&?-.
are: ‘at e = 0.11, a(A3C) = f 2 ; = 0.24 S(&) = AI; e = 0.30, AX) = 1 0 . 5 ; e = 0.37 qm) = k0.30; e = 0.42,4aX) = *0.25,6 = 1.07, &(AX) = f O . 1 . These uncertainties are not large enough to influence the character of the (X. - ?~’)i-. data and do not influence the character of the denved entropy curve. D. R. ROSSIN’GTON (Alfred University).--Is the concept of spreadmg pressure invalidated by s m chemisorption?
J. W. WHALEN.-I believe the consensus is that: the C O I I cept of “spreading pressure” is confined to non-localized adsorption, i.e., free mobility is r uired in the film; in c 8 8 e ~involving localized adsorptione%e concept of “spreading pressure’’ is not valid; however, we have lost only the physical concept; the function defined by the equation utilized in this work is not influenced by localization or nonlocslization of the film.
HEATS OF’ IMlMERSIOPi. V. THE Ti02-Hz0 SYSTEM-VARIATIOSS WITH PARTICLE SIZES AND OUTGASSING TEMPERATURE BY W. H. WADE m N. HACKERMAN Departmznt of Chemistsy, Univcrady of Texas, Austin, Tezas Rsuind March .W, 1961
The heats of immersion of both anatase and rutile in water have been obtained as a function of particle size and outgassing temperature. The heats of immersion of both crystalline modilications were found to decrease with decreasing particle size for Hamples whose specific surface area varied from approximately 7 to 250 m.*/g. All samples showed a similar variation of imrnersional heat with outgassing temperature, namely, maxima were observed a t 3OO-35Oo,
Introduction Previous measurements from this Laboratory1-* demonstrated two trends in the immersional heats per cm.* (Mi)of Si02 and AlZOa in H20: (i) a marked dependence of AHi on particle size, and (ii) rather characteristic behaviors with outgassing temperature. For Sios in HzO, in general, AHi increases, passes through a maximum, and then decreases with increasing outgassing temperature. On the other lbnd, A l 2 0 a in HzOexhibits a monotonic increase of AH,with outgaasing temperature. This interpretahion has been in terms of gradual endothermic loss of physically adsorbed water a t Iower outgassing temperatures and surface hydroxyl groups a t higher temperatures. The difference between SiOz antd AlzOI is that the dehydroxylated Si02 surface does not rehydrate rapidly, whereas the A120ssurface does. The variation of AHi with particle size has been explained as a fundamental variation of surface amorphous character with particle size.’-‘ Several studies pertinent to the present work have been reported for TiOl. Harkins and coworkers4 selected a barrel of anatase with a specific surface area of 13.8 m.*/g. as a standard of comparison for surface studies. They reported a AHi of 512 ergs/cm.z for this material outgassed a t 500’. Zettlemoyer, et d.,5 made this measurement for a 7.3 m.z/g. rutile sample outgassed a t 40O0, and obtained 550 ergs/cm.2. Recently, Yatess obtained the infrared spectra of several anatase and rutile samples. They demonstrated the loss of physically adsorbed water below 350’ outgassing temperature. This Flras shown by the absence of any H-C-H bending modes although there were prominent OH (1) A. C. Makridea and N. Haekeman. J . Phys. Chem, 6% 594 (1959). (2) W. II. Wade, R. L. Every and N. Hackerman, ibid., 64, 355
(1960).
(3) W. H. Wade and N. IIaekerman. ibid.. 64, 1196 (1960). (4) W. D. Harkios, “The Physical Chemistry of Surface Films.” Reinhold Publ. Conp.. New York. N. Y.. 1953. ( 5 ) A. C. Zettlemoyer. G . J. Young. J. J. Cheesick and F- J L K d e y , J . Phys. C h . . 67, 649 (1953). (6) D. J. C. Y a w . ibid., 66. 746 (1961).
stretching modes a t 350’, indicating surface hydroxyl groups. This conflicts with Zettlemoyer,’ who assumes there are no surface OH groups on Ti02 since the bulk hydroxide is unstable. The present study was undertaken t,o assess the AHi of anatase and rutile as a function of both particle size and of outgassing temperature.
Experimental Samples.-The source of all samples was the National Lead Company, South Amboy, N J . They are listed in Table I. Samples F and I are those Yates used in his infrared studies.6 The samples AI, At, and & were prepared in this Laboratory by grinding large single crystals In an agate mortar, with subsequent sedimentation and fractionation in water. Only three of the many fractions obtained are reported on here. The B.E.T. surface areas were measured by Kr adsorption ae previously described.8 The samples pnor to immersion were outgassed at IO4 mm. for three days in Pyrex bulbs and were sealed off on the outgassing apparatus. The outgassing temperatures in Table I1 are accurate to f 5”. Calorimeter.-The calorimeter already has been describedl and likewise the sample bulbs.’ Heat output from sample immersion continued over a 5 to 10 minute period. Sample weights varied from 0.1 to 5 g., depending on the specific surface area. All measurements were run in duplicate with a usual agreement of 2 to 3y0.
Results The variations of AH; with outgassing temperature for samples A-I are listed in Table I1 and illustrated in Fig. 1. Particle Sue Effect.-A variation with particle size is once again prominent, and both crystalline modifications of TiO, were obtained in a reasonable spectrum of particle sizes. If at any given outgassing temperature the AH{s for the two modifications are considered separately, tbere is a general decrease of M€i with decreasing particle size. Moreover, a t a given outgassing temperature, the AHi for anatase is approximately 80 to 180 ergs/ cm.* greater then for rutile samples with approximately the same particle size. This might be inferred from Yates’ infrared data6 in which his ana(7) A. C. Zettiemoyer. Chem. Rem.. 69, 937 (1959). (8) M. J . Joneieh and N. Hackerman, J . I’hus. Chem.. 67, 874 (1953).
W. H. WADEAND NORMAN HACKERMAN
1682
Vol. 65
TABLE I Manufacturere
Code
Sample
MP MP MP MP MP MP MP MP MP
A's
B C D E F G
H I
1643-1 1634 1663-4 1663-2 1643-2 1208 1643-4 1663-1 1579
Cr stslliee
Purity
mokoation
%
Si@
ZnO
rutile rutile anataae anatase rutile rutile anatase rutile anatase
99.9 99.9 99.5 99.8 99.7 99.8 99.5 99.8 99.4
0.04 0.04 0.05 0.2 0.2
0.01 0.01
Impuritieb---
Nb
Other
0.01 0.01
0.001 0.001 0.5 0.1 0.2
0.1 0.2
0.1
Surface area (m.V/p.)
1 . 1 1 , 9.4, 24.5 6.45 7.65 10.50 114 I58
0.25
174 188 25 1
0.65
TABLE I1
azIi(ERQS/CM.') It,
1.11
100 150 200 250 300 350 400 450
B
Ai
A¶
A1
("C.)
9.40
24.5
C
580
529
251
407 484
592 701 779 852 89 1 908 909 902
504 575 628 672 695 693 677 650
328 419 496 563 573 544 449 413
204 286 308 326 330 317 281 226
415 493 557 585 586 570 540 507
293 345 376 401 409 408 398 384
352 441 506 552 570 557 515 456
200 300
400
T ("C.). Fig. 1.
ta,se saniples showed two OH bands, and rutile only one. However, the somewhat risky asswnption must be made that the extent of OH coverage correlates with the energetics of physical adsorption. It should be noted that the present authors consider Ti02 a poor choice for a "standard" adsorbent in adsorption studies. This material apparently cannot be obtained in greater than 99.976 purity (t,hisis best found as seen from Table I), its surface is quite reactive,6 and there appears to be some chemical reduction (as evidenced by color changes when heated i n ~ a c u o ) .This ~ ~ ~last property has been at,tribut,ed to adsorbed organic dyes used 3s p H indicators in the precipitation of TiOz. i t , was to eliminat'e thls last difficulty, as well as to obtain large part,icle size samples, that the rutile single c:ryst.als werp ground and fractionated, These sarnpies '$1, Az, and -43 which had never been '9) A . C X.>*t!,ii,oycr private communication.
I
188
I51
200
H
174
P?'' 100
G
158
/-
400
F
114
ANATASE RUTILE
I
E
10.50
593 640 657 645 612
--
D
7.65
542
619
Sample, m.z/g.
6.45
in contact with organic substances displayed the same color change behavior as did samples F and G. Color changes were not observed for samples other than A, F and G. The three samples A,, Az and A3 could be prepared in only small amounts due to a limited supply of starting material, and it was not feasible to subdivide them to the extent that AHi could be obtained as a function of outgassing temperature. Instead, the three samples were outgassed at 250' only. For these samples there is a regular decrease of AHi with decreasing particle size. The values are reasonably consistent with the other rutile samples outgassed a t 250'. Effect of Outgassing Temperature.-The effect of outgassing temperature is similar to that for the SiOz-HzO system in that the immersional heats for both anatase and rutile increase, pass through a maximum, and then decrease. The prominence of the maximum varies from sample t,o sample and is barely discernible for the coarsest anatase sample. The maximum occurs a t 300 and 350°, whereas for SiO, the usual position of the maximum was a t 250°, indicat,ive of a higher bond energy for titanol groups than for silanol groups. By analogy to SiOz the removal of titanol groups might be irreversible on the time scale of the ca,lorimet,ric measurements, hence the decrease of AHi with outgassing temperature above 300' because of the reduced opportunity for hydrogen bonding. An infrared study for the kinetics of rehydration with outgassing temperatures higher than those used by .Tates6is necessary to sbed more light on this problem.'O (10) Aiter preparation of ttiis manuscript, recent work by Hcliabaugh and Chessick" iri:rr,iiuces an added complication to the beassing ta;iiporatiire. They Iiitd that samples vacuum outgassed at. .150" 1mve AF1i.s considerably higher chan for the same saninlen aubseqi;ent!y t r e a d with Or at 450". the indication being tiist there is a direct connrvbion between A H l and t h e extent of reduciion of the Ti+' fa a ioivcr oxidation state on outgassing. Applied zo the preerrit w o r k , thih w o i d d indicate moore pronounced maxima .rinrt, the r?4ii?t!g>n 'i . ~ i , r h i i h t t 4 i yTiinre erteasive the 'iigher the
Oct., 1961
ADSORPTION OF OIIAWL~XLE SULFONATES AT METAL-OIL INTERFACE
Conclusions The data continue to affirm that there is an inherent characteristic of adsorptive behavior, namely that the heah of adsorption are directly dependent on particle size. There is a uniform trend for both crystalline modifications of TiOz. The behavior with outgassing temperature is similar to that for SiOz; it is interpretable in terms of the progressive loss of physically adsorbed water and chemically bonded surface hydroxyl groups. It is fruitless to say that any one of the TiOz samples could be picked as the “representative one” without more insight into its surface structure. Acknowledgment.-The authors express appreciation to the American Petroleum Institute for their continued interest and support. Some surface areas were measured by Mr. H. D. Cole and his assistance was greatly appreciated. Dr. 11. J. C. Yates was very helpful in supplying both TiO, samples and a preprint of his paper6 which had been submitted to Journal of Physical Chemistry. DTSCUSSIOK 1). S. MACIVEF: (Gulf Research and Development Company) -Concerning Professor Wade’s observations relative to the heats of immersion of A120,and Ti02 in water, I mightmake two comments. In the first place, the heat of immersion of AI&, is dependent not only on such factors as particle size, outgassing temperature, etc., but also on the crystalline structure of the A . 1 2 0 3 . In the case of the high area aluminas such as y-Al&, several crystal modifications outgassing temperature and only becomes important a t temperatures above 200 t o 300’. Presumably, t h e A H i measurements a t higher outgassing temperatures for samples not treated with oxygen also include a heat source in thal oxygen in the colorimeter oxidizes t h e reduced Ti02 during t h e inimersional measurements. (11) C. M. Hollabaugh and J. ,J. Chessick. J . Phys. Chem.. 6S, 109 (1961).
1683
exist and attempts to compare immersional heats of a series of aluminas must take this factor into consideration. Secondly, I would think that, in the case of TiOz, plots of AH^ us. weight loss during outgassing might be more informative than plots of AHi us. outgassing temperature (Fig. 1). Have the former plots been made:? K. H. WADE.-^ would hasten to concur that gamma, chi, etc.-aluminas have not been characterized; however, the a-aluminas which are well characterized show a uniform decrease in AHi with decreasing particle sizc. Your point regarding TiO, is well taken and no plots of the type you mention have been made. Many Ti02 samples lose weight in excess of that attributable to surface losses. Presumably, decomposition occurs at higher outgassing temperatures. I,. H. REYEFLSON (University of Minnesota) .-How were your samples outgassed:) Outgassing can remove oxygen atoms from the surface so that the surface is Ti& not TiO:. This was proved in our laboratories by sorption of KO2 and magnetic susceptibility studies on TiO?. NO: gave up an oxygen at,om to fill each hole which had lost oxygen during outgassing. W. H. \?;ADE.--AI~ Ti02 samples were outgassed at the temperatures noted and a t 10-6 mm. for approximat.ely 100 hours. kV. I). Ross (E. I. du Pont Company).-The comment has been made that ‘Pi02 can lose oxygen upon heating, even if riot contaminated by organic material. A distinction should be made between anatase and rutile. Rutile is the more stable and can be heated strongly with no appreciable loss of oxygen. Anatase loses oxygen more readily: I ani not sure how strongly it can be outgassed. I t has been remarked thxt some metallic impurities affect oxygen loss: with this I agree. W. H. R’Ai)~.--Oneof the rutile samples reported in the present study showed some evidence of decomposition although it is of the highest purity attainable. I am not sure whet,her the correct explanation has yet been offered for the loss of oxygen by some Ti02 samples. A. C. ZEWLEMOYER(Lehigh University).-Our laboratory has shown that the loss of oxygen from rutile may he identified with the presence of traces of organic substances.
THE ADSORPTION OF OIL-SOLUBLE SULFONATES AT THE METAL/OIL INTERFACE BY WILLARD D. BASCOM AND C. R. SINGLETERRY U.S. Naval Research Laboratory, Washington 26, D. C. Received March 80,1961
It has been found possiblc to isolate adsorbed films of thc salts of dinoriylnaphthalenesulfonic acid on stainless steel surfaces by retraction from aromatic hydrocarbon solution. The wetting behavior of various series of liquids on the resulting film-coated surfaces suggests that the molecules adsorb to give monomolecular films by attachment of the polar sulfonate heads to the metal oxide surface with the hydrocarbon tails outward. The molecules are sufficiently close packed to yield a surface having properties similar to those of polyethylene. A study of the wettability of the soap monolayers by a series of alkylnaphthalene liquids indicates that adsorption from water-saturated solution is independent of the soap cation and is the result of dipole interactions between the hydrated sulfonate ion- air with the metal oxide surface. Adsorption from anhydrous solution does depend upon the choice of cation. Here dipore interactions between the unhydrated ion-pair and the metal-oxide surface appear to be supplemented by coordination of the cation with the oxygen of the oxide film.
Introduction Many stiidiwi have been made of thc adsorption of polar-non-po’lar solutes from non-aqiinous solution oilto oxide-coated metal surfaces. Most of these investigations, however, have been cmcerned with the carboxylic acid and amine derivatives of straight-chain hydrocarbons and fluorocarbons. The adsorptive behavior of the soaps of high molecular weight acids has received relatively minor attention despite their wide use as corrosion inhibitors and sludge dispersants in liihricating oils. A
more complete knowledge of soap adsorption at the solid-oil interface would permit a het,tcr understanding of the role of such soaps i i i thew technological areas. It has been found at this Laboratory, for instance, that the effectiveness of oil-soluble soaps in diminishing ice adhesion in lubricated syst’emsis in part. related to their adsorption at the oilmetal interface. The work reported here concerns the adsorptioii of various salts of dinonylnaphthalenesulfonic acid on stainless &el. These, compounds, n-cll char-
