Displacement of Ammonium from Aerosol Particles by Uptake of Triethylamine

The displacement of ammonium by triethylammonium (TEAH) in aerosol particles of about 15–35 μm in diameter was investigated using an electrodynamic balance (EDB) coupled with in situ Raman spectroscopy. The phase state of particles played a crucial role in the extent of triethylamine (TEA) uptake. At 50 or 75% relative humidity (RH), the heterogenous uptake of about 40-ppm TEA by aqueous ammonium salts of sulfate [(NH₄)₂SO₄], bisulfate (NH₄HSO₄), nitrate (NH₄NO₃), chloride (NH₄Cl), and oxalate [(NH₄)₂C₂O₄] led to increases in particle mass of over 90%. A complete displacement of ammonium by TEAH was confirmed by direct EDB mass measurements and the Raman spectra obtained. TEAH sulfate was formed during the exposure of aqueous droplets of (NH₄)₂SO₄ and NH₄HSO₄ to TEA vapor at 50% RH; but a fraction of it decomposed to TEAH bisulfate when the TEA supply was removed. Crystalline solid particles of (NH₄)₂SO₄ and (NH₄)₂C₂O₄ experienced small mass increases of <5%, both of which were attributed to the hindered mass transfer of TEA in crystalline solids. However, TEA reacted with the amorphous solid NH₄NO₃ particle at <3% RH as effectively as if it was in the aqueous NH₄NO₃ droplet (50% RH) and formed TEAH nitrate. On the other hand, the amorphous NH₄HSO₄ solid particle reacted with TEA at <3% RH to form crystalline (NH₄)₂SO₄ and liquid TEAH bisulfate and sulfate. The formation of rather inert crystalline (NH₄)₂SO₄ suppressed the ammonium exchange.

Copyright 2012 American Association for Aerosol Research     

高压二氧化碳电镀钴薄膜颗粒形貌

本文研究了高压二氧化碳电镀钴薄膜颗粒形貌的影响。实验高压二氧化碳分别为液态((15 MPa,25℃),亚临界态((15 MPa,30℃),超临界态((15 MPa,40℃)。高压二氧化碳电镀在高压釜中进行电镀,电镀液使用20%体积分数的高压二氧化碳和80%体积分数的钴电镀液。本文同时研究了温度和电流密度的影响。钴薄膜颗粒形貌随着温度的下降和电流密度的上升由片状转变为棱锥状以及半球状结构。     

Hydrated Binders and Preserving Agents for Lime Refractories

Basically new binding and preserving agents for refractories containing free CaO are described. The efficiency of these hydrated agents comes from the specific properties of supersaturated phosphate solutions used for their preparation.     

水辅助超临界二氧化碳制备TPU发泡颗粒

利用水和超临界二氧化碳作为共发泡剂,采用快速泄压法制备热塑性聚氨酯弹性体(TPU)发泡颗粒,分别考察了加水量、饱和温度和饱和时间对TPU发泡颗粒性能的影响。结果表明,当饱和温度为180℃、饱和时间为30 min时,随着加水量的增加,TPU发泡颗粒的边缘厚度明显降低,当加水量为4 mL时,发泡颗粒的边缘厚度比不添加水时下降了63.0%,同时发泡倍率提高了89.8%。当加水量为2 mL、饱和时间为30 min时,饱和温度的升高使得发泡倍率随之升高,饱和温度为190℃时的发泡倍率比饱和温度为150℃时提高了94.8%。当加水量为2 mL、饱和温度为180℃时,饱和时间超过1 h后,随着饱和时间的延长,发泡倍率和泡孔密度减小,边缘厚度和泡孔平均直径增大,并出现通孔结构。     

Indentation Creep of Hydrated Soda–Lime Silicate Glass Determined by Nanoindentation

Time-dependent deformation behavior was investigated for soda–lime silicate glass with various water contents, using a nanoindentation technique. The complete indentation curve, loading and unloading part, is analyzed. It is shown that this deformation behavior may be represented in terms of a simple mechanical model analogous to a viscoelastic system. Values for Young's modulus were derived, a retardation spectrum was deduced, and apparent viscosity values were calculated. Structural rearrangements of the glass appear to be responsible for the observed changes of the viscoelastic properties. Water in the glass reduces Young's modulus and yield stress and thus promotes viscous flow.     

Scattering and Absorption by Elongated Aerosol Particles

Recently we developed a new technique, the iterative extended boundary condition method, which is suitable for calculating the scattering and absorption by elongated particles in a broad frequency range, including at resonance. This paper briefly describes this technique, illustrates its capabilities, and presents the results of its most recent extensions. This includes the implementation of a sectioning procedure and the use of a new segmentation method for calculating scattering by very long oriented chains of aerosols. Results of absorption cross sections in two different frequency ranges, visible and infrared, and for two different polarizations, parallel and end-fire polarizations, will be presented. The range of validity of some reported relationships between scattering from a single particle and from coagulated particles are discussed. It is shown that in the end-fire polarization case the sum of the absorption by separate n particles (P _sum) is more than the absorption by a chain of n coagulated particles (P _end-fire), while in the parallel polarization case, the ratio between P _parallel/P _end-fire may be as high as a factor of 4. This observation emphasizes the importance of taking the polarization into account in calculating light scattering by elongated chains of aerosols.     

以水合二氧化锰混凝去除原水中的污染物

以高锰酸钾还原法制备的水合MnO2对模拟原水进行了混凝实验,探讨了水合MnO2作为新型净水剂在给水处理中应用的可行性;并对水合MnO2粒子的结构及界面性质进行了表征,探讨了其除污染的可能机制。结果表明：该水合二氧化锰具有丰富的表面羟基、晶型为δ-MnO2、比表面积为151．422m^2／g。在较低投量时（2～3mg／L）即表现出对原水的优良的混凝效能,可使滤后水浊度降至1NTU以下。     

Controlled Synthesis of Nanosized Particles by Aerosol Processes

Solid particles in the 1 nm < d_p < 100 nm size range form in gases as a result of gas phase condensation, particle collision processes, and solid-state processes. The relative rates of sintering and collision determine the size and morphology of the spheroidal primary particles. Rapid sintering is equivalent to the classical theory of coagulation with instantaneous coalescence. When the sintering rate is slow compared with the collision rate, fine primary particles form and aggregate into irregularly shaped agglomerates. The growth of primary particles in an aerosol generator that is cooling at a constant rate was studied theoretically. The most important process parameter determining particle diameter is the maximum gas temperature, because the rate of sintering is a sensitive function of temperature. Aerosol volume loading and cooling rate are important when the rate of particle growth is limited by collision processes. Experiments on the formation of alumina particles were made to study these effects. Predictions of primary particle size did not agree well with experimental measurements, which is attributed to an inadequate understanding of solid-state diffusion processes in nanosized particles. Other experiments showed that low concentrations of sodium and potassium additives reduce the primary particle size of silica.     

Size Measurements of Latex Particles by Laser Aerosol Spectrometer

Size measurements of PSL (polystyrene latex) particles in a size range from 0.109 to 0.330 μm were made by laser aerosol spectrometer (PMS, LAS-X). The results were compared with those by electron microscopy. For example, the geometric standard deviation, σ_g, of nominally 0.176-μm PSL particles was measured as 1.05, assuming that their sizes distribute log-normally. The value of 1.05 was very close to 1.02 measured by electron microscopy. It was found that the spectrometer had very high size resolution, although the size resolution of the light scattering type spectrometer has been said to be poor. For some samples of PSL particles, however, there were large differences between particle sizes measured by LAS-X and those by electron microscopy. It was also found that LAS-X had a problem in calibration of size response curve.     

Field Charging of Fine Aerosol Particles by Unipolar Ions

Unipolar charging of fine aerosol particles by gaseous ions has been investigated in the presence of an electric field with a strength of E ≤ 4 kV/cm. It has been found that, when the ion conductivity of the medium in the charging zone is kept constant, variation of the ion mobility spectrum caused by change in the ion polarity or by addition of vapor of various liquids does not affect the particle charging. The measured mean particle charge for the particle radii, ranging from 0.05 to 1.5 μm, is shown to be in agreement with the theoretical data calculated as a sum of charges acquired by the particles owing to the diffusion and field charging mechanisms.     

Effect of Carbon Dioxide on the Reactivity of the Oxidation of Boron Particles

Carbon dioxide produced in the primary combustion of propellants apparently affects the combustion of boron. In this study, the thermodynamic and kinetic properties of the combustion of boron particles in a CO₂ environment (solely or as a mixture with other gases) were investigated using thermogravimetric analyses. For the combustion of boron in an atmosphere containing 10 % oxygen, in addition to a large initial weight gain, a second increase in weight was observed when the temperature reached 1150 °C. However, when the combustion was carried out in pure CO₂ atmosphere, the sample lost weight at temperatures above 1300 °C. The above results indicated that the layer of boron oxide covering the boron particles had a significant effect on the combustion process. With a limiting concentration of O₂ (10 %), the initial temperature and effective activation energy slightly decreased as the content of CO₂ increased from 0 to 30 %. However, a further increase in the CO₂ content (50 %) increased the effective activation energy, indicating the inhibitory effects of CO₂ at higher concentrations. Furthermore, the weight and the rate of weight gain gradually increased with increasing CO₂ content. This behavior was attributed to the improvement in the diffusion of the oxidant. This study conclusively revealed that the inclusion of an optimal level of CO₂ in a reaction environment containing O₂ facilitated the combustion of boron particles.     

Bipolar Charging of Ultrafine Aerosol Particles

The stationary bipolar charging characteristics of aerosol particles in the size range between 4.5 and 40 nm have been studied using a new technique whereby the particles neutralized by a ²⁴¹Am radioactive source are enlarged and directly observed in an electric field. The number ratio of charged particles to total particles obtained in this study was found to deviate from the charge distribution obtained from Boltzmann's law and to agree well with that calculated with the bipolar charging theory of Fuchs using his values for the ion properties. The ratio of positively charged to negatively charged particles was found to be approximately 0.35:0.65.

     

Transport Phenomena with Single Aerosol Particles

This is a review of theory and experiments related to single aerosol particle transport processes. The theories of mass, heat, momentum, and charge transfer are outlined, with emphasis on mass transport in the continuum and noncontinuum regimes. Included in the discussion of mass transfer are single and multicomponent droplet evaporation, a comparison of the results of solutions of the Boltzman equations for Knudsen aerosol evaporation and growth and experimental methods for the study of single droplet evaporation or growth. Of particular concern here are the experimental apparati and techniques developed for single particle measurements. These range from the Millikan oil drop experiment through the electrostatic balance (the Millikan condenser with automatic stabilization of the particle) to the electrodynamic balance. The principles and applications of these instruments are reviewed.     

Electrodynamic Focusing of Charged Aerosol Particles

An electrodynamic screen for focusing charged particles carried by an airflow stream has been constructed and tested. The screen has the shape of a cone frustum with half-angle of 8° and is 17 cm long. Entrance and exit diameters are 7.0 and 2.5 cm, respectively. Electrodes forming the screen are three 0.71-mm diameter stainless-steel wires configured as a triple-start helix with 2.0-mm pitch. A three-phase power supply drives each wire with a line-to-ground voltage of 2300 V at 350 Hz with a phase difference of 120° between adjacent wires. Test particles of 5.2-μm aerodynamic diameter with electric charge of 1850–6080 elementary units per particle in an aerosol having a mean flow velocity of 4.3×10^?2 m/s parallel to the vertically oriented cone axis are confined and focused with essentially no particle loss. Minimum distance of approach of the test particles to the screen, as found from computer simulation of particle trajectories, solution of the particle equations of motion by linear approximation, and experimental observation, are in good agreement.     

Electrostatic and Inertial Collection of Aerosol Particles by Water Droplets

Inertial impaction and electrostatic attraction are generally the two most important mechanisms for the collection of charged micron-sized particles by charged droplets. An experiment was carried out to determine the collision efficiencies of charged 142-μm-radius water droplets for charged micron-sized particles under different values of the electrostatic force. Experimental results agree well with a trajectory model that used a numerically derived flow field for the 142-μm-radius droplets.     

Detection and Analysis of Aerosol Particles by Laser-Induced Breakdown Spectroscopy

Laser-induced breakdown spectroscopy (LIBS) was evaluated as a means for quantitative analysis of the size, mass, and composition of individual micron-to submicron-sized aerosol particles over a range of well-characterized experimental conditions. Conditional data analysis was used to identify LIBS spectra that correspond to discrete aerosol particles under low aerosol particle loadings. The size distributions of monodisperse particle source flows were measured using the LIBS technique for calcium- and magnesium-based aerosols. The resulting size distributions were in good agreement with independently measured size distribution data. A lower size detection limit of 175 nm was determined for the calcium- and magnesium-based particles, which corresponds to a detectable mass of approximately 3 femtograms. In addition, the accuracy of the LIBS technique for the interference-free analysis of different particle types was verified using a binary aerosol system of calcium-based and chromium particles.     

Aerosol Generation of Nonspherical Particles by Desublimation of Copper Phthalocyanine

A novel generator for a defined test aerosol consisting of nonspherical particles was developed based on the desublimation of copper phthalocyanine during adiabatic cooling. Employing a brush disperser, copper phthalocyanine powder is dosed and dispersed in a nitrogen flow and sublimated in a tube furnace. Downstream the furnace new particles are formed due to the adiabatic expansion and the desublimation of the material in a laval nozzle. The generated particles were characterized employing a scanning mobility particle sizer and an aerosol particle mass analyzer to determine the size distribution and the dynamic shape factor. For the operating parameters of the generator examined here, particles with a mobility diameter between 30 and 600 nm were generated. The measured values for the dynamic shape factor of the particles were confirmed by scanning electron microscopy analysis.     

The Conversion of Carbon Monoxide and Carbon Dioxide by Nitrogenases

Nitrogenases are the only known family of enzymes that catalyze the reduction of molecular nitrogen (N₂) to ammonia (NH₃). The N₂ reduction drives biological nitrogen fixation and the global nitrogen cycle. Besides the conversion of N₂, nitrogenases catalyze a whole range of other reductions, including the reduction of the small gaseous substrates carbon monoxide (CO) and carbon dioxide (CO₂) to hydrocarbons. However, it remains an open question whether these ‘side reactivities’ play a role under environmental conditions. Nonetheless, these reactivities and particularly the formation of hydrocarbons have spurred the interest in nitrogenases for biotechnological applications. There are three different isozymes of nitrogenase: the molybdenum and the alternative vanadium and iron-only nitrogenase. The isozymes differ in their metal content, structure, and substrate-dependent activity, despite their homology. This minireview focuses on the conversion of CO and CO₂ to methane and higher hydrocarbons and aims to specify the differences in activity between the three nitrogenase isozymes.     

Synthesis of Silicon Carbide–Silicon Nitride Composite Ultrafine Particles Using a Carbon Dioxide Laser

The synthesis and the structure of silicon carbide-silicon nitride (SiC─Si₃N₄) composite ultrafine particles have been studied. SiC─Si₃N₄ composite ultrafine particles were prepared by irradiating a SiH₄, C₂H₄, and NH₃ gas mixture with a CO₂ laser at atmospheric pressure. The composition of composite powders changed with the reactant gas flow rate. The carbon and nitrogen content of the powder could be controlled in a wide range from 0 to 30 wt%. The composite powder, which contained 25.3 wt%. carbon and 5.8 wt% nitrogen, had a (β-SiC structure. As the nitrogen con- tent increased, SiC decreased and amorphous phase, Si₃N₄, Si appeared. The results of XPS and lattice constant measurements suggested that Si, C, and N atoms were intimately mixed in the composite particles.     

Detection of Spatial Correlations among Aerosol Particles

Most approaches for evaluating rates of fundamental processes in aerosol science depend upon the implicit assumption that aerosol particles are independently and identically distributed in space. The validity of this assumption has not been examined in several decades, despite the fact that the presence of correlations can be shown to alter theoretical expressions significantly for such phenomena as attenuation of electromagnetic radiation and coagulation rate. Here, we provide evidence that the classification of the positions of aerosol particles as a Poisson process--even under stationary conditions--is often in error. In particular, small-scale aerosol clustering is experimentally demonstrated. Some consequences of these findings are discussed.