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71.
This work investigates the effects of reduced accessible surface area of aggregate particles and of surface energy on relevant particle formation and growth mechanisms during titania formation from the vapour phase at industrial process conditions. Growth due to surface reaction and due to condensation is related to the fraction of the surface area that is exposed to the collision with single molecules. Surface shielding is found to hamper surface reaction and condensation once fractal aggregates start to form. It leads to significantly retarded precursor consumption and produces aggregate particles, which consist of more, but smaller primary particles. Surface energy data are varied within a range as proposed by available literature data. Moderate and high surface energy values result in a thermodynamic barrier to the formation of new particles and are shown to reduce the formation of seed particles by several orders of magnitude. This leads to the formation of aggregate particles which consist of a rather small number of primary particles and mainly grow by surface reaction. The primary contribution of condensation to growth of individual primary particles is shown to be very little. However, condensation should not be neglected as it has a strong impact on particle formation rates and hence on product characteristics such as the number of primary particles and primary particle size. 相似文献
72.
Dependence of urban air pollutants on meteorology 总被引:2,自引:0,他引:2
Elminir HK 《The Science of the total environment》2005,350(1-3):225-237
Dependence of air pollutants on meteorology is presented with the aim of understanding the governing processes pollutants phase interaction. Intensive measurements of particulate matter (PM10) and gaseous materials (e.g., CO, NO2, SO2, and O3) are carried out regularly in 2002 at 14 measurement sites distributed over the whole territory of Great Cairo by the Egyptian Environmental Affairs Agency to assess the characteristics of air pollutants. The discussions in this work are based upon measurements performed at Abbassiya site as a case study. The nature of the contributing sources has been investigated and some attempts have been made to indicate the role played by neighboring regions in determining the air quality at the site mentioned. The results hint that, wind direction was found to have an influence not only on pollutant concentrations but also on the correlation between pollutants. As expected, the pollutants associated with traffic were at highest ambient concentration levels when wind speed was low. At higher wind speeds, dust and sand from the surrounding desert was entrained by the wind, thus contributing to ambient particulate matter levels. We also found that, the highest average concentration for NO2 and O3 occurred at humidity相似文献
73.
Schneider T Sundell J Bischof W Bohgard M Cherrie JW Clausen PA Dreborg S Kildesø J Kaergaard SK Løvik M Pasanen P Skyberg K 《Indoor air》2003,13(1):38-48
The relevance of particle mass, surface area or number concentration as risk indicators for health effects in non-industrial buildings has been assessed by a European interdisciplinary group of researchers (called EUROPART) by reviewing papers identified in Medline, Toxline, and OSH. Studies dealing with dermal effects or cancer or specifically addressing environmental tobacco smoke, house dust-mite, cockroach or animal allergens, microorganisms and pesticides were excluded. A total of 70 papers were reviewed, and eight were identified for the final review: Five experimental studies involving mainly healthy subjects, two cross-sectional office studies and one longitudinal study among elderly on cardiovascular effects. From most studies, no definite conclusions could be drawn. Overall, the group concluded that there is inadequate scientific evidence that airborne, indoor particulate mass or number concentrations can be used as generally applicable risk indicators of health effects in non-industrial buildings and consequently that there is inadequate scientific evidence for establishing limit values or guidelines for particulate mass or number concentrations. 相似文献
74.
Michael Fox 《Journal of Failure Analysis and Prevention》2008,8(4):353-361
When self-pressurized containers, or aerosols, are accidentally dropped they are susceptible to puncture. The likelihood of
puncture depends on the distance of the fall, the nature of the object that the aerosol might strike, the orientation of the
impact, and the aerosol’s materials of construction, including microstructure. Due to the flammable nature of the propellants
common to aerosols as well as other flammable contents, the accidental puncture of an aerosol has on occasion resulted in
significant personal injury and property damage. While the Department of Transportation regulates several aspects of aerosol
containers, there are no government regulations concerning puncture resistance. Likewise, there are no standard tests for
the puncture resistance of aerosol containers. This article presents two different test methods that can be used to quantify
the puncture resistance of aerosol containers. One mode of puncture is not a pure puncture, but rather an impact-induced circumferential
puncture or crack. This is due to the anisotropic microstructure of the body material of most 3-piece steel aerosol containers.
Experimental testing has shown that the most common type of aerosol container is highly vulnerable to impact-induced impact
circumferential puncture. Free falls from a little as 20.32 cm (8 in.) onto wood pyramids are able to induce this type of
puncture. This is a hidden and unexpected vulnerability inherent in most 3-piece steel aerosol containers. Experimental tests
show that this susceptibility to impact-induced circumferential puncture as well as pure puncture can be greatly reduced,
if not eliminated, by using container bodies with more isotropic microstructures. 相似文献
75.
气溶胶细粒子与能见度的相关性研究 总被引:1,自引:0,他引:1
为了分析气溶胶粒子特别是细粒子(PM2.5)对能见度的影响,本文从理论上建立了气溶胶细粒子与能见度的关系,分析了谱分布、PM2.5/PM10和细粒子消光所占总消光比重的关系。利用2004年8月在北京的测量数据与理论计算对比表明:建立的气溶胶细粒子与能见度的关系是合理的。这对治理污染提高城市能见度是很有指导意义的。 相似文献
76.
M. Alonso F.J. Alguacil J.P. Santos N. Jidenko J.P. Borra 《Journal of aerosol science》2007,38(12):1230-1239
This paper presents the results of an experimental investigation on the deposition of multiply charged particles on wire screens by the combined mechanisms of diffusion and image force. Experiments were performed with particles having diameters between 25 and 65 nm (transition regime), carrying 0, +1, +2 or +3 elementary charges, and using three different flow rates, two types of wire screen, and two types of test aerosol. The single fiber efficiencies for the mechanisms of image force, ηIM, and diffusion, ηD, are of the same order of magnitude and, furthermore, they are both much smaller than one. Under these conditions, the total capture efficiency can be approximated as the sum of the efficiencies by diffusion and image force deposition. Theoretically, ηIM is proportional to the square root of a dimensionless number, KIM, which includes all the relevant parameters cited above (i.e., particle size and charge, aerosol flow rate and screen geometry). The available correlations for ηIM, obtained from experiments with particles carrying a large number of elementary charges (KIM>10-5), predict that image force should not have any effect in the case of the small particles with very few number of charges that we have tested in our experiments (in our experimentation, KIM ranged between 10-7 and 10-5). Our results, the only ones available to date for this particle size range, show that there is indeed a clear, measurable effect. Although our experimental results are best fitted by the correlation , it is shown that the expression , which is in agreement with the theoretical 1/2 exponent for KIM, also reproduces reasonably well the measured values. 相似文献
77.
为考察电子烟气溶胶中玻璃纤维的结构状态和释放趋势,建立了电子烟气溶胶中玻璃纤维的定性定量分析方法,通过电子显微镜对气溶胶中玻璃纤维进行定性观察,采用电感耦合等离子体质谱仪(Inductively Coupled Plasma Mass Spectrometry,ICP-MS,ICP-MS)定量测定气溶胶中玻璃纤维(以SiO2计)的释放量。按照CORESTA推荐的电子烟抽吸模式抽吸电子烟,通过每轮抽吸30口(连续抽吸4轮,共120口),测定每轮样品的SiO2释放量,比较分析4轮样品之间的玻璃纤维释放量差异。结果表明:①定性方法操作简单,采用该方法易于鉴别玻璃纤维,且结果准确度高;定量方法灵敏度高,准确性和重复性较好。②15种电子烟气溶胶中均有玻璃纤维,其直径分布在7.6~28.3μm之间,长度差别较大,从几何尺寸和物理形态可以推测其为人造玻璃纤维。③电子烟气溶胶中玻璃纤维的释放量为47~432μg/200口。④玻璃纤维的释放量与抽吸口数无关,玻璃纤维的释放呈现无规律、随机的特点。 相似文献
78.
Aerosol deposition of silicon-substituted hydroxyapatite coatings for biomedical applications 总被引:1,自引:0,他引:1
Byung-Dong Hahn Dong-Soo Park Jong-Jin Choi Woon-Ha Yoon Du-Sik Shin 《Thin solid films》2010,518(8):2194-8090
Silicon-substituted hydroxyapatite (Si-HA) coatings on commercially pure titanium (Ti) were prepared by aerosol deposition using Si-HA powders. Si-HA powders with the chemical formula Ca10(PO4)6 − x(SiO4)x(OH)2 − x, having silicon contents up to x = 0.5 (1.4 wt.%), were synthesized by solid-state reaction of Ca2P2O7, CaCO3, and SiO2. The Si-HA powders were characterized by X-ray diffraction (XRD), X-ray fluorescence spectrometry, and Fourier transform infrared spectroscopy. The corresponding coatings were also analyzed by XRD, scanning electron microscopy, and electron probe microanalyzer. The results revealed that a single-phase Si-HA was obtained without any secondary phases such as α- or β-tricalcium phosphate for both the powders and the coatings. The Si-HA coating was about 5 µm thick, had a dense microstructure with no cracks or pores, and showed a high adhesion strength ranging from 28.4 to 32.1 MPa. In addition, the proliferation and alkaline phosphatase activity of MC3T3-E1 preosteoblast cells grown on the Si-HA coatings were significantly higher than those on the bare Ti and pure HA coating. These results revealed the stimulatory effects induced by silicon substitution on the cellular response to the HA coating. 相似文献
79.
Yong Ho Kim 《Powder Technology》2008,182(1):25-32
Ipratropium bromide (IB) was micronized by means of a CO2-based aerosol solvent extraction system (ASES) in order to improve the particle shape and size characteristics for use in inhalation therapy. The particle size parameter most relevant to pulmonary delivery is the aerodynamic diameter. In this study, ASES experiments were conducted using various liquid solvents for IB such as dimethylformamide (DMF), ethanol (EtOH), and mixtures of ethanol and acetone (EtOH/Ac). Several operating parameters were varied including temperature, pressure, IB concentration in the liquid solution, and the solution injection rate. The particles were analyzed by scanning electron microscopy (SEM). The true density of the particles was measured using a pycnometer and the mass median aerodynamic diameter (MMAD) determined. The results indicate that the size and morphology of the microparticles are most sensitive to solvent choice. Optimum results were obtained when IB particles were precipitated from DMF. The particles were more regular in shape, slightly elliptical, not agglomerated, and within the aerodynamic diameter range of 0.6-3.0 μm. Fourier transform infrared (FTIR) studies indicate no structural deformation as result of the ASES process. The regional depositions of inhaled IB particles were estimated using a multiple-path model of particle deposition (MPPD). The results indicate that IB particles with MMAD in the range of 2-3 μm deposited mainly in the respiratory airways in the lung. 相似文献
80.
Yuanjing Zheng Anker Degn Jensen Jan Erik Johnsson Joakim Reimer Thgersen 《Applied catalysis. B, Environmental》2008,83(3-4):186-194
In this work, deactivation of a commercial type V2O5-WO3-TiO2 catalyst by aerosols of potassium compounds was investigated in two ways: (1) by exposing the catalyst in a lab-scale reactor to a layer of KCl particles or fly ash from biomass combustion; (2) by exposing full-length monolith catalysts to pure KCl or K2SO4 aerosols in a bench-scale reactor. Exposed samples were characterized by activity measurements, SEM-EDX, BET/Hg-porosimetry, and NH3 chemisorption. The work was carried out to support the interpretation of observations of a previous study in which catalysts were exposed on a full-scale biomass fired power plant and to reveal the mechanisms of catalyst deactivation.Slight deactivation (about 10%) was observed for catalyst plates exposed to a layer of KCl particles at 350 °C for 2397 h. No deactivation was found for catalyst plates exposed for 2970 h to fly ash (consisting mainly of KCl and K2SO4) collected from an SCR pilot plant installed on a straw-fired power plant. A fast deactivation was observed for catalysts exposed to pure KCl or K2SO4 aerosols at 350 °C in the bench-scale reactor. The deactivation rates for KCl aerosol and K2SO4 aerosol exposed catalysts were about 1% per day and 0.4% per day, respectively.SEM analysis of potassium-containing aerosol exposed catalysts revealed that the potassium salt partly deposited on the catalyst outer wall which may decrease the diffusion rate of NO and NH3 into the catalyst. However, potassium also penetrated into the catalyst wall and the average K/V ratios (0.5–0.75) in the catalyst structure are high enough to explain the level of deactivation observed. The catalyst capacity for NH3 chemisorption decreased as a function of exposure time, which reveals that Brønsted acid sites had reacted with potassium compounds and thereby rendered inactive in the catalytic cycle. The conclusion is that chemical poisoning of active sites is the dominating deactivation mechanism, but physical blocking of the surface area may also contribute to the loss of activity in a practical application. The results support the observation and mechanisms of deactivation of SCR catalysts in biomass fired systems proposed in a previous study [Y. Zheng, A.D. Jensen, J.E. Johnsson, Appl. Catal. B 60 (2005) 253]. 相似文献