Deposition efficiency

Developments. Electrolytic refining requires a large capital investment, and labor costs per kilogram of copper produced are high. Most refineries have traditionally operated at current densities of about 240 A/m. Thus, a tank house area of approximately 40 m is required per ton of copper produced daily. The use of higher current densities reduces capital requirements but may impair deposition efficiency and product quaUty. 

The major advance in the way in which column eluate is deposited on the belt was the introduction of spray deposition devices to replace the original method which was simply to drop liquid onto the belt via a capillary tube connected directly to the outlet of the HPLC column. These devices, based on the gas-assisted nebulizer [5], have high deposition efficiencies, transfer of sample can approach 100% with mobile phases containing up to 90% water, and give constant sample deposition with little band broadening. 

The deposition of ultrafine particles has been measured in replicate hollow casts of the human tracheobronchial tree. The deposition pattern and efficiency are critical determinants of the radiation dose from the short lived decay products of Rn-222. The experimental deposition efficiency for the six airway generations just beyond the trachea was about twice the value calculated if uniform deposition from laminar flow is assumed. The measured deposition was greater at bifurcations than along the airway lengths for 0.2 and 0.15 ym diameter particles ... 

This paper will present some results of a set of experiments carried out in the hollow airway cast system with ultrafine particles which are or particular interest for the calculation of the dose to the bronchial epithelium from the short lived radon daughters. Detailed deposition efficiencies and intrabronchial distributions are presented elsewhere (Cohen, et al., 1986). 

The ratios of the experimental to the calculated values for deposition efficiency for each generation are shown for each of the experiments in Figures 2-4. The error bars represent the standard error derived from the mean measured deposition fraction for the generation. A coefficient of variation was calculated for the measured deposition in each generation which was used to obtain an estimate of the standard error of the ratio. It was assumed that no additional variability in the ratio was introduced by the calculated deposition fraction. The mean ratio for all six sets of cast measurements is shown in Figure 5. The error bars in Figure 5 represent the standard error of the mean of the six experiments. 

For each of the three particles sizes studied, the deposition efficiency in the trachea was much greater than predicted if uniform deposition is assumed. In each data set the ratio at the lower flow rate exceeded that at a higher flow. If the increase results from turbulence introduced by the larynx it might be expected to be more effective at the higher flow rate. The discrepency may result from the jet formed downstream of the larynx. The center line velocity substantially exceeds the mean velocity of the air stream and secondary circulation patterns are set up near the wall which can act as dead zones (Ultman, 1 985) ... 

A study by S.C. Soderholm of the University of Rochester is in progress to relate the deposition efficiency of volatile aerosols of disulfoton in humans to physical properties of the airborne system,... 

A well-distributed deposition of Pt/C nanocatalyst and Nafion ionomer on bofh hydrophilic and hydrophobic carbon-based electrodes has been successfully obfained using a Pt/C concentration of 1.0 g/L, an electrical field of 300 V/cm, and a deposition time of 5 minutes [118]. The deposition of Pt/C nanocatalysts and Nafion solution via the electrophoretic process gives rise to higher deposition efficiency and a uniform distribution of catalyst and Nafion ionomer on the PEMFC electrodes. 

It is interesting to note that Brenner and Riddell (2-4) accidentally encountered electroless deposition of nickel and cobalt during electrodeposition of nickel-tungsten and cobalt-tungsten alloys (in the presence of sodium hypophosphite) on steel tubes in order to produce material with better hardness than that of steel. They found deposition efficiency higher than 100%, which was explained by an electroless deposition contribution to the electrodeposition process. 

Deposition efficiencies for particles in the respiratory tract are generally presented as a function of their aerodynamic diameter (e.g. [8,12]). Large particles (> 10 pm) are removed from the airstream with nearly 100% efficiency by inertial impaction, mainly in the oropharynx. But as sedimentation becomes more dominant, the deposition efficiency decreases to a minimum of approximately 20% for particles with an aerodynamic diameter of 0.5 pm. When particles are smaller than 0.1 pm, the deposition efficiency increases again as a result of dif-fusional displacement. It is believed that 100% deposition due to Brownian motion might be possible for particles in the nanometer range. 

Many reviews on the relevant technical aspects for drug nebulization are available (e.g. [43 5]. The greatest disadvantages of nebulizers are their poor deposition efficiency (see Section 3.11) and low output rate (e.g. [46]). Several developments have been reported to improve their efficacy, like the use of open vents or breath-assisted open vents [47] and adapted aerosol delivery [48]. A renewed interest in nebulizer therapy may also come from the generation of special aerosols, such as hposomes [49]. 

An important aspect of inhalable PAHs is their distribution as a function of particle size in ambient aerosols since size is a key parameter in determining aerosol lung deposition efficiencies (see Chapter 2.A.5). 

Turning now from equilibrium considerations, let us investigate the deposition of gas-phase particles, called soot, on the tube walls. The Si02 soot particles are 0.02-0.1 p.m in diameter and are entrained in the gas flow. Without the proper temperature gradient, they would remain in the gas stream and be exhausted. However, the traveling hot zone produces a temperature gradient so that the particles drift toward and deposit on the wall by thermophoresis (cf. Section 7.2.4.1). The thermophoretic deposition efficiency for this process is about 60%. 

Something of the complexity of factors affecting the efficiency of metal deposition—the competing reaction always being H co-deposition—can be seen in Fig. 7.171 where there is a maximum in chromium deposition efficiency at about 200 g... 

The introduction of ultramicroelectrodes (described in Chap. 12) holds great promise for stripping measurements [51-53]. In particular, microelectrodes offer enhanced deposition efficiency (and hence efficient preconcentration from qui-... 

From Eq. (8.2) it is obvious that the Stokes number Stk and thus the deposition efficiency by impaction increase with increasing particle size and airflow velocity. Impaction occurs most frequently in the upper respiratory tract (pharynx, larynx, and main trachea), where particles larger than 5 p,m are trapped because of their size and the fast and turbulent airflow exerted. Also in the upper tracheobronchial region, impaction is the most prominent mechanism (Hinds 1998). 

Pulmonary deposition efficiency Location of pulmonary deposition Pulmonary residence time (dissolution rate and other factors) Oral bioavailability Degree of oral deposition Systemic clearance Volume of distribution Protein binding... 

Pulmonary deposition efficiency depends on physicochemical characteristics, such as density of the aerosol or dry powder particles [33-35], Generally, particle diameters less than than 5 pm are required for efficient pulmonary delivery [36, 37], Pulmonary deposition also depends on the nature of the delivery device and differs between metered dose inhalers (MDIs). For example, pulmonary deposition expressed as the ratio of pulmonary versus total (pulmonary + oral) absorbed drug, ranged from 15-55% for a number of salbutamol devices and from 66-85% for drugs with lower oral bioavailabilities such as budesonide. 

Traditionally, pulmonary deposition of MDIs has been in the range of 10-20% [38-40], An increase in pulmonary deposition efficiency of MDIs has been achieved with the use of spacer devices [41-46], Aerosol deposition in the human lung has also been optimized after administration from a microprocessor-controlled pressurized MDI [47, 48], Improvement of pulmonary deposition of up to 40%... 

Both step index and graded index fibers have been prepared by this process, using Ge02 und B203 as dopant materials. Deposition efficiencies of about 45% have been obtained. The deposition rate is typically between 0.4—1.6 g/min and blanks yielding 10 km fibers have been made. 

A short review of the OVPO and the MCVD method is given. A more detailed discussion of the PCVD method is presented. Emphasis has been laid on the description of experiments in which pure and Ge02 -oxide doped silica have been deposited. It turns out that the PCVD method has some unique properties such as deposition without soot formation in the gas phase, moderate substrate temperature, high deposition efficiency and the possibility of rapid reactor movement. Besides germanium, other dopant elements such as boron and fluorine have also been successfully deposited simultaneously with silica. 

Figure 2. Deposition efficiency of particles in the human respiratory tract.

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