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Preparation of nanometer copper borate with supercritical carbon dioxide drying
Powder Technology 102 Ž1999. 171–176
Preparation of nanometer copper borate with supercritical carbon dioxide drying Z.S. Hu ) , J.X. Dong, G.X. Chen, F. Lou Department of Petrochemistry, Logistic Engineering College, Changjiang 2nd Str., Chongqing 400042, China Received 24 September 1997; received in revised form 31 August 1998; accepted 16 September 1998
Abstract A supercritical carbon dioxide drying technique was developed to prepare nanometer particle. The process of the technique mainly consisted of a preparation of gel in aqueous solution, filtering, replacement of the water in the precipitate with a mixture of n-propanol and benzene, supercritical drying. The technique can be industrialized easily and can be widespreadly used in the preparation of nanometer metal hydroxide, salt that are insoluble in water and propanol. Copper borate with a particle size of 10–20 nm, a surface area of 247.7 m2rg and a pore volume of 1.059 mlrg, was prepared using the method. The surface area and the pore volume were much larger than that of the sample prepared using precipitation method. q 1999 Elsevier Science S.A. All rights reserved. Keywords: Nanometer particle; Carbon oxide; Supercritical drying; Copper borate
1. Introduction Nanometer particles possess many special properties w1,2x. With the development of application research, serial preparation techniques of nanometer particles have been developed, such as microemulsification technique w3–6x, phase transfer technique w7,8x, and supercritical drying. The characteristics of supercritical drying is that solvent was removed completely without gas–liquid interface i.e., without the influence of interface tension w9x. Ethanol supercritical drying technique was ever employed to prepare SiO 2 aerogel w10–12x and nanometer catalyst w9x. The separation of water from ethanol, i.e., the recovery of ethanol after supercritical drying, however, is very difficult because of the formation of a constant boiling mixture. Yin et al. w13,14x, prepared ceramic material with methanol supercritical drying. Recently, much attention has been paid to carbon dioxide supercritical drying w11,15,16x because carbon dioxide is very cheap and can be regenerated easily by a cycle system. Unfortunately, a poor solubility of water in supercritical carbon dioxide extremely restrains
)
Corresponding author. Fax: q86-23-68756443
its application. Tewari et al. w17,18x successfully prepared transparent silica aerogel with hydrolysis of SiŽOC 2 H 5 .4 in alcohol and then carbon dioxide supercritical drying. van Bommel et al. w15x, prepared crack-free aerogel using similar technique. Aloxides, comparing with inorganic salt, generally are much expensive and there are no corresponding alcoxide for many metal elements. In the investigation of Mizushima et al. w11x, water in wet gel was replaced with ethanol, then the ethanol was extracted using supercritical carbon dioxide. Unfortunately, similar as ethanol supercritical drying, there still is the recovery difficult of ethanol from water. Recently, supercritical carbon dioxide was used to activate silica gel by Sato w19x, in which water at the activation points in the silica gel was removed by supercritical carbon dioxide. n-Propanol is not miscible with water at room temperature and when being heated, such as only 313 K, n-propanol and water with a ratio of 1:1 become miscible. In the present investigation, water in gel or precipitate was replaced with a mixture solvent of n-propanol and benzene, then the n-propanol, benzene, and remaining water were extracted using supercritical carbon dioxide because the solubility of n-propanol and benzene in supercritical carbon dioxide is excellent. No metal alcoholate was used in the preparation of the gel and no added treatments were needed for the regeneration of the mixture organic solvent
0032-5910r99r$ - see front matter q 1999 Elsevier Science S.A. All rights reserved. PII: S 0 0 3 2 - 5 9 1 0 Ž 9 8 . 0 0 1 9 0 - 9
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Z.S. Hu et al.r Powder Technology 102 (1999) 171–176
Fig. 1. Schematic diagram of the apparatus to replace water with carbon oxide. Ž1. Flask, Ž2. Oil–water separation tube.
because the solvent will be separated from water at room temperature. The recovered solvent can be used directly in the next preparation. The above procedure is a universal preparation technique of nanometer particles from water soluble salt and precipitant. Therefore, this investigation aims at developing the above supercritical carbon dioxide drying technique of nanometer particles preparation.
2. Experimental Chemicals: Analytical reagent grade borax, copper nitrate, n-propanol and benzene, commercial carbon dioxide. All of these chemicals are manufactured in China. 2.1. Preparation of nanometer copper borate Oil-soluble boron-containing compounds w20x and copper-containing compounds w21x are excellent antiwear additive of lubricating oil. Nanometer copper borate could also be an excellent antiwear additive of lubricating oil and can
Fig. 2. Schematic diagram of carbon dioxide supercritical dry apparatus.
Fig. 3. The morphology of the copper borate prepared using carbon dioxide supercritical drying. Magnification: 100 000=.
be dispersed in base oil stably, which, however, cannot be prepared using ethanol supercritical drying because Cu2q will be reduced by supercritical ethanol. Therefore, copper borate was taken as an example in the following preparation research. As a comparison, precipitation method was also employed in the preparation. 2.1.1. Precipitation method Copper nitrate amounting to 22.0 g and 34.7 g borax was dissolved in 100 ml distilled water at about 354 K, respectively. The borax solution was dropped into the copper nitrate solution with stirring. Filtered with suction.The precipitate was washed five times with 50 ml distilled water. Then, the precipitate was directly dried at 293 K for 2 h. 2.1.2. Carbon dioxide supercritical drying Replacement of water in the precipitate with n-propanol and benzene: the same preparation procedure of precipitate as the above was used in this section. An apparatus w22x, given in Fig. 1, was used to substitute water in the precipitate with n-propanol and benzene. Benzene was used to lower the boiling point of the solution and to
Fig. 4. The morphology of the copper borate prepared using precipitation method. Magnification: 100 000=.
Z.S. Hu et al.r Powder Technology 102 (1999) 171–176
173
Fig. 5. XRD spectra of the copper borate prepared using carbon oxide supercritical drying.
decrease the solubility of water in the organic phase. Copper borate precipitate, 200 ml propanol and 100 ml benzene were added in the flask, which was then heated. The water in vapor, after being cooled, was separated from propanol and benzene in the oil–water separation tube. The organic solvent was returned into the flask. Therefore, a simple distillation can remove most of the water in the precipitate. The distillation was stopped when the boiling point did not rise or the volume of the water stopped increasing. Supercritical drying: An apparatus was designed for supercritical carbon dioxide drying. The schematic diagram of the apparatus is given in Fig. 2. After filtering, the copper borate with n-propanol and benzene was added in
supercritical drying tube. Then, the tube was heated to 313 K. Carbon dioxide was pumped into the tube to a pressure of about 16 MPa. Closed stop valve 2, opened stop valve 3 and adjusted the needle valve to keep a pressure of 6–6.5 MPa in solvent regeneration tube. After circulating for 2.5 h, closed the pump and let off carbon dioxide as well as organic solvent. 2.2. Characterization Morphology and particles size of copper borate were measured with Hitachi H-600 Transmission Electron Microscopy, 200 kV; XRD spectra of the nanometer particles was measured with DX max-g A X-ray diffractometer, Cu
Fig. 6. XRD spectra of the copper borate prepared using precipitation method.
Z.S. Hu et al.r Powder Technology 102 (1999) 171–176
174
Fig. 7. Pore distribution of the copper borate prepared using precipitation method. Pore diameter Žnm., pore volume Žmlrg..
target, voltage: 40 kV. The BET surface area and pore structure of the product were measured using N2 adsorption with Micromeritics ASAP 2000. Before the measurement, all of these samples were treated at 393 K for 2 h.
3. Results and discussion 3.1. Morphology of copper borate In ethanol supercritical drying, solvent was removed completely without surface tension effect so that there will not appear coagulation of particles. For the process of
carbon dioxide supercritical drying, given in Section 2, two treatments can result in a coagulation of particles. The first was thermal treatment in the replacement of water with n-propanol and benzene, where the existence of water will promote the coagulation and recrystallization. The solubility of water in the mixture of n-propanol and benzene at room temperature cannot be neglected. If the remaining water in the solvent was not removed along with n-propanol and benzene by supercritical carbon dioxide, the preparation would fail. A representative photograph of copper borate particles prepared using the above process is given in Fig. 3. The particle size was 10–20 nm. This result indicates that the coagulation among particles
Fig. 8. Pore distribution of the copper borate prepared using carbon oxide supercritical drying. Cu 3 B 2 O6 : x, Na 4 B18 O 29 11H 2 O: Ø , Na 4 B10.2 O17.37H 2 O: I.
Z.S. Hu et al.r Powder Technology 102 (1999) 171–176 Table 1 Pore structure data and surface area of the copper borate Sample
˚ .a D ŽA
V Žmlrg. b
S Žm2 rg. c
Supercritical drying Precipitation method
171.1 64.0
1.059 0.252
247.7 157.3
a
BJH desorption average pore diameter. BJH cumulative desorption pore volume. c BJH cumulative desorption surface area. b
in the thermal treatment to replace water was not marked and that the mixture solvent may have acted as a carrier of remaining water in supercritical carbon dioxide drying, which promoted the removal of the water. The photograph of the copper borate prepared with precipitation method is given in Fig. 4. It can be found that a marked coagulation existed. 3.2. XRD characterization The XRD spectra of copper borate prepared with the above process and precipitation method are given in Figs. 5 and 6, respectively. The diffraction peaks of Cu 3 B 2 O6 are found in both spectra and the peaks were very dispersive, which indicated that the crystallite were very small. The other peaks partly resulted from sodium borate Na 4 B 18 O 29 11H 2 O or Na 4 B 10.2 O 17.37H 2 O. 3.3. Surface area and pore structure of the copper borate Pore size distribution of the copper borate prepared with precipitation method and supercritical carbon dioxide drying are given in Figs. 7 and 8, respectively. The sample,
175
prepared using the former method, possessed two kinds of pores. The small ones with a diameter of about 3.7 nm correspond to the voids among original particles. The bigger pores with a diameter of about 60 nm, therefore, correspond to the voids among coagulated ones of the original particles. A unimodal peak pore with a diameter of about 15 nm is shown in Fig. 8. The size of the voids, formed by a heap of sphere particles, is about one-third of the sphere diameter. Therefore, the pores of the copper borate, prepared with supercritical carbon dioxide drying technique, seems to be too large compared with its particle size. This resulted from texture of gel w23x. An acromion in Fig. 8, comparing with the second peak in Fig. 7, resulted from some coagulated particles, which probably were formed in thermal treatment of replacing water with organic solvent. The pore structure data and surface area are given in Table 1. It can be seen that the pore volume and surface area of the sample prepared with the supercritical drying were much larger than that of the sample prepared by precipitation method. A schematic illustration of the formation of particles size and pore structure is given in Fig. 9 w24x.
4. Conclusions A nanometer particle preparation technique of supercritical carbon dioxide drying was developed. Copper borate with a particle size of 10–20 nm, a surface area of 247.7 m2rg and a pore volume of 1.059 mlrg, was prepared using the method. The surface area and pore volume were much larger than that of the sample prepared with precipitation method. The copper borate possessed a unimodal
Fig. 9. A schematic illustration of the formation of secondary particles and pore structure.
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Z.S. Hu et al.r Powder Technology 102 (1999) 171–176
pore structure, whereas the copper borate prepared using precipitation method showed a bimodal pore size distribution.
w9x w10x w11x w12x
References
w13x w14x w15x w16x
w1x P.L. Zhang et al., J. Silicate 22 Ž1994. 141–146, ŽChinese.. w2x Q.R. Zhang, High Temperature Superconductivity, Zhejiang University Press, pp. 451–503, 1992 ŽChinese.. w3x H. Sato, T. Hirai, I. Komasawa, Ind. Eng. Chem. Res. 34 Ž1995. 2493. w4x G. Masao et al., J. Colloid Interface Sci. 93 Ž1983. 293. w5x K. Kazue et al., J. Am. Chem. Soc. 105 Ž1983. 2574. w6x W.N. Maclay, E.M. Gindler, J. Colloid Sci. 18 Ž1963. 343. w7x Z.S. Hu, S.Y. Chen, S.Y. Peng, J. Colloid Interface Sci. 182 Ž1996. 461–464. w8x Z.S. Hu, S.Y. Chen, S.Y. Peng, J. Colloid Interface Sci. 182 Ž1996. 457–460.
w17x w18x w19x w20x w21x w22x w23x w24x
S. Gakkai, Shokubai 39 Ž1997. 275–280. Y. Mizushima, M. Hori, J. Mater. Sci. 30 Ž1995. 1551. Y. Mizushima, M. Hori, J. Mater. Res. 10 Ž1995. 1424. S.B. Xiong, Z.M. Ye, Z.G. Liu, W.P. Ding, X.Q. Zheng, Y.P. Zhu, C.Y. Lin, Materials Letters 32 Ž1997. 165. S. Yin, Y. Fujishiro, T. Sato, Kidorui 28 Ž1996. 178. S. Yin, Y. Fujishiro, T. Sato, Br. Ceram. Trans. 95 Ž1996. 258. M.J. van Bommel, A.B. de Haan, J. Mater. Sci. 29 Ž1994. 943. J. Robertson, M.B. King, J.P.K. Seville, IChemE Res. Event, Eur. Conf. Young Res. Chem. Eng., 2nd Vol. 2 Ž1996., p. 988. P.H. Tewari, A.J. Hunt, Lofftus, Materials Letters 3 Ž1985. 363. P.H. Tewari, A.J. Hunt, Milpitas, United States Patent 4,610,863. Sato Shinya, Jasco Rep. 1997, Anniv. Vol., 23–25 ŽJapan.. A.G. Horodysky et al., United State Patent 4,906,390. R.G. Xiong, H. Wang, J.L. Zuo, C.M. Liu, X.Y. You, J.X. Dong, P. Zhang, J. Tribology 118 Ž1996. 676. Z.S. Hu, et al., China Patent. Applied No.: 94248349,9. J. Zarzycki, M. Parssas, J. Phalippou, J. Mater. Sci. 17 Ž1982. 3371. Z.S. Hu, J.X. Dong, G.X. Chen, Preparation of Nanometer Titanium Oxide with n-Butanol Supercritical Drying, Powder Technol. 101 Ž1999. 205–210.
Preparation of nanometer copper borate with supercritical carbon dioxide drying Z.S. Hu ) , J.X. Dong, G.X. Chen, F. Lou Department of Petrochemistry, Logistic Engineering College, Changjiang 2nd Str., Chongqing 400042, China Received 24 September 1997; received in revised form 31 August 1998; accepted 16 September 1998
Abstract A supercritical carbon dioxide drying technique was developed to prepare nanometer particle. The process of the technique mainly consisted of a preparation of gel in aqueous solution, filtering, replacement of the water in the precipitate with a mixture of n-propanol and benzene, supercritical drying. The technique can be industrialized easily and can be widespreadly used in the preparation of nanometer metal hydroxide, salt that are insoluble in water and propanol. Copper borate with a particle size of 10–20 nm, a surface area of 247.7 m2rg and a pore volume of 1.059 mlrg, was prepared using the method. The surface area and the pore volume were much larger than that of the sample prepared using precipitation method. q 1999 Elsevier Science S.A. All rights reserved. Keywords: Nanometer particle; Carbon oxide; Supercritical drying; Copper borate
1. Introduction Nanometer particles possess many special properties w1,2x. With the development of application research, serial preparation techniques of nanometer particles have been developed, such as microemulsification technique w3–6x, phase transfer technique w7,8x, and supercritical drying. The characteristics of supercritical drying is that solvent was removed completely without gas–liquid interface i.e., without the influence of interface tension w9x. Ethanol supercritical drying technique was ever employed to prepare SiO 2 aerogel w10–12x and nanometer catalyst w9x. The separation of water from ethanol, i.e., the recovery of ethanol after supercritical drying, however, is very difficult because of the formation of a constant boiling mixture. Yin et al. w13,14x, prepared ceramic material with methanol supercritical drying. Recently, much attention has been paid to carbon dioxide supercritical drying w11,15,16x because carbon dioxide is very cheap and can be regenerated easily by a cycle system. Unfortunately, a poor solubility of water in supercritical carbon dioxide extremely restrains
)
Corresponding author. Fax: q86-23-68756443
its application. Tewari et al. w17,18x successfully prepared transparent silica aerogel with hydrolysis of SiŽOC 2 H 5 .4 in alcohol and then carbon dioxide supercritical drying. van Bommel et al. w15x, prepared crack-free aerogel using similar technique. Aloxides, comparing with inorganic salt, generally are much expensive and there are no corresponding alcoxide for many metal elements. In the investigation of Mizushima et al. w11x, water in wet gel was replaced with ethanol, then the ethanol was extracted using supercritical carbon dioxide. Unfortunately, similar as ethanol supercritical drying, there still is the recovery difficult of ethanol from water. Recently, supercritical carbon dioxide was used to activate silica gel by Sato w19x, in which water at the activation points in the silica gel was removed by supercritical carbon dioxide. n-Propanol is not miscible with water at room temperature and when being heated, such as only 313 K, n-propanol and water with a ratio of 1:1 become miscible. In the present investigation, water in gel or precipitate was replaced with a mixture solvent of n-propanol and benzene, then the n-propanol, benzene, and remaining water were extracted using supercritical carbon dioxide because the solubility of n-propanol and benzene in supercritical carbon dioxide is excellent. No metal alcoholate was used in the preparation of the gel and no added treatments were needed for the regeneration of the mixture organic solvent
0032-5910r99r$ - see front matter q 1999 Elsevier Science S.A. All rights reserved. PII: S 0 0 3 2 - 5 9 1 0 Ž 9 8 . 0 0 1 9 0 - 9
172
Z.S. Hu et al.r Powder Technology 102 (1999) 171–176
Fig. 1. Schematic diagram of the apparatus to replace water with carbon oxide. Ž1. Flask, Ž2. Oil–water separation tube.
because the solvent will be separated from water at room temperature. The recovered solvent can be used directly in the next preparation. The above procedure is a universal preparation technique of nanometer particles from water soluble salt and precipitant. Therefore, this investigation aims at developing the above supercritical carbon dioxide drying technique of nanometer particles preparation.
2. Experimental Chemicals: Analytical reagent grade borax, copper nitrate, n-propanol and benzene, commercial carbon dioxide. All of these chemicals are manufactured in China. 2.1. Preparation of nanometer copper borate Oil-soluble boron-containing compounds w20x and copper-containing compounds w21x are excellent antiwear additive of lubricating oil. Nanometer copper borate could also be an excellent antiwear additive of lubricating oil and can
Fig. 2. Schematic diagram of carbon dioxide supercritical dry apparatus.
Fig. 3. The morphology of the copper borate prepared using carbon dioxide supercritical drying. Magnification: 100 000=.
be dispersed in base oil stably, which, however, cannot be prepared using ethanol supercritical drying because Cu2q will be reduced by supercritical ethanol. Therefore, copper borate was taken as an example in the following preparation research. As a comparison, precipitation method was also employed in the preparation. 2.1.1. Precipitation method Copper nitrate amounting to 22.0 g and 34.7 g borax was dissolved in 100 ml distilled water at about 354 K, respectively. The borax solution was dropped into the copper nitrate solution with stirring. Filtered with suction.The precipitate was washed five times with 50 ml distilled water. Then, the precipitate was directly dried at 293 K for 2 h. 2.1.2. Carbon dioxide supercritical drying Replacement of water in the precipitate with n-propanol and benzene: the same preparation procedure of precipitate as the above was used in this section. An apparatus w22x, given in Fig. 1, was used to substitute water in the precipitate with n-propanol and benzene. Benzene was used to lower the boiling point of the solution and to
Fig. 4. The morphology of the copper borate prepared using precipitation method. Magnification: 100 000=.
Z.S. Hu et al.r Powder Technology 102 (1999) 171–176
173
Fig. 5. XRD spectra of the copper borate prepared using carbon oxide supercritical drying.
decrease the solubility of water in the organic phase. Copper borate precipitate, 200 ml propanol and 100 ml benzene were added in the flask, which was then heated. The water in vapor, after being cooled, was separated from propanol and benzene in the oil–water separation tube. The organic solvent was returned into the flask. Therefore, a simple distillation can remove most of the water in the precipitate. The distillation was stopped when the boiling point did not rise or the volume of the water stopped increasing. Supercritical drying: An apparatus was designed for supercritical carbon dioxide drying. The schematic diagram of the apparatus is given in Fig. 2. After filtering, the copper borate with n-propanol and benzene was added in
supercritical drying tube. Then, the tube was heated to 313 K. Carbon dioxide was pumped into the tube to a pressure of about 16 MPa. Closed stop valve 2, opened stop valve 3 and adjusted the needle valve to keep a pressure of 6–6.5 MPa in solvent regeneration tube. After circulating for 2.5 h, closed the pump and let off carbon dioxide as well as organic solvent. 2.2. Characterization Morphology and particles size of copper borate were measured with Hitachi H-600 Transmission Electron Microscopy, 200 kV; XRD spectra of the nanometer particles was measured with DX max-g A X-ray diffractometer, Cu
Fig. 6. XRD spectra of the copper borate prepared using precipitation method.
Z.S. Hu et al.r Powder Technology 102 (1999) 171–176
174
Fig. 7. Pore distribution of the copper borate prepared using precipitation method. Pore diameter Žnm., pore volume Žmlrg..
target, voltage: 40 kV. The BET surface area and pore structure of the product were measured using N2 adsorption with Micromeritics ASAP 2000. Before the measurement, all of these samples were treated at 393 K for 2 h.
3. Results and discussion 3.1. Morphology of copper borate In ethanol supercritical drying, solvent was removed completely without surface tension effect so that there will not appear coagulation of particles. For the process of
carbon dioxide supercritical drying, given in Section 2, two treatments can result in a coagulation of particles. The first was thermal treatment in the replacement of water with n-propanol and benzene, where the existence of water will promote the coagulation and recrystallization. The solubility of water in the mixture of n-propanol and benzene at room temperature cannot be neglected. If the remaining water in the solvent was not removed along with n-propanol and benzene by supercritical carbon dioxide, the preparation would fail. A representative photograph of copper borate particles prepared using the above process is given in Fig. 3. The particle size was 10–20 nm. This result indicates that the coagulation among particles
Fig. 8. Pore distribution of the copper borate prepared using carbon oxide supercritical drying. Cu 3 B 2 O6 : x, Na 4 B18 O 29 11H 2 O: Ø , Na 4 B10.2 O17.37H 2 O: I.
Z.S. Hu et al.r Powder Technology 102 (1999) 171–176 Table 1 Pore structure data and surface area of the copper borate Sample
˚ .a D ŽA
V Žmlrg. b
S Žm2 rg. c
Supercritical drying Precipitation method
171.1 64.0
1.059 0.252
247.7 157.3
a
BJH desorption average pore diameter. BJH cumulative desorption pore volume. c BJH cumulative desorption surface area. b
in the thermal treatment to replace water was not marked and that the mixture solvent may have acted as a carrier of remaining water in supercritical carbon dioxide drying, which promoted the removal of the water. The photograph of the copper borate prepared with precipitation method is given in Fig. 4. It can be found that a marked coagulation existed. 3.2. XRD characterization The XRD spectra of copper borate prepared with the above process and precipitation method are given in Figs. 5 and 6, respectively. The diffraction peaks of Cu 3 B 2 O6 are found in both spectra and the peaks were very dispersive, which indicated that the crystallite were very small. The other peaks partly resulted from sodium borate Na 4 B 18 O 29 11H 2 O or Na 4 B 10.2 O 17.37H 2 O. 3.3. Surface area and pore structure of the copper borate Pore size distribution of the copper borate prepared with precipitation method and supercritical carbon dioxide drying are given in Figs. 7 and 8, respectively. The sample,
175
prepared using the former method, possessed two kinds of pores. The small ones with a diameter of about 3.7 nm correspond to the voids among original particles. The bigger pores with a diameter of about 60 nm, therefore, correspond to the voids among coagulated ones of the original particles. A unimodal peak pore with a diameter of about 15 nm is shown in Fig. 8. The size of the voids, formed by a heap of sphere particles, is about one-third of the sphere diameter. Therefore, the pores of the copper borate, prepared with supercritical carbon dioxide drying technique, seems to be too large compared with its particle size. This resulted from texture of gel w23x. An acromion in Fig. 8, comparing with the second peak in Fig. 7, resulted from some coagulated particles, which probably were formed in thermal treatment of replacing water with organic solvent. The pore structure data and surface area are given in Table 1. It can be seen that the pore volume and surface area of the sample prepared with the supercritical drying were much larger than that of the sample prepared by precipitation method. A schematic illustration of the formation of particles size and pore structure is given in Fig. 9 w24x.
4. Conclusions A nanometer particle preparation technique of supercritical carbon dioxide drying was developed. Copper borate with a particle size of 10–20 nm, a surface area of 247.7 m2rg and a pore volume of 1.059 mlrg, was prepared using the method. The surface area and pore volume were much larger than that of the sample prepared with precipitation method. The copper borate possessed a unimodal
Fig. 9. A schematic illustration of the formation of secondary particles and pore structure.
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Z.S. Hu et al.r Powder Technology 102 (1999) 171–176
pore structure, whereas the copper borate prepared using precipitation method showed a bimodal pore size distribution.
w9x w10x w11x w12x
References
w13x w14x w15x w16x
w1x P.L. Zhang et al., J. Silicate 22 Ž1994. 141–146, ŽChinese.. w2x Q.R. Zhang, High Temperature Superconductivity, Zhejiang University Press, pp. 451–503, 1992 ŽChinese.. w3x H. Sato, T. Hirai, I. Komasawa, Ind. Eng. Chem. Res. 34 Ž1995. 2493. w4x G. Masao et al., J. Colloid Interface Sci. 93 Ž1983. 293. w5x K. Kazue et al., J. Am. Chem. Soc. 105 Ž1983. 2574. w6x W.N. Maclay, E.M. Gindler, J. Colloid Sci. 18 Ž1963. 343. w7x Z.S. Hu, S.Y. Chen, S.Y. Peng, J. Colloid Interface Sci. 182 Ž1996. 461–464. w8x Z.S. Hu, S.Y. Chen, S.Y. Peng, J. Colloid Interface Sci. 182 Ž1996. 457–460.
w17x w18x w19x w20x w21x w22x w23x w24x
S. Gakkai, Shokubai 39 Ž1997. 275–280. Y. Mizushima, M. Hori, J. Mater. Sci. 30 Ž1995. 1551. Y. Mizushima, M. Hori, J. Mater. Res. 10 Ž1995. 1424. S.B. Xiong, Z.M. Ye, Z.G. Liu, W.P. Ding, X.Q. Zheng, Y.P. Zhu, C.Y. Lin, Materials Letters 32 Ž1997. 165. S. Yin, Y. Fujishiro, T. Sato, Kidorui 28 Ž1996. 178. S. Yin, Y. Fujishiro, T. Sato, Br. Ceram. Trans. 95 Ž1996. 258. M.J. van Bommel, A.B. de Haan, J. Mater. Sci. 29 Ž1994. 943. J. Robertson, M.B. King, J.P.K. Seville, IChemE Res. Event, Eur. Conf. Young Res. Chem. Eng., 2nd Vol. 2 Ž1996., p. 988. P.H. Tewari, A.J. Hunt, Lofftus, Materials Letters 3 Ž1985. 363. P.H. Tewari, A.J. Hunt, Milpitas, United States Patent 4,610,863. Sato Shinya, Jasco Rep. 1997, Anniv. Vol., 23–25 ŽJapan.. A.G. Horodysky et al., United State Patent 4,906,390. R.G. Xiong, H. Wang, J.L. Zuo, C.M. Liu, X.Y. You, J.X. Dong, P. Zhang, J. Tribology 118 Ž1996. 676. Z.S. Hu, et al., China Patent. Applied No.: 94248349,9. J. Zarzycki, M. Parssas, J. Phalippou, J. Mater. Sci. 17 Ž1982. 3371. Z.S. Hu, J.X. Dong, G.X. Chen, Preparation of Nanometer Titanium Oxide with n-Butanol Supercritical Drying, Powder Technol. 101 Ž1999. 205–210.