INTRODUCTION
CHAPTER 3 CHAPTER 3
3.4 Additional Sorption Measurements
N2 at 77 K and open only to C02 at 195 K[38]. Upon partial combustion, the pores enlarge because of the combined effect of heterogeneous reaction between the carbon at the pore walls and the oxidizer and enhanced structural rearangement caused by the catalytic effects of 0 2 • After this treatment, the pore openings are sufficiently large for N 2 to penetrate in BET measurements.
total surface areas of these two materials derived from Medek's[46] equation, using Dubinin's parameters is 560 m2 /g for part (a) and 684 m2 /g for part (b).
Pore volume measurements by means of C02 adsorption at 297 K were also applied to the unoxidized material that was pyrolyzed to 800 K. The void volume was 0.0223 cm2 /g, corresponding to a porosity of E = .03, which is less than that determined with helium (E = 0.11). These values show that the voids of the initial material are small and impermeable. The C02 surface area for this material was calculated to be 59 m2 / g.
4 Conclusions
Uniform size glassy carbon spheres have been manufactured by controlled atom- ization. The polymer precursor was furfuryl alcohol, but other highly crosslinked polymers can also be used. The production and curing time required to generate solid particles are very brief because of the small size of the spheres. The sphere size can be varied, and both solid and hollow spheres can be produced.
The pore structure and the chemical properties of the particles can be varied by the addition of pore-forming agents. The particles carbonized at 800 K contain a vast network of micropores of very fine size (less than 10A). These micropores are closed and inaccessible to N2 at 77 K. The shape of these pores is rather irregular and their size distribution is broad. Upon carbonization at elevated temperatures, the carbon matrix shrinks. This densification makes space for the voids to grow.
The void shapes become more rounded, and the pore size distribution narrows. Ox- idation accelerates pore growth by the combined effect of catalysis of graphitization reactions and by heterogeneous reaction that leads to gasification of the carbon matrix. In addition, oxidation enlarges the pore openings and reduces the resis- tance to pore diffusion in the particle. Oxidation at elevated temperatures induces multiphase graphitization to some of the copolymer particles.
All of the glassy carbon materials produced in this study possess m1cropores only, with the exception of the carbon black containing particles that also possess transitional pores superimposed on the micropore network, and the cenospheres that contain macro pores and large voids (bubbles). Finally, the glassy carbon spheres produced are hard, and their compressibility varies from very small values to zero depending on the copolymer nature and the heat treatment. Bulk quantities of spherical glassy carbon chars can be produced by an array of acoustically excited aerosol generators, and if monodispersivity is not a requirement, they can be pro- duced by a high output spray nozzle.
5 Acknowledgements
This research was supported by the U.S. Department of Energy University Coal Programs Grant Number DE-FG22-84PC70775. The authors gratefully acknowl- edge technical assistance from Scott Northrop, George Gavalas, Patric Kohen, Bob Hously, Bob Johnson, Sten Samson and Larry Henling.
6 Notation
SYMBOL DESCRIPTION UNITS
a correlation distance
A
ac lattice constant
A
Ac specific total area m2/g
AHg specific Mercury area m2/g
J
interlayer spacingA
dvoid av. segment dimension in voids
A
dsolid av. segment dimension in solid
A
h wave vector magnitude
i/A
I(h)
relative radiation intensitylm range of inhomogeneity
A
La crystallite stack width
A
Le crystallite stack height
A
m mass g
p pressure atm
r radial distance cm
rp pore radius cm
Rg radius of gyration
A
R universal gas constant atm cm3 /mole K
s
SAXS total surface area m2/gv
inhomogeneity volume cm3/gVHg specific Mercury pore volume cm3/g
O'. contact angle
I '
probability /olT)
E porosity
Pu electron density
O'a apparent density g/cm3
O'Hg Mercury density g/cm3
O'He true(Helium) density g/cm3
O'x-ray x-ray density g/cm3
a surface tension of mercury dyne/cm
7 References
l. E. Fitzer, W. Schaefer and S. Yamada, Carbon 7, 643 (1969).
2. C. Moreno-Castilla, 0. P. Mahajian, H. J. Jung, M. A. Vannice, and P. L.
Walker, Jr., Absts. 14th Biennial Conf. on Carbon, Pennsylvania State Uni- versity (1979), p.26.
3. C. Moreno-Castilla, 0. P. Mahajian and P. L. Walker, Jr., Carbon 18, 271 (1980).
4. C. N. Satterfield, "Mass Transfer in Heterogeneous Catalysis," Massachussets Institute of Technology Press (1970).
5. E. E. Hucke, United States Patent Publication 3,859,421 (1975).
6. J. L. Schmitt, Jr., P. L. Walker, Jr. and G. A. Castellion, United States Patent Publication 3,978,000 ( 1976).
7. P. L. Walker, Jr., A. Oya, 0. P. Mahajan, Carbon 18, 377 (1980).
8. Y. A. Levendis and R. C. Flagan, Combust. Sci. and Tech. 53, 117 (1987).
9. I. Fernandez-Morales, A. Guerrero-Ruiz, F. J. Lopez-Garzon, I. Rodriguez- Ramos and C. Moreno-Castilla Carbon 22, 3, 301 (1984).
10. C. L. Senior and R. C. Flagan, Twentieth Symposium (International) on Com- bustion, The Combustion Institute, Pittsburg, PA. p.921 (1986).
11. R. N. Berglund and B. Y. H. Liu, Environ. Sci. and Tech. 7, 147 (1973).
12. P. S. Northrop, R. G. Gavalas and R. C. Flagan, Langmufr 3, 300 (1987).
13. J. Yan and Q. Zhang, Particle Characterization 3, 20 (1986).
14. A. Wheeler Adv.£n Catalysis 3, 249 (1951).
15. I. W. Smith and R. J. Tyler, Fuel 51, 312 (1972).
16. J. J. F. Scholten, from Porous Carbon Sol£ds, edited by R. L. Bond, Academic Press, London (1967).
17. P. Zwietering and D. W. van Krevelen, Fuel 33, 331 (1954).
18. R. Perret and W. Ruland, J. Appl. Cryst. 5, 183 (1972).
19. G. M. Jenkins, K. Kawamura and L. L. Ban, Proc. R. Soc. Lond. A. 327, 501 (1972).
20. D. B. Fischbach, Chem. and Phys. of Carbon 7, 1 (1971).
21. J. Morgan and B. E. Warren, J. Chem. Phys. 6, 666 (1938) 22. M. A. Short and P. L. Walker, Jr., Carbon 1, 3 (1963).
23. B. E. Warren, Phys. Rev. 59, 693 (1941).
24. T. Noda and M. Inagaki, Carbon 2, 127 (1964).
25. D. B. Fischbach and M. E. Rorabaugh, Carbon 21, 429 (1983).
26. J. D Brooks and G. H. Taylor, Chem. and Phys. of Carbon 4, 243 (1968).
27. P.A. Oberlin and F. Rousseaux, J. Appl. Cryst. 1, 218 (1968).
28. R. E. Franklin, Proc. Roy. Soc. (London) A209, 196 (1951).
29. S. Nakamura, T. Ishii and S. Yamada, Sympos£um on Carbon, Tokyo (1964).
30. P. Cornuault, F. du Chaffaut, J. Rappeneau, M. Yvars and A. Fillatre, Carbon 6, 857 {1968).
31. Y. Hishiyama, .\1. Inagaki, S. Kimura and S. Yamada, Carbon 12, 249 (1974).
32. K. Kawamura and T. Tsuzuku, Carbon 12, 352 (1973).
33. K. Kamiya and K. Suzuki, Carbon 13, 317 (1975).
34. M. M. Dubinin, G. M. Plavnik and E. D. Zaverina, Carbon 2, 261 (1964).
35. S. Bose and R. H. Bragg, Carbon 19, 289 (1981).
36. G. D. Wignal and C. J. Pings, Carbon 12, 51 (1974).
37. W. S. Rothwell, J. Appl. Phys. 39, 3, 1840 (1968).
38. R. G. Jenkins and P. L. Walker, Jr., Carbon 14, 7 (1976).
39. A. Guinier and G. Fournet, Small Angle Scattering of X-Rays John Wiley, New York (1955).
40. P. Debye, H. R. Anderson and H. Brumberger, J. Appl. Phys. 28, 679 (1957).
41. P. W. Schmidt and R. Hight, Jr., Acta Cryst. 13, 480 (1960).
42. B. Chu and D. M. Tan Creti, Acta Cryst. 18, 1083 (1964).
43. G. Porod, Small Angle X-Ray Scattering edited by H. Brumberger, Gordon &
Beach, New York (1969).
44. D. Tchoubar and J. Mering, J. Appl. Cryst. 2, 128 (1969).
45. M. M. Dubinin, Chem. Rev. 60, 235 (1960).
46. J. Medek, Fuel 56, 131 (1977)
8 List of figures
1. Schematic of the char production technique.
2. Schematic of the particle generation system and thermal reactor.
3. SEM photographs of plain polymer particles.
4. SEM photographs of (a) a cenosphere made from 18% tannic acid and PFA (b)a particle made from 25% carbon black and PFA.
5. SEM photographs of partially burned plain polymer (PFA). particles at 1500 K for 2 sec in air (a) surface, (b) section.
6. TEM photographs of plain polymer chars (a) carbonized at a particle temper- ature of ~ 1500 K in N 2 for 2 sec and (b) partially burned in air at a particle temperature of ~ 1500 K for 2 sec.
7. BET and SAXS surface area versus burn-off for plain polymer chars.
8. Mercury porosimetry pore size distribution.
9. Wide-angle x-ray diffraction profiles of carbonized and partially combusted glassy carbons.
10. SEM photographs of particles made from 18% tannic acid and PFA a)section of unoxidized particle, b )detail of partially burned particle.
11. Experimental SAXS intensity profiles for carbonized and partially burned glassy carbons (apperture of slits 0.1°, 0.1°, 0.1° and 0.018°).
12. Debye plot for glassy carbons.
13. Porod plot for heat-treated and activated glassy carbons.
14. Porod invariant plot for heat-treated and activated glassy carbons.
15. Guinier plot for heat-treated and activated glassy carbons.
Pol)mer with Pore Former
PLAIN POLYMER
DEC AUN (21%)
OE CALIN (37%)
GLYCEROL (20%) GLYCEROL ( 20%) TRITON (3%) GLYCEROL ( 35%) TRITON (7%) GLYCEROL ( 20%) TRITON (3%) PEG (3%) PEG (9%)
PEG (18%)
TANNIC ACID ( 8%)
TANNIC ACID (17%)
TANNIC ACID (50:C)
PLAIN T ANNIC ACID
CARBON BLACK (25:C)
PURE CARBON BLACK
PEG (9%)
TANNIC ACID ( 8%)
TANNIC ACID ( 17%) GLYCEROL ( 20%) TRITON (3%) PEG (3%)
era
Apparent solid and pores
less than 7 ;;.m g/cmJ
1.23
1.17
1.25
1.24
1.24
1.26
1.25
1.23
1.17
1.31 ave.
1.33
1.35
----
0.88
----
TABLE Ia
DENSITIES AND POROSITIES
CT Hg CT He E
Mercury Helium Total
solid and pores porosity
less \hon 32A %
g/cmJ g/cmJ
1.28 1.37 11
1.21 1.36 14
1.29 1.35 8
1.30 1.39 11
1.29 1.37 10
1.29 1.33 6
1.28 1.32 6
1.26 1.43 14
1.25 1.39 16
1.35 ave. 1.38 6.0 ave.
1.35 1.39 4
1.37 1.40 ----
---- 1.45 ----
1.28 1.45 39
---- 1.86 ----
TABLE Ib
PARTIALLY BURNED MATERIALS
1.25 1.31 2.0 37
1.21 1.5 2.1 42
1.205 1.85 2.2 45
1.21 1.25 2.1 39.5
£
...
below 32A macro and radius transitional porosity pores
% cm3/g
6.8 0.08
11 ----
4 0.032
6.3 0.029
6.4 0.028
3 0.027
3.2 0.026
12 0.030
10.5 0.054
2.5 eve. 0.031
2.5 0.010
---- ---- ---- ----
11.6 0.358
---- ----
34 0.041
28 0.043
16 0.00
37.5 0.023