Structure Prediction Based on Hydrophobic to Hydrophilic Volume Ratios in Small Molecule Amphiphilic Organic Crystals

The structure type for the crystal of 4,4'-bis-(2-hydroxy-ethoxyl)-biphenyl 1 has been predicted by using the previously developed interfacial model for small organic molecules. Based on the calculated hydrophobic to hydrophilic volume of 1, this model predicts the crystal structure to be of lamellar or bicontinuous type, which has been confirmed by the X-ray single-crystal structure analysis (C20H26O6, monoclinic, P21/C, a = 16.084(1), b = 6.0103(4), c = 9.6410(7) A, β9 = 103.014(2)°, V= 908.1(1) A3, Z = 2, Dc= 1.325 g/cm3, F(000)=388,μ = 0.097 mm-1, MoKα radiation, λ = 0.71073 A, R = 0.0382 and wR = 0.0882 with I > 2σ(I) for 7121 reflections collected, 1852 unique reflections and 170 parameters). As predicted, the hydrophobic and hydrophilic portions of 1 form in the lamellae. The same interfacial model is applied to other amphilphilic small molecule organic systems for structural type prediction.

MASS PRODUCTION OF NANOPARTICLES BY HIGH GRAVITY REACTIVE PRECIPITATION TECHNOLOGY WITH LOW COST

Mass production of nanoparticles at low cost has attracted much attention from industrial and academic circles. In this paper, a novel method, the high gravity reactive precipitation (HGRP) technology, of manufacturing CaCO3 nanoparticles, presently scaled-up to an annual capacity of 10,000 tons, is presented. This paper describes the process principle, the process design and experiments on the syntheses of 15-30 nm CaCO3, 30-50 nm SiO2, 20-30 nm TiO2, 20-60 nm ZnO, 20-30 nm ZnS, 30 nm SrCO3, 40-70 nm BaTiO3, stick-like nano BaCO3 as well as nano-fibrillar aluminum hydroxide measuring 1-10 nm in diameter and 50-300 nm in length, using liquid-liquid, gas-liquid and gas-liquid-solid reactant systems. The advantage of using the HGRP technology is illustrated by comparison to conventional methods.

SPATIAL AND SEASONAL DISTRIBUTIONS OF ATMOSPHERIC CARBONACEOUS AEROSOLS IN PEARL RIVER DELTA REGION, CHINA

Concentrations and spatial distributions of organic carbon (OC) and elemental carbon (EC) in atmospheric particles were measured at 8 sites in four cities (Hong Kong, Guangzhou, Shenzhen and Zhuhai) of Pearl River Delta Region (PRDR), China during 2001 winter period and 2002 summer period. PM2.5 (particie diameter smaller than 2.5 um) and PM10 (particie diameter smaller than 10 um) samples were collected on pre-fired quartz filters with mini-volume samplers and analyzed using thermal optical reflectance (TOR) method. The average PM2.5and PM10 Ievel were 60.1 and 93.1 μg·m-3, respectively, with PM2.5 constituting 65.3% of the PM10 mass. The average OC and EC concentrations in PM2.5 were 12.0 and 5.1 μg·m-3, respectively, while those in PM10 were 16.0 and 6.5 μg·m-3, respectively. The carbo-naceous aerosol accounted for 37.2% of the PM2.5 and 32.8% of the PM10. The highest concentrations of OC and EC were observed at Guangzhou city in both vvinter and summer seasons. The average OC/EC ratios were 2.4 for PM2.5 and 2.5 for PM10, indicating the presence of secondary organic aerosols. The OC and EC in PRDR were found to be strongly correlated (correlation coefficients > 0.6), which implied that similar emission source contribute to the ambient carbon particles.

INFLUENCE OF ASIAN DUSTS ON THE PHYSICOCHEMICAL PROPERTIES OF ATMOSPHERIC AEROSOLS IN TAIWAN DISTRICT——USING THE PENGHU ISLANDS AS AN EXAMPLE

Using the Penghu Islands as an example, this study investigates the influence of Asian dusts on the physicochemical properties of atmospheric aerosols in Taiwan District in the year of 2002. An aerosol-sampling site was established at Xiaumen, the Penghu Islands, to collect sea level atmospheric aerosols for further analysis of their phys-icochemical properties. This study revealed that, during the sampling campaign, three Asian dust storms were trans-ported from North China and Mongolia to the Penghu Islands. The mass concentrations of atmospheric aerosols, par-ticularly PM2.5~10, were generally 2~3 times higher than the regular level. An increase of coarse particle mode in the size distribution of atmospheric aerosols further validated the invasion of Asian dusts. Moreover, the comparison of wa-ter-soluble ionic species, carbonaceous content, and metallic content of atmospheric aerosols indicated that Asian dusts could significantly influence the chemical properties of atmospheric aerosols in Taiwan District. A significant increase of Cl-, Br-, Na+, K+, SO42-, Mg2+ and Ca2+ concentration on coarse particle mode was observed. It suggested that not just natural soil dusts and oceanic spray, but also anthropogenic pollutants could accompany Asian dusts. Source appor-tionment of atmospheric aerosols indicated that the concentration (percentage) of aerosol particles contributed from soil dusts increased significantly from 20.98 mg.m-3 (29.2%) to 60.37 mg.m-3 (47.7%), and then decreased to the regular level of 22.44 mg.m-3 (28.2%).

CHARACTERIZATIONS AND RELATIONSHIPS BETWEEN OUTDOOR AND INDOOR BIOAEROSOLS IN AN OFFICE BUILDING

Characterizations and relationships between indoor and outdoor bioaerosols were examined in an occupied office building, equipped with an air conditioning (HVAC) system, in Tempe, Arizona, USA. A two-stage microbial air sampler was used to collect bioaerosols both inside and outside the office at fixed locations in space and at regular time intervals from August to December, 2000. Simultaneous measurements of bioaerosol, temperature, relative humidity, light intensity and wind speed were performed to explore the effects of environmental factors on bioaerosol levels. Twenty species of airborne bacteria and four genera of airborne fungi were found in our samples. The particle sizes of most outdoor and indoor bioaerosols were larger than 8.0 mm. According to the measurements of sampling days, the concentrations of outdoor bioaerosols were highest in the morning, but declined in the afternoon and reached the lowest point in the evening. The concentration peak of indoor bioaerosol (especially at the lower level) occurred in the evening, suggesting that the concentration of indoor bioaerosols follows that of outdoors, but with a time delay due to the lag associated with indoor-outdoor air exchange. With regard to the effects of four environmental factors temperature, relative humidity, light intensity, and wind speed, the relative humidity had the most pronounced influence on the outdoor bioaerosol concentrations with the number of bacteria and fungi increasing sharply on a day of high relative humidity in the desert area.

THERMODYNAMIC ANALYSIS AND EXPERIMENTAL VERIFICATION FOR SYNTHESIZING SILICON NITRIDE NANOPARTICLES USING RF PLASMA CVD

Silicon nitride nanoparticles were synthesized by radio-frequency (RF) plasma chemical vapor deposi-tion (PCVD) using silicon tetrachloride and ammonia as precursors, and argon as carrier gas. By assuming chemical thermodynamic equilibrium in the system, a computer program based on chemical thermodynamics was used to cal-culate the compositions of the system at different initial concentrations and final temperatures. At first, five elements and thirty-four species were considered. The effects of temperatures, and concentrations of ammonia, hydrogen and nitrogen on the equilibrium compositions were analyzed. It was found that the optimal reaction temperature range should be 1200 to 1500 K to obtain the highest conversion and yield of Si3N4. The inlet position of ammonia should be lower than that of silicon tetrachloride, and both should be located at the tail of the plasma torch. The best mole ratio of ammonia to silicon tetrachloride was found to be about 6. Later, the influences of water (and oxygen) were considered, and 17 additional species were included in the computations. It was found that oxygen or water content in the raw materials should be as low as possible in order to have high nitride content in the produced Si3N4. Nitrogen or hydrogen might be used to replace some or even all the argon to improve the yield of silicon nitride and reduce the cost. The ratio of ammonia to silicon tetrachloride should be high enough to obtain high conversion, but not exces-sively high to reduce the oxygen content due to the existence of water in ammonia. The simulated results were veri-fied by experiments.

REVEALING MICROSTRUCTURE OF FINE PARTICLES BY TEM

This paper introduces a method of cutting nano-scaled thin films from fine particles by using the technique of metal encapsulation. The interior morphology and microstructure of fine particles are then examined by TEM or HREM.

PREPARATION AND CHARACTERIZATION OF SUPERPARAMAGNETIC FUNCTIONAL POLYMERIC MICROPARTICLES

Superparamagnetic poly(styrene-divinylbenzene-glycidyl methacrylate) (Pst-DVB-GMA) microparticles were prepared via a modified suspension polymerization process. A magnetic fluid was first prepared by a chemical co-precipitation method. Then magnetic microparticles were produced by mixing the monomers and the magnetic fluid with water in the presence of a stabilizer poly(vinyl pyrrolidone) (PVP) to form a suspension, and finally benzoyl peroxide was added to initiate the co-polymerization. The morphology and magnetic properties of the microparticles were examined by TEM and VSM. The spherically shaped microparticles, with a size range of 4 to 7 urn, showed distinct Superparamagnetic characteristics. XRD was used to investigate the structure of the magnetite particles dispersed in the polymer matrix. The microparticles with epoxy groups on their surface can be applied directly to the separation of biomolecules.

STUDY ON AEROSOL TRANSMISSION ROUTES OF HEMORRHAGIC FEVER WITH RENAL SYNDROME (HFRS)

The present paper reviews our studies on transmission routes and prophylactic measures of Hemorrhagic Fever with Renal Syndrome (HFRS), including aerosol inhalation, skin injury/mucosa, insect vectors, peroral infection and vertical transmission. The results show that HFRS is transmitted by Hantaan virus via multi-routes. One of them, the aerosol transmission, is perhaps the main route transmitting HFRS from mouse to human beings. The injury and mu-cosa is the main transmission route from mouse to mouse and also an important agent from mouse to human beings. The peroral infection may occur in very serious pollution of foods. The insect vectors may play an important role in the focus of HFRS and in the transmission of HFRS from mouse to human. The epidemiological significance of vertical transmission is yet uncertain. According to the results, four proposals should be emphasized including killing insects and mice, long lasting and combined prophylactics, intensive studies on prophylactic measures on viral aerosols and the blocking of transmission of HFRS from mouse to human via aerosols.

MODELING TWO-PHASE FLOW IN PULSED FLUIDIZED BED

Mathematical models for pulsed fluidization are systematically discussed. Several undetermined constitutive relationships are included in the General Two-Fluid Model (GTFM), the adjustable parameters of which are always chosen at will to some extent. Although there are no adjustable parameters in the Basic Two-Fluid Model (BTFM), its eigenvalues are complex numbers and it is ill-posed for initial-value problems. The Local Equilibrium Model (LEM), a further simplification of BTFM, is discussed at length. Although the model is very simple, it is highly capable of simulating complex processes in pulsed fluidization over a broad range of operating parameters, and its numerical results well fit experimental results in both the variation of bed height and the distribution of particle concentration as fluidizing velocity varies.

DISPERSION OF NANODIAMOND AND ULTRA-FINE POLISHING OF QUARTZ WAFER

Mechanochemical Modification (MCM) of nanodiamond surface with DN-10 was studied in relation to the performance of nanodiamond in polishing quartz wafers. Results show that the modified nanodiamond is more stable in the pH range 8~11. A super smooth surface with an average roughness of 0.214 nm was achieved using a nanodia-mond-based slurry regulated by N-(2-hydroxyethyl)ethylenediamine. It is suggested that the principal ultra-fine polishing mechanism of quartz wafer involves atom-level removal under the synergism of chemical and mechanical actions.

PROGRESS IN THREE-DIMENSIONALLY ORDERED SELF-ASSEMBLY OF COLLOIDAL SiO2 PARTICLES

Three-dimensionally ordered self-assembly of monodispersed colloidal SiO2 particles involving a structure with periodic alternation of refractive indices represents an advanced field of particuology, colloidal chemistry, materials science, optical physics and information science. Study on such self-assembly not only lays the foundation for the development of advanced functional materials, but also is significant in understanding the principles of nano- and micro-scale processes. Recent progress in three-dimensionally ordered self-assembly of colloidal SiO2 particles is reviewed, inclusive of the authors investigations.

SYNTHESIS OF NiO NANOPARTICLES IN ETHYLENE GLYCOL

NiO nanoparticles with well-dispersed property were prepared via a wet chemical method in ethylene glycol (EG) without soluble polymer as a protective agent. The mechanism of chemical process was proposed based on color change during the experiment. The dispersion function of EG was discussed.

CHOOSING STRUCTURE-DEPENDENT DRAG COEFFICIENT IN MODELING GAS-SOLID TWO-PHASE FLOW

IntroductionGas-solid two-phase flow is often encountered in chemical reactors for the process industry. For industrial users, design, scale-up, control and optimization for these reactors require a good understanding of the hydrodynamics of gas-solid two-phase flow. For researchers, exploration and prediction of the complex phenomena call for a good comprehension of the heterogeneous structure and of the dominant mechanisms of gas-solid and solid-solid interactions.

POROSITY CALCULATION OF MIXTURES OF FIBROUS PARTICLES

The initial forming of fiber blend to high green density, i.e. the packing of fibrous particles, is important to the reinforcement of composite materials. It is very useful to develop a general predictive method for the optimum selection of particle mixtures for the property control of ceramie or composite products. This paper presents such a mathematical modei developed on the basis of the similarity analysis between the spherical and non-spherical particle packings and assesses its applicability to the packing of fibrous particles with discrete and/or continuous length distributions. The re-sults indicate that the modei can predict this packing system well and hence provide an effective way to solve various packing problems in the composite materials processing.

A NUMERICAL STUDY OF THE STRESS DISTRIBUTIONIN HOPPER FLOW

The stress distributions of granular flow in a cylindrical hopper with flat bottom are investigated by means of a combined approach of discrete element method (DEM) and averaging method. The filling and discharge of the hopper flow are first simulated at a particle level by means of a modified DEM. The results are then used to determine the velocity and stress profiles of the hopper flow by means of an averaging method. The analysis is focused on a central section plane of the hopper due to the relatively perfect axial symmetry. The velocity profiles are illustrated to be consistent with those obtained by the previous experiments, confirming the validity of the proposed approach. The distributions of four components of the planar stress tensor at different heights are quantified. It is shown that the vertical normal stress increases with increasing the height near the central axis, the horizontal normal stress varies more slowly at a higher level and is almost constant when the height is equal to or greater than about 12 particle diameter, and the magnitudes of two shear stresses are equal at the central zone of the hopper but not so at the points near the walls. The dependence of stress distributions on the wall mechanical properties such as sliding resistance and rolling resistance is also discussed.

EFFECT OF POLYETHYLENEIMINE ON THE PROPERTIES OF CONCENTRATED SUSPENSIONS OF TITANIUM DIOXIDE MICROBEADS

The effect of polyethyleneimine (PEI) concentration on the properties of titanium dioxide (TiO2) suspen-sions is studied with or without the addition of an electrolyte (barium acetate). Measurements of the apparent viscosity and the stability of TiO2 suspensions showed that PEI is an effective dispersant for TiO2 particles in suspension in the absence of an electrolyte, not only reducing the viscosity of the suspension but also increasing its stability. In the pres-ence of an electrolyte, however, small quantities of polyethyleneimine could neither disperse the TiO2 particles nor de-crease the viscosity of the TiO2 suspensions; only PEI concentrations beyond saturation adsorption could perceptively improve the stability of TiO2 suspensions.

EFFECT OF VERTICAL BAFFLES ON PARTICLE MIXING AND DRYING IN FLUIDIZED BEDS OF GROUP D PARTICLES

This study reports the effect of vertical baffles on the group D powder mixing and drying characteristics in a batch fluidized bed dryer. Results obtained in this study showed that operating the fluidized bed dryer with vertical baffles gave better particle mixing. This is due to the fact that the vertical baffles acted to limit the growth of small bubbles into large bubbles and the small bubbles caused more vigorous mixing in the bed of particles before finally erupting at the bed surface. Thus, insertion of vertical baffles is a useful way to process group D particles in a fluidized bed, especially when the fluidized bed is large.