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Surface studies on carbon: Immersional energetics of spheron 6 in water
Carbon, 1971. Vol. 13. pp. 47-50.
Pergamon Press.
Printed m Great Britain
SURFACE STUDIES ON CARBON: IMMERSIONAL ENERGETICS OF SPHERON 6 IN WATER S. S. BARTONand B. H. HARRISON Departmentof Chemistryand ChemicalEngineering,RoyalMilitaryCollegeof Canada,Kings&on, Ontario,Canada (Received I4 June 1974)
heatsof immersionof Spheron6 degassedat temperaturesup to IOOOThave been measured in water. The removal of surface complexes as CO, CO,, HZ and HZ0 during the degassinghas also been followed Abstract-The
quantitatively using a mass spectrometer system. It was found that the changes in the immersional energetics could be accounted for by the removal of oxygen complexes and that complexes desorbing as hydrogen do not appear to affect the heat of immersion in water. Theheat of immersionin water of that part of the surface of Spheron 6 covered with oxygen complexes was found to be 140ergs. cmm2.
INTRODUCTION The surface properties of carbons and graphite are strongly influenced by the amount of oxygen complexes on their surfaces. Because the oxygen free surface of carbons and graphite is hydrophobic, and the portion covered by oxygen complexes is hydrophilic, changes in the surface properties are most easily observed through the interaction with water. Indeed, during the degassing of graphite, changes in the heat of immersion in water could be directly related to the removal of oxygen complexes[l]. Besides containing a considerable amount of combined oxygen, carbon blacks also contain large amounts of hydrogen which is located both on the surface of the particles and in their interior. This hydrogen has been retained by the carbon during the pyrolysis of the raw material in the manufacturing process[2]. The present investigation was undertaken to see whether the large quantities of hydrogen found in carbon blacks had any influence on the heat of immersion. 1.
in good agreement with and within the range of values given by other investigators[3-91. Bulbs were broken in succession in de-ionized distilled water (20 ml.) with values being reproducible to k-O.05cal . g-‘. Samples of approximately 1 g. were used, and the normal corrections applied to the calculation of the heat of immersion. The carbon samples were degassed in a quartz tube at the appropriate temperature and then transferred, under a vacuum < low6Torr, to thin walled spherical Pyrex glass bulbs for the immersion measurements [ I]. The desorbed gases were transferred, using a diffusion pump, to a mass spectrometer system for analysis [ 1, IO]. In some cases an Ion pump was used to create a vacuum < lo-‘Torr during degassing. The improved vacuum did not appear to have any influence on the heat of immersion measurements. The surface areas of samples, degassed at temperatures up to lOOO”C, were measured by low temperature nitrogen adsorption at 77°K in a conventional volumetric adsorption apparatus[ll]. Surface areas were computed by the BET method using 16.2 A’ as the cross-sectional area of the adsorbed nitrogen molecule. Carbon samples degassed at temperatures up to WC were found to have a surface area of 116? 3 m*g-‘, while the carbon degassed at 1000°C had a surface area of 98 + 2 m’g-‘.
2. EXPERIMENTAL Heats of immersion were measured in triplicate, and sometimes quadruplicate, on samples of Spheron 6 degassed at temperatures up to 1ooo”C. Measurements were made using the same isothermal change of phase calorimeter that was used in an earlier study[l]. The calorimeter was calibrated by both the electrical method and the standard reaction between 2-amino-2(hydroxymethyl)-1,3 propanediol (Tris or Tham) and 0.1 N HCI. This calibration was also checked by measuring the heat of immersion of ‘Graphon’ a well characterised adsorbent in both water and hexane. Recorded heats of 32 ergs . cm-’ and 119ergs . cm-* were
3. RESULTS ANDDlSCUSSlON effect of degassing temperature on the heats of immersion of Spheron 6 in water has been measured over the temperature range 0-1000°C. The major gaseous species desorbed as carbon samples were heated at temperatures up to 1OOtYC were CO, CO*and Hz. Figure 1 displays the amount of each component that was desorbed when samples were degassed at various
The
47
S. S. BARTON and B. H. HARRISON
0
I
I 200
600 400 TEMPERATURE
600 (‘Cl
loot
Fig. I. Amountsof CO, CO?,and Hz desorbedwhen samplesof Spheron6 wereheatedat various temperatures up to 1000°C. temperatures. Besides these major components a small amount of water was also observed at temperatures up to 300°C. The desorption of hydrogen began at temperatures as low as 500°C but did not become significant until about 700°C. The total quantity of each component desorbed is shown in Table 1, together with the data of other investigators. The maximum degassing temperature used in the various studies is also recorded. Although the removal of oxygen complexes is essentially complete at 1OOO”C, hydrogen removal is not. It was found that the desorption of hydrogen had not yet reached a maximum at lOOO”C, the highest temperature used in this study, and considerably more may still be released at higher temperatures. Even after making some allowance for the different maximum degassing temperatures, it can be seen in Table 1 that quite wide variations exist in the amounts of CO* and HZ desorbed. On the other hand the total amount of
CO desorbed appears to be reasonably constant. The results of Rivin are an exception. Assuming that all the CO and CO2 in the present study originated from the surface of the carbon an estimate of the area occupied by the oxygen complexes can be made. By analogy with studies on graphite where a crosssectional area of 8.3 A’ has been assigned to a carbon atom on the edge plane of graphite[l, 161, the area occupied by the carbon atoms removed as CO and CO*in this study would be 82.7 I-&-‘. This would indicate that 70 per cent of the surface is covered with oxygen complexes. The location of the hydrogen that is desorbed is uncertain. Some of the hydrogen could be combined to form functional groups such as hydroxyl (phenolic), carboxyl, while the rest may be directly combined with the carbon both on the surface and in the interior of the carbon particles. The variation in the heat of immersion of Spheron 6 in water with degassing temperature is shown in Fig. 2. The heats are displayed on a unit area basis by using the BET surface area of the carbon degassed at the same temperature. The surface area of the carbon was found to remain constant when it was degassed at temperatures up to 900°C but there was approximately a 20 per cent drop
0
200
400
DEGASSING
600
This Study Puri and Bansal Anderson and Emmett Colltharp and Hackerman Rivin
1000 (OC)
Fig. 2. Heat of immersion of Spheron 6, degassed at various temperatures, in water.
Table 1. Gases evolved on thermal treatment of Spheron 6 Quantity pmoles g-‘.
Authors
800
TEMPERATURE
CO
CO2
Hz
Hz0
Max Temp (“Cl
1395 1326 1331 1380 1920
205 156 237 420 240
1520 1420 2376 1820 1640
120 289 338 70 70
1000 1200 1200 1000 1300
Ref.
1121 [131 r141 WI
Surface studies on carbon
49
when it was degassed at 1000°C. This was noticed in value found for Graphon (Spheron 6 heat-treated at earlier studies[“l, 171 and it was suggested by Polley et 27OO”C),i.e. 32 erg cm-*. The potential evolution of large quantities of hydrogen at temperatures above 1000°Cthus al.[17] that this may be due to loss of porosity. The effect of degassing temperature on the heat of has a very small effect on the heat of immersion. From the data of Fig. 3 it is possible to estimate the heat immersion in water is similar to that found with carbons[7,18] and graphite[l] where the heat of immer- of immersion unit area (ho) of the hydrophilic oxide sion was characterised by a slight increase on degassing covered surface on Spheron 6 by using the same up to 200°C followed by a continuous decrease in the heat reasoning that was used with ~aphitetl]. Assuming that as the degassing temperature was raised to 1000°C.Up to ho is independent of the extent of coverage of the oxygen complexes then the heat of immersion can be represented 2OO”C,as water is desorbed from the oxygen complexes, an increase in the heat of immersion is expected. This is by the equation then followed by the removal of oxygen complexes as the Hi = S&b - SoFohbf SoFoho, degassing temperature is raised to 1ooO”C.Removal of these complexes reduces the chance of hydrogen bonding between the surface and the water resulting in a where ST represents the total BET surface area of the carbon, continuous decrease in the heat of immersion as they are removed. Attempts to relate the changes in the heat of SOrepresents the total surface area of the carbon which was covered with oxygen complexes immersion to the removal of oxygen complexes are shown before degassing, in Fig. 3. In this figure the amounts of CO and COZ desorbed are expressed as millimoles of oxygen per gram Fo represents the fractional coverage of this surface with oxygen after degassing, of carbon. It can be seen that the decrease in the heat of immersion upon removal of the oxygen complexes can be and hb represents the heat of immersion/unit area of the oxide free surface i.e. 36ergs. cm-‘. linearily related to the total amount of oxygen removed as Once again using the linearity of Fig. 3 to support the CO + COt but cannot be so related to the removal of COzas assumptions calculations show that ho= 140ergs . cmm2. found by Puri et al. 1191for activated charcoals. The removal of hydrogen between 800°C and 1000°C Since this value is very close to the surface enthalpy of water (118 ergs. cm-*) it follows that the net heat of does not appear to influence the heat of immersion. Support for this argument may be found in the adsorption of water on these oxygen complexes is small, observation that the heat of immersion of Spheron with the differential heat of adsorption closely approachdegassed at 1000°C,i.e. 36ergs cm-‘, is very close to the ing the heat of liquefaction. Water adsorption isotherms measured by various investigators [5,21-231 show classiOXYGEN RESORBED AS CO2 @noies.g-‘1 cal Type III behaviour which is also characterised by the differential heat of adsorption being very close to the heat of liquefaction of water. Oi The value of ho for Spheron 6 is close to a value of 17.5ergs. cme2 found for the oxygen complexes on graphite[l]. It must be pointed out that there is a certain amount of uncertainty associated with both these values. This uncertainty comes in part from the estimation of the area occupied by the oxygen complexes and also from this assumption that all the desorbed oxygen originated from the surface of the carbon. There is a considerable difference in the variation of the heat of immersion of Spheron 6 in water with degassing temperature between the present results and those of Wade[7]. Wade found with his sample a dramatic decrease at about 900°C in the heat of immersion which did not seem related to the removal of oxygen complexes. The absolute values of the heats of immersion of the present studies are much lower than those reported by 0 400 800 Wade[7]. A search of the literature shows quite a wide TOTAL OXYGEN DESORBED (CO + COpI variation in the heat of immersion of Spheron 6 in water. Fig. 3. Heat of immersion of Spheron 6 in water in relation to the amount of oxygen desorbed as CO, A, and to the total oxygen Robert [6] recorded a value of 96 ergs. cm-* for a sample degassed at 150°Cwhilst Millard et al. [5] recorded a value desorbed as CO and CO20.
50
S. S. BARTON and B. H. HARRISON
of 150ergs. cm-* for a sample degassed at 300°C. The heat of immersion for a sample degassed at 300°C in the present study in 103ergs. cme2 and from the study by Wade[7] it is 135ergs. cm-*. Thus, values ranging from 100 to 150ergs. cme2 have been reported which may signify that different batches of the carbon can vary considerably in their surface properties. These differences in heat of immersion values together with the variation in amounts of evolved gas noted in Table 1 may possibly be associated with the relative state of oxidation of the surfaces of the various samples. 4.CONCLUSION
REFERENCES
1. Barton S. S. and Harrison B. H., Carbon 10,245 (1972). 2. Studebaker M. L., Rubber Chem. Technol. 30, 1400(1957). 3. Healey F. H., Chessick J. J., Zettlemoyer A. C. and Young G. .I., J. Phys. Chern. 58, 887 (1954). 4. Kraus G., J. Phys. Chem. 59, 343 (1955). 5. Millard B., Caswell E. G., Leger E. E. and Mills D. R., J. Phys. Chem. 59, 976 (1955). 6. Robert L., Rev. Gen. Caoutchouc. 41, 371 (1964). 7. Wade W. H., J. Coil. Interface Sci. 31, 111 (1969). 8. Clint J. H., Clunie J. S., Goodman J. F. and Tate J. R., Nature 223, 52 (1969). 9. Everett D. H. and Findenegg G. H., Nature 223, 53 (1%9). 10. Barton S. S., Harrison B. H. and DollimoreJ., XS. Far. 169, 1039(1973). 11. Barton S. S., Beswick P. G. and Harrison B. H., J.C.S. Far. I 68, 1647(1972). 12. Puri B. R. and Bansal R. C., Carbon 1, 451 (1964). 13. Anderson R. B. and Emmett P. H., J. Phys. Chem. 56, 753 (1952). 14. Coltharp M. T. and Hackerman N., J. Phys. Chem. 72, 1171 (I%@. 15. Rivin D., Rubber Chem. Technol. 36, 729 (1%3). 16. Laine N. R., Vastola F. J. and Walker P. L.. Jr.. J. Phvs. , Chem. 67, 2030 (1963). 17. Polley M. H., Schaeffer W. D. and Smith W. R., J. Phys. Chem. 57, 469 (1953). 18. Brusset H., Martin J. J. P. and Mendelbaum H. G., BuU.Sot.
Comparison of the results of this investigation and those of other investigators shows that considerable variations exist in the heat of immersion of different samples of Spheron 6 in water. Similar variations are also observed in the amount of the oxygen complexes, especially the complexes decomposing to COz, which are removed when the carbon is heated to temperatures = 1000°C. With the sample of Spheron 6 used in this study it was found that the decrease in the heat of immersion in water as the carbon was degassed at increasingly higher temperatures could be directly related to the removal of the oxygen complexes as CO and CO,. The heats of immersion of the oxygen covered and the oxygen free surface of Spheron 6 in water were found to be 140ergs . cm-’ and 36 ergs . cmm2respectively.
Interface Sci. 45, 542 (1973). 21. Emmett P. H. and Anderson R. B., J. Am. Chem. Sot. 67,1492
Acknowledgements-The authors would like to acknowledge the eenerous financial assistance of the Defence Research Board of Canada under Grant number 9530-72 and to thank the Cabot Corporation for supplying the sample of Spheron 6.
(1945). 22. Pierce C., Smith R. N., Wiley J. W. and Cordes H., L Am. Chem. Sot. 73, 4551 (1951). 23. Anderson R. B. and Emmett P. H., J. Phys. Chem. 56, 756 (1952).
Chim. France 7, 2346 (1%7). 19. Puri B. R.. Sinnh D. D. and Sharma L. R.. .I Phvs. , Chem. 62.
756 (195Sj. 20. Barton S. S., Evans M. J. B. and Harrison B. H., J. Co/l.
Pergamon Press.
Printed m Great Britain
SURFACE STUDIES ON CARBON: IMMERSIONAL ENERGETICS OF SPHERON 6 IN WATER S. S. BARTONand B. H. HARRISON Departmentof Chemistryand ChemicalEngineering,RoyalMilitaryCollegeof Canada,Kings&on, Ontario,Canada (Received I4 June 1974)
heatsof immersionof Spheron6 degassedat temperaturesup to IOOOThave been measured in water. The removal of surface complexes as CO, CO,, HZ and HZ0 during the degassinghas also been followed Abstract-The
quantitatively using a mass spectrometer system. It was found that the changes in the immersional energetics could be accounted for by the removal of oxygen complexes and that complexes desorbing as hydrogen do not appear to affect the heat of immersion in water. Theheat of immersionin water of that part of the surface of Spheron 6 covered with oxygen complexes was found to be 140ergs. cmm2.
INTRODUCTION The surface properties of carbons and graphite are strongly influenced by the amount of oxygen complexes on their surfaces. Because the oxygen free surface of carbons and graphite is hydrophobic, and the portion covered by oxygen complexes is hydrophilic, changes in the surface properties are most easily observed through the interaction with water. Indeed, during the degassing of graphite, changes in the heat of immersion in water could be directly related to the removal of oxygen complexes[l]. Besides containing a considerable amount of combined oxygen, carbon blacks also contain large amounts of hydrogen which is located both on the surface of the particles and in their interior. This hydrogen has been retained by the carbon during the pyrolysis of the raw material in the manufacturing process[2]. The present investigation was undertaken to see whether the large quantities of hydrogen found in carbon blacks had any influence on the heat of immersion. 1.
in good agreement with and within the range of values given by other investigators[3-91. Bulbs were broken in succession in de-ionized distilled water (20 ml.) with values being reproducible to k-O.05cal . g-‘. Samples of approximately 1 g. were used, and the normal corrections applied to the calculation of the heat of immersion. The carbon samples were degassed in a quartz tube at the appropriate temperature and then transferred, under a vacuum < low6Torr, to thin walled spherical Pyrex glass bulbs for the immersion measurements [ I]. The desorbed gases were transferred, using a diffusion pump, to a mass spectrometer system for analysis [ 1, IO]. In some cases an Ion pump was used to create a vacuum < lo-‘Torr during degassing. The improved vacuum did not appear to have any influence on the heat of immersion measurements. The surface areas of samples, degassed at temperatures up to lOOO”C, were measured by low temperature nitrogen adsorption at 77°K in a conventional volumetric adsorption apparatus[ll]. Surface areas were computed by the BET method using 16.2 A’ as the cross-sectional area of the adsorbed nitrogen molecule. Carbon samples degassed at temperatures up to WC were found to have a surface area of 116? 3 m*g-‘, while the carbon degassed at 1000°C had a surface area of 98 + 2 m’g-‘.
2. EXPERIMENTAL Heats of immersion were measured in triplicate, and sometimes quadruplicate, on samples of Spheron 6 degassed at temperatures up to 1ooo”C. Measurements were made using the same isothermal change of phase calorimeter that was used in an earlier study[l]. The calorimeter was calibrated by both the electrical method and the standard reaction between 2-amino-2(hydroxymethyl)-1,3 propanediol (Tris or Tham) and 0.1 N HCI. This calibration was also checked by measuring the heat of immersion of ‘Graphon’ a well characterised adsorbent in both water and hexane. Recorded heats of 32 ergs . cm-’ and 119ergs . cm-* were
3. RESULTS ANDDlSCUSSlON effect of degassing temperature on the heats of immersion of Spheron 6 in water has been measured over the temperature range 0-1000°C. The major gaseous species desorbed as carbon samples were heated at temperatures up to 1OOtYC were CO, CO*and Hz. Figure 1 displays the amount of each component that was desorbed when samples were degassed at various
The
47
S. S. BARTON and B. H. HARRISON
0
I
I 200
600 400 TEMPERATURE
600 (‘Cl
loot
Fig. I. Amountsof CO, CO?,and Hz desorbedwhen samplesof Spheron6 wereheatedat various temperatures up to 1000°C. temperatures. Besides these major components a small amount of water was also observed at temperatures up to 300°C. The desorption of hydrogen began at temperatures as low as 500°C but did not become significant until about 700°C. The total quantity of each component desorbed is shown in Table 1, together with the data of other investigators. The maximum degassing temperature used in the various studies is also recorded. Although the removal of oxygen complexes is essentially complete at 1OOO”C, hydrogen removal is not. It was found that the desorption of hydrogen had not yet reached a maximum at lOOO”C, the highest temperature used in this study, and considerably more may still be released at higher temperatures. Even after making some allowance for the different maximum degassing temperatures, it can be seen in Table 1 that quite wide variations exist in the amounts of CO* and HZ desorbed. On the other hand the total amount of
CO desorbed appears to be reasonably constant. The results of Rivin are an exception. Assuming that all the CO and CO2 in the present study originated from the surface of the carbon an estimate of the area occupied by the oxygen complexes can be made. By analogy with studies on graphite where a crosssectional area of 8.3 A’ has been assigned to a carbon atom on the edge plane of graphite[l, 161, the area occupied by the carbon atoms removed as CO and CO*in this study would be 82.7 I-&-‘. This would indicate that 70 per cent of the surface is covered with oxygen complexes. The location of the hydrogen that is desorbed is uncertain. Some of the hydrogen could be combined to form functional groups such as hydroxyl (phenolic), carboxyl, while the rest may be directly combined with the carbon both on the surface and in the interior of the carbon particles. The variation in the heat of immersion of Spheron 6 in water with degassing temperature is shown in Fig. 2. The heats are displayed on a unit area basis by using the BET surface area of the carbon degassed at the same temperature. The surface area of the carbon was found to remain constant when it was degassed at temperatures up to 900°C but there was approximately a 20 per cent drop
0
200
400
DEGASSING
600
This Study Puri and Bansal Anderson and Emmett Colltharp and Hackerman Rivin
1000 (OC)
Fig. 2. Heat of immersion of Spheron 6, degassed at various temperatures, in water.
Table 1. Gases evolved on thermal treatment of Spheron 6 Quantity pmoles g-‘.
Authors
800
TEMPERATURE
CO
CO2
Hz
Hz0
Max Temp (“Cl
1395 1326 1331 1380 1920
205 156 237 420 240
1520 1420 2376 1820 1640
120 289 338 70 70
1000 1200 1200 1000 1300
Ref.
1121 [131 r141 WI
Surface studies on carbon
49
when it was degassed at 1000°C. This was noticed in value found for Graphon (Spheron 6 heat-treated at earlier studies[“l, 171 and it was suggested by Polley et 27OO”C),i.e. 32 erg cm-*. The potential evolution of large quantities of hydrogen at temperatures above 1000°Cthus al.[17] that this may be due to loss of porosity. The effect of degassing temperature on the heat of has a very small effect on the heat of immersion. From the data of Fig. 3 it is possible to estimate the heat immersion in water is similar to that found with carbons[7,18] and graphite[l] where the heat of immer- of immersion unit area (ho) of the hydrophilic oxide sion was characterised by a slight increase on degassing covered surface on Spheron 6 by using the same up to 200°C followed by a continuous decrease in the heat reasoning that was used with ~aphitetl]. Assuming that as the degassing temperature was raised to 1000°C.Up to ho is independent of the extent of coverage of the oxygen complexes then the heat of immersion can be represented 2OO”C,as water is desorbed from the oxygen complexes, an increase in the heat of immersion is expected. This is by the equation then followed by the removal of oxygen complexes as the Hi = S&b - SoFohbf SoFoho, degassing temperature is raised to 1ooO”C.Removal of these complexes reduces the chance of hydrogen bonding between the surface and the water resulting in a where ST represents the total BET surface area of the carbon, continuous decrease in the heat of immersion as they are removed. Attempts to relate the changes in the heat of SOrepresents the total surface area of the carbon which was covered with oxygen complexes immersion to the removal of oxygen complexes are shown before degassing, in Fig. 3. In this figure the amounts of CO and COZ desorbed are expressed as millimoles of oxygen per gram Fo represents the fractional coverage of this surface with oxygen after degassing, of carbon. It can be seen that the decrease in the heat of immersion upon removal of the oxygen complexes can be and hb represents the heat of immersion/unit area of the oxide free surface i.e. 36ergs. cm-‘. linearily related to the total amount of oxygen removed as Once again using the linearity of Fig. 3 to support the CO + COt but cannot be so related to the removal of COzas assumptions calculations show that ho= 140ergs . cmm2. found by Puri et al. 1191for activated charcoals. The removal of hydrogen between 800°C and 1000°C Since this value is very close to the surface enthalpy of water (118 ergs. cm-*) it follows that the net heat of does not appear to influence the heat of immersion. Support for this argument may be found in the adsorption of water on these oxygen complexes is small, observation that the heat of immersion of Spheron with the differential heat of adsorption closely approachdegassed at 1000°C,i.e. 36ergs cm-‘, is very close to the ing the heat of liquefaction. Water adsorption isotherms measured by various investigators [5,21-231 show classiOXYGEN RESORBED AS CO2 @noies.g-‘1 cal Type III behaviour which is also characterised by the differential heat of adsorption being very close to the heat of liquefaction of water. Oi The value of ho for Spheron 6 is close to a value of 17.5ergs. cme2 found for the oxygen complexes on graphite[l]. It must be pointed out that there is a certain amount of uncertainty associated with both these values. This uncertainty comes in part from the estimation of the area occupied by the oxygen complexes and also from this assumption that all the desorbed oxygen originated from the surface of the carbon. There is a considerable difference in the variation of the heat of immersion of Spheron 6 in water with degassing temperature between the present results and those of Wade[7]. Wade found with his sample a dramatic decrease at about 900°C in the heat of immersion which did not seem related to the removal of oxygen complexes. The absolute values of the heats of immersion of the present studies are much lower than those reported by 0 400 800 Wade[7]. A search of the literature shows quite a wide TOTAL OXYGEN DESORBED (CO + COpI variation in the heat of immersion of Spheron 6 in water. Fig. 3. Heat of immersion of Spheron 6 in water in relation to the amount of oxygen desorbed as CO, A, and to the total oxygen Robert [6] recorded a value of 96 ergs. cm-* for a sample degassed at 150°Cwhilst Millard et al. [5] recorded a value desorbed as CO and CO20.
50
S. S. BARTON and B. H. HARRISON
of 150ergs. cm-* for a sample degassed at 300°C. The heat of immersion for a sample degassed at 300°C in the present study in 103ergs. cme2 and from the study by Wade[7] it is 135ergs. cm-*. Thus, values ranging from 100 to 150ergs. cme2 have been reported which may signify that different batches of the carbon can vary considerably in their surface properties. These differences in heat of immersion values together with the variation in amounts of evolved gas noted in Table 1 may possibly be associated with the relative state of oxidation of the surfaces of the various samples. 4.CONCLUSION
REFERENCES
1. Barton S. S. and Harrison B. H., Carbon 10,245 (1972). 2. Studebaker M. L., Rubber Chem. Technol. 30, 1400(1957). 3. Healey F. H., Chessick J. J., Zettlemoyer A. C. and Young G. .I., J. Phys. Chern. 58, 887 (1954). 4. Kraus G., J. Phys. Chem. 59, 343 (1955). 5. Millard B., Caswell E. G., Leger E. E. and Mills D. R., J. Phys. Chem. 59, 976 (1955). 6. Robert L., Rev. Gen. Caoutchouc. 41, 371 (1964). 7. Wade W. H., J. Coil. Interface Sci. 31, 111 (1969). 8. Clint J. H., Clunie J. S., Goodman J. F. and Tate J. R., Nature 223, 52 (1969). 9. Everett D. H. and Findenegg G. H., Nature 223, 53 (1%9). 10. Barton S. S., Harrison B. H. and DollimoreJ., XS. Far. 169, 1039(1973). 11. Barton S. S., Beswick P. G. and Harrison B. H., J.C.S. Far. I 68, 1647(1972). 12. Puri B. R. and Bansal R. C., Carbon 1, 451 (1964). 13. Anderson R. B. and Emmett P. H., J. Phys. Chem. 56, 753 (1952). 14. Coltharp M. T. and Hackerman N., J. Phys. Chem. 72, 1171 (I%@. 15. Rivin D., Rubber Chem. Technol. 36, 729 (1%3). 16. Laine N. R., Vastola F. J. and Walker P. L.. Jr.. J. Phvs. , Chem. 67, 2030 (1963). 17. Polley M. H., Schaeffer W. D. and Smith W. R., J. Phys. Chem. 57, 469 (1953). 18. Brusset H., Martin J. J. P. and Mendelbaum H. G., BuU.Sot.
Comparison of the results of this investigation and those of other investigators shows that considerable variations exist in the heat of immersion of different samples of Spheron 6 in water. Similar variations are also observed in the amount of the oxygen complexes, especially the complexes decomposing to COz, which are removed when the carbon is heated to temperatures = 1000°C. With the sample of Spheron 6 used in this study it was found that the decrease in the heat of immersion in water as the carbon was degassed at increasingly higher temperatures could be directly related to the removal of the oxygen complexes as CO and CO,. The heats of immersion of the oxygen covered and the oxygen free surface of Spheron 6 in water were found to be 140ergs . cm-’ and 36 ergs . cmm2respectively.
Interface Sci. 45, 542 (1973). 21. Emmett P. H. and Anderson R. B., J. Am. Chem. Sot. 67,1492
Acknowledgements-The authors would like to acknowledge the eenerous financial assistance of the Defence Research Board of Canada under Grant number 9530-72 and to thank the Cabot Corporation for supplying the sample of Spheron 6.
(1945). 22. Pierce C., Smith R. N., Wiley J. W. and Cordes H., L Am. Chem. Sot. 73, 4551 (1951). 23. Anderson R. B. and Emmett P. H., J. Phys. Chem. 56, 756 (1952).
Chim. France 7, 2346 (1%7). 19. Puri B. R.. Sinnh D. D. and Sharma L. R.. .I Phvs. , Chem. 62.
756 (195Sj. 20. Barton S. S., Evans M. J. B. and Harrison B. H., J. Co/l.