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Table of Content
24 August 2004, Volume 20 Issue 4
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Articles
Influence of Mg
2+
on Initial Stages of CaCO
3
Scale Formed on Metal Surface
CHEN Tao, Anne Neville, YUAN Ming-dong
2004, 20(4): 381-385.
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Magnesium ions, which exist in formation water and injection water under downhole conditions in the oil and gas production industry, are a key determinant in the CaCO
3
scale formation.Many studies have focused their attention on the effect of magnesium on the kinetics, the morphology and the content of Mg in the CaCO
3
scale.Little attention has been paid to the effect of Mg
2+
on the initial stages of CaCO
3
formation on a metal surface.In this study, an electrochemical technique was used to study the influence of Mg
2+
on the initial stages of CaCO
3
scale formed on a metal surface.With this electrochemical technique, the reduction of the dissolved oxygen in an analysis solution is considered on the surface of a rotating disk electrode (RDE) under potentiostatic control.The rate of oxygen reduction on the surface of the RDE enables the extent of surface coverage of scale to be assessed.With this electrochemical technique, a new insight into the effect of Mg
2+
on CaCO
3
scale formed on a metal surface is given.
Ti-modified Mesoporous Molecular Sieves Containing both Selective Oxidation and Photocatalysis Centers
GUO Zong-ying, HE Jing, David G. Evans, DUAN Xue, ZHU Yue-xiang, XIAO Tian-cun
2004, 20(4): 386-391.
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Mesoporous molecular sieves possessing high mesopore volumes and large specific surface areas were prepared and characterized by means of XRD, low temperature N
2
adsorption-desorption measurements,FT IR, Raman, UV-visible diffuse reflectance and XPS spectroscopy.The materials contain both framework and extra-framework Ti centers which exhibit selective oxidation catalytic activity and photocatalytic activity respectively.The catalysis of selective oxidation was studied with the hydroxylation of benzene with hydrogen peroxide and photochemical activity was studied by the yields of · OH and H
2
O
2
, respectively.
Improved Denitrification of Municipal Sludge in Biofilm-electrode Reactor
ZHANG Le-hua, JIA Jin-ping, WANG Ya-lin, YANG Ji
2004, 20(4): 392-395.
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The denitrification of municipal sludge was improved by combining biofilm process with the electrochemical effect in a single novel reactor.Experiments in this reactor[electric current 60 mA, hydraulic retention time (HRTs) 6.0 h] showed that the removal of CODCr, ammonia nitrogen and total nitrogen in the biofilm-electrode reactor were 2.5%, 1.2%, 14.9%, respectively, higher than those in a traditional biofilm reactor.
Formation of High-quality Advanced High-k Oxide Layers at Low Temperature by Excimer UV Lamp-assisted Photo-CVD and Sol-gel Processing
YU J. J.
2004, 20(4): 396-402.
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We have successfully demonstrated that high quality and high dielectric constant layers can be fabricated by low temperature photo-induced or -assisted processing.Ta
2
O
5
and ZrO
2
have been deposited at t＜400 ℃by means of a UV photo-CVD technique and HfO
2
by photo-assisted sol-gel processing with the aid of excimer lamps.The UV annealing of as-grown layers was found to significantly improve their electrical properties.Low leakage current densities on the order of 10
-8
A/cm
2
at 1 MV/cm for deposited ultrathin Ta
2
O
5
films and ca.10
-6
A/cm
2
for the photo-CVD ZrO
2
layers and photo-irradiated sol-gel HfO
2
layers have been readily achieved.The improvement in the leakage properties of these layers is attributed to the UV-generated active oxygen species O(1D) which strongly oxidize any suboxides to form more stoichiometric oxides on removing certain defects, oxygen vacancies and impurities present in the as-prepared layers.The photo-CVD Ta
2
O
5
films deposited across 10.16-cm Si wafers exhibit a high thickness uniformity with a variation of less than ±2.0% being obtained for ultrathin ca.10 nm thick films.The lamp technology can in principle be extended to larger area wafers, providing a promising low temperature route to the fabrication of a range of high quality thin films for future ULSI technology.
Production of Ammonium Lactate by Fed-batch Fermentation of Rhizopus oryzae from Corncob Hydrolysate
BAI Dong-mei, LI Shi-zhong, LIN Fang-qian
2004, 20(4): 403-406.
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L- (+)-Lactic acid production from corncob hydrolysate as a cheap carbohydrate source by fed-batch fermentation of Rhizopus oryzae HZS6 was studied.After 96 h of fermentation in a 5 L fermentor, the final concentration of ammonium L-(+)-lactate, average productivity(based on initial xylose concentration) and max(+)-lactate was 98.8%.
Surface Characterisation of Silicon Based MEMS
LI J., CUI Z., M. A. Baker
2004, 20(4): 407-410.
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Polysilicon Microelectromechanical systems (MEMS) are the subject of intensive researches.Surface chemistry and topography of a MEMS test structure fabricated at Sandia National Laboratory, USA, were studied by means of scanning electron microscopy(SEM), X-ray photoelectron spectroscopy(XPS) and atomic force microscopy (AFM).XPS C
1s
and Si
2p
, spectra from the polysilieon components, silicon nitride substrate and a reference silicon wafer were compared.The results confirm the presence of a self-assembled monolayer (SAM) on the MEMS surface.An island-like morphology was found on both polysilicon and silicon nitride surfaces of the MEMS.The islands take the form of caps, being up to 0.5 μm in diameter and 20 nm in height.It is concluded that the co-existence of columnar growth and equiaxed growth during the low pressure chemical vapor deposition(LPCVD) of these layers leads to the observed morphology and the islands are caps to the columnar structures.
X-ray Multiple Diffraction Topographic Imaging Technique For Growth History Study of Habit Modifying Impurity Doped Crystals
LAI X., MA C., K. J. Robert, M. C. Miller
2004, 20(4): 411-416.
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A novel crystal characterization instrument has been built up in which a combination of X-ray multiple diffraction and X-ray topography is applied to enabling the cross-correlation between micro-crystallographic symmetry and its spatial dependence in relation to lattice defects.This facility is used to examine, in a selfconsistent manner, growth sector-dependant changes to both the crystallographic structure and the lattice defects associated with the action of habit-modifying additives in a number of representative crystal growth systems.In addition, the new instrument can be used to probe micro-crystallographic aspects (such as distortion to crystal symmetry) and relate these in a spatially resolved manner to the crystal defect structure in crystals doped with known habit modifiers.
Opto-thermal Moisture Content and Moisture Depth Profile Measurements in Organic Materials
XIAO Peng, GUO Xin-xin, CUI Ying-xin, Robert E. Imhof, Dane Bicanic
2004, 20(4): 417-420.
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Opto-thermal transient emission radiometry(OTTER) is a infrared remote sensing technique, which has been successfully used in in vivo skin moisture content and skin moisture depth profiling measurements.In present paper, we extend this moisture content measurement capability to analyze the moisture content of fruit (tomato, grape, etc.) skins, and to study the relationship between fruits ripening process and their surface moisture and moisture depth profiles.
Decomposition of Organic Compounds in Coke Plant Wastewater by Ultrasonic Irradiation and Its Combined Process
XU Jin-Qiu, WANG Jing-wei, WANG Jing-wei
2004, 20(4): 421-428.
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The paper deals with the degradation of the organic compounds in the coke plant wastewater by the combined process of ultrasonic irradiation and activated sludge.The influence factors of the ultrasonic degradation effect such as air atmosphere, initial concentration, ultrasonic power density and the category and consumption of catalyst were investigated.A water quality model was used to explain the degradation of different kinds of organic compounds in the coke plant wastewater by ultrasonic irradiation.After the wastewater was treated by the combined process of ultrasonic irradiation and activated sludge, the COD degradation efficiency was 95.74 %, which is 63.49% higher than that by the process of activated sludge alone.
Synthesis of Novel Benzoylphenylurea Chitin Inhibitors From Chlorothalonil ( Ⅱ )
LIN Jun, MAO De-shou, XU Rong, YAN Sheng-jiao, YANG Li-juan, LI Jun-feng, LIU Fu-chu
2004, 20(4): 429-432.
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Six novel benzoylphenylurea chitin inhibitor derivatives were synthesized in the yields of 30%-50%from the readily available starting material chlorothalonil 1 via sequential fluorine exchange, aminolysis, hydrolysis and acylation reactions.
Synthesis of Silsesquioxane Cages from Phenyl-cis-tetrol,1,3-Divinyltetraethoxydisiloxane and Cyclopentyl Resins
LIU Zhi-hua, Alan R. Bassindale, Peter G. Taylor
2004, 20(4): 433-436.
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The synthesis of T
8
, T
10
and T
12
silsesquioxane cages from a range of starting materials: phenyl-cistetrol, 1,3-divinyltetraethoxydisiloxane and cyclopentyl T resins by using tetra n-butylammonium fluoride (TBAF) as the catalyst is described in this paper.The reaction yields obtained
via
the current route are better compared to those
via
the literature routes.Some of the cage compounds have been characterized by X-ray crystallography.
Images of Azurin Protein Studied by AFM
WANG Nan, WANG Yuan-liang
2004, 20(4): 437-439.
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A zurins, a wild type and a genetically mutant K27 altered one, were immobilized on annealed gold surface and investigated by means of atomic force microscopy.It was found that the surface coverage and height distribution of the adsorbed protein molecules are different from each other, which is possibly the result of the different orientation on the surface.It is believed that the wild type azurin is connected to gold surface by the disulphide bridge; while the mutant, K27C, might be through the thiol groups of the cysteine residues on their surface.
Hierarchical Self-organization of Complex Systems
CHAI Li-he, WEN Dong-sheng
2004, 20(4): 440-445.
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Researches on organization and structure in complex systems are academic and industrial fronts in modern sciences.Though many theories are tentatively proposed to analyze complex systems, we still lack a rigorous theory on them.Complex systems possess various degrees of freedom, which means that they should exhibit all kinds of structures.However, complex systems often show similar patterns and structures.Then the question arises why such similar structures appear in all kinds of complex systems.The paper outlines a theory on freedom degree compression and the existence of hierarchical self-organization for all complex systems is found.It is freedom degree compression and hierarchical self-organization that are responsible for the existence of these similar patterns or structures observed in the complex systems.
CFD Simulation of a Hydrogen/Argon Plasma Jet Reactor for Coal Pyrolysis
CHEN H. G., XIE K. C.
2004, 20(4): 446-451.
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A Computational Fluid Dynamics (CFD) model was formulated for DC arc hydrogen/argon plasma jet reactors used in the process of the thermal H
2
/Ar plasma pyrolysis of coal to acetylene.In this model, fluid flow, convective heat transfer and conjugate heat conductivity are considered simultaneously.The error caused by estimating the inner-wall temperature of a reactor is avoided.The thermodynamic and transport properties of the hydrogen/argon mixture plasma system, which are usually expressed by a set of discrete dats, are fitted into expressions that can be easily implemented in the program.The effects of the turbulence are modeled by two standard k-s equations.The temperature field and velocity field in the plasma jet reactor were calculated by employing SIMPLEST algorithm.The knowledge and insight obtained are useful for the design improvement and scale-up of plasma reactors.
Characterizations of Skeletal Iron Catalysts Prepared from Rapidly and Naturally Quenched Fe-Al Alloys
LUO Ge, YAN Shi-run, QIAO Ming-hua, ZHANG Kai, HU Hua-rong, HE He-yong, FAN Kang-nian
2004, 20(4): 452-456.
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Surface morphology, physical-chemical properties of skeletal iron catalysts prepared by leaching of the rapidly quenched(RQ) and naturally quenched(NQ) Fe-Al alloys with an aqueous solution of NaOH were characterized by using a series of techniques including XRD, BET, XPS, SEM, H
2
and CO-TPD.It was found that the RQ skeletal iron catalyst exhibits a smaller particle size, larger specific surface area and pore volume than the NQ one.The H
2
and CO-TPD experiments showed that the RQ skeletal iron exhibits stronger affinity for H
2
and milder affinity for CO compared with the NQ one.But the NQ skeletal catalyst shows a better thermal stability than the RQ catalyst.
Methane Dry Reforming over Alumina Supported Co Catalysts
CHEN Xiao-wei, XIAO Tian-cun, Sergio L. González Cortés, Malcolm L. H. Green
2004, 20(4): 457-461.
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A series of Co/γ-Al
2
O
3
catalysts were prepared with the impregnation method and characterized by means of the BET specific surface area, X-ray diffraction(XRD), thermogravimetric analysis (TGA) and Laser Raman spectroscopy.The Co/γ-Al
2
O
3
catalysts were activated by using H
2
, 20% CH
4
/H
2
or CH
4
, respectively.There was no obvious difference between the activities of the Co/γ-Al
2
O
3
catalyst activated by using the different activation methods for methane dry reforming.The catalytic properties of the Co/γ-Al
2
O
3
catalysts with different Co loadings were also investigated.The optimized Co loading for the Co/γ-Al
2
O
3
catalyst pretreated with 20% CH
4
/H
2
is around 12% (mass fraction).
Gas Holdups of Small and Large Bubbles in a Large-scale Bubble Column with Elevated Pressure
JIN Hai-bo, YANG Suo-he, ZHANG Tong-wang, TONG Ze-min
2004, 20(4): 462-465.
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Gas holdups of large bubbles and small bubbles were measured by means of dynamic gas disengagement approach in the pressured bubble column with a diameter of 0.3 m and a height of 6.6 m.The effects of superficial gas velocity, liquid surface tension, liquid viscosity andsystem pressure on gas holdups of small bubbles and large bubbles were investigated.The holdup of large bubbles increases and the holdup of small bubbles decreases with an increase of liquid viscosity.Meanwhile, the holdup of large bubbles decreases with increasing the system pressure.A correlation for the holdup of small bubbles was obtained from the experimental data.
Regulation of Power Conversion in Fuel Cells
SHEN Mu-zhong, ZHANG J., K. Scott
2004, 20(4): 466-469.
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Here we report a regulation about power conversion in fuel cells.This regulation is expressed as that total power produced by fuel cells is always proportional to the square of the potential difference between the equilibrium potential and work potential.With this regulation we deduced fuel cell performance equation which can describe the potential vs.the current performance curves, namely, polarization curves of fuel cells with three power source parameters: equilibrium potential E0; internal resistance R; and power conversion coefficient K.The concept of the power conversion coefficient is a new criterion to evaluate and compare the characteristics and capacity of different fuel cells.The calculated values obtained with this equation agree with practical performance of different types of fuel cells.
Tungsten Promoted Ni/Al
2
O
3
Catalysts for Carbon Dioxide Reforming of Methane to Synthesis Gas
XIAO Tian-cun, Thomas Suhartanto, Andrew P. E. York, Malcolm L. H. Green
2004, 20(4): 470-477.
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A series of tungsten promoted alumina supported nickel catalysts has been prepared for the carbon dioxide reforming of methane to synthesis gas.The catalysts have been characterized by means of XRD, TEM,and Laser Raman spectroscopy.It is shown that the addition of tungsten to the nickel catalyst can stabilize the catalyst and increase the resistance to carbon deposition.Adding a suitable amount of tungsten can also increase the catalyst activity to be close to that of supported noble metal catalysts.The carburisation of the tungsten modified nickel catalyst decreases the catalyst activity at lower reaction temperatures(＜1123K),but has no effect on the catalyst performance at higher reaction temperatures.The alumina supported nickel catalyst modified by 0.67 % (mass fraction)WOs has the equivalent equilibrium constant of the dry reforming reaction to that of alumina supported 5% (mass fraction) Ru at 873 K, and also has a lower activation energy for dry reforming than the latter.
Hydrodynamic Behavior in a Tapered Bubble Column
ZHANG Kai, ZHAO Yu-long, ZHANG Bi-jiang
2004, 20(4): 478-482.
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The experiment was conducted to explore the hydrodynamics in a conical column with a height of 3.00 m, and a taper angle of 1.91°.Three regimes occur in succession with increasing superficial gas velocity.Overall gas holdup increases with an increase in gas velocity and a decrease in solid concentration or static slurry height.Axial solid holdup becomes more uniform with increasing gas velocity, while axial gas holdup decreases from the bottom to the top.Both dry and wet pressure drops across the gas distributor increase with an increase in superficial gas velocity.
A CFD Model for Fluid Dynamics in a Gas-fluidised Bed
ZHANG Kai, Stefano Brandani
2004, 20(4): 483-488.
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A modified particle bed model derived from the two-fluid momentum balance equations was employed to predict the gas-fluidised bed behaviour.Additional terms are included in both the fluid and the particle momentum balance equations to take into account the effect of the dispersed solid phase.This model has been extended to two-dimensional formulations and has been implemented in the commercial code CFX 4.3.The model correctly simulates the homogeneous fluidisation of Geldart Group A and the bubbling fluidisation of Geldart Group B in gas-solid fluidised beds.
Characterization of the Engineering Flow in a Miniaturised Bioreactor by Computational Fluid Dynamics
ZHANG Hu, Parviz Ayazi Shamlou
2004, 20(4): 489-493.
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Three approaches based on computational fluid dynamics(CFD) techniques have been assessed for their ability to describe the engineering flow environment in a miniaturized mechanically agitated bioreactor.The three approaches tested were the source-sink(SS), the multiple reference frames(MRF) and the sliding grids (SG).In all the cases, the predictions of the velocity components agree with reported experimental data.However, the analysis of the results of the turbulent intensities predicted by the three approaches indicates the MRF and the SG techniques under predicted turbulent intensities are comparable to both experimental measurements and the SS method.The predicted power number and pumping number based on the SS approach are closer to typical reported experimental values compared to those obtained from the MRF and SG methods.
Thermodynamic Foundation for High Temperature Electrochemistry
ZHANG W., E. A. Charles, J. Congleton
2004, 20(4): 494-500.
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Thermodynamic concepts required for the thermodynamic calculation of the potentials of electrodes for high temperature applications are briefly reviewed.A thermodynamic approach to the calculation of half cell potentials and the standard chemical potential of an electron at high temperatures which are related to the Standard Hydrogen Electrode(SHE) is discussed.As examples, an external Ag/AgCl reference electrode and a YSZ (Ag|O
2
) pH sensor for high temperature applications are analyzed by using the thermodynamic approach to derive a high temperature pH measurement equation.The two electrodes are employed to measure high temperature pH and the measured pH was compared with the calculated pH by using a solution chemistry method.Concepts and principles for electrode kinetics are also briefly introduced and a modification to the Tafel equations is suggested.
Investigation of Adsorption of Xanthan Gum on Enamel by Tapping Mode Atomic Force Microscopy
LI Hao-ying
2004, 20(4): 501-503.
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By using tapping mode atomic force microscopy(TMAFM), a polymer layer was found on the enamel surface after the exposure to xanthan gum solutions.The layer thickness is closely related to the exposure time and the concentration of xanthan gum solution.The thickness data were evaluated by a Kruskal-Wallis test and Box-Whisker Plot at a 95% confidence level(p＜0.05), and a statistically significant difference among the thickness data groups was demonstrated.After the exposure to 1000, 400, 100 mg/L xanthan gum solutions, the mean of layer thickness at the adsorption equilibrium is in the ranges of 103.5_122.06,82.4_88.94 and 45.27_55.55 nm, respectively.This phenomenon suggests that the viscosity modifying agents in the beverage might be adsorbed on the enamel surface during consumption, which may form a barrier that can protect the enamel from being attacked by acid and therefore reduce dental erosion.
Structure and Properties of Self-reinforced Material Made from Ultra-high Molecular Weight Polyethylene-montmorillonite Nanocomposite
WANG Qing-zhao, LIAO Xian-ling, LIU Zong-lin
2004, 20(4): 504-510.
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High-strength and high-modulus ultra-high molecular weight polyethylene(UHMWPE), named self-reinforced material, was obtained by the elongation of UHMWPE-montmorillonite nanocomposite at melting temperature.According to the scanning electron microscope (SEM) analysis, a great deal of fibrillar texture formed in the direction of elongation, and the tensile fractured surface was similar to that of highly oriented fiber.The transmission electron microscope (TEM) and selective area electron diffraction(SAED) analyses reveal that the reinforced phase of the self-reinforced material is an extended chain crystal and its size is about 50_ 200 nm wide and several microns long, and the montmorillonite layers are broken up to pieces in the size from 100 to 10 nm.The broken layers which have a huge surface area interacting strongly with macromolecules reduces the entanglement density of UHMWPE and induces the chain orientation in flow field.It is supposed that the astriction of montmorillonite layers to polyethylene chains is not only end-tethered but also side-tethered.The differential scan calorimetry(DSC) analysis shows that there are two endothermal peaks for the self-reinforced material, of which the peak at a higher temperature (136.4 ℃) is ascribed to the melting of the reinforced phase.
Temperature Controlled Lateral Pattern Formation in Confined Polymer Thin Films
ZHANG Hao-li, David G. Bucknall
2004, 20(4): 511-515.
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The thermal induced topography change in a model system consisting of a polymer film on a Si substrate capped by a thin metal layer has been studied by using AFM.Regular lateral patterns over large areas were observed on the surface when the system was heated to a sufficiently high temperature.2D-FFT analysis to the AFM images indicates that the patterns are isotropic and have well defined periodicities.The periodicities of the characteristic patterns are found to depend strongly on the annealing temperature.The study of the kinetics of the formation reveals that such a topography forms almost instantaneously once the critical temperature is reached.It is suggested that this wave-like surface morphology is driven by the thermal expansion coefficient mismatch of the different layers.This method for generating regular wave-like patterns could be used as a general method for patterning various organic materials into micro/nanostructures.
Editor-in-Chief:
Jihong YU
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CN 22-1183/O6
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