NOTES
June, 1962
and 59 mole % V206,occurs in the system 2Liz0.5VzO6-VzOj. Canneri's reported melting point for the metavanadate, 618', is in excellent agreement with our value of 616'. Canneri did not, however, detect the 2:17 or 2 : s salts. In the composition interval from 50-25 mole % T 7 2 0 6 , there is again fair agreement of thermal data but little agreement in interpretation. Canneri shows a eutectic a t 575' and 35.5 mole % Vz06which is probably the same one we found a t 592' and 35 mole %. Extrapolation of his eutectic halt data to zero halt led him to believe that this triple point existed in the whereas our data system I&O ~VzO~-2LizO~Vz0~, indicate t'hat the system in question is LizO.VZOs-3Li20. V 2 0 6 . There is somewhat better agreement between the present work and that of Kohlmuller and Martin, ignoriiig the question of metastability for the moment. They find a eutectic a t 594' and 79 mole %, in good agreement with our values of 591' and 77.5 mole % V206, Pig. 1. Kohlmuller and Martin concluded, however, that this triple point occurs in the system Vz06-LiOz.3Vs05 rather than in the system (metastable) vZo6--2LiZo' 5VzOa. Considering the rather large discrepancy in composition for this phase, its melting point is not in disagreement; 601' reported by the French authors and 603' found here. They also report a eutectic at 67 mole % VzO, and 560', in good agreement with our values of 69 mole '% and 560'. Their reported melting point for the metavanadate, 624') is not, however, in good agreement with the values given by Canneri and us, since it appears outside the range of expected error, ca. k 3 ' . One further eutectic is reported by Kohlmuller and Martin, a t 46 mole % V2OSand 596', in good agreement with the presently reported values of 45 mole % and 592'. They give a melting point for 3LiZO.V2O5of 1154' and phase transformations at 662 and 730O. While the melting point determined by us, 1152', agrees well with their value, the number of and temperatures for the phase iiiversions do not. We detected an anomaly at 724' which might be correlated with their 730' heat effect, but did not detect oiic! around 662'. Two others were observed, however, a t 773 and 1036'. No explanat i o n ('an bt: offered for these discrepancies. As for
1185
the failure by previous workers to detect the 2 :17 salt, it is to be pointed out that it was not detected by us either in cooling studies, its presence being observed only fortuitously in the process of preparing samples for density analyses. C. Some Comments on Compound Repetition. -If the working hypothesis on compound repetition in oxide-oxide has general validity, then the system Naz0-Vz05 should definitely contain the compound 2Naz0.5Vz05. This phase should melt incongruently and exhibit a greater submergence of its liquidus field than does the corresponding lithium analog. It is not unlikely, based on the slight field submergence evidenced by the lithium salt, that a phase with the same stoichiometry should occur in the system K20-Vz0, with a greatly submerged field. I n our previous work on the latter system,6 where conventional thermal analysis techniques were employed together with rather cursory X-ray analysis (X-ray studies were conducted only a t apparent compound locations), no such phase was detected. This possible omission indicates a re-investigation of the potassium system is warranted, and such is contemplated. The occurrence of congruently melting 1:1 compounds in both the lithium and potassium systems requires the existence of a congruently mlelting sodium analog. A similar consideration applies to the occurrence of a congruently melting 3 : l sodium salt. The 2:15 lithium compound presents something of an enigma. While it exhi'bits a fairly submerged liquidus field, its deduced liqpidus curve is not coincident with that for Vz06. This would indicate the possibility of a repetition in the next higher weight system. I n the previous work on tantalate systems, however, it has been found that difficulty in generating a stable phase is accompanied by failure of that ratio to repeat in the next higher system. Furthermore, compounds having such high proportions of one component to the other have not been found to repeat to any great extent even when not attended by difficulty in forming them. Based on the above, the occurrence of a 2: 15 sodium salt does not appeiar likely. Certainly no stable potassium analog is to be expected.
NOTES SURFACE CARROh-IUM IONS PRODUCED BY IRRADIATING SILICA G E L BY
HAROLD
w.KORN
Chemislr DivGrion Oak Ridge National Laboratory Operated b y Unaon Carbide &!orpomtio~lov the U.8. Atomic Energy Co&nteszon, Oak Rzdge, Tenn. Receioed December dpI, 1981
Recent experiments a t this Laboratory have shown that the radiation-induced reactions between hydrogen or methane and well-degassed deuterated
silica gel give relatively largc yields of deuteratcd products. These yields are, depending on pretreatment of the gel, in the neighborhood of 3 to 5 molecules per 100 e.v. absorbed by the ye1 for the reaction Hz + SiOs/z(OD) --+ HD + SiOsjs(OH) (1) and from 0.6 to 1.5 molecules per 100 e.v. absorbed for the reaction' CHI
+ SiOsI*(OD)
--f
CHsD
+ SiOa/z(OH) (2)
( I ) H. W. Kolm, J . Phys. Chem., 66, 1017 (1962).
NOTES
1186
Vol. 66
TABLE1 COLORS O F ADSORBED
Adsorbate
Benzene Phenylrnethane Diphenylmethane Triphenylmethane Naphthalene Anthracene Phenanthrene 1,l-Diphenylethylene Triphenylethylene o-Terphenyl m-Terphenyl p-Terphenyl p-Quaterphenyl Wurster's blue Biphenyl Diphenyl ether Triphenylene
Adsorbed on cracking catalyst
Very faint yellow Yellow-pink Light yellow Bright yellow Pink Green Blue-gray Chartreuse Green and brown Turquoise Pink Blue-purple Buff-orange Blue Red Pink Blue-gray
X o t observable Not observable Orange and chartreuse Bright yellow Pink Chartreuse Chartreuse Yellow Brown and yellow Turquoise Deep yellow Deep yellowBuff-orange Blue-purple Blue-green Pale blue Blue-gray
This research demonstrated that these reactions are initiated on the gel surface. Speculation about the mechanism of such reactions led us to the conclusion that trhe reactive intermediates produced by the radiation probably were ionic in. nature. A recent report on the observation of stable surface carbonium ions2 prompted us to perform some experiments which indicate that positive ions in the gel formed during the irradiation of silica gel can transfer their charge to adsorbed species, thus leading to stable carbonium ions. Silica gel and silica-alumina cracking catalysts previously degassed at 520 f 10" were used as adsorbents. Samples were prepared in pairs using 10 g. of each adsorbent for one member. After the adsorbent had cooled, 100 to 200 mg. of organic adsorbate was distilled from a side-arm onto the adsorbent. In all cases the silica-alumina immediately assumed a definite color, probably characteristic of the carbonium ion f ~ r m e d , ~ -whereas s the silica gel became only a faint off-white.6 The silica gel plus organic adsorbate samples then was irradiated for about an hour a t -78" in a 600curie Co60 y source (about 2 X lo5 r.). Many irradiated gels plus organic adsorbate samples became the color of their unirradiated silicaalumina counterparts (Table I). On the basis of stability and identical color, several samples (vix., triphenylmethane, naphthalene, p-quaterphenyl) when irradiated on silica gel obviously formed the same species as those formed by adsorption on silica-alumina. The similarity in color for others (Wurster's blue, anthracene, triphenylethylene, 1,I-diphenylethylene) was very striking and the small color differences could be due to variations in dispersion, local concentration gradients, or the superimposed slight radiation coloring of the glass and gel.' When diphenyl ether or biphenyl on ( 2 ) H. P. Leftin, J . Phys. Chem., 64, 1714 (1960). (3) J. K. Fogo, ziizd., 65, 1919 (1961). (4) J. J. Rooney and R. C. Pink, Proc. Chsm. Soc , 70 (1961) ( 5 ) D. A l . Brouwer, chemzstry and Industry (London), No. 6, 77 (1961). ( 6 ) The adsorption of biphenjl on silica gel gives a n Immediate red
coloration (7) f l 1%' Kolin
\-a/?(!? 184, 07Q (1471)
COMPOUSDL
Adsorbed on silica gel and irradiated
Remarks (irradiated samples)
Fades quickly Very stable, 25' Very stable, 25" Extensive decomposition Extensive decomposition Fades quickly Very stable, 25' Very stable, 25" Not changed on irradiation Fades quickly
silica gel was irradiated, a colored species which differed from that produced by adsorption onsilica-alumina mas formed. Phenanthrene and triphenylethylene when adsorbed on the cracking catalyst give variable mixtures of dark colors, probably indicative of extensive decomposition. The colors observed are summarized in Table I. NO color was observed upon irradiation if the organic adsorbates were adsorbed on silica gel which was not dehydrated a t an elevated teniperature. This s h o w that the color was not due to ions formed by simply irradiating the dispersed organic material. Furthermore, unless the silica gel is dehydrated at an elevated temperature, it initiates little isotopic exchange (reactions 1 and 2). Thus adsorbed water appears to interfere with the chargetransfer process. If a sample of properly dehydrated silica gel with adsorbed triphenylmethane is exposed to 2537 A. ultraviolet light, an orange color characteristic of the triphenylmethyl free radical is observed. Since this orange color is noticeably different from the yellow color (characteristic of the triphenylmethylcarbonium ion) observed upon y-irradiation, one may assume that where the color pairs are similar, tthe color of irradiated organic compound plus silica gel is not due to the formation of free radicals. In those sample pairs which fail to show similarities, such as diphenyl ether, different modes of carbonium ion formation such as hydride ion abstraction, proton addition, or electron abstraction might account for the color differences, or the color on the irradiated gel in these cases may be due to the presence of free radicals. Since it is well recognized that silica alumina is a strong acid,s the net effect of irradiating silica may be simply to increase its acidity. The creation of such acid sites may explain the increase of the catalytic activity of the gel upon i r r a d i a t i ~ n . ~ . ~ ~ (8) Ti. A. Renesi, J . Phys. Chem., 61,970 (19573. (9) H. Pines and J. Ravoire, ihid., 66, 1859 (1961). (10) 11. Vi. Tcolin and Ti:. T I . Tiivlor. ibid., 63,W 6 ( l R i 9 )
