THE SYSTEM
Fe203-Cr203
521
REFERENCES (1) HARXED,H. S., A N D OWES, B. B.: The Physical Chemistry of Electrolytic Solutions. Reinhold Publishing Corporation, New York (1943). (2) JONES, J. H.: J. Am. Chem. SOC.66, 1353 (1943). (3) ROBIKEON, R. A., AND SINCLAIR, D. .4.: J. Am. Chem. SOC.66, 1830 (1934). G., PRENTISS, S.S.,A N D JONES,P . T . : J. Am. Chem. SOC.60, 803 (1934). (4) SCATCHARD, R . H . , A K D LEVIES,B. J.: J. Am. Chem. S O C .68, 333 (1946). (5) STOKES,
X-RAY DIFFRACTION STUDIES Ii\; THE SYSTEM Fe203-Cr203L W. 0. MILLIGAK
AXD
L. MERTEZi
Department nf Che?nzstrU, The Race Institute, Houston, Texas Recezced October 8 , 1946
An unusual mutual protective action has been observed in mixed gels of cupric and ferric oxides (4)and of nickel and aluminum oxides ( 5 ) . In both oxide pairs, the constituents mutually protected each other against crystallization, even a t high temperatures. Thus ferric oxide prevented or retarded the crystallization of cupric oxide, and nickel oxide prevented marked crystallization of aluminum oxide in samples heated below 1000°C. for a period of 2 hr. In this paper these results have been extended to include thesystem Fe203-Cr203,in which the components are closely similar in crystal structure and in lattice constants. EXPERIMENTAL
Preparation of samples Mixed gels of hydrous ferric and chromic oxides were prepared by the addition of an equivalent amount of ammonium hydroxide to mixtures of solutions of ferric nitrate (0.5 X with respect to Fe203)and chromic nitrate (0.5 M with respect to Crz03),using a rapid mixing device described elsewhere (IO). The amounts of the ferric and chromic nitrate solutions were chosen so that there was obtained a series of eleven samples containing 0, 10, 20, 30,40, 50, 60, 70,80, 90, and 100 mole per cent of ferric oxide. The dual gels were washed in a centrifuge until the supernatant liquid no longer gave a test for nitrate ions. After the moist gels were dried in air a t room temperature, separate portions of each of the mmples were heated for 2-hr. periods a t various temperatures. In a similar manner, a second series of eleven gels was prepared, using sodium hydroxide as the precipitant. In order to attempt to ascertain any possible effect of adsorbed sodium hydroxide or silica from the alkali solution employed, separate experiments were 1 Presented before the Division of Colloid Chemistry a t the 109th Meeting of the American Chemical Society, which was held in Atlantic City, New Jersey, April 8-12,1946.
\
522
W. 0. MILLIGAN IN3 L. MERTEN
carried out, using redistilled ammonium hydroxide iis thc precipitant. Small amounts (about 1 per cent) of ( a ) sodium hydroxide and (h) dialyzed silica sol were deliberately added to moist chromic oxide gels prepared as described above. The treated gels wcrc allowed to d y in air at ronm t,emperntiire nnd wcrc heated for periods of 2 hr. at 40OOC. and 45OOC. S-ray diflractim analysis
X-ray diffraction patterns were obtained for the air-dried ant1 heat-treat,ed mixed oxide gels described above, using chromium K, x-radiation. The 6 x-radiation mas removed by vanadium pentoxide filters.
P E W L U OF X . U Y ANALYSIS
Air-dried
10.. . . , . / 10 11.. . , I 0
I 1
00
100
~
;\iiiorphous AmorphouR Aniorphouu Amorphous Amorphous Amorphous hmorphous Amorphous Amorphous Crys~alline' Crystalliriet
300T
~
~
'
Crystalline Amorphous Amorphous Amorphous Amorphous Amorphous Aniorphous Amorphous Amorphous Amorphous Amorphous
'
350T.
,
Crystalline Crystalline Amorphous .Amorphous Amorphous Amorphous Crystallinr
'
Crystalline Crystalline
'
1
4M)andSWT.
Crystallinr Crystallinr Crystalline C rys talli 11 tx Crystalline Crystalline Crystalline$ Crystalline Cryetallincb Crystalline Crystallinp
* Faint but broad lines of a new crystalline phase. t Intense and sharper lines of this new crystalline phase. $4OODC.sample very faintly crystalline.
The results of the x-ray examination are given in tables 1 to 3. Some of the diffraction patterns are given in chart form in figures 1to 3. DISCUSSION
Samples p ~ e ~ i p i t d eby d ammonium h y d r o d All of the air-dried samples were found to be amorphous to x-rays (table 1, figure 1) except the gels containing 100 and 90 per cent chromic oxide. The x-radiogram observed for the air-dried pure chromic oxide gel is distinct from the pattern of anhydrous chromic oxide and does not appear to correspond to the x-radiogram reported by Simon, Fischer, and Schmidt (7) for CrtOs.H20 prepared in a bomb a t high temperature and pressure. The x-ray diffraction data of these investigators were presented in the form of an unlabeled chart, from which quantitative values for the interplanar spacings cannot be obtained. However, from a consideration of the relative intensities of the lines, it does not appear likely that the new x-radiogram for hydrous chromic oxide gel corresponds to
THE SYSTEM
FezOs-CrtOs
523
t l i i ~monohydrate.
Hydrous chromic oxide gels previously prepared in this iaboratory (11) and reported in the literature (for a survey consult reference 8) t,aw been found to give amorphous x-ray and electron-diffraction patterns. Hydrous chromic oxide gels precipitated by sodium hydroxide and described 2.0
3.0
5.0
1.5
1.2
Mole Fe203
Cr203
(Standard Fe203)
l
~
i
I I ,I1
I
I!
I I /I1
I
I1
I
100
0
90
10
80
20
70
30
60
40
50
50
40
60
30
70
20
80
10
90
0
100
I
Ir
I
I1
(Standard C r Z O g )
I
5.0
3.0
2.0
1.5
1.2
FIG. 1. X - r a y diffractionpattern8 of Fe2Os-Cr2Oagels precipitated by ammoniaanddried in ai!
belov are likewise amorphous to x-rays. In contrast to the above results, Baccaredda and Reati (1) reported that a chromic oxide gel gave an electronThe pattern diffraction Wttern closely similar to the pattern of a-&08.3&0. reported in this present paper does not agree exactly with the interplanar spacing reported by Baccaredda and Fkati, but the pattern does resemble very closely th? s-radiogram of hayerite.
524
W. 0. MILLIQAN AND L. MERTEN
It will be noted that the gels exhibiting this new crystalline phase were prepared from neutral or slightly acid solution, suggesting that this phase may be a basic salt. In order to test this possibility a chromic oxide gel was prepared as described above from chromic chloride. The x-radiogram of the gel made from the chloride agreed exactly with that of the gel made from the nitrate. These results suggest that the new crystalline phase is not a basic salt, since it is unreasonable that a basic chromium nitrate and a basic chromium chloride mould exhibit identical x-radiograms. The x-radiogram of the new crystalline phase does not agree with the pattern of possible impurities such as ammonium nitrate. It will be noted from table 2 that this crystalline phase decomposed around 50-60°C., in contrast to the behavior of or-AlzOs.3H20(2, 9), and the resulting TABLE 2 Heut-treatment of chromic oxide gel
Precipitated by ammonia
Precipitated by podium hydroxide
"C.
[Air-dried] 50
100 150 200
300 350 400 500
Crystalline * Crystalline* Amorphous Amorphous Amorphous Amorphous Crystalline t Crystallinet Crystallinet
* New low-temperature crystalline phase, found in t Cr&.
Amorphous
Amorphous Crystallinet Crystalline$ gels precipitated by ammonia.
+
$ CrzOs new high-temperature crystalline phase, found in gels precipitated by sodium hydroxide.
product remained amorphous a t temperatures as high as 300°C. These data suggest that the new gel is not a hydrous form of a second crystalline modification of CrzOa. By a process of elimination, and because of the close similarity to the x-radiogram of bayerite, it is suggested that the new chromic oxide gel is actually a hydrate. Isobaric dehydration studies for the conclusive identification of this hydrate are in progress. It will be noted in table 1 that more than 10 mole per cent of ferric oxide retards or prevents the crystallization of the new chromic oxide crystalline phase, and that all other members of the series are amorphous t o x-rays, in confirmation of previous x-ray and electron-diffraction results obtained in this laboratory (11). Heat-treatment at various temperature levels (table 1 and figures 2 and 3) resulted in the formation of crystalline products which consist of solid solutions of or-FezOs and ( 3 2 0 3 . The observed variations in interplanar spacings agree
THE SYSTEM
525
Fe203-Cr203
closely with the results obtained by Passerini (6) and Wretblad (12) for the mixed oxides heated to higher temperatures. Marked mutual protection is observed at temperatures as high as 350OC As little as 30 mole per cent of Crz03 retards or prevents crystallization of 3.0
5.0
2.0
1.2
1.5
Mole % FeZ03 CrpOa
(Standard FeZ03)
I I
I
I
I
i
100
0
90
10
80
20
L
1 70
30
60
40
50
50
40
60
30
70
20
80
10
90
0
100
( S t a n d a r d Ca 2 0 3 )
5.0
3.0 2.0 1.5 1.2 FIG.2. X-ray diffraction patterns of Fe20r-Cr20r gels precipitated by ammonia and heated a t 350%.
cu-Fe,o3, whereas 40 or 50 mole per cent of Fe& retards the crystallization of Cr2O3.
Sampbs precipitated by sodium hydrost% The x-radiograms of the air-dried samples of the series of dual gels precipitated by sodium hydroxide were found to be entirely amorphous. No indication was
526
W. 0. AMILLIGAN AXD L. MERTYB
found of the new crystalline phase observed in the chromic oxide gels precipitated by ammonium hydroxide. Some of the air-dried gels were also examined using chromium K. x-radiation rendered monochromatic by means of a quartz crystal monochromator. An exposure time of 24-100 hr. was required. The resulting 5.0
3.0
2.0
1.5
1.2
Mole %
Fe203
Cr203
-
(Standard Fep03)
100
0
90
10
80
20
70
30
60
40
50
50
40
60
30
70
20
BO
10
90
0
100
(Standard C r Z O g )
5.0 3.0 2.0 1.5 1.2 FIG 3 X-ray diffraction patterns of Feg01-Cr203Krls prrcipitated by ainnioxita and heated a t 500°C.
x-radiograms were of the amorphous type. Therc w~tslittle or no evidence of more than one or two amorphous bands. The x-ray results for the samples heat-treated a t 300°C. demonstrate that the gels remain amorphous a t a higher temperature level than was found for the series of gels precipitated by ammonium hydroxide. At 400OC. the phenomenon of mutual protection is observed clearly (table 3). All of the results suggest
THE SYSTEM
Fez03-CrzOt
527
that the series of gels precipitated by sodium hydroxide crystallizes a t much higher temperatures than the series of gels precipitated by ammonium hydroxide. X-radiograms of the samples deliberately cont,aminated with silica or sodium hydroxide show that a small amount of silica (about 1 per cent) retards the crystallization of pure chromic oxide, whereas small amounts of sodium hydroxide (about 1.O per cent) engender a new crystalline anhydrous phase to be discussed below. I t will be recalled that Got@ (3) observed that small amounts of silica will retard the crystallization of ferric oxide. This present work extends the protective action of small amounts of silic,a to dual systems of chromic and ferric oxides. I t will be noted from table 3 that the gels precipitated by sodium hydroxide and containing 50-100 per cent chromic oxide develop at temperatures of 400-500°C. TABLE 3 Fe208-Cr20agels precipitated b y sodium hydroxide
-
MOLE PER CENT
1
Fn01 CrtOs
1
Air-dried
i
Amorphous*
90
I
80 70
5 . .. . 60 6.....j50 7 . . . . . . ( 40
____~ 300*C.
10
1
20 30
Amorphous'
~
40 50
60 8 . . . . . ~ 3 0 70 9. . . . 20 80 10. . 10 I 90 1 1 . .. . I 0 100
..I
--___
RESULTS O F X-RAY ANALYSIS
~
~
1
1 ~
AmorDhous .4morphous Amorphous* .4morphous , Amorphous Amorphous* Amorphous Smorphous .Amorphous* I .4morphous Amorphous Amorphous* i .4morphous
1 ~
~
1
' .AmorDhous Amorphous Crystalline i Amorphous Crystallinet Amorphous Crystalline$ Crystalline$ Crystalline$ , ~
'
~
i ~
~
~
i I
j
Crvstalline Cr&alliue Crystalline Crystalline$ Crystalline$ Crystalline$ Crystalline$ Crystalline$ Crystalline$
* Using quartz-crystal monochromator. t Very faint pattern. $ Fe20J-Cr,0s psttrrn plus lines of new crystalline phase.
Pure chromic oxide gel deliberately contaminated with about 1 per cent sodium hydroxide likewise exhibits t,his new pattern. The possibility has been considered that this pattern is for a new crystalline form of chromic oxide engendered by the presence of the sodium, analogous to the formation of P-AlzOain the presence of sodium. another possibility is the formation of a sodium chromite. The identification of these extra diffraction lines will require a careful study of the system Cr203-ITaz0. REFERENCES (1) H A W A H E D D A A N D U E A T I : ;itti Xocongr. intern. chim. 2, BO (1935). (2) FRICKE A N D SEVERIS:%. anorg. allgem. C h e m 206, 287 11!13Pj. i3) GdTTC: %. physik Chem. 46B,223 (1940). (4) ~ f I J . l . l r : A N , m i ) HOLVE?:J..4m. Chem. Soc.63.140 (1941).
528
NANCY CORBIK, MARY .4LEXANDER, AND GUST.4V EGLOFF
(5) MILLIGAN AND MERTES.J . Phys. Chem. 60,465 (1946). (6) PASSERINI: Gam. chim. ital. 60, 644 (1930). (7) SIMON, FISCHER, AND SCHMIDT: Z. anorg. allgem. Chem. 186, 1 O i (1930).
(8) WEIBER: Inorganic Colloid Chemistry. Vol. I I . The HUdrous Oxides and Hydroxides. JohnWileyandSons, Inc.,KewYork (19351. (9) WEISER AND MILLIGAN: J. Phys. Chem. 38,1175 (1934). (10) WEISERAND MILLIGAN: J. Phys. Chem. 40,1071 (1936). J.Phys. Chem. 44, 1081 (1940). (11) WEISERAND MILLIQAN: (12) WRETBLAD: Z. anorg. allgem. Chem. 189,329 (1930).
T H E ANTOINE VAPOR-PRESSURE EQUATION FOR MONONUCLEAR AROMATIC HYDROCARBONS KAKCY CORBI?;, hlARY ALEXANDER,
AND
GUSTAV EGLOFF
Uniewrsal Oil Products Company, Chicago, Illinois Recsived September 84,1946
The present study was undertaken to determine whether the variation of the constants of the Antoine equation logp = A
-
B
__
t+C
with the number of carbon atoms could be utilized to predict vapor pressures and boiling points of compounds for which experimental data are inadequate. The results indicate that these properties can be reasonably predicted for the normal akylbenzene series and the 2-methyl-2-phenylalkane series. For other types of akylbenzenes the variations are too great to permit satisfactory use. The vapor pressure and boiling point can, however, be estimated for phenyl-substituted normal alkanes if the boiling point a t 760 mm. is known. The Antoine equation is valid over a greater pressure range then is the widely used equation logp = A
- BT-
=
A
-
B
t
+ 273.16
where p = pressure in mm., T = absolute temperature, and t = temperature in "C. A plot of the reciprocal of the absolute temperature against the logarithm of the pressure usually exhibits a slight curvature, which increases at lower pressures. Although the linear equation represents the data quite well between about 200 and 800 mm., it cannot be extended much below 200 mm. A more convenient representation of vapor-pressure data is given by the Antoine equation when the constant C is chosen to give as nearly a linear function as possible in the pressure range under consideration. This equation makes possible the use of data between about 800 mm. and 10 mm.
