Ultrafine Particle Deposition in a Human Tracheobronchial Cast

The deposition of 0.20, 0.15, and 0.04 μm diameter particles was measured in a human central airway cast using a variable larynx with cyclic inspiratory flow. Data were compared with theoretical predictions for deposition from laminar flow for the first seven airway generations. With the exception of tracheal deposition, which on average exceeded predictions by a factor of 9, the measured deposition was about twice that predicted. The enhanced deposition is attributable to secondary swirling flows. Less enhancement is observed at higher inspiratory flow rates as turbulence increases. The surface density of particles deposited at bifurcations was approximately 20% greater than along the airway lengths. This increased deposition at bifurcations should be considered when calculating tissue dose for particles which act before the initial deposit is removed by clearance processes.     

Particle Deposition in a Cast of Human Tracheobronchial Airways

Abstract

Regional particle deposition efficiency and deposition patterns were studied experimentally in a human airway replica made from an adult cadaver. The replica includes the oral cavity, pharynx, larynx, trachea, and four generations of bronchi. This study reports deposition results in the tracheobronchial (TB) region. Nine different sizes of monodispersed, polystyrene latex fluorescent particles in the size range of 0.93–30 μm were delivered into the lung cast with the flow rates of 15, 30, and 60 l min^{? 1}. Deposition in the TB region appeared to increase with the increasing flow rate and particle size. Comparison of deposition data obtained from physical casts showed agreement with results obtained from realistic airway replicas that included the larynx. Deposition data obtained from idealized airway models or replicas showed lower deposition efficiency. We also compared experimental data with theoretical models based on a simplified bend and bifurcation model. A deposition equation derived from these models was used in a lung dosimetry model for inhaled particles, and we demonstrated that there was general agreement with theoretical models. However, the agreement was not consistent over the large range of Stokes number. The deposition efficiency was found as a function of the Stokes number, bifurcation angle, and the diameters of parent and daughter tubes. An empirical model was developed for the particle deposition efficiency in the TB region based on the experimental data. This model, combined with the oral deposition model developed previously, can be used to predict the particle deposition for inertial effects with improved accuracy.     

Intercomparison of Approximation Algorithms for the Determination of the Size Distribution of the Unattached Fraction of Radon Progeny

Starting in 1996, nonlinear approximation algorithms used for the determination of size distributions of ''unattached'' radon progeny from measurements made with diffusional size classification instruments were compared. Seven participants (one American and six European) took part using various techniques (Simplex, Expectation Maximization, Extreme Value Estimation, Twomey, and Random Walk) which are widely used for this type of work. Simulated input data was supplied to the participants. Their output data indicated that the quality of the results varied according to the algorithm used. This was particularly the case when retrieving parameters from bimodal distributions where large inaccuracies were shown. Variations were found between participants using basically identical algorithms. The influence of measurement uncertainties was investigated and indicated a serious reduction of retrieval accuracy, especially for algorithms with better than average performance for precise data. This work suggests that when high precision results are required, a random walk algorithm should be used and attention should be paid to reducing errors in the input penetration data.     

Particle Deposition in a Cast of Human Oral Airways

Oral and nasal airways are entryways to the respiratory tract. Most people breathe through the nasal airway during rest or light exercise, then switch to oral/nasal breathing during heavy exercise or work. Resistance through the oral airways is much lower than through the nasal airways, so fewer aerosol particles are deposited in the oral airways. Aerosol drugs are usually delivered by inhalation to the lung via the oral route for that reason. Oral deposition data from humans are limited, and those available show great intersubject variability. The purpose of this study was to investigate the effects of particle size and breathing rate on the deposition pattern in a human oral airway cast with a defined geometry. The airway replica included the oral cavity, pharynx, larynx, trachea, and 3 generations of bronchi. The oral portion of the cast was molded from a dental impression of the oral cavity in a human volunteer, while the other airway portions of the cast were made from a cadaver. Nine different sizes of polystyrene latex fluorescent particles in the size range of 0.93-30 mu m were used in the study. Regional deposition was measured at a constant inspiratory flow rate of 15, 30, and 60 L min^-1. Deposition in the oral airway appeared to increase with an increasing flow rate and particle diameter. Deposition at the highest flow rate of 60 L min^-1 was close to 90% for particles >20 mu m. Particles> about 10 mu m deposited mainly in the oral cavity. Deposition efficiency has been found to be a unique function of the Stokes number, suggesting that impaction is the dominant deposition mecha nism. Oral deposition can be approximated by a theoretical deposition model of inertial impaction in a 180 degrees curved tube, assuming perfect mixing in a turbulent flow. Our model suggests that the minimum dimension near the larynx and the average cross-sectional area are important parameters for oral airway deposition; however, additional data from the oral airway replica are needed to ascertain whether these are indeed the critical dimensions. Information from the present study will add to our knowledge of the deposition mechanism, the correlation of particle deposition with airway geometry, and eventually the best way to deliver aerosol drugs.     

Deposition of Ultrafine Aerosols in a Human Oral Cast

This paper reports experimental measurements of the total deposition of ultrafine aerosols in a human oral airway cast. A clear polyester resin cast of the upper airways of a normal human adult, including the nasal airways, oral cavity, tongue, nasopharynx, and larynx, was made from a postmortem solid cast. Measured pressure drop in the oral airway was slightly lower than in the nasal airway. The measured oral flow resistance was similar to the values reported for human volunteers breathing through the mouth at rest and for spontaneously opening of the mouth. Aerosol deposition data in the cast for monodisperse NaCl aerosols between 0.2 and 0.005 μm in diameter deposited in the cast were obtained for inspiratory and expiratory flow rates of 4, 20, and 40 L/min. Deposition efficiency increased with decreasing particle size and flow rate indicating that turbulent diffusion was the dominant mechanism for deposition. Higher deposition efficiency was observed for inspiratory flow in the oral airway than for expiratory flow. Oral deposition and nasal deposition for inspiratory flow were similar, but oral deposition was lower for expiratory flow. Deposition efficiency can be expressed as a function of the flow rate and diffusion coefficient of the particle.     

Long-Term Measurements of Equilibrium Factor and Unattached Fraction of Short-Lived Radon Decay Products in a Dwelling - Comparison with Praddo Model

According to the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR 1993), the dose due to the inhalation of radon decay products represents almost 50% of the total natural radiation dose to the general population. The scientific community is interested in the assessment of the risk induced by domestic radon exposure. The dosimetric models used to estimate the dose are very sensitive to unattached fraction and size distributions, which makes the characterization of the indoor radon decay products aerosol necessary. For this purpose, longterm measurements of unattached fraction (f_p ) and equilibrium factor (F) were taken in a dwelling under typical indoor domestic aerosol conditions. An original device consisting of an annular diffusion channel set in parallel with an open filter was developed and calibrated to continuously measure the unattached fraction. Moreover, radon activity concentration and particle concentration were simultaneously monitored. With aged aerosol, particle concentration was found to be very low (between 500 and 5000 cm^-3), radon activity concentration ranged from 240 to 2800 Bq m^-3, and the mean values of f_p and F were, respectively, 0.31 (0.08-0.67) and 0.16 (0.04-0.45). With aerosol sources, the high increase in particle concentration led to a negligible unattached fraction and raised the equilibrium factor. A correlation relationship was determined between these two parameters under different aerosol conditions. Finally,our experimental results were compared to results obtained with the PRADDO model; this comparison showed a good agreement between these two different approaches.     

Theory of Cast Formation in Electrophoretic Deposition

The rate of cast formation in electrophoretic deposition is described by a combination of the equation of continuity for the suspension phase with expressions for the particle velocity and the movement of the cast-suspension boundary. The assumptions necessary to arrive at the well-known equations of Hamaker (1940) and Avgustinik (1962) are summarized, and it is shown that, in both equations, a factor is missing that tends to unity only for diluted suspensions. After incorporation of this factor, it is possible to understand better the more-than-linear increase of cast formation with increasing suspension concentration as reported by several authors.     

Plasma-Enhanced Chemical Vapor Deposition of Boron Nitride Using Polymeric Cyanoborane as Source

The plasma-enhanced chemical vapor deposition (PECVD) of boron nitride films was studied using polymeric cyanoborane, (CNBH₂) n , a material previously examined by thermally activated CVD. The PECVD procedure yields boron nitride coatings containing ≅20 wt% paracyanogen as a contaminant. This impurity can be removed by heat treatment under vacuum or in an ammonia atmosphere. The boron nitride coatings are hexagonal and appear to be boron deficient. The PECVD process takes place at 300°C, measured at the backside of the substrate, as compared with 600°C in the thermally activated CVD process.     

Deposition of Ultrafine Particles in Human Tracheobronchial Airways of Adults and Children

Inhalation exposure to ultrafine particles, including radon progeny and other combustion aerosols, has been implicated in potential health risks of ambient and indoor environments. These particles deposit in the respiratory tract mainly by diffusion. The purpose of this study was to determine the deposition pattern of nanometer-sized particles in the human tracheobronchial (TB) airways of children and young adults. The deposition was determined for 1.75, 10, and 40 nm ²¹²Pb particles at flow rates corresponding to respiratory minute volumes at rest and during moderate exercise. The 1.75 nm particles were unattached clusters, whereas the 10 and 40 nm particles were silver particles with attached ²¹²Pb clusters. Replicate casts of the upper TB airways of 3, 16, and 23 year old humans were used, including the larynx, trachea, and bronchial airways down to generations 5-8. Deposition in each generation and total deposition were measured by counting the ²¹²Pb gamma photopeak in a NaI (Tl) detector. The effects of airway geometry, particle size, and flow rate on deposition efficiency were studied. The deposition of the 1.75 nm particle, corresponding to unattached indoor radon progeny, was substantially higher than that of the 10 and 40 nm particles. The dependence of particle deposition on the flow rate was relatively weak, and deposition efficiencies were only slightly higher at the lower flow rates. The deposition models for diffusion from parabolic flow underestimated aerosol deposition, whereas the diffusion deposition predicted for plug flow overestimated the TB deposition. The deposition models resulting from this study can be used for developing lung deposition models and in the risk assessment of radon progeny and ultrafine ambient particles.     

Mass Transfer of Diffusive Species with Nonconstant In-Flight Formation and Removal in Laminar Tube Flow. Application to Unattached Short-Lived Radon Daughters

This article deals with convective-diffusive aerosol transport with in-flight formation and removal and is applied to the unattached fraction of short-lived radon decay products. Two novel contributions to previous studies are given in this numerical and experimental work: on the one hand, we solve the mass-transport equations for all the short-lived radon daughters; on the other hand, we include the ²¹⁸Po neutralization into the mass-transport equation of the first radon decay product. Concerning the mass-transfer of all short-lived radon daughters, numerical calculations lead to the development of simple correlations for the ²¹⁴Pb and ²¹⁴Bi penetration fractions. Those correlations can be used to determine the diffusion coefficient of ²¹⁴Pb and ²¹⁴Bi using the 2-filter method. In our experiments, a diffusion coefficient equal to 5 X 10^-6 m² s^-1 is found for the ²¹⁴Pb. Concerning the ²¹⁸Po neutralization, better agreement is observed between our numerical and experimental results when ²¹⁸Po neutralization is taken into account. These results confirm the neutralization rates found by Howard and Strange (1994).     

Pore Narrowing and Formation of Ultrathin Yttria-Stabilized Zirconia Layers in Ceramic Membranes by Chemical Vapor Deposition/Electrochemical Vapor Deposition

Chemical vapor deposition (CVD) and electrochemical vapor deposition (EVD) have been applied to deposit yttria-stabilized-zirconia (YSZ) on porous ceramic media. The experimental results indicate that the location of YSZ deposition can be varied from the surface of the substrates to the inside of the substrates by changing the CVD/EVD experimental conditions, i.e., the concentration ratio of the reactant vapors. The deposition width is strongly dependent on the deposition temperature used. The deposition of YSZ inside the pores resulted in pore narrowing and eventually pore closure, which was measured by using permpor-ometry. However, deposition of YSZ on top of porous ceramic substrates (outside the pores) did not result in a reduction of the average pore size. Ultrathin, dense YSZ layers on porous ceramic substrates can be obtained by suppressing the EVD layer growth process after pore closure.     

Flow Characteristics of a Vertical Spinning Disk, Low-Pressure Vapor Deposition Apparatus

The flow characteristics of a new vertical spinning disk, low-pressure vapor deposition apparatus were studied. The nominal boundary-layer thickness dependence on the reactor pressure, substrate rotation rate, and substrate temperature were examined with the aid of a smoke that was generated from hydrolyzed TiCl₄ vapor. The measured nominal boundary layer thickness was found to have a strong dependence on the reactor pressure and the substrate rotation rate, whereas the temperature dependence was not easily resolved by the present method. The experimental data and the theoretical prediction were found to agree within the accuracy of the measurements.     

化学气相沉积法合成碳纳米管研究进展

碳纳米管由于其独特的结构和优异的电学、光学、力学、热学等物理化学性能,在材料、电子器件、传感器、催化剂和能源等领域具有广泛的应用前景,但是如何低成本批量制备高品质的碳纳米管是实现碳纳米管大规模应用的关键。本文综述了近年来化学气相沉积法合成碳纳米管的研究进展,表明化学气相沉积法是大规模可控制备碳纳米管最有效的方法,并对其未来的发展方向进行了分析和展望。     

Thermophoretic Deposition of Small Particles in the Modified Chemical Vapor Deposition (MCVD) Process

Thermophoresis is conclusively established as the particulate deposition mechanism in the MCVD process by comparing experimental measurements and quantitative theoretical predictions. The deposition efficiency, E , is defined as the fraction of the silica in the gas stream (initially as SiCl₄) that is deposited. For normal MCVD operating conditions, the deposition efficiency is only a function of the equilibrium temperature, T_e , at which the gas and walls equilibrate downstream of the torch and the temperature, T_r , at which reaction occurs. The deposition efficiency is ∼0.8[1-( T _e/ T _r)]. It is determined that T_e is a strong function of the torch traverse velocity, the traverse length, the temperature of the ambient environment, and the tube wall thickness but only a weak function of the gas flow rate. At high gas flow rates, the efficiency is limited by incomplete reaction.     

Partition of Hydrogen in the Modified Chemical Vapor Deposition Process

In the modified chemical vapor deposition (MCVD) process for making glass fibers, most of the hydrogen coming into the reaction from hydrogen-bearing impurities in the starting materials is not incorporated in the glass. It is instead mostly converted to HCl, which is not absorbed by the newly formed silica particles, and passes out the exhaust stack. The residual partial pressure of H₂O formed in equilibrium with HCl in the presence of O₂ and Cl₂ accounts quantitatively for the OH appearing in the glass when the known solubility of H₂O in silica is considered. The H₂O/HCl equilibrium is quenched at a temperature below that of the reaction zone at a value for which the rate of reaction approximates the transit time across the deposition zone. Quantitative agreement is obtained for published OH concentrations produced by SiHCl₃ doping.     

Co／Mo催化剂制备碳纳米管的研究

以氧化铝凝胶负载Co／Mo合金为催化剂，C2H2为碳源，用CVD法合成了纯度较商的多壁碳纳米管（MWCNT）。通过甩TEM和XRD等方法，对碳纳米管（CNTs）进行了表征，表明制备的碳纳米管具有较高的石墨化程度。研究得出当催化剂的沉淀pH=7．5，H2为还原气和载气，升温速率为50℃／min时，碳纳米管的纯化后的产率高达85％，为下一步的大规模化生产打下了良好构基础。     

Palladium Membrane Formed in Macropores of Support Tube by Chemical Vapor Deposition with Crossflow through a Porous Wall

Abstract

Palladium acetate vapor was sublimed at a reduced pressure and was evacuated through the porous wall of an α-alumina support tube of 1.8 mm i.d. and 2.4 mm o.d. Due to chemical vapor deposition (CVD), a thin palladium membrane was formed in macropores of the support. The membrane part was about 50 mm in length and was used without any pretreatment. The palladium membrane, prepared at a maximum CVD temperature of 400°C, showed hydrogen permeance and selectivity to nitrogen higher than 10^?6 mol·m^?2·s^?1·Pa^?1 and 1000 at 300–500°C, respectively. Even after the permeation temperature was repeatedly varied between 100 and 300°C in a hydrogen atmosphere, the membrane exhibited no hydrogen embrittlement. The amount of palladium deposited in pores of the support tube was 22 g/m² of the outer surface of the tube. The thickness of the palladium membrane calculated from this value was 4.4 μm.