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Formation of flaky graphite single crystals by chemical transport
LETTERS
94
TO THE EDITORS
Figure 1 shows the weight increases of pyrolytic carbons deposited on the various substrates at 600°C and IOTorr of a 50-50 vol. % &HZ-H2 mixture. The electroless-plated nickel substrate is much more active than the other substrates. The densities of the carbon deposits on the electroless-plated nickel substrates were also measured and were found to increase with decreasing gas pressures, e.g., carbon deposited at 50Torr was sooty, whereas that at 10Torr had a density of 2.0 to 2.1 g/cm” and looked slightly lustrous. However, the deposits on the other substrates were sooty and were easily peeled off. Figures 2 and 3 show the surface and the anglelapped section of the carbon deposit on the electroless-plated nickel substrate, respectively. It is observed that the carbon deposit has few cracks and is adherent to the nickel substrate. The adhesive strength between the carbon deposit and the electroless-plated nickel substrate was large, as much as about 20 kg/cm2 as measured with a tensile testing machine. X-ray powder diffraction of the deposit gave a strong peak between 3.37 and 3.39 A, corresponding to the interlayer spacing of the planes in the carbon. It was confirmed by the X-ray diffractometry
Carbon
1971, Vol. 9, pp. 94-96.
Formation
Pergamon
Press.
that the surface structure of electroless-plated nickel was completely amorphous. Therefore, it can be considered that the active properties of this nickel as a dehydrogenating agent must be due to its amorphous structure, i.e. aggregates of lattice defects. Further studies are in progress to understand both the catalytic properties of electroless-plated nickel, e.g. the effect of heat treatment and the kinetics of carbon deposition.
REFERENCES 1. Karu A. E. and Beer M., J. Appl. Phys. 3’7, 2179 (1966). 2. Presland A. E. B. and Walker P. L. Jr., Carbon 7, 1 (1969). 3. Yamamoto Y., Kinzoku Binran, p. 1093. Maruzen Co. (1955). 4. Gutzeit G., Plating46, 1158 (1969). Central Research Laboratory, Hitachi, Ltd., Kokubunji, Tokyo,
TADASHI TETSUO
SAITO GEJYO
Japan
Printed in Great Britain
of Flaky Graphite Single Crystals by Chemical Transport (Received 4 June 1970)
There has been a number of works done to obtain single crystals of graphite by using different crystallization from graphite melt techniques: [l-3], precipitation from carbon-saturated melts of metals[4-91 and decomposition of carbides [lo-121. In the present work, results of deposition of flaky graphite crystals from gaseous phase by the decomposition of aluminum carbide Al& are reported. The experimental procedure was as follows: A mixture of fine powder of aluminum metal and carbon black (a fine particle furnace black) was heat-treated at 1600°C for 2 hr in a graphite crucible (13 X 10 X 30 mm) in an atmosphere of argon, to form aluminum carbide. The resultant aluminum carbide was decomposed in situ at various temperatures of .2000-2500°C under a reduced pressure of about lo-’ Torr. Temperature at the
upper surface of the lid and at the bottom of the crucible were measured by an optical pyrometer. It is considered that the temperature of the upper surface of the lid corresponds to the temperature of deposition and the temperature of the bottom corresponds to that of feed (aluminum carbide). However, the measured surface temperature of the lid is believed to be lower than the true temperature of the inner surface of the lid (the deposition temperature), because no correction was made for the deviation from the black body The observed temperature of the condition. bottom of the crucible is probably not much lower than the true temperature, because the deviation from the black body condition is less than that in the case of the lid. Flaky graphite crystals deposited at the inner surface of the lid of the crucible, only when the crucible was heated at a temperature between 2200 and 2406”C, and the observed temperature at the lid was lower than that at the bottom of the crucible. It was found that an apparent temperature difference of 20-40°C between the lid and bottom
Fig. 2. Electron
micrograph
of surface of carbon deposited on electroless-plated same conditions as in Fig. 1.
nickel substrate at the
Fig. 3. Angle-lapped section of carbon on electroless-plated nickel deposited at the same conditions as in Fig. 1. (a) carbon deposit; (b) electroless-plated nickel; (c) iron base; angle of lapping- IO”.
LETTERS
TO THE
of the crucible was most suitable to obtain the flaky graphite crystals. When the observed temperature at the lid was higher than that at the bottom, no deposit was found on the inside surface of the lid. When the deposition temperature was less than 22OO”C,aluminum carbide was found in the crucible and the deposited graphite was less lustrous. Gas permeability of the graphite crucible was an important factor in obtainix~~ lustrous flakes of graphite. If the crucible of glassy carbon (gas-impermeable) was used, the deposit was only composed of alulnirlul~ carbide. When the lid was loose, the gases escaped very easily out of the crucible and no deposit of any kind could he obtained. A schematical cross-section of the resultant. deposit is shown in Fig. I. Many flakes of graphite deposited with their flaky surfaces (c-plane of graphite) perpendicular to the surface of- the lid. A large graphite flake was deposited covering these flakes. The reason why graphite flakes deposited in such a way, is not clear. Examples of deposited graphite are shown in Fig. 2. A Laue photograph of one of these flakes is shown in Fig. 3. Every flake of deposited graphite was a single crystal. The lattice constant c,, of these flakes was determined by using a powdet method, re”ferring to the inner standard of silicon, as 6.7073 A, and found to be equal to that of natural graphite.
-
95
EDITOR
The formation of the flaky graphite crystals is thought to be caused by the chemical transport of carbon atoms through some gaseous carbide of aluminum, (such as for instance A&C,) from the lower part of the crucible to the fid. in other words, from the raw material to the deposition surface. Chupka, el a1.[13], found a small amount of Al& gas, besides aluminum vapor, in the gaseous decomposition products of aiu~~ir~~~rn carbide Al&,. Gaseous carbide Al&, may be formed by the reaction. ‘LAlz,C:,(s) = 2Al (g) + SAI,C, (g), or by the reaction between aluminum carbon, 2Ai (g) + 2C (s) -- Al&
(g).
(I)
vapor and
(2)
Foster, et n1.[10] reported the single crystal formation of graphite in decomposition of aluminum carbide and Ishii[ 121 also reported the formation of hexagonal plate crystals of graphite in the decomposition of silicon carbide in Freou gas. In these cases, carbon atoms may have been transported in the form of gaseous compounds as in the present work. Although single crystals so far obtained by the present technique were only a few millimeters in size, one can expect to obtam larger crystals with controlled structure by introducing improvements into the present technique.
Graphite flakes
REFERENCES
Fig. 1. Schematic cross-section of graphite crucible showing mutual positions of the deposited graphite flakes and of the raw material Al&.
I. Basset M. J.,f. Phys. Rad. 10,217(1937). 2. Noda T. and Matsuoka H., k’ngyo Kagaku Zmshi 63,456 (1960). 3. NodaT. and Kato H., Carbon 3,289 (1965). 4. Niwa K. and Shimaoka G., J. Metal. 9, 431 (1957). 5. Li P. C., Nature 19!2,864 (1961). 6. Tulloch H. J. C. and Young D. A., Nature 211, 730(1966). 7. Austerman S. B., Myron S. M. and Wagner J. W., Carbon 5,549 (1967).
96
LETTERS
TO THE
8. Noda T., Sumiyoshi Y. and Ito N., Carbon 6, 831 (1968). 9. Yoshida H., Private communication. 10. Foster L. M., Long G. and Stumpf H. C., Am. Mineralogist 43,285 (1958).
EDITOR
11. Badami D. V., Carbon 3,53 (1965). 12. Ishii T., Denki Kagaku 35,688 (1967). 13. Chupka W. A., Berkowitz J., Giese C. F. and Inghram M. G.,J. Phys. Chem. 62,611 (1958).
94
TO THE EDITORS
Figure 1 shows the weight increases of pyrolytic carbons deposited on the various substrates at 600°C and IOTorr of a 50-50 vol. % &HZ-H2 mixture. The electroless-plated nickel substrate is much more active than the other substrates. The densities of the carbon deposits on the electroless-plated nickel substrates were also measured and were found to increase with decreasing gas pressures, e.g., carbon deposited at 50Torr was sooty, whereas that at 10Torr had a density of 2.0 to 2.1 g/cm” and looked slightly lustrous. However, the deposits on the other substrates were sooty and were easily peeled off. Figures 2 and 3 show the surface and the anglelapped section of the carbon deposit on the electroless-plated nickel substrate, respectively. It is observed that the carbon deposit has few cracks and is adherent to the nickel substrate. The adhesive strength between the carbon deposit and the electroless-plated nickel substrate was large, as much as about 20 kg/cm2 as measured with a tensile testing machine. X-ray powder diffraction of the deposit gave a strong peak between 3.37 and 3.39 A, corresponding to the interlayer spacing of the planes in the carbon. It was confirmed by the X-ray diffractometry
Carbon
1971, Vol. 9, pp. 94-96.
Formation
Pergamon
Press.
that the surface structure of electroless-plated nickel was completely amorphous. Therefore, it can be considered that the active properties of this nickel as a dehydrogenating agent must be due to its amorphous structure, i.e. aggregates of lattice defects. Further studies are in progress to understand both the catalytic properties of electroless-plated nickel, e.g. the effect of heat treatment and the kinetics of carbon deposition.
REFERENCES 1. Karu A. E. and Beer M., J. Appl. Phys. 3’7, 2179 (1966). 2. Presland A. E. B. and Walker P. L. Jr., Carbon 7, 1 (1969). 3. Yamamoto Y., Kinzoku Binran, p. 1093. Maruzen Co. (1955). 4. Gutzeit G., Plating46, 1158 (1969). Central Research Laboratory, Hitachi, Ltd., Kokubunji, Tokyo,
TADASHI TETSUO
SAITO GEJYO
Japan
Printed in Great Britain
of Flaky Graphite Single Crystals by Chemical Transport (Received 4 June 1970)
There has been a number of works done to obtain single crystals of graphite by using different crystallization from graphite melt techniques: [l-3], precipitation from carbon-saturated melts of metals[4-91 and decomposition of carbides [lo-121. In the present work, results of deposition of flaky graphite crystals from gaseous phase by the decomposition of aluminum carbide Al& are reported. The experimental procedure was as follows: A mixture of fine powder of aluminum metal and carbon black (a fine particle furnace black) was heat-treated at 1600°C for 2 hr in a graphite crucible (13 X 10 X 30 mm) in an atmosphere of argon, to form aluminum carbide. The resultant aluminum carbide was decomposed in situ at various temperatures of .2000-2500°C under a reduced pressure of about lo-’ Torr. Temperature at the
upper surface of the lid and at the bottom of the crucible were measured by an optical pyrometer. It is considered that the temperature of the upper surface of the lid corresponds to the temperature of deposition and the temperature of the bottom corresponds to that of feed (aluminum carbide). However, the measured surface temperature of the lid is believed to be lower than the true temperature of the inner surface of the lid (the deposition temperature), because no correction was made for the deviation from the black body The observed temperature of the condition. bottom of the crucible is probably not much lower than the true temperature, because the deviation from the black body condition is less than that in the case of the lid. Flaky graphite crystals deposited at the inner surface of the lid of the crucible, only when the crucible was heated at a temperature between 2200 and 2406”C, and the observed temperature at the lid was lower than that at the bottom of the crucible. It was found that an apparent temperature difference of 20-40°C between the lid and bottom
Fig. 2. Electron
micrograph
of surface of carbon deposited on electroless-plated same conditions as in Fig. 1.
nickel substrate at the
Fig. 3. Angle-lapped section of carbon on electroless-plated nickel deposited at the same conditions as in Fig. 1. (a) carbon deposit; (b) electroless-plated nickel; (c) iron base; angle of lapping- IO”.
LETTERS
TO THE
of the crucible was most suitable to obtain the flaky graphite crystals. When the observed temperature at the lid was higher than that at the bottom, no deposit was found on the inside surface of the lid. When the deposition temperature was less than 22OO”C,aluminum carbide was found in the crucible and the deposited graphite was less lustrous. Gas permeability of the graphite crucible was an important factor in obtainix~~ lustrous flakes of graphite. If the crucible of glassy carbon (gas-impermeable) was used, the deposit was only composed of alulnirlul~ carbide. When the lid was loose, the gases escaped very easily out of the crucible and no deposit of any kind could he obtained. A schematical cross-section of the resultant. deposit is shown in Fig. I. Many flakes of graphite deposited with their flaky surfaces (c-plane of graphite) perpendicular to the surface of- the lid. A large graphite flake was deposited covering these flakes. The reason why graphite flakes deposited in such a way, is not clear. Examples of deposited graphite are shown in Fig. 2. A Laue photograph of one of these flakes is shown in Fig. 3. Every flake of deposited graphite was a single crystal. The lattice constant c,, of these flakes was determined by using a powdet method, re”ferring to the inner standard of silicon, as 6.7073 A, and found to be equal to that of natural graphite.
-
95
EDITOR
The formation of the flaky graphite crystals is thought to be caused by the chemical transport of carbon atoms through some gaseous carbide of aluminum, (such as for instance A&C,) from the lower part of the crucible to the fid. in other words, from the raw material to the deposition surface. Chupka, el a1.[13], found a small amount of Al& gas, besides aluminum vapor, in the gaseous decomposition products of aiu~~ir~~~rn carbide Al&,. Gaseous carbide Al&, may be formed by the reaction. ‘LAlz,C:,(s) = 2Al (g) + SAI,C, (g), or by the reaction between aluminum carbon, 2Ai (g) + 2C (s) -- Al&
(g).
(I)
vapor and
(2)
Foster, et n1.[10] reported the single crystal formation of graphite in decomposition of aluminum carbide and Ishii[ 121 also reported the formation of hexagonal plate crystals of graphite in the decomposition of silicon carbide in Freou gas. In these cases, carbon atoms may have been transported in the form of gaseous compounds as in the present work. Although single crystals so far obtained by the present technique were only a few millimeters in size, one can expect to obtam larger crystals with controlled structure by introducing improvements into the present technique.
Graphite flakes
REFERENCES
Fig. 1. Schematic cross-section of graphite crucible showing mutual positions of the deposited graphite flakes and of the raw material Al&.
I. Basset M. J.,f. Phys. Rad. 10,217(1937). 2. Noda T. and Matsuoka H., k’ngyo Kagaku Zmshi 63,456 (1960). 3. NodaT. and Kato H., Carbon 3,289 (1965). 4. Niwa K. and Shimaoka G., J. Metal. 9, 431 (1957). 5. Li P. C., Nature 19!2,864 (1961). 6. Tulloch H. J. C. and Young D. A., Nature 211, 730(1966). 7. Austerman S. B., Myron S. M. and Wagner J. W., Carbon 5,549 (1967).
96
LETTERS
TO THE
8. Noda T., Sumiyoshi Y. and Ito N., Carbon 6, 831 (1968). 9. Yoshida H., Private communication. 10. Foster L. M., Long G. and Stumpf H. C., Am. Mineralogist 43,285 (1958).
EDITOR
11. Badami D. V., Carbon 3,53 (1965). 12. Ishii T., Denki Kagaku 35,688 (1967). 13. Chupka W. A., Berkowitz J., Giese C. F. and Inghram M. G.,J. Phys. Chem. 62,611 (1958).