the U tube leg containing the capillary. The boundary between the molten salts was observed easily and remained sharp due to density difference. An alternating current was applied to the cell, and the boundary observed with a cathetometer. The heads of liquid in the two legs of the U tube were carefully balanced by the addition or removal of lead chloride from the cathode side after spectrographic carbon electrodes had been inserted into salt in the arms of the cell. When the boundary was observed not to move for a period of one-half hour, direct current was substituted quantitatively for the alternating current, and measurements on the motion of the boundary were made. The anode was placed into the zinc chloride and the cathode into the lead chloride. Thus the zinc ion was made to follow the lead ion. A number of observations were made during the course of a run. It is necessary to keep air containing moisture away from the zinc chloride, or i t becomes too viscous to pass through the capillary easily.
Results The transport number is calculated by means of an equation, assuming that the only flow through +,hedisk is due to electrical transport t+
prR2 X 96500 X Ah equiv. wt. of salt X amperes X seconds
where density of salt at temp. of run = diameter of capillary at temp. of run Ah = difference of height a t beginning and ending of run
&
=
The result of ten runs including 80 observations 0.04 at 550’ in excelon PbC12 was t f = 0.24 lent agreement with the value reported by other methods. The current used was 20 ma. The requirements for a following ion are that it be of sufficiently different density to make a good boundary and that its total conductivity be less than the salt under investigation. The membrane must be in the salt being investigated; the cell
Vol. 62
may be arranged to have the following indicator ion on the top or the bottom of the cell, depending upon the density relationships. HEATS OF COMBUSTION. VII. T H E HEATS OF COMBUSTION O F SOME AMINO ACIDS BY TOSHIO TSUZUICI, D. 0. HARPERAND HERSCHEL HUNT Department of Chemistry and Purdue Research Foundation, Purdue University, Lafayette, Indiana Received June 6 ,1968
The heats of combustion of L-isoleucine, glycine, L-phenylalanine, L-tryptophan, L-threonine and Lalanine have been determined by means of a nonadiabatic calorimeter. The method is exactly the same as that described by previous workers in this Laboratory. The acids were furnished by Dr. J. P. Greenstein of the National Cancer Institute, Bethesda, Maryland, and are better than 99.9% pure. The heats of combustion of the amino acids at constant volume and 25” for the reaction producing gaseous carbon dioxide, gaseous SO3, liquid water and gaseous nitrogen, are given in Table I. The standard deviations were calculated in accordance to the recommendations of Rossini and Deming.2 The atomic weights for the computations are 0 = 16, C = 12.011, H = 1.0080, S = 32.07, and N = 14.008; 1 thermochemical calorie = 4.1833 int. joules. TABLE I Amino acid
L-Phenylalanine (s), CsHllOzN L-Tryptophan (s), CI~HIZOZNZ L-Isoleucine (s), C~H1302N L-Threonine (s), CdHs03N L-Alanine (s), CaH702N Glycine (s), CzHaOzN L-Methionine (8) , C~HIIO~SN
Heat of Combustion, koal./rnole
1110.5 i 0 . 2 1345.5 i . 2 855.2 & . 2 490.9 i . 2 376.9 f . 5 230.9 i . 2 759.2 f . 2
The heat of combustion of L-phenylalanine is given in the literature3as 1,114.05 kpal./mole. The heat of combustion of insulin was found to be 5,382.2 f 0.2 cal./g. The authors wish to express appreciation t o the National Science Foundation for sponsoring this research and to Dr. John 0. Hutchens of the University of Chicago for coordinating it with his entropy work. (1) T. Tsuzuki and H. Hunt, THISJOURNAL,61, 1668 (1957). (2) F. D. Rossini and W. E. Deming, J . Wash. h a d . S c i . , 29, 416 (1939). (3) E. Fischer and F. Wrede, Akad. wiss. Berl Sitzungsber., 687 (1904).
+
(1) F. R. Duke and R. W. Laity, THISJOURNAL, SO, 549 (1955). (2) F. R. Duke and R. A. Fleming, J . Electrochen. SOC.,in press. (3) F. R. Duke and J. P. Cook, Iowa Slate Coll. J . Sei., 32, 35 (1957).
THE VAPOR PRESSURE OF CADMIUM AND ZINC CHLORIDES BY H. BLOOMA N D B. J. WELCH University of Auckland, Auckland, New Zealand Received June 19, 1968
In the course of an investigation of the vapor pressures of molten salt mixtures, the vapor pressures of pure CdClz and ZnClz were determined by
