April, 1962
1,rquI~TEMPERATURE RANGE,DENSITY, AND
CRITICAL CONSTANTS OF
MAGNESIUM737
THE LIQUID TEMPERATURE RANGE, DENSITY, AND CRITICAL CONSTANTS OF MAGNESIUM1 BY P. J. hfCGONIGAL,2 A. D. KIRSHENBAUM, AND A. V. GROME Research Institute of Temple University, Philadelphia
44, Pennsylvania
Received November 13,1961
The density of liquid magnesium was measured over its normal liquid range (923-1390°K.) by the Archimedean method. The dependence of density on temperature is expressed by the linear equation D g./cm.3 = 1.834-2.647 X 10-4 T OK. with a probable error of f0.0014 g./cm.s. The density of liquid magnesium is 1.590 g./cm.3 at its melting point and 1.466 g./ The volume increase on fusion is 2.96% of the liquid volume. The estimated critical constants 0111.3 at its boiling point. of magnesium are: To = 3850 f 400”K., Po = 1730 (+800 or -700) atm., V , = 59 i 8.0 cm.S, and Do = 0.41 i.0.05 g./cm.3. Density values and the temperature coefficient obtained experimentally are in reasonable agreement with those predicted on the basis of an average reduced temperature us. reduced density diagram constructed from data on six metals.
bismuth,10 Iead,ll silver,12 gallium,13 and tin. l 4 Introduction Except for mercury ideal gas vapor pressures were It has been ~hosvn3.~ that the critical temperature of a metal can be estimated from its entropy used in construction of the vapor branch. This of vaporization, use of the reduced temperature us. curve is shown in Fig. 2. Use of the average entropy of vaporization curve for mercury (the of the reported values for the density at the melting only metal whose critical temperature has been point, 1.587 g./cm.a, led to predicted density values experimentally determined5), and application of of 1.447 g . / ~ m .at~ the boiling point and 0.36 the law of rectilinear diameter and the theorem of g . / ~ m a. ~t the critical point. Values of 1.466 and corresponding states. According to this theorem 0.41 g./cm.3, respectively, were obtained from the a metal having a given entropy of vaporization experimental data for magnesium. should be a t the same reduced temperature as Experimental Procedure mercury when mercury has that entropy of vaporiThe liquid magnesium was contained under an argon atzation. In this work 30,750 cal./g. atom was used mosphere in a low-carbon steel tube which was positioned as the heat of vaporization a t the normal boiling in a bath of liquid lead. The lead was agitated to ensure uniform temperature distribution. Heating was accompoint of 139OoEC6 The entropy of vaporization plished by means of a furnace with a Nichrome V winding then is 22.1 cal./g. atom-deg., which corresponds on an alundum core. to a reduced temperature of 0.36 on the entropy of A specially adapted analytical balance was used to devaporization us. reduced temperature curve of mer- termine the apparent decrease in weight of a low-carbon float which had a volume of approximately 13 cm.S cury, The critical temperature calculated by this asteel t room temperature. The exact volume of each float method is 3850 i 4OOOK. The error is arbitrarily used was determined by calibration in absolute ethanol. estimated as f10%. The volume of the float was corrected for thermal expanPublished data on the density of liquid mag- sion.l6 Surface tension corrections for the thin iron wire nesium, as seen in Fig. 1, show considerable dis- that supported the float were made using the data of Girov.l6 of these data gave values of 571 dynes/cm. agreement. Reported temperature coefficients aExtrapolation t the melting point and 439 dynes/cm. a t the normal boilvary from -0.8 X to -18.1 X loU4g./crna3 ing point. In no case did the surface tension correction deg. Density data presented in the Liquid Metals amount to more than 0.5% of the total weight loss. Surface Handbook,’ after critical evaluation of all published tension values of 355 dynes/cm. a t the melting point and 300 a t the boiling point were calculated from a general data, give -10.4 X over the range 924 to dynes/cm. empirical relationship between the surface energy and the 1023”K., as the best value. This temperature critical temperature of a metal, as deveioped recently .l7 coefficient differs markedly from the value -3.0 The published experimental values of the surface tension more accurate for use in making the corX g . / ~ mdeg., . ~ which was predicted on a semi- were considered Since the density determinations were made in empirical basis utilizing the average reduced rections. a steel apparatus it was necessary to correct for the amount temperature us. reduced density curve, constructed of dissolved iron. The corrections were made on a weight from the most reliable density data on merc~ry,8~9basis using the values of Fahrenhorst and Bulian18 for the (1) This work was supported by the National Science Foundation under Grant 15540. (2) A report of this work will constitute a portion of a dissertation t o be submitted by P. J. McGonigal t o the Graduate Council of Temple University in partial fulfillment of the requirements for the degree of Doctor of Phgosophy. (3) A. V. Grosse, T h e Liquid Range of Metals and Some of their Physical Properties a t High Temperatures,” Research Institute of Temple University, September 5, 1960. (4) A. V. Grosse, J . Inorg. & Nuclear Chem., 22, 23 (1961). (5) F. Birch, Phzls. bat., 41, 641 (1932.) (6) D. R. Stull and G. C. Sinke, “Thermodynamio Properties of the Elements,” American Chemical Society, Advances i n Chemistry Series, Vol. 18, 1956. (7) “Liquid Metals Randbook,” 2nd Ed., R. N. Lyon, Editor-inchief, Sponsored by tho Committee on the Rasic Properties of Liquid Metals, Office of Naval Research, Department of the Navy, in Collaboration with the Ai,omio Energy Commission and the Bureau of Ships, Department of the Navy, Washington, D. C., June, 1952, NAVEXOS P-733 (Rev.). ( 8 ) J. Bender, Phusilc. Z.,16, 246 (1915).
solubility of iron in liquid magnesium. Several samples taken during the experiments and analyzed for iron content were in agreement with the published values. The solubility of iron in liquid magnesium is 0.035-0.04070 a t 973°K. (9) J. Bender, ibid., 19,410 (1918). (10) A. D. Kirshenbaum, Final Report on High Temperature In-
organic Chemistry to the National Soience Foundation, Research Grant NSF-G 15540, October, 1961. (11) A. D. Kirshenbaum, J. A. Cahill, and A. V. Grosse, J . Inorp. & Nuclear Cham., 22,33 (1961). (12) A. D. Kirshenbaum, J. A. Cahill, and A. V. Grosse, ibid., in press, 1962. (13) W. H. Hothar, Proc. Phzls. SOC.(London), 48, 699 (1936). (14) A. L. Day, R. B. Sosman, and J. C. Hostetter, Am. J . Scz., 57, 1 (1914). (15) G. Tammann and G. Bandel, Archiv Eisenhueltenu., 7, 671 (1934). (16) V. G. Girov, Trans. Aluminum-Magnesium Inst. (Russian), 14, 99 (1937). (17) A. V. Grosse. J . Inora. & Nuclear Chem.. in Dress. 1962. (18) E. Fahrenhorst and E. Bulian, 2.Metallb., Si,3 1 i1941).
P E R ATU R E, K. of liquid magnesium.
T EM
Fig. 1.-Density
and 0.560% at 1373OK. The largest correction was 2.25% (at 1365'K.) of the corrected density. Temperature measurement was accomplished by means of a calibrated Chromel-Slumel thermocouple. The thermocouple was sheathed in a steel tube viith a closed end inserted directly into the liquid magnesium. The magnesium used in this work was supplied by A. D. Mackay, Inc., and had a stated purity of 99.95Yob. An analysis supplied with the metal listed impurities in p.p.m. as follows: Zn 100; Mn, Fe, Ni, each 50; A1 40; Pb, C, Si, each 30; Au 10. The oxide coating on the magnesium waa carefully removed before use.
Results Density determinations were made over essentially the whole normal liquid range of magnesium. Least squares treatment of the experimental data gave the linear relationship D ~./cm= . ~ 1.834 - 2.647 X
T
TABLE I DENSITY,ATOMIC VOLUME,SPECIFICVOLUME,A N D CoEFFICIENT OF CUBICAL EXPANSION OF LIQCIDNAGNESIUX Temp.,
Density, g./cm.3
OK.
923 m.p. 950 1000 1050 1100 1150 1200 1250 1300 1350 1390 b.p.
1.590 1.583 1.569 1.556 1.543 1.530 1.516 1.503 1.490 1.477 1,466
komic volume, cm.a/g.
atom
Specific volume, cm.$/g.
Coefficient of cubical expansion X 100 (OK.-')
15.30 15.36 15 50 15.63 15.76 15.90 16.04 16.18 16.32 16.46 16.59
0.6289 .6317 ,6373 ,6427 ,6481 ,6536 .6596 .6653 .6711 .6770 ,6821
166.5 167.2 168.7 170.1 171.5 173 .O 174.6 176.1 177 6 179.2 180.6
OK.
The probable error is f 0.0014 g . / ~ m . ~Figure . 1 is a plot of our experimental data corrected for expansion of the float, iyon solubility, and surface tension. For purposes of comparison the results of other i n ~ e s t i g a t o r s ~ also ~ - ~ are * shown. Smoothed densities, atomic volumes, specific volumes, and coefficients of cubical expansion are listed in Table I. The volume change on fusion is 2.96% of the liquid volume based on this work, the X-ray data (19) J. D. Edwards and C. 8. Taylor, Trans. Am. Inst. Mining Met. Eng~s.,69, 1070 (1923). (20) K. Arndt a n d G. Ploets. 2. physik. Chem., 130, 184 (1927). (21) Engelhardt, Handbuch der techn. E'lektroehem., 3, 178 (1934). (22) 1%.Grothe and C. Xangelsdorf, Z. ~ v e t a l l k . 29, , 352 (1937). (23) E. Pelrel a n d I?. Sauerwald, ibid., 33, 229 (1941). (24) E. Gebhardt, ;VI. Reciter, and E . TrLgner, ibid., 46, 90 (1955).
TABLE I1 LIQU~D AND V A P O R DENSITIESOF h%AGXESIUX ABOVE ITS NORMAL BOILINGPOINT
CILCULATED
Li
Vap.
T,OK.
D,g.Pirn.8
D,gJcrn.3
1500 2000 2500 3000 3500
1.438 1.300 1.151 0.989 0.815
0.0005 ,0052 .0208 ,0514 .0932
reported by Foote and Jette,26 and the solid density data of Pelzel and S a u e r ~ a l d . ~ ~ On the basis of our experimental results and the estimated value of 3850 & 400'K. for the critical temperature, t,he critical densit,y and crit,ical (2.3) F. Foote and E. R . .I?tte, Phys. Rea., 68, 81 (1940).
April, 1962
LIQUID‘ h M P E R A T U R E RANGE,DENSITY, AND
CRITICAL COKSTASTS O F ~ / k G N E S I U M
739
TABLE I11 LITERATURE DATAON Lit. ref.
19 20 21 22 23
7 24
THE
DENSITYOF LIQUIDMAGNESIUM
Temp. rsnge,
Density g./om.a
Authors
Year
Edwards and Taylor Arndt and Ploetz Not given, reported by Engelhardt Grothe and Mangelsdorf Pelzel and Sauerwald Liquid M[etals Handbook
1923 1927 1934 1937 1941 1952
923-973 923-1023 923-1023 953-1123 973-1073 924-1023
1.572 1.601 1.590 1.588 1.585 1.573
Gebhardt, Becker, and TrLgner This work
1955 1961
973-1 173 923-1390
1.585 1.590
OK.
m.p,
-dD x
dT
Method
10‘
5.5 18.1 0.8 1.8 2.00 10.4
2.40 2.647
Py cnometric Archimedean
...*.....
Archimedean Archimedean Summary and crit. eval. of prev. data
.. .... .
Archimedean
atomic volume were estimated by application of the law of reclilinear diameters, Le., the critical density lies on the line whose algebraic equation is one-half that of the liquid density os. temperature line. The critical density and critical atomic volume of magnesium are estimated to be 0.41 0.05 g . / ~ r n . ~ and 59 8.0 cm.3, respectively, based on our experimental lilquid density data. The critical pressure was obtained by extrapolation of ideal gas vapor pressure data6 and is 1730 ($800 or -700) atm. The errors in the critical density, critical atomic volume, and critical pressure are based on the estimated error in the critical temperature. Figure 3 shows the complete liquid range diagram of magnesium. The liquid density curve was constructed by subtracting the vapor density at a giveii temperature from the liquid density given by extrapolation of the experimentally obtained straight line. Table I1 shows calculated liquid and vapor densities from 1500 to 3500’K. Comparison with Literature Data.-A comparison of the reported density data in liquid magnesium is shown in Table I11 and Fig. 1. The disagreement in the extreme values of the temperature coefficient is striking. The data of Grothe and REDUCED DENSITY. Mangelsdorf,22Pelzel and S a ~ e r w a l d and , ~ ~ Gebhardt, Becker, and TragnerZ4are in reasonable Fig. 2.-Reduced density us. reduced temperature-average curve for Hg, Bi, Ag, Pb, Sn, Ga. agreement with each other and with this work. The data of Edwards and Taylor,19 Ariidt and Ploetz,20 and those reported by Engelhardt21 are in definite disagreement. The low values of Edwards and Taylor as obtained over a short temperature range may possibly be explained on the basis of gas bubbles trapped in their pycnometer. Arndt and Ploetz used a float whose volume was less than one-half ,oo ~ m . thus, ~ ; errors in weighing would be relatively I large in view of the small apparent decrease in weight. Also, the temperature range over which ; Ariidt and Plortz made measurements is small. The source of the data report;ed by Engelhardt is not given. Again, the temperature range is small. The error in the temperature coefficient depends to a large extent on the temperature range investigated. I n this work values were obtained over Fig. 3.-The liquid range diagram for magnesium.
*
o5
TEMPEllAlURL
*I(
740
E. G. SHAFRIN AND W. A. ZISMAN
essentially the entire normal liquid range (467’) compared with a previous maximum range of 200O. Acknowledgment.-The financial support of
Vol. 66
the National Science Foundation is gratefully acknowledged. We thank Mr. J. A. Cahill for his assistance and encouragement and Mrs. Lucia Streng for performing the iron analyses.
EFFECT OF PROGRESSIVE FLUORINATION OF A FATTY ACID ON THE WETTABILITY OF ITS ADSORBED IhIONOLAYER BY E, G. SHAFRIN AND W. A. ZISMAN Chemistry Division, U.8. Naval Research Laboratory, Washington 26, D. C. Received November 14, 1961
A study has been made of the wettability of monomolecular films of a series of heptadecanoic acids with substitutions in the 17-position of perfluoroethyl (+-ethyl), +propyl, +pentyl, and +heptyl groups. Films of these segmented acids were prepared by adsor tion from the melt on chromium; films of the +he tyl compound also were prepared on platinum, nickel, quartz, and soda-gme glass. Films adsorbed on metal substrates exiibited uniformly high contact angles; those on siliceous surfaces were more wettable and more vulnerable to attack by sessile drops of hydrogen-bonding liquids. There was little differencein wettability between the longest terminally fluorinated aliphatic acid and a fully fluorinated acid containing the same perfluoroalkyl moiety (+-octanoic acid, reported previously). Acids with terminal fluorocarbon segments shorter than +heptyl were more wettable than the analogous fully fluorinated acids. This and the differences in the effects of homology for the two types of acids are discussed in terms of the configuration and orientation of the adsorbed molecules. Models are proposed which take into account the effect of differences in size and van der Waals forces of fluorocarbon and hydrocarbon chains, the steric hindrance to intramolecular bending, and the re ulsive effects of uncompensated dipoles a t the junction of the - C H r and - C F r chains. Future experiments are proposec?to confirm the structure of these models.
Introduction Previous investigations a t this Laboratory have revealed that regular and predictable changes in the contact angles of liquids result from changes in the chemical structure and physical packing of the outermost atoms or atomic groupings in the solid surface being wetted.’t2 Least wettable of the surfaces studied were those containing the highest concentration and closest packing of perfluoromethyl groups in the exposed surface.a-6 Trifluorination of the omega-carbon atom on a long-chain fatty acid or amine was proposed7 as a way of combining the desirable properties of limited wettability associated with a CF3-rich surface, the closeness of molecular packing resulting from the strong intermolecular cohesive forces between adjacent aliphatic hydrocarbon chains, and the potentially lower cost of compounds having a low degree of fluorination. Although a solid coated with such a film proved less wettable than one covered with a film of stearic acid, it was more wettable than one coated with a film of the perfluorinated fatty acid.* The difference in wetting behavior was attributed to the presence of the strong dipole in the CF3-CHr linkage; whereas in the fully fluorinated compounds there is internal compensation between the dipole moment contributions of the -CF8 group and its neighboring - C F r groups in the chain, in the trifluoromethyl-substituted acid the moment of the -CF3 dipole is not (1) W. A. Zisman, “Relation of Chemical Constitution to the Wetting and Spreading of Liquids on Solids” in “A Decade of Basic and Applied Science in the Navy,” Office of Naval Research, published by the U. 8. Government Printing Office, Washington, D. C., 1957. (2) E. G. Shafrin and W. A. Zisman, J . Phgs. Chem., 64, 519 (1960). ( 3 ) F. Schulman and W. A. Zisman, J . Colloid Sei., 7 , 465 (1952). (4) E. F. Hare, E. G. Shafrin, and W. A. Zisman, J . Phye. Chem., 68, 236 (1954). (5) M. K. Bernett and W. A. Zisman, ibid., 64, 1292 (1960). (6) M. K. Bernett and W. A. Zisman, zbid., 66, 2266 (1961). (7) E. G. Shafrin and W. A. Zisman, kbid., 61, 1046 (1957).
compensated by the adjacent -CH2- dipoles of the chain. The resultant uncompensated and strong dipole is located in the outermost portion of the adsorbed monolayer. Since the external electrostatic field of force of the dipole varies as the inverse fourth power of the distance, there results an additional attraction for the molecules of the wetting liquid; hence the surface is made more wettable than one coated by the perfluoro fatty acid. Measurements of the mechanical and electrical properties of such a substance, when spread on water as an insoluhle monolayer, were found by Fox*to be in accord with the above concept. Replacing the w-perfluoromethyl group by an w-perfluoroethyl. w-perfluoropropyl, or other wperfluoroalkyl segment removes the e1ect)riccenter of gravity of the uncompensated dipole further from the exterior surface of the adsorbed monolayer; hence, the longer the perfluoroalkyl group, the smaller should be the effect of the dipole on the wetting behavior of a liquid resting on the outermost surface of the adsorbed monolayer. Providing there are no repulsive forces between neighboring uncompensated dipoles within the monomolecular layer strong enough to seriously interfere with obtaining close packing of the adsorbed molecules, the monolayer then should exhibit the same wetting properties as an equally condensed film of a perfluoroalkanoic acid of the same chain length. A suitable series of fluorinated heptadecanoic acids has been synthesized recently a t the Jackson Laboratory of the E. I. du Pont de Kemours and Company by E.0. Brace and co-workersDwith the perfluoroheptyl group the longest terminal perfluorocarbon moiety. Pure specimens of these (8) H. W. Fox, ibid., 61, 1058 (1957). (9) N. 0. Brace, “Long-Chain Alkanoic and Alkenoic Acids with Pwfluoroalkyl Terminal Segments,” preaented at the Symposium on Bdvances in Fluorine Chemistry, American Chemical Society Meeting, Chicago, Ill., Sept. 3 , 1961.
