- Email: [email protected]
Properties of ultrafine diamond clusters from detonation synthesis
Diamond and Related Materials, 3 (1993) 160-162
160
Properties of ultrafine diamond clusters from detonation synthesis A. L. Vereschagin*, G. V. Sakovich, V. F. Komarov and E. A. Petrov Synthesis by Explosion Company, Sosialisticheskai Str 1, Biysk 659322 (Russian Federation) (Received August 24, 1992; accepted in final form May 5, 1993)
Abstract The properties of ultrafine diamonds obtained from explosives are described. This product has an unusual combination of properties, which make it very attractive as a component of new composite materials. Results are presented of investigations of the composition, structure, surface and reactivity of the diamond-like carbon phase.
1. Introduction It is common knowledge that the conditions of synthesis exert a considerable influence on the morphology of forming products. For instance, powders produced by the plasmochemical process are characterized by having a particular structure, a special character of phase modification, thermal and oxidative stability and sinterability. So they differ from powders produced by ordinary methods [1]. The present paper provides generalized results concerning an investigation of properties of the diamondlike carbon phase (DLCP). This phase is produced by detonation of the explosive benzene, 2-methyl-l,3,5trinitro/1,3,5-triazine, hexahydro-l,3,5-trinitro (TNT/ RDX 60/40).
2. Elemental composition According to the results of element analysis the DLCP contains: carbon, up to 88%; hydrogen, 1.0%; nitrogen, 2.5%; oxygen, up to 10% [2]. After thermal treatment, this ratio between elements remains the same up to 1273 K in reducing (hydrogen) and neutral (argon) atmospheres. The content of carbon in DLCP samples goes up to a maximum point in the range 973-1073 K, while the content of hydrogen and nitrogen practically remains constant. The maximum density of DLCP has been achieved by heating in an argon atmosphere up to 1073 K and its value is 3.21 g cm-31
3. Morphology When purified of impurities the DLCP presents a powder, its specific surface area being equal to
250_350 m 2 g-1 and porosity to 0.3-1.0 cm 3 g-l, with the average diameter of a pore being 7.5-12.5 nm. Heating up to 1273 K does not diminish the specific surface area. In water suspensions, the DLCP has particles of dimensions up to 0.05 p.m, but in the dry form there is a polydispersed powder. On heating in a noble gas atmosphere, beginning from 873 K, the DLCP particles start growing and taking the form of fragile spherelike particles, their dimensions being within the range 150-200 p.m. Such particles can be destroyed at a load of about 10-15kgfmm -2. In that case there is no formation of polycrystal.
4. Phase composition and microstructure Depending on the synthesis conditions, in the condensed products of explosion can be seen either the formation of a single cubic diamond phase or this phase with the amorphous phase as an impurity (up to 70%). The X-ray diagram of a DLCP sample has five reflections, which are characterized through the following distribution of intensities: (111), 35.0% (44%); (220), 14.0% (22%); (113), 0.5% (18%); (400), 0.3% (4%); (331), 0.2% (12%). (The values in parentheses are the reflection values for the standard according to ASTM Index 6-675.) We can possibly say that the predominance in the spectrum of reflection from the (11 I) plane is due to the spherical form of the DLCP particles. The DLCP microstructure parameters are presented in Table 1, where they are compared with data on diamonds manufactured by other variants of detonation synthesis. As indicated in Table 1, the DLCP obtained by exploding TNT/RDX 60/40 is characterized by having the highest values of type II microstresses (according to the
*Author to whom correspondence should be addressed. 0925-9635/93/$6.00
© 1993 - - Elsevier Sequoia. All rights reserved
A. L. Vereschagin et al. / Uhrafine diamond clusters /?om detonation synthesis TABLE 1. Microstructure of diamonds from detonation synthesis Coherent reflection size (nm) 4 6 5 10 5o15
Microstress
Aa/a (%)
(GPa)
1.0 0.45 0.1
10 4.5 1.0
Parameters of crystal lattice (nm)
Reference
0.3562 _+ 0.0004 0.3572+_0.0004
3 4
method of fourth moments [5]) and, as a result, by the most deformed crystal lattice. The value of the DLCP microstresses does not change before graphitization at 1473 K. The strongly deformed structure of the DLCP is therefore stable at high temperatures. However, a high reactivity is expected to appear in the DLCP.
161
activation of the above-mentioned gases vary in the range 23.0-48.5 kJ mol 1, which means they have chemical bonds with the DLCP surface. As shown by X-ray photoelectronic spectroscopy, the DLCP is characterized by the symmetric C ls peak with AE~:z=3.3eV: the surface charge value amounts to +3.3 eV. After argon bombardment the form of the carbon peak remains unchanged and the surface charge reaches + 6.2 eV; AEt/2 = 2.9 eV. The conclusion can be drawn here that carbon under the surface layer at a depth of 10 nm is only presented in the diamond phase. In a basic sample, nitrogen and oxygen are found to be impurities, their relative atom contents being O/C = 0.027 and N/C=0.020. When argon bombardment is finished, the content of such impurities decreases to values lower than the sensitivity limit of the spectrometer.
7. Nuclear magnetic resonance (NMR) spectroscopy 5. Thermal analysis 7.1. " C
The complex thermal analysis of the DLCP in both air atmosphere and noble gases has given rise to results as follows. On heating in air at a rate of 10 K rain-1 the DLCP oxidizes at 703 K [6], while diamond types such as DAS, DAG and ASM 1/0 (produced in explosions of mixtures of explosive with soot (DAS) or graphite (DAG), or made by static synthesis with an average powder size of less than 1 lam (ASM)) start their oxidation at 863 K, 843 K and 923 K respectively [7]. On heating in neutral atmosphere up to 1273 K, there is a loss of weight equal to 3-4%. Heating in CO2 atmosphere within the range 443 753 K involves a sample weight increase of approximately 5%. This can apparently be connected with both the absorption of CO2 and the substitution of lighter molecules. Heating in a hydrogen atmosphere is followed by the evolution of HCN.
The NMR spectrum in the DLCP consists of four signals (Fig. 1). The signal a=34.5ppm is relative to diamond carbon, besides it has a "shoulder" on the highfield side at something like 30 ppm. This signal is connected both with the non-equivalence of carbon atoms in the sample microstructure and possibly with available defects or an amorphous phase. Weak lines at a = 68 ppm and a = 53 ppm can be explained by the influence of partly oxidized structures or by nitrogen atoms in the composition of the samples. 7.2. 'H
Three crossing lines were registered. The group having a chemical shift cr=2.2 ppm is considered to be an isolated C-OH group, while the line with a = 3.8 ppm relates to interactive C-OH groups. The signal a = 6.7 ppm is probably linked to S-OH groups, which have been formed on the sample surface during chemical purification.
6. Investigation of surface composition According to IR spectroscopy data, there are on the surface of DLCP carbonyl, carboxyl, methyl and nitryl groups. After voltamperimetric analysis the availability of carbonyl, carboxyl and quinone groups was found. On heating their concentration decreases, and beginning at a temperature of 973 K they cannot be identified through the method of polarography. Indirect information about the composition of surface groups is provided through the composition analysis of thermodesorption gases. Using gas chromatography [2] the evolution of carbon dioxide (81.8%), nitrogen (6.0%) and methane (10.2%) was determined. The energies of desorption
34"5
Fig. I. C13 N M R spectrum of the DLCP.
162
A. L. Vereschagin et al. / Ultrafine diamond clusters from detonation synthesis
8. Electron spin resonance (ESR) spectroscopy
through experiments with calorimetry of combustion. Calculated on this basis the enthalpy values of DLCP formation together with the surface energy contribution amounts to 3482 kJ kg -1. The lower experimental enthalpy value could be possibly explained by surface oxygen-containing groups available on the DLCP surface.
The signal at room temperature is a singlet with a g factor of 2.003 and a semiwidth equal to 6.3e-8.3e. The concentration of paramagnetic particles changes from 2.7 x 10is to 2.0 x 10is g-1 (Fig. 2). The parameters of the signal are closer to those of the ESR spectrum from broken bonds on the diamond surface (g= 2.0027 and AH1/2=5.5e) [8]. A similar signal was registered in explosive diamonds of AB type [9]. Attention is drawn to the fact that, in spite of the high concentration of nitrogen atoms in the DLCP (somewhere near 1.6 x 1021 g-l), the triplet signal produced by the added nitrogen atoms, which substitute for carbon in the diamond lattice, has not been registered. Much more detailed investigation seems to be necessary for making an analysis of nitrogen in the DLCP.
Thus the DLCP has a variety of properties which help to distinguish it from the known different types of synthetic diamond and, in spite of its high reaction capacity, the DLCP is stable as shown by its physical and chemical properties in neutral and reducing atmospheres up to 1273 K.
9. Electrophysieal characteristics
References
The specific surface resistance of the DLCP is maximum for the samples heated at 573 K and has a value of 1.0 x 1012 f] m. The next heating reduces the resistance to (6.0 x 101°)-(2.0 x 1011) fl m. If the heating is in an atmosphere of carbon dioxide, the resistance decreases immediately to 2.3 x 10af/ m at temperatures higher than 1173 K. This is probably the proof of the first graphitization stage. The dielectic constants of the samples amount to Eo1=2.4-2.7, E1o=1.7-2.0 and E1.5= 1.7-2.0. The tangent of the angle of dielectric losses equals between 8.5 x 10 -3 and 1.0 x 10 -2.
10. Energy saturation The experimental contribution of the surface value to the enthalpy of DLCP formation was determined
Fig. 2. ESR spectrum of the DLCP.
11. Conclusion
1 S.V. Gurov and V. N. Troitsky, Properties of ultradispersed powders obtained by plasmochemical method, Plasmochemistry-89, Vol. 1, Moscow, 1989, pp. 114-130. 2 L. A. Petrova, A. L. Vereschagin, V. V. Novoselov, P. M. Bryliakov and N. V. Shein, Composition analysis of surface groups in diamond like carbon phase, Superhard Mater., 4 (1989) 3-5. 3 V. I. Trefilov, G. I. Savvakin, V. V. Skorokhod, U. M. Solonin and B. V. Fenochka, Several physical and chemical properties of diamond obtained by explosion at high temperatures, Powder Metall., 1 (1979) 32-36. 4 A. V. Ananin, O. N. Breusov, V. N. Drobyshev, G. E. Ivanchihina, A. I. Rogacheva, V. E. Tatsiy and I. G. Shunina, Thermographic and X-ray analysis of diamonds manufactured by detonation synthesis, Superhard Mater., 5 (1986) 11-14. 5 A. L. Vereschagin, L. A. Petrova, I. I. Zolotuchina, V. V. Novoselov, V. A. Kliuchnikov and P. M. Bryliakov, Energy saturation and reaction capacity of diamond clusters, Problems of explosion and combustion, Proc. Xlth All-Union Syrup. on Combustion and Explosion, November 19-24, 1989, Suzdal, Chernogolovka, 1989, pp. 107-109. 6 A. L. Vereschagin, G. M. Ulianova, V. V. Novoselov, L. A. Petrova and P. M. Bryliakov, Complex thermal analysis of diamond like carbon phase in a controlled atmosphere, Superhard Mater., 5 (1990) 20-22. 7 0 . N. Breusov, V. M. Volkov, V. N. Drobyshev and V. P. Tatsiy, Experimental and theoretical analysis of diamond micropowders by DTA method, Interaction of Diamond with Gas and Liquid Media, Institute for Superhard Materials, Akademi Nauk Ukraine, Kiev, 1984, pp. 19-35. 8 N. D. Samsonenko and E. V. Sobolev, ESR and its dependence from diamond surface, JETP Lett., 5 (9) (1967) 304-307. 9 A. V. Beliankina, T. A. Nachalnaia, U. I. Sozin and L. A. Shulman, X-ray data and ESR spectrum of explosive diamonds, Synthetic Diamonds, (5) (1975) 5-7.
160
Properties of ultrafine diamond clusters from detonation synthesis A. L. Vereschagin*, G. V. Sakovich, V. F. Komarov and E. A. Petrov Synthesis by Explosion Company, Sosialisticheskai Str 1, Biysk 659322 (Russian Federation) (Received August 24, 1992; accepted in final form May 5, 1993)
Abstract The properties of ultrafine diamonds obtained from explosives are described. This product has an unusual combination of properties, which make it very attractive as a component of new composite materials. Results are presented of investigations of the composition, structure, surface and reactivity of the diamond-like carbon phase.
1. Introduction It is common knowledge that the conditions of synthesis exert a considerable influence on the morphology of forming products. For instance, powders produced by the plasmochemical process are characterized by having a particular structure, a special character of phase modification, thermal and oxidative stability and sinterability. So they differ from powders produced by ordinary methods [1]. The present paper provides generalized results concerning an investigation of properties of the diamondlike carbon phase (DLCP). This phase is produced by detonation of the explosive benzene, 2-methyl-l,3,5trinitro/1,3,5-triazine, hexahydro-l,3,5-trinitro (TNT/ RDX 60/40).
2. Elemental composition According to the results of element analysis the DLCP contains: carbon, up to 88%; hydrogen, 1.0%; nitrogen, 2.5%; oxygen, up to 10% [2]. After thermal treatment, this ratio between elements remains the same up to 1273 K in reducing (hydrogen) and neutral (argon) atmospheres. The content of carbon in DLCP samples goes up to a maximum point in the range 973-1073 K, while the content of hydrogen and nitrogen practically remains constant. The maximum density of DLCP has been achieved by heating in an argon atmosphere up to 1073 K and its value is 3.21 g cm-31
3. Morphology When purified of impurities the DLCP presents a powder, its specific surface area being equal to
250_350 m 2 g-1 and porosity to 0.3-1.0 cm 3 g-l, with the average diameter of a pore being 7.5-12.5 nm. Heating up to 1273 K does not diminish the specific surface area. In water suspensions, the DLCP has particles of dimensions up to 0.05 p.m, but in the dry form there is a polydispersed powder. On heating in a noble gas atmosphere, beginning from 873 K, the DLCP particles start growing and taking the form of fragile spherelike particles, their dimensions being within the range 150-200 p.m. Such particles can be destroyed at a load of about 10-15kgfmm -2. In that case there is no formation of polycrystal.
4. Phase composition and microstructure Depending on the synthesis conditions, in the condensed products of explosion can be seen either the formation of a single cubic diamond phase or this phase with the amorphous phase as an impurity (up to 70%). The X-ray diagram of a DLCP sample has five reflections, which are characterized through the following distribution of intensities: (111), 35.0% (44%); (220), 14.0% (22%); (113), 0.5% (18%); (400), 0.3% (4%); (331), 0.2% (12%). (The values in parentheses are the reflection values for the standard according to ASTM Index 6-675.) We can possibly say that the predominance in the spectrum of reflection from the (11 I) plane is due to the spherical form of the DLCP particles. The DLCP microstructure parameters are presented in Table 1, where they are compared with data on diamonds manufactured by other variants of detonation synthesis. As indicated in Table 1, the DLCP obtained by exploding TNT/RDX 60/40 is characterized by having the highest values of type II microstresses (according to the
*Author to whom correspondence should be addressed. 0925-9635/93/$6.00
© 1993 - - Elsevier Sequoia. All rights reserved
A. L. Vereschagin et al. / Uhrafine diamond clusters /?om detonation synthesis TABLE 1. Microstructure of diamonds from detonation synthesis Coherent reflection size (nm) 4 6 5 10 5o15
Microstress
Aa/a (%)
(GPa)
1.0 0.45 0.1
10 4.5 1.0
Parameters of crystal lattice (nm)
Reference
0.3562 _+ 0.0004 0.3572+_0.0004
3 4
method of fourth moments [5]) and, as a result, by the most deformed crystal lattice. The value of the DLCP microstresses does not change before graphitization at 1473 K. The strongly deformed structure of the DLCP is therefore stable at high temperatures. However, a high reactivity is expected to appear in the DLCP.
161
activation of the above-mentioned gases vary in the range 23.0-48.5 kJ mol 1, which means they have chemical bonds with the DLCP surface. As shown by X-ray photoelectronic spectroscopy, the DLCP is characterized by the symmetric C ls peak with AE~:z=3.3eV: the surface charge value amounts to +3.3 eV. After argon bombardment the form of the carbon peak remains unchanged and the surface charge reaches + 6.2 eV; AEt/2 = 2.9 eV. The conclusion can be drawn here that carbon under the surface layer at a depth of 10 nm is only presented in the diamond phase. In a basic sample, nitrogen and oxygen are found to be impurities, their relative atom contents being O/C = 0.027 and N/C=0.020. When argon bombardment is finished, the content of such impurities decreases to values lower than the sensitivity limit of the spectrometer.
7. Nuclear magnetic resonance (NMR) spectroscopy 5. Thermal analysis 7.1. " C
The complex thermal analysis of the DLCP in both air atmosphere and noble gases has given rise to results as follows. On heating in air at a rate of 10 K rain-1 the DLCP oxidizes at 703 K [6], while diamond types such as DAS, DAG and ASM 1/0 (produced in explosions of mixtures of explosive with soot (DAS) or graphite (DAG), or made by static synthesis with an average powder size of less than 1 lam (ASM)) start their oxidation at 863 K, 843 K and 923 K respectively [7]. On heating in neutral atmosphere up to 1273 K, there is a loss of weight equal to 3-4%. Heating in CO2 atmosphere within the range 443 753 K involves a sample weight increase of approximately 5%. This can apparently be connected with both the absorption of CO2 and the substitution of lighter molecules. Heating in a hydrogen atmosphere is followed by the evolution of HCN.
The NMR spectrum in the DLCP consists of four signals (Fig. 1). The signal a=34.5ppm is relative to diamond carbon, besides it has a "shoulder" on the highfield side at something like 30 ppm. This signal is connected both with the non-equivalence of carbon atoms in the sample microstructure and possibly with available defects or an amorphous phase. Weak lines at a = 68 ppm and a = 53 ppm can be explained by the influence of partly oxidized structures or by nitrogen atoms in the composition of the samples. 7.2. 'H
Three crossing lines were registered. The group having a chemical shift cr=2.2 ppm is considered to be an isolated C-OH group, while the line with a = 3.8 ppm relates to interactive C-OH groups. The signal a = 6.7 ppm is probably linked to S-OH groups, which have been formed on the sample surface during chemical purification.
6. Investigation of surface composition According to IR spectroscopy data, there are on the surface of DLCP carbonyl, carboxyl, methyl and nitryl groups. After voltamperimetric analysis the availability of carbonyl, carboxyl and quinone groups was found. On heating their concentration decreases, and beginning at a temperature of 973 K they cannot be identified through the method of polarography. Indirect information about the composition of surface groups is provided through the composition analysis of thermodesorption gases. Using gas chromatography [2] the evolution of carbon dioxide (81.8%), nitrogen (6.0%) and methane (10.2%) was determined. The energies of desorption
34"5
Fig. I. C13 N M R spectrum of the DLCP.
162
A. L. Vereschagin et al. / Ultrafine diamond clusters from detonation synthesis
8. Electron spin resonance (ESR) spectroscopy
through experiments with calorimetry of combustion. Calculated on this basis the enthalpy values of DLCP formation together with the surface energy contribution amounts to 3482 kJ kg -1. The lower experimental enthalpy value could be possibly explained by surface oxygen-containing groups available on the DLCP surface.
The signal at room temperature is a singlet with a g factor of 2.003 and a semiwidth equal to 6.3e-8.3e. The concentration of paramagnetic particles changes from 2.7 x 10is to 2.0 x 10is g-1 (Fig. 2). The parameters of the signal are closer to those of the ESR spectrum from broken bonds on the diamond surface (g= 2.0027 and AH1/2=5.5e) [8]. A similar signal was registered in explosive diamonds of AB type [9]. Attention is drawn to the fact that, in spite of the high concentration of nitrogen atoms in the DLCP (somewhere near 1.6 x 1021 g-l), the triplet signal produced by the added nitrogen atoms, which substitute for carbon in the diamond lattice, has not been registered. Much more detailed investigation seems to be necessary for making an analysis of nitrogen in the DLCP.
Thus the DLCP has a variety of properties which help to distinguish it from the known different types of synthetic diamond and, in spite of its high reaction capacity, the DLCP is stable as shown by its physical and chemical properties in neutral and reducing atmospheres up to 1273 K.
9. Electrophysieal characteristics
References
The specific surface resistance of the DLCP is maximum for the samples heated at 573 K and has a value of 1.0 x 1012 f] m. The next heating reduces the resistance to (6.0 x 101°)-(2.0 x 1011) fl m. If the heating is in an atmosphere of carbon dioxide, the resistance decreases immediately to 2.3 x 10af/ m at temperatures higher than 1173 K. This is probably the proof of the first graphitization stage. The dielectic constants of the samples amount to Eo1=2.4-2.7, E1o=1.7-2.0 and E1.5= 1.7-2.0. The tangent of the angle of dielectric losses equals between 8.5 x 10 -3 and 1.0 x 10 -2.
10. Energy saturation The experimental contribution of the surface value to the enthalpy of DLCP formation was determined
Fig. 2. ESR spectrum of the DLCP.
11. Conclusion
1 S.V. Gurov and V. N. Troitsky, Properties of ultradispersed powders obtained by plasmochemical method, Plasmochemistry-89, Vol. 1, Moscow, 1989, pp. 114-130. 2 L. A. Petrova, A. L. Vereschagin, V. V. Novoselov, P. M. Bryliakov and N. V. Shein, Composition analysis of surface groups in diamond like carbon phase, Superhard Mater., 4 (1989) 3-5. 3 V. I. Trefilov, G. I. Savvakin, V. V. Skorokhod, U. M. Solonin and B. V. Fenochka, Several physical and chemical properties of diamond obtained by explosion at high temperatures, Powder Metall., 1 (1979) 32-36. 4 A. V. Ananin, O. N. Breusov, V. N. Drobyshev, G. E. Ivanchihina, A. I. Rogacheva, V. E. Tatsiy and I. G. Shunina, Thermographic and X-ray analysis of diamonds manufactured by detonation synthesis, Superhard Mater., 5 (1986) 11-14. 5 A. L. Vereschagin, L. A. Petrova, I. I. Zolotuchina, V. V. Novoselov, V. A. Kliuchnikov and P. M. Bryliakov, Energy saturation and reaction capacity of diamond clusters, Problems of explosion and combustion, Proc. Xlth All-Union Syrup. on Combustion and Explosion, November 19-24, 1989, Suzdal, Chernogolovka, 1989, pp. 107-109. 6 A. L. Vereschagin, G. M. Ulianova, V. V. Novoselov, L. A. Petrova and P. M. Bryliakov, Complex thermal analysis of diamond like carbon phase in a controlled atmosphere, Superhard Mater., 5 (1990) 20-22. 7 0 . N. Breusov, V. M. Volkov, V. N. Drobyshev and V. P. Tatsiy, Experimental and theoretical analysis of diamond micropowders by DTA method, Interaction of Diamond with Gas and Liquid Media, Institute for Superhard Materials, Akademi Nauk Ukraine, Kiev, 1984, pp. 19-35. 8 N. D. Samsonenko and E. V. Sobolev, ESR and its dependence from diamond surface, JETP Lett., 5 (9) (1967) 304-307. 9 A. V. Beliankina, T. A. Nachalnaia, U. I. Sozin and L. A. Shulman, X-ray data and ESR spectrum of explosive diamonds, Synthetic Diamonds, (5) (1975) 5-7.