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2003 Volume 19 Issue 11
2003, 19(11): 993-995
doi: 10.3866/PKU.WHXB20031101
Abstract:
Nanodiamond (ND) prepared by explosive detonation has primary particles of 4～6 nm in diameter, but it under es severe aggregation in forming aggregates of hundreds of nm,even several μm in diameter. A new method for the deaggregation of nanodiamond (ND) is developed and some preliminary results using this method are presented: ND is first graphitized in nitrogen at 1 000 ℃ during which thin graphite layers are formed on the surface of the diamond particles and at the particle boundaries. The sample is then oxidized by air at 450 ℃ to remove the formed graphite layers. After such treatment the sample is suspended in water by ultrasonics, and the particle size distributions were measured by the laser scattering method. It has been found that the diameter of about 50％(w) of the ND particles can be reduced to less than 50 nm, while such ultrafine particles are absent in the suspension of the untreated ND. It is suggested that the deaggregation is caused by the removal of the graphite layers formed at the particle boundaries in the stage of oxidation. It is also found that after oxidation, some aggregates with larger diameters (1 000～2 000 nm) are formed, which can be explained by the formation of inter-particle ethereal bondings (C-O-C) during the oxidation by air.
Nanodiamond (ND) prepared by explosive detonation has primary particles of 4～6 nm in diameter, but it under es severe aggregation in forming aggregates of hundreds of nm,even several μm in diameter. A new method for the deaggregation of nanodiamond (ND) is developed and some preliminary results using this method are presented: ND is first graphitized in nitrogen at 1 000 ℃ during which thin graphite layers are formed on the surface of the diamond particles and at the particle boundaries. The sample is then oxidized by air at 450 ℃ to remove the formed graphite layers. After such treatment the sample is suspended in water by ultrasonics, and the particle size distributions were measured by the laser scattering method. It has been found that the diameter of about 50％(w) of the ND particles can be reduced to less than 50 nm, while such ultrafine particles are absent in the suspension of the untreated ND. It is suggested that the deaggregation is caused by the removal of the graphite layers formed at the particle boundaries in the stage of oxidation. It is also found that after oxidation, some aggregates with larger diameters (1 000～2 000 nm) are formed, which can be explained by the formation of inter-particle ethereal bondings (C-O-C) during the oxidation by air.
2003, 19(11): 996-1000
doi: 10.3866/PKU.WHXB20031102
Abstract:
A new kinetic model for the electrolytic codeposition of α-Al2O3 particles with Co-Ni alloys on a rotation disk electrode is presented, which is based on the balance of force acting on a particle near the electrode surface. Adsorption strength of particles on the electrode was used to describe the force intensity of the interaction between the particles and the electrode. The critical adsorption strength was used to classify the adsorption into effective adsorption and non-effective adsorption. Only when the adsorption strength of a particle is above the critical value, the adsorption becomes effective and may be incorporated into the deposit. The probability of the particles being effective adsorption dependents on the average adsorption strength, which is effected by the force acting on the particle. A kinetic mathematical model relating the content of embedded particles to suspension concentration was deduced. This relationship was verified experimentally by the codeposition systems of α-Al2O3/Co-Ni at the current density ranged from 1 to 20 A•dm－2. The variation of the content of particles in deposits with current density is an overall balance of two opposing effects, which leads to a maximum on the particle content against current density curves. Some model parameters were determined also by comparing theory and experimental data.
A new kinetic model for the electrolytic codeposition of α-Al2O3 particles with Co-Ni alloys on a rotation disk electrode is presented, which is based on the balance of force acting on a particle near the electrode surface. Adsorption strength of particles on the electrode was used to describe the force intensity of the interaction between the particles and the electrode. The critical adsorption strength was used to classify the adsorption into effective adsorption and non-effective adsorption. Only when the adsorption strength of a particle is above the critical value, the adsorption becomes effective and may be incorporated into the deposit. The probability of the particles being effective adsorption dependents on the average adsorption strength, which is effected by the force acting on the particle. A kinetic mathematical model relating the content of embedded particles to suspension concentration was deduced. This relationship was verified experimentally by the codeposition systems of α-Al2O3/Co-Ni at the current density ranged from 1 to 20 A•dm－2. The variation of the content of particles in deposits with current density is an overall balance of two opposing effects, which leads to a maximum on the particle content against current density curves. Some model parameters were determined also by comparing theory and experimental data.
2003, 19(11): 1001-1004
doi: 10.3866/PKU.WHXB20031103
Abstract:
The Pt/C catalyst (Pt/C(s)) was prepared with solid phase reaction method and its electrocatalytic activity for the ethanol oxidation was studied. XRD and TEM measurements indicated that the average diameter and the crystalline extent of Pt particles in Pt/C(s) are 3.8 nm and 2.38, respectively, which are much lower than the average diameter (8.5 nm) and the crystalline extent (5.56) of the Pt/C(l) catalyst prepared with the traditional liquid phase reaction method(Pt/C(l)). Therefore, the electrocatalytic activity of Pt/C(s) for the ethanol oxidation is much better than that of Pt/C(l). Cyclic voltammograms and chronoamperometric curves both confirmed this conclusion.
The Pt/C catalyst (Pt/C(s)) was prepared with solid phase reaction method and its electrocatalytic activity for the ethanol oxidation was studied. XRD and TEM measurements indicated that the average diameter and the crystalline extent of Pt particles in Pt/C(s) are 3.8 nm and 2.38, respectively, which are much lower than the average diameter (8.5 nm) and the crystalline extent (5.56) of the Pt/C(l) catalyst prepared with the traditional liquid phase reaction method(Pt/C(l)). Therefore, the electrocatalytic activity of Pt/C(s) for the ethanol oxidation is much better than that of Pt/C(l). Cyclic voltammograms and chronoamperometric curves both confirmed this conclusion.
2003, 19(11): 1005-1009
doi: 10.3866/PKU.WHXB20031104
Abstract:
A series of Ba1－xSrxTiO3 were prepared by sol-gel method. The crystal structure and phase transition of Ba1－xSrxTiO3 were studied by XRD、DSC and Raman spectra. The results suggest that the Sr dopant can decrease the cell volume effectively. With the increasing of the Sr dopant content, a axis and c axis become shorter and shorter and the value of c axis decreases more quickly than that of a axis. The axial ratio c/a approaches 1 gradually according to the increase of the Sr dopant content. At x=0.3 and room temperature, the cell aberrance occurs and Ba1－xSrxTiO3 exits mainly in cubic paraelectric phase. With the increase of Sr dopant, the potential well becomes shallow which results that the phase transition temperature becomes low and heat of phase transition becomes small and the phase transition becomes diffusive. There exists heat stagnation in phase transition. The Raman study suggests that the A1(TO2) optical phonon peak at 515 cm－1 splits into two peaks gradually while their intensity vary reversely. The other lower frequency phonon modes shift to the lower frequency while the higher frequency phonon modes shift to the higher frequency while each optical phonon peak becomes lower and broader. At room temperature, the transition of Ba1－xSrxTiO3 occurs from a ferroelectric tetra nal to a paraelectric cubic phase at x=0.30,which the Raman spectra support the order-disorder ferroelectric phase transformation.
A series of Ba1－xSrxTiO3 were prepared by sol-gel method. The crystal structure and phase transition of Ba1－xSrxTiO3 were studied by XRD、DSC and Raman spectra. The results suggest that the Sr dopant can decrease the cell volume effectively. With the increasing of the Sr dopant content, a axis and c axis become shorter and shorter and the value of c axis decreases more quickly than that of a axis. The axial ratio c/a approaches 1 gradually according to the increase of the Sr dopant content. At x=0.3 and room temperature, the cell aberrance occurs and Ba1－xSrxTiO3 exits mainly in cubic paraelectric phase. With the increase of Sr dopant, the potential well becomes shallow which results that the phase transition temperature becomes low and heat of phase transition becomes small and the phase transition becomes diffusive. There exists heat stagnation in phase transition. The Raman study suggests that the A1(TO2) optical phonon peak at 515 cm－1 splits into two peaks gradually while their intensity vary reversely. The other lower frequency phonon modes shift to the lower frequency while the higher frequency phonon modes shift to the higher frequency while each optical phonon peak becomes lower and broader. At room temperature, the transition of Ba1－xSrxTiO3 occurs from a ferroelectric tetra nal to a paraelectric cubic phase at x=0.30,which the Raman spectra support the order-disorder ferroelectric phase transformation.
2003, 19(11): 1010-1014
doi: 10.3866/PKU.WHXB20031105
Abstract:
Ab initio molecular orbital calculation was employed to optimized the geometry structure of poly (vinylidine fluoride) (PVDF) all-trans molecule. The calculated result is consistent with that of experiment. In our calculation, two different values of bond angle C－C－C were found, i.e.112.8° and 113.3°.The infrared intensity spectrum was obtained from frequencies calculation of the all-trans molecule. In the range of 400～4 000 cm－1,the IR spectra of polarized and unpolarized β-phase PVDF film (30 μm thick) have been measured. The calculated IR intensity spectrum is in od agreement with observed IR spectrum. The vibrational modes in the range of 400～4 000 cm－1 were divided into six series, series Ⅰ(544～415 cm－1), series Ⅱ(913～792 cm－1), series Ⅲ(1 353～998 cm－1), series Ⅳ(1 458～1 361 cm－1), seriesⅤand Ⅵ. Only series Ⅲ of all the vibrational modes causes the change of the dipole moment of PVDF molecule, and is related to the spontaneous polarization.
Ab initio molecular orbital calculation was employed to optimized the geometry structure of poly (vinylidine fluoride) (PVDF) all-trans molecule. The calculated result is consistent with that of experiment. In our calculation, two different values of bond angle C－C－C were found, i.e.112.8° and 113.3°.The infrared intensity spectrum was obtained from frequencies calculation of the all-trans molecule. In the range of 400～4 000 cm－1,the IR spectra of polarized and unpolarized β-phase PVDF film (30 μm thick) have been measured. The calculated IR intensity spectrum is in od agreement with observed IR spectrum. The vibrational modes in the range of 400～4 000 cm－1 were divided into six series, series Ⅰ(544～415 cm－1), series Ⅱ(913～792 cm－1), series Ⅲ(1 353～998 cm－1), series Ⅳ(1 458～1 361 cm－1), seriesⅤand Ⅵ. Only series Ⅲ of all the vibrational modes causes the change of the dipole moment of PVDF molecule, and is related to the spontaneous polarization.
2003, 19(11): 1015-1019
doi: 10.3866/PKU.WHXB20031106
Abstract:
Cationic Gemini surfactant, ethanediyl-α,β-bis(cetyldimethylammonium bromide)(16-2-16), was synthesized and characterized. The dynamic surface and interface tensions have been measured using pendant drop method on the air-water surface and dodecane-water interface. The relative contact angle of the aqueous solution on the silica gel powder has been obtained by modified Washburn method. The relationship between the contact angle and the dynamic surface (interface) tension has been discussed. Compared with conventional cationic surfactants, cetyldimethylammonium bromide(CTAB，cmc 1.0 ×10－3 mol•L－1), 16-2-16 has very low cmc value (1.8 ×10－5 mol•L－1). The most hydrophilic condition between the surfactant aqueous solution and the modified silica powder appears near the cmc for both 16-2-16 and CTAB. The best laboratory mimic oil recovery(Fig.1 and Table 2) is also reached around the cmc for the two surfactants, but the efficiency for 16-2-16(68％) is higher than the one for CTAB(63％).
Cationic Gemini surfactant, ethanediyl-α,β-bis(cetyldimethylammonium bromide)(16-2-16), was synthesized and characterized. The dynamic surface and interface tensions have been measured using pendant drop method on the air-water surface and dodecane-water interface. The relative contact angle of the aqueous solution on the silica gel powder has been obtained by modified Washburn method. The relationship between the contact angle and the dynamic surface (interface) tension has been discussed. Compared with conventional cationic surfactants, cetyldimethylammonium bromide(CTAB，cmc 1.0 ×10－3 mol•L－1), 16-2-16 has very low cmc value (1.8 ×10－5 mol•L－1). The most hydrophilic condition between the surfactant aqueous solution and the modified silica powder appears near the cmc for both 16-2-16 and CTAB. The best laboratory mimic oil recovery(Fig.1 and Table 2) is also reached around the cmc for the two surfactants, but the efficiency for 16-2-16(68％) is higher than the one for CTAB(63％).
2003, 19(11): 1020-1024
doi: 10.3866/PKU.WHXB20031107
Abstract:
Hydrophobically modified polyacrylamide(HMPAM) has been synthesized. The behavior and microstructure of HMPAM in aqueous solution, compared with polyacrylamide (PAM) have been studied by means of fluorescence and UV spectra, atomic force microscope and apparent viscosity test. The critical association concentration of HMPAM has been determined by the change of the value of I3/I1 of the fluorescence spectra. The results of fluorescence, UV and viscosity test show that with the increase of HMPAM concentration, hydrophobic domain, supermolecular aggregate and even space network structure can be formed in the solution by the hydrophobic association of HMPAM. The latter has been further confirmed by atomic force microscope. A mechanism for the increase of the viscosity of HMPAM solution has been suggested.
Hydrophobically modified polyacrylamide(HMPAM) has been synthesized. The behavior and microstructure of HMPAM in aqueous solution, compared with polyacrylamide (PAM) have been studied by means of fluorescence and UV spectra, atomic force microscope and apparent viscosity test. The critical association concentration of HMPAM has been determined by the change of the value of I3/I1 of the fluorescence spectra. The results of fluorescence, UV and viscosity test show that with the increase of HMPAM concentration, hydrophobic domain, supermolecular aggregate and even space network structure can be formed in the solution by the hydrophobic association of HMPAM. The latter has been further confirmed by atomic force microscope. A mechanism for the increase of the viscosity of HMPAM solution has been suggested.
2003, 19(11): 1025-1029
doi: 10.3866/PKU.WHXB20031108
Abstract:
The lanthanum doped modified spinel lithium manganate LiMn2－xLaxO4 (x=0,0.01, 0.02, 0.03, 0.04, 0.05, 0.10) used for cathode of lithium-ion batteries was prepared by solid-state method. The structure of the prepared cathode material was characterized by XRD. The effects of doping lanthanum on stabilizing the crystal structure were analyzed in terms of the material structure, charge and discharge testing results and cycle performance. The cycle performance of the modified material was obviously improved at both normal temperature and high temperature. Moreover, when the x in LiMn2－xLaxO4 was less than 0.04,high capacity can be observed. For instance, LiMn1.99La0.01O4 and LiMn1.98La0.02O4 have as high capacity as 122.4 mAh•g－1 and 116.7 mAh•g－1(see Fig.5(a)) respectively compared with the 120.8 mAh•g－1 of LiMn2O4. In addition, these two cathode materials can hold 95.60％ and 97.46％ of the initial capacity respectively after 50 cycles.
The lanthanum doped modified spinel lithium manganate LiMn2－xLaxO4 (x=0,0.01, 0.02, 0.03, 0.04, 0.05, 0.10) used for cathode of lithium-ion batteries was prepared by solid-state method. The structure of the prepared cathode material was characterized by XRD. The effects of doping lanthanum on stabilizing the crystal structure were analyzed in terms of the material structure, charge and discharge testing results and cycle performance. The cycle performance of the modified material was obviously improved at both normal temperature and high temperature. Moreover, when the x in LiMn2－xLaxO4 was less than 0.04,high capacity can be observed. For instance, LiMn1.99La0.01O4 and LiMn1.98La0.02O4 have as high capacity as 122.4 mAh•g－1 and 116.7 mAh•g－1(see Fig.5(a)) respectively compared with the 120.8 mAh•g－1 of LiMn2O4. In addition, these two cathode materials can hold 95.60％ and 97.46％ of the initial capacity respectively after 50 cycles.
2003, 19(11): 1030-1034
doi: 10.3866/PKU.WHXB20031109
Abstract:
The effects of cell temperature on the rate discharge capability, lithium ion diffusion rate and charge transfer activity of LiNi3/8Co2/8Mn3/8O2 were investigated by using X-ray diffractometry(XRD), X-ray photoelectron spectroscopy(XPS), constant-current charge-discharge test, cyclic voltammetry and electrochemical impedance spectroscopy(EIS). The experimental data show that the rate discharge capability of LiNi3/8Co2/8Mn3/8O2 is improved by increasing cell temperature. Both the charge transfer activity and the lithium ion diffusion rate in LiNi3/8Co2/8Mn3/8O2 increase at elevated temperatures. The activation energy for charge transfer is more than twice that for the lithium ion diffusion. The results indicate that the electrochemical reaction kinetics of LiNi3/8Co2/8Mn3/8O2 is mainly limited by charge transfer process. The charge transfer process is more affected by temperature than the lithium diffusion process. Improvement of the rate discharge capability of LiNi3/8Co2/8Mn3/8O2 at elevated temperatures is mainly caused by the increase of charge transfer rate in LiNi3/8Co2/8Mn3/8O2.
The effects of cell temperature on the rate discharge capability, lithium ion diffusion rate and charge transfer activity of LiNi3/8Co2/8Mn3/8O2 were investigated by using X-ray diffractometry(XRD), X-ray photoelectron spectroscopy(XPS), constant-current charge-discharge test, cyclic voltammetry and electrochemical impedance spectroscopy(EIS). The experimental data show that the rate discharge capability of LiNi3/8Co2/8Mn3/8O2 is improved by increasing cell temperature. Both the charge transfer activity and the lithium ion diffusion rate in LiNi3/8Co2/8Mn3/8O2 increase at elevated temperatures. The activation energy for charge transfer is more than twice that for the lithium ion diffusion. The results indicate that the electrochemical reaction kinetics of LiNi3/8Co2/8Mn3/8O2 is mainly limited by charge transfer process. The charge transfer process is more affected by temperature than the lithium diffusion process. Improvement of the rate discharge capability of LiNi3/8Co2/8Mn3/8O2 at elevated temperatures is mainly caused by the increase of charge transfer rate in LiNi3/8Co2/8Mn3/8O2.
2003, 19(11): 1035-1038
doi: 10.3866/PKU.WHXB20031110
Abstract:
Carbon hollow spheres were prepared via catalytic pyrolysis with kaolin supported nickel nitrate as catalyst. The hollow carbon spheres were synthesized by the catalytic pyrolysis of C2H2 mixed with N2 at 850 ℃. The characterization of catalyst and hollow carbon spheres were carried out by XRD, TEM, SEM and Raman spectroscopy. The TEM and SEM images suggested that the carbon spheres with diameter about 500 nm were hollow. SEM images and XRD patterns of catalyst suggested some information about the possible formation mechanism of hollow spheres.
Carbon hollow spheres were prepared via catalytic pyrolysis with kaolin supported nickel nitrate as catalyst. The hollow carbon spheres were synthesized by the catalytic pyrolysis of C2H2 mixed with N2 at 850 ℃. The characterization of catalyst and hollow carbon spheres were carried out by XRD, TEM, SEM and Raman spectroscopy. The TEM and SEM images suggested that the carbon spheres with diameter about 500 nm were hollow. SEM images and XRD patterns of catalyst suggested some information about the possible formation mechanism of hollow spheres.
2003, 19(11): 1039-1043
doi: 10.3866/PKU.WHXB20031111
Abstract:
In order to prepare high temperature resistant SiC fibers, polyaluminocarbosilane (PACS)was synthesized by reaction of polysilacarbosilane (PSCS) with Al(AcAc)3 (AcAc: acetylacetonate). Through melting spinning of PACS, air-curing, ceramination at 1300 ℃ and sintering at 1800 ℃ SiC(Al) ceramic fibers with high temperature resistance were obtained. 29Si MAS-NMR, AES, XRD, Raman spectra and SEM suggested that the composition of SiC(Al) fibers is close to stoichiometric ratio with much lower content of oxygen, free carbon and SixCyOz phase than that of common SiC fibers resulted in a character of high temperature resistance. In addition, densification and crystalline inhabitation by aluminum are crucial to the high temperature resistance of SiC(Al) fibers.
In order to prepare high temperature resistant SiC fibers, polyaluminocarbosilane (PACS)was synthesized by reaction of polysilacarbosilane (PSCS) with Al(AcAc)3 (AcAc: acetylacetonate). Through melting spinning of PACS, air-curing, ceramination at 1300 ℃ and sintering at 1800 ℃ SiC(Al) ceramic fibers with high temperature resistance were obtained. 29Si MAS-NMR, AES, XRD, Raman spectra and SEM suggested that the composition of SiC(Al) fibers is close to stoichiometric ratio with much lower content of oxygen, free carbon and SixCyOz phase than that of common SiC fibers resulted in a character of high temperature resistance. In addition, densification and crystalline inhabitation by aluminum are crucial to the high temperature resistance of SiC(Al) fibers.
2003, 19(11): 1044-1048
doi: 10.3866/PKU.WHXB20031112
Abstract:
MoS2 was prepared by a hydrothermal method at a relatively lower temperature(200 ℃) and shorter reaction duration(24 h). The resulting product samples were investigated by means of transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). The lubricating behavior of the prepared MoS2 sample as an additive in paraffin oil was examined on an MPX-2000 friction and wear tester. The worn steel surface was analyzed by means of Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) to investigate the lubricating mechanism of the synthetic MoS2 in the paraffin oil. It was found that the synthetic MoS2 as an additive in the paraffin oil showed better friction-reducing and antiwear ability than a commercial MoS2 of a diameter 3～5 μm in the same base stock and was more suitable for the situation of heavy load and long time running. MoS2 functioned to reduce the friction and wear of the steel-steel system by forming a transfer film on the worn steel surface but not by tribochemical reaction and diffusion and permeation therewith.
MoS2 was prepared by a hydrothermal method at a relatively lower temperature(200 ℃) and shorter reaction duration(24 h). The resulting product samples were investigated by means of transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). The lubricating behavior of the prepared MoS2 sample as an additive in paraffin oil was examined on an MPX-2000 friction and wear tester. The worn steel surface was analyzed by means of Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) to investigate the lubricating mechanism of the synthetic MoS2 in the paraffin oil. It was found that the synthetic MoS2 as an additive in the paraffin oil showed better friction-reducing and antiwear ability than a commercial MoS2 of a diameter 3～5 μm in the same base stock and was more suitable for the situation of heavy load and long time running. MoS2 functioned to reduce the friction and wear of the steel-steel system by forming a transfer film on the worn steel surface but not by tribochemical reaction and diffusion and permeation therewith.
2003, 19(11): 1049-1053
doi: 10.3866/PKU.WHXB20031113
Abstract:
PS/Ag composite microspheres with core-shell structure were prepared by a seeded emulsion polymerization. The surface of PS/Ag microspheres as prepared was functionalized by PMMA. Its morphology and structure were characterized by TEM, XRD, TG, DTA and FT-IR, etc. The results show that Ag nanocore is spherical and its average diameter is about 12 nm. The average diameter of composite microphere is about 25 nm with a narrow size distribution. It is also found that composite nanoparticles can be well dispersed in organic solvent. Their tribological properties as additives in liquid paraffin were investigated with a four-ball tribometer. The results indicate, with the lubrication of liquid paraffin containing PMMA/PS/Ag nanoparticles, the wear-scar diameter is far smaller as compare with pure liquid paraffin. Moreover its maximum non-seizure load is above 1000 N and that of pure liquid paraffin is below 400 N. This shows that composite nanospheres have a od anti-wear performance.
PS/Ag composite microspheres with core-shell structure were prepared by a seeded emulsion polymerization. The surface of PS/Ag microspheres as prepared was functionalized by PMMA. Its morphology and structure were characterized by TEM, XRD, TG, DTA and FT-IR, etc. The results show that Ag nanocore is spherical and its average diameter is about 12 nm. The average diameter of composite microphere is about 25 nm with a narrow size distribution. It is also found that composite nanoparticles can be well dispersed in organic solvent. Their tribological properties as additives in liquid paraffin were investigated with a four-ball tribometer. The results indicate, with the lubrication of liquid paraffin containing PMMA/PS/Ag nanoparticles, the wear-scar diameter is far smaller as compare with pure liquid paraffin. Moreover its maximum non-seizure load is above 1000 N and that of pure liquid paraffin is below 400 N. This shows that composite nanospheres have a od anti-wear performance.
2003, 19(11): 1054-1058
doi: 10.3866/PKU.WHXB20031114
Abstract:
The multiple scattering cluster (MSC) method has been employed to calculate the chlorine 1s near edge X-ray absorption fine structure (NEXAFS) of the Cl adsorbed on GaAs(111) surface. A series of specially designed clusters have been used to mimic the Cl/GaAs(111) geometry for finding the local geometrical structures of the system. The physical origin of the peaks in NEXAFS spectra has been revealed. MSC calculation shows that the Cl atom is adsorbed on the top site, the Cl－Ga bond length is (0.213±0.005) nm and the Ga－As bond length in surface layer is (0.235±0.005) nm. The comparison between above results and those of EXAFS experiment and the Slab model calculation has been made and discussed.
The multiple scattering cluster (MSC) method has been employed to calculate the chlorine 1s near edge X-ray absorption fine structure (NEXAFS) of the Cl adsorbed on GaAs(111) surface. A series of specially designed clusters have been used to mimic the Cl/GaAs(111) geometry for finding the local geometrical structures of the system. The physical origin of the peaks in NEXAFS spectra has been revealed. MSC calculation shows that the Cl atom is adsorbed on the top site, the Cl－Ga bond length is (0.213±0.005) nm and the Ga－As bond length in surface layer is (0.235±0.005) nm. The comparison between above results and those of EXAFS experiment and the Slab model calculation has been made and discussed.
2003, 19(11): 1059-1063
doi: 10.3866/PKU.WHXB20031115
Abstract:
Various chemical association models have been developed to fit the NMR chemical shift data of mixtures. However, pure chemical models retain the primary disadvantage of multiple adjustable parameters, which must be obtained especially for systems with a large number of different aggregates formed. A novel associated model based on statistic associating fluid theory (SAFT), which has less parameter, is proposed for correlating NMR chemical shift data for mixtures. The root mean square deviations (RMSD) of correlation for alcohol＋ N,N-dimethylformamide (DMF) systems are less than 1.01％. Furthermore, the difference of δH－x curve trend between methanol＋DMF system and methanol＋hexane system is discussed. The crossing－association between alcohol and DMF which is stronger than self-association of alcohols is regarded as the main reason of such difference.
Various chemical association models have been developed to fit the NMR chemical shift data of mixtures. However, pure chemical models retain the primary disadvantage of multiple adjustable parameters, which must be obtained especially for systems with a large number of different aggregates formed. A novel associated model based on statistic associating fluid theory (SAFT), which has less parameter, is proposed for correlating NMR chemical shift data for mixtures. The root mean square deviations (RMSD) of correlation for alcohol＋ N,N-dimethylformamide (DMF) systems are less than 1.01％. Furthermore, the difference of δH－x curve trend between methanol＋DMF system and methanol＋hexane system is discussed. The crossing－association between alcohol and DMF which is stronger than self-association of alcohols is regarded as the main reason of such difference.
2003, 19(11): 1064-1068
doi: 10.3866/PKU.WHXB20031116
Abstract:
The effect of pH of solution on the interaction between TH(thionine) and CT-DNA was studied using electrochemical and spectroscopic methods. The electrochemical results indicated that the interaction between TH and CT-DNA is in the intercalative mode in the pH 7.2 phosphate buffer solution, but both intercalative and electrostatic modes exist in the pH 6.5 phosphate buffer solution. Fluorescence spectroscopic results showed that the fluorescence intensity of TH is efficiently quenched by CT-DNA bases. The quenching constant, KSV obtained from the Stern-Volmer equation for the pH 6.5 solution is larger than that for the pH 7.2 solution indicating that the interaction between TH and CT-DNA in the pH 6.5 solution is stronger than that in the pH 7.2 solution. The conclusion is confirmed by the results of CD spectroscopic measurements.
The effect of pH of solution on the interaction between TH(thionine) and CT-DNA was studied using electrochemical and spectroscopic methods. The electrochemical results indicated that the interaction between TH and CT-DNA is in the intercalative mode in the pH 7.2 phosphate buffer solution, but both intercalative and electrostatic modes exist in the pH 6.5 phosphate buffer solution. Fluorescence spectroscopic results showed that the fluorescence intensity of TH is efficiently quenched by CT-DNA bases. The quenching constant, KSV obtained from the Stern-Volmer equation for the pH 6.5 solution is larger than that for the pH 7.2 solution indicating that the interaction between TH and CT-DNA in the pH 6.5 solution is stronger than that in the pH 7.2 solution. The conclusion is confirmed by the results of CD spectroscopic measurements.
2003, 19(11): 1069-1072
doi: 10.3866/PKU.WHXB20031117
Abstract:
The surface pressure-area per molecule isotherm of Gemini surfactant [propilidene-1,3- bis(dimethyloctadecylammonium bromide), PBDOAB] at an air/liquid interface of 0.005 mol•L-1 aqueous NaBr solution has been measured. The cross-sectional area of PBDOAB at the air/liquid interface has been obtained. Domain morphology formed by PBDOAB at the air/liquid has been investigated via BAM. Results show that PBDOAB forms condensed monolayer; that the circular domain morphology has been observed and that in the circular domains the molecular orientations of the PBDOAB is of central symmetry at the air/liquid interface of the aqueous NaBr solutions. It is proved that the chemical structure of Gemini surfactants strongly influences their properties at the air/liquid interface.
The surface pressure-area per molecule isotherm of Gemini surfactant [propilidene-1,3- bis(dimethyloctadecylammonium bromide), PBDOAB] at an air/liquid interface of 0.005 mol•L-1 aqueous NaBr solution has been measured. The cross-sectional area of PBDOAB at the air/liquid interface has been obtained. Domain morphology formed by PBDOAB at the air/liquid has been investigated via BAM. Results show that PBDOAB forms condensed monolayer; that the circular domain morphology has been observed and that in the circular domains the molecular orientations of the PBDOAB is of central symmetry at the air/liquid interface of the aqueous NaBr solutions. It is proved that the chemical structure of Gemini surfactants strongly influences their properties at the air/liquid interface.
2003, 19(11): 1073-1077
doi: 10.3866/PKU.WHXB20031118
Abstract:
Provisional data of the atomic average van der Waals radii including all common metal elements in crystals are proposed, which is derived from the available data of the average atom volume in crystals. Average volume of elements at 298 K was obtained by a statistical analysis of the Cambridge Structural Database. The present van der Waals radii are compared with the other systems proposed previously by Pauling, Bondi, Batsanov, Allinger or Zefirov. The van der Waals radii of lanthanide and actinide elements are peculiar to the other systems since they have never appeared in literature. It is worthy to note that all the radii presented in this work are more suitable to organic and metal-organic compounds. Moreover, the characteristics of this system, some current problems of van der Waals radii application and further study in this area are also discussed.
Provisional data of the atomic average van der Waals radii including all common metal elements in crystals are proposed, which is derived from the available data of the average atom volume in crystals. Average volume of elements at 298 K was obtained by a statistical analysis of the Cambridge Structural Database. The present van der Waals radii are compared with the other systems proposed previously by Pauling, Bondi, Batsanov, Allinger or Zefirov. The van der Waals radii of lanthanide and actinide elements are peculiar to the other systems since they have never appeared in literature. It is worthy to note that all the radii presented in this work are more suitable to organic and metal-organic compounds. Moreover, the characteristics of this system, some current problems of van der Waals radii application and further study in this area are also discussed.
2003, 19(11): 1081-1084
doi: 10.3866/PKU.WHXB20031119
Abstract:
A Monte Carlo simulation is performed to study the dependence of collision frequency on interparticle distance for a system composed of two hard-sphere particles. The simulation quantitatively shows that the collision frequency drops down sharply as the distance between two particles increases. This characteristic provides a useful evidence for the collision-reaction dynamics of aggregation process for the two-particle system described in Ref.[1].
A Monte Carlo simulation is performed to study the dependence of collision frequency on interparticle distance for a system composed of two hard-sphere particles. The simulation quantitatively shows that the collision frequency drops down sharply as the distance between two particles increases. This characteristic provides a useful evidence for the collision-reaction dynamics of aggregation process for the two-particle system described in Ref.[1].
2003, 19(11): 1081-1084
doi: 10.3866/PKU.WHXB20031120
Abstract:
The rheological characteristics of aqueous solutions of an amphoteric guar gum derivative, namely E-AMPHO-S, were studied in terms of the effects of its concentration, added salts and temperature by means of a rotating rheometer. It was found that E-AMPHO-S solutions investigated behaved as non-Newtonian shear-thinning fluids. With the increase of E-AMPHO-S concentration from 0.1％ to 2.0％(g•mL－1), the consistency coefficient increased while the viscosity behavior index decreased. The thixotropic response became stronger when E-AMPHO-S concentration was increased from 1.0％ to 3.0％(g•mL－1). The obvious viscosity behavior of “anti-polyelectrolye solution” was observed in aqueous salt solutions containing calcium chloride. The zero shear viscosity (η0) could be obtained by using Spencer-Dillon equation, and the temperature dependence of η0 could be expressed by a relation of the form of the Arrhenius equation.
The rheological characteristics of aqueous solutions of an amphoteric guar gum derivative, namely E-AMPHO-S, were studied in terms of the effects of its concentration, added salts and temperature by means of a rotating rheometer. It was found that E-AMPHO-S solutions investigated behaved as non-Newtonian shear-thinning fluids. With the increase of E-AMPHO-S concentration from 0.1％ to 2.0％(g•mL－1), the consistency coefficient increased while the viscosity behavior index decreased. The thixotropic response became stronger when E-AMPHO-S concentration was increased from 1.0％ to 3.0％(g•mL－1). The obvious viscosity behavior of “anti-polyelectrolye solution” was observed in aqueous salt solutions containing calcium chloride. The zero shear viscosity (η0) could be obtained by using Spencer-Dillon equation, and the temperature dependence of η0 could be expressed by a relation of the form of the Arrhenius equation.
2003, 19(11): 1085-1088
doi: 10.3866/PKU.WHXB20031121
Abstract:
The complex of Zn Ac2•2H2O and Threonine was prepared in the mixed solvent of water - acetone, the composition of the complex was identified as Zn(Thr) Ac2•2H2O by chemical, elemental analyses. The structure and thermal stability of the title complex were investigated by IR, XRD and TG - DTG. Enthalpy of solution of the complex was determined at 298.15 K in water by microcalorimetry.Standard molar enthalpy of formation of Zn(Thr)2＋(aq,∞) and that of Zn(Thr) Ac2•2H2O (s)were calculated to be (955.24 ± 5.70) kJ•mol-1 and (-570.92±5.71) kJ•mol-1,respectively.
The complex of Zn Ac2•2H2O and Threonine was prepared in the mixed solvent of water - acetone, the composition of the complex was identified as Zn(Thr) Ac2•2H2O by chemical, elemental analyses. The structure and thermal stability of the title complex were investigated by IR, XRD and TG - DTG. Enthalpy of solution of the complex was determined at 298.15 K in water by microcalorimetry.Standard molar enthalpy of formation of Zn(Thr)2＋(aq,∞) and that of Zn(Thr) Ac2•2H2O (s)were calculated to be (955.24 ± 5.70) kJ•mol-1 and (-570.92±5.71) kJ•mol-1,respectively.
2003, 19(11): 1089-1092
doi: 10.3866/PKU.WHXB20031122
Abstract:
The solubilities of the Cs2SO4-C2H5OH-H2O aqueous two-phase system at 0, 10, 20 and 40 ℃ had been studied using microequipment for solubility determination. It was found that the effect of temperature on the phase equilibrium was insignificant within the investigated range. There appeared two phases, alcoholic phase and water phase in the liquid phase. The solubility of Cs2SO4 in water, C2H5OH and mixed solvent had been determined and the refractive index of the liquid phases was also determined. The phase diagram indicated that C2H5OH was salted out by Cs2SO4 from this system and the equilibrium solid phase is Cs2SO4. The complete phase diagram of the system were also presented in the article， in which we found five zones.
The solubilities of the Cs2SO4-C2H5OH-H2O aqueous two-phase system at 0, 10, 20 and 40 ℃ had been studied using microequipment for solubility determination. It was found that the effect of temperature on the phase equilibrium was insignificant within the investigated range. There appeared two phases, alcoholic phase and water phase in the liquid phase. The solubility of Cs2SO4 in water, C2H5OH and mixed solvent had been determined and the refractive index of the liquid phases was also determined. The phase diagram indicated that C2H5OH was salted out by Cs2SO4 from this system and the equilibrium solid phase is Cs2SO4. The complete phase diagram of the system were also presented in the article， in which we found five zones.
2003, 19(11): 1093-1096
doi: 10.3866/PKU.WHXB20031123
Abstract:
A series of W-Fe-M catalysts with high BET surface area were prepared by mixing Mg(NO3)2•6H2O,ammonium tungstate, citric acid, Fe(NO3)3•9H2O and H2O,followed by drying at 150 ℃ and decomposing at 550 ℃.Using these catalysts, bundled SWCNTs with diameter 1～3 nm for each tube, were synthesized in a fluidized reactor. The maximum yield of SWCNTs was 36 mg/100 mg. TEM, micro-Raman and TPO (temperature programmed oxidation) results showed that the products were SWCNTs of high purity and almost defect-free. From the EDAX results and phase-diagram of W-Fe, we deduced that the active phase for SWCNTs growth was a solid solution or an intermetal compound of tungsten and iron.
A series of W-Fe-M catalysts with high BET surface area were prepared by mixing Mg(NO3)2•6H2O,ammonium tungstate, citric acid, Fe(NO3)3•9H2O and H2O,followed by drying at 150 ℃ and decomposing at 550 ℃.Using these catalysts, bundled SWCNTs with diameter 1～3 nm for each tube, were synthesized in a fluidized reactor. The maximum yield of SWCNTs was 36 mg/100 mg. TEM, micro-Raman and TPO (temperature programmed oxidation) results showed that the products were SWCNTs of high purity and almost defect-free. From the EDAX results and phase-diagram of W-Fe, we deduced that the active phase for SWCNTs growth was a solid solution or an intermetal compound of tungsten and iron.
