- Email: [email protected]
SAXS investigations on the porosity of pitch based carbon fibres
614
In IR spectra of the above two PEO-intercalated GO, together with the absorption peaks of host GO, those at 1100 cm-i and 2800 cm-i due to -CH2-0-CHzand -CH2- of the intercalated PEO were strongly observed. Absorption peaks due to ether group appeared at the same positions for the nanocomposites with different I, values, however, slight shifts were observed for the absorption peaks derived of -CHz- group. The similar PEO-intercalated GO with k = 1.3nm containing Li or K was also formed from O.lM LiOH or KOH aqueous solution, respectively, however, intercalation of PEO into GO did not occur when 0.1 M Ca(OH), or Ba(OH), was used as solvent because a colloidal solution was not formed.
4.
6.
8.
2. 3.
Y.-J. Liu, D. C. DeGroot, J. L. Schindler, C. R. Kannewurf and M.G. Kanatzidis, Chem. Mater., 3, 992 (1991). I. Lagadic, A. Leaustic and R. Clement, /. Chem. Sot. Chem. Commun., 1396 (1992). L. F. Nazar, Z. Zhang and D. Zinkweg, .I. Am. Ckm.
207 (1994).
J. P. Lemmon, J. Wu, C. Oriakhi and M. M. Lerncr, Electrochim.
Acta, 40, 2245 (1995).
10.
J. P. Lemmon
Il.
commun., 94, 533 (1995). C.-G. Wu, D.C. DeGroot,
REFERENCES I.
P. Aranda and E. Ruiz-Hitzky, Chem. Mater., 4, 1395 (1992). R. Bissessur, M. G. Kanatzidis, J. L. Schindler and C. R. Kannewurf, .I. Chem. Sot. Chem. Cornnun., 1582 (1993). J. Wu and M. M. Lerner, Chrm. Mater., 5, 835 (1993). R. A.Vaia, H. Ishii and E. P. Giannelis, Chem. Muter., 5, 1694 (1994). J. P. Lemmon and M. M. Lerner, Chem. Mater., 6,
12. 13. 14.
and M. M. Lerner,
Solid
slrnr
H. 0. Marcy, J. L. Schindler, C. R. Kannewurf, T. Bakas, V. Papaefthymlou, W. Hirpo, J. P. Yesinowski, Y.-J. Liu and M. G. Kanatzidis, .I. Am. Chem. Sot., 117, 9229 (1995). B. C. Brodie, Phil. Trans. Roy. Sot. kmdon, A149, 6 11960). W.~Scholz and H.P. Boehm, 2. nnoq. nll~. Chem., 369, 327 (1969). T. Nakajima, A. Mabuchi and R. Hagiwara, Curbon, 26, 357 (1988).
Sot., 114, 6239 (1992).
SAXS investigations
on the porosity of pitch based carbon fibres
N. COHAUT and J.M GUBT Centrc de Recherche sur la Matihe DivisCe, Universite d’ Orleans- CNRS, rue de Chartres, BP 6759,45067 Orleans CCdex 2, France R. DJDUSZKO Institute of Vacuum Technology, ul Dluga 44/50,00-241 Warsaw, Poland. (Received 12 September 1995; uccepted in revised form 12 March 1996)
Key Words - Pitch based carbon fibre, SAXS.
P55 and P120 (Amoco Performance Products, Inc.), two commercially available mesophase petroleum pitch (MPP) based carbon fibres were studied. These fibrcs have respectively a high (380 GPa) and ultra high (820 GPa) Young’s modulus according to values taken from manufacturer’s data sheets. Crystallographic parameters deduced from wide angle x-ray scattering were published previously ] l-21. These data showed a higher densification of the carbon layer arrangement and an optimum degree of carbon layer orientation with respect to the fibre axis, concerning the Pl20 fibres. To provide evidence of a porous texture oriented along the fibre axis, flat plate SAXS patterns were first performed on carbon fibres. The observed disk shaped intensity suggested two directions of analysis: consequently, recordings were made parallel and perpendicular to the fibre axis with a 12kW Rigaku rotating anode x-ray generator. With regards to SAXS investigations on carbon materials, studies [3-51 developed extensively over many years show that the assumption of a two phase system voids-dense packed carbon matter is not strictly verified at large angles In fact, where Porod’s law is usually observed. measurements performed in this range integrate voids of a few angstroms generated by imperfections in carbon layer stackings.
The additional contribution of these 2D density fluctuations to the scattering intensity is now well known. For an isotropic system studied in pinhole collimation, the intensity is decomposed into two terms, the first relative to pores-dense matter contrast and the second relative to 2D density fluctuations within the supposed dense matter.
For a two-phase system with a clean interface such as between voids and carbon matter, 11(q) may obey Porod’s law given in the case of an isotropic sample studied in pinhole collimation by the relation: lim iq4.11(q) q+w4Tc
=+ m
Where Tm is the mean length of chords in dense matter. The porosity including pore sizes defined by the angular range [p/q,,; p/qmin] is deduced from the intensity in absolute scale [6] according to the following expression:
67.5
p=1 2.12
1600-
~2.1(s>.dq
1400.
and IZOO-
S”=p=_ 4.p m
B
1,.(1-P)
lOOO-
z-
where Ip is the mean length of chords in pores and Sv, the specific surface area defined as the inner surface by unit of matter volume. Sv may be given by unit of matter weight if the density of matter rmat is known. Structural parameters, porosity and specific surface area may be obtained (Table 1) after correction of the 12(q) component which obeys a linear variation in Porod’s representation as shown in Fig. 1. Pore size distribution was determined by Glatter’s indirect transformation method [7], which deduces from the experimental scattering curve and by means of Fourier transforms, the aspect of the size distribution of pores all with the same a priori known shape. Considering the P55 fibres, Porod’s law is verified for the transverse and longitudinal scattering and consequently, structural parameters S,, Irn and Ip may be calculated (Table 1). Because the obtained values seem to be independent of the scattering direction, pores were regarded as mildly elongated and were assumed to have a spherical shape for the pore size distribution evaluation using Glatter’s method. The pore size distribution deduced from the transverse scattering of P55 fibre (Fig. 2) reveals, after correction of 2D interlamellar fluctuations, a distribution of pore radii centered around 14 A. This value is in agreement
Fig. 1. Pored’s law for transverse scattering (I to fibre axis). -’ as observed; : after 2D interlamellar density fluctuations.
800~ 600400zoo-
0
R(A) Fig. 2. P55 fibre. Volume size distribution of pores deduced using Glatter’s method, after correction of 2D interlamellar distance fluctuation effects. with the mean pore radius of 17A deduced from the Ip parameter with the expression : R = 3/4 Ip The SAXS behaviour of the P120 fibres differs from those of an isotropic system as previously observed. This anisotropy modifies the porosity expression and Porod’s law which, in this case, take the following form:
P=
&
q.I(q).dq
and &n+.q3I(q)
= f Ill
Glatter’s method applied to this fibre does not produce satisfying results with the assumption of spherical shape for pores and will be extended to the assumption of highly oriented cylindrical or ellipso’idal shapes of pores. However, in the case of highly elongated micropores, strictly oriented parallel to the libre axis, the mean chord Ip depends on the dimension and shape of transversal sections of micropores, if the scattering is recorded perpendicularly to the fibre axis. In the assumption of circular section, the mean diameter D is given by D=WIp and so is equal to 27A for the P120 fibre. This higher transverse dimension compared to that calculated for the P55 fibre shows that the organization of carbon layers into rigid lamellar sheets at a high temperature treatment tends, on the one hand,
Table 1. P55 and P120 characteristics of porous system defined by SAXS measurements * deduced from the density of graphite and from interlamellar distances of graphite and fibres. (r=2.27 g/cm3) and dgr(m2)= 3.35A Diameter (mm)
PC%)
s,,,,
‘ap (g/cm 3,
‘mat* (g/cm 3,
svap. (m2/g)
pa *. (4)
10
2.02
2.20
0.198
10.2
I axis /I axis
168 193
23 23
12.1 10.6
106 92
10
2.18
2.25
0.183
3.1
I axis
2700
54
2
7
(m2k)
616
to eliminate some small pores and on the other hand, to enhance some others, giving less numerous hut larger pores and leading to a weaker global porosity. For commercial PSS and P120 fihres, the mean surface area may he compared to values deduced from the apparent density rap, given by the manufacturers (Table 1) by the followmg expression available in the assumption for an infinite rod-like filament with a diameter D:
In the case of PI20 fihre, the increase in carbon layer stiffness involves an elongation and a coalescence of micropores, leading to a global porosity decrease. High specific surface areas deduced by SAXS show that the microporosity is closed. This is a predominant factor in explaining the high potential of carbon fihres to yield adsorbent carbon materials after an activation treatment, that is to say after the opening of pores. l
l
4 Svap. = D
REFERENCES
.pap, The comparison reveals the occurence of a closed microporosity which induced very high values for the specific surface compared to those given by adsorption measurements, particularly for the PS5 fihre. The present study gives the following results: Even if a preferred orientation of carbon layers along the fihre axis is classically observed by WAXS, the generated porosity may he considered as isotropic for PS5 fihre. l
A turbostratic
N. Cohaut, Thesis, University of Orleans, France (1993). *. N. Cohaut, J.M Guet and D. Tchoubar, Ext. Abst. of 2lst Biennial Conf. Buffalo, NY (1993). 3 C. Schiller and J. Mering, C.R Acad. Sci., Paris, B264, 241(1967). 4. R. Perret and W. Ruland , J. Appl. Cryst., 3,535 (1970). 5. J.M Guet, Coal science and Technology 15, Elsevier Science, (1990) p. 103. D. Tchoubar and J. Mering, 1. Appl. Cryst., 2, 128 6. (1969). 7, 0. Glatter and 0. Kratky, Small Angle X-Ray Scattering, Academic Press (1982).
carbon with high specific surface area from 1,4-benzenedimethanol
H.A. Yu, T. KANEKO and S. YOSHJMURA Yoshimura n-Electron Materials Project, ERATO, JRDC Nishhro-317, Numazu, Shizuoka410-03, Japan s. OTANI Department of Material Science and Technology, School of High-Technology for Human Welfare, Tokai University, Nishino-3 17, Numazu, Shizuoka 410-03, Japan (Received 7 December 1995: accepted in revised,form I9 Much
Key Words
1996)
1,4-benzenedimethanol, turbostratic carbon, specific surface area.
The carbon material used for a negative electrode in a high capacity lithium-ion secondary battery can he roughly classified into the following two groups: graphite with high crystallinity, and turhostratic carbon with a large d-spacing (doo2)_ Research efforts [l-2] have made it clear that a secondary cell using the latter carbon material increases generally in its capacity with increase in d-spacing of the carbon material. In the present work, l$henzenedimethanol has been used as the study material to prepare a turhostratic carbon to he examined as a potential candidate for the negative electrode of the lithium-ion secondary battery in the near future.
HOCH2*M20H 1,4-henzenedimethanol Having two -OH groups at its para-positions, 1,4_henzenedimethanol is used as a cross-linking agent in organic reactions. The synthesis of COPNA resin starting from condensed polycyclic aromatic comp-
ounds also uses 1,4-henzenedimethanol as a crosslinking agent [3]. It was found that such COPNA resin synthesized with the use of I ,4_benzenedimethanol as a cross-linking agent can he converted into a form of non-graphitizing carbon by heat-treatment, indifferent to the starting materials of the resin [4-51. This is probably due to the fact that l,4-henzenedimethanol can cross-link COPNA resin with a highly developed three dimensional structure. It should be, however, noted here that 1,4_henzenedimethanol can also polymerize into its own polymer through its intermolecular dehydration in the course of the synthesis of COPNA resin [3]. However, the study of the preparation of 1,4-henzenedimethanol polymer and its carbonization product has not been reported. In the present work, we prepared 1$benzenedimethanol polymer in a medium of concentrated sulfuric acid, and heat-treated the polymer under an argon atmosphere to A number of obtain its carbonization product. carbonization products of 1,4_benzenedimethanol polymer were prepared with different heat-treatment temperatures, and analyzed in their structures by such methods as x-ray diffraction and specific surface area measurement. These results are reported below.
In IR spectra of the above two PEO-intercalated GO, together with the absorption peaks of host GO, those at 1100 cm-i and 2800 cm-i due to -CH2-0-CHzand -CH2- of the intercalated PEO were strongly observed. Absorption peaks due to ether group appeared at the same positions for the nanocomposites with different I, values, however, slight shifts were observed for the absorption peaks derived of -CHz- group. The similar PEO-intercalated GO with k = 1.3nm containing Li or K was also formed from O.lM LiOH or KOH aqueous solution, respectively, however, intercalation of PEO into GO did not occur when 0.1 M Ca(OH), or Ba(OH), was used as solvent because a colloidal solution was not formed.
4.
6.
8.
2. 3.
Y.-J. Liu, D. C. DeGroot, J. L. Schindler, C. R. Kannewurf and M.G. Kanatzidis, Chem. Mater., 3, 992 (1991). I. Lagadic, A. Leaustic and R. Clement, /. Chem. Sot. Chem. Commun., 1396 (1992). L. F. Nazar, Z. Zhang and D. Zinkweg, .I. Am. Ckm.
207 (1994).
J. P. Lemmon, J. Wu, C. Oriakhi and M. M. Lerncr, Electrochim.
Acta, 40, 2245 (1995).
10.
J. P. Lemmon
Il.
commun., 94, 533 (1995). C.-G. Wu, D.C. DeGroot,
REFERENCES I.
P. Aranda and E. Ruiz-Hitzky, Chem. Mater., 4, 1395 (1992). R. Bissessur, M. G. Kanatzidis, J. L. Schindler and C. R. Kannewurf, .I. Chem. Sot. Chem. Cornnun., 1582 (1993). J. Wu and M. M. Lerner, Chrm. Mater., 5, 835 (1993). R. A.Vaia, H. Ishii and E. P. Giannelis, Chem. Muter., 5, 1694 (1994). J. P. Lemmon and M. M. Lerner, Chem. Mater., 6,
12. 13. 14.
and M. M. Lerner,
Solid
slrnr
H. 0. Marcy, J. L. Schindler, C. R. Kannewurf, T. Bakas, V. Papaefthymlou, W. Hirpo, J. P. Yesinowski, Y.-J. Liu and M. G. Kanatzidis, .I. Am. Chem. Sot., 117, 9229 (1995). B. C. Brodie, Phil. Trans. Roy. Sot. kmdon, A149, 6 11960). W.~Scholz and H.P. Boehm, 2. nnoq. nll~. Chem., 369, 327 (1969). T. Nakajima, A. Mabuchi and R. Hagiwara, Curbon, 26, 357 (1988).
Sot., 114, 6239 (1992).
SAXS investigations
on the porosity of pitch based carbon fibres
N. COHAUT and J.M GUBT Centrc de Recherche sur la Matihe DivisCe, Universite d’ Orleans- CNRS, rue de Chartres, BP 6759,45067 Orleans CCdex 2, France R. DJDUSZKO Institute of Vacuum Technology, ul Dluga 44/50,00-241 Warsaw, Poland. (Received 12 September 1995; uccepted in revised form 12 March 1996)
Key Words - Pitch based carbon fibre, SAXS.
P55 and P120 (Amoco Performance Products, Inc.), two commercially available mesophase petroleum pitch (MPP) based carbon fibres were studied. These fibrcs have respectively a high (380 GPa) and ultra high (820 GPa) Young’s modulus according to values taken from manufacturer’s data sheets. Crystallographic parameters deduced from wide angle x-ray scattering were published previously ] l-21. These data showed a higher densification of the carbon layer arrangement and an optimum degree of carbon layer orientation with respect to the fibre axis, concerning the Pl20 fibres. To provide evidence of a porous texture oriented along the fibre axis, flat plate SAXS patterns were first performed on carbon fibres. The observed disk shaped intensity suggested two directions of analysis: consequently, recordings were made parallel and perpendicular to the fibre axis with a 12kW Rigaku rotating anode x-ray generator. With regards to SAXS investigations on carbon materials, studies [3-51 developed extensively over many years show that the assumption of a two phase system voids-dense packed carbon matter is not strictly verified at large angles In fact, where Porod’s law is usually observed. measurements performed in this range integrate voids of a few angstroms generated by imperfections in carbon layer stackings.
The additional contribution of these 2D density fluctuations to the scattering intensity is now well known. For an isotropic system studied in pinhole collimation, the intensity is decomposed into two terms, the first relative to pores-dense matter contrast and the second relative to 2D density fluctuations within the supposed dense matter.
For a two-phase system with a clean interface such as between voids and carbon matter, 11(q) may obey Porod’s law given in the case of an isotropic sample studied in pinhole collimation by the relation: lim iq4.11(q) q+w4Tc
=+ m
Where Tm is the mean length of chords in dense matter. The porosity including pore sizes defined by the angular range [p/q,,; p/qmin] is deduced from the intensity in absolute scale [6] according to the following expression:
67.5
p=1 2.12
1600-
~2.1(s>.dq
1400.
and IZOO-
S”=p=_ 4.p m
B
1,.(1-P)
lOOO-
z-
where Ip is the mean length of chords in pores and Sv, the specific surface area defined as the inner surface by unit of matter volume. Sv may be given by unit of matter weight if the density of matter rmat is known. Structural parameters, porosity and specific surface area may be obtained (Table 1) after correction of the 12(q) component which obeys a linear variation in Porod’s representation as shown in Fig. 1. Pore size distribution was determined by Glatter’s indirect transformation method [7], which deduces from the experimental scattering curve and by means of Fourier transforms, the aspect of the size distribution of pores all with the same a priori known shape. Considering the P55 fibres, Porod’s law is verified for the transverse and longitudinal scattering and consequently, structural parameters S,, Irn and Ip may be calculated (Table 1). Because the obtained values seem to be independent of the scattering direction, pores were regarded as mildly elongated and were assumed to have a spherical shape for the pore size distribution evaluation using Glatter’s method. The pore size distribution deduced from the transverse scattering of P55 fibre (Fig. 2) reveals, after correction of 2D interlamellar fluctuations, a distribution of pore radii centered around 14 A. This value is in agreement
Fig. 1. Pored’s law for transverse scattering (I to fibre axis). -’ as observed; : after 2D interlamellar density fluctuations.
800~ 600400zoo-
0
R(A) Fig. 2. P55 fibre. Volume size distribution of pores deduced using Glatter’s method, after correction of 2D interlamellar distance fluctuation effects. with the mean pore radius of 17A deduced from the Ip parameter with the expression : R = 3/4 Ip The SAXS behaviour of the P120 fibres differs from those of an isotropic system as previously observed. This anisotropy modifies the porosity expression and Porod’s law which, in this case, take the following form:
P=
&
q.I(q).dq
and &n+.q3I(q)
= f Ill
Glatter’s method applied to this fibre does not produce satisfying results with the assumption of spherical shape for pores and will be extended to the assumption of highly oriented cylindrical or ellipso’idal shapes of pores. However, in the case of highly elongated micropores, strictly oriented parallel to the libre axis, the mean chord Ip depends on the dimension and shape of transversal sections of micropores, if the scattering is recorded perpendicularly to the fibre axis. In the assumption of circular section, the mean diameter D is given by D=WIp and so is equal to 27A for the P120 fibre. This higher transverse dimension compared to that calculated for the P55 fibre shows that the organization of carbon layers into rigid lamellar sheets at a high temperature treatment tends, on the one hand,
Table 1. P55 and P120 characteristics of porous system defined by SAXS measurements * deduced from the density of graphite and from interlamellar distances of graphite and fibres. (r=2.27 g/cm3) and dgr(m2)= 3.35A Diameter (mm)
PC%)
s,,,,
‘ap (g/cm 3,
‘mat* (g/cm 3,
svap. (m2/g)
pa *. (4)
10
2.02
2.20
0.198
10.2
I axis /I axis
168 193
23 23
12.1 10.6
106 92
10
2.18
2.25
0.183
3.1
I axis
2700
54
2
7
(m2k)
616
to eliminate some small pores and on the other hand, to enhance some others, giving less numerous hut larger pores and leading to a weaker global porosity. For commercial PSS and P120 fihres, the mean surface area may he compared to values deduced from the apparent density rap, given by the manufacturers (Table 1) by the followmg expression available in the assumption for an infinite rod-like filament with a diameter D:
In the case of PI20 fihre, the increase in carbon layer stiffness involves an elongation and a coalescence of micropores, leading to a global porosity decrease. High specific surface areas deduced by SAXS show that the microporosity is closed. This is a predominant factor in explaining the high potential of carbon fihres to yield adsorbent carbon materials after an activation treatment, that is to say after the opening of pores. l
l
4 Svap. = D
REFERENCES
.pap, The comparison reveals the occurence of a closed microporosity which induced very high values for the specific surface compared to those given by adsorption measurements, particularly for the PS5 fihre. The present study gives the following results: Even if a preferred orientation of carbon layers along the fihre axis is classically observed by WAXS, the generated porosity may he considered as isotropic for PS5 fihre. l
A turbostratic
N. Cohaut, Thesis, University of Orleans, France (1993). *. N. Cohaut, J.M Guet and D. Tchoubar, Ext. Abst. of 2lst Biennial Conf. Buffalo, NY (1993). 3 C. Schiller and J. Mering, C.R Acad. Sci., Paris, B264, 241(1967). 4. R. Perret and W. Ruland , J. Appl. Cryst., 3,535 (1970). 5. J.M Guet, Coal science and Technology 15, Elsevier Science, (1990) p. 103. D. Tchoubar and J. Mering, 1. Appl. Cryst., 2, 128 6. (1969). 7, 0. Glatter and 0. Kratky, Small Angle X-Ray Scattering, Academic Press (1982).
carbon with high specific surface area from 1,4-benzenedimethanol
H.A. Yu, T. KANEKO and S. YOSHJMURA Yoshimura n-Electron Materials Project, ERATO, JRDC Nishhro-317, Numazu, Shizuoka410-03, Japan s. OTANI Department of Material Science and Technology, School of High-Technology for Human Welfare, Tokai University, Nishino-3 17, Numazu, Shizuoka 410-03, Japan (Received 7 December 1995: accepted in revised,form I9 Much
Key Words
1996)
1,4-benzenedimethanol, turbostratic carbon, specific surface area.
The carbon material used for a negative electrode in a high capacity lithium-ion secondary battery can he roughly classified into the following two groups: graphite with high crystallinity, and turhostratic carbon with a large d-spacing (doo2)_ Research efforts [l-2] have made it clear that a secondary cell using the latter carbon material increases generally in its capacity with increase in d-spacing of the carbon material. In the present work, l$henzenedimethanol has been used as the study material to prepare a turhostratic carbon to he examined as a potential candidate for the negative electrode of the lithium-ion secondary battery in the near future.
HOCH2*M20H 1,4-henzenedimethanol Having two -OH groups at its para-positions, 1,4_henzenedimethanol is used as a cross-linking agent in organic reactions. The synthesis of COPNA resin starting from condensed polycyclic aromatic comp-
ounds also uses 1,4-henzenedimethanol as a crosslinking agent [3]. It was found that such COPNA resin synthesized with the use of I ,4_benzenedimethanol as a cross-linking agent can he converted into a form of non-graphitizing carbon by heat-treatment, indifferent to the starting materials of the resin [4-51. This is probably due to the fact that l,4-henzenedimethanol can cross-link COPNA resin with a highly developed three dimensional structure. It should be, however, noted here that 1,4_henzenedimethanol can also polymerize into its own polymer through its intermolecular dehydration in the course of the synthesis of COPNA resin [3]. However, the study of the preparation of 1,4-henzenedimethanol polymer and its carbonization product has not been reported. In the present work, we prepared 1$benzenedimethanol polymer in a medium of concentrated sulfuric acid, and heat-treated the polymer under an argon atmosphere to A number of obtain its carbonization product. carbonization products of 1,4_benzenedimethanol polymer were prepared with different heat-treatment temperatures, and analyzed in their structures by such methods as x-ray diffraction and specific surface area measurement. These results are reported below.