Research and development of catalytic processes for petroleum and natural gas conversions in the Dalian Institute of Chemical Physics

The Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences has a long history in the R&D of catalysts and catalytic processes for petroleum and natural gas conversions in China. In this paper, results and features of some commercialized petrochemical catalysts and processes as well as newly developed processes for natural gas conversion in the pilot-plant stage are described. (C) 1999 Elsevier Science B.V. All rights reserved.

Environmental Mechanics Research in China

By recalling mankind's path during past 50 years in the present article, we mainly highlight the significance of environmental issues today. In particular, two major factors leading to environment deterioration in China such as water resources and coal burning are stressed on. Present-day environmental issues are obviously interdisciplinary, of multiple scales and multi-composition in nature. Therefore, a process-based approach for environment research is absolutely necessarily. A series of sub-processes, either physical, chemical or biological, are subsequently analyzed in order to established reasonable parameterization scheme and credible comprehensive model. And we are now in a position to answer questions still open to us, improve existing somewhat empirical engineering approaches and enhance quantitative accuracy in prediction. To illustrate this process-based research approach, three typical examples associated with the Yangtze River Estuary, Loess Plateau and Tenggeli Desert environments have been dealt with respectively. A theoretical model of vertical flow field accounting for runoff and tide interaction has been established to delineate salinity and sediment motion which are responsible for the formation of mouth bar at the outlet and the ecological evolution there. A kinematic wave theory combined with the revised Green-Ampt infiltration formula is applied to the prediction of runoff generation and erosion in three types of erosion region on the Loess Plateau. Three approaches describing water motion in SPAC system in arid areas at different levels have been improved by introducing vegetation sub-models. However, we have found that the formation of a dry sandy layer and biological crust skin are additional primary causes leading to deterioration of water supply and succession of ecological system.

Dissipative particle dynamics simulation of wettability alternation phenomena in the chemical flooding process

Wettability alternation phenomena is considered one of the most important enhanced oil recovery (EOR) mechanisms in the chemical flooding process and induced by the adsorption of surfactant on the rock surface. These phenomena are studied by a mesoscopic method named as dissipative particle dynamics (DPD). Both the alteration phenomena of water-wet to oil-wet and that of oil-wet to water-wet are simulated based on reasonable definition of interaction parameters between beads. The wetting hysteresis phenomenon and the process of oil-drops detachment from rock surfaces with different wettability are simulated by adding long-range external forces on the fluid particles. The simulation results show that, the oil drop is liable to spread on the oil-wetting surface and move in the form of liquid film flow, whereas it is likely to move as a whole on the water-wetting surface. There are the same phenomena occuring in wettability-alternated cases. The results also show that DPD method provides a feasible approach to the problems of seepage flow with physicochemical phenomena and can be used to study the mechanism of EOR of chemical flooding.

Characterization of m-plane ZnO thin film on gamma-LiAlO2 (100) substrate by metal-organic chemical vapor deposition

Non-polar (1 (1) over bar 00)m-plane ZnO thin film has been prepared on gamma-LiAlO2 (100)substrate via the low pressure metal organic chemical vapor deposition. Obvious intensity variation of the E-2 mode in the polarized Raman spectra and the absorption edge shift in the polarized optical transmission spectra indicate that the m-plane film exhibits optical anisotropy, which have applications in certain optical devices, such as the UV modulator and polarization-dependent beam switch. From the atomic force microscopy images, highly-oriented uniform-sized grains of rectangular shape were observed. (c) 2008 Elsevier B.V. All rights reserved.

Chemical Constituents from the Leaves and Stems of Schisandra lancifolia

A new nortriterpenoid, 20-hydroxymicrandilactone D (1) and a novel lignan glycoside, lancilignanside A (2) were isolated from leaves and stems of Schisandra lancifolia, together with three known nortriterpenoids (3-5) and nine known phenolics (6-14). The structures of new compounds 1 and 2 were determined by detailed analysis of their 1D and 2D NMR spectra, and chemical evidences. In addition, compounds 1-2, 6-7, and 9-11 showed anti-human immunodeficiency virus (HIV)-1 activities with 50% effective concentration (EC50) in the range of 3.0-99.0 mu g/ml. Compound 12 was not bioactive in this assay with EC50 more than 200 mu g/ml.

Development of a biotic index using the correlation of protozoan communities with chemical water quality

A method of comparing data on protozoan communities with chemical parameters is presented. Using data from an extensive survey of the River Hanjiang in China, each species of protozoa has been given a species pollution value (SPV) related to its occurrence in waters with different degrees of pollution. A comprehensive chemical index is calculated for each site based on water quality standards for eight chemical parameters. The index is calculated from the relationship between the observed levels of each chemical at a site, compared with the limits of the drinking water quality standards of the People's Republic of China. From the distribution of each species at sites with differing chemical index values, a SPV is calculated. The SPV for each species is obtained by summing the logarithmic value of 10 times the chemical pollution divided by the number of chemical parameters, then divided by the stations where the species occurs. The community pollution value (CPV), which is the average SPVs of all protozoa at a site, is used to evaluate water quality. The CPV has been shown to have a close correlation with the degree of water pollution. It is not necessary for all the protozoa in a sample to have SPVs listed in this paper, provided at least 56% of the protozoa in a sample have an SPV value, the CPV will be applicable.

Impact of thickness of GaN buffer layer on properties of AlN/GaN distributed Bragg reflectors grown by metalorganic chemical vapor deposition

We studied the impact of the thickness of GaN buffer layer on the properties of distributed Bragg reflector (DBR) grown by metalorganic chemical vapor deposition (MOCVD). The samples were characterized by using metallographic microscope, transmission electron microscope (TEM), atomic force microscopy (AFM), X-ray diffractometer (XRD) and spectrophotometer. The results show that the thickness of the GaN buffer layer can significantly affect the properties of the DBR structure and there is an optimal thickness of the GaN buffer layer. This work would be helpful for the growth of high quality DBR structures.

Normal incidence p-i-n Ge heterojunction photodiodes on Si substrate grown by ultrahigh vacuum chemical vapor deposition

We report on normal incidence p-i-n heterojunction photodiodes operating in the near-infrared region and realized in pure germanium on planar silicon substrate. The diodes were fabricated by ultrahigh vacuum chemical vapor deposition at 600 degrees C without thermal annealing and allowing the integration with standard silicon processes. Due to the 0.14% residual tensile strain generated by the thermal expansion mismatch between Ge and Si, an efficiency enhancement of nearly 3-fold at 1.55 mu m and the absorption edge shifting to longer wavelength of about 40 nm are achieved in the epitaxial Ge films. The diode with a responsivity of 0.23 A/W at 1.55 mu m wavelength and a bulk dark current density of 10 mA/cm(2) is demonstrated. These diodes with high performances and full compatibility with the CMOS processes enable monolithically integrating microphotonics and microelectronics on the same chip.

Photoluminescence and lasing properties of InAs/GaAs quantum dots grown by metal-organic chemical vapour deposition

Photoluminescence (PL) and lasing properties of InAs/GaAs quantum dots (QDs) with direrent growth procedures prepared by metalorganic chemical vapour deposition are studied. PL measurements show that the low growth rate QD sample has a larger PL intensity and a narrower PL line width than the high growth rate sample. During rapid thermal annealing, however, the lowgrowth rate sample shows a greater blue shift of PL peak wave length. This is caused by the larger InAs layer thickness which results from the larger 2-3 dimensional transition critical layer thickness for the QDs in the low-growth-rate sample. A growth technique including growth interruption and in-situ annealing, named indium flush method, is used during the growth of GaAs cap layer, which can flatten the GaAs surface effectively. Though the method results in a blue shift of PL peak wavelength and a broadening of PL line width, it is essential for the fabrication of room temperature working QD lasers.

Characterization of ZnMgO hexagonal-nanotowers/films on m-plane sapphire synthesized by metal organic chemical vapour deposition

ZnMgO hexagonal-nanotowers/films grown on m-plane sapphire substrates were successfully synthesized using a vertical low-pressure metal organic chemical vapour deposition system. The structural and optical properties of the as-obtained products were characterized using various techniques. They were grown along the non-polar [1 0 (1) over bar 0] direction and possessed wurtzite structure. The ZnMgO hexagonal-nanotowers were about 200 nm in diameter at the bottom and 120 nm in length. Photoluminescence and Raman spectra show that the products have good crystal quality with few oxygen vacancies. With Mg incorporation, multiple-phonon scattering becomes weak and broad, and the intensities of all observed vibrational modes decrease. The ultraviolet near band edge emission shows a clear blueshift (as much as 100 meV) and broadening compared with that of pure ZnO products.

Photoluminescence properties of tensile-strained GaAsP/GaInP single quantum wells grown by metal organic chemical vapor deposition

Tensile-strained GaAsP/GaInP single quantum well (QW) laser diode (I-D) structures have been grown by low-pressure metal organic chemical vapor deposition (LP-MOCVD) and related photoluminescence (PL) properties have been investigated in detail. The samples have the same well thickness of 16 nm but different P compositions in a GaAsP QW. Two peaks in room temperature (RT) PL spectra are observed for samples with a composition larger than 0.10. Temperature and excitation-power-dependent PL spectra have been measured for a sample with it P composition of 0.15. It is found that the two peaks have a 35 meV energy separation independent of temperature and only the low-energy peak exists below 85 K. Additionally, both peak intensities exhibit a monotonous increase as excitation power increases. Analyses indicate that the two peaks arise from the intrinsic-exciton recombination mechanisms of electron-heavy hole (e-hh) and electron-light hole (e-hh). A theoretical calculation based oil model-solid theory, taking, into account the spin-orbit splitting energy, shows good agreement with our experimental results. The temperature dependence of PL intensity ratio is well explained using the spontaneous emission theory for e-hh and e-hh transitions. front which the ratio can be characterized mainly by the energy separation between the fill and Ill states.

Well-Aligned Zn-Doped InN Nanorods Grown by Metal-Organic Chemical Vapor Deposition and the Dopant Distribution

We report the synthesis and characterization of Zn-doped InN nanorods by metal-organic chemical vapor deposition. Electron microscopy images show that the InN nanorods are single-crystalline structures and vertically well-aligned. Energy-dispersive X-ray spectroscopy analyses suggest that Zn ions are distributed nonhomogenously in InN nanorods. Simulations based on diffusion model show that the doping concentration along the radial direction of InN nanorod is bowl-like from the exterior to the interior, the doping concentration decreases, and Such dopant distribution result in a bimodal EDXS spectrum of Zn across the nanorod. The study of the mechanism of doping effect is useful for the design of InN-based nanometer devices. Also, high-quality Zn-doped InN nanorods will be very attractive as building blocks for nano-optoelectronic devices.'

Kinetically controlled InN nucleation on GaN templates by metalorganic chemical vapour deposition

This paper presents a study on the nucleation and initial growth kinetics of InN on GaN, especially their dependence on metalorganic chemical vapour deposition conditions. It is found that the density and size of separated InN nano-scale islands can be adjusted and well controlled by changing the V/III ratio and growth temperature. InN nuclei density increases for several orders of magnitude with decreasing growth temperature between 525 and 375 degrees C. At lower growth temperatures, InN thin films take the form of small and closely packed islands with diameters less than 100 nm, whereas at elevated temperatures the InN islands grow larger and become well separated, approaching an equilibrium hexagonal shape due to enhanced surface diffusion of adatoms. The temperature dependence of InN island density gives two activation energies of InN nucleation behaviour, which is attributed to two different kinetic processes related to In adatom surface diffusion and desorption, respectively.