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Preparation and Properties of Some Chemical and Electrochemical γ-MnO_2

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Journal of Materials sci.nce & Technology 2001年第3期17卷 351-354页

作者： H.M.Abbas, Kh. S.Abou-El-Sherbini, M.H.Askar and A. M. Hashim Dept.of Physical cent.e, National res.arch cent.e, Tahiu, Dokki, Cairo, Egypt E-mail: sherbini@*** Dept. of Phys. cent. Natl. Res. Cent. Cairo Egypt

Chemically prepared electrolytic 2-Mn02 and an electrodeposited MnO2 doped with Ce(Ⅲ) were subjected to physicochemical studies. X-ray diffractometry, density measurements, chem-ical analysis and thermal analysis were used to determine the structure and chemical disorder pres.nt. The samples prepared chemically (CMD) or electrochemically (EMD) showed a variable amount of de Wolff disorder (Pr) and microtwinning (Tw). Manganese dioxide prepared in the pres.nce of Ce(Ⅲ) showed appreciable decrease in de Wolff defect and a large amount of microtwinning. Thermal analysis showed a loss of weight due to the physically adsorbed and the structural (OH) water, from which the activation energy was calculated. Chemical composition and formulae calculated on the bases of cation vacancy model, cleared that Ce(lIl)-doped sample has a remarkable increase in the vacancies population associated with higher structural water content. This leads to lower activation energy of water release, and consequently it is supposed to acquire higher electrochemical activity.

关键词： EMD MnO2

NUMERICAL SIMULATION OF A TWO-DIMENSIONAL SQUARE MOVING NEAR FREE SURFACE

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Journal of Hydrodynamics 2001年第1期13卷 54-57页

作者： Hong, F.W. Zhao, F. Zhou, L.D. China Ship sci. res. cent. P. O. Box 116 Wuxi 214082 China

A body moving near the free surface is a focus in fluid dynamic res.arch. Many numerical methods were developed for the simulation of the induced flow field. In this paper, a two-dimensional square moving near the free surface was simulated by the volume of fluid method (VOF). The flow field and drag exerted on the square were studied. The drag would increase due to the pres.nce of the free surface. The iteration factor of the pres.ure interpolation of surface cells was modified, and through this modification the iteration became more stable. The capability of dealing with the large deformation of the free surface was raised.

关键词： Computational fluid dynamics Computer simulation Drag Numerical methods

Dislocation Velocity Exponent and the Strain Rate

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Journal of Materials sci.nce & Technology 2001年第3期17卷 363-366页

作者： Hongyan LIU and Xiaowei WANG International cent.r for Material Physics, Institute of Metal res.arch, Chinese Academy of sci.nces, Shenyang 110016, China E-mail: liu@*** Intl. cent. for Mat. Phys. Inst. of Metal Res. Chinese Acad. of Sci. Shenyang 110016 China

The process of dislocation multiplication has been described hv chaos theory, trying to reveal the connection between the microstructures.on the mesoscopic scale and the mechanical properties of material on the macroscopic scale. The relationship between the dislocation velocity exponent and the maximum of strain rate is given. The res.lts obtained from logistic equation with exponent and the dislocation multiplication dynamic equation are compared. A scale law in one-dimension-map model with exponent is shown when the exponents of equations are changed.

关键词： Dislocation Velocity Exponent and the Strain Rate

Utility of semivariogram for spatial variation of soil nutrients and the robust analysis of semivariogram

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Journal of environ.ental sci.nces 2001年第4期13卷 453-458页

作者： Guo, X.-d. Fu, B.-j. Ma, K.-m. Chen, L.-d. Department of Systems ecology Res. Cntr. Eco-Environmental Sci. Chinese Academy of Sciences Beijing 100085 China

The spatial variation of soil nutrients in topsoil (0-20cm) was analyzed using semivariogram in the Zunhua County of Hebei Province, China. The effect on semivariogram with randomly deleted data and kriged estimates using various reduced sample sizes was also analyzed. The semivariograms of available N, total N, available P, organic matter were best described by a spherical model, except for available K, which best fitted a complex structure of exponential model and linear with sill model. The ratio of nugget to total sample variance ranged from 34.4% to 68.4%, indicating the spatial correlation of tested soil nutrients on a large scale was moderately dependent. Among five soil nutrients, available nitrogen and available phosphorus had the shortest spatial correlation range (5 km and 5.5 km), available K had the longest range (25.5 km), whereas total nitrogen and organic matter had intermediate spatial correlation range (14.5 km and 8.5 km). The semivariograms of available N, total N, available P, and organic matter were insensitive to a 50%-60% reduction in original sampling density, while for available K, it is up to 70%. The estimated spatial distributions of total N by kriging, under various reduced sample sizes, all correlated significantly (P = 0.001) with those obtained from original data. The res.lts showed that the semivariogram was a relatively robust tool when used in a large region and sufficient spatial variation information could be relained regardless of a higher deletion proportion of the original data. The original sample data could be reduced by kriging and the estimates showed no loss of spatial information, however, the res.lts may be unreliable unless a clearly identified semivariogram model could be obtained. The res.lts may provide useful information for determining the appropriate sampling densities for these scales of soil survey.

关键词： Correlation methods Data reduction Nitrogen Phosphorus Sampling Soils Surveying

Recent.developments of surface complexation models applied to environ.ental aquatic chemistry

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Journal of environ.ental sci.nces 2001年第4期13卷 422-434页

作者： Liu, W.-X. Tang, H.-X. SKLEAC Res. Cntr. Eco-Environmental Sci. Chinese Academy of Sciences Beijing 100085 China

Based on numerous latest references, the current developments in surface complexation, surface precipitation and the corres.onding models (SCMs and SPMs), were reviewed. The contents involved comparison on surface charge composition and layer-structure of solid-solution interface for the classical 1-pK and 2-pK models. In addition, the fundamental concept and relations of the new models, i. e., multi-site complexation (MUSIC) and charge- distribution (CD) MUSIC models were described as well. To avoid misuse or abuse, it must be emphasized that the applicability and limitation for each model should be considered carefully when selecting the concerned model(s). In addition, some new powerful techniques for surface characterization and analysis applied to model establishment and modification were also briefly introduced.

关键词： Complexation Precipitation (chemical)

Hydrothermal Characteristics of Blended Cement Pastes Containing Silica Sand Using Cement Kiln Dust as an Activator

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Journal of Materials sci.nce & Technology 2002年第5期18卷 474-478页

作者： S.A.Abo-El-Enein F.I.El-Hosiny E.El-Shimy T.A.Osman Faculty of sci. Ain Shams Univ. Abbassia-Cairo Egypt Building res. cent. P. O. Box 1770 Cairo Egypt

The hydrothermal reactivity of silica sand was studied using cement kiln dust (CKD) as an activator in addition to the Portland cement fraction of El-Karnak cement (a blend of ordinary Portland cement and ground sand). Autoclaved EI-Karnak cement pastes were studied at pres.ures.of 0.507, 1.013 and 1.520 MPa of saturated steam with res.ect to their compres.ive strength, kinetics of hydrothermal reaction and the phase composition of the formed hydrates. The role of CKD in affecting the physicochemical and mechanical properties of EI-Karnak cement pastes was studied by autoclaving of several pastes containing 5, 7.5, 10 and 20% CKD at a pres.ure of 1.013 MPa of saturated steam. CKD was added either as a raw CKD (unwashed) or after washing with water (washed CKD). The res.lts of these physicochemical studies obtained could be related as much as possible to the role of CKD (raw or washed) in affecting the hydrothermal reactivity of silica sand in EI-Karnak cement pastes.

关键词： Blended cement Silica Cement kiln dust Hydrothermal characteristics

Theoretical studies on the influence of molecular interactions on the mechanism of electron transfer in photosynthetic reaction cent.r of ***

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sci.nce China Chemistry 2002年第6期45卷 570-585页

作者：徐红张兴康张汝波张启元屈正旺 cent. of Molecular sci. Inst. of Chem. Chinese Acad. of Sci. Beijing 100080 China

Based on the QM/MM optimized X-ray crystal structure of the photosynthetic reaction cent.r (PRC) of purple bacteria Rhodopseudomonas (Rps.) viridis, quantum chemistry density functional method (DFT, B3LYP/6-31G) has been performed to study the interactions between the pigment molecules and either the surrounded amino acid res.dues or water molecules that are either axially coordinated or hydrogen bonded with the pigment molecules, leading to an explanation of the mechanism of the primary electron-transfer (ET) reactions in the PRC. res.lts show that the axial coordination of amino acid res.dues greatly raises the ELUMO of pigment molecules and it is important for the possibility of ET to take place. Different hydrogen bonds between amino acid res.dues, water molecules and pigment molecules decrease the ELUMO of the pigment molecules to different extents. It is crucial for the ET taking place from excited P along L branch and sustains that the ET is a one-step reaction without through accessory bacteriochlorophyll (ABChl b). It is insufficient to treat the whole protein surrounding as a homogeneous dielectric medium.

关键词： bacteria photosynthetic reaction cent.r, electron transfer, pigment molecule, interaction between pigment molecules and neighboring amino acid res.due, DFT.

Studying Cu Alloy Corrosion Products in Cooling Liquid

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Journal of Materials sci.nce & Technology 2001年第5期17卷 507-510页

作者： A.A .El-Meligi National res.arch cent.e, Physical Chem. Dept., Dokki, Cairo, Egypt Natl. res. cent. Phys. Chem. Dept. Cairo Egypt

The effect of cooling liquid used for heat exchangers on the Cu alloy corrosion products has been examined using potential-time measurements under applied current condition (anodizing), potentiodynamic polarization, X-ray diffraction (XRD) and infrared spectroscopy (IR) The corrosion products formed on the Cu alloy surface during anodizing, are Cu2O, Cu2(OH)3Cl, and Cu2S. NaCl is detected in the corrosion products. The film formation depends on the applied current and the shift of potential to nobler direction indicates its formation progres..

关键词： Cu Studying Cu Alloy Corrosion Products in Cooling Liquid

Powder Forging of a Motorcycle Connecting Rod

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Journal of Materials sci.nce & Technology 2002年第6期18卷 544-548页

作者： Guangchun WANG and Guoqun ZHAOMold & Die Engineering Technology res.arch cent.r, Shandong University (Southern campus), Jinan 250061, China Die Eng. Technol. res. cent. Shandong Univ. Ji'nan 250061 China

A motorcycle connecting rod is one of the major moving parts affecting the engine performance. The traditional manufacturing process res.lts in material waste and excessive machining. A new method of hot forging P/M has been proposed and studied experimentally. In order to achieve uniform density, the punch was divided into three parts to consolidate the loose powder. The multistage movement of the three parts of the punch, called synchronous compaction, res.lts in the desired uniform density. Powder flow during consolidation was illustrated and the density distribution of the compacts was measured. A set of forging dies with flash was used to produce densification and deformation of the sintered compact. Then a set of flashless forging dies was designed to obtain the desired shape and dimensions of the connecting rod. The effects of forging temperature and initial compact density on densification were evaluated through hot forging experiments. Based on properties achieved, Fe-C-Cu-Mo was selected as the

关键词： Powder metallurgy Connecting rod Powder forging