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Effective Debye parameter of graphitized cokes
Cmbon,1975. Vol. 13. pp.307-308. Pergamon Press.
Printed in Great Britain
EFFECTIVE DEBYE PARAMETER GRAPHITIZED COKES
OF
M. INAGAKI Faculty of Engineering, Nagoya University, Furo-cho, Chikusa-ku,Nagoya 464,Japan (Received 10December
1974)
Abstract-The effective Debye parameter &is obtained from the intensities of the (OOJ)diffraction lines measured for a number of kinds of coke heat treated to temperatures between 24.50and 3000”$.The value of B,,‘ decrease with decreasing average unit-cell height L. Cokes with various textures when r?, 5 6.75 A have different values of B.,. QS coke, prepared by carbonization of quinolin-soluble pitch in a magnetic field, shows the smallest value of B,,,. Needle-like cokes give slightly larger values, and Gilsonite coke, which has an onion-like layer-plane texture, gave the largest value (about twice that of QS coke). B,,, depends on out-of-plane (c-axis) displacements of carbon atoms, and the range of values observed seemed to be related to a decrease in the static displacement component with increasing texture. The effective Debve B,, can be used as a measure of layer-plane perfection for . oarameter . quell-~rap~iti~edcarbons. 1.INTRODUCTION
21 the effective Debye parameter BErrhas been shown to be a useful structural parameter for the c~aracter~zation of crystalline powders. For natural graphite, the Bcfrvalue increases remarkably as a result of grinding[3]. The c-axis mean lattice constant G (or the mean interlayer spacing &/2) is widely used to characterize the structure of disordered carbons in the course of the graphitization. However, the author has shown[4] that the intensity ratio ~(~4)~~(002) of the (004) and (002) layer-plane diffraction lines differs significantly for various carbons which have the same L value but were heat treated at different temperature. This intensity ratio can be measured over a wide range of degrees of graphitization, but elaborate corrections to the observed diffraction intensity are necessary. The effective Debye parameter can be determined more easily than the intensity ratio if high order (OOI) lines are present. Therefore, this parameter is suitable for comparison of the detailed structural state of well-graphitized carbons. In the present work, the values of B,rr were determined for a number of kinds of coke heat treated at high temperature, The experimental results are discussed in relationship to the unit cell height L and to the texture of the cokes. In previous
was calculated from the observed slope of a plot of log(l,~,/l,~,,,) against sin* 0/h’ according to the relation.
papers[l,
foba is the observed integrated intensity, Ifhcuris the theoretical intensity including Lorentz-polarisation factor, structure factor and multiplicity, and k is a scale factor. For all samples, the average unit cell height & was determined from the (004) line and using silicon as an internal standard. 3. RESULTSANDDISCUSSION
In Fig. 1, the relationships between log(lobS/lthen,)and sin’ @/A* observed on various cokes are shown. Figure 2 shows the dependence on heat treatment temperature for Kendal coke. The values of &t for the cokes are plotted as a function of c0 in Fig. 3. The experimental error in B,rr was estimated from the scatter of the experimental points for the (002), (004), (006) and (008) lines. Poorly-graphitized samples give relatively large error (about rtO.2) in B,n. This is caused by absence of the (008) line and also by poor resolution of the (006) line from the neighbouring (112) line. For the
2. EXPERIMENTAL Samples of different types of coke were heat-treated at various temperatures between 2450 and 3OOOYin flowing
nitrogen. All samples were crushed in an agate mortar for the X-ray diffraction studies. Because grinding has been known to increase the B,ff-value[2, 31, it was done for as short a time as possible (less than 1 min). For each sample, the integrated intensities of the layer-plane diffraction lines (002), (004), (006), (and (008), whenever possible), were measured by using a scintillation counter and pulse height analyser. The integrated intensity was obtained by subtracting the background intensity from the total intensity scanned over a suitable range of Bragg angle. The effective Debye parameter Berr
Fig. 1. The relationships between log (lobs/lfheor) and (sin20/h*)for various cokes heat-treated at high temperature.
307 CAR Vol. 13, No.4-D
308
M.
00
t
*
@I
26OO’C. A, IO min
\
I
INAGAKI
0.3
0.2
&B/X2 Fig 2. Therelationshipsbetweenlog(lob./lfhcor) and (sin*e/A’)for
Kendalcokeheat-treatedat varioustemperatures. 9.0
-
6.0
-
7.0 -
6.0 -
5.0 4 ', 4.0 @I= 3.0 -
2.0 -
Ia
’
6.72
6.71
*
”
6.73
”
6.74 0 c,. A
” 6.75
’
6.76
0
’ 6.77
Fig. 3. The relation between the average unit-cell height L and the effective Debye parameter BCRfor various cokes: 8, Gilsonite coke;~,Texascoke;A,Wilmingtoncoke;0,GLcoke;~,Premium coke; V, Kaiser-Aluminum coke; A, Kendal coke; 0, Conoco No. 1 coke; 0, polyvinylchloride coke; $, QS coke. samples (E, < ca. 6.75 A), however, the are determined with a relatively small error
well-graphitized
&t-values (about kO.02). The value of B,tr decreases with increasing heat treatment temperature (Fig. 2); in other words, the Berr-value decreases rapidly with decfease of the cospacing (Fig. 3). Below about 6*76A, however, the changes become small and for each coke B,tt seems to approach a specific value strongly dependent on the tPrivate communication by Dr. Y. Hishiyama.
texture of the coke. The needle-like Conoco No. 1 and Kendal cokes have relatively small values of B,tr. Polyvinylchloride coke also has a small value of Bert; it has been confirmed by microscopic observations that this coke has a similar needle-like texture as Conoco No. 1. On the other hand, Texas and Wilmington cokes have relatively large value of Berr. The strong dependence of the Ben-value on texture can be understood by comparing QS coke with Gilsonite coke, both heat-treated at 3000% The QS coke, which was prepared by carbonization of a quinolin-soluble pitch in a magnetic field [5] and which has been found to show a very high value of magnetoresistance and a high degree of preferred orientation,t shows the smallest value of B,tt. Gilsonite coke, which has a spherically symmetric onion-like texture [6], gives the largest value of B,tt. Grinding of natural graphite has an effect opposite to that of graphitization. The &-value was found to increase rapidly in the first stages of grinding without any appreciable change in the c,-spacing, and then both B.R and E, increased[3] with continued grinding. The parameter B,tr must be related to the mean square displacement of atoms from their average positions in the equilibrium structure[7]. However, the mean square displacement is considered to consist of two components, the dynamic and the static displacements[7]. The former is the thermal vibration of atoms around the average position and the latter is due to defects in the structure. There have been some attempts to separate the thermal vibration component from the observed B,u value[8]. However, such a separation involves significant uncertainties, Although the thermal vibration component may be assumed to have a unique value for ideally perfect graphite, this value is not known. Furthermore, the relationship between the dynamic and static components is not clear. Therefore, the author prefers to use the observed B,rr value itself as a structural parameter. The value of B,rr obtained from the (001) lines depends on the out-of-plane (c-axis) displacements of the carbon atoms and therefore can be used as a measure of the perfection of the layer planes in well-graphitized carbons.
REFERENCES
I. Inagaki M., Furuhashi H., Ozeki T., Mugishima H. and Naka S., J. Mat. Sci. 6, 1520(1971). 2. Inagaki M., Furuhashi H., Ozeki T. and Naka S., J. Mat. Sci. 8, 312 (1973). 3. Inaaaki M.. Muaishima H. and Hosokawa K., Tanso 1973(No. 74),76. 4. Inagaki M., J. Appl. Cryst.5, 295 (1972). 5. Imamura K.. Honda H. and Kakiyama H., Tanso 1974(No. 76), 20. 6. InagakiM.,TamaiY.andNakaS., Tanso 1973(No. 75), 118. 7. International Tables for X-ray Crystallography, Vol. III, p. 233. The Kynoch Press, Birmingham (1962). 8. Shiraishi M., Kobayashi K. and Toyoda S., Carbon 10, 553 (1972).
Printed in Great Britain
EFFECTIVE DEBYE PARAMETER GRAPHITIZED COKES
OF
M. INAGAKI Faculty of Engineering, Nagoya University, Furo-cho, Chikusa-ku,Nagoya 464,Japan (Received 10December
1974)
Abstract-The effective Debye parameter &is obtained from the intensities of the (OOJ)diffraction lines measured for a number of kinds of coke heat treated to temperatures between 24.50and 3000”$.The value of B,,‘ decrease with decreasing average unit-cell height L. Cokes with various textures when r?, 5 6.75 A have different values of B.,. QS coke, prepared by carbonization of quinolin-soluble pitch in a magnetic field, shows the smallest value of B,,,. Needle-like cokes give slightly larger values, and Gilsonite coke, which has an onion-like layer-plane texture, gave the largest value (about twice that of QS coke). B,,, depends on out-of-plane (c-axis) displacements of carbon atoms, and the range of values observed seemed to be related to a decrease in the static displacement component with increasing texture. The effective Debve B,, can be used as a measure of layer-plane perfection for . oarameter . quell-~rap~iti~edcarbons. 1.INTRODUCTION
21 the effective Debye parameter BErrhas been shown to be a useful structural parameter for the c~aracter~zation of crystalline powders. For natural graphite, the Bcfrvalue increases remarkably as a result of grinding[3]. The c-axis mean lattice constant G (or the mean interlayer spacing &/2) is widely used to characterize the structure of disordered carbons in the course of the graphitization. However, the author has shown[4] that the intensity ratio ~(~4)~~(002) of the (004) and (002) layer-plane diffraction lines differs significantly for various carbons which have the same L value but were heat treated at different temperature. This intensity ratio can be measured over a wide range of degrees of graphitization, but elaborate corrections to the observed diffraction intensity are necessary. The effective Debye parameter can be determined more easily than the intensity ratio if high order (OOI) lines are present. Therefore, this parameter is suitable for comparison of the detailed structural state of well-graphitized carbons. In the present work, the values of B,rr were determined for a number of kinds of coke heat treated at high temperature, The experimental results are discussed in relationship to the unit cell height L and to the texture of the cokes. In previous
was calculated from the observed slope of a plot of log(l,~,/l,~,,,) against sin* 0/h’ according to the relation.
papers[l,
foba is the observed integrated intensity, Ifhcuris the theoretical intensity including Lorentz-polarisation factor, structure factor and multiplicity, and k is a scale factor. For all samples, the average unit cell height & was determined from the (004) line and using silicon as an internal standard. 3. RESULTSANDDISCUSSION
In Fig. 1, the relationships between log(lobS/lthen,)and sin’ @/A* observed on various cokes are shown. Figure 2 shows the dependence on heat treatment temperature for Kendal coke. The values of &t for the cokes are plotted as a function of c0 in Fig. 3. The experimental error in B,rr was estimated from the scatter of the experimental points for the (002), (004), (006) and (008) lines. Poorly-graphitized samples give relatively large error (about rtO.2) in B,n. This is caused by absence of the (008) line and also by poor resolution of the (006) line from the neighbouring (112) line. For the
2. EXPERIMENTAL Samples of different types of coke were heat-treated at various temperatures between 2450 and 3OOOYin flowing
nitrogen. All samples were crushed in an agate mortar for the X-ray diffraction studies. Because grinding has been known to increase the B,ff-value[2, 31, it was done for as short a time as possible (less than 1 min). For each sample, the integrated intensities of the layer-plane diffraction lines (002), (004), (006), (and (008), whenever possible), were measured by using a scintillation counter and pulse height analyser. The integrated intensity was obtained by subtracting the background intensity from the total intensity scanned over a suitable range of Bragg angle. The effective Debye parameter Berr
Fig. 1. The relationships between log (lobs/lfheor) and (sin20/h*)for various cokes heat-treated at high temperature.
307 CAR Vol. 13, No.4-D
308
M.
00
t
*
@I
26OO’C. A, IO min
\
I
INAGAKI
0.3
0.2
&B/X2 Fig 2. Therelationshipsbetweenlog(lob./lfhcor) and (sin*e/A’)for
Kendalcokeheat-treatedat varioustemperatures. 9.0
-
6.0
-
7.0 -
6.0 -
5.0 4 ', 4.0 @I= 3.0 -
2.0 -
Ia
’
6.72
6.71
*
”
6.73
”
6.74 0 c,. A
” 6.75
’
6.76
0
’ 6.77
Fig. 3. The relation between the average unit-cell height L and the effective Debye parameter BCRfor various cokes: 8, Gilsonite coke;~,Texascoke;A,Wilmingtoncoke;0,GLcoke;~,Premium coke; V, Kaiser-Aluminum coke; A, Kendal coke; 0, Conoco No. 1 coke; 0, polyvinylchloride coke; $, QS coke. samples (E, < ca. 6.75 A), however, the are determined with a relatively small error
well-graphitized
&t-values (about kO.02). The value of B,tr decreases with increasing heat treatment temperature (Fig. 2); in other words, the Berr-value decreases rapidly with decfease of the cospacing (Fig. 3). Below about 6*76A, however, the changes become small and for each coke B,tt seems to approach a specific value strongly dependent on the tPrivate communication by Dr. Y. Hishiyama.
texture of the coke. The needle-like Conoco No. 1 and Kendal cokes have relatively small values of B,tr. Polyvinylchloride coke also has a small value of Bert; it has been confirmed by microscopic observations that this coke has a similar needle-like texture as Conoco No. 1. On the other hand, Texas and Wilmington cokes have relatively large value of Berr. The strong dependence of the Ben-value on texture can be understood by comparing QS coke with Gilsonite coke, both heat-treated at 3000% The QS coke, which was prepared by carbonization of a quinolin-soluble pitch in a magnetic field [5] and which has been found to show a very high value of magnetoresistance and a high degree of preferred orientation,t shows the smallest value of B,tt. Gilsonite coke, which has a spherically symmetric onion-like texture [6], gives the largest value of B,tt. Grinding of natural graphite has an effect opposite to that of graphitization. The &-value was found to increase rapidly in the first stages of grinding without any appreciable change in the c,-spacing, and then both B.R and E, increased[3] with continued grinding. The parameter B,tr must be related to the mean square displacement of atoms from their average positions in the equilibrium structure[7]. However, the mean square displacement is considered to consist of two components, the dynamic and the static displacements[7]. The former is the thermal vibration of atoms around the average position and the latter is due to defects in the structure. There have been some attempts to separate the thermal vibration component from the observed B,u value[8]. However, such a separation involves significant uncertainties, Although the thermal vibration component may be assumed to have a unique value for ideally perfect graphite, this value is not known. Furthermore, the relationship between the dynamic and static components is not clear. Therefore, the author prefers to use the observed B,rr value itself as a structural parameter. The value of B,rr obtained from the (001) lines depends on the out-of-plane (c-axis) displacements of the carbon atoms and therefore can be used as a measure of the perfection of the layer planes in well-graphitized carbons.
REFERENCES
I. Inagaki M., Furuhashi H., Ozeki T., Mugishima H. and Naka S., J. Mat. Sci. 6, 1520(1971). 2. Inagaki M., Furuhashi H., Ozeki T. and Naka S., J. Mat. Sci. 8, 312 (1973). 3. Inaaaki M.. Muaishima H. and Hosokawa K., Tanso 1973(No. 74),76. 4. Inagaki M., J. Appl. Cryst.5, 295 (1972). 5. Imamura K.. Honda H. and Kakiyama H., Tanso 1974(No. 76), 20. 6. InagakiM.,TamaiY.andNakaS., Tanso 1973(No. 75), 118. 7. International Tables for X-ray Crystallography, Vol. III, p. 233. The Kynoch Press, Birmingham (1962). 8. Shiraishi M., Kobayashi K. and Toyoda S., Carbon 10, 553 (1972).