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Formation of diamond in the system of Ag2CO3 and graphite at high pressure and high temperatures
Journal of Crystal Growth 213 (2000) 411}414
Priority communication
Formation of diamond in the system of Ag CO and graphite at high pressure and high temperatures Liling Sun , Minoru Akaishi *, Shinobu Yamaoka Core Research for Evolutional Science and Technology (CREST) of Japan Science and Technology (JST), c/o NIRIM, Japan National Institute for Research in Inorganic Materials (NIRIM), 1-1 Namiki, Tsukuba-shi, Ibaraki 305-0044, Japan Received 3 December 1999; accepted 14 March 2000 Communicated by T. Nishinaga
Abstract Diamonds were reproductively formed from graphite in the presence of Ag CO and Ag O at 7.7 GPa and 1500}20003C for 0.5}27 h. The complete conversion from graphite to diamond was con"rmed in the samples obtained at temperatures above 18003C for 0.5}2 h, but no diamond was detected in the system of Ag and graphite under these conditions. To make clear the mechanism of diamond formation from graphite}Ag CO system, decomposition temperatures of Ag CO and Ag O were investigated at 7.7 GPa and it was found that they were 1000 and 12003C, respectively. Then, the decomposition products of Ag, CO and O were present instead of the carbonate in the diamond-forming condition. Since O should react with graphite to form CO in the HP}HT condition, our experi mental results strongly suggest that #uid CO has a strong catalytic action for the formation of diamond from graphite. 2000 Elsevier Science B.V. All rights reserved. Keywords: Formation of diamond; High pressure and high temperature; CO #uid
As diamond-forming solvent-catalysts, 12 transition metals including iron, cobalt and nickel were "rst reported by General Electric researchers four decades ago [1]. In the 1990s, non-metallic compounds such as carbonates, sulfates and hydroxides were added to the family of solvent-catalysts [2,3]. On the other hand, it is believed that natural diamonds were crystallized in the magma of upper or lower mantle under high pressure}high temperature (HP}HT) conditions in the diamond * Corresponding author. National Institute for Research in Inorganic Materials (NIRIM), 1-1 Namiki, Tsukuba-shi, Ibaraki 305-0044, Japan. Tel.: #81-298-51-3354, ext 501; fax: #81298-51-2768. E-mail address: [email protected] (M. Akaishi).
stable region [4}6]. Fluid phases composed of carbon, oxygen and hydrogen, generally called C}O}H #uids, are thought to have played an important role in the formation of natural diamonds because gases such as water, hydrogen, carbon dioxide, methane, etc. were detected as inclusions in them [7}10]. In this context, we carried out synthesis experiments of diamond from the system of graphite and C}O}H #uids in the diamond stable region at 7.7 GPa, and con"rmed that well-developed octahedral diamond crystals could be nucleated spontaneously above 14003C [11]. Also, diamond crystals were successfully synthesized from graphite in the presence of water which is the intermediate component of the C}O}H #uids [12]. On the other
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L. Sun et al. / Journal of Crystal Growth 213 (2000) 411}414
hand, CO is one of the end components of the C}O}H #uids, and provides oxidizing property to the #uid. It is very interesting to investigate the catalytic action of CO for diamond formation from the viewpoint of oxidized #uid condition. It is well known that Ag CO can decompose into Ag, CO and O above 2203C at ambient pressure [13]. Besides, O formed by the decomposition reacts with graphite and forms CO at HP}HT conditions [14]. Therefore, to investigate the catalytic action of CO for the transformation from graphite to dia mond, Ag CO was used as a source material for providing CO atmosphere. The carbonate was treated in a graphite capsule at HP}HT in the thermodynamically stable region of diamond, and change of the capsule was examined after the treatment. Besides, to check the catalytic ability of Ag O and Ag, they were also treated in the capsule. The starting materials were Ag CO (99% pu rity, Merck Japan Co. Ltd.), Ag O (99% purity, Wako Pure Chemical Industries), Ag wire with an outer diameter of 4 mm (99.99% purity, Furuya Metal Co. Ltd.) and graphite rods (high-purity grade, Tokai Carbon Company). No diamondforming metallic impurities such as Fe, Co and Ni were detected in the Ag CO and Ag O by emis sion spectrochemical analysis. The graphite rod was machined into a cylindrical capsule as shown in Fig. 1. The carbonate or oxide powder was
Fig. 1. Sample assembly for synthesis of diamond: (1) pyrophyllite sleeve, (2) steel ring, (3) Ta foil, (4) Mo outer capsule, (5) Mo inner capsule, (6) graphite heater, (7) NaCl}20 wt% ZrO pow der compact, (8) NaCl}10 wt% ZrO powder compact, (9) graphite capsule, (10) Ag CO , Ag O or Ag.
packed into the capsule, which was then capped with a graphite disk. Ag wire was also packed into the capsule by a similar way to that of the powder. Then the capsule was inserted into a Mo doublecapsule similar to that used in the previous experiment [11]. High-pressure experiments were carried out by using a belt-type high-pressure apparatus with a bore diameter of 32 mm. Pressure and temperature measurements were done by the same method as reported previously [12]. Samples were treated at HP}HT conditions of 7.7 GPa and 1500}20003C for 0.5}27 h. Then, they were taken out from the capsule and investigated using an optical microscope, scanning electron microscope (SEM), X-ray di!ractometer and Raman spectrometer. To investigate the decomposition behavior of Ag CO and Ag O at 7.7 GPa, Ag CO and Ag O were treated at 1000 and 12003C for 0.5 h, respectively, using the same sample assembly as shown in Fig. 1. Although the graphite capsule remained unreactive, it was clear from X-ray diffraction patterns that Ag CO decomposed into Ag O and CO , and Ag O decomposed into Ag and O as shown in Fig. 2. These results show that Ag CO was completely decomposed to Ag, CO and O in the present synthesis experiments per formed at 1500}20003C and 7.7 GPa. To investigate a catalytic action of these chemical species for synthesis of diamond from graphite, samples of graphite and Ag CO , Ag O or Ag were treated at HP}HT conditions of 1500}20003C and 7.7 GPa for 0.5}27 h using the sample assembly shown in Fig. 1. In the system of graphite and Ag CO , graphite capsules were completely converted to diamond in the experiments at 1800, 1900 and 20003C for 2, 0.5 and 0.5 h, respectively. To con"rm diamond formation at lower temperatures in this system, samples were treated at 1500}17003C for various holding times. At 17003C, diamond was not detected in the sample after being treated for 2 h, but was detected inside the graphite capsule in the experiment of 5 h. At 1600 and 15003C, diamonds were partly formed in the center portion of the innner wall of the graphite capsule in the experiments of 12 and 27 h, respectively. To investigate the detailed morphology of diamond crystals obtained in the system of Ag CO
L. Sun et al. / Journal of Crystal Growth 213 (2000) 411}414
413
Fig. 2. X-ray di!raction patterns of Ag CO and Ag O after the treatment of 7.7 GPa and (a) 10003C and (b) 12003C for 0.5 h, respectively.
and graphite, the crystals were observed by SEM. On the cross section of the samples obtained at 1800}20003C and 7.7 GPa for 0.5}2 h, diamond crystals with columnar structure were observed elongated along the axis parallel to the compressed direction as shown in Fig. 3. The elongated crystals were 200}700 lm in length which was 2}7 times greater than the width. This morphology clearly shows that the diamonds were grown from the solution with high supersaturation of carbon. On the other hand, in the samples obtained below 17003C, diamond crystals had a morphology of
well-developed +1 1 1, faces with smooth and #at surfaces although the size was limited to 20 lm as shown in Fig. 4. This morphology clearly shows that the diamonds were crystallized from the solution with moderate supersaturation of carbon. Since it is considered that the excess oxygen decomposed from Ag O reacts with graphite to form CO at HP}HT conditions [14], the CO thus formed must also be a #uid or solvent in the present system in which graphite dissolves and diamond crystallizes. This is also supported from the experimental results that when Ag O was used as
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L. Sun et al. / Journal of Crystal Growth 213 (2000) 411}414
To clarify the diamond-formation mechanism in the system of graphite and Ag CO , pure Ag was loaded into the graphite capsule and treated at the highest temperature of 20003C for 0.5 h in the present study. Graphite did not react with molten Ag and no diamond was detected. This result shows that Ag does work as a diamond-forming catalyst. As described above, diamond crystals were synthesized at 1500}20003C and 7.7 GPa for 0.5}27 h in the systems of graphite and Ag CO or Ag O but no diamonds could be formed from graphite in the presence of Ag. Because at these HP}HT conditions, the carbonate was completely decomposed into Ag, CO and O , and O eventually became CO by the reaction of graphite, the present experi mental results strongly suggest that CO acts as the catalytic solvent for the transformation from graphite to diamond.
Acknowledgements Fig. 3. Secondary electron images (SEI) of the diamond crystals obtained at 7.7 GPa and 18003C for 2 h. (a) overall view, (b) enlargement of (a).
The authors wish to thank Mr. Y. Yajima (NIRIM) for the emission spectrochemical analysis.
References
Fig. 4. SEI of the diamond crystals obtained at 7.7 GPa and 16003C for 12 h.
a starting material instead of Ag CO , diamonds were clearly formed under the same P}¹ conditions as those in Ag CO .
[1] H.P. Bovenkerk, F.P. Bundy, H.T. Hall, H.M. Strong, R.H. Wentorf Jr., Nature 184 (1959) 1094. [2] M. Akaishi, H. Kanda, S. Yamaoka, J. Crystal Growth 104 (1990) 578. [3] M. Akaishi, H. Kanda, S. Yamaoka, Jpn. J. Appl. Phys. 29 (1990) L1172. [4] H.O.A. Meyer, Am. Miner. 70 (1985) 344. [5] H.O.A. Meyer, in: P.H. Nixon (Ed.), Mantle Xenoliths, Wiley, Chichester, England, 1987, p. 502. [6] F.R. Boyd, J.J. Gurney, S.H. Richardson, Nature 315 (1985) 387. [7] C.E. Melton, A.A. Giardini, Am. Miner. 59 (1974) 775. [8] C.E. Melton, A.A. Giardini, Nature 263 (1976) 309. [9] M. Schrauder, O. Navon, Nature 365 (1993) 42. [10] O. Navon, I.D. Hutcheon, G.R. Rossman, G.J. Wasserburg, Nature 335 (1988) 784. [11] M. Akaishi, S. Yamaoka, J. Crystal Growth 209 (2000) 999. [12] S.M. Hong, M. Akaishi, S. Yamaoka, J. Crystal Growth 200 (1999) 326. [13] The Merck Index, in: Paul G. Stecher (Ed.), Merk & Co., Inc., Rathway, NJ, USA, 1968, p. 947. [14] P. Deines, Geochem. Cosmochim. Acta 44 (1980) 943.
Priority communication
Formation of diamond in the system of Ag CO and graphite at high pressure and high temperatures Liling Sun , Minoru Akaishi *, Shinobu Yamaoka Core Research for Evolutional Science and Technology (CREST) of Japan Science and Technology (JST), c/o NIRIM, Japan National Institute for Research in Inorganic Materials (NIRIM), 1-1 Namiki, Tsukuba-shi, Ibaraki 305-0044, Japan Received 3 December 1999; accepted 14 March 2000 Communicated by T. Nishinaga
Abstract Diamonds were reproductively formed from graphite in the presence of Ag CO and Ag O at 7.7 GPa and 1500}20003C for 0.5}27 h. The complete conversion from graphite to diamond was con"rmed in the samples obtained at temperatures above 18003C for 0.5}2 h, but no diamond was detected in the system of Ag and graphite under these conditions. To make clear the mechanism of diamond formation from graphite}Ag CO system, decomposition temperatures of Ag CO and Ag O were investigated at 7.7 GPa and it was found that they were 1000 and 12003C, respectively. Then, the decomposition products of Ag, CO and O were present instead of the carbonate in the diamond-forming condition. Since O should react with graphite to form CO in the HP}HT condition, our experi mental results strongly suggest that #uid CO has a strong catalytic action for the formation of diamond from graphite. 2000 Elsevier Science B.V. All rights reserved. Keywords: Formation of diamond; High pressure and high temperature; CO #uid
As diamond-forming solvent-catalysts, 12 transition metals including iron, cobalt and nickel were "rst reported by General Electric researchers four decades ago [1]. In the 1990s, non-metallic compounds such as carbonates, sulfates and hydroxides were added to the family of solvent-catalysts [2,3]. On the other hand, it is believed that natural diamonds were crystallized in the magma of upper or lower mantle under high pressure}high temperature (HP}HT) conditions in the diamond * Corresponding author. National Institute for Research in Inorganic Materials (NIRIM), 1-1 Namiki, Tsukuba-shi, Ibaraki 305-0044, Japan. Tel.: #81-298-51-3354, ext 501; fax: #81298-51-2768. E-mail address: [email protected] (M. Akaishi).
stable region [4}6]. Fluid phases composed of carbon, oxygen and hydrogen, generally called C}O}H #uids, are thought to have played an important role in the formation of natural diamonds because gases such as water, hydrogen, carbon dioxide, methane, etc. were detected as inclusions in them [7}10]. In this context, we carried out synthesis experiments of diamond from the system of graphite and C}O}H #uids in the diamond stable region at 7.7 GPa, and con"rmed that well-developed octahedral diamond crystals could be nucleated spontaneously above 14003C [11]. Also, diamond crystals were successfully synthesized from graphite in the presence of water which is the intermediate component of the C}O}H #uids [12]. On the other
0022-0248/00/$ - see front matter 2000 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 2 - 0 2 4 8 ( 0 0 ) 0 0 4 0 8 - 5
412
L. Sun et al. / Journal of Crystal Growth 213 (2000) 411}414
hand, CO is one of the end components of the C}O}H #uids, and provides oxidizing property to the #uid. It is very interesting to investigate the catalytic action of CO for diamond formation from the viewpoint of oxidized #uid condition. It is well known that Ag CO can decompose into Ag, CO and O above 2203C at ambient pressure [13]. Besides, O formed by the decomposition reacts with graphite and forms CO at HP}HT conditions [14]. Therefore, to investigate the catalytic action of CO for the transformation from graphite to dia mond, Ag CO was used as a source material for providing CO atmosphere. The carbonate was treated in a graphite capsule at HP}HT in the thermodynamically stable region of diamond, and change of the capsule was examined after the treatment. Besides, to check the catalytic ability of Ag O and Ag, they were also treated in the capsule. The starting materials were Ag CO (99% pu rity, Merck Japan Co. Ltd.), Ag O (99% purity, Wako Pure Chemical Industries), Ag wire with an outer diameter of 4 mm (99.99% purity, Furuya Metal Co. Ltd.) and graphite rods (high-purity grade, Tokai Carbon Company). No diamondforming metallic impurities such as Fe, Co and Ni were detected in the Ag CO and Ag O by emis sion spectrochemical analysis. The graphite rod was machined into a cylindrical capsule as shown in Fig. 1. The carbonate or oxide powder was
Fig. 1. Sample assembly for synthesis of diamond: (1) pyrophyllite sleeve, (2) steel ring, (3) Ta foil, (4) Mo outer capsule, (5) Mo inner capsule, (6) graphite heater, (7) NaCl}20 wt% ZrO pow der compact, (8) NaCl}10 wt% ZrO powder compact, (9) graphite capsule, (10) Ag CO , Ag O or Ag.
packed into the capsule, which was then capped with a graphite disk. Ag wire was also packed into the capsule by a similar way to that of the powder. Then the capsule was inserted into a Mo doublecapsule similar to that used in the previous experiment [11]. High-pressure experiments were carried out by using a belt-type high-pressure apparatus with a bore diameter of 32 mm. Pressure and temperature measurements were done by the same method as reported previously [12]. Samples were treated at HP}HT conditions of 7.7 GPa and 1500}20003C for 0.5}27 h. Then, they were taken out from the capsule and investigated using an optical microscope, scanning electron microscope (SEM), X-ray di!ractometer and Raman spectrometer. To investigate the decomposition behavior of Ag CO and Ag O at 7.7 GPa, Ag CO and Ag O were treated at 1000 and 12003C for 0.5 h, respectively, using the same sample assembly as shown in Fig. 1. Although the graphite capsule remained unreactive, it was clear from X-ray diffraction patterns that Ag CO decomposed into Ag O and CO , and Ag O decomposed into Ag and O as shown in Fig. 2. These results show that Ag CO was completely decomposed to Ag, CO and O in the present synthesis experiments per formed at 1500}20003C and 7.7 GPa. To investigate a catalytic action of these chemical species for synthesis of diamond from graphite, samples of graphite and Ag CO , Ag O or Ag were treated at HP}HT conditions of 1500}20003C and 7.7 GPa for 0.5}27 h using the sample assembly shown in Fig. 1. In the system of graphite and Ag CO , graphite capsules were completely converted to diamond in the experiments at 1800, 1900 and 20003C for 2, 0.5 and 0.5 h, respectively. To con"rm diamond formation at lower temperatures in this system, samples were treated at 1500}17003C for various holding times. At 17003C, diamond was not detected in the sample after being treated for 2 h, but was detected inside the graphite capsule in the experiment of 5 h. At 1600 and 15003C, diamonds were partly formed in the center portion of the innner wall of the graphite capsule in the experiments of 12 and 27 h, respectively. To investigate the detailed morphology of diamond crystals obtained in the system of Ag CO
L. Sun et al. / Journal of Crystal Growth 213 (2000) 411}414
413
Fig. 2. X-ray di!raction patterns of Ag CO and Ag O after the treatment of 7.7 GPa and (a) 10003C and (b) 12003C for 0.5 h, respectively.
and graphite, the crystals were observed by SEM. On the cross section of the samples obtained at 1800}20003C and 7.7 GPa for 0.5}2 h, diamond crystals with columnar structure were observed elongated along the axis parallel to the compressed direction as shown in Fig. 3. The elongated crystals were 200}700 lm in length which was 2}7 times greater than the width. This morphology clearly shows that the diamonds were grown from the solution with high supersaturation of carbon. On the other hand, in the samples obtained below 17003C, diamond crystals had a morphology of
well-developed +1 1 1, faces with smooth and #at surfaces although the size was limited to 20 lm as shown in Fig. 4. This morphology clearly shows that the diamonds were crystallized from the solution with moderate supersaturation of carbon. Since it is considered that the excess oxygen decomposed from Ag O reacts with graphite to form CO at HP}HT conditions [14], the CO thus formed must also be a #uid or solvent in the present system in which graphite dissolves and diamond crystallizes. This is also supported from the experimental results that when Ag O was used as
414
L. Sun et al. / Journal of Crystal Growth 213 (2000) 411}414
To clarify the diamond-formation mechanism in the system of graphite and Ag CO , pure Ag was loaded into the graphite capsule and treated at the highest temperature of 20003C for 0.5 h in the present study. Graphite did not react with molten Ag and no diamond was detected. This result shows that Ag does work as a diamond-forming catalyst. As described above, diamond crystals were synthesized at 1500}20003C and 7.7 GPa for 0.5}27 h in the systems of graphite and Ag CO or Ag O but no diamonds could be formed from graphite in the presence of Ag. Because at these HP}HT conditions, the carbonate was completely decomposed into Ag, CO and O , and O eventually became CO by the reaction of graphite, the present experi mental results strongly suggest that CO acts as the catalytic solvent for the transformation from graphite to diamond.
Acknowledgements Fig. 3. Secondary electron images (SEI) of the diamond crystals obtained at 7.7 GPa and 18003C for 2 h. (a) overall view, (b) enlargement of (a).
The authors wish to thank Mr. Y. Yajima (NIRIM) for the emission spectrochemical analysis.
References
Fig. 4. SEI of the diamond crystals obtained at 7.7 GPa and 16003C for 12 h.
a starting material instead of Ag CO , diamonds were clearly formed under the same P}¹ conditions as those in Ag CO .
[1] H.P. Bovenkerk, F.P. Bundy, H.T. Hall, H.M. Strong, R.H. Wentorf Jr., Nature 184 (1959) 1094. [2] M. Akaishi, H. Kanda, S. Yamaoka, J. Crystal Growth 104 (1990) 578. [3] M. Akaishi, H. Kanda, S. Yamaoka, Jpn. J. Appl. Phys. 29 (1990) L1172. [4] H.O.A. Meyer, Am. Miner. 70 (1985) 344. [5] H.O.A. Meyer, in: P.H. Nixon (Ed.), Mantle Xenoliths, Wiley, Chichester, England, 1987, p. 502. [6] F.R. Boyd, J.J. Gurney, S.H. Richardson, Nature 315 (1985) 387. [7] C.E. Melton, A.A. Giardini, Am. Miner. 59 (1974) 775. [8] C.E. Melton, A.A. Giardini, Nature 263 (1976) 309. [9] M. Schrauder, O. Navon, Nature 365 (1993) 42. [10] O. Navon, I.D. Hutcheon, G.R. Rossman, G.J. Wasserburg, Nature 335 (1988) 784. [11] M. Akaishi, S. Yamaoka, J. Crystal Growth 209 (2000) 999. [12] S.M. Hong, M. Akaishi, S. Yamaoka, J. Crystal Growth 200 (1999) 326. [13] The Merck Index, in: Paul G. Stecher (Ed.), Merk & Co., Inc., Rathway, NJ, USA, 1968, p. 947. [14] P. Deines, Geochem. Cosmochim. Acta 44 (1980) 943.