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Synthesis of diamond from graphite-carbonate system under very high temperature and pressure
578
Journal of Crystal Growth 104 (1990) 578—581 North-Holland
PRIORITY COMMUNICATION SYNTHESIS OF DIAMOND FROM GRAPHITE-CARBONATE SYSTEMS UNDER VERY HIGH TEMPERATURE AND PRESSURE Minoru AKAISHI, Hisao KANDA and Shinobu YAMAOKA National Institute for Research in Inorganic Materials, 1-1, Namiki, Tsukuba-shi, Ibaraki 305, Japan Received 30 March 1990
Although transition metals such as Fe, Co, Ni and their alloys have been used as diamond-producing solvent-catalysts under very high temperature and pressure, non-metallic compounds such as carbonates and oxides have also been claimed in the patents as the catalysts. In the present study, to make clear the catalytic effect of carbonates on the formation of diamond, high pressure experiments were carried Out in the mixture of graphite and the carbonates of Li, Na, Mg, Ca and Sr. Diamond could reproducibly be synthesized from graphite in the presence of these carbonates at high pressure and temperature of 7.7 GPa and 2150°C. Although starting graphite was completely transformed to diamond in the presence of the carbonates, no transformation to diamond could be detected from graphite only at the same pressure and temperature condition. Therefore, it can be concluded that the carbonates have strong solvent-catalytic effect on the transformation of graphite to diamond.
The success in diamond synthesis was first announced publicly by the General Electric research group in 1955 [1]. It became clear from their later report [2] that diamond can be reproducibly synthesized from graphite in the presence of 12 metals of Fe, Co, Ni, Ru, Rh, Pa, Ir, Os, Pt, Cr,
amond, details have not been published in scientific journals. Among the compounds, carbonates are worthy to be considered because they are listed in both methods in the patents and some compounds like CaCO3 are commonly present in the earth. In the
Mn, Ta and their alloys, which act as solventcatalysts under high pressure and high temperature conditions in the thermodynamically stable region of diamond [3]. Besides these metals, binary alloy systems such as Nb—Cu were also found to have the catalytic effect by Wakatsuki [4]. On the other hand, non-metallic compounds have also been reported to act as the catalysts in the patents. There are two categories. One is to produce diamond as a decomposition product of carbon-containing compounds such as carbides [5] and carbonates [6]. The other is the conversion from graphite in the presence of the compounds such as carbonates, oxides, hydroxides and chlorides [7], where the compounds are considered to act as solvent-catalysts. Although both methods are very interesting for considering not only the synthesis mechanism of diamond in non-conventional process but also the genesis of natural di-
present study, therefore, high pressure experiments were carried out in some graphite—carbonate systems to confirm the catalytic effects which had been claimed in the patents [7]. As starting materials were used powders of spectroscopic grade graphite made by Nippon Carbon Co. and reagent grade carbonates of Li2CO3, Na2CO3 and SrCO3 purchased from Kanto Chemical Co., CaCO3 purchased from Wako Pure Chemical Industries and laboratory made MgCO3. Purities above 99% were guaranteed in the carbonate reagents. 20 vol% of each carbonate was added to graphite and mixed in acetone in an agate mortar. The powder mixture was dried in an oven at about 120°Cand loaded in a capsule made of Mo foil at 200 MPa. Two of the encapsulated samples were then placed in an outside Mo capsules in such a way that both were sandwiched with three disks of
0022-0248/90/$03.50 © 1990
—
Elsevier Science Publishers B.V. (North-Holland)
M. Akaishi et al.
__________
______
_________________ __________
ii
/ Synthesis of diamondfrom graphite-carbonate systems
~ I I
3 4 5 6 7
8
10 mm Fig. 1. Sample assembly for high pressure and high temperature treatment: (1) NaCl—2Owt% Zr02 pressure medium; (2) NaCl—10 wt% Zr02 pressure medium; (3) steel ring; (4) graphite heater; (5, 7) sample; (6, 8) Mo foil.
pressure medium as shown in fig. 1. The sample was treated under the condition of 7.7 GPa and 2150°Cfor 20 mm. To elucidate the effect of the carbonates, pure graphite was also encapsulated in the same manner and treated at the same condition. High pressure experiments were carried out using a modified belt type high pressure apparatus with a bore diameter of 30 mm, similar to that reported previously [8]. Pressure was calibrated at room temperature using the known pressure induced phase transitions of Bi, Ti and Ba. Temperature was estimated from the extrapolated relation between input power and the bytemperature which hadthe been obtained in advance measuring the temperature up to 1800°C using a Pt—6% Rh/Pt—30%Rh thermocouple without correction for the pressure effect of the electromotive force. The obtained sample, which was a solid lump, was ground with a diamond wheel to remove the Mo foil on the top ends and investigated by X-ray diffraction. In all the samples treated at 2150°C, starting graphite was completely transformed to diamond, whereas no diamond was detected in the graphite sample without the carbonates. As a typical example, X-ray diffraction patterns in the system of C—CaCO 3 were shown in fig. 2. Fig. 2A shows that of the starting material, where all the reflection lines were assigned to graphite and calcite (low pressure form of CaCO3) with the marks of open circles and triangles, respectively. An X-ray pattern after the high pressure and temperature treatment was quite different from that of the starting material as shown in fig. 2B,
579
where reflection lines of graphite disappeared and the two strongest lines could be assigned to (111) and (220) of diamond. The other lines were assigned to aragonite form of CaCO and NaC1 with the (high markspressure of closed triangles and 3) squares, respectively. NaC1 is thought to be the contamination from the pressure transmitting medium, but has not any catalytic effect on the diamond formation because graphite heater contacted with NaC1 does not transform to diamond. To remove those materials, the sample was treated by a hot mixture of HC1 and HNO3. After the acid treatment, the reflection lines based on diamond were only observed as shown in fig. 2C, where a small peak is that of Kfl of diamond (111). This X-ray result suggests that CaCO3 acted as the catalysis for the transformation from graphite to diamond without the decomposition of itself. Since CaCO3 is considered to be in liquid state at the condition of 7.7 GPa and 2150°C[9], graphite may be dissolved into liquid CaCO3 and precipitate as diamond crystal. This indicates that the (A)
Graphite
°
tI J~Ici -~
(B)
Aragonite
U-
• NaCI • Diamond
c —
___________
(C)
20
I
40
I
60
I
80
Cuka, 2e(deg Fig. 2. X-ray diffraction patterns in the system of C—CaCO3 (A) starting material; (B) obtaining sample treated at 7.7 GPa and 2150°C;(c) the same sample after acid treatment.
580
M. Akaishi eta!. / Synthesis of diamondfrom graphite-carbonate systems
Fig. 3. Scanning electron micrographs of the diamonds synthesized from graphite and the compounds of (A) CaCO
3 (B) MgCO3 (C)
SrCO1 (D) Na2CO3.
carbonate acted as catalytic solvent like the conventional metal catalysts. Aragonite was thought to be crystallized from the liquid phase during quenching at high pressure. It has been known that if an amount as small as 1% conventional catalytic elements is present in the system, diamond can be synthesized from graphite at very high temperature and pressure condition [10]. To check the possibility of the metallic catalyst contamination, impurity levels of 12 conventional catalytic elements in the starting CaCO3, Na2C03 and SrCO3 were examined qualitatively using an inductively coupled plasma emission spectroscopy (ICP) method, where 100 mg of each reagent was dissolved into 100 ml of 0.1N HC1 solution made by distilled and deionized water and reagent grade HCI. It was found that the content of these elements was as small as that of standard HC1 solution. Besides, to crosscheck the impurity effect, very pure CaCO3 (above 99.999% purity, obtained from Rare Metallic Co.) was used and the same experiment was carried out, the result of which was the same. These facts suggest
that the carbonates themselves acted as the catalysts. As for the CaCO3-containing sample, experiments were also carried out at different temperatures of 2000 and 1800°Cat 7.7 GPa. About half of the graphite was transformed to diamond at 2000 °C but no transformation occurred at 1800°C. This shows that a much higher temperature than normally expected in nature [11] is necessary in this transformation reaction. This discrepancy cannot be explained at present. The synthesized diamond was observed by an optical microscope and a scanning electron microscope (SEM). Even after the acid treatment mentioned above, the samples remained as the aggregates of small diamond grains with the size of a few to 20 ~tm, as shown in fig. 3, which shows SEM photographs of the diamond obtained in the present study. They were colorless and transparent or translucent. Most of the crystals were round in shape and a well faceted one was seldom seen. In the present study, it became clear that the carbonates of Li, Na, Mg, Ca and Sr can act as
M. Akaishi eta!.
/
Synthesis of diamond from graphite-carbonate systems
the catalysts for diamond transformation from graphite at 7.7 GPa and 2150 °C probably in liquid phase. However, we have just started this study and there remain many problems to be solved such as transformation region of temperature and pressure, phase diagram in the C— carbonate system, etc. The authors are grateful to Drs. Y. Komatsu and T. Sasaki and Mr. Y. Yajima for ICP measurements.
References [11 F.P. Bundy, H.T. Hall, H.M. Strong and RH. Wentorf, Jr., Nature 176 (1955) 51. [2] H.P. Bovenkerk, F.P. Bundy, H.T. Hall, H.M. Strong and RH. Wentorf, Jr., Nature 184 (1959) 1094.
581
[3] R. Berman and F. Simon, Z. Electrochem. 59 (1955) 333. [4] M. Wakatsuki, Japan. J. Appl. Phys. 5 (1966) 337. [5] For example, E. Wolf et al., German (East) Patent: DD 259,147 (1988) CA 110 (1989) 138104h; U. Gerlach et al., German (East) Patent: DD 257,375 (1988): CA 110 (1989) 98127j. [6] e.g., E. Woermann, German Patent: 2,721,644 (1978): CA 90 (1978) 124033r. [7] e.g., A.A. Shulzhenko and A.F. Getman, German Patent: 2,1441,139 (1972): CA 76 (1972) 156242k; German Patent: 2,124,145 (1971): CA 76 (1972) 61439r; German Patent: 2,032,083 (1971): CA 76 (1972) 16236m; German Patent: 2,032,013 (1971): CA 76 (1972) 16237n. [8] 0. Fukunaga, S. Yamaoka, T. Endob, M. Akaishi and H. Kanda, in: High Pressure Science and Technology, Vol. 1, Ed. K.D. Timmerhaus and MS. Barber (Plenum, New York, 1979) pp. 846—852. [9] A.J. Irving and P.J. Wyllie, Geochim. Cosmochim. Acta 39 (1975) 35. [10] F.P. Bundy, Nature 241 (1973) 116. [11] H.O.A. Meyer, Am. Mineralogist 70 (1985) 344.
Journal of Crystal Growth 104 (1990) 578—581 North-Holland
PRIORITY COMMUNICATION SYNTHESIS OF DIAMOND FROM GRAPHITE-CARBONATE SYSTEMS UNDER VERY HIGH TEMPERATURE AND PRESSURE Minoru AKAISHI, Hisao KANDA and Shinobu YAMAOKA National Institute for Research in Inorganic Materials, 1-1, Namiki, Tsukuba-shi, Ibaraki 305, Japan Received 30 March 1990
Although transition metals such as Fe, Co, Ni and their alloys have been used as diamond-producing solvent-catalysts under very high temperature and pressure, non-metallic compounds such as carbonates and oxides have also been claimed in the patents as the catalysts. In the present study, to make clear the catalytic effect of carbonates on the formation of diamond, high pressure experiments were carried Out in the mixture of graphite and the carbonates of Li, Na, Mg, Ca and Sr. Diamond could reproducibly be synthesized from graphite in the presence of these carbonates at high pressure and temperature of 7.7 GPa and 2150°C. Although starting graphite was completely transformed to diamond in the presence of the carbonates, no transformation to diamond could be detected from graphite only at the same pressure and temperature condition. Therefore, it can be concluded that the carbonates have strong solvent-catalytic effect on the transformation of graphite to diamond.
The success in diamond synthesis was first announced publicly by the General Electric research group in 1955 [1]. It became clear from their later report [2] that diamond can be reproducibly synthesized from graphite in the presence of 12 metals of Fe, Co, Ni, Ru, Rh, Pa, Ir, Os, Pt, Cr,
amond, details have not been published in scientific journals. Among the compounds, carbonates are worthy to be considered because they are listed in both methods in the patents and some compounds like CaCO3 are commonly present in the earth. In the
Mn, Ta and their alloys, which act as solventcatalysts under high pressure and high temperature conditions in the thermodynamically stable region of diamond [3]. Besides these metals, binary alloy systems such as Nb—Cu were also found to have the catalytic effect by Wakatsuki [4]. On the other hand, non-metallic compounds have also been reported to act as the catalysts in the patents. There are two categories. One is to produce diamond as a decomposition product of carbon-containing compounds such as carbides [5] and carbonates [6]. The other is the conversion from graphite in the presence of the compounds such as carbonates, oxides, hydroxides and chlorides [7], where the compounds are considered to act as solvent-catalysts. Although both methods are very interesting for considering not only the synthesis mechanism of diamond in non-conventional process but also the genesis of natural di-
present study, therefore, high pressure experiments were carried out in some graphite—carbonate systems to confirm the catalytic effects which had been claimed in the patents [7]. As starting materials were used powders of spectroscopic grade graphite made by Nippon Carbon Co. and reagent grade carbonates of Li2CO3, Na2CO3 and SrCO3 purchased from Kanto Chemical Co., CaCO3 purchased from Wako Pure Chemical Industries and laboratory made MgCO3. Purities above 99% were guaranteed in the carbonate reagents. 20 vol% of each carbonate was added to graphite and mixed in acetone in an agate mortar. The powder mixture was dried in an oven at about 120°Cand loaded in a capsule made of Mo foil at 200 MPa. Two of the encapsulated samples were then placed in an outside Mo capsules in such a way that both were sandwiched with three disks of
0022-0248/90/$03.50 © 1990
—
Elsevier Science Publishers B.V. (North-Holland)
M. Akaishi et al.
__________
______
_________________ __________
ii
/ Synthesis of diamondfrom graphite-carbonate systems
~ I I
3 4 5 6 7
8
10 mm Fig. 1. Sample assembly for high pressure and high temperature treatment: (1) NaCl—2Owt% Zr02 pressure medium; (2) NaCl—10 wt% Zr02 pressure medium; (3) steel ring; (4) graphite heater; (5, 7) sample; (6, 8) Mo foil.
pressure medium as shown in fig. 1. The sample was treated under the condition of 7.7 GPa and 2150°Cfor 20 mm. To elucidate the effect of the carbonates, pure graphite was also encapsulated in the same manner and treated at the same condition. High pressure experiments were carried out using a modified belt type high pressure apparatus with a bore diameter of 30 mm, similar to that reported previously [8]. Pressure was calibrated at room temperature using the known pressure induced phase transitions of Bi, Ti and Ba. Temperature was estimated from the extrapolated relation between input power and the bytemperature which hadthe been obtained in advance measuring the temperature up to 1800°C using a Pt—6% Rh/Pt—30%Rh thermocouple without correction for the pressure effect of the electromotive force. The obtained sample, which was a solid lump, was ground with a diamond wheel to remove the Mo foil on the top ends and investigated by X-ray diffraction. In all the samples treated at 2150°C, starting graphite was completely transformed to diamond, whereas no diamond was detected in the graphite sample without the carbonates. As a typical example, X-ray diffraction patterns in the system of C—CaCO 3 were shown in fig. 2. Fig. 2A shows that of the starting material, where all the reflection lines were assigned to graphite and calcite (low pressure form of CaCO3) with the marks of open circles and triangles, respectively. An X-ray pattern after the high pressure and temperature treatment was quite different from that of the starting material as shown in fig. 2B,
579
where reflection lines of graphite disappeared and the two strongest lines could be assigned to (111) and (220) of diamond. The other lines were assigned to aragonite form of CaCO and NaC1 with the (high markspressure of closed triangles and 3) squares, respectively. NaC1 is thought to be the contamination from the pressure transmitting medium, but has not any catalytic effect on the diamond formation because graphite heater contacted with NaC1 does not transform to diamond. To remove those materials, the sample was treated by a hot mixture of HC1 and HNO3. After the acid treatment, the reflection lines based on diamond were only observed as shown in fig. 2C, where a small peak is that of Kfl of diamond (111). This X-ray result suggests that CaCO3 acted as the catalysis for the transformation from graphite to diamond without the decomposition of itself. Since CaCO3 is considered to be in liquid state at the condition of 7.7 GPa and 2150°C[9], graphite may be dissolved into liquid CaCO3 and precipitate as diamond crystal. This indicates that the (A)
Graphite
°
tI J~Ici -~
(B)
Aragonite
U-
• NaCI • Diamond
c —
___________
(C)
20
I
40
I
60
I
80
Cuka, 2e(deg Fig. 2. X-ray diffraction patterns in the system of C—CaCO3 (A) starting material; (B) obtaining sample treated at 7.7 GPa and 2150°C;(c) the same sample after acid treatment.
580
M. Akaishi eta!. / Synthesis of diamondfrom graphite-carbonate systems
Fig. 3. Scanning electron micrographs of the diamonds synthesized from graphite and the compounds of (A) CaCO
3 (B) MgCO3 (C)
SrCO1 (D) Na2CO3.
carbonate acted as catalytic solvent like the conventional metal catalysts. Aragonite was thought to be crystallized from the liquid phase during quenching at high pressure. It has been known that if an amount as small as 1% conventional catalytic elements is present in the system, diamond can be synthesized from graphite at very high temperature and pressure condition [10]. To check the possibility of the metallic catalyst contamination, impurity levels of 12 conventional catalytic elements in the starting CaCO3, Na2C03 and SrCO3 were examined qualitatively using an inductively coupled plasma emission spectroscopy (ICP) method, where 100 mg of each reagent was dissolved into 100 ml of 0.1N HC1 solution made by distilled and deionized water and reagent grade HCI. It was found that the content of these elements was as small as that of standard HC1 solution. Besides, to crosscheck the impurity effect, very pure CaCO3 (above 99.999% purity, obtained from Rare Metallic Co.) was used and the same experiment was carried out, the result of which was the same. These facts suggest
that the carbonates themselves acted as the catalysts. As for the CaCO3-containing sample, experiments were also carried out at different temperatures of 2000 and 1800°Cat 7.7 GPa. About half of the graphite was transformed to diamond at 2000 °C but no transformation occurred at 1800°C. This shows that a much higher temperature than normally expected in nature [11] is necessary in this transformation reaction. This discrepancy cannot be explained at present. The synthesized diamond was observed by an optical microscope and a scanning electron microscope (SEM). Even after the acid treatment mentioned above, the samples remained as the aggregates of small diamond grains with the size of a few to 20 ~tm, as shown in fig. 3, which shows SEM photographs of the diamond obtained in the present study. They were colorless and transparent or translucent. Most of the crystals were round in shape and a well faceted one was seldom seen. In the present study, it became clear that the carbonates of Li, Na, Mg, Ca and Sr can act as
M. Akaishi eta!.
/
Synthesis of diamond from graphite-carbonate systems
the catalysts for diamond transformation from graphite at 7.7 GPa and 2150 °C probably in liquid phase. However, we have just started this study and there remain many problems to be solved such as transformation region of temperature and pressure, phase diagram in the C— carbonate system, etc. The authors are grateful to Drs. Y. Komatsu and T. Sasaki and Mr. Y. Yajima for ICP measurements.
References [11 F.P. Bundy, H.T. Hall, H.M. Strong and RH. Wentorf, Jr., Nature 176 (1955) 51. [2] H.P. Bovenkerk, F.P. Bundy, H.T. Hall, H.M. Strong and RH. Wentorf, Jr., Nature 184 (1959) 1094.
581
[3] R. Berman and F. Simon, Z. Electrochem. 59 (1955) 333. [4] M. Wakatsuki, Japan. J. Appl. Phys. 5 (1966) 337. [5] For example, E. Wolf et al., German (East) Patent: DD 259,147 (1988) CA 110 (1989) 138104h; U. Gerlach et al., German (East) Patent: DD 257,375 (1988): CA 110 (1989) 98127j. [6] e.g., E. Woermann, German Patent: 2,721,644 (1978): CA 90 (1978) 124033r. [7] e.g., A.A. Shulzhenko and A.F. Getman, German Patent: 2,1441,139 (1972): CA 76 (1972) 156242k; German Patent: 2,124,145 (1971): CA 76 (1972) 61439r; German Patent: 2,032,083 (1971): CA 76 (1972) 16236m; German Patent: 2,032,013 (1971): CA 76 (1972) 16237n. [8] 0. Fukunaga, S. Yamaoka, T. Endob, M. Akaishi and H. Kanda, in: High Pressure Science and Technology, Vol. 1, Ed. K.D. Timmerhaus and MS. Barber (Plenum, New York, 1979) pp. 846—852. [9] A.J. Irving and P.J. Wyllie, Geochim. Cosmochim. Acta 39 (1975) 35. [10] F.P. Bundy, Nature 241 (1973) 116. [11] H.O.A. Meyer, Am. Mineralogist 70 (1985) 344.