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Effects of the additive NaN3 added in powder catalysts on the morphology and inclusions of diamonds synthesized under HPHT
Diamond & Related Materials 15 (2006) 10 – 14 www.elsevier.com/locate/diamond
Effects of the additive NaN3-added in powder catalysts on the morphology and inclusions of diamonds synthesized under HPHT Z.Z. Liang a, X. Jia a,b,*, P.W. Zhu a, H.A. Ma a, C.Y. Zang a, J.M. Qing a, Q.F. Guan a a
National Lab of Superhard Materials, Jilin University, Changchun 130012, China b Henan Polytechnic University, Jiaozuo 454000, China
Received 23 March 2005; received in revised form 3 May 2005; accepted 6 June 2005 Available online 1 September 2005
Abstract In this paper, the effects of the additive NaN3 added in powder catalysts to synthesize nitric diamond were studied in a cubic anvil highpressure and high-temperature apparatus (SPD-6 1200). Diamond crystals with perfect shape were successfully synthesized using NaN3added Fe90Ni10 catalyst under pressure 5.4 GPa and temperature 1600 K for 15 min. The temperature and pressure of crystals growth were increased with an increase of the content of NaN3. The V-shape section for the diamond’s growth, which is the region between the solvent/ carbon eutectic melting line and diamond/graphite equilibrium line under pressure and temperature, was moved upwards. The synthetic diamonds exhibited perfect cubo-octahedral shape or octahedral shape with green or densely green in color. However, some orderly accidented lines were observed on the surfaces of most of the diamond crystals synthesized with NaN3-added in Fe90Ni10. These lines might be formed during the procedure of crystal growth according to the results of the scanning electron microscope images. Moreover, the Mo¨ssbauer spectrometry for these diamonds indicated that the concentrations of inclusions formed by iron in diamonds were changed and iron nitride was detected. D 2005 Elsevier B.V. All rights reserved. Keywords: Diamond; Powder catalyst; Nitrogen; Inclusion
1. Introduction It is well known that there are a lot of impurities in diamonds synthesized by the high-pressure and high-temperature (HPHT). Parts of impurities can enter into diamond with the types of substitutes or inclusions [1 –8]. Different impurities have different influences on the properties of diamond. Some properties of diamond can be improved by certain elements in the diamond. For example, n-type or ptype diamonds doped with phosphorus and boron, respectively, used as electronic and optoelectronic devices, have been prepared by chemical vapor deposition (CVD) [9]. Furthermore, the lithium, phosphorus and nitrogen have been considered extensively for enhancing the emission capability of diamond films [10,11]. Therefore, it is * Corresponding author. National Lab of Superhard Materials, Jilin University, Changchun 130012, China. Fax: +86 431 5168858. E-mail address: [email protected] (X. Jia). 0925-9635/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.diamond.2005.06.003
significant for enriching the kinds and expanding the applied fields of diamond that some atoms are doped in the diamond. Although there are many reports on the preparation of n-type or p-type diamonds by CVD, the preparation of n-type diamonds by HPHT are seldom reported. In general, the doped diamond synthesized by HPHT was mainly carried out by adding additive to the mixture of the graphite powder and the catalyst powder. Consequently, the growth of diamond was affected directly by these additives added. For example, the nucleation of diamond was effectively enhanced by the additives of B4C, h-SiC and C60 fullerence particles added by a spot-coating process [12]. Furthermore, the characteristics of catalyst were changed by some elements added in the catalyst with very small concentration [13]. The trace elements in the catalyst will result in the changes on the color, shape and intensity of diamond and the distribution of the inclusion in the diamond. Nitrogen is one of the most common impurities in natural and synthetic diamond. Nitrogen influences the physical
Z.Z. Liang et al. / Diamond & Related Materials 15 (2006) 10 – 14
properties of diamond significantly [1 – 6,9], including mechanical, electric and thermal properties, especially most optical properties of diamond [14,15]. It will influence the potential applications of diamond in industry and high-tech fields [2– 5]. Therefore, many researchers have focused on the nitrogen in diamond synthesized by HPHT. However, up to date, how to dope nitrogen into diamond is an open question. In this paper, it was reported that diamond doped nitrogen, which was from the additive azide added in powder catalysts, was synthesized by HPHT. High purity NaN3 was performed as the source of nitrogen, and diamond crystals with perfect shape were synthesized with NaN3added Fe90Ni10 catalyst under a pressure of up to 5.4 GPa and a temperature of around 1600 K for 15 min. This work might be helpful to the further study on the doping-nitrogen diamond.
2. Experimental The scalelike graphite powders and the catalyst powders Fe90Ni10 with 75 Am in diameter were used in our study. The additive azide is NaN3 (99.99% in purity). The graphite powder and the catalyst powder (1 : 1, wt/wt) were mixed for 4 h firstly, and then were shaped with the form of pole for synthesizing diamond. The content of NaN3 added in catalysts is in the range of 0.1¨2 wt%. The sample assembly for diamond synthesis by HPHT is shown in Fig. 1. A graphite tube was introduced as heater. To figure out the effect of nitride NaN3, two kinds of diamonds were prepared. One kind of sample was synthesized from the graphite and catalysts powders directly and another sample was synthesized with additive NaN3 added in powder catalysts. The diamonds were synthesized in a cubic anvil high-pressure and high-temperature apparatus (SPD6 1200) with a sample chamber of 23 mm on an edge (Fig. 2) under pressure 5.4 GPa and temperature 1600 K for 15 min. The pressure was estimated by the oil press load, which was calibrated by a curve that was established based on the pressure-induced phase transitions of bismuth, thallium, and barium. The temperature was determined
11
Fig. 2. The schematic diagram of a reaction cell for diamond growth by HPHT in high-pressure and high-temperature apparatus (SPD-6 1200).
from a relation between the temperature and input power, which had been calibrated using a Pt6%Rh – Pt30%Rh thermocouple [13]. The measurement error in temperature and pressure was less than 5%. The collected samples were disposed in a bottle of boiling mixture of H2SO4 and HNO3, and then observed with an optical microscopy and scanning electron microscope on a LINK-ISIS JSM5310. The iron-inclusions in diamond crystal were characterized on an OXFORD MS500 transmission Mo¨ssbauer spectroscopy at room temperature. The spectra were recorded using a 57Co/Pd source.
3. Results and discussion 3.1. The effect of the additive NaN3 on the conditions of synthesis The pressure and temperature for diamonds synthesized by HPHT were studied firstly. The synthetic conditions for diamonds with different contents of additive NaN3 were shown in Table 1. It was found that the pressure and temperature for diamond synthesized with additive NaN3 were obviously higher than that without additive NaN3. The nucleation of diamond was decreased by additive NaN3 added in powder graphite and catalyst with the same pressure. The more additive NaN3 was added, the Table 1 The synthetic conditions of diamond with different NaN3 content (C4 > C3 > C2 > C1 > C0 = 0) Content additive NaN3 (wt%)
Fig. 1. The sample assembly for diamond synthesized by HPHT.
C0 = 0 C1 C2 C3 C4
The synthesis conditions Pressure (GPa)
Temperature (K)
5.10 5.25 5.40 5.63 5.70
1520 1570 1600 1650 1740
12
Z.Z. Liang et al. / Diamond & Related Materials 15 (2006) 10 – 14
Fig. 3. The sketch map of V-shape section (the region between the solvent/ carbon eutectic melting line and diamond/graphite equilibrium line) of the diamond crystals synthesized with powder catalyst and additive NaN3 moves upwards. (a) The V-shapes section of the diamond crystals synthesized without additive NaN3, (b) the V-shapes section of the diamond crystals synthesized with additive NaN3.
less nucleation of diamond appeared in the sample synthesized by HPHT, and the more high-pressure was needed. Furthermore, the alterable range of temperature for diamond synthesis was obviously decreased in the same synthetic pressure when additive NaN3 was added in the raw materials. This result was explained further by the sketch map shown in Fig. 3. The temperature and pressure of crystals growth were increased with the increase of the content of NaN3. In other words, the Vshape section for the diamond’s growth, which is the region between the solvent/carbon eutectic melting line and diamond/graphite equilibrium line under pressure and temperature, was moved upwards (a Y b) since the additive NaN3 was added in the raw materials. That is to say, the temperature and pressure for diamond synthesis should be increased with an increase of the contents of NaN3. Based on these results, the characteristics of catalyst might be changed by the additive NaN3. It was worthy of further investigation. 3.2. The effect of the additive NaN3 on the diamond crystals In general, the nitrogen source to diamond synthesis is difficult to be introduced. In this study, nitrogen dope was realized by adding NaN3, which is easy to decompose the
active nitrogen under HPHT, to the mixtures of the graphite powders and the catalyst powders. The samples were taken out of the high-pressure reaction cell after the pressure released and dissected along the longitudinal direction in the middle of samples. The surfaces of the cross section dissected were observed by optical microscopy which was used to analyze the nuclei and growth of diamond. It was found that diamonds synthesized with both catalyst powder and additive NaN3 were distributed homogeneously in the reaction chamber. The unreactive graphite and the catalysts were disposed in a boiling mixture of H2SO4 and HNO3 and synthesized diamonds were left. The surface configuration of diamond synthesized by HPHT with powder materials was observed carefully under an optical microscopy. Diamond crystals synthesized with pure catalysts Fe90Ni10 exhibit a cubooctahedral shape or perfect octahedral shape, and polycrystalline diamond crystals were not observed. Furthermore, the crystal shape was predominant with both {100} and {111} faces. The surfaces of diamond synthesized with catalysts without additive NaN3 were slippery and flat and no melting holes were found. These crystals were yellow in color. The photographs, which were taken under an optical microscopy, for diamond crystals synthesized with catalyst powders added NaN3, were shown in Fig. 4. The crystal size was about 200 Am for octahedral shape and 300 Am for cubo-octahedral morphology. The same pressure was required to synthesize diamonds with both the octahedron and cubo-octahedron shapes. However, the synthetic temperature for octahedral diamond was higher than that for cubo-octahedron about 50 K. Diamond crystals synthesized with catalysts added NaN3 exhibit a cubooctahedral shape or perfect octahedral shape and the crystal shape was predominant with both {100} and {111} faces, too. However, the color of crystals synthesized with additive NaN3 was obviously changed under optical microscopy. Most of crystals were green or densely green observed under optical microscopy. It was worth noting that one part of crystal was green and another part of the same crystal was yellow. The crystals with octahedral shape were more transparent but much less green than the crystals with cubo-octahedral shape.
Fig. 4. The photographs of diamond crystals synthesized with NaN3-added catalyst powder. (a) Diamond crystals exhibit a cubo-octahedral shape, (b) diamond crystals exhibit octahedral shape.
Z.Z. Liang et al. / Diamond & Related Materials 15 (2006) 10 – 14
Furthermore, there were some accidented lines on most of the surfaces of diamond synthesized with NaN3-added catalysts Fe90Ni10. The scanning electron microscopy was used to analyze the surface configuration of the diamond synthesized by HPHT more carefully. The scanning electron microscope images for typical crystals synthesized with catalysts were shown in Fig. 5. The surfaces of diamond synthesized with catalysts without additive NaN3 were slippery and flat (Fig. 5(a)). However, some accidented lines were distributed orderly on the surfaces of the diamond crystals synthesized with additive NaN3 (Fig. 5(b)). Fig. 5(c) is the photograph enlarged from the sections marked by circle in Fig. 5(b). The accidented lines arranged orderly on the surfaces of the diamond crystals might be formed during the procedure of crystal growth. The width of each line was about 5¨8 Am, and the depth and width of the concave lines formed by the bordering upon developing grains of diamond was 2¨5 and 2¨4 Am. However, the accidented growing lines didn’t exist in the diamond synthesized without additive NaN3. These results indicated that the array of crystal lattice might be changed during the process of diamond synthesized by HPHT with the additive NaN3 added to the mixtures of the graphite powders and the catalyst powders. When the additive NaN3 was mixed with powder catalysts, the characteristics of lubricity for the diamond surfaces were destroyed with different degrees, especially in the {111} face. The accidented lines on most of the surfaces of the diamond synthesized with NaN3-added Fe90Ni10 might help to improve the characteristics of diamond-coated tools for these accidented lines would result in the improvement of the adhesive ability.
13
Fig. 6. Transmission Mo¨ssbauer spectra (recorded at room temperature) of synthesis diamonds. (a) The transmission Mo¨ssbauer spectra of diamond crystals synthesized without additive NaN3, (b) the transmission Mo¨ssbauer spectra of diamond crystals synthesized with catalyst powder added NaN3.
3.3. The effect of the additive NaN3 on the components of inclusion formed by iron in crystals A lot of inclusions were observed with dot form in the crystals synthesized without NaN3 in Fe90Ni10 and with the form of fog in the crystals synthesized with NaN3added under optical microscopy. Due to green or densely green in color, the transparence of diamond synthesized with NaN3-added was not as good as that of crystals synthesized without NaN3. However, the crystals synthesized with NaN3-added were transparent still. In order to analyze the kinds of inclusion in diamond, local states of iron in the inclusions of crystal were investigated on an OXFORD MS-500 transmission Mo¨ssbauer spectroscopy at room temperature.
Fig. 5. The scanning electron microscope photographs of diamond crystals. (a) The slippery and flat surfaces of diamond synthesized with catalysts without additive NaN3, (b) the accidented lines arranged orderly on the faces of the diamond synthesized with catalysts added additive NaN3, (c) the amplificatory photograph of the accidented lines in the sections marked by circle in (b).
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Z.Z. Liang et al. / Diamond & Related Materials 15 (2006) 10 – 14
Table 2 The composition and content of inclusion formed by iron in diamonds Catalyst
Fe90Ni10 Fe90Ni10 + NaN3
The composition and content of inclusion formed by iron (wt%) Fe3C
Fe – Ni alloy
FeN
46.8 18.9
53.2 49.6
– 31.5
The transmission Mo¨ssbauer spectra (recorded at room temperature) of synthetic diamonds were shown in Fig. 6. The results of transmission Mo¨ssbauer spectra for diamond synthesized without additive NaN3 are in a good agreement with Fe3C phase and Fe – Ni alloy phase (Fig. 6(a)). The forms of iron in the inclusions of crystal synthesized without additive NaN3 were presented mainly of two kinds. Table 2 showed the composition and content of inclusion formed by iron in diamonds, which were estimated from the transmission Mo¨ssbauer spectra. The contents of Fe3C phase and Fe – Ni alloy phase were 46.8% and 53.2%, respectively. However, the transmission Mo¨ssbauer spectra of diamonds synthesized with NaN3-added catalysts corresponded not only to Fe3C phase and Fe –Ni alloy phase (Fig. 6(b)), but also to the presence of iron nitride phase. The Mo¨ssbauer spectra with H f = 185.6 KOe in Fig. 6(b) correspond to iron nitride phase (H f, hyperfine magnetic field). These results are in agreement with the results in Ref. [16]. The parameters given by Kopcewicz vary somewhat depending on the method of sample preparation and experimental conditions. However, the hyperfine parameters in the transmission Mo¨ssbauer spectra are consistent with most of the results reported in the literature [16]. Based on the results of Mo¨ssbauer spectrometry, the kinds of inclusion in diamond synthesized with NaN3-added the mixture of the graphite powders and the catalyst powders were changed and the inclusion of iron nitride was formed. It was obviously seen from Table 2 that the contents of Fe3C phase, Fe– Ni alloy phase and iron nitride phase were 18.9%, 49.6% and 31.5%, respectively. The results obtained in this study indicated that the additive NaN3 was suitable to decrease the contents of Fe3C phase and Fe –Ni alloy phase in diamond’s inclusion.
4. Conclusion Diamond crystals with perfect shape were successfully synthesized using NaN3-added Fe90Ni10 catalyst under pressure 5.4 GPa and temperature 1600 K for 15 min. The temperature and pressure of crystals growth increased with an increase of the content of NaN3. The V-shape section for
the diamond’s growth, which is the region between the solvent/carbon eutectic melting line and diamond/graphite equilibrium line under pressure and temperature, was moved upwards. The synthetic diamonds with NaN3-added were presented perfect cubo-octahedral shape or octahedral shape with green or densely green. Whereas the crystals synthesized without NaN3-added were yellow in color. Furthermore, there were some orderly accidented lines on most of the surfaces of diamond synthesized with NaN3-added in Fe90Ni10 catalyst. The forms of the inclusions in diamond were changed by the additive NaN3-added. The results of the Mo¨ssbauer spectrometry for these diamonds indicated that the concentrations of inclusions formed by iron in diamonds were changed and iron nitride was detected.
Acknowledgment The authors are grateful to Dr N. Zheng and Dr X.Y. Hua for their assistance in the course of the work. This work was supported by the National Science Foundation of China under Grant Nos. 50172018.
References [1] E.A. Ekimov, V.A. Sidorov, E.D. Bauer, N.N. Mel’nik, N.J. Curro, J.D. Thompson, S.M. Stishov, Nature 4 (2004) 428. [2] Hisao Kanda, Minoru Akaishi, Shinobu Yamaoka, Diamond Relat. Mater. 8 (1999) 1441. [3] Yu. Borzdov, Yu. Pal’yanov, I. Kupriyanov, V. Gusev, A. Khokhryakov, A. Sokol, A. Efremov, Diamond Relat. Mater. 11 (2002) 1863. [4] W. Kindlein Jr., R.P. Livi, N.M. Balzaretti, J.A.H. da Jornada, Diamond Relat. Mater. 9 (2000) 22. [5] W. Kaiser, W.L. Bond, Phys. Rev. 115 (1959) 857. [6] C.D. Clark, A.T. Collins, G.S. Woods, in: F. Field (Ed.), The Properties of Natural and Synthetic Diamond, Academic, London, 1992, p. 35. [7] I. Kiflawi, H. Kanda, S.C. Lawson, Diamond Relat. Mater. 11 (2002) 204. [8] H. Kanda, K. Watanabe, Diamond Relat. Mater. 8 (1999) 1463. [9] R. Kalish, Carbon 37 (1999) 781. [10] C.F. Shih, K.S. Liu, I.N. Lin, Diamond Relat. Mater. 9 (2000) 1591. [11] Soo-Hyung Seo, Tae-Hoon Lee, Young-Do Kim, Chang-Kyun Park, Jin-Seok Park, Thin Solid Films 447 (2004) 212. [12] Wang Siqing, Lu Haibo, Ma Fukang, Mu Yufeng, J. Cryst. Growth 162 (1996) 69. [13] Z.Z. Liang, X. Jia, C.Y. Zang, P.W. Zhu, H.A. Ma, G.Z. Ren, Diamond Relat. Mater. 14 (2005) 243. [14] Ilene M. Reinitz, Emmanuel Fritsch, James E. Shigley, Diamond Relat. Mater. 7 (1998) 133. [15] Alan T. Collins, Hisao Kanda, Hiroshi Kitawaki, Diamond Relat. Mater. 9 (2000) 113. [16] Kopcewicz, J. Appl. Phys. 71 (1992) 4219.
Effects of the additive NaN3-added in powder catalysts on the morphology and inclusions of diamonds synthesized under HPHT Z.Z. Liang a, X. Jia a,b,*, P.W. Zhu a, H.A. Ma a, C.Y. Zang a, J.M. Qing a, Q.F. Guan a a
National Lab of Superhard Materials, Jilin University, Changchun 130012, China b Henan Polytechnic University, Jiaozuo 454000, China
Received 23 March 2005; received in revised form 3 May 2005; accepted 6 June 2005 Available online 1 September 2005
Abstract In this paper, the effects of the additive NaN3 added in powder catalysts to synthesize nitric diamond were studied in a cubic anvil highpressure and high-temperature apparatus (SPD-6 1200). Diamond crystals with perfect shape were successfully synthesized using NaN3added Fe90Ni10 catalyst under pressure 5.4 GPa and temperature 1600 K for 15 min. The temperature and pressure of crystals growth were increased with an increase of the content of NaN3. The V-shape section for the diamond’s growth, which is the region between the solvent/ carbon eutectic melting line and diamond/graphite equilibrium line under pressure and temperature, was moved upwards. The synthetic diamonds exhibited perfect cubo-octahedral shape or octahedral shape with green or densely green in color. However, some orderly accidented lines were observed on the surfaces of most of the diamond crystals synthesized with NaN3-added in Fe90Ni10. These lines might be formed during the procedure of crystal growth according to the results of the scanning electron microscope images. Moreover, the Mo¨ssbauer spectrometry for these diamonds indicated that the concentrations of inclusions formed by iron in diamonds were changed and iron nitride was detected. D 2005 Elsevier B.V. All rights reserved. Keywords: Diamond; Powder catalyst; Nitrogen; Inclusion
1. Introduction It is well known that there are a lot of impurities in diamonds synthesized by the high-pressure and high-temperature (HPHT). Parts of impurities can enter into diamond with the types of substitutes or inclusions [1 –8]. Different impurities have different influences on the properties of diamond. Some properties of diamond can be improved by certain elements in the diamond. For example, n-type or ptype diamonds doped with phosphorus and boron, respectively, used as electronic and optoelectronic devices, have been prepared by chemical vapor deposition (CVD) [9]. Furthermore, the lithium, phosphorus and nitrogen have been considered extensively for enhancing the emission capability of diamond films [10,11]. Therefore, it is * Corresponding author. National Lab of Superhard Materials, Jilin University, Changchun 130012, China. Fax: +86 431 5168858. E-mail address: [email protected] (X. Jia). 0925-9635/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.diamond.2005.06.003
significant for enriching the kinds and expanding the applied fields of diamond that some atoms are doped in the diamond. Although there are many reports on the preparation of n-type or p-type diamonds by CVD, the preparation of n-type diamonds by HPHT are seldom reported. In general, the doped diamond synthesized by HPHT was mainly carried out by adding additive to the mixture of the graphite powder and the catalyst powder. Consequently, the growth of diamond was affected directly by these additives added. For example, the nucleation of diamond was effectively enhanced by the additives of B4C, h-SiC and C60 fullerence particles added by a spot-coating process [12]. Furthermore, the characteristics of catalyst were changed by some elements added in the catalyst with very small concentration [13]. The trace elements in the catalyst will result in the changes on the color, shape and intensity of diamond and the distribution of the inclusion in the diamond. Nitrogen is one of the most common impurities in natural and synthetic diamond. Nitrogen influences the physical
Z.Z. Liang et al. / Diamond & Related Materials 15 (2006) 10 – 14
properties of diamond significantly [1 – 6,9], including mechanical, electric and thermal properties, especially most optical properties of diamond [14,15]. It will influence the potential applications of diamond in industry and high-tech fields [2– 5]. Therefore, many researchers have focused on the nitrogen in diamond synthesized by HPHT. However, up to date, how to dope nitrogen into diamond is an open question. In this paper, it was reported that diamond doped nitrogen, which was from the additive azide added in powder catalysts, was synthesized by HPHT. High purity NaN3 was performed as the source of nitrogen, and diamond crystals with perfect shape were synthesized with NaN3added Fe90Ni10 catalyst under a pressure of up to 5.4 GPa and a temperature of around 1600 K for 15 min. This work might be helpful to the further study on the doping-nitrogen diamond.
2. Experimental The scalelike graphite powders and the catalyst powders Fe90Ni10 with 75 Am in diameter were used in our study. The additive azide is NaN3 (99.99% in purity). The graphite powder and the catalyst powder (1 : 1, wt/wt) were mixed for 4 h firstly, and then were shaped with the form of pole for synthesizing diamond. The content of NaN3 added in catalysts is in the range of 0.1¨2 wt%. The sample assembly for diamond synthesis by HPHT is shown in Fig. 1. A graphite tube was introduced as heater. To figure out the effect of nitride NaN3, two kinds of diamonds were prepared. One kind of sample was synthesized from the graphite and catalysts powders directly and another sample was synthesized with additive NaN3 added in powder catalysts. The diamonds were synthesized in a cubic anvil high-pressure and high-temperature apparatus (SPD6 1200) with a sample chamber of 23 mm on an edge (Fig. 2) under pressure 5.4 GPa and temperature 1600 K for 15 min. The pressure was estimated by the oil press load, which was calibrated by a curve that was established based on the pressure-induced phase transitions of bismuth, thallium, and barium. The temperature was determined
11
Fig. 2. The schematic diagram of a reaction cell for diamond growth by HPHT in high-pressure and high-temperature apparatus (SPD-6 1200).
from a relation between the temperature and input power, which had been calibrated using a Pt6%Rh – Pt30%Rh thermocouple [13]. The measurement error in temperature and pressure was less than 5%. The collected samples were disposed in a bottle of boiling mixture of H2SO4 and HNO3, and then observed with an optical microscopy and scanning electron microscope on a LINK-ISIS JSM5310. The iron-inclusions in diamond crystal were characterized on an OXFORD MS500 transmission Mo¨ssbauer spectroscopy at room temperature. The spectra were recorded using a 57Co/Pd source.
3. Results and discussion 3.1. The effect of the additive NaN3 on the conditions of synthesis The pressure and temperature for diamonds synthesized by HPHT were studied firstly. The synthetic conditions for diamonds with different contents of additive NaN3 were shown in Table 1. It was found that the pressure and temperature for diamond synthesized with additive NaN3 were obviously higher than that without additive NaN3. The nucleation of diamond was decreased by additive NaN3 added in powder graphite and catalyst with the same pressure. The more additive NaN3 was added, the Table 1 The synthetic conditions of diamond with different NaN3 content (C4 > C3 > C2 > C1 > C0 = 0) Content additive NaN3 (wt%)
Fig. 1. The sample assembly for diamond synthesized by HPHT.
C0 = 0 C1 C2 C3 C4
The synthesis conditions Pressure (GPa)
Temperature (K)
5.10 5.25 5.40 5.63 5.70
1520 1570 1600 1650 1740
12
Z.Z. Liang et al. / Diamond & Related Materials 15 (2006) 10 – 14
Fig. 3. The sketch map of V-shape section (the region between the solvent/ carbon eutectic melting line and diamond/graphite equilibrium line) of the diamond crystals synthesized with powder catalyst and additive NaN3 moves upwards. (a) The V-shapes section of the diamond crystals synthesized without additive NaN3, (b) the V-shapes section of the diamond crystals synthesized with additive NaN3.
less nucleation of diamond appeared in the sample synthesized by HPHT, and the more high-pressure was needed. Furthermore, the alterable range of temperature for diamond synthesis was obviously decreased in the same synthetic pressure when additive NaN3 was added in the raw materials. This result was explained further by the sketch map shown in Fig. 3. The temperature and pressure of crystals growth were increased with the increase of the content of NaN3. In other words, the Vshape section for the diamond’s growth, which is the region between the solvent/carbon eutectic melting line and diamond/graphite equilibrium line under pressure and temperature, was moved upwards (a Y b) since the additive NaN3 was added in the raw materials. That is to say, the temperature and pressure for diamond synthesis should be increased with an increase of the contents of NaN3. Based on these results, the characteristics of catalyst might be changed by the additive NaN3. It was worthy of further investigation. 3.2. The effect of the additive NaN3 on the diamond crystals In general, the nitrogen source to diamond synthesis is difficult to be introduced. In this study, nitrogen dope was realized by adding NaN3, which is easy to decompose the
active nitrogen under HPHT, to the mixtures of the graphite powders and the catalyst powders. The samples were taken out of the high-pressure reaction cell after the pressure released and dissected along the longitudinal direction in the middle of samples. The surfaces of the cross section dissected were observed by optical microscopy which was used to analyze the nuclei and growth of diamond. It was found that diamonds synthesized with both catalyst powder and additive NaN3 were distributed homogeneously in the reaction chamber. The unreactive graphite and the catalysts were disposed in a boiling mixture of H2SO4 and HNO3 and synthesized diamonds were left. The surface configuration of diamond synthesized by HPHT with powder materials was observed carefully under an optical microscopy. Diamond crystals synthesized with pure catalysts Fe90Ni10 exhibit a cubooctahedral shape or perfect octahedral shape, and polycrystalline diamond crystals were not observed. Furthermore, the crystal shape was predominant with both {100} and {111} faces. The surfaces of diamond synthesized with catalysts without additive NaN3 were slippery and flat and no melting holes were found. These crystals were yellow in color. The photographs, which were taken under an optical microscopy, for diamond crystals synthesized with catalyst powders added NaN3, were shown in Fig. 4. The crystal size was about 200 Am for octahedral shape and 300 Am for cubo-octahedral morphology. The same pressure was required to synthesize diamonds with both the octahedron and cubo-octahedron shapes. However, the synthetic temperature for octahedral diamond was higher than that for cubo-octahedron about 50 K. Diamond crystals synthesized with catalysts added NaN3 exhibit a cubooctahedral shape or perfect octahedral shape and the crystal shape was predominant with both {100} and {111} faces, too. However, the color of crystals synthesized with additive NaN3 was obviously changed under optical microscopy. Most of crystals were green or densely green observed under optical microscopy. It was worth noting that one part of crystal was green and another part of the same crystal was yellow. The crystals with octahedral shape were more transparent but much less green than the crystals with cubo-octahedral shape.
Fig. 4. The photographs of diamond crystals synthesized with NaN3-added catalyst powder. (a) Diamond crystals exhibit a cubo-octahedral shape, (b) diamond crystals exhibit octahedral shape.
Z.Z. Liang et al. / Diamond & Related Materials 15 (2006) 10 – 14
Furthermore, there were some accidented lines on most of the surfaces of diamond synthesized with NaN3-added catalysts Fe90Ni10. The scanning electron microscopy was used to analyze the surface configuration of the diamond synthesized by HPHT more carefully. The scanning electron microscope images for typical crystals synthesized with catalysts were shown in Fig. 5. The surfaces of diamond synthesized with catalysts without additive NaN3 were slippery and flat (Fig. 5(a)). However, some accidented lines were distributed orderly on the surfaces of the diamond crystals synthesized with additive NaN3 (Fig. 5(b)). Fig. 5(c) is the photograph enlarged from the sections marked by circle in Fig. 5(b). The accidented lines arranged orderly on the surfaces of the diamond crystals might be formed during the procedure of crystal growth. The width of each line was about 5¨8 Am, and the depth and width of the concave lines formed by the bordering upon developing grains of diamond was 2¨5 and 2¨4 Am. However, the accidented growing lines didn’t exist in the diamond synthesized without additive NaN3. These results indicated that the array of crystal lattice might be changed during the process of diamond synthesized by HPHT with the additive NaN3 added to the mixtures of the graphite powders and the catalyst powders. When the additive NaN3 was mixed with powder catalysts, the characteristics of lubricity for the diamond surfaces were destroyed with different degrees, especially in the {111} face. The accidented lines on most of the surfaces of the diamond synthesized with NaN3-added Fe90Ni10 might help to improve the characteristics of diamond-coated tools for these accidented lines would result in the improvement of the adhesive ability.
13
Fig. 6. Transmission Mo¨ssbauer spectra (recorded at room temperature) of synthesis diamonds. (a) The transmission Mo¨ssbauer spectra of diamond crystals synthesized without additive NaN3, (b) the transmission Mo¨ssbauer spectra of diamond crystals synthesized with catalyst powder added NaN3.
3.3. The effect of the additive NaN3 on the components of inclusion formed by iron in crystals A lot of inclusions were observed with dot form in the crystals synthesized without NaN3 in Fe90Ni10 and with the form of fog in the crystals synthesized with NaN3added under optical microscopy. Due to green or densely green in color, the transparence of diamond synthesized with NaN3-added was not as good as that of crystals synthesized without NaN3. However, the crystals synthesized with NaN3-added were transparent still. In order to analyze the kinds of inclusion in diamond, local states of iron in the inclusions of crystal were investigated on an OXFORD MS-500 transmission Mo¨ssbauer spectroscopy at room temperature.
Fig. 5. The scanning electron microscope photographs of diamond crystals. (a) The slippery and flat surfaces of diamond synthesized with catalysts without additive NaN3, (b) the accidented lines arranged orderly on the faces of the diamond synthesized with catalysts added additive NaN3, (c) the amplificatory photograph of the accidented lines in the sections marked by circle in (b).
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Z.Z. Liang et al. / Diamond & Related Materials 15 (2006) 10 – 14
Table 2 The composition and content of inclusion formed by iron in diamonds Catalyst
Fe90Ni10 Fe90Ni10 + NaN3
The composition and content of inclusion formed by iron (wt%) Fe3C
Fe – Ni alloy
FeN
46.8 18.9
53.2 49.6
– 31.5
The transmission Mo¨ssbauer spectra (recorded at room temperature) of synthetic diamonds were shown in Fig. 6. The results of transmission Mo¨ssbauer spectra for diamond synthesized without additive NaN3 are in a good agreement with Fe3C phase and Fe – Ni alloy phase (Fig. 6(a)). The forms of iron in the inclusions of crystal synthesized without additive NaN3 were presented mainly of two kinds. Table 2 showed the composition and content of inclusion formed by iron in diamonds, which were estimated from the transmission Mo¨ssbauer spectra. The contents of Fe3C phase and Fe – Ni alloy phase were 46.8% and 53.2%, respectively. However, the transmission Mo¨ssbauer spectra of diamonds synthesized with NaN3-added catalysts corresponded not only to Fe3C phase and Fe –Ni alloy phase (Fig. 6(b)), but also to the presence of iron nitride phase. The Mo¨ssbauer spectra with H f = 185.6 KOe in Fig. 6(b) correspond to iron nitride phase (H f, hyperfine magnetic field). These results are in agreement with the results in Ref. [16]. The parameters given by Kopcewicz vary somewhat depending on the method of sample preparation and experimental conditions. However, the hyperfine parameters in the transmission Mo¨ssbauer spectra are consistent with most of the results reported in the literature [16]. Based on the results of Mo¨ssbauer spectrometry, the kinds of inclusion in diamond synthesized with NaN3-added the mixture of the graphite powders and the catalyst powders were changed and the inclusion of iron nitride was formed. It was obviously seen from Table 2 that the contents of Fe3C phase, Fe– Ni alloy phase and iron nitride phase were 18.9%, 49.6% and 31.5%, respectively. The results obtained in this study indicated that the additive NaN3 was suitable to decrease the contents of Fe3C phase and Fe –Ni alloy phase in diamond’s inclusion.
4. Conclusion Diamond crystals with perfect shape were successfully synthesized using NaN3-added Fe90Ni10 catalyst under pressure 5.4 GPa and temperature 1600 K for 15 min. The temperature and pressure of crystals growth increased with an increase of the content of NaN3. The V-shape section for
the diamond’s growth, which is the region between the solvent/carbon eutectic melting line and diamond/graphite equilibrium line under pressure and temperature, was moved upwards. The synthetic diamonds with NaN3-added were presented perfect cubo-octahedral shape or octahedral shape with green or densely green. Whereas the crystals synthesized without NaN3-added were yellow in color. Furthermore, there were some orderly accidented lines on most of the surfaces of diamond synthesized with NaN3-added in Fe90Ni10 catalyst. The forms of the inclusions in diamond were changed by the additive NaN3-added. The results of the Mo¨ssbauer spectrometry for these diamonds indicated that the concentrations of inclusions formed by iron in diamonds were changed and iron nitride was detected.
Acknowledgment The authors are grateful to Dr N. Zheng and Dr X.Y. Hua for their assistance in the course of the work. This work was supported by the National Science Foundation of China under Grant Nos. 50172018.
References [1] E.A. Ekimov, V.A. Sidorov, E.D. Bauer, N.N. Mel’nik, N.J. Curro, J.D. Thompson, S.M. Stishov, Nature 4 (2004) 428. [2] Hisao Kanda, Minoru Akaishi, Shinobu Yamaoka, Diamond Relat. Mater. 8 (1999) 1441. [3] Yu. Borzdov, Yu. Pal’yanov, I. Kupriyanov, V. Gusev, A. Khokhryakov, A. Sokol, A. Efremov, Diamond Relat. Mater. 11 (2002) 1863. [4] W. Kindlein Jr., R.P. Livi, N.M. Balzaretti, J.A.H. da Jornada, Diamond Relat. Mater. 9 (2000) 22. [5] W. Kaiser, W.L. Bond, Phys. Rev. 115 (1959) 857. [6] C.D. Clark, A.T. Collins, G.S. Woods, in: F. Field (Ed.), The Properties of Natural and Synthetic Diamond, Academic, London, 1992, p. 35. [7] I. Kiflawi, H. Kanda, S.C. Lawson, Diamond Relat. Mater. 11 (2002) 204. [8] H. Kanda, K. Watanabe, Diamond Relat. Mater. 8 (1999) 1463. [9] R. Kalish, Carbon 37 (1999) 781. [10] C.F. Shih, K.S. Liu, I.N. Lin, Diamond Relat. Mater. 9 (2000) 1591. [11] Soo-Hyung Seo, Tae-Hoon Lee, Young-Do Kim, Chang-Kyun Park, Jin-Seok Park, Thin Solid Films 447 (2004) 212. [12] Wang Siqing, Lu Haibo, Ma Fukang, Mu Yufeng, J. Cryst. Growth 162 (1996) 69. [13] Z.Z. Liang, X. Jia, C.Y. Zang, P.W. Zhu, H.A. Ma, G.Z. Ren, Diamond Relat. Mater. 14 (2005) 243. [14] Ilene M. Reinitz, Emmanuel Fritsch, James E. Shigley, Diamond Relat. Mater. 7 (1998) 133. [15] Alan T. Collins, Hisao Kanda, Hiroshi Kitawaki, Diamond Relat. Mater. 9 (2000) 113. [16] Kopcewicz, J. Appl. Phys. 71 (1992) 4219.