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2001 Volume 17 Issue 4
2001, 17(04): 289-291
doi: 10.3866/PKU.WHXB20010401
Abstract:
The molecular parameters of ArH＋ have been calculated with different quantum chemistry methods and basis sets.Based on the data from QCISD/AugccpVTZ ab initio calculation for different configurations of ArH＋ and the experimental data,an accurate potential curve for ArH＋ has been constructed.The molecular properties,such as dissociation energy,equilibrium bond length,and vibrational energy levels,can be accurately reproduced.
The molecular parameters of ArH＋ have been calculated with different quantum chemistry methods and basis sets.Based on the data from QCISD/AugccpVTZ ab initio calculation for different configurations of ArH＋ and the experimental data,an accurate potential curve for ArH＋ has been constructed.The molecular properties,such as dissociation energy,equilibrium bond length,and vibrational energy levels,can be accurately reproduced.
2001, 17(04): 292-294
doi: 10.3866/PKU.WHXB20010402
Abstract:
The selective oxidation of phenylethane with air catalyzed byμ-oxobismanganese porphyrins was studied . It is shown that the main products are hypnone and α-phenylethanol . The selectivity of products at alpha position is 100 ％. With by extending the reaction, the amount byproduct increase , the selectivity at α-phenylethanol descends and that of hypnone slightly increases, but the total selectivity decrease. With the temperature raising, the yield of hypnone and α-phenylethanol relevantly increase, but their selectivity descends. A 3h induction period appeared when the solvent was benzene and chlorobenzol, and they have no influence on the yield of the products;No induction period was obseves when the solvent was butanone and cyclohexanone, and it makes the yield of products increase .
The selective oxidation of phenylethane with air catalyzed byμ-oxobismanganese porphyrins was studied . It is shown that the main products are hypnone and α-phenylethanol . The selectivity of products at alpha position is 100 ％. With by extending the reaction, the amount byproduct increase , the selectivity at α-phenylethanol descends and that of hypnone slightly increases, but the total selectivity decrease. With the temperature raising, the yield of hypnone and α-phenylethanol relevantly increase, but their selectivity descends. A 3h induction period appeared when the solvent was benzene and chlorobenzol, and they have no influence on the yield of the products;No induction period was obseves when the solvent was butanone and cyclohexanone, and it makes the yield of products increase .
2001, 17(04): 295-299
doi: 10.3866/PKU.WHXB20010403
Abstract:
The electrochemical polymerization of thionine in the aqueous acetic solution has been carried out using cyclic voltammetry. Polythionine is a blue material. Its color can be quickly changed by applied potential. Polythionine has a od electrochemical reversibility, stability and a fast charge transfer ability in the solution of 0.50 mol•dm－3 HCl to the solution of acetate of pH 6.0. Visible and FTIR spectra of polythionine have been presented in this paper. Based on FTIR spectra, a suggestion for mechanism of polymerization of thionine is presented.
The electrochemical polymerization of thionine in the aqueous acetic solution has been carried out using cyclic voltammetry. Polythionine is a blue material. Its color can be quickly changed by applied potential. Polythionine has a od electrochemical reversibility, stability and a fast charge transfer ability in the solution of 0.50 mol•dm－3 HCl to the solution of acetate of pH 6.0. Visible and FTIR spectra of polythionine have been presented in this paper. Based on FTIR spectra, a suggestion for mechanism of polymerization of thionine is presented.
2001, 17(04): 300-304
doi: 10.3866/PKU.WHXB20010404
Abstract:
The exchange rate constants of the labile protons in quercetin with water and the selfdiffusion coefficients of quercetin in DMSOd6 solutions with different water concentrations and at different temperatures are studied. When the water concentration or the temperature is changed,both exchange rates and diffusion coefficients are changed,but there is no correlation between these two changes. This indicates that chemical exchange of the labile protons with water and selfdiffusion of the quercetin molecule are two independent motions in solutions and chemical exchange is not controlled by diffusion. However,the apparent selfdiffusion coefficients of the labile protons are obviously affected by chemical exchange.
The exchange rate constants of the labile protons in quercetin with water and the selfdiffusion coefficients of quercetin in DMSOd6 solutions with different water concentrations and at different temperatures are studied. When the water concentration or the temperature is changed,both exchange rates and diffusion coefficients are changed,but there is no correlation between these two changes. This indicates that chemical exchange of the labile protons with water and selfdiffusion of the quercetin molecule are two independent motions in solutions and chemical exchange is not controlled by diffusion. However,the apparent selfdiffusion coefficients of the labile protons are obviously affected by chemical exchange.
2001, 17(04): 305-309
doi: 10.3866/PKU.WHXB20010405
Abstract:
Surfacemodified titanium dioxide nanoparticles are synthesized in organic media via solgel method. The chemical structure of nanoparticles as well as its formation mechanism are discussed on the basis of Fouriertransform infrared spectroscopy (FTIR), Xray photoelectron spectroscopy (XPS), transmission electron microscopy(TEM), and Xray diffraction (XRD). The results confirm the existence of organic layer, which was connected with the inorganic nuclei by bidentate coordination.The average diameter of nanoparticles is about 68 nm. Although poor crystallinity obtained, the anatase phase of TiO2 could be inferred.The existence of organic ligands would greatly impact the nucleation and surface coordination of nanoparticles. The formation mechanism is postulated as a competitive reaction between polymerization and inhibition processes. Finally, the structural model for organo capped TiO2 nanoparticles is proposed.
Surfacemodified titanium dioxide nanoparticles are synthesized in organic media via solgel method. The chemical structure of nanoparticles as well as its formation mechanism are discussed on the basis of Fouriertransform infrared spectroscopy (FTIR), Xray photoelectron spectroscopy (XPS), transmission electron microscopy(TEM), and Xray diffraction (XRD). The results confirm the existence of organic layer, which was connected with the inorganic nuclei by bidentate coordination.The average diameter of nanoparticles is about 68 nm. Although poor crystallinity obtained, the anatase phase of TiO2 could be inferred.The existence of organic ligands would greatly impact the nucleation and surface coordination of nanoparticles. The formation mechanism is postulated as a competitive reaction between polymerization and inhibition processes. Finally, the structural model for organo capped TiO2 nanoparticles is proposed.
2001, 17(04): 310-313
doi: 10.3866/PKU.WHXB20010406
Abstract:
The core levels and valence band spectra of LnCu2O4(Ln=Gd, Nd) were recorded by XPS. It has been observed that the Ln 3d binding energies of LnCu2O4 are 0.8－0.9 eV lower than that of the corresponding rare earth oxide. On the other hand, the Cu 2p binding energies of LnCu2O4 are 0.4－0.5 eV higher than that of CuO. This has been explained by the Cu→O→Ln charge transfer in Ln－O－Cu linkage of LnCu2O4. The XPS results also show that there is no mixed valence of Cu in LnCu2O4. The Xray induced valence bands reveal that the center of Ln 4fCu 3dO 2p valence band for Nd0.97Cu2O4 has a 3.4 eV lower binding energy compared to the center for Gd0.98Cu2O4. Besides, the width of valence band for Nd0.97Cu2O4 is narrower than that of Gd0.98Cu2O4.
The core levels and valence band spectra of LnCu2O4(Ln=Gd, Nd) were recorded by XPS. It has been observed that the Ln 3d binding energies of LnCu2O4 are 0.8－0.9 eV lower than that of the corresponding rare earth oxide. On the other hand, the Cu 2p binding energies of LnCu2O4 are 0.4－0.5 eV higher than that of CuO. This has been explained by the Cu→O→Ln charge transfer in Ln－O－Cu linkage of LnCu2O4. The XPS results also show that there is no mixed valence of Cu in LnCu2O4. The Xray induced valence bands reveal that the center of Ln 4fCu 3dO 2p valence band for Nd0.97Cu2O4 has a 3.4 eV lower binding energy compared to the center for Gd0.98Cu2O4. Besides, the width of valence band for Nd0.97Cu2O4 is narrower than that of Gd0.98Cu2O4.
2001, 17(04): 314-318
doi: 10.3866/PKU.WHXB20010407
Abstract:
The effect ofβ-CD on the properties of SDS micelle was studied by the determination of the diffusion coefficient D and the aggregation number N of SDS micelle,and the distribution coefficient ofβ-CD between the micellar phase and the continuous water phase. The results show that the distribution ofβ-CD in the micellar phase increases and the diffusion coefficient D and the aggregation number N will decrease with addedβ-CDwhen the concentration ofβ-CD is lower. The distribution ofβ-CD in the continuous water phase increases and the influence ofβ-CD on D and N are reduced remarkably when the concentration ofβ-CD is higher. When the SDS concentration is less than the first CMC,the inclusion compounds ofβ-CD with SDS monomer form in the molecular ratio of 1∶1. Mixed spherical micelle could be prepared in the molecular ratio of 1:8 forβ-CD/SDS when the SDS concentration is higher than the first CMC.
The effect ofβ-CD on the properties of SDS micelle was studied by the determination of the diffusion coefficient D and the aggregation number N of SDS micelle,and the distribution coefficient ofβ-CD between the micellar phase and the continuous water phase. The results show that the distribution ofβ-CD in the micellar phase increases and the diffusion coefficient D and the aggregation number N will decrease with addedβ-CDwhen the concentration ofβ-CD is lower. The distribution ofβ-CD in the continuous water phase increases and the influence ofβ-CD on D and N are reduced remarkably when the concentration ofβ-CD is higher. When the SDS concentration is less than the first CMC,the inclusion compounds ofβ-CD with SDS monomer form in the molecular ratio of 1∶1. Mixed spherical micelle could be prepared in the molecular ratio of 1:8 forβ-CD/SDS when the SDS concentration is higher than the first CMC.
2001, 17(04): 319-323
doi: 10.3866/PKU.WHXB20010408
Abstract:
The corrosion gain weight of electroplated zinc in atmosphere containing different concentrations of CO2 under thin electrolyte film were measured by means of quartz crystal microbalance.Equations of corrosion gain weight were derived from the experiments under the same condition.Atmospheric corrosion mechanism of zinc under thin electrolyte film was also discussed by the equation of corrosion gain weight,combined with Infrared absorption spectroscopy and Xray energy dispersion spectroscopy.Protective features was elucidated by analysis of the morphology of atmospheric corrosion layer on zinc using SEM.
The corrosion gain weight of electroplated zinc in atmosphere containing different concentrations of CO2 under thin electrolyte film were measured by means of quartz crystal microbalance.Equations of corrosion gain weight were derived from the experiments under the same condition.Atmospheric corrosion mechanism of zinc under thin electrolyte film was also discussed by the equation of corrosion gain weight,combined with Infrared absorption spectroscopy and Xray energy dispersion spectroscopy.Protective features was elucidated by analysis of the morphology of atmospheric corrosion layer on zinc using SEM.
2001, 17(04): 324-328
doi: 10.3866/PKU.WHXB20010409
Abstract:
The geometric configurations, electronic structures and polymerization thermodynamic properties of (Cl2AlNH2)n and (H2AlNH2)n(n=1～5) are investigated using HF/631G and B3LYP/631G methods, and the chemical bond strength of the two kinds of compound series are compared , and the reason of forming plane skeleton for AlnNn is analyzed. The results show that Cl2AlNH2 and H2AlNH2 molecules are of plane configuration C2 (EC), and their Al－N bond is a double bond which consists of a σtype bond and a type bond(Cl2AlNH2)n and (H2AlNH2)n(n=1～5) molecules are of Dnh symmetry, and their Al－N bond representsσtype single bond. The stability order of (Cl2AlNH2)n and (H2AlNH2)n molecules are 3 > 2 > 4 > 5 > 1 and 8 > 7 > 9 > 10 > 6,respectively.
The geometric configurations, electronic structures and polymerization thermodynamic properties of (Cl2AlNH2)n and (H2AlNH2)n(n=1～5) are investigated using HF/631G and B3LYP/631G methods, and the chemical bond strength of the two kinds of compound series are compared , and the reason of forming plane skeleton for AlnNn is analyzed. The results show that Cl2AlNH2 and H2AlNH2 molecules are of plane configuration C2 (EC), and their Al－N bond is a double bond which consists of a σtype bond and a type bond(Cl2AlNH2)n and (H2AlNH2)n(n=1～5) molecules are of Dnh symmetry, and their Al－N bond representsσtype single bond. The stability order of (Cl2AlNH2)n and (H2AlNH2)n molecules are 3 > 2 > 4 > 5 > 1 and 8 > 7 > 9 > 10 > 6,respectively.
2001, 17(04): 329-332
doi: 10.3866/PKU.WHXB20010410
Abstract:
The mechanism of photocarrier generation and transport in conjugated polymer is studied. After analyzing thermalization of polaronexcitons which were formed through relaxation by dissociation electronhole pairs produced by photoexcitation initially. We infer that polarons along the polymer chains recombine rapidly and polarons between chains generate photocurrent. After investigating the transport mechanism of chargecarrier in conjugated polymer, a formula of conductivity of copolymers can be derived from chargecarriers generation and transport model (see Eq(6)), the calculated values agree with experimental data very well (see Table 2). We conclude that the conductance and photoluminescence in conjugated polymer could be attributed to polaron hopping between chains.
The mechanism of photocarrier generation and transport in conjugated polymer is studied. After analyzing thermalization of polaronexcitons which were formed through relaxation by dissociation electronhole pairs produced by photoexcitation initially. We infer that polarons along the polymer chains recombine rapidly and polarons between chains generate photocurrent. After investigating the transport mechanism of chargecarrier in conjugated polymer, a formula of conductivity of copolymers can be derived from chargecarriers generation and transport model (see Eq(6)), the calculated values agree with experimental data very well (see Table 2). We conclude that the conductance and photoluminescence in conjugated polymer could be attributed to polaron hopping between chains.
2001, 17(04): 333-337
doi: 10.3866/PKU.WHXB20010411
Abstract:
The model enzymatic inhibition mechanism by inhibitor oxamate has been studied at the HF/321G level. All the conclusions can be summarrized as follows:(a)the conformations of the optimized model inhibitor oxamate and substrate are much more similar with each other,which leads to an unidentified action of the substrate and inhibitor by Llactate dehydrogenase(LDH); (b)the electronic distribution of the inhibitor is favorable for the combination of oxamate to LDH active site; (3)the space of LDH active site is contracted by the inducedfit interaction between the LDH and the inhibitor;(4) the molecular fragment methyl of substrate and the residue Gln102 of LDH probably play an important role in the enzymatic reaction.
The model enzymatic inhibition mechanism by inhibitor oxamate has been studied at the HF/321G level. All the conclusions can be summarrized as follows:(a)the conformations of the optimized model inhibitor oxamate and substrate are much more similar with each other,which leads to an unidentified action of the substrate and inhibitor by Llactate dehydrogenase(LDH); (b)the electronic distribution of the inhibitor is favorable for the combination of oxamate to LDH active site; (3)the space of LDH active site is contracted by the inducedfit interaction between the LDH and the inhibitor;(4) the molecular fragment methyl of substrate and the residue Gln102 of LDH probably play an important role in the enzymatic reaction.
2001, 17(04): 338-342
doi: 10.3866/PKU.WHXB20010412
Abstract:
ESR and UV spectrum of the aqueous solution of sodium dodecyl sulfate(SDS)/poly(ethylene oxide)(PEO) were measured at room temperature respectively, the concentration of PEO was 0.5％(mass fraction), and the concentration of SDS (mSDS) was up to 50 mmol•kg－1. 2,4dinitrophylhydrazone of 2,2,6,6tetramethyl4 piperidine1oxyl (TemponeDNPH) was synthesized and used as ESR probe. The binding site of SDSPEO interaction, the micropolarity and microviscosity information of the microenvironments have been determined by ESR. UV spectrum gives information on the environment of 2,4dinitrophylhydrazone group. The hyperfine coupling constant and the rotational correlation time of the spin probe reflect the microenvironment of the polymermicelle aggregates. The micropolarity of the solutions decreases with increasing SDS concentration, the polymermicelle aggregate forms a more compact structure at the binding site and the binding site between PEO and SDS micelles yields a strong increase of the microviscosity at the micellepolymer interface. Spin probe is located near the surface of the micelle. 2,4 dinitrophylhydrazone group may be adjacent to the sulphate groups, and the nitroxide group penetrates a small distance into the hydrocarbon core of the micelle. The critical aggregation concentration (CAC)and polymer saturation point (PSP) of SDS0.5 ％PEO at room temperature are approximately 4 and 28 mmol•kg－1, respectively.
ESR and UV spectrum of the aqueous solution of sodium dodecyl sulfate(SDS)/poly(ethylene oxide)(PEO) were measured at room temperature respectively, the concentration of PEO was 0.5％(mass fraction), and the concentration of SDS (mSDS) was up to 50 mmol•kg－1. 2,4dinitrophylhydrazone of 2,2,6,6tetramethyl4 piperidine1oxyl (TemponeDNPH) was synthesized and used as ESR probe. The binding site of SDSPEO interaction, the micropolarity and microviscosity information of the microenvironments have been determined by ESR. UV spectrum gives information on the environment of 2,4dinitrophylhydrazone group. The hyperfine coupling constant and the rotational correlation time of the spin probe reflect the microenvironment of the polymermicelle aggregates. The micropolarity of the solutions decreases with increasing SDS concentration, the polymermicelle aggregate forms a more compact structure at the binding site and the binding site between PEO and SDS micelles yields a strong increase of the microviscosity at the micellepolymer interface. Spin probe is located near the surface of the micelle. 2,4 dinitrophylhydrazone group may be adjacent to the sulphate groups, and the nitroxide group penetrates a small distance into the hydrocarbon core of the micelle. The critical aggregation concentration (CAC)and polymer saturation point (PSP) of SDS0.5 ％PEO at room temperature are approximately 4 and 28 mmol•kg－1, respectively.
2001, 17(04): 343-347
doi: 10.3866/PKU.WHXB20010413
Abstract:
Adsorption thermodynamic functions for some organic solvent molecules on the surface of beta cyclodextrin(β-CD）have been measured using gas chromatographic technique.The experimental results confirm thatβ-CD molecule can form hostguest adduct with adsorbate molecule(guest) as it can in aqueous solution and show that when there is a strong intermolecular force between the host and the guest a type of synergistic interaction exists between,the inner cave and some hydroxyl groups of the CD molecule simultaneously with the apolar/hydrophobic and the polar/hydrophilic parts of the guest molecule.The experimental results also show that a phenomenon of mutual compensation between enthalpy and entropy relates closely with molecular recognize and the sum of the absolute values of adsorption enthalpy and entropy could be considered as a criterion to differentiate intermolecular force of the recognize.
Adsorption thermodynamic functions for some organic solvent molecules on the surface of beta cyclodextrin(β-CD）have been measured using gas chromatographic technique.The experimental results confirm thatβ-CD molecule can form hostguest adduct with adsorbate molecule(guest) as it can in aqueous solution and show that when there is a strong intermolecular force between the host and the guest a type of synergistic interaction exists between,the inner cave and some hydroxyl groups of the CD molecule simultaneously with the apolar/hydrophobic and the polar/hydrophilic parts of the guest molecule.The experimental results also show that a phenomenon of mutual compensation between enthalpy and entropy relates closely with molecular recognize and the sum of the absolute values of adsorption enthalpy and entropy could be considered as a criterion to differentiate intermolecular force of the recognize.
2001, 17(04): 348-355
doi: 10.3866/PKU.WHXB20010414
Abstract:
By using AM1 and DFT methods in Gaussian 98 program package, quantum chemistry theoretical research was carried out for the pyrolysis mechanism of cyclohexane, used as carbon matrix compound for preparing carbon/carbon composition material with the rapid chemical liquid deposition method. Reaction paths studied are showed as scheme at p355. By thermodynamic and kinetic calculations of six possible pyrolysis channels, the main reaction channel was found. (1) confirmed by both AM1 and DFT calculation results,the main pyrolysis reaction channel is the breaking of C－C bond firstly, followed by a series of intermediates,and finally the productiom of ethene and 2butene. That is reaction channel(2b),which is in accordance with the massspectrometric data. (2) Except for the main pyrolysis channel, the order of producing final products from the easiest to the most difficult ones is methylcyclopentane >cyclohexene >4methylcyclopentene >1,3butadiene. This is supported by results of thermodynamic and kinetic calculation. (3) AM1 method is recommended to study the pyrolysis mechanism of larger molecular systems, while the thermodynamic data computed by DFT method coincide better with the experimental results.
By using AM1 and DFT methods in Gaussian 98 program package, quantum chemistry theoretical research was carried out for the pyrolysis mechanism of cyclohexane, used as carbon matrix compound for preparing carbon/carbon composition material with the rapid chemical liquid deposition method. Reaction paths studied are showed as scheme at p355. By thermodynamic and kinetic calculations of six possible pyrolysis channels, the main reaction channel was found. (1) confirmed by both AM1 and DFT calculation results,the main pyrolysis reaction channel is the breaking of C－C bond firstly, followed by a series of intermediates,and finally the productiom of ethene and 2butene. That is reaction channel(2b),which is in accordance with the massspectrometric data. (2) Except for the main pyrolysis channel, the order of producing final products from the easiest to the most difficult ones is methylcyclopentane >cyclohexene >4methylcyclopentene >1,3butadiene. This is supported by results of thermodynamic and kinetic calculation. (3) AM1 method is recommended to study the pyrolysis mechanism of larger molecular systems, while the thermodynamic data computed by DFT method coincide better with the experimental results.
2001, 17(04): 356-360
doi: 10.3866/PKU.WHXB20010415
Abstract:
The mixed phosphate Li3PO4•BiPO4 was prepared from coprecipitation method. The crystal structure,chemisorption properties and LSSR behaviors of this material have been investigated by the techniques of XRD,IR,TPD and LSSR. The main phase is monoclinic BiPO4 and Li3PO4 dispersed in molecular state in the BiPO4. There are the Lewis basic sites O2－ in the P=O or P－O－Bi bonds and Lewis acid site Bi3＋ or Li＋ appeared on the surface of mixed phosphate. Two methyl hydrogen in isobutane molecule can be chemisorbed on the terminal oxygen of neighboring P=O bonds on the surface of mixed phosphate. Under the conditions of 0.1 MPa and 200℃ with the 1050 cm－1 laser photons excited the P=O bonds 1000 times,the conversion of isobutane is about 11.3％ with the selectivity of the product MAA over 72％. Based on the experiment results ,a mechanism of LSSR has been proposed for the isobutane selective oxidation to MAA.
The mixed phosphate Li3PO4•BiPO4 was prepared from coprecipitation method. The crystal structure,chemisorption properties and LSSR behaviors of this material have been investigated by the techniques of XRD,IR,TPD and LSSR. The main phase is monoclinic BiPO4 and Li3PO4 dispersed in molecular state in the BiPO4. There are the Lewis basic sites O2－ in the P=O or P－O－Bi bonds and Lewis acid site Bi3＋ or Li＋ appeared on the surface of mixed phosphate. Two methyl hydrogen in isobutane molecule can be chemisorbed on the terminal oxygen of neighboring P=O bonds on the surface of mixed phosphate. Under the conditions of 0.1 MPa and 200℃ with the 1050 cm－1 laser photons excited the P=O bonds 1000 times,the conversion of isobutane is about 11.3％ with the selectivity of the product MAA over 72％. Based on the experiment results ,a mechanism of LSSR has been proposed for the isobutane selective oxidation to MAA.
2001, 17(04): 361-363
doi: 10.3866/PKU.WHXB20010416
Abstract:
2001, 17(04): 364-366
doi: 10.3866/PKU.WHXB20010417
Abstract:
CobaltPhthalocyanine/Iron (CoPc/Fe) nanocomposite particles were prepared using mehods of organicinorganic composite in situ with cobaltphthalocyanine(CoPc) and carbonyl iron. The structure of composite particles was characterized by density measurement, XRD, SEM and TEM. The results show that CoPc/Fe nanocomposites with density of 3.99 g•cm－3 were almost microsized regular spheroids consisting of α-Fe nanoparticles with average diameter 20 nm in inner and CoPc layer on the surface of spheroids. Further, microwave electromagnetic parameters of CoPc/Fe nanocomposite particles was measured, and the dependences of εr and μr on frequency were investigated. Compared with carbonyl iron powders, the composite permittivity εr significantly decreases while composite permability μr changes slightly, which may increases the width of microwave absorbing frequency.
CobaltPhthalocyanine/Iron (CoPc/Fe) nanocomposite particles were prepared using mehods of organicinorganic composite in situ with cobaltphthalocyanine(CoPc) and carbonyl iron. The structure of composite particles was characterized by density measurement, XRD, SEM and TEM. The results show that CoPc/Fe nanocomposites with density of 3.99 g•cm－3 were almost microsized regular spheroids consisting of α-Fe nanoparticles with average diameter 20 nm in inner and CoPc layer on the surface of spheroids. Further, microwave electromagnetic parameters of CoPc/Fe nanocomposite particles was measured, and the dependences of εr and μr on frequency were investigated. Compared with carbonyl iron powders, the composite permittivity εr significantly decreases while composite permability μr changes slightly, which may increases the width of microwave absorbing frequency.
2001, 17(04): 367-371
doi: 10.3866/PKU.WHXB20010418
Abstract:
Metallic titanium was electrochemically dissoluted in absolute ethanol in the presence of Et4N•Br(as electroconductive additive),The electrolyte solution was then directly hydrolysized to obtain nanocrystalline TiO2.The powder obtained was calcined at 720℃ for 1 h.FTIR,Raman spectra,XRD and TEM were used to investigate the structure and particle size of the powder.Studies showed that the nanocrystalline TiO2 prepared by this method was of monocline structure with high textural stability and narrow size distribution of 10－20 nm,and its Raman spectra showed a shift of about 25 cm－1.The experiments also showed that the product yield could be improved by controlling the temperature under 50－60℃,selecting R4N•Br as conductive additive and preventing titanium anode from being passivated.The electrochemical dissolution of metal anode may be recommanded as a promising technique for the synthesis of nanomaterials.
Metallic titanium was electrochemically dissoluted in absolute ethanol in the presence of Et4N•Br(as electroconductive additive),The electrolyte solution was then directly hydrolysized to obtain nanocrystalline TiO2.The powder obtained was calcined at 720℃ for 1 h.FTIR,Raman spectra,XRD and TEM were used to investigate the structure and particle size of the powder.Studies showed that the nanocrystalline TiO2 prepared by this method was of monocline structure with high textural stability and narrow size distribution of 10－20 nm,and its Raman spectra showed a shift of about 25 cm－1.The experiments also showed that the product yield could be improved by controlling the temperature under 50－60℃,selecting R4N•Br as conductive additive and preventing titanium anode from being passivated.The electrochemical dissolution of metal anode may be recommanded as a promising technique for the synthesis of nanomaterials.
2001, 17(04): 372-376
doi: 10.3866/PKU.WHXB20010419
Abstract:
Under ideally polarizable conditions, TiO2 film electrode/solution electrolyte interface exhibited frequency dispersion, The effects of external factors such as the concentration of KNO3, various electrolytes and applied potentials near the flat band potential on the CPE behavior of TiO2 film electrode were studied in electrolyte solution by using A.C. impedance spectra. It was found that concentration of KNO3 had a significant effect on the CPE exponent n only when the concentration is smaller than 0.1 mol•L－1. In this concentration range, the CPE exponent n went up with increase of KNO3 concentration, once the concentration was larger than this value, however, the CPE exponent n approached to a constant, irrelevant of the concentration. Near the flat band potential, the influence of applied potential on the exponent n depended on the selected frequency range. When the frequency was in lower range, that is smaller than 0.1 Hz, this influence was obvious,on the other hand, it bore no relation to applied potential in higher frequency. Types of electrolytes only affected the CPE constant Q, having nothing to do with the CPE exponent n.
Under ideally polarizable conditions, TiO2 film electrode/solution electrolyte interface exhibited frequency dispersion, The effects of external factors such as the concentration of KNO3, various electrolytes and applied potentials near the flat band potential on the CPE behavior of TiO2 film electrode were studied in electrolyte solution by using A.C. impedance spectra. It was found that concentration of KNO3 had a significant effect on the CPE exponent n only when the concentration is smaller than 0.1 mol•L－1. In this concentration range, the CPE exponent n went up with increase of KNO3 concentration, once the concentration was larger than this value, however, the CPE exponent n approached to a constant, irrelevant of the concentration. Near the flat band potential, the influence of applied potential on the exponent n depended on the selected frequency range. When the frequency was in lower range, that is smaller than 0.1 Hz, this influence was obvious,on the other hand, it bore no relation to applied potential in higher frequency. Types of electrolytes only affected the CPE constant Q, having nothing to do with the CPE exponent n.
2001, 17(04): 377-380
doi: 10.3866/PKU.WHXB20010420
Abstract:
When surface potential of the particles, ,is high,sinh y can be approximated by ≈ey/2 in the nonlinear PoissonBoltzmann equation.Thus,we present a simple method of calculating the interaction force and energy per unit area between two dissimilar plates with high potentials at constant surface potential.These formulae could be applicable to the case of repulsive case,in which the derivative of y must vanish at an interior point,and a minimum ymin=u always exists.A turning point at ～kh≈2(1)e－y1/2 for the repulsion or attraction between dissimilar planar surfaces.These formulae are divergent at 阧∞,and zero point at kh≈2 .This means that they can only be used at 阧 < 2 and accurate location is at kh ≤ 4. Agreement of the approximation for force,Eq.（13）,is od with the exact numerical values of the interaction of dissimilar plates given by Devereux [6] for high surface potentials.For y1 ≥5 kh ≤ 3.0 the relative errors of Eq.(13) are less than 5％,and for kh ≤ 3.5 relative errors are less than 10％.For the interaction energy,Eq.(15),the applicable range extends to kh =4.0.Beyond this range the error increases rapidly.The higher surface potential is the better the precision of Eq.（13）and Eq.( 15).The condition of the strong interaction has been satisfied.
When surface potential of the particles, ,is high,sinh y can be approximated by ≈ey/2 in the nonlinear PoissonBoltzmann equation.Thus,we present a simple method of calculating the interaction force and energy per unit area between two dissimilar plates with high potentials at constant surface potential.These formulae could be applicable to the case of repulsive case,in which the derivative of y must vanish at an interior point,and a minimum ymin=u always exists.A turning point at ～kh≈2(1)e－y1/2 for the repulsion or attraction between dissimilar planar surfaces.These formulae are divergent at 阧∞,and zero point at kh≈2 .This means that they can only be used at 阧 < 2 and accurate location is at kh ≤ 4. Agreement of the approximation for force,Eq.（13）,is od with the exact numerical values of the interaction of dissimilar plates given by Devereux [6] for high surface potentials.For y1 ≥5 kh ≤ 3.0 the relative errors of Eq.(13) are less than 5％,and for kh ≤ 3.5 relative errors are less than 10％.For the interaction energy,Eq.(15),the applicable range extends to kh =4.0.Beyond this range the error increases rapidly.The higher surface potential is the better the precision of Eq.（13）and Eq.( 15).The condition of the strong interaction has been satisfied.
2001, 17(04): 381-384
doi: 10.3866/PKU.WHXB20010421
Abstract:
The relationship of the electric conductivity of single and multicomponent of colloidal catalyst FeCl3Al(iBu)3Phen with their concentration was studied in hydrogenated gasoline solvent at 25℃,meanwhile,the UVVis spectra of the corresponding component of the catalyst were detected.The experimental results showed that Al(iBu)3 existed in associated state and dissociated into ion couple.The reaction between Al(iBu)3 and FeCl3 was the main reaction to form colloidal core.The Fe(III) on the surface of the colloidal particles was reduced to lower valence by Al(iBu)3.The stable complex formed by the reaction between Phen and Fe(II) could prevent Fe(II) from being reduced to lower valence.The colloidal particles were comparatively stable by means of the electric double layer yielded by a proper excess of Al(iBu)3.The stable colloidal particles could be formed in the optimal ratio of the catalyst components.
The relationship of the electric conductivity of single and multicomponent of colloidal catalyst FeCl3Al(iBu)3Phen with their concentration was studied in hydrogenated gasoline solvent at 25℃,meanwhile,the UVVis spectra of the corresponding component of the catalyst were detected.The experimental results showed that Al(iBu)3 existed in associated state and dissociated into ion couple.The reaction between Al(iBu)3 and FeCl3 was the main reaction to form colloidal core.The Fe(III) on the surface of the colloidal particles was reduced to lower valence by Al(iBu)3.The stable complex formed by the reaction between Phen and Fe(II) could prevent Fe(II) from being reduced to lower valence.The colloidal particles were comparatively stable by means of the electric double layer yielded by a proper excess of Al(iBu)3.The stable colloidal particles could be formed in the optimal ratio of the catalyst components.
