Gas diffusion method

The UF6 gas that passes through the membrane is thus very slightly enriched in the lighter, faster-moving isotope. After repeating the process many thousands of times, a separation of isotopes can be achieved. Approximately 85% of the Western world s nuclear fuel supply—some 5000 tons per year—is produced by this gas diffusion method. 

Gas diffusion from a donor stream—in which the analyte chemically is converted to a volatile species—into an acceptor stream, where the two streams run in parallel separated by a suitable gas-permeable membrane, is a highly selective technique particularly well suited for adaptation into FI A, because in nonsegmented streams the diffusion unit can be made extremely small and the flow rates may be considerably reduced. Although in the first FI A gas-diffusion method, developed by Baadenhuijsen and Seuren-Jacobs [57] for the determination of carbon dioxide in plasma, a nonporous dimethyl silicone rubber membrane was used, hydrophobic microporous membranes such as Teflon or isotactic polypropylene have proven to be more versatile diffusion barriers, since they can be used for a greater variety of gases. 

Preparation of Copper Sulfide and Gold Nanoparticles Dispersed in Hydroxypropylcellulose—Silica Film with Gas Diffusion Method... 

In this p r, we report the preparation, structure characterization and properties of CuS and Au nano-particles dispersed in HPC-silica films with gas diffusion method. 

As an example, an SIA system exploiting dialysis technique is presented. The sample is dialyzed online to remove polymeric substances in order to avoid their interference with subsequent UV spectro-photometric measurements. The equipment for this system is similar to the one used for SIA—gas diffusion method, just using a dialysis membrane instead of a diffusion one (see Figure 3.22). 

The classic method for isotope separation utilizes a gas diffusion method in cells. Each cell is divided into two parts, separated by a barrier pierced with a lot of tiny holes. On one side of the barrier an under-pressure is maintained, on the other side an over-pressure. The fluoride is fed in to the part with overpressure and diffuses through the barrier. The mean speed of the molecules of a gas is lower if the molecular weight is higher. It can be calculated that the diffusion speed for is 1.0043 times higher than that for When... 

Seok B, Flelmig D, Williams MW, Liptzin D, Chowanski K, Hueber J (2009) An automated system for continuous measurements of trace gas fluxes through snow an evaluation of the gas diffusion method at a subalpine forest site, Niwot Ridge, Colorado. Biogeochemistry 95 95... 

Dhaouadi, A., L. Monser, S. Sadok, and N. Adhoum. 2007. Validation of a flow-injection-gas diffusion method for total volatile basic nitrogen determination in seafood products. Food Chem. 103(3) 1049-1053. 

Different combinations of stable xenon isotopes have been sealed into each of the fuel elements in fission reactors as tags so that should one of the elements later develop a leak, it could be identified by analyzing the xenon isotope pattern in the reactor s cover gas (4). Historically, the sensitive helium mass spectrometer devices for leak detection were developed as a cmcial part of building the gas-diffusion plant for uranium isotope separation at Oak Ridge, Tennessee (129), and heHum leak detection equipment is stiU an essential tool ia auclear technology (see Diffusion separation methods). 

Gas Diffusivity For prediction of the gas diffusivity of binary hydrocarbon-hyarocarbon gas systems at low pressures (below about 500 psia [3.5 MPa]) the method of Gilliland given by Eq. (2-150) is recommended. 

In the late 1800s, the development of the kinetic theory of gases led to a method for calculating mmticomponent gas diffusion (e.g., the flux of each species in a mixture). The methods were developed simnlta-neonsly by Stefan and Maxwell. The problem is to determine the diffusion coefficient D, . The Stefan-Maxwell equations are simpler in principle since they employ binary diffnsivities ... 

Surface Area Determination The surface-to-volume ratio is an important powder property since it governs the rate at which a powder interacts with its surroundings. Surface area may be determined from size-distribution data or measured directly by flow through a powder bed or the adsorption of gas molecules on the powder surface. Other methods such as gas diffusion, dye adsorption from solution, and heats of adsorption have also been used. It is emphasized that a powder does not have a unique surface, unless the surface is considered to be absolutely smooth, and the magnitude of the measured surface depends upon the level of scrutiny (e.g., the smaller the gas molecules used for gas adsorption measurement the larger the measured surface). 

The mechanisms and reasons of catalytic activity of polyaniline (PANI)-type conducting polymers toward oxygen reduction in acidic and saline solutions are investigated by electrochemical and quantum-chemical methods. The PANI/thermally expanded graphite compositions were developed for realization of fully functional air gas-diffusion electrodes. Principally new concept for creation of rechargeable metal-air batteries with such type of catalysts is proposed. The mockups of primary and rechargeable metal-air batteries with new type of polymer composite catalysts were developed and tested. 

It is well known that the performance of the air gas-diffusion electrode is influenced not only by the activity of the catalyst, but also by all transport processes taking place in its porous structure. In addition, the transport hindrances in the electrode are function not only of its overall structure, but also of the porous structure and the surface properties of the catalyst. Methods for diagnostic of the activity and the transport properties of air gas-diffusion electrodes were proposed [9]. 

An experimental method is proposed for estimation of the transport hindrances in air gas-diffusion electrodes. As a measure of the transport hindrances in the air gas-diffusion electrodes is introduced the difference AE between the potentials of one and the same electrode when operating with air and with pure oxygen at one and the same current density. The difference AE can be theoretically described by the equation ... 

The described method for the diagnostic of the activity and the transport hindrances in air gas-diffusion electrodes is very useful in the research of porous catalysts for air electrodes. The comparison of the activity and the transport hindrances of air electrodes with catalysts from various types of active carbon allow a proper selection to be accomplished. 

Air gas-diffusion electrodes were developed, suitable for use in metal-air cell with alkaline or with saline electrolytes. A variety of carbon-based catalysts are used in these air electrodes. Methods for the estimation of the activity and the transport hindrances are proposed and used successfully for the optimization of the carbon-based catalysts. 

Kaisheva A., Iliev I., Gamburzev S., Comparative methods fo estimation of the activity and the transport hindrances of air gas-diffusion electrodes, J.Power Sources, 1984 13 181 - 195. 

Similar to screen printing, the spray coating method [95] is widely used for catalyst fabrication, especially in labs. The major difference between the two is that the viscosity of the ink for spray coating is much lower than that for screen printing. The application apparatus can be a manual spray gun or an auto-spraying system with programmed X-Y axes, movable robotic arm, an ink reservoir and supply loop, ink atomization, and a spray nozzle with adjustable flux and pressure. The catalyst ink can be coated on the gas diffusion layer or cast directly on the membrane. To prevent distortion and swelling of the membrane, either it is converted into Na+ form or a vacuum table is used to fix the membrane. The catalyst layer is dried in situ or put into an oven to remove the solvent. 

---