800
JOHN G. MILLER
Vol. 65
has an unknown isomeric composition, yielded the ject of a future investigation will be to elucidate same equilibrium constants for the interaction the properties of these interactions as they affect with TTA and with hydrochloric acid. The sub- the extraction of metal ions.
AX INFRARED SPECTROSCOPIC STUDY OF THE ISOTHERMAL DEHYDROXYLATION OF KAOLINITE AT 470' BY JOHN G. MILLER The Department of Chemistry, University of Pennsylvania, Philadelphia, Pa. Received November IO, 1.960
The thermal dehydroxylation of kaolinite has been investigated by infrared spectroscopic examination of the mineral throughout the course of reaction at 470". The results show that continuous formation of the metakaolinite phase starts during the early stages of dehydroxylation but does not prevent quantitative study of the bands due to the hydroxyl groups. The intensities of these bands give indication of the number of hydroxyl groups remaining when dehydroxylation is finished at 470" and mark the point of dehydration at which the octahedral sheet has been destroyed. The assignments of the bands in the spectrum of kaolinite have been inspected in view of the results found here.
Introduction The thermal dehydroxylation of kaolinite has been studied by many techniques.' Recent work2" has demonstrated the use of infrared absorption spectroscopy as an additional technique. That work was concerned primarily with study of the end-products a t the completion of reaction a t each temperature. It should be helpful, therefore, to see whether infrared spectroscopy can be applied to the kaolinite during the course of its dehydroxylation. The results of such an application are reported below and demonstrate the information that may be obtained from such investigations. Experimental Kaolinite Samples.-Eight different samples of highly purified Georgia kaolinite were used to measure the infrared s ectrum of the dry mineral before thermal treatment. bhese samples were kindly supplied by the Minerals and Chemicals Philipp Corporation of Menlo Park, New Jersey. The average particle size determined by sedimentation fractionation ranged from less than 0.2 up to 2 p for seven of the samples, the eighth being 5 p . Five of the samples were chosen to provide a range of article size, crystallinity (as judged from the viscosity o? their water suspensions), and extent of mechanical working. None of these factors affected the positions of the band centers or caused any change in the amount of scattering. The uniformity of these aspects of their spectra probably waB due to the uniformity of the preparation of the KBr disks used for the measurements; the grinding probably brought the kaolinite to nearly the same final particle size in each case. The principal spectral differences obtained related to the relative intensities of the members of the doublet near 3700 cm.-1, as will be discussed below. After trial of the other samples, the specimen of larger average particle size was selected for study of the dehydroxylation. This choice was made when it was discovered that the rate of loss of water for this sample was especially well suited to the measurements. The convenient behavior of this sample at 470' allowed making spectroscopic observation of it at 14 different points along the course of its dehydration. This material was closely monodisperse, 73% (1) R. E. Grim, "Clay Mineralogy," McGraw-Hill Book Co., New York, N. Y.,1953, Chapter 9. (2) R. Roy, D. M. Roy and E. E. Francis, J. Am. Ceram. SOC., 88, 198 (1955).
(3) A. Hidalgo, J. M. Serratosa and M. Jubriaa, Analea edafol. y Seiol. vegetal (Madrid), 16, 607 (1956). (4) V. Stubican and H. H. GOnthard, Nature, 179, 542 (1957). (5) V. Stubicgn, Minera~og.Mag., 81,3 8 (1959). (6) V. S t u b i c h and R. Roy, Am. Ceram. Xoc. Bull., 89, 141, 188 (1960).
of its particles lying within the 4-8 p size range. It was dried to constant weight at 110' to remove adsorbe! water The and then was dehydroxylated completely a t 1000 loss of water in this determination was 13.85% by weight, showing that the n value in the formula for kaolinite, Ah08.2SiOrnH20, was 1.98 for this sample. X-Ray diffraction revealed a trace of anatase as the only impurity present. The metakaolin was prepared by heating one of the samples for two hours at 820'. Methods of Measurement.-A Perkin-Elmer Model 21 infrared spectrophotometer with sodium chloride optics was used to measure all of the spectra. The kaolin specimens were dispersed in KBr, 1 mg. of clay to 300 mg. of KBr, grinding after mixing. A ressure of 92,400 p.s.i. was applied to form the disks. &gher pressures were apt to cause the disks to adhere to the die. In the dehydroxylation procedure, approximately 3 g. of kaolinite was heated in a porcelain crucible in a furnace held a t 470 f 4'. At this temperature the rate of dehydroxylation was moderate and heating periods of convenient length could be used a t each stage. The crucible was weighed promptly after the sample was brought back to balance temperature in the desiccator in which it was stored. As might be expected despite the reasonably slow loss of hydroxyl groups, it was observed that the surface layers were prone to more rapid loss than the underlying material. It was neceesary, therefore, to stir the material before taking samples for the spectral measurements and to make each heating period short enough that no large gradient of loss occurred throughout the mass. As a check on this sampling and the over-all accuracy of the estimates of the extent of reaction a t each stage, the following observations are given. In the prolonged study of the single sample from n = 1.98 down to n = 0.22, this material was put through 21 separate heating periods a t 470' over a period of nearly three months. In that time it had undergone 40 different weighings and the removal of 15 different I-mg. portions for spectroscopic measurements. Despite all this handling, the following check was obtained on the n = 0.219 value a t which the sample was calculated to have arrived. Calcination a t 1000" caused the loss of 0.0523 g. out of 2.8304 g. total weight of sample, compared with 0.0494 g. calculated for n = 0.219. The accumulated error was therefore, only 0.0029 g. in all. The original sample weighed 3.2429 g. Additional check on the procedure was found, as described below, in the regularity of the change of absorbance of certain of the spectral bands with change inn. Although the method of study was not designed to investigate the kinetics of the isothermal dehydroxylation, the plot of n against total time of heating was smooth. When the first-order velocity constants were calculated from the n values at different times, it was found that the k value (av. = 9.8 x 10-3 &.-I) was constant within 10% until n reached 0.77; thereafter, k diminished steadily. The reaction became very slow by the time n reached the
.
May, 1961
ISOTHERMAL DEHYDROXYLATIOT OF KAOLINITE
SO 1
value 0.22 and the study was discontinued a t this point. This kinetic behavior is similar to that observed by Bmdley and Nakahira' in thk temperature range.
Results and Discussion The Infrared Spectrum of Kaolinite before 1 pictures the specThermal Treatment.-Figure trum of dry, fully hydrated kaolinite, and, to show the profound effect of dehydroxylation, the spectrum of nietaka,olinite formed from it a t 820'. The positio:ns of the centers of the prominent bands of the kaolinite were nearly exactly the same for all of t8he eight samples, alt'hough the resolution of closely neighboring bands was poor in some cases. The following positions for the different bands are the average values: A, 2.69 p (3718 cm.-'); 13, 2.72 p (3677 cm.-'); C, 9.05 p (1105 cm.-I); D, 9.15 p (1093 cm.-'); E, 9.72 p (1029 cm.-'); F, 9.94 ,u (1006 cm.-'); G, 10.74 p (931 cm.-'); H, ll.OC) p (909 cm.-'); I, 12.70 p (787 cm.-l); J, 13.33 p (750 em.-'); and K, 14.45 p (692 crn.-l). These values are in good agreement with those reported by ot,her workers.2-6,B Bands A and 13 are certainly due to stretching vibrations of relat.ively unassociated 0-H groups. The band 5.: h near the upper-frequency limit for such vitsratioris and must indeed be due to hydroxyl groups nearly free of hydrogen bonding to other atoms. Th.e B band is situated very close to A and it's idispla'eement (approximately 40 cm. -I), if due to hydrogen bonding, would indicate only very weak bonding. Explanati80iisbased on the structure of kaolinite have been g..ven for the occurrence of this doublet, ,4 and B. I\lacka,y, Wadsworth and Cutler*' have suggested that the A band arises from the hydroxyl groups in t,he basal hydroxyl plane shown a t A in Fig. 2 n-hidi is drawn according to the structure proposed by Brindley and R o b i n ~ o n . ~The B band was a.;t'rihukd to the int,ralattice hydroxyl groups in the plane shown as B in Fig. 2. They reasoned t2ic.t the hydroxyl groups in plane A by be less associated than the intrathemselves ~.hould lattice groups which are surrounded by oxygen atoms. This, sepurately, is an incorrect argument, for the hydroxy! gj'oups in the plane by themselves can be highly ae:jociated wit,h each other, each hydroxyl group being surrounded by oxygen at'oms there also. .Furihcrmore, the spacing of the oxygen atoms is the Sanie ! n the two planes under compari-
,Ll
j
Fig. 1.-The
j 4
~
5
1 6
8 Wc*Clinglh
7
9 ipl,
'0
spectra of kaolinite ((-
00
L-'
LdAJ-.?-L-.L.. I1
I7
I3
14
) and metakaolin
- - -).
bo
Fig. 2.-The unit layers of kaolinite along the a and b axes and the stacking of the unit layers: 0,oxygen; OH; e, Al; 0 , Si.
a,
son. It is also universally agreed that in the stacking of the unit layers of kaolinite the basal OIL groups provide a strong cementing action by hydrogen bonding to the basal oxygen atoms (plane C, Fig. 2) of the adjacent unit layers. Lyon and TuddenhamS1 agreed with the assignments made by Mackay, et al., and used them to explain their observations regarding the relative intensities of the two bands for these related minerals: kaolinite (A > B), halloysite and dickite (B > A), and the micas (A = 0). The diminution of the relative intensity of the A band in this series was ascribed to the replacement of hydroxyl groups by oxygen atoms in plane A until in the micas this plane has the same relative population as plane B. This would appear to agree with the observation that the montmorillonites also show (7) G. R.Bririrllcy and 31. Nakahira, Clay Mineral Bull., 3 , 114 only the 13 band.*' l o (1867). (5) (a) J. h i . R u n t , M. P. W s h e r d a n d L. C. Bonham, Anal. Chem., The work of Serratosa and Bradley'' and of 2 2 , 1475 (1950); (b) W. D. Keller a n d E. E . Pickett, A m . J . Sei., F a r m e P on the effects of the kind, number and 248, 264 (ISSO); (c) €I. Adler, E. E. Bray, N. P. Stevens, J. hi. H u n t , distribution of the cations in the octahedral layers V. D. Keller, E. .E. Pickett and P. F. Kerr, A m . Petroleum Inst., Proj. upon the frequencies and intensities of such 0-H 49, Rept. 8 (1960): (d) I?. J. Launer, A m . Mineral., S T , 764 (1952); (e) J. Ai, H u n t and D. 8. Tiirner, Anal. Chem., 2 5 , 1169 (1963); (f) stretching bands in clay minerals bears upon T . I-.Mackay, XI. E. Wadsworth and I. B. Cutler, U. S.Atomic Energy these assignments. They found that although Comm. Contract No. AT-(49-1)-633, Tech. Rept. 7 (Nov. 1, 1954); the 0-H stretching frequency of intralnttice hy(g) L. A. Romo, J . CoZloitZ Sci.. 9 , 359 (1954); (h) P. G. Nabin, Proc. droxyl groups in the trioctahedral minerals is near 1k.t Katl. Conf. o n Clays and Clay Minerals, 1952; Calif. Dept. Nat. Resources, D ~ LM. i n e s Bul'., 169, 112 (195.5); (i) -4. Hidalgo and J. M. the upper limit for unassociated groups, the freSerratosa, A n d e s edajol. y fisiol. vegetal ( M a d n ' d ) , 14, 269 (1955); quency for dioctahedral intralattice OH groups is ( j ) L. A. Romo, J. Pibus. Chem.. 6 0 , 957 (1956); (k) S. G. Garcia, H. Reutelspacher and W. r'laip. Anales real sac. espan., 3 s . y quim. (Madrid),52B,369 (1956): (1) TI'. 37. Tcddenham and R . J. P. Lyon, Anal. Chem., 31, :377 (19:9); (m) R. J. P. Lyon a n d W. Jf. Tuddenham, Nature, 185, 535 (1960). (9) G . W. Brindley and K. Robinson, Mineralog. Mag., 27, 242 (1946).
(10) R. 0. French, hi. E. Wadqworth, M. A. Cook and I. B. Cutler, U. S. Atomic Energy Comm. Contract No. AT-(49-1)-633, Tech. Rept. 3 (Feb. 1954). (11) J. M. Serratosa a n d W. F. Bradley, J . Phys. Chem., 6 2 , 1164 (1958). (12) V. C. Farmer, Minerolog. Mag., 31, 829 (1958).
JOHHG. MILLER
802
somewhat lower, e g., 3620 em.-‘ in muscovite and 3630 in montmorillonite. From this it would appear that in the dioctahedral kaolin minerals band B is indeed due to the intralattice OH groups. This would, simply by elimination, ascribe -4to the groups in the basal plane. The explanations of the high-frequencysf and the relative intensitysm of the h band need further investigation. A s pointed out above, the basal plane hydroxyl groups which apparently give rise to this absorption are probably involved in a t least two different kinds of association. The bonds between groups within the plane should be of strength equal to those for the intralattice hydroxyls but those cementing the unit layers together would be considerably weaker due to their large 0-0 distance These extremely weakly bonded OH groups may be the source of the A band. Roy, Roy and Francis? have taken the sharp definition and high frequency of the 0-H stretching bands to imply that there is no evidence a t all of hydrogen bonding betneeu m i t layers, but it should be realized that even if such bonds are weak, their large number per unit area would cause a strong cementing It is possible also, as implied by Mackay, ef nl , that there are in the basal plane some OH groups which are ent~relyfree of association of any type. It would iwni reasonable, therefore, that some of the h a d plane hydroxyl groups mould contribute t o the 13 band, oihcrs to A, the relative amounts depending upon the regularity of the stacking of the iuiit layer-, z e , upon the degree of order or crystallinity in the samples. This recalls the opinion oi Roy and that such steric condition5 makc it difficult to correlate distances measured by S-I a) techiiiques n ith absorption in the OH region 01 the infiared, z.e., that the extent of disorder in stac~kinghas a large effect on these absorption< I n this ~oiiiiectioii,observations made here with different sample. of kaolinite showed that the A/B intenhity ratio certainly was not fixed, and that in some case5 B 1va5 e\en more intense than A. hlthough no thorough study was niade of the problem, the Tamples of low-viscosiiy,unworked material of larger pniticle size shon-ed B B,’A ratio greater than unity whereas in the other samples the riorm:tl ratio 11 as shown or the bands were of nearly exactly equal intensity. Of the two dickite samples whose spectra n ere gir-en by JIackay, et UZ.,~‘ one showed B > A, the other had X > B. Dickite appears to have a rather unstable arrangement of iuccessive layers14 5 Using a spectrometer of higher r e d \ ing pox er, RoinoYJactually found three bands 111 this region (2.70, 2 73 and 2.76 p.) for a sample of hydrothermally treated kaolinite. The implication of his work would be that band B can be resolved into a doublet, but more study would be needed to prove this. His spectrum indicates that the (13) D M. Roy and R. Rov, Geochzm et Cosmocham. Acta, 11, 72 (1957) (1-1) Reference 1, P 50 (1i i 4 B Searle and R W. Grimshaw, “The Chemistrj and Physics of ClaJ 3rd ~d Interscienre Publishers, I n c Nen York, 1u Y 1959 {I
133
-
T’ol. 65
sample contained adsorbed water molecules. It has been our experience that dry kaolinite does not show the associated-OH band in the region 2.82.9 p so often quoted for kaolinite. Due to the great difference in absorbancy index for the stretching and bending vibrations in water molecules, amounts of water too small to show a noticeable band at 6.15 p will cause an appreciable absorption a t 2.8-2.9 p . Of the other bands, C, D, G and H have been assigned38*,k,16 by both empirical and theoretical means to vibrations of the A1-OH bonds in the octahedral sheets, the first doublet arising from stretching vibrations and the second from bending vibrations. The splitting into doublets has been ascribed3 to the lack of regular octahedral symmetry. Bands E, F, I and K have been attributed3rsbtsd *l to Si-0 vibrations. Band J remains unassigned, although Roy, Roy and Francis? have stated that both I and J probably are related t o dl-OH bonds for the reason that they disappear on dehydroxylation. 9 s discussed below, our observations are in agreement with their assignment of J. The Dehydroxylation of Kaolinite.-Reviews1~2 of the studies of the dehydroxylation of kaolinite reveal the great interest in such investigations. Although the kinetic studies necessarily inrolve determinations of the state of the mineral during the course of the reaction at constant teniperature, such studies have been limited to weight determinations rather than examinations of structure. On the other hand, examinations of structure h a w been limited to the end-products of the dehydroxylation at each temperature. Although the rate of loss of OH groups becomes exceedingly rapid for kaolin even a t 500°, it is possible to follow the 1055 stepwise at slightly lower temperatures, especially for material of larger particle size and better rrystallinity. Knowledge of the mechanism of the dehydroxylation should be helpful not only in explaining the nature of the phases produced during the loss of OH groups but also in controlling the effects of the dchydration reaction upon these phases aiid the phase< produced fiom them at still higher temperatureb Infrared spectroscopy should be one of the best methods of study of this reaction because it is one of the best methods of inrestigating the behavior of hydroxyl groups. The worli reported here represents, t o the best of our knowledge, the first application of thiq technique t o the rourse of the reaction rathei than to the end-products. Attention mas focusml on hand5 -4 and H, n-hich are most certainly due to OH groups aiid whir11 are strong and iharp. I‘igures 3 and 1 show the appearancae of thew band5 at -ex era1 different stages of dehydroxylation rThe wave length of the band center< was affected w r y little by the dehydroxylation and although imi- band5 appeared gradually due to the gronth of the metakaolin phase, these bands did not interfere greatly with the observations of band5 and €I. -1lthough ~~
. ! A
(16) 1. Hidalgo and 31 31 Serratosa Anal?? real soc e r p a n , fis w i m . ( M a d r i d ) , SZB, 101 (1936).
11
ISOTHERMAL DEHYDROXYLATION OF KAOLINITE
May, 1961
bands A and R were of equal intensity and were for that reason merged in the starting material, as soon as dehydroxylation started B became slightly less int,ense than A and the difference in intensity increa,sed until n reached the value 0.56 'Or *= and then decreased again until a t n = 0.42 the bands merged again. Thereafter, a new and broad band due to 0-H stretching arose a t higher wave length, showing; that some of the OH groups were taking 011 a decidedly different function. This c new band remained after A and B had disappeared, and the hydroxyl groups causing it probably remain 30 at even higher temperatures as shown by the spectrum of rnetakaolin. I Continuous formation of metakaolin started in 2.7 the early stages of dehydroxylation as revealed by the spectra but its bands did not prevent quantitative treatment of the A and H bands by the conventional base-line procedure. This fortunate Fig. 3.-The behavior circumstance was due to the fact that the absorption of metakaolin a t these wave lengths is not greatly different from the base-line value of the absorption of the original kaolinite. The absorbance, A , was c2alculated by the equation A = log ( I o / I ) where , I and Io were the per cent. trans70 mission values at the band peak and a t the baseline at the same frequency. The spectra were first corrected for slight and random variations in scattering which probably were due to slight variations in preparation of the disks. Table I shows the absorbance values obtained for the two bands at different stages of the dehydroxylation. These results, except for the values of the original kaolinite ( n = 1.98) are plotted in Figs. 5 and 6. The straight lines are least-squares lines and :ire giT-en by the equations A = (0.172 i 0.007)[n-- (0.12 f 0.03)] for the A band, and A = (0.304 f 0.008)[n - (0.28 f 0.02)] for H, where the probable errors of the absorbancy index (the slope terms) and intercept terms are shown. Fig. 4.-The behavior The observed values of absorbance for these bands for the original kaolinite are much higher than given by these formulas. 0.3L The absorbance behavior of band A indicates that in the more fully hydroxylated material, at
803
t
of the A band during dehydrosylation.
of the H band during dehydroxylation.
I
TABLEI THE BASE-LINE(Io) AND R.4XD-CESTER ( I ) P E R CEXT. TRANSWISSIQX VALUESAND THE ABSORBAWE( A ) FOR THE HYDROXYL R ~ u D -AS A FUSCTION OF THE EXTEXT OF 'dYnRoxYL%TIOx ( n ) ---UaIid
A (2.69 p ) - -
n
IO
I
-4
I 98
63.4 6:L9 63.2
19.2 3i 8 -12.3 39.2 42 7 46.9
0519 ,228
1 43 1 20 1 17
10 85
-t i
66 60 56 12 .3 7 30
2(i 22
(i0.6
60.2 60.2 ,51.9 62 9 6.2 (i ,50 . 3 6'2.2 8i1.0 CiC. 5 52. 8 UO 1 ,i6 0 62.0 5 7 . 6 59.8 61.5 .ic,.8 .;!I, 8
.IT(i ,189 ,152
,109 ,084 ,095 ,061
,050 . 033 ,032 .012 ,022
-Band
IO
H (11 00 I
p)-
A
38 0 51 1 40 9
5 0 22 4 25 0
0 881 358 300
46 2 48 2 52 5 50 9 41 7 48 7 46 5 47 5 50 1 54 7 50 2
25 4 32 G
262 170
Fig. 5.-The
35 7 39 5 31 2 42 5
168
least before n has reached the value 1.43, the 0- TI stretching ribration obeys a different absorbancy index than in the range \There dehydroxylation h,l.: caused n to reach lower values. Furthermore, the appearance of a new stretching-vibration band niicl the definite disappearance of the A (and B) band at around n = 0.12 show that some of the hydroxyl groups have taken on a new role before n has reached the range for whirh Fig. 3 is drawn.
110 116
059 048 018 012
11 6 45 0
48 7 5-2 7 50 2
0 0
I C
2
4
6
6
IC
2
14
6
absorbance of band A as a function of
8
/l
A. R. AKDERSON AXD EDWIN J. HART
804
0.3
1 0
Fig. &-The
, G“4 I .2
4
, 6
1 8
1
-0
12
I4
I6
18
20
absorbance of band H as a function of n.
Similar conclusions with respect to the A1-OH groups may be taken from the decay of band H shown in Fig. 6. The intercept value, n = 0.28, indicates that the destruction of the octahedral sheet is complete a t that point. The persistence of band A beyond that point may mean that OH groups are still attached to aluminum cations after loss of the octahedral structure. That these bands have a greater absorbancy index a t states of greater hydroxylation was confirmed by measurements of a sample prepared by mixing 0.4 mg. of the original kaolinite with 0.6 mg. of the material which had reached the n value,
Vol. 65
0.659, giving a synthetic material with an effective value n = 1.16. The absorbance observed at band A was 0.265 and a t band H was 0.314 for this sample, which would place n at much higher values than 1.16 according to the absorbancy index for the lower ranges shown in Figs. 5 and 6. These findings confirm and extend earlier studies showing destruction of the octahedral sheet before essential change in the tetrahedral sheet in kaolin and also the existence of OH groups beyond the point of loss of the octahedral configuration,2-W. 17 Finally, some observations of bands I and J were made during the dehydroxylation to examine the assignment by Roy, Roy and Francis2 of those bands to A1-OH vibrations. Those bands do indeed disappear continuously during dehydroxylation rather than being converted into or submerged by the broad metakaolinite band which centers around 12.3 f i . The observations of band J are the more certain in this respect and it would appear that this band probably is due to A1-OH groups. Acknowledgment.-It is a great pleasure to acknowledge the assistance given by C. G. Albert, W. L. Haden, Jr., G. A. Hemstock, T. D. Oulton, and E. W. Sawyer, Jr., of the Minerals and Chemicals Philipp Corporation, and by R. E . Grim, of the University of Illinois. (17) G. Kulhicki and R. E. Grim, Minerdog. Mag., SZ, 53 (1959).
HYDROGEN YIELDS IN THE RADIOLYSIS OF AQUEOUS HYDROGEX PEROXIDE’ BY A. R. ANDERSON~ AND EDWIN J. HART Argonne National Laburatory, Argonne, Illinois Received November If, 1960
Hydrogen and oxygen yields have been determined for the -pray and deuteron radiolysis of aqueous hydrogen peroxide over a concentration range from pure water to 96% hydrogen peroxide by volume. The observed decrease in hydrogen yields with increasing concentration of hydrogen peroxide is in good agreement with the Flanders-Fricke computations on the one radical diffusion model for both 7-ray and deuteron radiolysis. I n order to fit the experimental data to the thecretical curve we need to use a rate constant for the scavenging reaction, H HzOz, in neutral solution about five times the value in acid solution (0.8 N H2SO9. This difference in rate constants is consistent with the existence of two reducing species in the radiolysis of water. r h e observed yields of oxygen are proportional to [H%O,]’/aup to hydrogen peroxide concentrations of about 3 M for the deuteron radiolysis of neutral solutions and for the y r a y radiolysis of both acid and neutral solutions; in acid solution, however, the oxygen yields are considerably lower. This increased stability in acid solution probably is associated vith a change in the propagation step in the chain decomposition of hydrogen peroxide.
+
Introduction The theory of track effects and the kinetics of the recombination of H and OH radicals in the radiation chemistry of water has been developed by a number of author^.^-^ I n the original model (1) Work performed under the auspices of the U. 9. Atomic Energy Commission. (2) Chemistry Division, A.E.R.E. Harwell, Nr. Didcot, Berkshire, England. (3) (a) D. E. Lea, “The Action of Radiation on Living Cells,” The Macniillan C o . , New York. N. Y.,1947; (b) A. H. Samuel and J. L. Magee, J . Chem. Phys., 21, 1080 (1953); (c) H.Fricke, Ann. N . Y. h a d . Sei., 69, 567 (1855). (4) H. A. Schwarr, J. Am. Chem. Soc., 7 7 , 4960 (1955). ( 5 ) S. K. Ganguly and J. L. Magee, J . Chem. Phys., 26, 129 (1956). (6) J. L. Magee and A. E. Samuel, ibid., 1 6 , 935 (1967).
proposed by Leajaathe H and OH radicals were assumed to be distributed initially according to symmetrical Gaussian functions, with the H atoms extending further into the fluid than the OH radicals. Samuel and Magee3b suggested that the radicals were formed by the dissociation of excited water molecules and consequently both species have the same initial distribution. Part of the radicals combine within the original volume of formation (spur) to give molecular products, hydrogen and hydrogen peroxide, while the re(7) D. A. Flanders and H. Fricke, ibid., 28, 1126 (1958). (8) P. J. Dyne and J. M. Kennedy, Can. J . of Chem., 8 6 , 1518 (1958). (9) H.Fricke and D. L. Phillips, J . Chem. Phya., 32,483 (1960).
