V. STUBIFAN AND RUSTTJM ROY
1348
*
i 0.01 X 10-3 mm. a t 77.3 0.05°1i.; our vapor pressure equation yields 1.81 to 1.86 X mm. for the temperature range 77.25 to 77.35%. It should be noted that Liang assumed his measured value to be related by the Knudsen equation to the true vapor pressure, as he had measured the pressure through a capillary (1.6 mm. i.d.), ie., he asthe sumed P 1 / P 2 = d T 1 / T 2 = 0.51; however,___present investigation sets Pl/Px = 0.59 # .\I TI/Tz for Liang's measurement (Psd = 6 X mm.).
TABLE I1 SMOOl'IiED TRANSPIR.4TION
-Ti Pl/1,2
1.000 0.950 ,900 .so0 ,700 .650 ,625 ,600 ,575 ,650 ,525 .SO8
H2 3.5 0.920 .500 .216 ,0930
.0590 .0420
,0250 009,50 .00095
... ...
FROM THIS
rNvESTIGA-
Pid -
=
.
I'ALUES
TION
77'. TI E 299 f 1'K.Ne A Xe 2.5 0.5 0.880 0.440 0.181 ,520 ,275 ,117 ,190 .0495 ,124 .0690 ,0555 ,0210 ,0395 .0370 ,0136 ,0250 ,0295 .0103 ,0117 ,00740 .0204
...
.
003:15 ,00064
...
...
.0117
,00480 .00086 . I .
.00450 .00215 .OOCI70 -lo-'
T
TI = 299 Ne 2.5 0.870 .505 .I77 ,0600 ,0236 ,00830 ,00157
Tz
=
.00021
.. .
...
900, f 1°K. Xe 0.4 .I90 ,118
,0485
.0179 .0103 .00690 .00375 .00130 -10-
Vol. 65
Summary Our smoothed transpiration values for hydrogen, neon, argon and xenon are presented in Table I1 for T I at 77 and 90°1 10 mm. Our work with xenon demonstrates that vapor pressure measurements afford a new method for studying thermal transpiration. High-temperature absolute transpiration measurements have also been found useful for fixin? low-temperature transpiration curves over a small range near PI/€', = 1. For the temperature range 70 to 90°K. the following vapor pressure equation for xenon is reconimended on the basis of this research log P(mm.) = -833 33/T
+ 8.045
Acknowledgment.-The authors are grateful to Drs. J. C. 14.Li, R. A. Oriani and 0 . D. Gonzalez for their infotinative discussions nad advice in the preparation of this paper.
PROTON RETENTION IX HEATED 1:1 CLAYS STUDIED BY IWRARED SPECTROSCOPY, WEIGHT LOSS AND DEUTERIUM UPTAKE BYV. STUBI~AN' AND Rusruni ROY ~ ' n n { r z b f 1 t ~ o\ io. t 60 66,('ollcyr of ,IItneral Industrzes, Penns?/lvnnzn Slate LTnzLcrsili/, I ' t i i z r t u i l q I'nrX, l i c r ~ n ? y l ? a f l ? ( ~ Receaued February i d , 1 9 0 1
Clearcut differmres brtwecn the weight loss curves automatically recorded bv a therinohalvnce have h ~ corrc4:ited n n it11 tlie extent of stacking disorder in the kaolin family. The amount of H + retained above the initial loss ( i e . , from 7001000°) decreases from the most disordered phase halloysite through the "fire-clay-type" synthetic liaolinite to "large" crystals of well-ordered kaolinite. The amount of H + retention could be determined quantitatively from infrared fipectra after resynthesizing the kaolinite with pure D20, but not by direct infrared examination. The absorption spectra of specimens of heated kaolinite and pyrophyllite were recorded from 11-25 1.1. The 538 cm.+ band in kaolinite, prcviously assignrd by us to some mode of Si-O-AlVI, disappears in the saniples heated between 600-950' and reappears at higher temperaturrs. The same band does not disappear in heated pyrophyllite but shifts progressively from 545 to 568 cm.-l. These data are compared with present theories concerning coordination changes in heated clays.
Introduction The kinetics of the loss of water from kaolinite upon heating has been studied many times and various mechanisms for the dehydroxylation process have been proposed on the basis of the data obtained.2-4 However, recent developments in infrared spectroscopy make it possible to obtain additional data concerning the dehydroxylation process in solids by studying the changes of absorption in the OH-spectral regions, where absorption bands appear which are the result of the presence of hydroxyl groups in the structure. (1) Visiting Associate Professor, Department of Geophysics and Geochemistry, The Pennsylvania State University (1960-1961). (2) P. RIurray and F. White, Trans. Brzt. Cer. Soc., 6 4 , 137, 151, 189 (1955). (3) G. W. Brindley and M. Nakahira, J. Am. Cer. SOC.,40, 346 (1957). (4) J. B. Holt, I. B. Cutler and M. E. Wadsworth, Am. Cerom. SOC. Bull., S9, 187 (1960).
Two such regions can be detected with certainty with the layer structure silicates which contain mainly aluminum ions in the octahedral sites. The first absorption region is between 3300 and 3800 cm.-l and the second between 900 and 960 em.-'. With a well crystallized and dry kaolinite in the first hydroxyl region, three distinct bands appear if a prism of high resolving power (CaF2or LiF prism) is ~ s e d . ~ - 7There is a t present no generally accepted theoretical explanation for the multiplicity of the absorption bands in the hydroxyl region with solids such as gibbsite, brucite or clay minerals. Some authors6.*-11 hence tried to correlate the ( 5 ) H. Beutelspacher. Landuirtsch. Forsch., 7 , 74 (195.6). (6) L. A. Romo, J . P h y s . Chsm., 60,987 (195G). (7) n. M. Roy and R . Roy, Geochsm. et Coamorhirn. A d n . 11, 72 (1957). ( 8 ) A. Auskern, M. S.Tliesis, Pennsylvania State Univcrsity, 1956.
(9) M. E. Wadsworth, T. L. hfackay and I. B. Cutler, Bull. Amer. Cer. Soc., 33, 15 (1955).
August, 1061
PROTON RETENTION IN HEATED 1:1 CLAYS
spectra in this region with the different degree of hydrogen bonding in clay minerals. Others’ on the basis of deuterium exchange came to the conclusion that there is no simple correlation between OH-absorption frequencies in clays and types of hydroxyls or extent of hydrogen bonding. However, in spite of the fact that the “fine structure” of the absorption bands in the first hydroxyl region is poorly understood, there is no doubt that absorption in this region is due to the stretching vibrations of proton against oxygen. The location of the second hydroxyl region recently was experimentally established by the substitution of D + for Hf under hydrothermal conditions. StubiEa:n13previously has studied the changes of infrared spectra in the first hydroxyl region with kaolin minerals and was able to show that the specimens obtained by relatively fast heating retain some of the protons even a t high temperatures (600SOOO). At the same time Kulbicki and Grim14 have also adduced evidence for the ret,ention of “water” in metakaolinite. However, to understand the mechanism of the proton retention a t such high temperatures, more quantitative data are necessary which can be obtained using deuterium uptake, hydrothermal synthesis and infrared spectroscopy. Furthermore, due to our extensive study12,15of the infrared spectra of synthetic layer structure silicates, it was possible to assign the absorption bands in -the region 400-5000 cm.-’ to the proper bonds and show the extreme sensitivity of the infrared spectra tlo the changes of the Metal-(0-Si) distances in such structures. It was interesting to study the extent to which infrared spectroscopy can reveal changes which occur on heating of clays and how the results obtained can be correlated with the present theories concerning the structure of high temperature phases. Experimental Materials.-The kaolinite used in this study was highly purified well cryst,allized Georgia kaolinite. The purification was done by ,sedimentation and the purity of material WEU checked carefully by X-rays. The specimen of halloysite from Eureka, which was used in its native form, was also highly pure and no other mineral such as gibbsite or micas could be detected by X-rays. For the resynthesis of the heated specimens of kaolinite and halloysite under hydrothermal conditions, DzO was used the purity of which was claimed to be 99.5%. Apparatus and Procedure .-Dehydration studies were carried out with a fully automat,ic thermobalance equip ed with a Mauer magnetic recording analytical balance. 8 h e investigated specimens, usually 0.5 g., were heated in two flat Pt dishlss (diameter = 27 mm.) which were suspended on a Pt wire in a Pt-wound furnace. The material to be heated waa loosely spread in thin layers in order to minimize t,he possible influence of thickness and compaction on the obtained results. The rate of heating waa 3”/min. The sydhesis of kaolinite-OD for the infrared investigation was done using specimens of kaolinite and halloysite heated in the therrnobalance up to the desired temperature (650, 800, .900, 1000”). When the desired temperature was reached, the specimens were taken out of the furnace and immediately quenched into DZO. The obtained siispension was t,ransferred to a gold tube, and hermetically (IO) H. Soholse and A. Dietsel, Naturzcvias., 42,342 (1955). (11) H. TV. van der Marel and J. H. L. Zwiers, S i l k Ind., 24, 319 (1959). (12) V. StubiEan arid Rustum Roy, Z. Kristallogr. (in press). (13) V. Stubifan, Min. Mag., 32,38 (1959). (14) G. Kulbicki and R. E. Grim, ibid.. 32,53 (1959). (15) V. StubiPsn and Rustum Roy, Am. Miner., 46,32 (1961).
1349
scaled. The hydrothermal synthesis of the kaolinite-OD was carried out in a “cold seal” or “test-tube” bomb previously described by Tuttle16 and Roy and Osborn.17 The condition of the synthesis was always kept constant a t 305” and 30,000 p.8.i. for 20 days. I n such a way a well crystallized kaolinite was obtained on which quantitative measurements of the residual OH-content with infrared spectroscopy was possible. Infrared measurements were made with a Perkin-Elmer model 21 double beam spectrometer using an NaCl prism. The calibration curve for the quantitative estimation of OH-groups was obtained by mixing intimately 15.0, 7.5, 6, 4.5, 1.5 and 0.75 mg. of well-crystallized kaolinite with KBr to obtain 3 g. of mixture. Three hundred mg. of each mixture was pressed in a vacuum die under 70,000 p.8.i. for 3 min. into a window with the area of 1.2 cm.*. With the specimens of kaolinite prepared hydrothermally in the presence of D20, always 30 mg. was mixed with KBr SO that a 3 g. mixture was obtained. Three hundred mg. of each mixture was pressed under the same conditions as mentioned before. Infrared spectra were obtained with the scanning speed 3, the gain 5-6, and for the quantitative measurements scale factor 4 cm./N was used. The s ectra of the heated specimens of kaolinite and pyrophylite were obtained using a KBr prism, and the scale factor 1 cm./p.
Results and Discussion I n Fig. 1 is shown the quantitative weight loss 3s 00
80
60
40
20
0 400
600 800 Temp., “C.
1000
Fig. 1.-Typical weight loss us. temperature curves obtained on a recording thermobalance for kaolinite, Georgia (full line), a disordered synthetic kaolinite (dotted line), and halloysite (meta), Eureka, Ind. (dashed line). The theoretical amount of “water” in kaolinite (13.9%) is expressed as 100%.
a function of temperature (obtained on a recording thermobalance) for three specimens which differ in degree of crystallinity and particle size. These included halloysite (meta) and poorly crystallized kaolinite (obtained hydrothermally from metakaolinite a t 300°, 1200 p.s.i. for two days) which represent disordered phase with small particle size, and well crystallized kaolinite from Georgia. The (16) 0.F. Tuttla, Bull. ffeol. Soc. Anaer., 60,1727 (1949). (17) R. Roy and E. F. Oeborn, Econ. ffeol.. 47,717 (1952).
Y.S T V B I ~ AASD N RIJSTUM ROY
1350
early stage of dehydroxylation of disordered phases occurs about 50’ below the ordered phase. Above 6OOoJ however, the hydroxyls are released only very slowly as a function of temperature, so that these phases contain more hydroxyls than well ordered Due to the inkaolinite heated above 600’. fluence of stacking order and particle size it is difficult to expect that the absolute values for the energy of activation for such reactions will have much significance. Quantitative infrared absorption measurements in the first hydroxyl region of the almost dehydrated samples yield values for the hydroxyl content which differ greatly from the thermobalance data (see Table I). These values were obtained by applying the calibration curve using well crystallized kaolinite as described earlier. The thermobalance indicated (under the conditions of our experiment), e.g., that with Georgia kaolinite heated to 650’, 21% of the water is still present, while in the infrared pattern there is no indication at all of any absorption in the hydroxyl region with the same specimen. The remarkable difference in the amount of hydroxyl revealed in the infrared pattern brought out by re-constituting under pressure a long range order phase is illustrated in Fig. 2. Moreover, fair
Vol. 65
T.4BLE 1 AMOUNTOF ‘‘TTATER”LEFT AT DIFFERENT TEMPERATURES A S FOUND BY (A) THERMOBALANCE, (B) DIRECT IKFRAREI) EXAMINATIOK, (C) AFTER RESYNTHESIS OF KAOLIXITE WITH D,O The total of 13.9% “water” in kaolinite is expressed as 100%.
A
B
C
7% % % Kaolinite, Georgia 650” 21 0 0 800 2.5 0 2 3 900 0 4 0 0 5 1000 0 0 0 0.0 Halloysite, Eureka 650’ 12.0 1 2 10 5 800 6 8 0 5 7 0 900 3 1 0 0 2 8 1000 0 0 0 0 0 0 0 Quantitative determination was not possible due to the appearance of the absorption band a t ca. 3 U, (Fig. 5).
modes involving stretching vibrations of the 0-H bond. I n a crystalline kaolinite the Al-OH distances as well as OH-0 bonds are determined by the structure and fall within narrow limits, consequently the vibrations of proton against oxygen give rise to the well defined bands. I n the almost Frequency, crn.-’. dehydroxylated products it is clear that there is a 4000 3000 2500 4000 3000 2500 wide spread of oxygen-proton distances in spite of the preservation of two dimensional order as shown by Roy, Roy and Francis. l8 Recently Dachille and were able to show the relation between infrared spectra and the coordination of metal ions in simple compounds. Recorded spectra (in the region 11-25 p ) of the heated specimens of kaolinite show considerable differences compared with the spectrum of the original kaolinite (Fig. 3). To evaluate the obtained results it is convenient to compare these spectra with the spectra of the heated specimens of pyrophyllite (Fig. 4). If mainly trivalent ions are present in the structure of a layer lattice silicate, a strong absorption band in the region 500-600 cm.-l appears. The frequency of this band depends on the Me3+-(OSi) distance and bond strength as was previously shown by StubiEan and R0yl28~~ who have described this band as Si-O-Alvl for the case when aluminum ions are involved in the octahedral sites [IO% of a layer silicate. With pyrophyllite heated a t 650’ (15 min.) or 750’ (4 hours), one can observe the gradual dis0-D placement of the Si-O-A.lvr band from 545 to 565 cm.-I, which indicates a small decrease in the AlFig. 2.-Influence of reconstitution of long order phase ( 0 4 )distance. The present understanding of the shown in the absorption in the OH-region with specimens of halloysite heated a t various temperatures (dashed lines), infrared spectra of such complex structures does and the same specimens after resynthesis with D20 (full not allow a more quantitative approach. However, lines). as with all anhydrous aluminosilicates containing aluminum ions in sixfold coordination (e.g., mullite, quantitative agreement can be obtained between sillimanite), the frequency of the corresponding the amount of hydroxyl groups obtained from the band is 560-565 cm. - l J consequently the infrared thermogravimetric and infrared measurements spectra do not indicate the change of the coordinaafter resynthesis of kaolinite with D,O from the tion of aluminum in the dehydroxylated product of heated specimens (Table I). pyrophyllite. On the basis of X-ray data, Grim The experimental results reported above may be (18) R. Roy, D. M. Roy and E. E. Francis, J. 9 m . Cemm. Soc., 38, explained if one considers the possible influence of 198 (1955). the surroundings in the crystals on the vibration (19) F. Dachille and R. Roy, 2. Krzstatlogr., 111, 462 (1959).
1
August, 1061
PROTON
Wave length, p. 16 20
12
I
1
RETEXTIOX IS H E l T E D 1: 1 CLAYS
24
12
I
I
1351
Wave length, p. 16 20 I
24
I
Si-0 I
l
800
I
I
600 500 Frequency, cm.-l.
41
Fig. 3.-:[nfrare(cl spectra of kaolinite, Georgia (full line) and of the same specimen heated a t different temperatures, showing the influence of the change of coordination of Al.
and Bradley2O and Bradley and Grim21 have proposed structurea of dehydrated montmorillonite or muscovite with aluminum in sixfold coordination, which agree with our observations. With heated specimens of kaolinite (Fig. 3) this same vibration mode completely disappears although it is in no way connected with OH ions, and the Si-0 bending frequency moves slightly toward a lower value. The infrared spectrum of metakaolinite is, in fact, almost identical with the spectrum of analcite and an AI2O3Si02glass. There is this clearcut evidence for a major coordination change of the A l 3 f and almost certainly a change to tetrahedral sites as in the glass and analcite, since the AIVLOSi band is completely lost and certainly there is no major change in the coordination of the Si4f. Unfortunately no new band corresponding to AIIV-OSi appears, but this is attributed to the (20) R. E. Grim and W. F. Bradley, J. Am. Ceram. Soc., 43, 242 (1940). (21) W. F. Bradley and R. E. Grim, Am. Mzner., 36, 182 (1951).
800
600 500 Frequency, cm.-l.
4 IO
Fig. 4.-Infrared spectra of a synthetic pyrophyllite (full line) and of the same specimen heated a t different temperstures, illustrating absence of a major coordination change for Al.
overlapping with main Si-0 stretching frequency at 800-1100 cm.-'. The shift from the 560 cm.-l for AIVLOSi is in the right direction and of the right magnitude for such a change. Thus the infrared spectra provide direct experimental proof of the change of the coordination in metakaolinite proposed by Buessem, et a1.,22 and also used in their dehydration scheme by Brindley and Nakahira. 2 3 It should be noted that a specimen of kaolinite heated at 950' shows a broad absorption band a t 565 cm.-l which indicates the persistence of aluminum ions in sixfold coordination under these conditions. Acknowledgment.-Work done on this study was sponsored by the American Petroleum Institute, Project 55. (22) L. Tscheischwili, W. R. T. Buessem and W. Weyl, Ber. deut. ker. Ges., 20, 249 (1939). (23) G. W. Brindley and 1\1. Ps'akahira, J. -4m. Cer. f l o c . , 44, 314 (1959).
